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I was looking at DIY wind turbines, and stumbled across this video : http://www.youtube.com/watch?v=oKqC5JsurOkIt got me thinking, could this work for an aeroplane? If an airfoil has a lift / drag ratio greater than 1, can it pull enough energy to drive the plane, overcoming the drag of the blade? I'm just thinking out loud, what do you reckon?
The essence of the problem is that, unlike a ship, a plane has nothing to push against.
Quote from: Bored chemist on 15/06/2010 20:19:58It's only because the water holds the ship back, that the windmill on a ship can continue to turn and gain energy to drive the ship.Does that mean if the ship was out of the water and put on stationary wooden saw horses, that the windmill on the ship would stop turning?
It's only because the water holds the ship back, that the windmill on a ship can continue to turn and gain energy to drive the ship.
you can see that windmill powered boats work. I bet you can't find a similar vid of a balloon.
After a short while the balloon would be travelling at the same speed as the air round it. In that event the windmill would stop. It wouldn't be able to provide any energy to pump water.
LeeE are you relating to these 3 condition with respect to airflow and airfoil.[attachment=12261]
It is possible to power an aircraft from the wind.One form is usually called a 'kite' and involves attaching it to the ground with a cable.Far less obviously, but it's also possible, you could use a cable to make use of wind shear. For example if you have the aircraft in the jet stream and lower a cable down out of the jet stream then you can make use of the very high windshear to power the aircraft, even drive it upwind, or downwind faster than the jet stream (yes, I know it sounds impossible or even ridiculous, but it definitely can be done- and it doesn't violate conservation laws, similar things are done with land yachts).It's also theoretically possible for a glider to make use of wind shear to maintain altitude by dipping in and out of the different air masses, but it's very difficult to make it work.What you can't do is get energy if there's no wind shear; there must always be a variation in speed.
If you think about it, that's what a kite does when you first launch it. Kite's make use of the difference in speed between the ground and the air.There's fiddly ways to do it with turbines, but I can't be bothered to go into it.
What you can't do is get energy if there's no wind shear; there must always be a variation in speed.
Thinking about this (in my dreams last night:), I think the key is that in the boat example, the driving propeller is in a fluid that is not moving relative to the boat, where as in a plane (or balloon:) the driving prop has to work in air that is already moving in the opposite direction.
So I need a plane with 10 km very low drag pole on it to extend the turbine into a jetstream, simple I'll cook up some Einsteinon in the microwave tonight and give it a go.
No, you put the aeroplane at the top in the jet stream, and then at the bottom of a tensile cable you put the lower section (in the simplest case it's just a drogue chute.) And then it basically just works like a kite.In the more complicated case the aeroplane has a windmill on it, the cable is an electrical cable, and the drogue is replaced with a propeller that is powered from the windmill via the cable and pulls the whole system upwind.
Alright, now lets say you have a remote controlled plane with a brushless motor, eventually the planes battery will die. Now look at a wind turbine, it generates its own power, so if you get what I am saying then you don't have to keep reading. In order to keep a wind powered plane in the air the propeller would need to generate its own power. That power goes to a generator which then goes to a motor and powers the plane.(WARNING: Do not try this on a real plane, these statements need to be tested on a home-made remote-controlled plane, DO NOT TRY)