can a plane takeoff on a conveyor belt? (mythbusters)

RBBailey

Well-known member
Jul 26, 2004
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Oregon
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Uh... as a pilot... never mind...

The answer is, yes, as long as the wheel bearings don't give out at the super speed at which they will be turning when the aircraft gets enough airspeed to start flying -- and if you had a long enough conveyor belt. Your take off distance would, after all, be the same as if you were not on the belt. The belt would only serve to keep you from accelerating to take off speed sooner.

Take off distance would not change.
Take off air speed would not change.
Take off time would change.
 
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kennith

Well-known member
Apr 22, 2004
10,891
172
North Carolina
Of course it will take off. The plane, unlike an automobile, gains forward motion by moving AIR, not the wheels. The wheels may spin freely all they want in the opposite direction, and so long as the bearings are designed to withstand twice the liftoff speed, there is no reason why the plane should not be right fine.

The question is silly. Sometimes that show really indulges people.

Cheers,

Kennith
 

kennith

Well-known member
Apr 22, 2004
10,891
172
North Carolina
RBBailey said:
Uh... as a pilot... never mind...

The answer is, yes, as long as the wheel bearings don't give out at the super speed at which they will be turning when the aircraft gets enough airspeed to start flying -- and if you had a long enough conveyor belt. Your take off distance would, after all, be the same as if you were not on the belt. The belt would only serve to keep you from accelerating to take off speed sooner.

Take off distance would not change.
Take off air speed would not change.
Take off time would change.

Beat me to it, dogonit.

Cheers,

Kennith
 

Rover Puppy

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Jun 10, 2004
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Tallahassee, Florida
My "guess" is no... but, I don't know much about airplanes.

I only know how lift is produced on helicopters.


I don't know if this will help... but, maybe you can figure it out by applying this to an airplane taking off??


A helicopter in flight is acted upon by 4 basic forces:

lift, gravity, thrust, and drag


Lift is the upward acting force. Gravity (or weight) is the downward acting force. Thrust is used the control direction of movement. Drag is the retarding force produced by air resistance.

Lift apposes weight and thrust opposes drag.

When a helicopter is in straight and level flight or a stabilized hover, the opposing forces balance each other.

Lift = Weight

Thrust = Drag.

Any inequality between thrust and drag while maintaing flight will result in acceleration or deceleration until the 2 forces are balanced again.

Lift comes from Bernaouli's Principle. This is relationship between pressure, fluid flow velocity and the potential energy of fluids (liquid and gases). As the velocity of the fluid increases, the pressure in the fluid decreases. As the velocity of the fluid decreases, the pressure in the fluid increases.

An example of Bernoulli's Principle is the venturi tube. It is a tube that is narrower in the middle than at the ends. As air passed through the tube, it speeds up as it reaches the narrow portion and slows down again as it passes through the narrow part.

Berrnoulli's Principle led to the creation of an airfoil.

Helicopter blades with an airfoil shape are used to create a pressure differential in the air.


An airfoil is any shape which is designed to produce lift. An airfoil has a leading edge, trailing edge, chord, and camber.

LEADING EDGE

The leading edge is the part of the airfoil that first meets the oncoming air.

TRAILING EDGE

The trailing edge is the aft end of the blade where the airflow over the upper surface joins the airflow over the lower surface.

CHORD LINE

The cord line is an imaginary straight line drawn from the leading edge to the trailing edge. The line has significance only in determing the rotor blade angle of attack.

CAMBER

The camber of an airfoil is the curvature of its upper (upper camber) and lower (lower camber) surfaces.

So, according to Bernouli's principle...

As there is an acceleration or increase in the velocity of the air as it flows around an airfoil shape, there is an acceleration of the relative wind as it flows above and below the surface of the rotor blade.

As air flows over the upper surface of the rotor blade, the curvature of the airfoil causes the speed of the airflow to increase. This increase in speed over the rotor blade causes a decrease in the presure over the airfoil.

At the same time, the relative wind hits the lower surface of the rotor blade which increase pressure.

As a result of the decreased pressure above the rotor blade and increased pressure below the blade, the upward force of lift is produced. Lift is generated across the entire rotor disc as it rotates.

(I wish I had a chalkboard so that I could draw you pictures while explaining this. It is hard to understand in just words.)

The question is... how does this apply to airplanes????
 
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Axel

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Staff member
Apr 1, 2004
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Quebec, Canada
www.discoweb.org
The problem is not clearly defined. The plane is travelling at takeoff speed relative to what? The conveyor belt or the ground? If takeoff speed is 150 kts, the conveyor belt moves at 150 knots in the reverse direction of the plane and the plane is moving at 150 kts relative to the conveyor belt, it would be stationary relative to the ground and surrounding air, and not take off. If the plane is moving at 150 kts relative to the ground and surrounding air, it would take off, but it would be moving at 300kts relative to the conveyor belt. Which is it? If the plane was a small model plane trying to take off inside a sealed train car, the speed of of the train would be close to irrelevant, but that's another matter.
 

Rover Puppy

Well-known member
Jun 10, 2004
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0
Tallahassee, Florida
Bear with me as I try to draw a few pictures in paint (this is my first try drawing in paint). If I can do it, it will give you an easy "visual".

I think that once I draw pictures and post them, I *think* you will see what is "missing" when the plane is on the conveyor belt.

This is the venturi tube. The directional arrows show the air moving throught the tube.

The red arrow indicates where there is:

Inceased Velocity and Decreased Pressure.
 

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p m

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Staff member
Apr 19, 2004
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Axel, you're overcomplicating things. The problem is as dumb as it gets. No, the plane will not take off the conveyor belt as the setup is described.

Disco fever said:
the plane's engines are pushing the air for thrust, if the wheels drove the plane it would be a different story.
Whatever drove the plane - engines (propellers) or the wheels - the story would have been the same. If the AIRspeed of the plane exceeds its stall speed, it will begin to lift off.
 

Rover Puppy

Well-known member
Jun 10, 2004
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0
Tallahassee, Florida
I still have my commercial license. However, I let my CFI (Certified Flight Instructor) license lapse.

You'll be happy to know that my flying skills are much better than my art skills! :rofl:

Jeepers, making pictures with "Paint" is like using an Etch-O-Sketch...

although, I'm not sure they are around anymore????

Since you too are an "older" baby boomer, you will probably remember Etch-O-Sketch!! :) :)
 

kennith

Well-known member
Apr 22, 2004
10,891
172
North Carolina
I really don't see why it's neccessary to have a show about it. That's like having a show to test whether or not golf balls are round. Of course they are round.

Like I said, the Mythbusters do indulge people quite a bit. I love the show, but sometimes I wonder just why they test certain things.

Cheers,

Kennith
 

MUSKYMAN

Well-known member
Apr 19, 2004
8,277
0
OverBarrington IL
kennith said:
I really don't see why it's neccessary to have a show about it. That's like having a show to test whether or not golf balls are round. Of course they are round.

Like I said, the Mythbusters do indulge people quite a bit. I love the show, but sometimes I wonder just why they test certain things.

Cheers,

Kennith

golf balls are not round...thats why they work:D

see now they have material for another show:banghead: