Talk:Wind gradient

>>During climb into increasing wind, the airspeed increases, allowing the plane to gain energy and climb faster.<<

That's not strictly true, but I'm not sure I can correct it without it confusing the hell out of everyone. It's one of those cases where if you know what's going on, you don't need the explanation, but if you don't, then a simple explanation will not help much. So I'll offer this explanation for comments. BTW, most people don't realise that you control the speed of a plane with the elevators, not the engine, the engine controls the rate of energy input into the system (otherwise how would a sailplane fly fast?) If you don't get that, then don't bother with the rest of this comment.

The energy of a sailplane is dependant on groundspeed, not airspeed, so a 1000kg plane travelling at 20m/s groundspeed has a kinetic energy of 0.5mv2 due to its motion, and a potential energy of mgh due to its height. An increase in wind speed affects neither of those things.

There is a lower airspeed limit called the stall speed below which the aircraft cannot fly, a pilot who flys below stall speed near the ground is called a dead pilot. This is fairly automatic on take-off, the plane remains a wheeled vehicle when below stall speed.

Once the plane has taken off with groundspeed=airspeed (assuming zero wind near the ground), and climbed through the wind gradient a little, the wind speed adds to the ground speed to increase the effective airspeed, and the pilot suddenly finds himself with an excess of airspeed over stall speed margin. He can then choose to slow the aircraft down by climbing, converting kinetic energy into potential energy in the process.

The energy remains constant, but the height and speed have changed in that manouvre.

To put it another way, a height has been reached at a safe airspeed on a windy day that could not have been reached on a still day with the same engine power, but the aircraft is covering the ground more slowly as a result.

I have not yet found a way to extract energy continuously from a wind gradient, by turning/climbing/diving repetatively. Am I being thick? Sailplanes and birds extract energy from updraughts, especially slope soaring on the windward sides of waves and hills. AFAIKS, dynamic soaring allows a little extra height to be gained for a given energy input, and nothing more.

Do we want to be that pedantic with energy? Speaking as a physicist, I say yes, but we could obscure the reasonable with the accurate NeilUK 07:31, 4 May 2006 (UTC)

Dynamic soaring

`AFAIKS, dynamic soaring allows a little extra height to be gained for a given energy input, and nothing more.' ... actually, it can do a lot more than that. R/C sailplanes have been able to reach speeds of 300 mph using dynamic soaring, which could be converted into 3000 feet of altitude if you could ignore air resistance. (Of course, you can't, but a 2000 feet gain seems attainable in the sort of plane (sleek, low drag) that could reach 300 mph via dynamic soaring.)

As for the `During climb into increasing wind, the airspeed increases, allowing the plane to gain energy and climb faster' claim, it's accurate enough. Your airplane knows nothing of it's groundspeed -- all that matters is it's airspeed, and anything that increases it's airspeed gives it more energy. It's all a matter of perspective ... dougmc 02:06, 10 May 2006 (UTC)

Merger?

Should this article on wind gradient be merged with wind shear? It looks like the articles define it identically. Thegreatdr 14:47, 28 November 2006 (UTC)

As said elsewhere, I'm not averse to merging this with wind shear, as long as gradient goes into shear and not vice versa. Evolauxia 23:49, 28 November 2006 (UTC)

I am against merging this with wind shear, since wind shear is a more abrupt phenomena, and therefore deserves its own page. [[ ]] 12:27, 5 February 2007 (UTC)