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...
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
Let's stay in the lower atmosphere for now. :D
Correct. Most sail boats wouldn't make it. But the USA-17 that BlackJack mentioned could do the following trick:
Start at the downwind mark and simultaneously release a balloon at the upwind mark. While the balloon floats:
upwind mark -> downwind mark
the boat goes:
downwind mark ->...
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)?
:thumbsup: Correct, efficient sail boats could do it. It is symmetrical to the downstream race:
Downstream race : Relative to the airmass B is going downstream, faster than the stream.
Upstream race : Relative to the water B (and C) are going downwind, faster than the wind.
No takers on this?:
Boat A:
Current : 10mph (relative to ground)
Wind : 10mph (relative to ground, same direction as current)
Boat B:
Current : 10mph (relative to ground)
Wind : 0mph (relative to ground)
I will add a bonus case
Boat C:
Current : 20mph (relative to ground)...
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.
To make it clear for the others:
Boat A:
Current : 10mph
True wind : 10mph down the current.
Boat B:
Current : 10mph
True wind : 0mph
Can any of the boats go against the current (up the river)?
Okay, but what about going upstream in the same wind conditions as in your question. Can one of the boats reach a point up the river from the starting point?
Yes
A is not making any progress downstream relative to the water. So any progress downstream relative to the water that B makes will bring it ahead of A.
It is trivial for a boat to make some minimal progress relative to the water, in the opposite direction than the airmass moves relative to...
There are no different principles utilized by different foils. Just different laws (based on models of different abstraction level), which are satisfied by all foils. Every foil accelerates the fluid opposite to the force it creates (Newtons 3rd). Every foil obeys Bernoulli's Laws.
But if by...
Yeah, I guess you mean the difference between attached flow at the blades and separated flow. But keep in mind that even with propellers the aim is to have attached flow, like on a wing.
It is exactly the angles a sailcraft would use on a broad reach with downwind VMG > windspeed. Look at the diagram below and replace:
boat velocity -> blade velocity
downwind VMG -> vehicle velocity
As you see vehicle velocity(downwind VMG) is 1.5 x true wind, and the blade is still pulled...
It's not wrong. But the transition between the cases 1-3 is smoother than you describe it. The airfoils are completely stalled at first, and then with increasing speed they gradually become unstalled (from the tips inwards) and start to work more efficiently.
Some of the differences you try...
A point on the propeller blade moves in a different direction than the vehicle . It is simple vector addition:
blade_velocity = cart_velocity + tangential_blade_velocity
And since tangential_blade_velocity is perpendicular to the cart_velocity & wind, the blade_velocity is not parallel to...
Propellers spin like that. Turbines spin the other way:
http://www.youtube.com/watch?v=nudBjrOF3LE
The propeller blades are going at an angle to the wind:
http://www.youtube.com/watch?v=UGRFb8yNtBo
Nope. Perpetual motion would be an isolated system, that keeps going. This is not isolated at all. It takes energy from the wind (air motion relative to ground) which is slowed down.
Start here:
http://en.wikipedia.org/wiki/Sailing_faster_than_the_wind#Speed_made_good
Example vector diagram:
Animated diagram:
http://www.youtube.com/watch?v=63hvQABLOaE
The air has always a relative velocity to the rotating airfoils,
Nope:
But I'm sure he could do...
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