Will it take off?

[Trash man]

Ok, so this is going around the 'net. HUGE threads of people arguing back and forth...

A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

The question is:

Will the plane take off or not? Will it be able to run up and take off?


The plane WILL take off. The wheels do not affect the thrust of the airplane, they just support it. People cant seem to grasp the concept that they are free rotating wheels and this is not a wind tunnel we are talking about.

[Steel2686]

Very interesting question. I'm going to play devil's advocate, and throw an argument out for the other side just to keep this thing rolling.

I believe the plane will NOT take off as it requires enough wind generated from the plane moving down the runway in order to take-off. The propulsion from the jet engines or propeller are not enough alone to lift the plane off the ground. The plane needs forward momentum.

[TraceZ]

Very interesting question. I'm going to play devil's advocate, and throw an argument out for the other side just to keep this thing rolling.

I believe the plane will NOT take off as it requires enough wind generated from the plane moving down the runway in order to take-off. The propulsion from the jet engines or propeller are not enough alone to lift the plane off the ground. The plane needs forward momentum.

But, the plane will have forward momentum. The plane will still move forward at the same rate as if the runway were not moving, the wheels will just be spinning faster.

The runway will not be able to stop the airplane from moving forward. The thrust from the prop will pull the plane forward regardless of what the computerized runway attempts to do. It could spin the runway up to -500 mph and the airplane would not care. The planes little wheels would just spin that much faster.

They key here is that the airplane does not grip the runway for traction to take off. It grips the air.

It would be slightly harder to take off on the mechanzed moving runway, due to the increased rolling resistance if the wheels, but not significant.

[e40]

If I understand the statement correctly, the conveyor would be counter-productive to getting the plane in the air. There needs to be air flowing over the wing to generate lift, and that's accomplished by thrust from the engines, moving the aircraft forward to the airspeed that's required to climb. So it would be like walking down the up escalator.

Airspeed is not like groundspeed in a car, remember. If you have a 20mph headwind, and your plane can lift off at 80mph, you only need 60mph of groundspeed. The wing doesn't care where it's source of airflow is from.

[Christopherrr]

maybe I'm one that can't grasp the concept...

but doesn't a plane need pressurized air to lift off...we all know how a wing works. But if the plane doesn't move...
here's a quick paint job...this is the image I'm seeing when I read the description of what's happening.

[2Fbodcru]

Well, I hope I don’t get flamed for saying this, because it’s not worth arguing over, but I don’t believe that the plane will take off. The reason being, is that you need wind/air resistance to create the lift under the wings that would allow it to get off of the ground. If the conveyor is keeping the plane in a neutral position, then it won’t have any wind resistance to lift it, unless it is a vertical take off type jet, like the Harrier or some of the other newer jets that they have now that use vertical lift.

Just imagine a submarine in the ocean going along at full throttle, in a straight forward direction, and then suddenly it gets caught in an underwater current that matches the forward thrust of the submarine, but in the opposite direction - it will cease to make forward motion and just sit in one spot.

[zebragirl83]

Well, I hope I don’t get flamed for saying this, because it’s not worth arguing over, but I don’t believe that the plane will take off. The reason being, is that you need wind/air resistance to create the lift under the wings that would allow it to get off of the ground. If the conveyor is keeping the plane in a neutral position, then it won’t have any wind resistance to lift it, unless it is a vertical take off type jet, like the Herrier or some of the other newer jets that they have now that use vertical lift.

I agree.... seems to me this would make the most sense... any pilots in the group? I have an ex that's a pilot... I'll ask him... but he's an idiot... so he will probably give me some B.S. answer to make himself sound smart... [thinks to herself] so maybe I won't ask him...

[Jeff_in_Atl]

A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

The statement is contradicting itself. It first says the plane is "standing" which implies it does not move yet later it says the plane moves in one directions. So there are 2 ways to look at it.

If you believe the plane is standing still then you believe basically just the conveyer is moving so it won't fly.

If you believe the plane "moves", then say for example the plane is moving forward at 100 mph then the conveyer is moving the opposite direction at 100 mph and if you had a speed sensor on the wheels they would show 200 mphs. So yes it would fly.

I know it doesn't say it but if a plane is standing still and say it is tethered with something like 100 feet of line to the nose wheel and it is hit with a 100 mph head wind it will fly like a kite. You can take an RC airplane and fly it into a strong head wind and get it to not move. I watched a guy land a plane without it moving.

[2Fbodcru]

Ok, maybe the submarine analogy wouldn’t be exactly the best one to use, so imagine a boat on top of the water, under the same conditions - a current going in the opposite direction, acting like the conveyor. I’m not an expert, but I believe that the boat would no longer make any forward progress if it were sitting on top of a current that matched the speed of the boat, but going in the opposite direction, because the resistance of the water would be neutralized... in my opinion anyway

[FroSSty]

lol..... no forward air speed no take off! No air/wind over the wing no take off. Its as simple as that. Plus I got another one...

Lets say you have a plane that could go 'exactly' the speed of light. You are standing inside of this plane with a laser. If you point it forward will light come out? You are already going the speed of light so how could the light go any faster? Now if you point it forward and walk backwards will it come out like a string? Seeing how you will be going a little slower than the speed of light? hmmmm... all these questions...

[Jeff_in_Atl]

lol..... no forward air speed no take off! No air/wind over the wing no take off. Its as simple as that. Plus I got another one...

Lets say you have a plane that could go 'exactly' the speed of light. You are standing inside of this plane with a laser. If you point it forward will light come out? You are already going the speed of light so how could the light go any faster? Now if you point it forward and walk backwards will it come out like a string? Seeing how you will be going a little slower than the speed of light? hmmmm... all these questions...

They found that out with high speed jets. The guns muzzle velocity was slower than the plane speed so when you shot the bullet at speed since the gun was moving the bullet came out at the plane speed plus the muzzle velocity but the air resistance was so high the plane would quickly pass the bullet. Air resistance quadruples as speed doubles.

Remember you have to add the plane speed to the speed of the laser light but there isn't enough force to keep the laser light going at 2X the speed of light. Let me know when you prove it.

[fastTa]

If I understand the statement correctly, the conveyor would be counter-productive to getting the plane in the air. There needs to be air flowing over the wing to generate lift, and that's accomplished by thrust from the engines, moving the aircraft forward to the airspeed that's required to climb. So it would be like walking down the up escalator.

Airspeed is not like groundspeed in a car, remember. If you have a 20mph headwind, and your plane can lift off at 80mph, you only need 60mph of groundspeed. The wing doesn't care where it's source of airflow is from.

Very good observation.

Guys, this one is very simple. The airplane will not have the capacity for "lift" off of the runway without sufficient wind velocity over the wings to lift it and to satisfy the balance of wind velocity and air pressure so that the jet engines can continue to provide thrust to further propel the plane once it actually lifts off the ground. The conveyor belt theory WILL be counterproductive just like noted above.

When I was stationed aboard the USS Abraham Lincoln (aircraft carrier), the Air Boss would always turn the ship into the wind when launching and landing aircraft. This reduced the speed neccesary for the aircraft to maintain to land or launch. It's all about the wind velocity and resulting air pressures.

[Steel2686]

Again, I see no way the plane could take off if it is in the same place. Thrust alone is not enough without air movement under and over the wings.

[FroSSty]

They found that out with high speed jets. The guns muzzle velocity was slower than the plane speed so when you shot the bullet at speed since the gun was moving the bullet came out at the plane speed plus the muzzle velocity but the air resistance was so high the plane would quickly pass the bullet. Air resistance quadruples as speed doubles.

Remember you have to add the plane speed to the speed of the laser light but there isn't enough force to keep the laser light going at 2X the speed of light. Let me know when you prove it.

you gotta remember that light is not an object such as a bullet... And the laser cannot go faster than the speed of light.

[Jeff_in_Atl]

you gotta remember that light is not an object such as a bullet... And the laser cannot go faster than the speed of light.

You are standing inside of this plane with a laser. If you point it forward will light come out?

True but inside the plane the air is not moving so the laser light will travel at the speed of light until it tries to come out of the plane.