quote:

Originally posted by Bose:
Teknoaxe,
If you pull a car in neutral with a rope you have to apply force to hold the car in place regardless of the speed of the conveyor belt. This should be equal to the rolling resitance force. It's a small force that's why you can pull the car, however if the conveyer belt starts to accelerate the force will increase proportionally.

In the show they didn't match the speed of airplane with the speed of conveyor belt in every milisecond. For the airplane to move forward it MUST move faster than the conveyor belt. If every milisec the speed of conveyour belt is exactly the same as the tire, the airplane will never move forward. In order to achive the same speed, the conveyor belt needs to accelerate 1000 time faster or maybe more than the accelleration that airplane gets from the propeller. Something that can't be done practically, the tire will burst.

quote:

Originally posted by teknoaxe:

quote:

Originally posted by Bose:
Teknoaxe,
If you pull a car in neutral with a rope you have to apply force to hold the car in place regardless of the speed of the conveyor belt. This should be equal to the rolling resitance force. It's a small force that's why you can pull the car, however if the conveyer belt starts to accelerate the force will increase proportionally.

In the show they didn't match the speed of airplane with the speed of conveyor belt in every milisecond. For the airplane to move forward it MUST move faster than the conveyor belt. If every milisec the speed of conveyour belt is exactly the same as the tire, the airplane will never move forward. In order to achive the same speed, the conveyor belt needs to accelerate 1000 time faster or maybe more than the accelleration that airplane gets from the propeller. Something that can't be done practically, the tire will burst.

The force exerted on the wheels will always be exceptionally small in comparison to the force applied by the propeller. That is why I received the criticism I did for posting the picture of the airplane and the car, because, really, the force applied at the wheels of the airplane is negligible. If that weren't so, it would be ridiculously hard for airplanes to take off in the first place.

In terms of physics, the force applied to the airplane will be the force of static friction on the wheels, which is essentially the normal force on the airplane times a static coefficient of friction, which is essentially the weight of the airplane on a flat surface times the static coefficient of friction.

I light Cessna weights in at 1320 lbs (takeoff weight) and if the asphalt has a coefficient of friction of .5, then the force of static friction will be 760 lbs, max. Anything greater, and the wheels would start skidding. This means there is a limit to the amount of force that can be applied to the wheels, where as the propeller can easily apply a greater thrust.

Also, no matter what the speed, a conveyor belt traveling at a constant speed is just that. There is no acceleration.

quote:

Originally posted by HamsterBoo:

quote:

Originally posted by teknoaxe:

quote:

Originally posted by Bose:
Teknoaxe,
If you pull a car in neutral with a rope you have to apply force to hold the car in place regardless of the speed of the conveyor belt. This should be equal to the rolling resitance force. It's a small force that's why you can pull the car, however if the conveyer belt starts to accelerate the force will increase proportionally.

In the show they didn't match the speed of airplane with the speed of conveyor belt in every milisecond. For the airplane to move forward it MUST move faster than the conveyor belt. If every milisec the speed of conveyour belt is exactly the same as the tire, the airplane will never move forward. In order to achive the same speed, the conveyor belt needs to accelerate 1000 time faster or maybe more than the accelleration that airplane gets from the propeller. Something that can't be done practically, the tire will burst.

The force exerted on the wheels will always be exceptionally small in comparison to the force applied by the propeller. That is why I received the criticism I did for posting the picture of the airplane and the car, because, really, the force applied at the wheels of the airplane is negligible. If that weren't so, it would be ridiculously hard for airplanes to take off in the first place.

In terms of physics, the force applied to the airplane will be the force of static friction on the wheels, which is essentially the normal force on the airplane times a static coefficient of friction, which is essentially the weight of the airplane on a flat surface times the static coefficient of friction.

I light Cessna weights in at 1320 lbs (takeoff weight) and if the asphalt has a coefficient of friction of .5, then the force of static friction will be 760 lbs, max. Anything greater, and the wheels would start skidding. This means there is a limit to the amount of force that can be applied to the wheels, where as the propeller can easily apply a greater thrust.

Also, no matter what the speed, a conveyor belt traveling at a constant speed is just that. There is no acceleration.

I think what the first person is missing is that the conveyor belt is not going back at the speed the WHEELS are going forward, it is going back at the speed the plane is going forward. A car has no "grip" apart from the treadmill, so it would stop; but a plane "grips" the air and pulls itself forward. The additional only force stopping this is the friction of the wheels on the increased groundspeed.
What you are saying is that if the plane is moving forward at 50 MPH (relative to ground) and the treadmill is moving back at 50, the wheels are now moving at 100 MPH (true) so the treadmill should now move back at 100 MPH (wrong). Treadmill is moving at speed of plane relative to ground (groundspeed), not treadmill (wheelspeed).

quote:

Originally posted by Huskertodd:
As an aircraft expert, I felt this myth was dumb. Aircraft generate lift by moving air across the wing, the Cambre forces the air to travel over the top of the wing faster than on the bottom, thus causing a low pressure area to from thus causing lift. You experiment provied nothing, as the wheels of aircraft only have axles no drive shafts. Thus pulling the conveyor under the wheels was no different than yanking a table cloth off a table leaving the dishs standing. To generate lift we need airspeed across the wing surface. The conveyor will not produce lift unless the plane moves with the conveyor, so if you started the conveyor slow enough to move an aircraft, then slow sped it up to 120 Kts, then yes your experiment would work. My aircraft weighed 86,000 lbs, thus would have required a lot of airspeed to get airborn. You should be able to disprove this myth on a simulator. The average person does not understand the physics of flight.

quote:

The average person does not understand the physics of flight.

quote:

If you people arn't satisfied with what you wanted done then you should have several brain scans done to ensure you were never through across a room as a baby!!!!!!!!!!!!!!!!!!1


(No Affense)