12-20-2007, 06:36 PM
I'm late to the party, but here's my two cents. I just finished driving all the way from NH, and for some reason I just read through this whole thing. I blame all of you... fuck you guys.
Here is your problem derek. If the treadmill was going in reverse at 4mph and the plane needed to be 88mph in order to take off, it would not require the extra thrust to get to 92 mph.
In a frictionless world: The engines would still only have to provide enough thrust to get to 88mph because the wind speed is the same.
In the real world: In order to get to the takeoff speed of 88 mph the engines would have to provide the same amount of thrust that would normally get the plane to about 88.1 mph, with that extra 0.1 mph (thats being generous) coming from overcoming the force of friction between the tire/ground and the wheel/bearing.
What you said kinda holds true if you're talking about wind speed. If a 4 mph wind is at the back of the plane, it has to move at 92 mph relative to the ground in order to take off.
The key point: (estimating here) 99% of the friction a plane sees is due to wind resistance while only 1% is due to the friction of the ground.
If a full size plane is sitting on a giant treadmill and you turn it on to 20 mph, the plane will still basically sit still. If you leave it there for ever, eventually the force of friction will make the plane move faster and faster until it's even with the treadmill.
Same physical problem with a different viewpoint: A plane lands at 20 mph, if you apply no brakes or reverse thrust, the plane will keep rolling for a very long time. Actually that example would have wind resistance working against it to slow it down.
HAULN-SS Wrote:If The plane needs 88mph to take off, and the treadmill is rolling in reverse at 4mph, then all the plane has to do is give it the same power as if were going to go 92mph, then it takes off.
Here is your problem derek. If the treadmill was going in reverse at 4mph and the plane needed to be 88mph in order to take off, it would not require the extra thrust to get to 92 mph.
In a frictionless world: The engines would still only have to provide enough thrust to get to 88mph because the wind speed is the same.
In the real world: In order to get to the takeoff speed of 88 mph the engines would have to provide the same amount of thrust that would normally get the plane to about 88.1 mph, with that extra 0.1 mph (thats being generous) coming from overcoming the force of friction between the tire/ground and the wheel/bearing.
What you said kinda holds true if you're talking about wind speed. If a 4 mph wind is at the back of the plane, it has to move at 92 mph relative to the ground in order to take off.
The key point: (estimating here) 99% of the friction a plane sees is due to wind resistance while only 1% is due to the friction of the ground.
If a full size plane is sitting on a giant treadmill and you turn it on to 20 mph, the plane will still basically sit still. If you leave it there for ever, eventually the force of friction will make the plane move faster and faster until it's even with the treadmill.
Same physical problem with a different viewpoint: A plane lands at 20 mph, if you apply no brakes or reverse thrust, the plane will keep rolling for a very long time. Actually that example would have wind resistance working against it to slow it down.
1993 BMW 325is
Sgt. Slaughter
Sgt. Slaughter