[wolfekeeper]

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.

[tommya300]

How do you get the craft to advance forward into a head wind?
Can you deflect the drag force tangential to the line of thrust and drag?
Isn't it all a combination in a vector sum at given angles?

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.

[wolfekeeper]

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.

[tommya300]

Someone get that kite to fly into a head wind as it is anchored to the ground with a cable 
Maybe they will witness an unexpected tail spin.

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.

[diecastblue (OP)]

@wolfekeeper Yes someone not over complicating things. I agree with you

What you can't do is get energy if there's no wind shear; there must always be a variation in speed.

, this is the conclusion I came to as well in post 5

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.

, and what I was trying to explain with my image, as long as there is a difference in speeds of fluid between the turbine and prop it is theoretical possible to push the ship with some force forward.

Also I was just browsing Youtube trying to find a good remote control sail plane / glider slope soaring video, there are many of them if you want to look Bored chemist, they will quite happily stay in the air / gain altitude for as long as the wind is blowing, no free energy there, just energy from the wind.

[wolfekeeper]

Yes, but that's slightly different, there the wind is blowing upwards up a slope and is lifting the aircraft, you don't need wind shear for that. But nevertheless that is just powered by the wind.

[diecastblue (OP)]

Here i one picked semi at random

[diecastblue (OP)]

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.

[ThinAirDesigns]

Several folks have already nailed this one: kinetic energy can be extracted only when there is relative motion.  

Generally it would be hard to find a shear layer within air or water that is distinct enough to allow useful extraction with only one craft -- though it is done in lee rotors with Rc planes (

 Also as others have mentioned, it is theoretically possible however to tether two distant craft capable of differing speeds together (say one in the jet stream and one in surface winds), extracting and transfering energy from one to the other via the tether and use this energy to propel the pair.

The intersection of mediums however offer more typical opportunities and allow for some feats that many feel violate the laws of physics.  An example of this is the Blackbird,  a vehicle which can travel directly downwind, faster than the wind - something even the fastest ice-boats and land-yachts cannot do.

newbielink:http://www.wired.com/autopia/2010/06/downwind-faster-than-the-wind/ [nonactive]

[wolfekeeper]

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.

[ThinAirDesigns]

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.

The sort of strange but cool thing about that arrangement is that the airplane is facing and flying backwards relative to it's intended path over the ground.  An around the world record might be possible with something like this 'backing' it's way around the globe.

[diecastblue (OP)]

@ThinAirDesigns Thanks for the two links, will make for some fun reading (when I'm not meant to be working at work I like things like DDWFTTW, that on the surface don't seem to make sense, it certainly dosn't make sense to me yet, think my favorite is the Monty Hall problem, but that has nothing to do with wind.

[daveshorts]

Yes essentially wind shear or wind-ground shear is where you can get energy from. The fastest model aircraft is I think a glider where the record sits at getting on for 400mph. They work in an area of high wind shear looping between the slow and fast moving air.

With high lift to drag ratios you can go a lot faster than the speed difference of the fluids

[bigred3000]

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)

[chris]

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)

Sorry to burst your balloon, but that would be what is otherwise known as a perpetual motion machine, which violates the laws of physics...

[algol]

To start with do you mean "auroplane" or "aircraft".

Then what do you mean by "powered".

If you mean "propelled" and you are happy with "aircraft" then the answer is its called a balloon.

But if you mean "propelled" and you really mean "aeroplane" then you have a problem.

An aeroplane is kept up by air flowing over its wings but for it to go forward under the impulse of wind it would need the air to be flowing in the opposite  direction.

If the aerofoil was reversed to accomodate for this then forward motion would cancel the lift.

Perhaps Magnus rotors instead of wings would work. That would enable wind to generate lift even if its from behind (exploited for propulsion). But Im not a physicist and can only speculate that forward motion would impart a Magnus effect in the reverse direction and cancel the lift.

Of course, you could put gigantic sales on a VTOL airplane in hover mode but then, its  wings will do no work and technically its not an "aeroplane" (its lifted by thrust).

So, yes you can have a wind propelled aircraft....BUT, no, it would not be an "aeroplane".

[algol]

...and before anyone points out I wrote "sales" not "sails"...I should point out that "gigantic sales" were indeed put on a VTOL aircraft by the British MOD which sold its entire Harrier fleet to the US Marine Corps for spare parts  at scrap value.