Help Design a Human-Powered Helicopter

Phrak

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

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?

Cyrus

You are under the false premise that they were not made of carbon fiber - they were.

Did you mean two hang gliders 900' apart?

Cyrus

Come again? Drag has nothing to do with mass.

Phrak

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?

Cyrus

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.

Phrak

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?

Cyrus

It's called coning. All rotors, including regular helicopters, do this.

Phrak

Sorry to be criptic. All I know is that torsional rigidity of a tube is to the forth power of the radius.

Phrak

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?

Phrak

[QUOTE=Cyrus;2475314]You are under the false premise that they were not made of carbon fiber - they were.]

carbon-carbon

Cyrus

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).

Phrak

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

"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

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.

Cyrus

How is a gyrocopter going to hover?

That's fairly obvious...

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).


Errr......okay. I'd like to see some calculations as to why you think this would work.

FredGarvin

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.