|
|
Post by Vashthestampede on Dec 8, 2005 23:33:00 GMT -5
Ok good that you mention the treadmill.
Think of it this way. Your on a treadmill with rollerblades. You remain stationary because the treadmill is keeping you in one spot. Now imagine you pull yourself along with a rope. Regardless of how fast the treadmill moves you will still be able to pull yourself along. The rope represents thrust.
And I'll take off my sig.
|
|
|
|
Post by mobey on Dec 9, 2005 0:00:41 GMT -5
not unless its a jump jet  without lift thrust is irrelevant and without forward motion you can't create low pressure above the wings and high pressure below the wings (lift) (alla bernoulli) |
|
|
|
Post by Vashthestampede on Dec 9, 2005 0:55:06 GMT -5
not unless its a jump jet without lift thrust is irrelevant and without forward motion you can't create low pressure above the wings and high pressure below the wings (lift) (alla bernoulli) Except the forward motion isn't produced by the wheels the forward motion is produced by thrust. The wheels cannot physically cause the plane to stop moving unless you apply the brakes. |
|
|
|
Post by Kozz on Dec 9, 2005 8:39:58 GMT -5
So the conveyer is just there to reduce drag from the wheels being in touch with the ground...
|
|
|
|
Post by retardedfury2p1 on Dec 9, 2005 9:11:33 GMT -5
No, the aircraft will not take off. In order to generate lift, an airfoil must have air pass over it's surface. If this conveyor belt runway is such that the aircraft will remain stationary, regardless of how much thrust is applied to it's engines, it will not allow the aircraft to move forward, thus generating no airflow over the airfoil, thus generating no lift, thus not allowing the aircraft to take off.
Now, if the 747 happens to have a headwind of, say, about 150kts, then maybe it could get airborne. All in all, I'm assuming this runway is basically like a dynamometer, and won't allow the airplane to move, no matter how fast it's wheels roll. Unless the phrase "the planes speed" contains some sort of jackassery from your teacher, at which point I would call the question BS.
At either rate, my BS in Aerospace Studies, pilot's license, and profession as an air traffic controller trump whatever your teacher tries to use to justify making this B747 fly(unless there's like a 150kt headwind, as previously stated).
It won't fly if it just sits there,
David
|
|
|
|
Post by retardedfury2p1 on Dec 9, 2005 9:18:24 GMT -5
Ok good that you mention the treadmill. Think of it this way. Your on a treadmill with rollerblades. You remain stationary because the treadmill is keeping you in one spot. Now imagine you pull yourself along with a rope. Regardless of how fast the treadmill moves you will still be able to pull yourself along. The rope represents thrust. And I'll take off my sig. But the original question indicated that the runway tracks and reacts to the aircrafts speed. Thus, the aircraft moves forward at 5kts, the runway moves backward at 5kts. Plane moves forward at 150kts, runway goes opposite direction at 150kts. There is no way to overcome the reaction of the runway, unless the runway has some sort of limit to how fast it can go. The rope thing is BS. There is no outside anchored object that the B747 can grab onto and pull itself along. It has only it's engines, which are the only thing a B747 has to push itself along with. Now if some giant 5 year old comes down from the sky and grabs the B747 like a toy and pulls it along, then your rope analogy would apply. Otherwise, it won't fly! David |
|
|
|
Post by retardedfury2p1 on Dec 9, 2005 9:23:06 GMT -5
Oh wait a minute! This question is some of the high school mind games BS! The runway is still long as hell, not short(I'm assuming). Yeah, it could take off. Might need to do short field take-off procedures, but it could do it.
This question is still BS, though. Darn it.
David
|
|
|
|
Post by Vashthestampede on Dec 9, 2005 10:35:39 GMT -5
Even if the wheels are spinning backwards the plane can still move forward as the wheels are allowed to spin free. Nowhere in the question does it say that the runway will keep the plane stationary.
|
|
|
|
Post by mobey on Dec 9, 2005 11:38:43 GMT -5
regardless there can be no forward motion if the conveyer matches the forward motion with oposite force. The wheels are free flowing, however they are still attached to the plane.
BTW if for some reason i missed it were possible. Every aircraft carrier in the world would have one. not to metion every airport.
|
|
|
|
Post by MerrSonn on Dec 9, 2005 12:26:14 GMT -5
That's the tricky thing. Although the speed of the runway will match the speed of the plane, it will have no effect on the speed of the plane. The wheels will move faster and faster, but the plane will continue to accelerate and move forward at its normal speed. There would be no advantage to doing things this way, it would take the same amount of runway for a plane to take off regardless of whether the runway was moving or not. The wording of the question is tricky.
|
|
|
|
Post by Vashthestampede on Dec 9, 2005 12:56:37 GMT -5
regardless there can be no forward motion if the conveyer matches the forward motion with oposite force. The wheels are free flowing, however they are still attached to the plane. BTW if for some reason i missed it were possible. Every aircraft carrier in the world would have one. not to metion every airport. The conveyor would not be helpful in making take off distances shorter or longer. So it would just be more complexity that is completely unneccesary. Ok think of it this way the plane could take off with its wheels locked if it were on ice because the wheels do not propel the plane. This is the same principle as the wheels do not control the direction of the plane they just reduced friction between the surfaces. |
|
Gen
Corporal
Confused and lost
Posts: 65
|
Post by Gen on Dec 9, 2005 13:12:05 GMT -5
Lol, way to go Vash, you've made us have to actually think about something. ;D We need more riddles like this.
Anybody else think the plane couldn't take off?
|
|
|
|
Post by RandyA on Dec 9, 2005 14:52:59 GMT -5
yeah i didnt think it would take off. but i assumed alot. and you know what they say  |
|
Jackson
Corporal
Dewaholic
Shut up with that filthy pig latin.
Posts: 62
|
Post by Jackson on Dec 9, 2005 15:25:39 GMT -5
I wish I had a treadmill so I could video a small clip of me on a skateboard pulling forward on a rope to prove that forward motion is possible.
How many times can we say it? the forward motion does not come from the wheels! It comes from the engines. The wheels are there to reduce friction!
|
|
GRRWingNut
Recruit
For all your flightline needs...
Posts: 11
|
Post by GRRWingNut on Dec 9, 2005 15:54:31 GMT -5
I love aviation!!!!!
I know a bunch about it!!!
I love this question!!!
The answer is yes. The reason for this is the airspeed, as mentioned before. The wheels do not power the aircraft. If that were the case, the aircraft would lose speed as soon as it lifted off and would crash.
If an aircraft was placed on a conveyor, or simply some mechanism to counteract exactly the motion of the wheels, the wheels would not turn.
However, this would not affect the airspeed of the aircraft, and would still allow it to gain enough airspeed to lift off.
In effect, the jet engine, or whatever means of thrust the aircraft has, would be powering the movement of the aircraft, and the conveyor.
The aircraft would lift off, but the wheels would remain motionless!!!!
The same question has been raging for a long time, and highly eperienced aviation professionals get stumped by it all the time. But it really is a simple question of physics.
jj
|
|
