the plane isn't physically moving if the it is moving at 5mph and the coneyor belt is moving in the exact opposite direction in 5mph. if it isn't moving, there would be no airflow around the wings.
the plane isn't physically moving if the it is moving at 5mph and the coneyor belt is moving in the exact opposite direction in 5mph. if it isn't moving, there would be no airflow around the wings.
Your sled statement is wrong, since the friction between them and the conveyer would probably be too great for the plane to overcome.
EDIT: I thought you meant the plane was on skids, on the conveyer. My mistake.
Look at the situation again, the 'treadmill' is not moving backwards at 5MPH while the wheels are rotating at 10MPH, the treadmill is also moving backwards at 10MPH. It doesn't allow the wheels to rotate faster than itself.
If the wheels spin at an insane speed, the belt will move backwards at an insane speed effectively imposing insane forces on that plane. The two really do cancel eachother out.
Wait.. are you making fun of me, or the ppl I'm quoting. i just said that someone should think about it.
You know what, fvck it. I am through with this thread and all the 10 year old morons who think that the plane won't take off because they don't realize the wheels and the ground mean absolutely nothing. The only thing that matters is the air.
No they don't cancel each other out. Assuming there's zero friction and assuming the tires don't fly apart, the tire speed would just keep increasing to infinity and the plane would keep going forward. The forces in action between the conveyer and the wheels are irrelevant.
I guess people don't see that you can't slow down a plane by trying to rotate its wheels more....:roll:
Mo0o
Lifer
- Jul 31, 2001
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The only fundamental understanding error here is that the wheels themselves do not propel the plane forward. The friction involved in the ball bearings offer such a negligible resistance that you might as well consider them to have no friction. In a car, the wheels has power applied to them through teh engine, allowing it to go forward, in an airplane the wheels simply allow the plane to go foward on the ground while propelled by the turbines. So the conveyer belt would not do anything once the engines wind up.
you just proved yourself wrong. you are correct that the wheels and the ground mean absolutely nothing. yes the only thing that matters is the air and since the plane is not actually moving there is zero airflow on the wings, hence no lift.
but its the motion relative to the ground that provides the forward movement to move the air over the wings to provide lift for the wings and takeoff. not flight, but takeoff.
Sleds do not hold traction to the surface they're travelling on. The rotation of the wheels is directly proportional to the movement of the belt. If the wheels are not spinning faster than the belt, they are not moving forward.
But don't you see that if there's zero friction betwen the wheels and the conveyer the wheels would just speed up indefinately to keep pace with the conveyer and the plane will keep moving forward?
That said, since the entire point of the thread was obviously just an exercise in critical thinking, given the limitations of the original scenario... I suppose then no, the plane wouldn't take off...
I know I said I was done, but I need to answer this. If the jets are producing thrust, then the plane is moving forward, hence air is moving over the wings, producing lift.
If you mean by the plane's wheels are rotating at 5MPH and the treadmill moving at 5MPH, then the actual location of the plane does not change, and unless there is wind blowing into the front of the aircraft, the plane is actually performing at 0 airspeed.
Airspeed is what determines the plane's flight performance and not the perception of the viewer from the ground. If the conveyor belt keeps going and the pilot cuts the engines, the plane will start moving backwards gradually and keep speeding up (backwards that is) until it matches the belt speed. Crank the engines again and it will reduce the backwards motion until it reaches par (meaning it looks still from afar.) When it reaches par and even more power is applied to the engine, the plane will visually move foward. Only then will there be any level of headwind. To take off, it's just a matter of the aircraft reaching the required takeoff headwind/airspeed, not how fast the wheels are spinning.
Headwind = what's shown on the airspeed indicator. Airspeed = direct relation to the performance of the aircraft.
And you can't slow down an object that is not tied to its wheels directly. You spin the treadmill, the wheels just spin more, if I am moving at 5 MPH and you spin the treadmill at 10000000000 RPM, I will still be moving at 5 MPH(assuming the wheels don't break).
I recant my position... Given the original post's stipulations, it won't take off unless the thrust of the engine is greater than the mass of the airplane. otherwise it's going to stay there.
The OP:
The constraints set out by the scenario tell me it's not going to happen, unless the engine has more thrust than weight. Of course in real life there's no way this is going to happen.
The OP:
The constraints set out by the scenario tell me it's not going to happen, unless the engine has more thrust than weight. Of course in real life there's no way this is going to happen.
So this is why I think my Purdue Engineering friend is incompetent. This is why we Cal students get the job.
Your assumption of 5MPH assumes that the wheels are spinning FASTER than the treadmill..... This is like walking at the same speed the treadmill is going. The treadmill is not at a fixed speed. It goes in reverse as fast as the wheel does.
Thus dv/dt = 0. Without any net motion there is no airflow, thus no takeoff.
So what is the upward force on the plane? What is counteracting gravity?
Would it not be lift? And wouldn't air over the wings be required for lift?
The engines would only propel the plane forward, not up. And doesn't the original question say that the conveyor belt counteracts all forward motion of the plane? So the plane would essentially require a vertical takeoff, no? Something would have to create that lift.
If I'm running on a treadmill and matching the speed of it exactly, and I spread my arms out, there's no drag on my arms, as they are stationary with respect to the air. Even if someone pushed me from behind, who wasn't on the treadmill, at the same rate that the treadmill accelerated, we'd have the same situation.
So what is holding the airplane up? And what gets it up in the first place? Unless the plane/engines are on a tilt, I don't see how it would be possible.
Would it not be lift? And wouldn't air over the wings be required for lift?
The engines would only propel the plane forward, not up. And doesn't the original question say that the conveyor belt counteracts all forward motion of the plane? So the plane would essentially require a vertical takeoff, no? Something would have to create that lift.
If I'm running on a treadmill and matching the speed of it exactly, and I spread my arms out, there's no drag on my arms, as they are stationary with respect to the air. Even if someone pushed me from behind, who wasn't on the treadmill, at the same rate that the treadmill accelerated, we'd have the same situation.
So what is holding the airplane up? And what gets it up in the first place? Unless the plane/engines are on a tilt, I don't see how it would be possible.
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