hmmm

AndersDK · Post by **AndersDK** » 17 Dec 2006, 13:39

jgra1 wrote:yeah thats what i thought.. but the wheels are free to rotate, the conveyor wants them backwards then thrust wants them forwards..
they cant do both..

Dont focus on the wheels - they dont provide thrust or any other forces - except anti-gravity on ground contact

jgra1 · Post by **jgra1** » 18 Dec 2006, 09:28

but...

ok...

Homer · Post by **Homer** » 18 Dec 2006, 20:01

jgra1 wrote:yeah thats what i thought.. but the wheels are free to rotate, the conveyor wants them backwards then thrust wants them forwards..
they cant do both..

Yes they can, it's how they normally work. You drive along, the bottom of the wheel is stationary (relative to the tarmac), the hub moves forward at the speed of the car, the top moves forward at twice the speed of the car..

If it's a free moving conveyor then the wheels won't rotate the belt will move forwards, in this situation the plane could take off with the brakes on. If the belt is moving backwards the wheels will simply rotate at double speed.

tomsheppard · Post by **tomsheppard** » 18 Dec 2006, 20:40

Having first verified that the angels on the head of the pin are sitting this one out, The wheels start to turn as the thrust builds up and ther reaction to the ground is matched by the conveyor belt sothe aircraft remains still because the thrust is opposed by the rotation of the conveyor. No airspeed is made so the 'plane remains on the ground. Unless it is a Harrier.

Homer · Post by **Homer** » 19 Dec 2006, 00:03

tomsheppard wrote:the thrust is opposed by the rotation of the conveyor.

How?

The wheels all but eliminate any force being transmitted from the conveyor to the aircraft, leaving a net forward thrust from the engines.

added: this should give you all the explanation you need.

FrenchLeave · Post by **FrenchLeave** » 20 Dec 2006, 18:12

But as the thrust makes it try to move forward, the wheels will rotate faster and the conveyer belt will accelerate to the same speed!

AndersDK · Post by **AndersDK** » 20 Dec 2006, 20:01

FrenchLeave wrote:But as the thrust makes it try to move forward, the wheels will rotate faster and the conveyer belt will accelerate to the same speed!

Dont focus on the wheels ...

Its NOT a car - but a plane

G4EIY · Post by **G4EIY** » 22 Dec 2006, 10:02

Hi Folks,

As its getting near to Chrismas, I thought I would have a go on this theoretical question..

Remember, "For every action there is an equal and opposite reaction"..

So, what force projects a plane - the thrust of the engine through the air.

As the air is not connected to the conveyor, you will have forward movement.

The conveyor may move, or it may not move depending on the frictional drag.

Put it another way, if chocks are placed in front of the wheels, when thrust is applied, the plane and conveyor will move together, or if not enough friction between the wheels, chocks and the conveor surface, then these will slide, but the plane will still continue to accelerate and move forward untill the required lift is produced, then the plane will take off.

Extreme care is required if Santa and his sleigh should land on this dam conveyor, as the only way he will get off is side ways !!...

Oh, on second thoughts, if they do manage to land on the conveyor, they won't be able to stop, will have to wait till they get to the end of the conveyor - Bump...

By the way, if any one wishes to track Santa's progress, then this is the link to use:

http://www.noradsanta.org/en/tracking.php

Happy Christmas to you all..

mrbump · Post by **mrbump** » 22 Dec 2006, 22:53

Anyone who has ever done mechanical engineering at higher level will see that when you draw a free body diagram for the WHOLE aeroplane, and resolve the forces at the prop/wings, the sum forward force is influenced by the forces at the wheels only by the drag created by the wheel bearings internal friction and the tyres on the surface. Therefore the wheels will spin at twice the speed as normal for any given ground speed (ground being the ground underneath the conveyor), but the rest of the takeoff will look like normal!!!

uhn113x · Post by **uhn113x** » 27 Dec 2006, 08:46

I would say that the wheels, conveyor, etc are nothing to do with it! How about a seaplane, with no wheels?

The movement is the reaction from the engine thrust against the engine; otherwise rockets would not work in space. The only issue with the wheels is drag; if we slow them down enough, insufficient airspeed will be reached - typically 120-150kts on a typical commercial jet.

Airspeed will increase until the set vR is reached, then there is sufficient lift (due to the aerofoil section) to rotate the aircraft by pulling the stick back. We are airborne.