Homemade Helicopter: For the People.

[mtworkowski@o]

BRAVO and very well put. What you say is true and relevant. Thank you!

 

[mtworkowski@o]

BRAVO and very well put. What you say is true and relevant. Thank you Breadbord.

 

[mtworkowski@o]

I remember my father scoffing at all the negative feelings about homemade flight. He took an old washing machine apart and replaced the drum and agitator with rotor blades made of styrofoam covered with fiberglass. I don't know what the foil profile was because I was just a kid. When he plugged in the electric motor the thing tried to pull itself from it's moorings. It had more than enough power to lift itself and then some. Understand, this was a piece of junk with no consideration to weight or anything else. My uncle owned a bike shop and wanted to build a real version to fly. It never happened but I was convinced that it could have.

 

[redargon]

This is a very interesting topic and seems to be a battle between the well grounded engineers (who studied their butts off for years and then worked their butts off to gain years of experience, so please respect their comments and advice) and the dreamers. Please also remember that most engineers are dreamers too and this is usually the reason why they studied engineering, in an attempt to realize these dreams, efficiently and safely). For the dreamers without a lot of background knowledge, use the inputs from the guys with knowledge and experience. You don't have to believe everything they say either and you can try to prove or disprove theories as you seem fit. Often dreamers stumble upon new ideas and concepts and break through to a new level. For entire projects though, this is often accompanied by sound advice from professionals. Einstein did not go through life thinking Newton was an uneducated toad, he realized Newton's contributions and added to them and molded them into a new more complete understanding of the universe.

For the dreamers who are serious about new designs or ideas, first learn a little design or ideation methodology. Have your idea, make sure you understand the idea and the requirements. Break it into simpler parts. Do some feasibility analysis of different concepts. Find solutions to each part (with or without help is up to you). Put it together and solve the entire problem. Double check everything. Put the plan into action. Keep people here up to date with your progress so that everyone knows where you are and where you're heading. Finding a plan on the internet could be like finding other "miracle cures" on the internet. There may also be good work in an interent plan, but use it wisely and question it, just as you question the experts here.

Let's see some brainstorms on here, I mean real diagrams, ideas, feasibility studies. Attach the work you've done. Ask questions like: Should I consider carbon fibre, because while reading about fracture mechanics, I learned... or: How can we model the drag of the rotor if I use these dimensions or this airfoil? What sort of powerplant would be a good option and what fuel does it use and how can I store this fuel? etc. You can argue all you like, but if a dream is to become a design, you have to put some work on the table. Let the critics dissect it and learn and grow and oppose too. This is the best way to move forward with any design.

This is just my 2 cents and an attempt to be neutral and helpful to all parties concerned. I hope this makes the following progress smoother.

In hoping for a brighter future with new designs, that are better than the last.

 

[mtworkowski@o]

Thanks for the note redargon,
It sounded like you where scolding me for something. Like maybe being too unrealistic, ignorant and lazy. That's just one of my faults. I'm working on it though. Sometimes I get sick of the naysayers. I guess it came out in my posts.
Thanks again.
ps I don't know which of my posts made you react that way or was it all of them?

 

[RonL]

This is a very interesting topic and seems to be a battle between the well grounded engineers (who studied their butts off for years and then worked their butts off to gain years of experience, so please respect their comments and advice) and the dreamers. Please also remember that most engineers are dreamers too and this is usually the reason why they studied engineering, in an attempt to realize these dreams, efficiently and safely). For the dreamers without a lot of background knowledge, use the inputs from the guys with knowledge and experience. You don't have to believe everything they say either and you can try to prove or disprove theories as you seem fit. Often dreamers stumble upon new ideas and concepts and break through to a new level. For entire projects though, this is often accompanied by sound advice from professionals. Einstein did not go through life thinking Newton was an uneducated toad, he realized Newton's contributions and added to them and molded them into a new more complete understanding of the universe.

For the dreamers who are serious about new designs or ideas, first learn a little design or ideation methodology. Have your idea, make sure you understand the idea and the requirements. Break it into simpler parts. Do some feasibility analysis of different concepts. Find solutions to each part (with or without help is up to you). Put it together and solve the entire problem. Double check everything. Put the plan into action. Keep people here up to date with your progress so that everyone knows where you are and where you're heading. Finding a plan on the internet could be like finding other "miracle cures" on the internet. There may also be good work in an interent plan, but use it wisely and question it, just as you question the experts here.

Let's see some brainstorms on here, I mean real diagrams, ideas, feasibility studies. Attach the work you've done. Ask questions like: Should I consider carbon fibre, because while reading about fracture mechanics, I learned... or: How can we model the drag of the rotor if I use these dimensions or this airfoil? What sort of powerplant would be a good option and what fuel does it use and how can I store this fuel? etc. You can argue all you like, but if a dream is to become a design, you have to put some work on the table. Let the critics dissect it and learn and grow and oppose too. This is the best way to move forward with any design.

This is just my 2 cents and an attempt to be neutral and helpful to all parties concerned. I hope this makes the following progress smoother.

In hoping for a brighter future with new designs, that are better than the last.

An excellent post, and welcome to the forum.
It sure is good when people say a little about themselves.

I would like to step up to your request in regards to new designs, and brainstorming, but to meet all the steps of your post would take me quite a distance into the future.
If I throw out the basic idea, with just a hand drawn sketch or two, then maybe it would motivate me to do the rest.

How far into the future do we take this first step ? I'm getting pretty old

Ron

 

[mtworkowski@o]

helicopter from junk!

I've got some time and the weather is nice so I've decide to get this home made helicopter thing on track. I found a gear reduction gearbox with right angle drive and I want to hear some opinions. This is the gearbox from a direct drive wahing machine. 150 bucks new. They last for 20 yrs in washing machines. I figure it should be a good starting point. Does anyone know what rpm these electric motors run at? On spin my machine sounds like around 250. I'm thinking that's right in the range I need for the rotors.
Sorry to be so rediculous but that's the way I've always built things. I'd use a razor blade to build a radio. And sometimes my stuff even works!

 

[mtworkowski@o]

That's a pretty high and mighty attitude from where I'm sitting. I've been through enough tech analysis and all the other crap for a lifetime. Most of the stuff we buy in the store is crap. And who designs it. Rignt. Now I don't want to implicate anybody but a nice answer would be something like: Check this and that and this is really important and if you have any questions ask. That's why we're here. We're not morons just because we don't live in the tech mainstream.

 

[Mech_Engineer]

Well I'm pretty sure a washing machine's gearbox will not do for a home-made helicopter. The reason they last 20 years is because they are paired with a properly-sized motor and were designed specifically for that application; not because they're indestructible due to massive over-engineering.

 

[mtworkowski@o]

I think your absolutely right, but I just can't help thinking that the torque load on the rotor shaft is comperable to a fully loaded washing machine. And I do believe that the thing is over spec. I'm going to get an old one and use my torque wrench to go max to break. How much drag do you think is on a 20 ft rotor at full collective and 500 lb. of weight? Climb can be a garbagety number. Let's just get a feel for the whole thing. Is drag the only thing I should look at in terms of torque loading on the gear box?

 

[Mech_Engineer]

You need to look at power throughput requirements and weight. A washing machine's motor is around 1-2 hp, the smallest ultralight helicopter kits I have seen use a 40hp 2-stroke engine. They also run the main rotor at about 400-500 rpm.

It seems to me that if a chopper is putting out 40 hp of lifting force at 400 rpm on the main rotor, that means the torque being imparted on the main rotor is 525 ft-lb (712 N-m). If you had a hypothetical rotor that only turned at 250 rpm (would have to be bigger, more drag) then you would need 840 ft-lbf for the same 40 hp.

 

[mtworkowski@o]

You need to look at power throughput requirements and weight. A washing machine's motor is around 1-2 hp, the smallest ultralight helicopter kits I have seen use a 40hp 2-stroke engine. They also run the main rotor at about 400-500 rpm.

It seems to me that if a chopper is putting out 40 hp of lifting force at 400 rpm on the main rotor, that means the torque being imparted on the main rotor is 525 ft-lb (712 N-m). If you had a hypothetical rotor that only turned at 250 rpm (would have to be bigger, more drag) then you would need 840 ft-lbf for the same 40 hp.

Thanks for the response. By power throughput I assume you mean that the required power is being drained off by losses in the driveline and that upstream power reqs are much higher than merely rotor reqs..Excellant point.
Would show me the crunch on those numbers? Just briefly. I'd be interested.
thanks

 

[Mech_Engineer]

With power delivery through rotating shafts, power is torque multiplied by angular speed. So, in the case of the engine on the chopper, if we assume all of the power produced by the engine is going to the main rotor then 40hp/400rpm gives you 525 ft-lb of torque (after some unit conversion, dividing the power in Watts by the angular speed in radians/second gives you the torque in Newton-meters). This probably isn't a very good approximation because the tail rotor would take power too and the transmission would not have 100% efficiency, but as a worst-case estimate it gives a ballpark idea of the transmission requirements.

The input shaft for the transmission will be going the same speed as the engine itself, which could be around 4000-5000 rpms (we'll call it 4000 for calculation simplicity, making the transmission a 10:1 gearbox). So if the engine is putting out 40 hp at 4000 rpms, its producing 52 ft-lb of torque. Basically this means the chopper's transmission needs to be able to handle an input shaft speed of 4000rpm and input torque of 52 ft-lb, and the output needs to be able to put out 10 times that torque at 1/10 the speed. I'm sure you'll find a washing machine's right-angle drive transmission is grossly undersized based on these requirements.

 

[mtworkowski@o]

With power delivery through rotating shafts, power is torque multiplied by angular speed. So, in the case of the engine on the chopper, if we assume all of the power produced by the engine is going to the main rotor then 40hp/400rpm gives you 525 ft-lb of torque (after some unit conversion, dividing the power in Watts by the angular speed in radians/second gives you the torque in Newton-meters). This probably isn't a very good approximation because the tail rotor would take power too and the transmission would not have 100% efficiency, but as a worst-case estimate it gives a ballpark idea of the transmission requirements.

The input shaft for the transmission will be going the same speed as the engine itself, which could be around 4000-5000 rpms (we'll call it 4000 for calculation simplicity, making the transmission a 10:1 gearbox). So if the engine is putting out 40 hp at 4000 rpms, its producing 52 ft-lb of torque. Basically this means the chopper's transmission needs to be able to handle an input shaft speed of 4000rpm and input torque of 52 ft-lb, and the output needs to be able to put out 10 times that torque at 1/10 the speed. I'm sure you'll find a washing machine's right-angle drive transmission is grossly undersized based on these requirements.

Am I right here? Power= Torque X RPM / 5252 so...Torque = Power X 5252/RPM
40hp X 5252/400 =525.2 ft.lb.

 

[mtworkowski@o]

You know we've made some assumptions here. A torque of 525 strikes me as the torque of 300hp Pontiac 389 from the early 60s. I think it was actually 425 lb.ft.
I know we're just dropping in that 40hp spec. for fun and it probably is close if it's being used by others, but something has to off here. Do you agree?

 

[mtworkowski@o]

No. I just got it. 10 to 1 gearing. thank you.

 

[Mech_Engineer]

Am I right here? Power= Torque X RPM / 5252 so...Torque = Power X 5252/RPM
40hp X 5252/400 =525.2 ft.lb.

Yup, that's correct.

 

[mtworkowski@o]

Thanks boss.

 

[RonL]

While you guys are calculating, I have been watching my lawn sprinkler and thinking about how air would spin it, if it were to be hooked to a air hose.

Now concerning a very light machine (almost anything can be done)
Without considering the source of air, but only the results, how much volume and pressure would produce thrust enough to lift 400 pounds, if there are two counter rotating rotors, seventeen feet in diameter ? (4 tips discharging air, pushing the blades in a forward direction).

I know there are many other factors involved, and speed of the rotors will depend mostly on pressure, but it seems that larger volume, lower pressure will be easier to produce.

Any help with the calculations ??

Ron

 

[mtworkowski@o]

I like it. I always thought compressed air was a really portable power source. Wait, you made me think of propane. A little diversion. Before Whittle envented the jet engine in England, a guy someplace else took a piston engine and ran a piston compressor to force air into a combution chamber with fuel. That's a jet engine. You know that propane tank near the grill. If you use propane instead of compressed air you will be getting the benefit of a fuel. The plumbing remains the same.( o rings etc.) I'm thinking ceramic chambers on the tips. No the whole thing is nuts. You had a better idea.
Carry on. Smoke 'em if you got 'em.

 

[RonL]

I like it. I always thought compressed air was a really portable power source. Wait, you made me think of propane. A little diversion. Before Whittle envented the jet engine in England, a guy someplace else took a piston engine and ran a piston compressor to force air into a combution chamber with fuel. That's a jet engine. You know that propane tank near the grill. If you use propane instead of compressed air you will be getting the benefit of a fuel. The plumbing remains the same.( o rings etc.) I'm thinking ceramic chambers on the tips. No the whole thing is nuts. You had a better idea.
Carry on. Smoke 'em if you got 'em.

I think some of my ideas about the use of propane, has gotten me on almost everyones ignore list.
And I have not even put my wildest idea forward yet.

Ron

 

[mtworkowski@o]

go for it. there is no list.

 

[Mech_Engineer]

Compressed gas is really a poor method for storing energy, since it takes large, heavy tanks to hold a large and/or high-pressure volume. Because aircraft need to be light, they need a high-energy density fuel that doesn't weigh much, and compressed air isn't even close to petroleum-based fuels in terms of energy per pound.

 

[mtworkowski@o]

I would agree. I use air powered tools now and then and the are excellent. But it's only because the real power source is my local electric grid via an air compressor. No, it's hard to beat the IC engine. And why bother?
Recently I saw the new aerotwin helicopter motor. Less than 100 lb. Some reasonable amount of HP. Liquid cooled. What's the big deal? Tell me why a motorcycle engine could'nt do a reasonably compitent job.

 

[RonL]

go for it. there is no list.

Go to "My PF" and look again

 

[mtworkowski@o]

subscription

Go to "My PF" and look again

Thanks, it looks like all is well.

 

[RonL]

Compressed gas is really a poor method for storing energy, since it takes large, heavy tanks to hold a large and/or high-pressure volume. Because aircraft need to be light, they need a high-energy density fuel that doesn't weigh much, and compressed air isn't even close to petroleum-based fuels in terms of energy per pound.

How quick the mind jumps to the negative of how things are done, do we need to store compressed air in large heavy tanks ? why not use it at the same rate we produce it ? my proposal would be to make the compressor (vane style) section a part of the rotating group (the hub section) the blades are hollow and serve as a momentary tank, the energy to start the process is positive and needs to be supplied from some external source, as kinetic energy builds in the rotating mass, the resistance of compression takes place at a 6" to 12" radius, while the thrust of the jet ejection takes place at a radius of 8-1/2 feet (quite a bit of leverage I think ?).
If intake volume, and compression are matched to supply the discharge at the outside diameter, then additional energy that needs to be supplied to the system, should be enough to compensate for bearing friction, compressor friction, and some thermal loss as the compressed air moves through the blades to the tips (one benefit might be less chance of ice buildup on the blades in some conditions).

This almost completely eliminates losses associated with conventional ICE driven compressor systems, (think carefully).
Also with a counter rotating set of blades, each blade rotating 180 degrees, makes one full cycle for the compressor, as one rotor turns the compressor rotor, and the other rotor turns the compressor housing.

With as little as two to five horsepower additional energy, you might get the same results as that 40 horsepower ICE produces.

Now i have given away some more of my IP rights.

Now let's hear it:uhh:

RonL

 

[mtworkowski@o]

Ron,
I'm sitting here putting my whole brain into this one. I think we have to go over this a bit slower and with more explanation. Words are 1/1000 of a picture, you'll remeber.

 

[redargon]

How quick the mind jumps to the negative of how things are done, do we need to store compressed air in large heavy tanks ? why not use it at the same rate we produce it ? my proposal would be to make the compressor (vane style) section a part of the rotating group (the hub section) the blades are hollow and serve as a momentary tank, the energy to start the process is positive and needs to be supplied from some external source, as kinetic energy builds in the rotating mass, the resistance of compression takes place at a 6" to 12" radius, while the thrust of the jet ejection takes place at a radius of 8-1/2 feet (quite a bit of leverage I think ?).
If intake volume, and compression are matched to supply the discharge at the outside diameter, then additional energy that needs to be supplied to the system, should be enough to compensate for bearing friction, compressor friction, and some thermal loss as the compressed air moves through the blades to the tips (one benefit might be less chance of ice buildup on the blades in some conditions).

This almost completely eliminates losses associated with conventional ICE driven compressor systems, (think carefully).
Also with a counter rotating set of blades, each blade rotating 180 degrees, makes one full cycle for the compressor, as one rotor turns the compressor rotor, and the other rotor turns the compressor housing.

With as little as two to five horsepower additional energy, you might get the same results as that 40 horsepower ICE produces.

Now i have given away some more of my IP rights.

Now let's hear it:uhh:

RonL

Your description is a little complicated. Not trying to be negative, but isn't what you are talking above coming close to perpetual motion? ie. using the rotor to generate lift and compress air to be used to spin the rotor to generate lift to compress air, etc.

 

[RonL]

Your description is a little complicated. Not trying to be negative, but isn't what you are talking above coming close to perpetual motion? ie. using the rotor to generate lift and compress air to be used to spin the rotor to generate lift to compress air, etc.

Very close indeed, and as I understand the first two laws of thermodynamics, there are three limits imposed. At what efficiency rate does a machine need to transfer energy in order to maintain it's own movement ?

I'm not sure where the complication is, if one understands the vane compressor, it will need to have a dual intake and exhaust ports system (two compression cycles) to keep things in alignment, and balance. Having a throttle control system at the tip discharge points might be needed. Other than a few design details, it is basically Air In, and Air Out.

Throwing in a small amount of electrical design, (storage and usage), really gets me excited.

 

[RonL]

Very close indeed, and as I understand the first two laws of thermodynamics, there are three limits imposed. At what efficiency rate does a machine need to transfer energy in order to maintain it's own movement ?

I'm not sure where the complication is, if one understands the vane compressor, it will need to have a dual intake and exhaust ports system (two compression cycles) to keep things in alignment, and balance. Having a throttle control system at the tip discharge points might be needed. Other than a few design details, it is basically Air In, and Air Out.

Throwing in a small amount of electrical design, (storage and usage), really gets me excited.

Maybe a better way to think of this is to forget the mechanics for a moment, and consider the thermal conditions of the air.

If each cubic foot of air that is taken into the compressor has a temperature xx, or xxx degrees, the energy to keep rotation going against compression, thrust, friction, and thermal loss (through conduction), will be reflected by a reduction of temperature, and pressure at the discharge points of the rotors. Each horsepower will require 42.44 BTU/Min. so the air will be cooler based on the energy needed to maintain this motion. The hotter the air the better this will work.

The losses between compression, and discharge will be small in relation to the large mass of air moving through the system.

Very few losses of energy outside the system.

After typing all this I'm not sure it makes any more sense.


Ron

 

[Mech_Engineer]

do we need to store compressed air in large heavy tanks ? why not use it at the same rate we produce it ?

If you propose to use compressed air for a power source, you need to carry it on-board. Otherwise you'll need to carry your required energy to compress the gas on-board in some other form, like gasoline.

If intake volume, and compression are matched to supply the discharge at the outside diameter, then additional energy that needs to be supplied to the system, should be enough to compensate for bearing friction, compressor friction, and some thermal loss as the compressed air moves through the blades to the tips (one benefit might be less chance of ice buildup on the blades in some conditions).

This isn't sounding good. You're saying you use the kinetic energy from the blades to drive a compressor that pumps air to spin the blades, so at most all this thing could do is spin the blades for a little bit until they run out of kinetic energy (you're neglecting external air drag on the blades also, probably one of the largest factors on a helicopter rotor).

With as little as two to five horsepower additional energy, you might get the same results as that 40 horsepower ICE produces.

With 5 horsepower of input, that will be your maximum output as well. The point of a helicopter's engine is to put out enough power to create a downward flow of air that in turn creates a thrust in the opposite direction. Moving all of that air takes a lot of energy, and since your special blades aren't "creating" any energy no matter how complex the rotary vane compressor approach is, they're just spinning around and will completely dependent on additional power input if they need to lift something.

Very close indeed, and as I understand the first two laws of thermodynamics, there are three limits imposed. At what efficiency rate does a machine need to transfer energy in order to maintain it's own movement ?

Being "very close to a prepetual motion machine" is probably not a good thing... To answer your question the only fundamental efficiency that all machines must live by is that their efficiency will be less than 100%. For a machine to continue moving indefinitely, it must have a power input that is equal to all losses in the system.

Your problem is that you're thinking of the rotor as the system, where all it needs to do is keep spinning. In fact the rotor is one part of a helicopter as a system, and the rotational kinetic energy stored in the rotor is small compared to the energy required to keep the helicopter aloft for say 5 minutes.

 

[mtworkowski@o]

It's OK Ron. Just stick your face out the door and close it hard on your head about 5 times. That usually clears my head. Keep thinking.

 

[mtworkowski@o]

What ever happened to Icanbuildit?

 

[Mech_Engineer]

Hopefully he didn't lose the rest of his fingers building his new helicopter...