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Offline blobranaTopic starter

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Human-powered helicopter
« on: August 13, 2004, 05:45:11 PM »
Hum,
A Human-powered helicopter doesn`t get off the ground...

for more info

Offline KennyR

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Re: Human-powered helicopter
« Reply #1 on: August 13, 2004, 06:41:16 PM »
If someone would actually have read up on the science, they could have saved their time and effort. The human body doesn't have the muscle or energy it needs to supply lift to its own weight. Our power to weight ratio is too feeble.
 

Offline blobranaTopic starter

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Re: Human-powered helicopter
« Reply #2 on: August 13, 2004, 07:14:17 PM »
Hum,
Luckily Dr Paul B MacCready didn`t read that...
The Gossamer Albatross was a human-powered aircraft, and on June 12, 1979 it completed a successful crossing of the English Channel ...










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Offline X-ray

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Re: Human-powered helicopter
« Reply #3 on: August 13, 2004, 07:59:04 PM »
This may at first sound callous, but their best bet is to get an amputee. His upper body strength will be formidable and he will weigh less than a walker. Also the action of winding wheelchair wheels may be convertible to the gearing system of the chopper.

I'm not saying they can do it, but if they want to keep the weight down and power up, that's an idea.
 

Offline Karlos

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Re: Human-powered helicopter
« Reply #4 on: August 13, 2004, 08:55:16 PM »
Quote

KennyR wrote:
If someone would actually have read up on the science, they could have saved their time and effort. The human body doesn't have the muscle or energy it needs to supply lift to its own weight. Our power to weight ratio is too feeble.


Power to weight isn't the issue here. Aeronautical engineering is. After all, whats the power to weight ratio of your average glider?

A human powered aircraft has already flown the channel, as blob points out...

int p; // A
 

Offline JaXanim

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Re: Human-powered helicopter
« Reply #5 on: August 13, 2004, 09:22:54 PM »
Winged aircraft ie. all aeroplanes, gliders as well as the Gossamer Albatross (GA) get lift from the passage of air over their aerofoiled surfaces.  This is achieved using a propellor or a jet engine to create forward motion through the atmosphere. A reltively slow airspeed can produce quite substantial lift, as evidenced by the peddling man powering GA's large but very light propellor. Helicopters on the other hand get lift from an equal and opposite reaction to downthrust.

Downthrust is created by the rotors (which have a small aerofoil section themselves) compressing air downwards into a relatively small column below the craft. In effect, the rotors press down and the craft rises. I suppose a small amount of lift is generated via the aerofoiled blades but nowhere near that of a formal wing.

As has been said, no man has enough energy to generate a downthrust equal to the combined weight of the craft and himself. No amount of gearing or body weight reduction will change that. Interesting thing is a bumble bee can do it with ease even though the principles of aerodynamics say it shouldn't.

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Offline blobranaTopic starter

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Re: Human-powered helicopter
« Reply #6 on: August 13, 2004, 10:12:30 PM »
Hum,
i don't think that driving an aerofoil around, and around, in a circle  would be any less powerful, than driving it forward, in one direction  (AKA  Gossamer)

Though the material stresses on it would , i imagine, be formidable to overcome

Offline Karlos

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Re: Human-powered helicopter
« Reply #7 on: August 13, 2004, 11:15:32 PM »
Quote

JaXanim wrote:

As has been said, no man has enough energy to generate a downthrust equal to the combined weight of the craft and himself




No, Kenny said that no human has the power to weight ratio to achieve powered flight, which is not true since it has been done. The method was unspecified. Although its fair to assume downthrust, given the thread title, I suppose :-)

Quote

No amount of gearing or body weight reduction will change that. Interesting thing is a bumble bee can do it with ease even though the principles of aerodynamics say it shouldn't.


Yeah, the humble bumble bee. Our A level maths/mechanics teacher (a former aeronautical engineer) used to bring that one up from time to time.

It basically demonstrates that there is more to aerodynamics than we fully appreciate (simply because we can't make the numbers fit), so perhaps there is hope for the helicopter yet...
int p; // A
 

Offline JaXanim

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Re: Human-powered helicopter
« Reply #8 on: August 13, 2004, 11:27:29 PM »
@blobrana

Not sure I understand your point.

Anyway, horizontal flight embraces three major forces:

Mass (gravity) which is down.
Lift (via the aerofoil or reaction to a down thruster) which is up.
Drag (air friction) which is backwards in the case of 'forward' motion through the air.

Provided lift exceeds mass, the craft will hover.
Provided the motive force exceeds the drag, the craft will move horizontally, ie: it will fly.

Aeroplanes get lift from the differential pressure above (low) and below the relatively vast wing aerofoil area. A very slow forward motion through the air will create a lot of lift if the aerofoil is pronounced (as in GA and typical gliders). A man has enough energy to achieve this lift if the total mass is low enough (as in GA). The craft also has to be designed with sufficient streamlining to allow drag to be minimised. Even so, GA flies very slowly, perhaps 10mph.

In the case of hovering, which only helicopters and vectored thrust planes can achieve, there is no drag because there's no motion. All the power of the engine is directed in opposition to the mass. In other words, the downthrust must equal the mass of the craft. The air is simply used as the down thrusting medium in the helicopter. In the Harrier, it's the high pressure exhaust stream.

So, no man has the energy to counterbalance the mass and can never power a hover. He can, however, power just sufficient forward motion, by overcoming the drag, and thereby get a hand from Mother Nature's lift as the air passes over the aerofoil.

As a matter of interest, the tips of a helicoper's rotor break the sound barrier. So yes, the stresses are immense.

Cheers,

JaX





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Offline blobranaTopic starter

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Re: Human-powered helicopter
« Reply #9 on: August 14, 2004, 01:19:52 AM »
@JaXanim

 hum,
what i mean is that it must be possible...

If the `gossamer` flew in a circle then  by  your logic it wouldn't fly...

The rotor blade  is like an aerofoil wing and  gives lift ,  just like an aeroplane; except it's moving in a circular path.

lift is lift - the motion that created  it doesn't depend on it being in a straight or circular path...

And if you say that someperson moved the  `gossamer ` with sufficient forward motion,  overcoming the drag, to get it to fly the by that logic it must be easier to fly a helicopter since there is no drag to overcome...



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Offline T_Bone

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Re: Human-powered helicopter
« Reply #10 on: August 14, 2004, 08:18:43 AM »
"Never assume the obvious is true" ;-)
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Offline blobranaTopic starter

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Re: Human-powered helicopter
« Reply #11 on: August 14, 2004, 01:16:28 PM »
Hum,
tnx.

@Dr Watson
I have no data yet. It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.

Offline Vincent

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Re: Human-powered helicopter
« Reply #12 on: August 14, 2004, 04:02:01 PM »
When I first saw the title of this thread I immediately thought...

Yes! we can finally burn some neds and get use out of them :-P

Pity no one's thought of that yet :lol:
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Offline KennyR

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Re: Human-powered helicopter
« Reply #13 on: August 14, 2004, 05:47:23 PM »
Vincent, your argument has one logical flaw: sh!te doesn't burn.
 

Offline Turambar

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Re: Human-powered helicopter
« Reply #14 on: August 14, 2004, 06:03:58 PM »
Ahh but it does, and its good for so many other things too. More here.