will it take off?

[JimParker]

The prop is also an airfoil. When its spinning, it is creating lift, not vertical lift but horizontal lift. If you have horizontal lift that overcomes the small bit of drag of the wheels spinning, the plane will move forward, thus creating vertical lift and off into the wild blue.

And that's the problem with everyone's logic - and I mean both sides!

If the conveyor is capable of infinite speed, it can also produce infinite DRAG at the wheels. Since acceleration occurs only if Thrust is greater than Drag, then it follows that the plane will NOT fly IF the conveyor is capable of creating enough drag (by turning the wheels at well-above-takeoff speed - maybe 10X to 20X that speed?). All you pilots, engineers, and mathematicians out there should remember that formula - it's part of basic ground school If Thrust = Drag, acceleration is ZERO.

On the other hand, if the conveyor is NOT able to turn that fast, and cannot change it's speed instantaneously to counteract the thrust provided by the propeller, the plane will eventually fly, becuse thrust will exceed drag for at least brief moments. When Thrust is greater than Drag, acceleration occurs.

Real world? The plane can (and will) take off, because the "perfect" conveyor doesn't exist.

Theoretical world described in the problem as stated? The plane will not move (it's so stated in the problem definition), and therefore won't take off.

 

[RobJ]

I’m no physicist, but I do know the plane can either move, or not move, but it can't do both of them at the same time.

Well crap....I guess I can have paper...or plastic. But I can't have both at the same time!!!

 

[RobJ]

I think someone also needs to count how many different ways "conveyor" was spelled in this thread. Probably count me in for a couple.

 

[RobS]

And that's the problem with everyone's logic - and I mean both sides!

If the conveyor is capable of infinite speed, it can also produce infinite DRAG at the wheels. Since acceleration occurs only if Thrust is greater than Drag, then it follows that the plane will NOT fly IF the conveyor is capable of creating enough drag (by turning the wheels at well-above-takeoff speed - maybe 10X to 20X that speed?). All you pilots, engineers, and mathematicians out there should remember that formula - it's part of basic ground school If Thrust = Drag, acceleration is ZERO.

On the other hand, if the conveyor is NOT able to turn that fast, and cannot change it's speed instantaneously to counteract the thrust provided by the propeller, the plane will eventually fly, becuse thrust will exceed drag for at least brief moments. When Thrust is greater than Drag, acceleration occurs.

Real world? The plane can (and will) take off, because the "perfect" conveyor doesn't exist.

Theoretical world described in the problem as stated? The plane will not move (it's so stated in the problem definition), and therefore won't take off.

Taking the theoretical even further...

The moving conveyor has friction with the air in contact with it. This will cause the air to move (boundary layer theory). As the conveyor speed increases so does the air speed and thickness of this layer of moving air. Eventually, the moving air will be thick (tall) enough to flow over the airplane wings. Even if this does not create flight, it will reduce the normal force on the landing gear which will provide a proportionate reduction in the drag force of the wheels on the conveyor. The reduction in drag will want to make the plane move faster but then there's that pesky infinite speed conveyor. It will move faster yet, creating even more airflow due to the boundary conditions. More airflow equals more lift. Eventually, the airflow will produce enough lift to balance the airplane just above the rapidly moving conveyor.

Thus we have flight at zero ground speed... theoretically.

 

[Farmwithjunk]

I`ll be glad when this plane runs out of fuel.

It ran out of fuel some time ago. If this plane leaves the ground now it's only because of all the HOT AIR.

 

[BillyP]

It ran out of fuel some time ago. If this plane leaves the ground now it's only because of all the HOT AIR.

Thanks for your contribution! Every little bit helps

 

[daTeacha]

The problem doesn't state the plane has wheels. Since everything has gotten theoretical, what if it had very slippery skis, like a bush plane? Then the boundary layer over the conveyor would tend to lift the skis as conveyor speed increased.

 

[shaley]

I'm with RobS. Boundary layer and Reynolds number is your friend. But seriously guys, ain't it time to do something else. Like, couldn't we argue who "sucks more with a box blade" for a while.

 

[RayH]

And that's the problem with everyone's logic - and I mean both sides!

If the conveyor is capable of infinite speed, it can also produce infinite DRAG at the wheels. Since acceleration occurs only if Thrust is greater than Drag, then it follows that the plane will NOT fly IF the conveyor is capable of creating enough drag (by turning the wheels at well-above-takeoff speed - maybe 10X to 20X that speed?). All you pilots, engineers, and mathematicians out there should remember that formula - it's part of basic ground school If Thrust = Drag, acceleration is ZERO.

On the other hand, if the conveyor is NOT able to turn that fast, and cannot change it's speed instantaneously to counteract the thrust provided by the propeller, the plane will eventually fly, becuse thrust will exceed drag for at least brief moments. When Thrust is greater than Drag, acceleration occurs.

Real world? The plane can (and will) take off, because the "perfect" conveyor doesn't exist.

Theoretical world described in the problem as stated? The plane will not move (it's so stated in the problem definition), and therefore won't take off.

Why and how would the conveyor ever need to counteract the thrust of the engine. They are not connected in any way. The conveyor does not need to counteract the thrust from the prop and the prop does not need to overcome the conveyor, thats why there are wheels that spin freely and are designed to offer little resistance. This, I think, is where the whole problem is. Some people believe that the conveyor offers resistance to the plane moving forward when it doesnt, at least not enough to make a difference.
I think everyone agrees that if the plane moves forward, it can fly. Thats pretty basic. I just dont understand what the "NO FLY" people believe is holding the plane back. Someone please tell me what is keeping the plane from moving forward when the engine is run up.

 

[MossRoad]

did i not say this was fun?!?!

Yes. It has been great fun arguing both sides... I had some good laughs and my head hurt for a couple seconds.