Ye' old general discussion board. Basically, for everything that isn't covered elsewhere. Come here to shoot the breeze, shoot your mouth off, or whatever suits your fancy. This forum is not for asking programming related questions.
jshpro2 wrote:Sure.. no one knows everything. I've had problems that feyd has gotten stumped on along with multiple other people that still have not been solved to this day. But I'll give it another shot:
Feyd ~ without cheating and trying it, what would happen if you put a slinky on an escalator??!?
- or -
what would happen if you tried to take an airplane off on a giant treadmill moving in the opposite direction of the planes movement?
The momentum of the escalator would cause the slinky to "slink"? when it reached the bottom...
As for the airplane thing...thats simple...
An airfoil generates lift by causing air flow to move faster over the top of the airfoil than the bottom, due to the cambered shape.
If the treadmill was moving at the same speed as the as the airplane would normally travel due to thrust, the the relative air flow would equal zero, thus no pressure differential, thus no lift.
If an airplane wing isn't generating lift, it's stalling, unless it's not airborn, in which case it remains on the ground until lift is generated.
Grim... wrote:?
It would move along it the same way it would move along a road
Better - what would happen if a jumbo jet tried to take off into a 180mph headwind?
Considering this is a theory only question and that FAA or DOT wouldn't allow any aircraft to take off under such conditions...
I speculate that, like a headwind of half it's force or velocity would allow the airplane to achieve V1 slightly quicker than on a day without any headwind.
An airplane uses an airspeed indicator...so even sitting at the end of the runway with zero thurst pointing into the wind, the ASI would register as 90MPH and if take off speed was 150MPH it would only need to reach 60 MPH ground speed before it could begin to take off.
But what your asking is what if the headwind already equaled the take off speed...
Sitting at a dead hault...the airplane would lift off, just like a kite...but would likely be far to unstable for controlled flight...
What happens if the wind stops completely or changes direction slightly or looses wind speed?
An engine generates continuous relaible thrust...thats why we use em'
agtlewis wrote:I am pretty sure I know the answer but I don't want to spoil it or speculate so I won't say anything,
It would just remain stationary relative go the ground below the treadmill. There would be no airflow over the wings at all so it would be the same thing as basically driving your car on it.
I disagree. Don't forget that airplanes achieve forward thrust through the Jet engines. I would hypothesize that regardless of the speed of the treadmill, the jet engines would continue to push the plane forward until it reached takeoff speed. Granted the tires may explode because they would be spinning so fast. Also, the plane might even be able to take off at a lower speed because of the air generated by the treadmill itself.
agtlewis wrote:I am pretty sure I know the answer but I don't want to spoil it or speculate so I won't say anything,
It would just remain stationary relative go the ground below the treadmill. There would be no airflow over the wings at all so it would be the same thing as basically driving your car on it.
I disagree. Don't forget that airplanes achieve forward thrust through the Jet engines. I would hypothesize that regardless of the speed of the treadmill, the jet engines would continue to push the plane forward until it reached takeoff speed. Granted the tires may explode because they would be spinning so fast. Also, the plane might even be able to take off at a lower speed because of the air generated by the treadmill itself.
Nope...it would sit there...unless the the engines produced enough thrust to push the aircraft faster than the treadmill
I run on a treadmill everyday for one hour...believe me...no matter how fast I go...so long as I don't go faster than the tread itself, I feel ZERO wind in my face...
Except for maybe the exhaust exiting my mouth like a turbine or the slight air current you can feel in my basement...
Hockey wrote:Nope...it would sit there...unless the the engines produced enough thrust to push the aircraft faster than the treadmill
I am pretty sure that the plane would be able to take off regardless of the speed of the treadmill. The plane uses the air for propulsion, even when it's on the ground. The speed of it's wheels spinning below it is not relevant to it's airspeed in a situation like this. Basically what your saying is that the engines would be forcing the plane to move forward (through the air), but that this effect would be canceled out by it's wheels spinning from the treadmill. I'm afraid I can't support that theory unless it's been proven, in which case I would love to read about it.
Hockey, you come up with a lot of 'interesting' stuff.
Hockey wrote:I run on a treadmill everyday for one hour...believe me...no matter how fast I go...so long as I don't go faster than the tread itself, I feel ZERO wind in my face...
A plane doesn't use it's wheels to power itself along (like you use your legs), so a treadmill wouldn't make any real difference, maybe a tiny amount of friction caused by wheel bearings, etc.
It's the air that has to be moving, and it would have to be moving in the same direction as the jet to stop it from taking off.
As for the 180mph headwind, if the wind dropped the jet would just move forward - it would still have to use it's engines to develop 180mph of thrust or it would move backward.
And it's not hypothetical - light aircraft can (and have) taken off in fairly 'light' headwinds, and gone straight upward.
The plane would not take off. The plane is at rest relative to the air, moving relative to the treadmill. There is no air current flowing over the wings. There is nothing to prove. You're saying that the air in the room is at rest relative to the treadmill's belt surface.. which it is not. If the air was moving in the same direction and speed as the treadmill's belt (at rest with the belt) it would be moving relative to the plane and generate lift but its not.
Edit = geez this is the stupidest thing to argue over.
Check out how many other people are arguing over it:
Hop onto a moving (flat) treadmill with rollerskates on, and - oh no! You fall off the back!
But hold onto the sides with your arms (jet engines) and you can stay still!
Apply some thrust with your arms (jet engines) and you move forward!
Your arms can move about three times your own body weight - a jet engine can move 3,000 times the jet's bodyweight - and there's two of them...