Will it take off?

It will. As said before, its the engines that produce the trust which generates lift by sucking air over/under the wing, not the wheels. However as the video below shows, that is not enough by itself. As long as the brakes are off and the wheels are spinning, it will take off.

[YOUTUBE]<object width="640" height="505"><param name="movie" value="http://www.youtube.com/v/AuRVUmyqnjU&hl=en_GB&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/AuRVUmyqnjU&hl=en_GB&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="640" height="505"></embed></object>[/YOUTUBE]

Does that make sense? :shrug: lol

Edit- btw the jet in the video is at takeoff thrust (says so if you watch the rest of that episode of TG).
 
Last edited:
The plane has to move relative to the ground ( actually relative to the airmass around it) for the drag induced lift to happen and for it to lift it off the ground. the drag induced lift is created by the relative velocity of the plane ( the aerodynamic foil) relative to the air, not by sucking air by the jet/turbo or other propulsion mechanisms ( the bernoulli's principle)

Assuming that there is (somehow ) a converyor belt which is travelling at the equal and opposite relative linear speed to the linear wheel speed; and there is no slip, no other factors coming into play; and the plane is not moving relative to a fixed point on the ground (and therefore the airmass around it) then the plane will not take off. It has nothing to do with the propulsion mechanism of the airplane. Of course finding such a conveyor belt in real life is a problem.

Conversely, if a plane without any propulsion was piggy riding on another airborne plane ( i.e the velocity relative to the airmass sourrounding it was enough to create a drag induced lift) and it got detached from the plane with propulsion, it will remain airbourne ( but lose heoght slowly) since its velocity relative to the airmass will ensure the lift. thats how the gliders work
 
Last edited:
david1701 said:
there will be a frictive force proportional to the radial velocity of the wheels, which will be going twice as fast ;)
Click to expand...

Not if the conveyor is moving at exactly the same speed as the wheels ;)
 
ujjwaldey8165 said:
Assuming that there is (somehow ) a converyor belt which is travelling at the equal and opposite relative linear speed to the linear wheel speed; and therefore there is no slip, no other factors coming into play; and the plane is not moving relative to a fixed point on the ground (and therefore the airmass around it, then the plane will not take off. It has nothing to do with the propulsion mechanism of the airplane. Of course finding such a conveyor belt in real life is a problem.
Click to expand...

But why would the plane not move relative to a fixed point on the ground :thinking: The wheel speed and the conveyor belt are actually totally irrelavent :) Sorry, but the propulsion mechanism has everything to do with it ... i.e. the plane is being pushed or pulled through the air ... not being driven along the conveyor :cool:
 
Splog said:
But why would the plane not move relative to a fixed point on the ground :thinking: The wheel speed and the conveyor belt are actually totally irrelavent :) Sorry, but the propulsion mechanism has everything to do with it ... i.e. the plane is being pushed or pulled through the air ... not being driven along the conveyor :cool:
Click to expand...

Ah, sure, i see the point. The drive is not on the wheels....
 
Last edited:
ujjwaldey8165 said:
Becuase as long as the plane is in contact with the ground the forward propulsion of the plane mass is via the wheels. If the conveyor belt is moving the opposite direction, then the wheels will stay in exactly the same spot relative to the ground
Click to expand...

But why is it via the wheels ? Aircraft use jets or props ... i.e pull or push through the air! surely the ground or conveyor is irrelevant :)

Edit: ...Oops posted between replies
 
Last edited:
Splog said:
It's not VTOL!

Why won't the plane move? The plane will move and it will take off :)
Click to expand...

Why will the plane move? It won't and it won't take off:)

From my understanding the conveyor belt will counter any forward wheel motion caused by the thrust of the plane's engines (see my previous analogy to runner on treadmill) ie the plane will remain stationary in space. Ergo no relative airflow, no lift vector, no take off-simples;)

Even better analogy - imagine a car on a rolling road. If you then strap a pair of aerofoil sections onto the car, will it fly? No!!:nono:
 
Last edited:
davek said:
Why will the plane move? It won't and it won't take off:)

From my understanding the conveyor belt will counter any forward wheel motion caused by the thrust of the plane's engines (see my previous analogy to runner on treadmill) ie the plane will remain stationary in space. Ergo no relative airflow, no lift vector, no take off-simples;)
Click to expand...

this is why I said it should be a fun discussion :D
 
davek said:
Why will the plane move? It won't and it won't take off:)

From my understanding the conveyor belt will counter any forward wheel motion caused by the thrust of the plane's engines (see my previous analogy to runner on treadmill) ie the plane will remain stationary in space. Ergo no relative airflow, no lift vector, no take off-simples;)

Even better analogy - imagine a car on a rolling road. If you then strap a pair of aerofoil sections onto the car, will it fly? No!!:nono:
Click to expand...

Davek , the wheels have no drive. The conveyor moving in the opposite direction will simply make the wheels spins at twice as fast. The plane will continue to move forward, because the drive is through the jet propulsion through the air.

I made the same mistake..:lol:
 
Last edited:
ujjwaldey8165 said:
Davek , the wheels have no drive. The conveyor moving in the opposite direction will simply make the wheels spins at twice as fast. The plane will continue to move forward, because the drive is through the jet propulsion through the air.

I made the same mistake..:lol:
Click to expand...

If I taxy my plane along the runway using engine thrust (causing the wheels to turn and propel me forward) and then (imagine) the runway starts to roll towards me (like a conveyor belt) then the result will be me sitting in my aircraft stationary relative to space, no airflow, no lift. My wheels will turn and I will remain taxying along the moving runway but I will never take-off. If you think otherwise I need a clearer explanation:) Thrust and lift are two different things.

PS I certainly don't understand the wheels going twice as fast stuff!
 
davek said:
If I taxy my plane along the runway using engine thrust (causing the wheels to turn and propel me forward) and then (imagine) the runway starts to roll towards me (like a conveyor belt) then the result will be me sitting in my aircraft stationary relative to space, no airflow, no lift. My wheels will turn and I will remain taxying along the moving runway but I will never take-off. If you think otherwise I need a clearer explanation:) Thrust and lift are two different things.

PS I certainly don't understand the wheels going twice as fast stuff!
Click to expand...
no the wheels will just turn faster as they are not connected to the drive. in theory they will turn twice as fast and make no difference to the aircrafts airspeed, but in reality as there is friction in the wheels the aircrafts airspeed will slow down but it will still take off providing in normal operating contitions it doesnt need full thrust to take off
 
waspjunior said:
The plane will take off as normal so long as the wheels can withstand travelling at twice the rpm as usual during the takeoff run. Nothing else changes.
Click to expand...

This.

Wheel bearings will be fine i'm sure...
 
davek said:
PS I certainly don't understand the wheels going twice as fast stuff!
Click to expand...

Neither do I! The speed of the belt is exactly the same as the wheels.
 
Splog said:
The speed of the belt is exactly the same as the wheels.
Click to expand...

If the speed of the belt and speed of the wheels are the same then the plane does not move, no matter if it is wheel driven or not. This is why I said the wheel bearings would melt. Given the co-efficient of friction in wheel bearings the conveyor and wheels must move at an extremely high speed for the energy from a jet engine to be dissipated through friction.

For the plane to move relative to a fixed point the belt and wheels must travel at different speeds unless one slips relative to the other.
 
onomatopoeia said:
For the plane to move relative to a fixed point the belt and wheels must travel at different speeds unless one slips relative to the other.
Click to expand...

That's what I was thinking. If the plane has forward thrust from its engines, it is physically impossible for the conveyor belt to move at the same speed as the wheels. The wheels will move faster, and there's no two ways about it.

And then, yes, the plane will take off.
 
onomatopoeia said:
If the speed of the belt and speed of the wheels are the same then the plane does not move, no matter if it is wheel driven or not. This is why I said the wheel bearings would melt. Given the co-efficient of friction in wheel bearings the conveyor and wheels must move at an extremely high speed for the energy from a jet engine to be dissipated through friction.

For the plane to move relative to a fixed point the belt and wheels must travel at different speeds unless one slips relative to the other.
Click to expand...

But if the plane doesn't move then the belt doesn't move :)
The speed of the wheels is irrelavent, other than to govern the speed of the belt! The speed of the wheels are exactly the same.

For the sake of discussion assume the wheel bearings are not knackered!
 
GrittyShaker said:
That's what I was thinking. If the plane has forward thrust from its engines, it is physically impossible for the conveyor belt to move at the same speed as the wheels. The wheels will move faster, and there's no two ways about it.

And then, yes, the plane will take off.
Click to expand...

Why can't the belt travel at the same speed as the wheels? :thinking:
 
Splog said:
Why can't the belt travel at the same speed as the wheels? :thinking:
Click to expand...

It can if the plane isn't moving, but as soon as there is forward thrust from the engines the plane will move forwards (irrespective of the speed of the belt) and the wheels will then be spinning faster than the belt is moving.

If you imagine a person walking on a moving escalator, in the opposite direction. In order to stay in one spot they have to walk at the same speed as the escalator. If the person wants to move forwards, they need to walk faster, but you can counteract that by moving the escalator faster, because the person is driven by their legs, which are in contact with the escalator.

The same thing can't be said about the plane. It's not driven by anything that's in contact with the belt, so if the plane has forward thrust it will move forwards no matter what the belt is doing. But its wheels will be spinning faster than the belt. Physics dictate that.

So there. :p :D
 
because the thrust from the plane would always try and push the plane forwards, so the wheels will always move faster than the belt, which will then speed up but then thrust will push the plane and make the wheels turn faster. do you see where this is going? the wheels and belt would up at impossible speeds if this could happen
 
:lol: read arguements about this so many times but yes it would take off as proven by mythbusters :lol:

reasons are because no power goes to the wheels so the fact they are spinning backwards in essence makes no differences to the thrust produced by the engine so it will take of with no problems, would just mean that the wheels are travelling twice as fast as normal at take off.
 
GrittyShaker said:
It can if the plane isn't moving, but as soon as there is forward thrust from the engines the plane will move forwards (irrespective of the speed of the belt) and the wheels will then be spinning faster than the belt is moving.
Click to expand...

So if the plane accelerates from 0 to 10mph and the belt does the same, why would the wheels be going faster than 10 mph :D
 
GrittyShaker said:
The same thing can't be said about the plane. It's not driven by anything that's in contact with the belt, so if the plane has forward thrust it will move forwards no matter what the belt is doing. But its wheels will be spinning faster than the belt. Physics dictate that.

So there. :p :D
Click to expand...

Sorry, but Physics dictate that the wheels will be exactly the same speed as the belt
 
Splog said:
So if the plane accelerates from 0 to 10mph and the belt does the same, why would the wheels be going faster than 10 mph :D
Click to expand...
Because if the wheels (assuming the wheels are driven, in this instance) accelerated to 10mph, then the plane would stay stationary. In order for the plane itself to accelerate to 10mph, the wheels have to be spinning faster than that. :D
 
alastairb said:
because the thrust from the plane would always try and push the plane forwards, so the wheels will always move faster than the belt, which will then speed up but then thrust will push the plane and make the wheels turn faster. do you see where this is going? the wheels and belt would up at impossible speeds if this could happen
Click to expand...

Why impossible speeds? a light aircraft can take off easily at 60 - 70 mph :)

Matt L said:
:lol: read arguements about this so many times but yes it would take off as proven by mythbusters :lol:

reasons are because no power goes to the wheels so the fact they are spinning backwards in essence makes no differences to the thrust produced by the engine so it will take of with no problems, would just mean that the wheels are travelling twice as fast as normal at take off.
Click to expand...

But if you are freewheeling downhill on a bike the wheels don't spin backwards and they don't spin twice as fast :D
 
Matt L said:
Surely thats not right unless the belt sped up with the plane, if the belt is set to say 50mph then the plane is moving forward at 50mph surely the wheels are doing 100 :thinking:
Click to expand...

But the point is that the belt always matches the speed of the wheels
 
Splog said:
But if the plane doesn't move then the belt doesn't move :)
Click to expand...

If the plane does move, the wheels are moving at a different speed from the belt. You explicitly stated that this was not the case. Are you redefining the experiment?

edited (twice) for spelling
 
kk back to the brief which way is the belt turning, does it pull the plane backwards (-ve v) or push it forwards (+ve v).

The speed of the wheels rel to the belt is (radVwheel*rad)-(Vbelt)
Vbelt=(radVwheel*rad) if going in same direction (pushing plane along) OR
Vbelt=-(radVwheel*rad) if going in opposite direction

1--1=2 ;)
 
alastairb said:
but that is physically impossible
Click to expand...

GrittyShaker said:
The only thing that dictates that the wheels will be the same speed as the belt is your original brief. :D

We can argue with your brief, but we can't argue with physics. :p
Click to expand...

I said the belt is exactly the same speed as the wheels i.e. the wheels dictate the speed of the belt :) and what part of physics do you refer to? :thinking:
 
david1701 said:
kk back to the brief which way is the belt turning, does it pull the plane backwards (-ve v) or push it forwards (+ve v).

The speed of the wheels rel to the belt is (radVwheel*rad)-(Vbelt)
Vbelt=(radVwheel*rad) if going in same direction (pushing plane along) OR
Vbelt=-(radVwheel*rad) if going in opposite direction

1--1=2 ;)
Click to expand...

The belt doesn't do anything to the plane! The belt will only move if the planes wheels turn.

The plane will take off and the speed of its wheels or the belt are totally irrelevant :D
 
GrittyShaker said:
Because if the wheels (assuming the wheels are driven, in this instance) accelerated to 10mph, then the plane would stay stationary. In order for the plane itself to accelerate to 10mph, the wheels have to be spinning faster than that. :D
Click to expand...

GrittyShaker said:
I already have! Twice! :D
Click to expand...

Do you mean the above statement? If so, care to suggest what aircraft uses 'driven' wheels for take off :thinking:

The speed of the wheels and belt are exactly the same. To clarify The tread of the wheels will travel exactly 10 miles in one hour if the planes speed was 10mph. :D
 
You must log in or register to reply here.
Back
Top