View Full Version : Help Design a Human-Powered Helicopter
jzvonek
Sep19-09, 12:32 AM
Hello,
I have started a website to facilitate the design of a human-powered helicopter. Please visit this website if you are interested in joining:
http://sites.google.com/site/humanpoweredhelicopter/
We need great engineers to solve this difficult problem. If interested in giving your time, please email me at jzvonek@gmail.com.
Thanks.
-John
russ_watters
Sep19-09, 02:30 AM
Difficult indeed! At face value it seems like an impossible problem!
berkeman
Sep19-09, 03:01 AM
Looking at the human-powered plane efforts, and being an amateur bicyclist, I see no way for a human-powered helicopter to be practical for more than a few seconds. Ouch.
First you need a good cyclist. Bringing the blades to velocity is an issue. I'd read the fine print over how to torque it up. The less stress on the pilot to overcome inertia under potentially adverse gearing could be a major issue.
Only 3 meters?? A lot of ground effect is in play. Can the rotor tips be closer to the ground than 3 meters?
Stability and control I would leave up to electronics if allowed.
The Gossamer Albatross had a wingspan of 47 feet with a root cord of about 6 feet. The top speed during the Channel crossing was 18 mph. Keep that in mind when you consider rotor diameter. Isn't it the last 1/4 of the rotor blade that does half the lifting?
So where are the rules of the game? A Wikipedia page isn't enough.
jzvonek
Sep19-09, 07:53 AM
Here is a link to the rules:
http://www.vtol.org/awards/hphregs.html
Also, the prize has just been increased to $250,000 from the original $20,000.
I don't know if ground effect would be significant with the slow-moving rotors of a human-powered helicopter. I've seen experiment results that show the effect dropping off quickly as the rotors move away from the ground (< 3m).
Stability and control will be major issues, and I believe electronics are not allowed by the rules.
And the problem is not impossible. We have better engineering tools than at any time in the past. We just have to take advantage of them.
mgb_phys
Sep19-09, 12:04 PM
When they say 'human powered' - do they count 'human fuelled'?
A gas turbine will run on bio-diesel !
Looks like you are going to need Leonardo on this one.
FredGarvin
Sep19-09, 05:42 PM
He's gonna need angels for this. They're the only way a human powered helicopter is going to get off the ground.
A gas turbine will run on bio-diesel !
It's people. Jet fuel is made out of people. They're making our jet fuel out of people.
I wouldn't be as quick to dismiss a human powered helicopter. But, according to the set of rules quoted, it has to take off and remain within a 10 meter square. This limits the blades to about 4 meter each.
I'm not versed in helicopter efficiency, but it seems that twice the rotor disk area should about double the efficiency. Earlier I noted that the Gossamer Albatross had a wingspan 47 foot span. This might compare to a 47 foot rotor disk.
FredGarvin
Sep19-09, 06:20 PM
I'll absolutely dismiss it. The power that can be provided by a good cyclist is somewhere in the area of 300 W. Not only will you be hard pressed to find a very light person that can put out that kind of continuous power, you have to deal with the structural aspects of aa helicopter. It does not lend itself to light and whispy structures like the Albatross did.
... you have to deal with the structural aspects of aa helicopter. It does not lend itself to light and whispy structures like the Albatross did.
Why is that?
FredGarvin
Sep19-09, 09:32 PM
Look at the rotor head and blades alone.
I wouldn't be as quick to dismiss a human powered helicopter. But, according to the set of rules quoted, it has to take off and remain within a 10 meter square. This limits the blades to about 4 meter each.
You are misreading the rules. It's not the whole vehicle; just one single point on the vehicle.
A reference point on the non-rotating part of the machine will be established an a means whereby the observers can judge that the machine stayed within the confines of the 10-meter square.
I'll absolutely dismiss it.
The basic feat has already been achieved, twice. Just not for the requisite time and height.
jzvonek
Sep19-09, 11:28 PM
D H is right. Human-powered helicopters have already gotten off the ground. A few great ideas on how to improve the design will win the prize.
You are misreading the rules. It's not the whole vehicle; just one single point on the vehicle.
A reference point on the non-rotating part of the machine will be established an a means whereby the observers can judge that the machine stayed within the confines of the 10-meter square.
Yes, I believe you're right. It's ambigiously written.
How is that ambiguous?
You're joking? Nowhere is it stated what parts of the craft cannot drift outside the square, or even for that matter if they are talking about the 'reference point' staying in the square.
Look at the rotor head and blades alone.
Well, it doesn't have to support a gun plateform, and there's more than one way to skin a cat. Look at the toy models available and their novel designs.
Ranger Mike
Sep20-09, 08:08 AM
He's gonna need angels for this. They're the only way a human powered helicopter is going to get off the ground.
It's people. Jet fuel is made out of people. They're making our jet fuel out of people.
Fred...them old Charlton Heston movies are really takin their toll on you, aren't they??
FredGarvin
Sep20-09, 08:21 AM
The basic feat has already been achieved, twice. Just not for the requisite time and height.Source please. A quick Google search showed a "helicopter" that barely got off the ground and which I agree is a human powered hovercraft, not a helicopter.
The competition states that they have never awarded this award.
I'll sit firm in my skepticism.
Current world record holder is apparently "Yuri I". In 1994, it achieved an altitude of 0.2 m and a time of 19.46 sec with a drift of 9.95 m. It has four separate rotors, all mounted below the frame. More details: Yuri I (http://www.humanpoweredhelicopters.org/yuri1/index.htm) at www.humanpoweredhelicopters.org
Thumb below is a clickable link to a full size image at the above website.
http://www.humanpoweredhelicopters.org/yuri1/YURI_1_thumb.jpg (http://www.humanpoweredhelicopters.org/yuri1/YURI_1.jpg)
FredGarvin
Sep20-09, 08:35 AM
My definition of "helicopter" differs GREATLY from theirs.
.2 meters is well within ground effect. It still looks like useless form of a hovercraft. But I guess everything has to start out somewhere.
FredGarvin
Sep20-09, 08:36 AM
Fred...them old Charlton Heston movies are really takin their toll on you, aren't they??Hey. MGB started it...
Ranger Mike
Sep20-09, 08:49 AM
Hey. MGB started it...
i stand corrected..a lot of pathos out there ,Pathos (pronounced /ˈpeɪθɒs/; Greek: πάθος)
russ_watters
Sep20-09, 11:02 AM
After looking at the rules, I believe the contest is doable. It only says you need to momentarily exceed 3 meters and total hover time is only 1 min. A cyclist can put out a lot more power for 1 min than s/he can for three hours.
Just keep in mind, this is nowhere close to the achievment of the Gossamer Albatross, which actually had sustained, controllable flight for close to 3 hours. This "helicpoter" prize seems pretty pointless to me.
This "helicpoter" prize seems pretty pointless to me.
Depends on the meaning of "pointless". As a viable form of transportation for the masses, I agree. (Then again, so is the Gossamer Albatross.) As a college engineering project, I disagree. Something like this could be quite instructive.
FredGarvin
Sep20-09, 01:52 PM
As a teaching tool I completely agree this is a good contest. However I still think that putting the moniker of helicopter to these machines is akin to me calling my 3 year old's tricycle a human powered car.
From http://www.humanpoweredhelicopters.org/davinci/index.htm
This is a picture of the Da Vinci 3, rotor tip, I think.
Is that a spool of kit string I spy in the rectangular cut-out?
http://www.humanpoweredhelicopters.org/davinci/image003.jpg
Joe, the guy with the yellow nametag will be the pilot for today's demonstration.
chayced
Sep20-09, 08:53 PM
What about cheating? Use a person to charge a spring then the spring to spin the rotors and lift the craft. Technically it's human powered, and it gives you enough power to actually lift off.
Beyond that I don't think it's possible, unless you are using huge rotors and then it's more of a spiraling airplane than a helicopter.
As a teaching tool I completely agree this is a good contest. However I still think that putting the moniker of helicopter to these machines is akin to me calling my 3 year old's tricycle a human powered car.
Pointless? But think of all the money and glad-handing. The professors get to publish on every meaningless detail, foundations get to disperse funds and claim to be important contributors, post grads get to slick-up their resumes, fundraisers get paid. It's bounty all around. They just have to get the silly contraption suitably aloft...
dr dodge
Sep22-09, 08:39 PM
in the rules it says no energy saving devices, but the rotor assy is exempt. use the rotors(2+ counter-rotating) as flywheels. it states a flight lenght, but I didn't see a total time duration. If it took 2 persons 2-5+ hours to slowly keep spinning up the rotors (w/ no lift) until lift off, I would think, in theory, the energy stored could excede the extra energy to then hang it in the air long enough
how long to the tour biker's ride continuously?
dr
dr dodge
Sep23-09, 04:40 PM
if the target web site has a way to contribute ideas I could not find it
so I am going to toss this out in here
if 3 rotors were used, each of different mass, smallest (in diameter) was heaviest, largest lightest, and a variable gearbox could divert torque between all 3, you could generate rotor speed with all of them, then feather the power to the largest diameter one to speed it up, and use the middle sized one for counter rotational stability. since reaction of pedaling would want to spin you around, you could offset that by having the middle rotor of equal "inertial mass" as the body, and compensating for no tail rotor. all lifting surfaces would not cover the next. from above it would look like 3 concentric circles
dr
liannagreyson
Nov19-09, 10:42 AM
Very nice post with a ton of informative information. I really appreciate the fact that you approach these topics from a stand point of knowledge and information
instead of the typical “I think” mentality that you see so much on the internet these days.
dr dodge
Nov19-09, 10:55 AM
I just checked the web site the OP was starting, and seems as though it is not being updated. so, I'm in if someone wants to take the lead and we build one. Since I have my own industrial park in the back yard, we should be able to do it on a shoe string.
dr
M Grandin
Nov22-09, 05:51 AM
If "Gossamer" manpowered planes work, at least I cannot see anything preventing two such planes connected together circulating around a common center = "helicopter". That may be boiled down to a man powered helicopter where the rotor is not driven by center shaft, but from from smaller propellers at rotor wing ends. Wing units (perhaps several parallel layers as in WWI combat planes) behind towing propellers, placed rather far out from center
shaft. Propellers could be driven by wires as in garden trimmers.
I agree it may appear less efficient letting rotor be towed by propeller - but I can see
gossamer planes (towed by propeller) lift while manpowered helicopters (driven by center shafts)
don't lift. In aerodynamics not always common sense applies. :cool:
M Grandin
Nov24-09, 07:25 PM
If "Gossamer" manpowered planes work, at least I cannot see anything preventing two such planes connected together circulating around a common center = "helicopter". That may be boiled down to a man powered helicopter where the rotor is not driven by center shaft, but from from smaller propellers at rotor wing ends. Wing units (perhaps several parallel layers as in WWI combat planes) behind towing propellers, placed rather far out from center
shaft. Propellers could be driven by wires as in garden trimmers.
I agree it may appear less efficient letting rotor be towed by propeller - but I can see
gossamer planes (towed by propeller) lift while manpowered helicopters (driven by center shafts)
don't lift. In aerodynamics not always common sense applies. :cool:
Sorry, according to http://flight.engr.ucdavis.edu/~smlarwood/documents/LarwoodSaiki1990.pdf
that kind of solutions have earlier been developed. But evidently not a success. At least not
hitherto. :cry:
I've read every paper on this subject and will be happy to answer any questions. I will say this, it's certainly possible, but you walk a very fine line. I see a lot of misinformation being stated in this thread.
Fred, PM me your email address. I can't send you pms because you have it turned off.
Mech_Engineer
Nov25-09, 09:59 AM
It seems to me that for a helicopter to achieve free flight (outside of the ground effect) it needs to push enough air down to have sufficient mass flow to maintain altitude. Based on the power requirements of other helicopters which are engine powered, it would have to have more than 10 horsepower available, far more than any bicyclist can achieve.
Edit- any 130-lb bicyclist anyway. Weight is the #1 killer on these things.
It seems to me that for a helicopter to achieve free flight (outside of the ground effect) it needs to push enough air down to have sufficient mass flow to maintain altitude. Based on the power requirements of other helicopters which are engine powered, it would have to have more than 10 horsepower available, far more than any bicyclist can achieve.
Edit- any 130-lb bicyclist anyway. Weight is the #1 killer on these things.
No, this is wrong and not based on any sort of calculation. Run the numbers and you will find you are off by an order of magnitude.
You are about right on the weight of the cyclist though.
BenchTop
Nov25-09, 08:41 PM
Do the rules prohibit offsetting the load with, say, lighter than air wings?
Do the rules prohibit offsetting the load with, say, lighter than air wings?
Lighter than air construction, and energy storage devices are explicitly prohibited. Check out the www.vtol.org website for the official rules, which goes over everything in detail.
After looking at the rules, I believe the contest is doable. It only says you need to momentarily exceed 3 meters and total hover time is only 1 min. A cyclist can put out a lot more power for 1 min than s/he can for three hours.
Just keep in mind, this is nowhere close to the achievment of the Gossamer Albatross, which actually had sustained, controllable flight for close to 3 hours. This "helicpoter" prize seems pretty pointless to me.
Then you need to study helicopters so you wont make such a naive statement! This is, in fact, harder, than a human powered airplane. McCready said so himself - if you don't know who he is Google him.
I had a thought (beware)...
A lot of stuctural weight is required to support the pilot in the middle.
http://www.humanpoweredhelicopters.org/yuri1/YURI_1.jpg
Now, it's well established by the Gossamer Albatross that a single Bryan Allen can power a plane over a comparatively long time span in straight and level flight. Flying in circles would require a bit more work, but over a shorter span of time.
Four of these things,
http://www.bfi.org/images/content/frontpage_events/gossamer.jpg
tethered to fly in a circle, mutually constrained by relatively light weight struts and cables, and powered by four Bryan Allens would be capable of achieving the desired result.
The craft should have an overall diameter of about 400 feet. That would take a big gymnasium.
Useless facts. The largest hanger in the world wouldn't be enough.
http://www.distant.ca/UselessFacts/fact.asp?ID=165
"CargoLifter hangar, located in Brand, Germany (60 kilometres south of Berlin) on a former Soviet military airport, is the largest self-supporting hangar in the world. With 360-meters in length, 210-meters in width and 107-meters in height the hanger was designed to accommodate the planned CargoLifter CL 160, a 260-meter long airship."
Self propelled helicoptering should be an outdoor sport.
Useless facts. The largest hanger in the world wouldn't be enough.
http://www.distant.ca/UselessFacts/fact.asp?ID=165
"CargoLifter hangar, located in Brand, Germany (60 kilometres south of Berlin) on a former Soviet military airport, is the largest self-supporting hangar in the world. With 360-meters in length, 210-meters in width and 107-meters in height the hanger was designed to accommodate the planned CargoLifter CL 160, a 260-meter long airship."
Self propelled helicoptering should be an outdoor sport.
Provided you have very calm winds, yes. Large indoor areas pose problems because the circulation of the air inside the (Gymnasium!) as a result of the induced velocity will cause the rotorcraft to inevitable drift outside the limits of the (10?) meter box.
Provided you have very calm winds, yes. Large indoor areas pose problems because the circulation of the air inside the (Gymnasium!) as a result of the induced velocity will cause the rotorcraft to inevitable drift outside the limits of the (10?) meter box.
It may be moot, since the widest indoor flat area I could find was about 260 meters, but I'm not following. The helicopter will induce some toroidal flow of air--up on the outside, and down in the middle. Will off-center cause positive feedback to draw it further off-center?
Mech_Engineer
Nov27-09, 03:49 PM
No, this is wrong and not based on any sort of calculation. Run the numbers and you will find you are off by an order of magnitude.
You are about right on the weight of the cyclist though.
What formulas should I be using to calculate the required power for a helicopter?
I looked at it from a thrust standpoint, and used the weight of the DaVinci III as a guide for human-powered helicopter dimensions. With a weight of 227 pounds, and an induced wind velocity of 35 mi/hr (I just guessed at this, the DaVinci III report had no specs), you have to push 142 lb/s of air for a total of 111,600 cfm, and that works out to 10.5 horsepower required to gain stable flight outside of the ground effect.
What formulas should I be using to calculate the required power for a helicopter?
I looked at it from a thrust standpoint, and used the weight of the DaVinci III as a guide for human-powered helicopter dimensions. With a weight of 227 pounds, and an induced wind velocity of 35 mi/hr (I just guessed at this, the DaVinci III report had no specs), you have to push 142 lb/s of air for a total of 111,600 cfm, and that works out to 10.5 horsepower required to gain stable flight outside of the ground effect.
You should write and run a BEMT code. I have no idea where your ad-hoc numbers come from. As a first order analysis, you could just use momentum theory itself (which does not require any code).
P = T^{3/2}/\sqrt{2\rho A}
Using R = 50' and T = 227lb, the power is 559.59 (whatever units it is fl-lb/s, or something...) or about 1.01 HP. This is obviously a first order analysis and one would have to use BEMT for better estimates at HOGE. An order of magnitude less than your estimate! (And we have not even gotten into any of the actual hard technical challenges!)
russ_watters
Nov27-09, 07:50 PM
Then you need to study helicopters so you wont make such a naive statement! This is, in fact, harder, than a human powered airplane.
You misunderstood my point. I know it is harder than a human powered airplane - and that's why they have to make the prize for such a small achievement.
In other words, you can't fly this thing across the English Channel.
You misunderstood my point. I know it is harder than a human powered airplane - and that's why they have to make the prize for such a small achievement.
In other words, you can't fly this thing across the English Channel.
My bad. You would have a hell of a time flying this thing even in a straight line! The power requirements are horrible, and the rotation of the blades mean the stresses quickly kill you, because things have to be build bulkier. It's a hell of a problem compared to the human powered airplane (HPA).
Momentum theory (http://en.wikipedia.org/wiki/Momentum_theory)
Blade element theory (http://en.wikipedia.org/wiki/Blade_element_theory)
My hopes are dashed (see my post #43) by the following outlandish rule...
http://www.vtol.org/awards/hphregs.html#4.
4.1.2 The machine shall be a rotary wing configuration capable of vertical takeoff and landing in still air, and at least one member of the crew shall be non-rotating.
Or...I will require a freshly made, newborn volunteer, as light in weight as possible, to function as the fifth crew member, suspended in a non rotating, centrally located bassinette.
After more internet searching than I expected in order to circumvent infant labor laws, I discovered that the "world's smallest midget" is 28 inches tall. With some proportional comparison, this yields a nominal body weight of 18 pounds. Erroring on the conservative side, I expect to obtain the services of a 25 pound dwarf to provide the requisite fifth, non-rotating crew member.
After providing for a crash cage and mechanism to provide non-rotation of the central crew member plus the supporting cables, the central mass should weigh an effective 50 pounds. With four cables tensioned at 200 pounds apiece running to each Condor pilot's center of lift, the fifth pilot should be suspended at an altitude of 1/16th the flight radius below each Condor's lifting surface.
After some back of the envelope considerations, the flight radius of each Condor should be about 400 feet. This implied that the fifth pilot will be suspended 25 feet below the lifting blades.
To meet the requirement:4.4.1 The flight requirements shall consist of hovering for one minute while maintaining flight within a 10-meter square. During this time the lowest part of the machine shall exceed momentarily 3 meters above the ground.the blades will be required to obtain 35 feet of altitude + 3 feet of suspended fifth pilot = 38 feet. This is within some small ground effect for each Condor (wingspan of 100 ft.).
The overall diameter of the Helicopter will be about 900 ft.
Will each Condor provide the centrifugal force necessary to tension the cables to the 5th crew member?
Each Condor will obtain about 25 feet per second, based upon the information from Wikipedia.
Using
v^2 = ar
were v =25 feet per second
and r = 400 feet
The centripital acceleration of each Condor will be 1.6 foot pounds per sec2. The mass of each Condor will be about 32 Kg plus pilot (wikipedia reference, again).
After some calculations, each Condor is capable of providing only 10 pounds of radial force to hold up the fifth crew member. This is unacceptable.
Ideas anyone?
mheslep
Nov29-09, 06:47 PM
I'll absolutely dismiss it. The power that can be provided by a good cyclist is somewhere in the area of 300 W. Not only will you be hard pressed to find a very light person that can put out that kind of continuous power, ...It's not very continuous, but olympic calibre athletes can do work at 600W for 6 minutes. Such an athlete might helo across a hefty lake then, never the channel.
It's not very continuous, but olympic calibre athletes can do work at 600W for 6 minutes. Such an athlete might helo across a hefty lake then, never the channel.
Damn, if they can do 600W for 6 mins thats extremely impressive.
mheslep
Nov30-09, 04:19 PM
Damn, if they can do 600W for 6 mins thats extremely impressive.
To my mind, olympic rowers in these time frames (6 minutes), out perform any other athlete type.
The athletes are frequently tested on ergometers (flywheel machines). The world record a few years ago was 5 min 36 s. (http://en.wikipedia.org/wiki/List_of_world_records_in_rowing#Indoor_Records) over 2000 meters. That's a continuous power output (http://concept2.co.uk/training/guide?article=watts_conversion) of 590W, i.e. work done on the machine. Over 500M (1m 16s) these guys can exceed 1HP. I've tested at the 2k distance a hundred times in competition and came in, ehem, somewhat lower. The typical top 10 school college rower (male) will rate at about 430W.
BTW, the do-it-yourself helo would have to hold that record holder's 97kg, 2m to get that power:
http://thamesrc.files.wordpress.com/2008/02/waddell.jpg
FredGarvin
Nov30-09, 04:33 PM
It's not very continuous, but olympic calibre athletes can do work at 600W for 6 minutes. Such an athlete might helo across a hefty lake then, never the channel.Yeah. I wouldn't use that as a data point. Those are definitely outliers from the norm.
mheslep
Nov30-09, 04:51 PM
Those are definitely outliers from the norm.So is this idea of a human powered helo. :wink:
Mech_Engineer
Nov30-09, 07:09 PM
The point is that a helicopter like is being proposed needs at least 1hp (745W) to fly (I'm still convinced it would be more, but flying within the ground effect does help). The problem is, every pound kills you, and "successful" designs like the Davinci III only had an available payload of 59kg (130lb) for the pilot. Even powerful professional athletes which are significatly heavier cannot sustain that kind of output for very long.
The point is that a helicopter like is being proposed needs at least 1hp (745W) to fly (I'm still convinced it would be more, but flying within the ground effect does help).
I just showed you a calculation concerning the power.
The problem is, every pound kills you, and "successful" designs like the Davinci III only had an available payload of 59kg (130lb) for the pilot. Even powerful professional athletes which are significatly heavier cannot sustain that kind of output for very long.
That's right exactly right, and the power goes with the weight^(3/2).
Does anyone know how high Allen flew crossing the English channel?
My second question would be, what is ground effect as a function of wingspan?
Edit: I've been searching for Bryan Allen's estimated power output and weight while crossing the channel and haven't found them.
FredGarvin
Dec1-09, 07:47 AM
Ground effect is essentially any height below one rotor diameter.
The aircraft was powered using pedals to drive a large two-bladed propeller. Piloted by amateur cyclist Bryan Allen, it completed the 35.8 km (22.2 mi) crossing in 2 hours and 49 minutes, achieving a top speed of 29 km/h (18 mph) and an average altitude of 1.5 metres (5 feet).
The empty mass of the structure was only 32 kg (71 lb), although the gross mass for the Channel flight was almost 100 kg (220 lb). To maintain the craft in the air it was designed with very long tapering wings (high aspect ratio), like those of a glider, allowing the flight to be undertaken with a minimum of power. In still air the required power was of the order of 0.4 horsepower (300 W), though even mild turbulence made this figure rise rapidly.
That's nearly full ground effect. The root of the wing was maybe 10 feet and the tips another 10 feet or so. This compares to a span of 100 feet.
I would expect that ground effect is exponential decaying with height.
I think I should discover the difference in total ground effect to none. That is "What is the maximum percent gain in lift due to ground effect?"
Didn't you like my last post Fred? This thread is about a contest with no practical application, isn't it?
Fred, on a more serious note, the contents of prize state nothing limiting supporting equipment. Ground effect could be sustained throughout the required excursion to 10 feet by ducting the blades with a circular fence.
How are you at hovercraft ducted fans?
Mech_Engineer
Dec3-09, 12:39 AM
Fred, on a more serious note, the contents of prize state nothing limiting supporting equipment. Ground effect could be sustained throughout the required excursion to 10 feet by ducting the blades with a circular fence.
How are you at hovercraft ducted fans?
You couldn't have a giant duct, because the rules state the lowest part of the "helicopter" has to attain the maximum height. The bottom portion of the "ducts" would therefore have to reach the height.
I doubt you could justify such a system weight-wise anyway.
dr dodge
Dec3-09, 11:42 AM
"4.1.4 No devices for storing energy either for takeoff or for use in flight shall be permitted. Rotating aerodynamic components, such as rotor blades, used for lift and/or control are exempt from consideration as energy storing devices"
couldn't you use multiple staged rotors with a gearing so it took maybe an hour to get everything rotating in a "no lift mode" then after critical rotation is reached, pull on the stick to get the pitch needed. during "run up" with a rotor not fighting for lift, I would think rotational velocity could be brought up high enough that inertia would then help keep it rotating with less immediate power needed?
just a little sprinkle to add to the current brainstorm
dr
"4.1.4 No devices for storing energy either for takeoff or for use in flight shall be permitted. Rotating aerodynamic components, such as rotor blades, used for lift and/or control are exempt from consideration as energy storing devices"
couldn't you use multiple staged rotors with a gearing so it took maybe an hour to get everything rotating in a "no lift mode" then after critical rotation is reached, pull on the stick to get the pitch needed. during "run up" with a rotor not fighting for lift, I would think rotational velocity could be brought up high enough that inertia would then help keep it rotating with less immediate power needed?
just a little sprinkle to add to the current brainstorm
dr
Why on earth would you do such a thing? Think of it this way, what do you think will happen to the stresses at the hub when you suddenly dump the collective? The change in AoA will give a large impulsive pitching moment - bye bye blades.
You couldn't have a giant duct, because the rules state the lowest part of the "helicopter" has to attain the maximum height. The bottom portion of the "ducts" would therefore have to reach the height.
I doubt you could justify such a system weight-wise anyway.
The fence or duct is attached to the ground, not the helicopter.
The fence or duct is attached to the ground, not the helicopter.
This is outside the spirit of the rules, and would not be allowed, for obvious reasons.
FredGarvin
Dec3-09, 10:51 PM
Didn't you like my last post Fred? This thread is about a contest with no practical application, isn't it?
I can't really comment on it basically because I'm not sure where you are going with it. The reason ground effect exists is because of the blockage of reingested vortices at the rotor tips. It's either blocking that reingestion or it's not. I doubt there is any exponential decay of ground effect, or however you want to put it.
[EDIT] OK. So I did some looking after writing that, and found some references that disprove what I wrote. Seddon shows a theoretical expression (making a few major assumptions) that seems to work well in most cases:
\left[\frac{T}{T_\inf}\right] = \frac{1}{1-\frac{R}{4Z}^2}
This is supported by Figure 7 from Knight and Hefner:
http://naca.central.cranfield.ac.uk/reports/1941/naca-tn-835.pdf
I also found this graphic which I am kicking myself because I have seen this before (a longggggg time ago)
http://www.dynamicflight.com/aerodynamics/ground_effect/geffthrust.gif
So it's not exponential, but it does decrease with increasing Z/R ratio. I stand humbly corrected.
This is outside the spirit of the rules, and would not be allowed, for obvious reasons.
So it's within the rules, but outside some unstated rules?
To continue with this unspirited concept, it occurs to me that it might be equally beneficial to have 'ceiling' effect to double things up. I'm not sure if this makes sense.
Edit: I've re-read the rules, and the spirit erules to eliminate hovercraft and other stuff outside the intended box). But to be fair, all these attempts would have exploited ground effect.
Mech_Engineer
Dec3-09, 11:32 PM
But to be fair, all these attempts would have exploited ground effect.
The only way one of these things can get off the ground is to exploit the ground effect. Too much power will be required to fly outside the ground effect, that's why these things barely make it a foot or two off the ground with 100ft rotor diameters.
The only way one of these things can get off the ground is to exploit the ground effect. Too much power will be required to fly outside the ground effect, that's why these things barely make it a foot or two off the ground with 100ft rotor diameters.
Additionally, the DaVinci III (with 100ft rotors) did not hover for very long because of stability. So you cannot say it was due to power issues. The Yuri had to stop its flight because it ran out of space due to drift. Again, a stability issue, not power. So sweeping statements about the power being too high are not strictly valid.
dr dodge
Dec4-09, 07:02 AM
"Why on earth would you do such a thing? Think of it this way, what do you think will happen to the stresses at the hub when you suddenly dump the collective?"
the main reason is that the total accumulated work over time is "banked" in an hour or two of "run up" in order to have momentum help to keep the rotors going with the available power from the pilot. Isn't the changing angle of attack what causes a conventional "rotor'd craft" to fly? If so, why in this application it assembly would self destruct?
dr
Mech_Engineer
Dec4-09, 09:58 AM
Additionally, the DaVinci III (with 100ft rotors) did not hover for very long because of stability. So you cannot say it was due to power issues. The Yuri had to stop its flight because it ran out of space due to drift. Again, a stability issue, not power. So sweeping statements about the power being too high are not strictly valid.
Stability or no, the guy is pedaling like a maniac and barely made it a foot off the ground. If power were not a major issue, the craft would have been able to take off and consistently gain altitude with time. Instead, it seems to be they lift off and stabilize in altitude at a very low height.
Stability or no, the guy is pedaling like a maniac and barely made it a foot off the ground. If power were not a major issue, the craft would have been able to take off and consistently gain altitude with time. Instead, it seems to be they lift off and stabilize in altitude at a very low height.
But they don't stabilize at a low height. The blades were so long that any small angular deflection results in a tip strike. My point is that they did not have the stability to try and get to any significant height.
the main reason is that the total accumulated work over time is "banked" in an hour or two of "run up" in order to have momentum help to keep the rotors going with the available power from the pilot.
This is fundamentally wrong if you look at the power output curve of a person and the power demands of the aircraft. You simply do not want to use such a method.
Isn't the changing angle of attack what causes a conventional "rotor'd craft" to fly? If so, why in this application it assembly would self destruct?
dr
My understanding of what you have described is to spin up the rotors for an hour (and waste the pilots energy for no reason with a bunch of gearing that adds unnecessary weight) and suddenly change the collective on the blades. You would have to change the AoA of the blades quickly, otherwise they will slow back down. So you now need a larger, heavier blade hub to absorb the large transient stresses. This is idea gets worse and worse any way you slice it.
My understanding of what you have described is to spin up the rotors for an hour (and waste the pilots energy for no reason with a bunch of gearing that adds unnecessary weight) and suddenly change the collective on the blades. You would have to change the AoA of the blades quickly, otherwise they will slow back down. So you now need a larger, heavier blade hub to absorb the large transient stresses. This is idea gets worse and worse any way you slice it.Not only that, but Dodge is essentially suggesting an energy storage scheme, in this case storing energy in the blades angular momentum, which is against the rules.
russ_watters
Dec4-09, 03:01 PM
So it's within the rules, but outside some unstated rules? Phrak, please drop this line of discussion, as it is distracting from the purpose of the thread. You're not the one who gets to interpret the rules of the contest, the people running it are. So it isn't useful to try an weasel around them for the purpose of discussing it in this forum, when it is obvious that such weaseling wouldn't fly with the organizers of the contest.
russ_watters
Dec4-09, 03:03 PM
Not only that, but Dodge is essentially suggesting an energy storage scheme, in this case storing energy in the blades angular momentum, which is against the rules. On that point, I'm not so sure the judges would agree. Yes, he's essentially saying to use the rotors as flywheels, but the judges may consider that acceptible. The rules certainly imply it where they give a specific exemption from that rule for rotors.
Not only that, but Dodge is essentially suggesting an energy storage scheme, in this case storing energy in the blades angular momentum, which is against the rules.
What he said is OK, it's not energy storage because the pilot put in his own energy to spin up the rotors and then went on with the flight. However, it's a useless endeavour.
What you could not do, is spin them up, and have someone else jump in and then take off. Or, store energy in a spring, and then come back an hour later and try to fly after you are refreshed, along with the help of the spring.
What he said is OK, it's not energy storage because the pilot put in his own energy to spin up the rotors and then went on with the flight. However, it's a useless endeavour.
What you could not do, is spin them up, and have someone else jump in and then take off. Or, store energy in a spring, and then come back an hour later and try to fly after you are refreshed, along with the help of the spring.You need not switch out the human. If they allow energy storage as long as it is 'the same continuous operator', then someone could leisurely store up 100 watt-hours in an hour of work/pedalling and then release it all via some mechanism (e.g. electric motor) at the rate of 6kw (8HP) for one minute of flight, collect $20k, thank you. But this is moot, storing energy is not the goal of this exercise.
I can't really comment on it basically because I'm not sure where you are going with it. The reason ground effect exists is because of the blockage of reingested vortices at the rotor tips. It's either blocking that reingestion or it's not. I doubt there is any exponential decay of ground effect, or however you want to put it.
[EDIT] OK. So I did some looking after writing that, and found some references that disprove what I wrote. Seddon shows a theoretical expression (making a few major assumptions) that seems to work well in most cases:
\left[\frac{T}{T_\inf}\right] = \frac{1}{1-\frac{R}{4Z}^2}
This is supported by Figure 7 from Knight and Hefner:
http://naca.central.cranfield.ac.uk/reports/1941/naca-tn-835.pdf
I also found this graphic which I am kicking myself because I have seen this before (a longggggg time ago)
http://www.dynamicflight.com/aerodynamics/ground_effect/geffthrust.gif
So it's not exponential, but it does decrease with increasing Z/R ratio. I stand humbly corrected.
Thanks Fred, that would help a great deal, but I'm afraid I can't figure out the variables.
There is a good and obvious reason storing energy in the angular momentum of the rotors is not significantly useful. The energy storage increases as omega squared. The drag of the rotors also increases as omega squared and (delited) [directly proportional to the excess mass deleted, as this is in error, as pointed out by Cyrus]. The power required to keep the excess mass aloft is proportional to the excess mass. The best one can do is weight the ends of the rotors and hope you still have excess stored energy after 5 minutes to stay aloft.
Without doing any heavy mental lifting, this means that you have a short time to use the energy to give you the pop up to the 3 meter requirement You are then are required to keep the excess mass aloft in ground effect.
Phrak, please drop this line of discussion, as it is distracting from the purpose of the thread. You're not the one who gets to interpret the rules of the contest, the people running it are. So it isn't useful to try an weasel around them for the purpose of discussing it in this forum, when it is obvious that such weaseling wouldn't fly with the organizers of the contest.
Didn't I already note that in a past thread?
I haven't come across a great deal of creative thinking on this thread. Two serious-money attempts at this have been made, without success, using fairly common approaches. Since then somewhat more rigid materials have become more commonly available. (How does the specific modulus of commercially fabricable carbon-carbon compare to aluminum or steel? The last two are equal.)
I offered a very feasible helicopter that no one seems to given noticed. Why is that? It’s difficult to expect much from one's fellow posters, without some prodding, after such a blank reception.
Do you have anything yourself?
Didn't I already note that in a past thread?
I haven't come across a great deal of creative thinking on this thread. Two serious-money attempts at this have been made, without success, using fairly common approaches. Since then somewhat more rigid materials have become more commonly available. (How does the specific modulus of commercially fabricable carbon-carbon compare to aluminum or steel? The last two are equal.)
You are under the false premise that they were not made of carbon fiber - they were.
I offered a very feasible helicopter that no one seems to given noticed. Why is that? It’s difficult to expect much from one's fellow posters, without some prodding, after such a blank reception.
Did you mean two hang gliders 900' apart?
The drag of the rotors also increases as omega squared and directly proportional to the excess mass.
Come again? Drag has nothing to do with mass.
Come again? Drag has nothing to do with mass.
My mistake. Drag increases as omega squared, but not proportional to the mass.
What do you think of wing tips on the rotors? I didn't seen any on the attempted craft. Would they contribute to adverse to the individual rotors around their axiis? Or result in flutter?
My mistake. Drag increases as omega squared, but not proportional to the mass.
What do you think of wing tips on the rotors? I didn't seen any on the attempted craft. Would they contribute to adverse to the individual rotors around their axiis? Or result in flutter?
To be formally correct, it increases with the tangential velocity, (r*omega)^2. I thought about wingtips but there was a reason why they were not justified. I cant remember right now, but I'll look up why and post later. Aerodynamically, there is only so much you can do here. In my mind, the key to getting this to work is a very clever structural design that is extremely light weight while meeting the stress requirements. This is much easier said that done. Quad anything means huge weight penalties, but inherent stability. A tip driven rotor, or coaxial means *significant* weight savings, but an unstable monster. Pick your poison.
To be formally correct, it increases with the tangential velocity, r*omega^2. I thought about wingtips but there was a reason why they were not justified. I cant remember right now, but I'll look up why and post later. Aerodynamically, there is only so much you can do here. In my mind, the key to getting this to work is a very clever structural design that is extremely light weight while meeting the stress requirements. This is much easier said that done. Quad anything means huge weight penalties, but inherent stability. A tip driven rotor, or coaxial means *significant* weight savings, but an unstable monster. Pick your poison.
I have concern over the upward bending of each rotor as a result of lift. This is forth order, isn't it? Do you number for this?
I have concern over the upward bending of each rotor as a result of lift. This is forth order, isn't it? Do you number for this?
It's called coning. All rotors, including regular helicopters, do this.
Sorry to be criptic. All I know is that torsional rigidity of a tube is to the forth power of the radius.
We've gotten out of sync. But now that I know you are talking about a hinged rotor rather than rigid, I think you will have too much coning, won't you? Is there a way to suppress it?
[QUOTE=Cyrus;2475314]You are under the false premise that they were not made of carbon fiber - they were.]
carbon-carbon
We've gotten out of sync. But now that I know you are talking about a hinged rotor rather than rigid, I think you will have too much coning, won't you? Is there a way to suppress it?
I didn't say anything specific to a hinged rotor. The rotor will cone no matter what the hub attachment. The only way to minimize this is to increase stiffness, which will inevitably come from a heavier blade - unless you can find a material that is stiff in the direction you need for the same weight (good luck).
I didn't say anything specific to a hinged rotor. The rotor will cone no matter what the hub attachment. The only way to minimize this is to increase stiffness, which will inevitably come from a heavier blade - unless you can find a material that is stiff in the direction you need for the same weight (good luck).
Then we are talking about the same thing, where the limiting factor upon weight considerations in rididity over strength.
Materials to compare are carbon fiber/carbon from mesophase pitch that has higher Youngs modulus compared to carbon fiber derived from the more common polyacrylonitrile--popular for it's strength.
However the carbon fiber/carbon may be prohibitively expensive. It is carbon fiber composite that undergoes a second and sometimes third process of reheating then reintroduction of matrix material.
dr dodge
Dec7-09, 08:31 AM
"4.1.4 No devices for storing energy either for takeoff or for use in flight shall be permitted. Rotating aerodynamic components, such as rotor blades, used for lift and/or control are exempt from consideration as energy storing devices"
its not against the rules
I can see how the added mass and complexity would start you down the road of diminishing returns
thanks for the explain
dr
rplatter
Dec7-09, 02:24 PM
Interesting problem.
I would suggest starting with something that already exists, like a gyrocopter.
And yes, I know they require forward momentum to get moving, but they are light and run on low power.
If you could get the blade moving fast enough, you could achieve lift off.
Stability is another factor. Some Gyrocopters use gravity similar to the way a hanglider does. Shifting the weight of the pilot angles the collective.
Height would be controlled by speed of the blade.
Rotation becomes the difficult part here. Both of the blades and of the craft.
Possibly a counter rotating blade unit, or an angled fin projecting into the down draft.
attaching power to the blade unit becomes touchy if you are using a free hanging pilot compartment. maybe a belt mechanism or a universal joint. I would offset the drive shaft from the blade hub so you could use some type of gearing at that point and to minimize the difficulty of construction.
Another approach would be to use laminar air flow and instead of a bunch of blades just have a saucer.
If you spin a smooth plate it will force air out from the center. (Tesla turbine)
shape it in a dome shape and the air going out will be directed down also.
The dome/saucer will also provide structural support to the entire structure.
I would imagine that a fairly soft but strong material could be used, a large mylar sheet or something. With a belt around the outside edge to provice rigidity. Just stretch it tight and smooth.
You still have to deal with the craft rotation, but that may be simple.
Interesting problem.
I would suggest starting with something that already exists, like a gyrocopter.
And yes, I know they require forward momentum to get moving, but they are light and run on low power.
How is a gyrocopter going to hover?
If you could get the blade moving fast enough, you could achieve lift off.
That's fairly obvious...
Stability is another factor. Some Gyrocopters use gravity similar to the way a hanglider does. Shifting the weight of the pilot angles the collective.
Height would be controlled by speed of the blade. Rotation becomes the difficult part here. Both of the blades and of the craft. Possibly a counter rotating blade unit, or an angled fin projecting into the down draft. attaching power to the blade unit becomes touchy if you are using a free hanging pilot compartment. maybe a belt mechanism or a universal joint. I would offset the drive shaft from the blade hub so you could use some type of gearing at that point and to minimize the difficulty of construction.
Err....okay. Try getting a person to pedal around 1 HP and see if they are also able to shift their body weight around (This isnt going to happen).
Another approach would be to use laminar air flow and instead of a bunch of blades just have a saucer. If you spin a smooth plate it will force air out from the center. (Tesla turbine) shape it in a dome shape and the air going out will be directed down also.
The dome/saucer will also provide structural support to the entire structure.
I would imagine that a fairly soft but strong material could be used, a large mylar sheet or something. With a belt around the outside edge to provice rigidity. Just stretch it tight and smooth. You still have to deal with the craft rotation, but that may be simple.
Errr......okay. I'd like to see some calculations as to why you think this would work.
FredGarvin
Dec7-09, 05:43 PM
Interesting problem.
I would suggest starting with something that already exists, like a gyrocopter.
And yes, I know they require forward momentum to get moving, but they are light and run on low power.
If you could get the blade moving fast enough, you could achieve lift off.
Stability is another factor. Some Gyrocopters use gravity similar to the way a hanglider does. Shifting the weight of the pilot angles the collective.
Height would be controlled by speed of the blade.
Rotation becomes the difficult part here. Both of the blades and of the craft.
Possibly a counter rotating blade unit, or an angled fin projecting into the down draft.
attaching power to the blade unit becomes touchy if you are using a free hanging pilot compartment. maybe a belt mechanism or a universal joint. I would offset the drive shaft from the blade hub so you could use some type of gearing at that point and to minimize the difficulty of construction.
Another approach would be to use laminar air flow and instead of a bunch of blades just have a saucer.
If you spin a smooth plate it will force air out from the center. (Tesla turbine)
shape it in a dome shape and the air going out will be directed down also.
The dome/saucer will also provide structural support to the entire structure.
I would imagine that a fairly soft but strong material could be used, a large mylar sheet or something. With a belt around the outside edge to provice rigidity. Just stretch it tight and smooth.
You still have to deal with the craft rotation, but that may be simple.
It's not an interesting problem because it is fundamentally flawed. It is a dead issue. Period.
You can throw terms like "laminar flow" or Tesla turbine but I don't think you really have any clue as to what you are talking about. A gyrocopter, while using less power, still requires ORDERS OF MAGNITUDE more power than a single human can provide (and those are olympian athletes). On top of it, they can't hover.
Let's stick to actual engineering discussions and not turn this into a thread that belongs in Skepticism & Debunking.
Interesting problem.
I appreciate your input rplatter. You're thinking far afield, and outside what at first blush appears unworkable. Nothing wrong with that, that I can see. It has a chance of lending inspirational direction.
dr dodge
Dec8-09, 07:09 AM
I would like to "refine" my previous input.
I am still sticking with the dual rotor assembly. if the inside "stability" rotor has more mass than the outside one it should work as an inertial gyro that should give some added stability to the system. you would drive the outer rotor off the inside one.
as far as the angle of attack problem, how about this. the outer blade is completely flat to start and then, when "critical rotation" is reached you inflate a series of tubes, one at a time. the "tube bladder" takes the flat rotor blade, and gently makes it an air foil. no blade angle changes. Using pressurized internal structural members would add rigidity making the material used potentially thinner than if just stand alone. the hardest part I can see is evenly inflating both rotors evenly to avoid instability. then use compressed air or air water "retro-rockets" for the lateral corrections, drive the compressor off of the inner disc. and use 2 people, that way one person is the "engine" and the second is "second engine" untill run up is completed, then they assist for power and pilot the craft. I can see an advantage in 2 persons because it would be very hard to concentrate on control while pedaling your butt off.
and a side note, if the rotors were on the ground you'd get an "extension" of ground effect
you may fire at will...lol
dr
Another approach would be to use laminar air flow and instead of a bunch of blades just have a saucer.
If you spin a smooth plate it will force air out from the center. (Tesla turbine) shape it in a dome shape and the air going out will be directed down also. The dome/saucer will also provide structural support to the entire structure. I would imagine that a fairly soft but strong material could be used, a large mylar sheet or something. With a belt around the outside edge to provice rigidity. Just stretch it tight and smooth. You still have to deal with the craft rotation, but that may be simple.
This may have some traction if it can stay within the bounds of mutable rules.
Though these so-called laminar flow lifting things don't appear to be very efficient, it may be possible to produce an efficient version powered by a central propeller.
The more air one can grab per unit load, the greater efficiency to maintain altitude--less dv/dt is required for each parcel of air. This is accomplished on fixed wing aircraft by increasing the wing span.
If the skirt can be made large and self supporting, or nearly so, it would have a small overhead in weight penalty, and support the total load upon a larger volume of air.
If the skirt can be made large and self supporting, or nearly so, it would have a small overhead in weight penalty, and support the total load upon a larger volume of air.
With no calculations to show the power requirements, or the estimated weight, this is really unsupported speculation. I would avoid such statements with nothing to back it up. His idea sounds absolutely terrible.
With no calculations to show the power requirements, or the estimated weight, this is really unsupported speculation. I would avoid such statements with nothing to back it up. His idea sounds absolutely terrible.
Yeah, I know, but so is human powered flight.
Brian_C
Dec13-09, 01:47 AM
Just for giggles, I made a spreadsheet which calculates the minimum required rotor diameter as a function of rotor thrust based on elementary momentum theory (see attached). For a 180 lb man who can output 300W (0.4 hp) of power, the minimum rotor diameter is 2656 ft. The rotor disc area is an incredible 127 acres. Note that the disc loading is measured in lb/acre. Also note that we're ignoring the weight of the vehicle, figure of merit, transmission losses, and a thousand other variables.
Not a very practical idea.
Just for giggles, I made a spreadsheet which calculates the minimum required rotor diameter as a function of rotor thrust based on elementary momentum theory (see attached). For a 180 lb man who can output 300W (0.4 hp) of power, the minimum rotor diameter is 2656 ft. The rotor disc area is an incredible 127 acres. Note that the disc loading is measured in lb/acre. Also note that we're ignoring the weight of the vehicle, figure of merit, transmission losses, and a thousand other variables.
Not a very practical idea.
This is completely wrong. Go back and check your work. (I've done all the calculations, in much, much more depth than you can possibly imagine -and no, i'm not going to share those results). You are orders of magnitude wrong. To give you an idea: I know the weight down to each rib in the past HPHs. When I see people say "such and such might work and the weight is possible" I simply shake my head at the lack of depth in their study of this topic. It's quite apparent too many people are making bogus claims, and/or doing bogus calculations. This is the second wrong calculation I've seen so far, especially considering I did a calculation for you that showed it was just over 1HP for a 100ft rotor... does a 2656 foot rotor seem reasonable to you? Or a disc area in acres......?? Such a statement would/should get you fired in the real world! If you presented this to my helicopter professor in graduate school he would promptly chew you out.
(If you haven't already noticed, I have a pet-peeve about engineers presenting results without doing sanity checks :smile:)
Side: Excel, really? Learn MATLAB.
mheslep
Dec13-09, 05:21 PM
Such a statement would/should get you fired in the real world! So will attitude. Maybe not quickly, but it you'll find yourself closer to the door everyday.
Side: Excel, really? Learn MATLAB. Many very, very talented engineers manage to use spreadsheets, or octave, numerical python, etc, and avoid the basic $1950 plus endless more thousands for toolboxes.
So will attitude. Maybe not quickly, but it you'll find yourself closer to the door everyday.
That's why I added a :smile:, it was meant as a friendly jab.
Many very, very talented engineers manage to use spreadsheets, or octave, numerical python, etc, and avoid the basic $1950 plus endless more thousands for toolboxes.
Spreadsheets..........<shudder>
No, but seriously, go back and rework your numbers BrianC. You should get a rotor radius of 193.2' using momentum theory with 0.4HP HOGE (I think you have a units error somewhere).
Solve for radius:
R=\frac{T^{3/2}}{\sqrt{2 \rho \pi } P}
T = 300 lbs (Airplane plus pilot)
\rho = 0.002 slug/ft^3
P = 0.4 HP * 550
FredGarvin
Dec13-09, 07:29 PM
I don't knock anyone for trying. Especially when it is in a realm where one may not have any particular feel for an expected result. That being said, there is a border where answers just aren't worth considering. If anyone thinks that practicing engineers don't make mathematical mistakes, then someone hasn't been in a real engineering job. That's why we have coworkers and others to bounce figures off of and to check behind us. There is no sane company out there that just takes an engineer's calculations and just runs with them. There should always be some kind of checker.
Spreadsheets are awesome when properly used.
I don't knock anyone for trying. Especially when it is in a realm where one may not have any particular feel for an expected result. That being said, there is a border where answers just aren't worth considering. If anyone thinks that practicing engineers don't make mathematical mistakes, then someone hasn't been in a real engineering job. That's why we have coworkers and others to bounce figures off of and to check behind us. There is no sane company out there that just takes an engineer's calculations and just runs with them. There should always be some kind of checker.
Spreadsheets are awesome when properly used.
If you want to blow your mind, calculate the shaft torques and see what they come out to....NASTY NASTY NASTY. The low rotor RPM makes the torque go insanely high.
FredGarvin
Dec13-09, 09:57 PM
Well yeah! Especially for a rotor disk that is half mile in diameter....give or take a few hundred feet...
I did my own sanity check on wikipedia's momentum theory (http://en.wikipedia.org/wiki/Momentum_theory) equation.
P = \sqrt{\frac{T^3}{2\rho A}}
Units[P] = \frac{md^2}{t^3}}
Assuming rho has units of mass per unit volume,
Units\left[ \frac{T^3}{2\rho A} \right]= m^2 d^4/t^6
I did my own sanity check on wikipedia's momentum theory (http://en.wikipedia.org/wiki/Momentum_theory) equation.
P = \sqrt{\frac{T^3}{2\rho A}}
Units[P] = \frac{md^2}{t^3}}
Assuming rho has units of mass per unit volume,
Units\left[ \frac{T^3}{2\rho A} \right]= m^2 d^4/t^6
How is this a sanity check? There is nothing wrong with the equation for momentum theory....
(BTW, rho is slugs/ft^3)
How is this a sanity check? There is nothing wrong with the equation for momentum theory....
(BTW, rho is slugs/ft^3)
I don't trust anyone's equations I have not derived myself.
I think your .002 value of air density may be off, but I've only visited one web site.
I don't trust anyone's equations I have not derived myself.
I think your .002 value of air density may be off, but I've only visited one web site.
0.002378 slug/ft^3
BTW: Not trusting others equations is a good thing!
With no calculations to show the power requirements, or the estimated weight, this is really unsupported speculation. I would avoid such statements with nothing to back it up. His idea sounds absolutely terrible.
Do you have any idea how to calculate the lift from one of these laminar air devices; I have no idea how to approach it?
Do you have any idea how to calculate the lift from one of these things; I have no idea how to approach it?
No clue - and that's what worries me. If you find anything let me know because I'd be really interested to see how. These things are pretty much the 'magic crystals' and 'healing pyramids' of aerospace, IMO.
No clue - and that's what worries me. If you find anything let me know because I'd be really interested to see how. These things are pretty much the 'magic crystals' and 'healing pyramids' of aerospace, IMO.
I've been scrolling around YouTube for one of the toy demos I once ran into, and can't find one anymore. Apparently I don't know the keywords to use.
Brian_C
Dec14-09, 04:59 AM
I made an algebraic error. Can you tell I'm not a helicopter engineer? See attached.
I think you would need to perform an iterative calculation to come up with realistic results. For a given body weight of the operator, you have to calculate the minimum rotor diameter, then update the total weight of the operator/vehicle based on the added weight of the rotors. When you plug the updated weight (thrust) into the momentum equations, you end up with an even larger rotor diameter! The results will probably not converge unless you use a super light-weight material.
I made an algebraic error. Can you tell I'm not a helicopter engineer? See attached.
I can't seem to open this MATLAB file. :wink:
You should never present your results in units of acres, but otherwise the diameter is now correct. You are pardoned of your engineering sin.... this time. :smile:
Edit to your edit: To go to the next level analysis, you need to write a BEMT code. Here you can account for prandtl tip losses, lift/drag for your chosen airfoil section, pitching moments, and ground effect. This is not pretty, and should not be attempted in excel (seriously, dont even think about it).
FredGarvin
Dec14-09, 08:20 AM
I think your .002 value of air density may be off, but I've only visited one web site.That is the standard day air density converted to sl/ft^3. It's right.
Brian_C
Dec14-09, 01:57 PM
Let's just forget this thread ever happened. :biggrin:
dr dodge
Dec14-09, 02:03 PM
a badger? did I hear a badger?
dinsdale?
dr
That is the standard day air density converted to sl/ft^3. It's right.
OK. I get .00237 slug/ft^2 for international standard density at sea level. Interesting that the thrust is the 1/3 power of the density, so that the variation in density is not so critical. On a crisp cold morning in Death Valley one could exptect to get about 8 to 9% better lift over standard day air density.
How is the standard day air density obtained?
Here's one for you, Cyrus. Have you done the scaling analysis on this sort of problem?
If the weight of the pilot is doubled, how does the size of the structure increase to obtain the same material stresses. The question akin to this is to obtain the same bending radiuses based on material rigidity. I'm not sure if this one should be compared against doubling the total mass or doubling a length, or what-have-you.
The last I can think of asking is how aerodynamic forces scale with a doubling in size of the airframe. (Should fluid velocity be kept constant or also double for this?)
mugaliens
Dec14-09, 11:37 PM
All things being equal, and discounting Reynold's numbers as the weight of the pilot is usually substantially less than than of the airframe and powerplant, whatever the overall weight increase of the pilot increases the total MGTOW, the airframe and powerplant would require a similar increase to achieve the same performance (same stall speed, time to climb, etc.)
Example: Your pilot initially weighs 150 lbs, but after feasting for two years arrives at 300 lbs. His old plane's empty weight + useable fuel was 3,000 lbs.
He has money galore, but loves his old plane, so he's commissioning the design and building of a new plane that'll match the old plane's performance characteristics exactly.
Percentage Increase: (3300-3150)/3150 = 4.8% increase in overall weight of the airframe and powerplant. Because weight increases as the cube of an single dimension, the pilot's new aircraft would have to be just 1.69% larger in any dimensional direction to accomodate the pilot's additional weight gain.
Thus, the new total weight of airframe and powerplant would be 3,050.7 lbs.
The last I can think of asking is how aerodynamic forces scale with a doubling in size of the airframe. (Should fluid velocity be kept constant or also double for this?)
Aerodynamic forces dont change due to airframe size, they depend on the rotor specifications. The "fluid velocity", is termed the rotor inflow, and be calculated (to first order) using the inflow equation.
All things being equal, and discounting Reynold's numbers as the weight of the pilot is usually substantially less than than of the airframe and powerplant, whatever the overall weight increase of the pilot increases the total MGTOW, the airframe and powerplant would require a similar increase to achieve the same performance (same stall speed, time to climb, etc.)
The Reynolds number does not change with the weight of the pilot (or weight in general), so I'm not sure where you're going with this. Also, the pilot weight here is substantial >%50 of the vehicle weight, so your analysis is not valid in this application.
Percentage Increase: (3300-3150)/3150 = 4.8% increase in overall weight of the airframe and powerplant. Because weight increases as the cube of an single dimension, the pilot's new aircraft would have to be just 1.69% larger in any dimensional direction to accomodate the pilot's additional weight gain.
Thus, the new total weight of airframe and powerplant would be 3,050.7 lbs.
This scaling rule is good for intial insights, but one can simply use the equation I provided to see exactly how the rotor radius changes in response to changes in vehicle weight.
I'll have to reread your posts tomorrow with better consideratioin, Cyrus. But this is the reason I ask: Of the 186 tour de France entrants in one year, their weight averaged 156 pounds. We might take this as the optimum weight for best cyclists. Human flight requires some more consideration, as I'm sure you know. The mass of the pilot and how this scales the weight of the aircraft becomes a factor.
But as a baseline, after some research, the average, midline, World Class, 156 pound cyclist can deliver 449 Watts = 0.603 HP = 331 ft-lb-sec-1 over a 5+ minute duration.
I would initially presume that HP/Mass_of_pilot is constant.
All things being equal, and discounting Reynold's numbers as the weight of the pilot is usually substantially less than than of the airframe and powerplant, ...
In this case, such as it is, as Cyrus has said, initially consider the pilot and airframe about equal. Maybe start with an initial estimate of the pilot at 140 lb. and airframe at 30% more, and go from there.
I would initially presume that HP/Mass_of_pilot is constant.
It decays, but the rate of decay would have to be found experimentally for a particular person.
All things being equal, and discounting Reynold's numbers as the weight of the pilot is usually substantially less than than of the airframe and powerplant, whatever the overall weight increase of the pilot increases the total MGTOW, the airframe and powerplant would require a similar increase to achieve the same performance (same stall speed, time to climb, etc.)
Example: Your pilot initially weighs 150 lbs, but after feasting for two years arrives at 300 lbs. His old plane's empty weight + useable fuel was 3,000 lbs.
He has money galore, but loves his old plane, so he's commissioning the design and building of a new plane that'll match the old plane's performance characteristics exactly.
Percentage Increase: (3300-3150)/3150 = 4.8% increase in overall weight of the airframe and powerplant. Because weight increases as the cube of an single dimension, the pilot's new aircraft would have to be just 1.69% larger in any dimensional direction to accomodate the pilot's additional weight gain.
Thus, the new total weight of airframe and powerplant would be 3,050.7 lbs.
OK. You motivate me to do this thing. The simplest is a rescaling of lengths. I prefer doubling. It makes things easier to consider. If materials density is constant then mass increases as 23, as you've noted.
However, aerodynamic forces, Lift and Drag will increase by the factor 22, from
L = k V^2 L^2
D = k V^2 L^2
where L is some typical length. (This will assume, the change in typical length doesn't significantely effect Reynolds number, as you've also noted.)
Aerodynamic moments increase as 23.
M = k V^2 L^3
I would initially presume that HP/Mass_of_pilot is constant.
It decays, but the rate of decay would have to be found experimentally for a particular person.
I'm not sure what you mean, but was saying that I would initially assume that over a population of world class cyclists that cycling power is proportional to the mass of the rider over a realistic weight range of, say 120 to 180 pounds.
mugaliens
Dec15-09, 11:34 PM
Good catch, Phrak. It's why modern larger jets are more efficient in terms of lb-miles travelled per lb of fuel consumed than modern smaller jets.
Given my computations for a light airplane, it won't amount to much at all.
Given the fact you're desiging for a human-powered helo, however, it'll mean a great deal.
I had an idea: Have you considered using solar concentrators, built into the wings, to gather sunlight, piping it down light-tubes to the center where it's used to power a Stirling engine to sping the prop? Or, in the case of your helo, you could have engines mounted about 2/3 of the way out along the rotors, and smaller props to push the rotors around?
Just a thought. I also thought about putting the cyclists out there, as well, if you want to keep the engines fully human.
Good catch, Phrak. It's why modern larger jets are more efficient in terms of lb-miles travelled per lb of fuel consumed than modern smaller jets.
Really, I'm not sure how this works out. Can you give details?
But there is still stress and strain to consider for human powered flight, in general.
Do you recall something called the Square-Cube rule, or square-cube law as applied to the strength of a bone or beam, or even a wing as it scales in length only? The idea is to keep material density unchanged, and the shapes of everything stay the same. It's just scaled up in size. Latently I found that the amazing Wikipedia provides it.
http://en.wikipedia.org/wiki/Square-cube_law
For Aerodynamic Forces:
"When a physical object maintains the same density and is scaled up, its mass is increased by the cube of the multiplier while its surface area only increases by the square of said multiplier. This would mean that when the larger version of the object is accelerated at the same rate as the original, more pressure would be exerted on the surface of the larger object."
For the Stength of a Beam:
"If an animal were scaled up by a considerable amount, its muscular strength would be severely reduced since the cross section of its muscles would increase by the square of the scaling factor while their mass would increase by the cube of the scaling factor."
Unfortunately Wikipeda doesn't present this in terms of the yield strength of a cantilivered beam (or wing) (or rotor), but we can replace "muscle strength" by "yield stress".
The strength of the beam increases as L2 and the mass increases as L3.
I'm still trying to find how rigidity scales.
I had an idea: Have you considered using solar concentrators, built into the wings, to gather sunlight, piping it down light-tubes to the center where it's used to power a Stirling engine to sping the prop? Or, in the case of your helo, you could have engines mounted about 2/3 of the way out along the rotors, and smaller props to push the rotors around?
The challenge in this thread is human powered flight, but check out the NASA Pathfinder.
http://www.nasa.gov/centers/dryden/news/FactSheets/FS-034-DFRC.html
Under the hot summer midday sun, you might expect one horse power per square yard of solar insulation. The best Solar electric panels are about 15% efficient, I think...
Just a thought. I also thought about putting the cyclists out there, as well, if you want to keep the engines fully human.
Well, I did too, but no one took me seriously. It would significantly reduce the weight-per-pilot requirement of the airframe--by as much as 50%. But there's a catch. There must be at least one crew member that cannot rotate but face the same direction throughout the flight.
(BTW, very cool stuff you had on the crosswind landing thread.)
What do you mean by "put the pilot out there." The rules clearly state the pilot cannot be rotating.
What do you mean by "put the pilot out there." The rules clearly state the pilot cannot be rotating.
"Cyclists", in plural, Cyrus. Say you have four blades and put the cyclists in the center of each blade. This means that the bending stress on the blades is cut in half. Belatedly, I recall (to first order, see Poison ratio) that the strain, that leads to coning, is also cut in half.
The rules state that at least one member of the crew must face in the same direction throughout the flight. So this ...complicates things.
How would you go about having at least one nonrotating crew member, where the crew, as the rules call them, are dispersed about the blades to save stuctual weight?
"Cyclists", in plural, Cyrus. Say you have four blades and put the cyclists in the center of each blade. This means that the bending stress on the blades is cut in half. Belatedly, I recall (to first order, see Poison ratio) that the strain, that leads to coning, is also cut in half.
Did you just throw in a bunch of words together hoping it would make sense? Sorry, no.
The rules state that at least one member of the crew must face in the same direction throughout the flight. So this ...complicates things.
A bit of common sense(:rolleyes:) shows that the rules were intended to imply that the rotorcraft needs an anti-torque device. You can email the rules committee if you want clarification and post their reply here.
Did you just throw in a bunch of words together hoping it would make sense? Sorry, no.
no, I did not :frown:
dr dodge
Dec18-09, 07:26 AM
dual rotors (internally pressurized for strength) for inertial stability
double cone/roller drive assy.
I am working on sketches for an RC model
dr
dual rotors (internally pressurized for strength) for inertial stability
double cone/roller drive assy.
I am working on sketches for an RC model
dr
What on earth does that mean. Internal pressure does not change material properties. And the rotation of the blades will cause all the air to............(think about it).
mugaliens
Dec20-09, 06:13 PM
Really, I'm not sure how this works out. Can you give details?
It's precisely as you noted: Volume and mass of an aicraft increase as the cube of a scaled length, as does the induced drag. However, their parasitic drag, which is most of the drag while at cruise, increases only as the square of a scaled length.
But there is still stress and strain to consider for human powered flight, in general.
Yes. However, all other factors being equal, you're more likely to be successful if you design it to be powers by eight cyclists than you are if it's designed to be powered by four, due to the cube-square issue, above.
Do you recall something called the Square-Cube rule, or square-cube law as applied to the strength of a bone or beam, or even a wing as it scales in length only? The idea is to keep material density unchanged, and the shapes of everything stay the same. It's just scaled up in size. Latently I found that the amazing Wikipedia provides it.
http://en.wikipedia.org/wiki/Square-cube_law
For Aerodynamic Forces:
"When a physical object maintains the same density and is scaled up, its mass is increased by the cube of the multiplier while its surface area only increases by the square of said multiplier. This would mean that when the larger version of the object is accelerated at the same rate as the original, more pressure would be exerted on the surface of the larger object."
As this applies to a wing, you're going to have higher wing loading with a scaled up version. This is why we can build scaled models of fighters that required steel and aluminum alloys while we can use balsa and plywood build a scaled R/C version that'll pull 20 Gs.
Under the hot summer midday sun, you might expect one horse power per square yard of solar insulation. The best Solar electric panels are about 15% efficient, I think...
Market leader's SunPower's panels conversion ratio is 19.3%. However, we're concerned less with electrical power output per square foot than we are with power per lb. The current world record is 41.6%, achieved on August 26, 2009. For thin-films, which are much lighter than crystalline, it's expected to range from 30% to more than 35% over the next decade.
Well, I did too, but no one took me seriously. It would significantly reduce the weight-per-pilot requirement of the airframe--by as much as 50%. But there's a catch. There must be at least one crew member that cannot rotate but face the same direction throughout the flight.
Yes, the pilot! Well, he can darn well pedal, too!
(BTW, very cool stuff you had on the crosswind landing thread.)
Thanks!
dr dodge
Dec21-09, 07:06 AM
Internal pressure does not change material properties. And the rotation of the blades will cause all the air to............(think about it).
pressure does change the properties of a sealed container. take a piece of plastic tubing good to 200 psi. no positive pressure differential, its limp as a ....whatever
put 200 psi positive pressure, you can hold one end and it will stand erect. rocket tanks have no structural rigidity without positive pressure.
and do you think all the air will fly out to the ends???
dr
pressure does change the properties of a sealed container. take a piece of plastic tubing good to 200 psi. no positive pressure differential, its limp as a ....whatever
put 200 psi positive pressure, you can hold one end and it will stand erect. rocket tanks have no structural rigidity without positive pressure.
and do you think all the air will fly out to the ends???
dr
My point was that it will change the rigidity of the structure, but not its strength. The strength is a material property inherent to the plastic. It will yield at some sigma stress value, air or no air.
As for the air going to the ends. Not "fly out", but it will "pile up" due to pressure gradient. There is going to be a radial acceleration. My friend is doing pneumatic trailing edge flap actuation on rotor blades and has this very problem. The centrifugal force is:
F_{cf}= \frac{M \Omega^2 R}{2}
dr dodge
Dec21-09, 01:58 PM
the added rigidity would decrease the structure needed.
obviously it does not change the strength
this then potentially would allow less mass of the rotors.
as far as "pile up", are you saying that the rotation would significantly increase the pressure inside the rotor at the ends?
dr
the added rigidity would decrease the structure needed.
obviously it does not change the strength
Perhaps, if you could resolve the centrifugal force problem. I suspect you would find the airfoil sections to be 'bulging' near the tips, and under inflated at the root.
this then potentially would allow less mass of the rotors.
as far as "pile up", are you saying that the rotation would significantly increase the pressure inside the rotor at the ends?
dr
It's certainly possible.
mugaliens
Dec23-09, 03:04 AM
It's certainly possible.
It's reality, and the fundemental basis behind radial-flow compressors.
dr dodge
Dec23-09, 08:32 AM
that means potentially, as its rotation increases, if a check valve at the root allows only air in then the rotor will self compress the inside air charge, adding rigidity as RPM's increase.
If properly designed, this pressure increase could then changing its shape as speed increases.
this would allow it to "free spin" at slow speeds then change its shape when up to critical rotation
maybe this gas pressure could also be applied to control lateral movement
dr
that means potentially, as its rotation increases, if a check valve at the root allows only air in then the rotor will self compress the inside air charge, adding rigidity as RPM's increase.
If properly designed, this pressure increase could then changing its shape as speed increases.
this would allow it to "free spin" at slow speeds then change its shape when up to critical rotation
maybe this gas pressure could also be applied to control lateral movement
dr
This sounds too complicated. I don't think it will work. Why go trough all this trouble when you can just make it out of ribs, stringers and a spar? You need to do a feasibility study on this idea and flesh it out more.
mugaliens
Dec26-09, 04:22 PM
Agreed, Cyrus.
All squirrel-cage blowers found in central a/c and heating units throughout homes and businesses are radial-compressors.
Dr. Dodge: "this then potentially would allow less mass of the rotors"
Assuming the internal pressure would be enough to counteract that from the external airflow, then yes. However, I don't know if this is the case, and would have to run the calcs to be sure.
I suspect, however, that it will not be, and that you'll have to ensure a rigid structure with shrunk skin, much like monokote over balsa ribs for R/C aircraft (or doped silk used on WWI aircraft).
jeff kimathi
May20-10, 11:41 AM
Agreed, Cyrus.
All squirrel-cage blowers found in central a/c and heating units throughout homes and businesses are radial-compressors.
Dr. Dodge: "this then potentially would allow less mass of the rotors"
Assuming the internal pressure would be enough to counteract that from the external airflow, then yes. However, I don't know if this is the case, and would have to run the calcs to be sure.
I suspect, however, that it will not be, and that you'll have to ensure a rigid structure with shrunk skin, much like monokote over balsa ribs for R/C aircraft (or doped silk used on WWI aircraft).
when you talk of all this does it end up to energy storing devices which are illegal by the rules.....according to me if the fixed wing was easily achieved why don't we just make these rotors just like a wing but not fixed i.e by incorporating an extended flap like trailing edge n with a built in pitch angle n make them coaxial blade settings this saves on weight n with efficient driving mechanism then we are definitely airborne rather than complicated mechanisms with more weight
when you talk of all this does it end up to energy storing devices which are illegal by the rules.....according to me if the fixed wing was easily achieved why don't we just make these rotors just like a wing but not fixed i.e by incorporating an extended flap like trailing edge n with a built in pitch angle n make them coaxial blade settings this saves on weight n with efficient driving mechanism then we are definitely airborne rather than complicated mechanisms with more weight
First and foremost, the fixed wing flight was not "easily achieved" by any stretch. But to your second comment, I fail to see the point of incorporating trailing edge flaps. You will have to justify this design, because doesn't make sense for this application. Moving on to a coaxial design, this will indeed save structural weight; however, and more importantly, it will be unstable (if you don't believe me, google the coaxial designs to see the common problem that plagued all of them). "then we are definitely airborne" :rofl:......sure, whatever you say :wink:. Honestly though, stability of a coaxial is a poor, and the actuation lag time constants are high. In short, you save weight but gain significant stability and control problems.
dr dodge
May21-10, 07:26 AM
if the design of the component does nothing but store energy, and nothing more, then it does IMHO violate the rules. I am not saying that, what I am saying is the flight has specific time goals, but if it takes 2 men (or women) 4 hours to bring the whole machine up to speed, then it is not an energy storage device. the idea is that you can only apply x amount of work/time so if you can not change the power you (as a person) can put out, then the only way to get the power you need is more time. because the counter rotating rotors are critical to the aircraft, and do the lifting once proper rotational speed is reached, they are not storing the energy, it is being used. The counter rotating rotors will add a natural "gyro stability" by not needing to offset the rotation with a tail rotor. You control the amount of lift by the amount of power you split between the two, but both are doing the work. simpler example: 2 dc electric motors connected together by their leads together. if you spin one, the other will turn. no energy storage. add a battery in between, charge it with one motor, and run the other. energy storage
dr
if the design of the component does nothing but store energy, and nothing more, then it does IMHO violate the rules. I am not saying that, what I am saying is the flight has specific time goals, but if it takes 2 men (or women) 4 hours to bring the whole machine up to speed, then it is not an energy storage device. the idea is that you can only apply x amount of work/time so if you can not change the power you (as a person) can put out, then the only way to get the power you need is more time. because the counter rotating rotors are critical to the aircraft, and do the lifting once proper rotational speed is reached, they are not storing the energy, it is being used. The counter rotating rotors will add a natural "gyro stability" by not needing to offset the rotation with a tail rotor. You control the amount of lift by the amount of power you split between the two, but both are doing the work. simpler example: 2 dc electric motors connected together by their leads together. if you spin one, the other will turn. no energy storage. add a battery in between, charge it with one motor, and run the other. energy storage
dr
I think you should reconsider this statement in light of the extremely low rotor rpm. There is no such stability, as I stated previously.
dr dodge
May21-10, 11:10 AM
????
a little less cryptic response would sure help
action-reaction works the same regardless of rpm
dr
????
a little less cryptic response would sure help
action-reaction works the same regardless of rpm
dr
The pole-zero structure of the open loop A stability matrix of the coaxial human powered helicopter at low RPM has right half plane poles. It is unstable, as was found out by the CalPoly HPH team, and the associated NASA TN.
dr dodge
May21-10, 12:04 PM
my discussion and input was mainly geared towards "energy storage"
but if coaxial rotors are so unstable, how come they work fine in rc toys?
much easier to fly than single rotor rc's
dr
mheslep
May21-10, 12:43 PM
The pole-zero structure of the open loop A stability matrix of the coaxial human powered helicopter at low RPM has right half plane poles. It is unstable, as was found out by the CalPoly HPH team, and the associated NASA TN.Several modern aircraft frames are inherently unstable, but made stable with computer controlled fly-by-wire in the loop. Is that a possibility here?
my discussion and input was mainly geared towards "energy storage"
but if coaxial rotors are so unstable, how come they work fine in rc toys?
much easier to fly than single rotor rc's
dr
Because they spin much, much faster. When your HPH rotors are spinning 12-15 rpm, good luck getting gyroscopic anything.
Several modern aircraft frames are inherently unstable, but made stable with computer controlled fly-by-wire in the loop. Is that a possibility here?
They tried it, but to no avail. The problem is that things happen so slow by the time you move your control surface, the blade has already rotated significantly before the blades move in response. So you are always 'behind the power curve' - so to speak.
Coaxials are the best in terms of reduced structural weight, but they are like trying to balance an upside down broom by its handle. If you can figure out stability, you will have a significantly lighter vehicle. Or you can go the quad rotor route as the Japanese did, but now you have huge structural weights. There is no easy answer. Do you want to try to make really light weight structures (that's not easy), or can you come up with a clever control scheme (that's not easy either)? Either choice has significant challenges.
So I got back home and found that NASA-TN. It's not on a coaxial rotor, but a single reaction drive rotor. However, stability of a coaxial rotor will still be a problem due to the excessively low rotor RPMs.
References
[1]NASA TM-101029 (http://www.humanpoweredhelicopters.org/articles/nasa_tm_101029_19890004067_1989004067.pdf)
IcedEcliptic
May22-10, 10:35 AM
I am impressed by the feat of engineering, but god, what of the fail-safe? You get off the ground, and presumably your "out" is a parachute, but there is a large range in which it will not deploy in time. This seems... odd.
I suppose you could spend a few hours spinning up a flywheel, but that is dangerous too if you're sitting near it. I would much rather consider dirigibles for human powered flight.
It's not legal to have flywheels, or to spin up rotors before hand, as per the rules. As for a parachute, why would you need one at 10 feet (if you run the numbers, you'll find that a person can't fly any higher than that)? There is no danger in those spinning rotors, because they max at around 20-25 rpm.
IcedEcliptic
May22-10, 04:49 PM
It's not legal to have flywheels, or to spin up rotors before hand, as per the rules. As for a parachute, why would you need one at 10 feet (if you run the numbers, you'll find that a person can't fly any higher than that)? There is no danger in those spinning rotors, because they max at around 20-25 rpm.
Falling from 10 feet can be unpleasant, or lethal depending on your landing. My point is that a parachute requires a couple thousand feet to fully deploy, but you can shatter wrists, ankles, or your neck from 10 feet. The rotors I understand play no role in the danger. I did not remember the flywheel portion.
I'm not saying that this is some terrible risk, but falling 10 feet and not being hurt requires luck, or preparation and control in the fall. I just don't see the point of removing energy storage in some form, even though I know the rules are the rules.
Falling from 10 feet can be unpleasant, or lethal depending on your landing. My point is that a parachute requires a couple thousand feet to fully deploy, but you can shatter wrists, ankles, or your neck from 10 feet. The rotors I understand play no role in the danger. I did not remember the flywheel portion.
I'm not saying that this is some terrible risk, but falling 10 feet and not being hurt requires luck, or preparation and control in the fall. I just don't see the point of removing energy storage in some form, even though I know the rules are the rules.
Sure, falling from 10 feet would not be pleasant: but no risk no reward :wink:. As for the energy storage, that's because the rules are so that one designs a good vehicle. Storing energy would be a cop-out.
IcedEcliptic
May22-10, 06:44 PM
Sure, falling from 10 feet would not be pleasant: but no risk no reward :wink:. As for the energy storage, that's because the rules are so that one designs a good vehicle. Storing energy would be a cop-out.
True, people take greater risks for lesser ends. Thanks for clarifying things!
jeff kimathi
May23-10, 09:34 AM
my discussion and input was mainly geared towards "energy storage"
but if coaxial rotors are so unstable, how come they work fine in rc toys?
much easier to fly than single rotor rc's
dr
that exactly my question to the guy who dismissed my idea of coaxial rotors...but looking at stability part and the weight saved plus the efficiency of having two sets of blades which increases the solidity i think coaxial would save tha day since by the rules there is provision for not more than two guys who would help support the machine...
jeff kimathi
May23-10, 09:52 AM
First and foremost, the fixed wing flight was not "easily achieved" by any stretch. But to your second comment, I fail to see the point of incorporating trailing edge flaps. You will have to justify this design, because doesn't make sense for this application. Moving on to a coaxial design, this will indeed save structural weight; however, and more importantly, it will be unstable (if you don't believe me, google the coaxial designs to see the common problem that plagued all of them). "then we are definitely airborne" :rofl:......sure, whatever you say :wink:. Honestly though, stability of a coaxial is a poor, and the actuation lag time constants are high. In short, you save weight but gain significant stability and control problems.
i never said 'a trailing edge flap' what i tried to put across was on the design of the blades as in we all know flaps are used at low speeds n increase the lift drag ratio at a certain predetermined settings so basically i thought according to ma research on former designs n with fact that we're rotating the blades at low speeds why don't we then as we design the ribs include a slight angle drop of the rear point of ribs they are not flaps but at aerodynamic point of view with final assembly of this rotor with these ribs they increase the angle onto which we meet RAF......on coaxial part i just goggled as u advised n surely stability was not that great problem...thank u
IcedEcliptic
May23-10, 11:02 AM
i never said 'a trailing edge flap' what i tried to put across was on the design of the blades as in we all know flaps are used at low speeds n increase the lift drag ratio at a certain predetermined settings so basically i thought according to ma research on former designs n with fact that we're rotating the blades at low speeds why don't we then as we design the ribs include a slight angle drop of the rear point of ribs they are not flaps but at aerodynamic point of view with final assembly of this rotor with these ribs they increase the angle onto which we meet RAF......on coaxial part i just goggled as u advised n surely stability was not that great problem...thank u
What did you read from your search that ignored the instabilities introduced by coaxial rotors?! I did the same thing, and was led to the opposite conclusion, over and over. To correct the instability requires... wait for it... more WEIGHT in the form of stabilizing surfaces or the means to control them.
i never said 'a trailing edge flap' what i tried to put across was on the design of the blades as in we all know flaps are used at low speeds n increase the lift drag ratio at a certain predetermined settings so basically i thought according to ma research on former designs n with fact that we're rotating the blades at low speeds why don't we then as we design the ribs include a slight angle drop of the rear point of ribs they are not flaps but at aerodynamic point of view with final assembly of this rotor with these ribs they increase the angle onto which we meet RAF......on coaxial part i just goggled as u advised n surely stability was not that great problem...thank u
I'm having a hard time understanding what you write in your posts, can you avoid using text-speak. As for stability, look at the NASA TM I provided you.
jeff kimathi
May24-10, 08:06 AM
What did you read from your search that ignored the instabilities introduced by coaxial rotors?! I did the same thing, and was led to the opposite conclusion, over and over. To correct the instability requires... wait for it...more WEIGHT in the form ofabilizing surfaces or the means to control them.
yeah that way i agree with u coz we need balance weights like in the case of rc types...and that makes it odd too but there are odds on every principle...
jeff kimathi
May24-10, 08:14 AM
I'm having a hard time understanding what you write in your posts, can you avoid using text-speak. As for stability, look at the NASA TM I provided you.
hey sorry never noticed my text-speak was just trying to explain ma unverified ideas.currently am working on a design model of both the rotor and coaxial design maybe when am through will email you the details...thanks for the NASA TM i got some mean full points
airport
Sep10-10, 07:09 AM
Nice post...Thank you very much!!......http://parkservice-flieger.de/Icons/smileycool.ico
mugaliens
Sep13-10, 06:48 AM
Because they spin much, much faster. When your HPH rotors are spinning 12-15 rpm, good luck getting gyroscopic anything.
Instead of using coaxial rotors, how about using counter-rotating rotors offset at opposite ends of a support boom? Would that be more stable? I would think it would have the same degree of stability/instability, but it actually make it more larger than is required, as well as more unwieldly, resulting in additional handling problems.
I know a good deal about airplane flight stability, but little about helo stability, even though I've flown two of 'em (not licensed - just fun rides). I'm having a difficult time picturing the instability part. Yes, technically counter-rotating rotors, whether coaxial or offset tend to counter gyroscopic forces. I get that part. But zero stability doesn't equate with negative stability i.e. it's not like flipping itself over is a more stable position than remaining in one position. Broomsticks balanced upside down on one's hand are dynamically unstable, yet kids manage to do it all the time, and the response rate required to stabilize that small of an object is much more rapid than for a human-powered helo with 30 feet of blade.
My thought towards what might be the best way to control the rotors is to use spoilers, not ailerons. Obviously, using a centralized blade-angling approach (swash plate (http://en.wikipedia.org/wiki/Swashplate_(helicopter))) for such large, slow-moving rotors is probably a poorer approach than controlling the lift of the blades more directly, through ailerons.
jeff kimathi
Sep13-10, 07:30 AM
is there any simple approach on to getting the leading edge radius of an airfoil model of say chord of 45cm and maximum thickness of 8cm with the point of max thickness being 1/4 of chord:confused :
mugaliens
Sep18-10, 02:47 AM
is there any simple approach on to getting the leading edge radius of an airfoil model of say chord of 45cm and maximum thickness of 8cm with the point of max thickness being 1/4 of chord:confused :
I'm sorry, but you're going to have to specify which of the many thousands of fully-wind-tunnel-tested airfoils you're talking about.
If you're proposing your own, then you're on your own.
FYI: the cat is now out of the bag so enjoy
uT4y4xb2UYI
I was on briefly on the team early on but had to stop to finish my research and graduate: in any event, these guys and gals are working hard at it, so keep your fingers crossed for them.
jeff kimathi
Jan4-11, 02:49 AM
FYI: the cat is now out of the bag so enjoy
uT4y4xb2UYI
I was on briefly on the team early on but had to stop to finish my research and graduate: in any event, these guys and gals are working hard at it, so keep your fingers crossed for them.
congratulations on your graduation...so whats new in you 4 us
helisphere
Feb4-11, 06:48 PM
The stability issue is an aerodynamic one. As the NASA-TM states the basic reason for the instability in the human powered helicopter is the high lock number of the blades. For those unfamiliar with this term and without getting unnecessarily technical, the lock number is basically the ratio of aerodynamic forces acting on the blade compared to the inertial forces acting on the blade.
Lock number = Aerodynamic Forces/Inertial forces
So it make sense that the low rotational speed, light weight blade and large blade area combination make for a very high lock number.
The inertial forces acting on a blade are stabilizing, just like a gyro, as per Newton's first law. The Aerodynamic forces are a little more complicated, but basically they make the helicopter and rotor unstable. The aerodynamics actually cause a combination of both positive and negative stability at different times but overall the result is undesireable and unstable. So with a high lock number the aerodynamic forces have a larger impact on the stability which means a less stable rotor.
Watch the following video starting at 4:30 to see some good examples of the stability issues of a helicopter rotor. I would suggest that the stability issue is just as solvable today in a human powered helicoper as it was in the 1940s in this model that eventually became the Bell 47, whether coaxial or not.
Also the little coaxial models that are very stable in a hover are not stable just because they have a higher RPM and lower blade lock numbers. They are stable because they have a weighted stabilizer bar that acts as a gyro and generates aerodynamic control inputs to a rotor that would other wise be unstable just like the model in the video below.
fast forward to 4:30
uir9Engj4v4
[QUOTE=Cyrus;3024938]
Refer to 1:50-2:05 minutes into the video.
uT4y4xb2UYI
Compare to the Gossamer Albatross
Empty weight: 32 kg (70 lb)
Loaded weight: 97.5 kg (215 lb)
This guy expects the craft to mass about 1500 kilograms gross as opposed to 97. I guess they're thinking solidly inside the box.
helisphere
Feb5-11, 12:11 AM
This guy expects the craft to mass about 1500 kilograms gross as opposed to 97. I guess they're thinking solidly inside the box.
Phrak,
I think he meant that for an airplane you only need to create a thrust of about 1/15 of the weight of the aircraft in order to achieve flight but with a helicopter you have to create a thrust equal to the weight of the aircraft. That would be 15 times more thrust to hover a helicopter than to fly an airplane.
Phrak,
I think he meant that for an airplane you only need to create a thrust of about 1/15 of the weight of the aircraft in order to achieve flight but with a helicopter you have to create a thrust equal to the weight of the aircraft. That would be 15 times more thrust to hover a helicopter than to fly an airplane.
Good thinking. That might be it, assuming a nominal L/D of about 6 to 1.
but I'd still give you ten to one odds UMD fails if the video is any indication of their design paradigm.
...
Watch the following video starting at 4:30 to see some good examples of the stability issues of a helicopter rotor. I would suggest that the stability issue is just as solvable today in a human powered helicopter...Is it? Lowering the lock number likely means adding mass to the blades - something the human powered helo can ill afford.
Thanks for the video. The demand by the executive suit to pilot the prototype leading to predictable disaster shows that the suits weren't any different back then. It's amazing the suit only suffered a broken arm.
This, http://vtol.org/awards/HPHCBooklet.pdf is the .pdf of the rules as set forth by The American Helicopter Society, http://vtol.org/awards/hph.html.
I draw your attention to the sketches pages 44 and 48 of http://vtol.org/awards/HPHCBooklet.pdf as counted in .pdf pages.
Is this not a viable design method?
helisphere
Feb7-11, 03:08 AM
mheslep,
My point was that the model in the video was also unstable but they made it stable and they didn't do it by lowering the lock number. They took a stable reference and made the blades fly to it.
Phrak,
Yes I think that is probably the best way to go. The problem with big slow rotors is little centrifugal force to keep the coning and bending moments down. Those designs distribute weight more evenly.
PedalPower
Feb11-11, 08:11 PM
I am impressed by the feat of engineering, but god, what of the fail-safe? You get off the ground, and presumably your "out" is a parachute, but there is a large range in which it will not deploy in time. This seems... odd.
I suppose you could spend a few hours spinning up a flywheel, but that is dangerous too if you're sitting near it. I would much rather consider dirigibles for human powered flight.
Fly off a dock on a calm day.....get it as high as possible, when tired....let off a little...then descend with a little auto rotation and dump in the lake. Fish it out with a boat and find the tag line, attached before lift off, with a tennis ball.
But don't make the frame out of balsa wood, need aluminum for the frame and plastic or carbon fiber for the props......
PedalPower
Feb11-11, 08:49 PM
When they say 'human powered' - do they count 'human fuelled'?
A gas turbine will run on bio-diesel !
Eat only beans for three days before, hook up a gas powered rocket engine under the seat, get the rotors going as a distraction, then .....ignition!.....if only they had smileys here!!
JaredJames
Feb11-11, 09:39 PM
Eat only beans for three days before, hook up a gas powered rocket engine under the seat, get the rotors going as a distraction, then .....ignition!.....if only they had smileys here!!
They do:
:biggrin: :blushing: :tongue: :rolleyes: ........
Phrak,
Yes I think that is probably the best way to go. The problem with big slow rotors is little centrifugal force to keep the coning and bending moments down. Those designs distribute weight more evenly.
We see these hopeful engineering teams taking the same dead end road. I'm perplexed as to why this seemingly obvious solution hasn't been tried.
A ten meter square target is not easy to hover over with a large machine, say 100 to 200 meter diameter, but this should be easily solved with software sending information from the pilot to those providing the peddle power and adjusting control surfaces.
PedalPower
Feb12-11, 08:42 AM
Thank you for your reassurance....my experience is generally restricted with structural and mechanical engineering skills and the advanced calculus was never mastered by me as far as aerodynamics are concerned.
Eventually we can run a test on the foil shape and the props surface areas/angle of attack to find the optimal rotation speed required to hover for 45 seconds, then lift to the height required........we honestly see the potential, but with so many attempts, the school based design teams were left with advancing the previous vehicles and trying to make their "hovercraft" sustain flight.......we have had success reinventing the Pedicab, the modern rickshaw, and are now moving onto the entry for the vehicle design summit this summer at MIT. With this engineering as a background we are able to achieve a greater advantage over other riders and gain the momentum to get going on this project.
We are hoping that the rotor speed will be accelerated from the internal hub gear we are including in the drive train, allowing us to get it up to speed on a gradient scale through gears 1-4, by fifth we hope to be at a 1-1 ratio with the internal hub, and will have generated 8.94 full rotations for every rotation of the main pedal powered wheel, if one rotation per second (definitely possible) is maintained, then we will have created a rotor with 40 sq ft of surface area traveling at 535 RPM's, far more than is needed to attain lift of a regular sized helicopter that usually runs at 400-460 RPM's and weighs a ton.
Although the rotors on a regular heli are also able to produce lift from adjusting the angle, we have a fixed angle of 2% that we feel will be enough to allow for the slipstream effect to be more fluid with less drag and still create lift, and direct the trailing edges' airflow directly into the main lift producing area of the next blade, after the vacuum has collapsed upon itself and returned to it's original density........by generating more momentum, and creating the final rotor rpm to sustain, with at least three gears left to get off to a higher altitude, there is no way we can lose.
Would you be interested in handling the advanced calculations as a co-conspirator/awardee??? We are merely looking for scientific calculations to back up our design, so we can obtain sponsorship with endorsements, to make the process go smoother.
JaredJames
Feb12-11, 12:04 PM
Would you be interested in handling the advanced calculations as a co-conspirator/awardee??? We are merely looking for scientific calculations to back up our design, so we can obtain sponsorship with endorsements, to make the process go smoother.
All the calculations and explanations regarding power are shown previously.
If you read back, you will see that a human being cannot, for a long enough period of time, provide enough power to generate the required lift. Making everything you wrote above irrelevant.
I'd also note that no one here will do the work for you - as previously, the calcs are a few pages back showing the power issues.
helisphere
Feb12-11, 04:59 PM
535 rotor RPM??? You don't say what your rotor diameter is but let's say that it's only 25 ft in diameter. That would give you a tip velocity of 535*2*pi*12.5/60 = 700 feet/sec. Typical helicopters don't use tip speeds any faster than this because of sonic compressibility effects and if your rotor were any bigger in diameter it would have a faster tip speed at that RPM. Lets say 40ft dia: 535*2*pi*20/60 = 1120 feet/sec This is Mach one!!!
In order for a 25 foot rotor to lift 200lbs: horsepower = sqrt(T^3/2*rho*A)/550 = 3.36 hp and this momentum theory calculation is for an IDEAL rotor which is not even possible to make.
And a 40 ft dia rotor: 2.10 hp
Testing shows a strong athlete can only make 0.7 to 0.8 hp
helisphere
Feb13-11, 05:45 AM
PedalPower,
Don't let me or anyone else discourage you. If this is something you really want to do then do your homework, find the answers and go for it! I'm not trying to smash anyone's dream, reality has a way of doing that on its own. I'm not your enemy, Love us, hate us, learn from us, I wish you the best, but it does seem there are a few things you don't understand about helicopters, especially the human powered type, but that doesn't have to be anything but temporary...
PedalPower
Feb13-11, 11:39 PM
535 rotor RPM???
Lets say 40ft dia: 535*2*pi*20/60 = 1120 feet/sec This is Mach one!!!
In order for a 25 foot rotor to lift 200lbs: horsepower = sqrt(T^3/2*rho*A)/550 = 3.36 hp and this momentum theory calculation is for an IDEAL rotor which is not even possible to make.
Testing shows a strong athlete can only make 0.7 to 0.8 hp
Maybe we should design it like this ........... http://www.clydecaldwell.com/photos/sandiego01/time_machine2.html
JaredJames
Feb13-11, 11:41 PM
EDIT: Link correction noted.
What does that design have to do with the human powered helicopter? That's a time machine.
PedalPower
Feb13-11, 11:44 PM
All the calculations and explanations regarding power are shown previously.
If you read back, you will see that a human being cannot, for a long enough period of time, provide enough power to generate the required lift. Making everything you wrote above irrelevant.
I'd also note that no one here will do the work for you - as previously, the calcs are a few pages back showing the power issues.
That's funny you say that cause there are numerous pictures of guys "doing it" and also videos, as well as a couple of really heavy looking ones created by the engineers of other helicopter companies, they ended up facing tragic endings before they tried to take off...these were placed on display in the many aerospace museums, and I have even seen a couple as a student on field trips to DC.
Try speaking for yourself..........others have interest, and you don't.
JaredJames
Feb13-11, 11:48 PM
That's funny you say that cause there are numerous pictures of guys "doing it" and also videos, as well as a couple of really heavy looking ones created by the engineers of other helicopter companies,
Please do show us these pictures and videos - especially those that fall within the rules of this challenge. The davinci III is the only one of note so far and it's not even close to within the challenge rules.
they ended up facing tragic endings before they tried to take off...these were placed on display in the many aerospace museums, and I have even seen a couple as a student on field trips to DC
They faced tragic endings before taking off? As in they were destroyed trying to take off? That means they didn't work.
Again, as per the posts above, they show you HP required and HP possible.
PedalPower
Feb13-11, 11:53 PM
EDIT: Link correction noted.
What does that design have to do with the human powered helicopter? That's a time machine.
So does your every reply come in the form of cynical metanoia, or can you take a joke?
"cynical metanoia" has a certain ring to it, jarednjames. Maybe Greg will let me change my screen name. Cynical_metanoid, perhaps. Of course you get first dibs, all things being fair.
JaredJames
Feb14-11, 12:36 AM
"cynical metanoia" has a certain ring to it, jarednjames. Maybe Greg will let me change my screen name. Of course you get first dibs, all things being fair.
I want to say 'oxymoron' but I can't work out what "metanoia" is. Only some sketchy definitions floating around.
I want to say 'oxymoron' but I can't work out what "metanoia" is. Only some sketchy definitions floating around.
I dunno. but it's gotta good if PeddlePower came up with it.
jeff kimathi
Apr24-11, 09:02 AM
pedalpower av read thru your comment n all i can tell you is that sometimes it takes one own effort without any much consultations to succeed in something especially these science related projects...i prefer you work it out practically n rely on the outcomes of your project to reason out the next move or your next modifications simply because critics will always out shine the kudos in real life situations.............i to am in the race to trying this task i decided to do my own design n try it to make the next move from my results simply because there are those who think they are more learned thus tend to look down to others which is a great threat to your success....av done my design with my colleagues n made the necessary parts n we are awaiting the assembly n then the trial of the machine....i mean no offense at all to any one of you registered in this forum...so go for what you think is right n let the outcomes determine your rights n wrongs
Yesterday student engineers from Maryland University were testing for the first time their quad-rotor human powered helicopter "Gamera" -after nearly 3 years of development. They will continue their tests today too and there will be a live stream.
promo:
http://www.youtube.com/watch?v=uT4y4xb2UYI&playnext=1&list=PL342EC9DE5332F42F
preparation:
http://www.youtube.com/watch?v=Ef9kqkpXI_k
yesterday's attempt:
a)short:
http://www.youtube.com/watch?v=A_bLNHr6qPU&feature=related
b)long: The whole 3h video capture from yesterday's live stream (needs Silverlight):
http://lecture.umd.edu/detsmediasite/SilverlightPlayer/Default.aspx?peid=dae7b8b7686a4639a0faa0f58ebd0865 1d
Website:
http://www.newsdesk.umd.edu/bigissues/release.cfm?ArticleID=2424
EDIT: Today's live link (it has started a while ago):
http://lecture.umd.edu/detsmediasite/SilverlightPlayer/Default.aspx?peid=25e3de8c875444169b873aecaa9f0473 1d
whynottry
Jun25-11, 08:23 AM
I believe that rpms overcome weight. All of the "successful" designs have focused on very low weight materials but they cannot produce high rpm of the rotor. If the rotor is a smooth disc that can deform into a lift producing rotor then a much-higher-than-needed rpm can be achieved before it starts moving air.
HowlerMonkey
Jun30-11, 01:59 PM
They need to change the powerplant's (awesome blonde chick) indexing between the pedals and the hand crank as well as change how her posture is aligned with the force she is exerting.
They could also make far more use of her power if they added as large a diameter flywheel to the pedal crank assembly.
It could be very light with most of it's mass concentrated on the outer diameter.
As it is now, much of the energy is being used up by flex.
whynottry
Jul1-11, 09:36 AM
flywheel equals weight. not gonna happen.
HowlerMonkey
Jul1-11, 10:43 AM
When you watch the video, it is easy to see how jerky the application of power is and the fact that the rapid acceleration and deceleration of the cranking motion is being absorbed by the structure rather than being applied to the props.
It only takes a couple of pounds to make a flywheel which has mass concentrated on outside diameter that would smooth out her pedaling and recover the lost energy.
Since the average human varys 1 or 2 (maybe more) pounds from day to day and the fact that this girl not fully shreaded, I think it would benefit far more than detract.
KyleFoster
Jul2-11, 11:39 PM
ok first off i didnt read every post. I am an Airframe and Powerplant mechanic, certified to work on anything that can fly and is certificated by the FAA.
Normal helicopters have around a 30 foot rotor diameter with the blades being approximately 15 feet long and around 1 foot wide. Normal rotor speeds on most helicopters is around 390 rpm's. To produce enough lift to lift a 500 pound helicopter with a ~200 pound pilot you would need about 200 rpm's of rotor speed.
Through gearing and designing a working flight control system you could do it with a normal person working the controls and pedals. Remember work smarter not harder.
With 4 axis controls it could be done.
If you build the frame from Plastic Tubing it would be strong enough and light enough for a short flight, just secure the glue joints with screws to increase the strength.
If you use gearing like a 18 speed bike to drive the main rotor and have a shaft go from the main "gearbox" to the tail gear it would be easy enough for a person of normal physical abilities to power it, and with the 4 axis controls you can regulate the amount of thrust and you will be able to keep it within the "square" so to speak.
The design would end up looking more like a modern helicopter than a wierd science project gone bad.
So this being said....it would be possible to fly it accross the channel if you have someone that knows how to fly it right since once its in flight you could basically autorotate, no power, for a certain distance then apply power climb to a few hundred feet and auto rotate again, the light weight of the frame and the aerodynamics of the blades would keep the aircraft in flight like a glider over longer distances.
Sorry for the long post.
HowlerMonkey
Jul6-11, 05:17 PM
Can you help me index the PRTs of a wright 3350?
I'm a bit rusty on the radials.
KyleFoster
Jul6-11, 11:10 PM
I have very limited experience on radial engines....most of my experience is on turbine helicopters ( bell 206 and UH60 blackhawk)
HowlerMonkey
Jul9-11, 07:27 PM
I was lucky to get my A&P back when radials were still part of the program.
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