Airplane on a Conveyor Belt...

[AKIron]

Assuming a belt capable of infinite and instant acceleration the wheels would never move. If the belt were capable of infinite acceleration but not instantaneously then the plane would move a bit and stop. Move a bit and stop. Eventually, it would come to the end of the belt and then roll on the ground for takeoff. That is one aspect not addressed previously I believe. So, we would have to define the length of the belt also. 

[Shuffler]

Assuming a belt capable of infinite and instant acceleration the wheels would never move. If the belt were capable of infinite acceleration but not instantaneously then the plane would move a bit and stop. Move a bit and stop. Eventually, it would come to the end of the belt and then roll on the ground for takeoff. That is one aspect not addressed previously I believe. So, we would have to define the length of the belt also.

The only way the plane will stop is if you hit the brakes. Otherwise the plane will be pulled through the air by the prop. The wheels will free roll and the belt will not affect the acceleration of the aircraft other than nominal friction of the wheel bearings.

[Wiley]

The only way the plane will stop is if you hit the brakes. Otherwise the plane will be pulled through the air by the prop. The wheels will free roll and the belt will not affect the acceleration of the aircraft other than nominal friction of the wheel bearings.

I am guessing that given the instant and infinite acceleration mentioned above the idea is that it would be going so fast that the nominal friction of the wheel bearings would overcome the engine's ability to pull it through the air.

More or less pointless argument at that stage.

It frankly shocks me that real life pilots would think that it wouldn't take off if the conveyer was moving at takeoff speed though.

I distinctly remember the Mythbusters episode and the test pilot claiming he was surprised it took off.  All I could think was I would never fly with a guy who had that poor a grasp on how the vehicle worked.

Wiley.

[AKIron]

If you want to deal with the practical instead of theoretical then let's create a scenario that is possible. A Cessna 172 sitting on a conveyor belt that can very quickly spin up to 2,000 miles per hour. What would happen to that Cessna at full power sitting on a conveyor spinning at 2,000 mph?

I think the tires would disintegrate, the gear collapse, and unless you have an ejection seat you would be toast.

[AKIron]

The point of Eskimo's belt sander video was to show there is inertia involved. Friction is of course necessary but not the force being demonstrated. When the belt accelerates there is a force applied to the wheels that is in opposition to the thrust. It is not insignificant.

[Shuffler]

If you want to deal with the practical instead of theoretical then let's create a scenario that is possible. A Cessna 172 sitting on a conveyor belt that can very quickly spin up to 2,000 miles per hour. What would happen to that Cessna at full power sitting on a conveyor spinning at 2,000 mph?

I think the tires would disintegrate, the gear collapse, and unless you have an ejection seat you would be toast.

You can always shoot the plane with a bazooka and see if that helps it fly.

Barring some kind of damage to the aircraft, the plane will fly.

[AKIron]

You can always shoot the plane with a bazooka and see if that helps it fly.

Barring some kind of damage to the aircraft, the plane will fly.

Barring some kind of damage? A Cessna with indestructible wheels? Are you reverting to the theoretical then? In that case give me my infinite acceleration conveyor belt.

There are some pretty fast real world conveyor belts btw: http://www.sacramentorubberproducts.com/story-time-interesting-facts-about-conveyor-belts/

I have doubts about the 900 miles a minute speed though.

[AKIron]

I think whoever wrote that article on the fastest conveyor belt got meters mixed up with miles.

[Wiley]

If you want to deal with the practical instead of theoretical then let's create a scenario that is possible. A Cessna 172 sitting on a conveyor belt that can very quickly spin up to 2,000 miles per hour. What would happen to that Cessna at full power sitting on a conveyor spinning at 2,000 mph?

I think the tires would disintegrate, the gear collapse, and unless you have an ejection seat you would be toast.

At that point, about all you're really discussing is how fast can the landing gear wheels spin before failure.

Wiley.

[AKIron]

Yes, that is the practical aspect of it.

In theory, so long as my belt can continue to accelerate it can exactly counter the thrust of the engine holding the plane stationary relative to the wind. There is an upper limit to this even theoretically and that is the speed of light. Of course when you get close to that limit strange things happen with mass and energy so all bets are off at that point.

[FLOOB]

Except that the belt does not counter the thrust of the propeller even a little bit and would not hold a plane stationary ever.

[FLOOB]

It frankly shocks me that real life pilots would think that it wouldn't take off if the conveyer was moving at takeoff speed though

I know right. I remember somebody on this forum asked how a wing creates lift and someone told him that a wing creates lift because it has an upward angle the air pushes up on the underside of the wing like the bow of a boat. I was surprised that any adult, let alone one who played this game for years, still did not understand how an airfoil works.

[Vraciu]

I know right. I remember somebody on this forum asked how a wing creates lift and someone told him that a wing creates lift because it has an uhpward angle the air pushes up on the underside of the wing like the bow of a boat. I was surprised that any adult, let alone one who played this game for years, still did not understand how an airfoil works.

Actually there is Newtonian action on the underside of a wing (depending on AOA).  Anyone who doubts this should stick a board out the window of a moving car. 

[AKIron]

You need to watch the belt sander video Eskimo made many years ago if you don't believe an accelerating belt will apply force to a wheel sitting on it. That force is applied to the plane through the axle and landing gear and is in opposition to the thrust produced by the plane's engine and prop.

[Reaper90]

This thread is a hilarious (and somewhat frightening/depressing) example of people who don't seem to have a firm grasp on why and how aircraft are able to attain flight.

The aircraft could care less about the ground speed of its wheels across a surface, only the airflow over the wings, which is a product of thrust created by the prop/turbine etc. The only way the speed of the "conveyor belt" would matter is if the aircraft's engine were powering its wheels to move it forward, then the surface speed of the conveyor would matter relative to the aircraft's speed forward. But, in our case, with the exception of a minimal amount of rotational resistance from the tires and parasitic drag caused by the bearings in the wheel hubs..... whether the tires are turning at 25 rpm or 2500rpm matters not (unless one of them blows from the excessive heat, but let's assume a perfect world and tires made of indestructanium). The method of propulsion is acting on the air around the aircraft, not on the ground, to propel the aircraft forward. Airspeed creates lift, not groundspeed. The only way this extra drag from the tires and bearings keeps the plane from becoming airborne is if the craft is so woefully underpowered that is can't overcome this extra drag... and I would say such an aircraft would already be utterly lacking in airworthiness, and a deathtrap. Look at the massively greater resistance that a seaplane contends with, trying to gather speed through and over water. Exponentially greater resistance than an asphalt runway.... yet the seaplane's thrust is more than enough to overcome the resistance.

The only other way a silly conveyor belt causes an aircraft not to be able to gather the speed required to rotate and become airborne is if the increased speeds experienced by the landing gear couple with excessive yaw from engine torque (why you have to apply opposite rudder to counteract torque during takeoff) to exert such side loads to the undercarriage that the aircraft ground loops or becomes unsteerable. Otherwise........ it flies.

This is a silly argument that even a basic understanding of "how do airplanes fly" should settle.