Help Design a Human-Powered Helicopter

[dr dodge]

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

 

[Cyrus]

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]

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]

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

 

[Cyrus]

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" ...sure, whatever you say . 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]

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

 

[Cyrus]

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]

?
a little less cryptic response would sure help
action-reaction works the same regardless of rpm

dr

 

[Cyrus]

?
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]

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]

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?

 

[Cyrus]

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.

 

[Cyrus]

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.

 

[Cyrus]

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]http://www.humanpoweredhelicopters.org/articles/nasa_tm_101029_19890004067_1989004067.pdf"

 

[IcedEcliptic]

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.

 

[Cyrus]

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]

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.

 

[Cyrus]

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 . 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]

Sure, falling from 10 feet would not be pleasant: but no risk no reward . 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]

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]

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" ...sure, whatever you say . 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]

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.

 

[Cyrus]

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]

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]

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]

Nice post...Thank you very much!...[PLAIN]http://parkservice-flieger.de/Icons/smileycool.ico

 

[mugaliens]

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 (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]

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]

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.

 

[Cyrus]

FYI: the cat is now out of the bag so enjoy



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.