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Will this plane fly??

MazDan

MazDan

Bluelight Crew
Joined
Feb 26, 2003
Messages
16,745
Location
Sydney Australia
This is a question that was put at another board I visit and it has resulted in some fairly excellent discussion.

Knowing the quality of minds we have available here at BL, I thought it would be interesting to give you all a chance to consider the possibilities and offer your own answers.

I can assure you there is a definitive answer one way or the other.

So......... Will this plane fly??

Here is the question..............

"On a day with absolutely calm wind, a plane is standing on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. The conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the airplane ever take off?"
 
Airplanes are able to take off because of the shape of the wing - air passing over the upper surface of the wing travels further (because of the curved shaped) and is, therefore at a lower pressure than that traveling under the wing. This creates lift.

In your scenario, as i understand it, the airplane is not moving forward through the air at all therefore there's no air passing over and under the wing. It will never take off.
 
Yes, it will fly. The movement of the conveyor belt is largely irrelevant. The plane doesn't use the wheels to take it off - it uses the air, unlike a car, which is propelled by the wheels and the ground. The conveyor belt has no impact on the air but will just create a bit more friction on the wheels, possibly requiring more power/thrust than normal.

The wheels will just spin faster, probably get munted quite quickly (for instance, the rubber will probably catch fire/explode) - but it is the air that is propelling the plane, not the wheels.
 
^incorrect. calm day (no wind), 0 acceleration...

if it isnt moving on the ground, then the air cant travel around the wings giving the plave lift.
 
^i could find the formula which tells you why it wont take off.

the acceleration being zero is what hampers it, along with the weight of the aircraft.
 
I don't think it will fly either... there is no displacement. It'd be the same thing as running on a treadmill, you don't get an artificial breeze blowing in your face. And on a side note, if it did work, don't you think that the military/private sector would have come up with something similar to that by now?
 
Well, the problem says that the plane is moving under it's own power. The conveyor belt is irrelevant as the engine would still be turning. Despite the conveyor belt the plane would eventually acquire lift and climb into the air.
 
-T{H}R- said:
Yes, it will fly. The movement of the conveyor belt is largely irrelevant.
Click to expand...
The fact that the conveyor belt is moving in the opposite direction to the plane at the same speed the plane is not moving forward means there is no movement of air across the wings.

What force will cause it to rise from the ground?
 
How long is the runway, and is there a latency issue with the conveyor matching the speed of the airplane?

I can give three possibilities for this depending on these variables.

1) If the runway is short enough, and the plane has a stall speed low enough with a somewhat laggy speed matching, it is quite possible for the plane to reach the end of the runway, and leave it behind. Thusly enabling itself to surpass it's stall speed and take off before the end of the tarmac.

2) Now, if the speed of the airplane is sufficiently countered with the conveyer with little to no latency, then the airplane would sit relatively still on the runway.

3) Finally,if the latency is slow enough, and the plane can throttle up quick enough to over come this conveyer fast enough to reach above it's stall speed and gather enough momentum it can possibly take flight right off of the runway.

There's too many variables which can alter the outcome. I mean is this runway surrounded by something? Does it have a curving tarmac that runs the whole length of the runway? etc.....
 
-T{H}R- said:
Yes, it will fly. The movement of the conveyor belt is largely irrelevant. The plane doesn't use the wheels to take it off - it uses the air, unlike a car, which is propelled by the wheels and the ground. The conveyor belt has no impact on the air but will just create a bit more friction on the wheels, possibly requiring more power/thrust than normal.

The wheels will just spin faster, probably get munted quite quickly (for instance, the rubber will probably catch fire/explode) - but it is the air that is propelling the plane, not the wheels.
Click to expand...

hmm... i'm actually starting to agree with you. the wheels do NOTHING on a plane right? they don't have anything to do with its acceleration. So, the faster the plane moves, the wheels will turn.. say, twice as fast. it would be the same thing as wearing rollerblades and that same runway, but using a hand rail to boost yourself forward(the propeller, or the jet), no matter how fast the conveyor belt goes, you can always move forward.
 
^but how far the plane moves in relation to its position do.

acceleration is measured distance over time.

the plane moves a total of 0 meters for an infinite time period.

and acceleration is required for the plane to reach escape velocity.
 
^You have a point, but that's if the plane is light enough, or has enough power to overcome it's weight. Which is what lift is all about, and thusly the stall speed is what has to be overcome. The speed relative to the ground is what matters when there's no wind.

KemicalBurn said:
^where the turbine engines are located on the plane also factor into it.
Click to expand...

I wasn't going to add that into the matter. he never said it was a turbine powered plane. For all we know it could be a VW powered kit plane.
 
^^^^^^^^ not necessarily. (EDIT this was sposed to be pointing at the supposed solution)

I dont disagree that that is a very convincing argument however it still doesnt address the fact that the (admittedly fictional) conveyor is wired to move backwards at the exact same speed as the plane moves forward hence at no time is the plane moving relative to the ground.

This still hasnt been explained.

The plane will not suddenly magically rise above the conveyor belt and hence it becomes redundant.

That magical rising wont happen until the plane is capable of moving through the air and at this stage it is unable to move forward.



I will say however that i remain able to be convinced in either direction.
 
KemicalBurn said:
^but how far the plane moves in relation to its position do.

acceleration is measured distance over time.

the plane moves a total of 0 meters for an infinite time period.

and acceleration is required for the plane to reach escape velocity.
Click to expand...

but see the riddle is misleading... the conveyor belt won't effect acceleration. the plane will still accelerate. A plane doesn't accelerate like a car... push of the wheels against the ground, the propeller or engine pushes it. so the conveyor belt is obselete(assuming the wheels don't blow up). The plane will move forward as normal. good thinking t-h-r... I would never have thought like that to begin with.
 
MazDan said:
^^^^^^^^ not necessarily. (EDIT this was sposed to be pointing at the supposed solution)

I dont disagree that that is a very convincing argument however it still doesnt address the fact that the (admittedly fictional) conveyor is wired to move backwards at the exact same speed as the plane moves forward hence at no time is the plane moving relative to the ground.

This still hasnt been explained.

The plane will not suddenly magically rise above the conveyor belt and hence it becomes redundant.

That magical rising wont happen until the plane is capable of moving through the air and at this stage it is unable to move forward.



I will say however that i remain able to be convinced in either direction.
Click to expand...

think of it this way... say you are on a treadmill with rollerblades. the treadmill is going at 200 mph(really strong rollerblades). you could grab the handrail(the propeller) and still move forward against the treadmill because the wheels serve no purpose in terms of acceleration. the plane will move foward fine.
 
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