will it take off?

[RayH]

So, do you think if the conveyor was inclined to 15 deg the plane would fly? This would cause about 25% of the weight of the plane along with the conveyor to try to roll it backwards. I don't see how in one instance it can gain forward motion and then with a slight incline it can't.

If the conveyor were inclined the plane would act just like it would on an inclined runway. The only thing different about taking off from the conveyor verses taking off from a conventional runway is the speed the wheels are turning, Nothing else changes, and if the wheels are freewheeling, they wont effect the movement of the plane at all.

 

[Egon]

Stall speed my friends, stall speed!

 

[MossRoad]

O.K. Last try (of course, I'm lying )....

Read these articles at the straight dope:


The Straight Dope: An airplane taxies in one direction on a moving conveyor belt going the opposite direction. Can the plane take off?
The Straight Dope: "A plane is standing on a runway. . ." No, it's not. Here's why.

In the question originally imposed, it seems like the plane will fly. I thought it would, too. But no one takes into account the force that the conveyor will exert on the plane. Read the first article... it supports the IT WILL FLY train of thought(even mentions roller blades, ropes, etc...). Then read the second article. It shows where most folks forget about the force exerted by the treadmill. If the treadmill was built to continue to accellerate to an infinite speed, the plane stands still.

 

[silverdollar6]

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

 

[RobJ]

Not at all like a wheel driven conveyance. The prop, jet, turbo prop, etc is driving the plane not the wheels. Wheels will spin freely at 2x the speed of the belt as the plane LIFTS OFF!! Go back and look at a few of the links for a better explanation. Conveyor has nothing to do with it other than adding a bit of resistance from the friction inherent in bearings and the tires rolling resistance. Keep thinking about it or look at the posted links, it will come to you. No "Duh" about it, the plane flies. Nothing to do with the belt generating wind either.

I think you are getting what drives the plane and what makes it fly mixed up. The prop, jet is simply moving the plane along the ground, keep it under the stall speed and it just rolls down the road.

What would happen if you used the same senerio on a jet powered car? No wheel power. Would the car move forward if the conveyer was going in the opposite direction? In your case the car would move forward.

To fly a plane needs air moving across the wing, it doesn need a prop or jet. Ever seen a glider?

 

[RobJ]

Please read the problem again. The conveyor is not matching the speed of the wheels. It is matching the speed of the plane.

The plane rolls on the ground before it can gain airspeed and the wing can create lift. So the belt matches the speed before it leaves the ground, no air moving over the wing.

Now a helo would fly!!

 

[rutwad]

The original question says "STANDING" which implies no movement. In that case, no movement = no flight.

But assuming no trickery in the question, can a plane take off from a conveyer belt if the belt matches the planes speed, but in an opposite direction.


ABSOLUTELY!

NO. 1
If a car was on a conveyer belt and was running 100mph according to the car's speedometer and the belt was moving 100 mph in the opposite direction, then the car would not move. It gets in propulsion from the ground, or conveyer belt in this case.

NO 2
Now although it may not be possible, imagine a plane pulling that same car and relative to the ground, they are both now moving 100 mph and the con. belt is still moving 100 mph in the opposite direction.

So why is the car not moving in no. 1, but it is in no. 2? In no. 2, the plane which is pulling the car is using AIR to pull it forward. Yet in no. 1 it is using it's wheels to provide acceleration. Therefore, in no. 1, of course it would not move relative to the ground.

SO FOR THOSE WHO THINK THE PLANE WILL NOT MOVE, DO YOU THINK IT GETS IT FORWARD MOVEMENT FROM IT'S WHEELS. IN THAT CASE, AS SOON AS THE PLANE LEFT THE GROUND, FRICTION WOULD SLOW IT BACK DOWN AND IT WOULD RETURN TO THE GROUND. THAT'S LIKE PUTTING WINGS ON A CAR. WHEN IT GETS UP TO SPEED, IT WILL LEAVE THE GROUND, BUT IMMEDIATELY RETURN BACK TO THE GROUND.


Now back to the original question, the plane gets it's propulsion by pulling itself through the air. Air provides the stationary resistance for the plane to accelerate against, The conveyer belt would have no relevance to the planes acceleration since it uses air.


If you held a radio controlled plane in the air and it was revved to full throttle, would you feel it pull? For those that think the wheels affect it, I guess you think it would not pull against you since it's wheels aren't touching the ground.


Imagine the cub scout wooden rally cars? Strap a large bottle rocket to it and place it on the con. belt. Will it move with propulsion coming from the bottle rocket? YES Now detack the rocket and attach motors from a radio controlled car to the wheels. Accelerate the car with the remote control motors attached to the wheels. Will it move now? NO


If a fish were swimming 3 mph directly against the flow of water which is flowing 3 mph in the opposite direction, you could watch the fish swim "in place". (Kinda like those swim at home pools, where the water is flowed through a short pool and you swim against the water) Now a fisherman catches that fish from an upstream direction. As he reels in at 3 mph, the fish moves closer to him at 3 mph. It moves now because it is getting it's moving force from something other than the flowing water.

So as long as the plane gets it's acceleration from something other than the "flowing water", it is going to accelerate and fly.

 

[daTeacha]

Is the speed of the plane that is supposed to match the conveyor belt its airspeed or its ground speed?

As has been stated, if the airspeed of the plane is high enough, it will fly even though the ground speed may not give that impression.

If the wind blows hard enough, a parked plane will lift off the ground. If tethered, it might "fly" in place. If not, it will likely flip over and break.

If the wind is blowing hard enough and a plane can fly slow enough, it could be seen to move backwards by an observer on the ground -- a 50 mph plane flying directly into a a steady 60 mph wind will have a ground speed of 10 mph backwards.

 

[Egon]

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

Running out of fuel may be difficult as the fueling truck can park right alongside and just keep filling it up.

Now if someone coulkd jimmy up the conveyor belt so it can't move maybe we could get lift off!

 

[turnkey4099]

So, do you think if the conveyor was inclined to 15 deg the plane would fly? This would cause about 25% of the weight of the plane along with the conveyor to try to roll it backwards. I don't see how in one instance it can gain forward motion and then with a slight incline it can't.

If the plane has enough power to take off a normal 15 degree slope, it also would on the coveyor. The airframe doesn't care one wit what speed the coveyor is doing, how fast the wheels are turning, how steep a slope, not even what direction the belt is turning (see my last post). All it cares about is airspeed and that will develop as soon as the engine fires up.

Remember that the plane is not fastened to the belt in any way at all other than whatever bearing friction exists and this being a theoretical thing, they are ideal bearings, i.e., frictionless.

Harry K