Sailing trivia (get in here if you like airplanes and treadmills)

[reksio]

Next question:

Can a glider (plane without engine) stay airborne permanently in an area with only still air and some downdrafts(sinking air), but no updrafts(rising air)?

No. Matter has a finite lifespan.

M'kay. The version for the smartass:

Can a glider flying in an area with only still air and some downdrafts, but no updrafts, reach the same altitude and groundspeed that he had 1 hour earlier during the same flight

A glider could stay "airborne" in the gasses collected at a Lagrangian point for a very long time.

Let's stay in the lower atmosphere for now.

 

[DominionSeraph]

But no.

Actually, I change my answer.

Yes, given sufficient downdraft you could.

 

[PlasmaBomb]

Where exactly do they say this?

It pretty much says that any glider must continually descend to maintain flying speed, but if the air that it is flying through is rising faster than the glider is descending, the glider will gain altitude.

I suppose that if you hit a down draft and gain speed more rapidly than you lose altitude you could trade the speed for altitude...?

Problem is that downdrafts tend to be turbulent and include a lot of wind shear... so I wouldn't fancy it...

Edit: You got an answer?

 

[Blackjack200]

It pretty much says that any glider must continually descend to maintain flying speed, but if the air that it is flying through is rising faster than the glider is descending, the glider will gain altitude.

I suppose that if you hit a down draft and gain speed more rapidly than you lose altitude you could trade the speed for altitude...?

Yeah, it seems like it should be theoretically possible, but those would have to be some wicked down drafts.

 

[reksio]

I suppose that if you hit a down draft and gain speed more rapidly than you lose altitude you could trade the speed for altitude...?

Yes, that is pretty much how it works. By pushing the nose down when entering a downdraft you will gain more kinetic energy than you loose in potential energy, because you accelerate the sinking air upwards taking kinetic energy from it. As soon you leave the downdraft you pull up again, and climb higher than you were before. See:
http://www.icarusengineering.com/Dynamic-Soaring-and-SE.htm

It is similar to sailing, where you gain energy from the velocity difference between water and air(true wind), and can achieve speeds higher than that difference. Here it is the velocity difference between air and air, and you can achieve speeds much higher than that difference. Current record is 468mph in 65mph horizontal winds, with a RC-glider:
http://www.youtube.com/watch?v=rfoxjNg-eg0

 

[Mr.IncrediblyBored]

They are probably just lazy programmers, and didn't nomalize the velocity vector. So when you press UP+LEFT you run 1.41 times faster than just with UP pressed. That's how it was in DOOM IIRC.

My mistake, here I was thinking I made a joke that didn't need a real response.