will it take off?

[dirt clod]

It would fly. There is air around the plane and the conveyor. It's not the ground speed that is relative it is the air speed. In order for it not to take off there would have to be no air movement. i'm not talking about the prop wash but the simple fact is if you move the plane at say 100mph and the the conveyor moves at 100mph with 0mph wind you have 100mph wind blowing over the wings so you have lift. It is the same with take offs into the wind take off is easier not becouse you have more ground speed but becouse you have more air speed. Wind speeds for the weather is given at what the wind speed is against a none moving object. So regardless of how fast the plane is removing in regards a fixed point on earth if the plane if the plane is moving through the air at lift speed it will lift. It's like flying a kite in the wind if you have enough wind you can stand in one place and the kite will lift up. but if not enough wind running forward might be required again it's not the ground speed but the air speed of the object measured as the force against the object. since the prop screws through the air the plane would have to have a postive air speed to have any movement on the conveyor otherwise it would sit still. Air movement = lift.

 

[Iowachild]

Boy, I'm getting deeper into this than I thought I would. Those who feel the plane would not be moving are still thinking in terms of the wheels driving the plane forward. This is not what happens.
I am a pilot, I know what moves the plane forward!
Let's use the example of the treadmill from Iowachild.

You are standing on one end of a long treadmill. You are holding on a cable coming from a winch at the far end of the treadmill (let's assume the cable has no weight so we don't have to worry about sag and stuff). For now, the treadmill is stationary but the cable is pulling at 3 mph. If you don't want friction burns from being dragged on the stationary belt, you will be walking at 3 mph. The cable keeps pulling you until you get to the other end of the treadmill.
Get on a treadmill, don't move your feet, than start the treadmill. What happened?
OK, reset back to the other end of the treadmill. I flip the lever coupling the motor that drives the winch to also drive the treadmill. Gearing is such that the treadmill runs at exactly the same linear speed as the winch but in the opposite direction. Again, your goal is to not be dragged so you must start walking but this time to keep up with the 3 mph pull of the cable your legs must run at a 6 mph pace to keep perfect balance. You will get to the end of the treadmill in the same time as the previous run but a little more winded.

Now substitute the movable runway for the treadmill, the plane for your body, the propeller for the cable and the wheels for your legs. Why won't the plane move?
Put a toy airplane on the treadmill, start it up. What happens to the toy plane? Now tie a string to the toy plane and just hold it, don't pull it just hold it. Now what happens?
The propeller does not care what is happening between the wheels and the runway. It is pulling against the air (assuming a tractor configuration). Finally, I got tractor into the discussion!!!!

Jeff

 

[spanky8N]

My guess is no flight. As fast as the prop could potentially move the plane the "treadmill"would negate that forward motion exactly. If you were standing next to this I am guessing you would hear a loud plane engine and a fast moving "treadmill" and the plane would have no forward motion. No forward motion means no lift. Thats is my guess.
Dan

I would like to add that I would never attempt this stunt without the ROPS up and ear protection in place!!

 

[HTWT]

The plane will lift off when it has enough air speed.
When the plane is stationary the belt does not move, it only moves when the plain moves forware. It will require the wheels to turn twice as fast but the belt moving in the opposite direction will create air movement that will inhance the lift for the plane. The plane will move forward it only has to overcome the friction in the tires.

 

[755inNY]

Then you should know that using feet against a treadmill is not a good comparison for what moves a plane through the air. I am a pilot too.
I think we gotta find ourselves a moving runway .

Jeff

 

[sparky2terra]

A plane on a conveyor belt - Wikipedia, the free encyclopedia

But, anyone could have written this.

 

[Tom_Veatch]

The airplane will fly.

The scenario is described in such a manner that one is led to intuitively conclude that the aircraft does not move relative to a fixed observer. Thus, no airspeed and no lift. But that is an invalid conclusion. The airframe/engine will move through the air completely independently of the conveyor whether they are separated by one foot or one mile as long as the connection between them can be assumed to be frictionless or nearly so.

To get an understanding to this, perform the following thought experiment. Imagine you have a strut with a wheel on the end of it. Stand on the ground beside the conveyor and, holding the strut, place the wheel in contact with the conveyor. Walk forward allowing the wheel to roll on the conveyor. As you begin to move forward, the conveyor begins to move aft at the same speed you're walking forward. Does your motion stop? No. Conveyor movement has no effect on your movement. The wheel is spinning twice as fast as it would be if the conveyor were stationary, but the wheel rotation doesn't cancel your forward motion.

The situation with the airplane is identical. The aircraft accelerates forward along the conveyor for the same reason you are able to walk forward alongside the conveyor. The force accelerating you (your feet and legs thrusting against the ground) and the force accelerating the airplane at takeoff power (the engine propelling a quantity of air and/or exhaust gasses to the rear) are completely independent of the conveyor. In both cases, you and the airplane move forward without regard to the movement or non-movement of the conveyor. Aircraft do not derive their motion as a consequence of contact of their wheels with the ground. The wheels are purely and simply idlers and transmit little or no horizontal force between the aircraft and the ground. (That is obviously a false statement while the aircraft is braking or steering, but is generally true in a still air takeoff.)

Of course the takeoff distance of the aircraft may be slightly shortened because of a small headwind induced by the conveyor's boundary layer (What do you know, Reynolds Number does have an effect! ). Likewise, it may be slightly lengthened because of increased power loss to rolling resistance of the wheel, bearing friction, tire deformation, etc, due to the higher than normal rotational speed of the tires. But those are higher order effects and can be justifiably neglected in this example.

 

[Iowachild]

Then you should know that using feet against a treadmill is not a good comparison for what moves a plane through the air. I am a pilot too.
I think we gotta find ourselves a moving runway .

Jeff

Of course it is, it's still because of friction. A propellor pulls an airplane through the air the same way threads pull a screw into wood. If this conveyor belt is moving backwards at 60 mph, friction between the belt and the tires of the plane will move the plane backwards at 60 mph. It will take the same thrust to keep the plane from moving backwards as it would take to move the air plane forward at 60 mph on a non-moving runway. To move forward the thrust would have to increase beyond that point. What's your ground speed when your indicated airspeed is 120 mph and you are into a 60 mph headwind. How about your ground speed with the same ISA of 120 mph and a tailwind of 60 mph?
If you find that moving runway, I'm taking all bets and then getting myself that new tactor!

 

[Duke4AZ]

Sorry guys, Jeff and Tom are dead on. The plane will take off based on the assumptions they are describing. That is of course unless someone forgot to mention the tailwind that exactly matches, but in the opposite direction, the speed of the conveyer belt, which matches, but in the opposite direction, the speed of the plane which now negates the airflow over the wings resulting in an airspeed of zero and not only is the airplane not going to take off, I want my money back so I can drive my tractor to NY instead of flying.

Sorry, Jeff, had to throw that in there. Lets see what pain that will inflict on the old cranial mass.

 

[hutch4472]

It doesnt matter if the drive power is going to drive wheels or to create thrust (props or jet). All the drive power is doing is allowing the object (aircraft) to stay in one place instead of moving backwards with the conveyour belt!

When I run on the treadmill (rarely) there is no wind in my face like when I jog along the street (also rarely). If I hold a kite in my hand and jog on the street it will get lift, if I jog on the treadmill with a kite in my hand it hangs limp by my side. NO LIFT. Hutch