Would It Take Off Or Not?

[Gnome]

I wouldn't be comfortable getting on a plane to fly abroad, that's relying on a conveyor belt to take off.

Give me good ol thrust any day! :D

[jaxx]

The engines (unless they are propeller driven (these maybe able to)) will not be able to move the amount of the air needed across the wings surface to create enough lift to get the plane of the ground. You need air resistance across the entire wings surface (both sides) to create the lift needed to get it of the ground.

Harrier jump jets are the exception as they have directional outlets. No other plane has this capability.

correct ;)

but i think your missing the point bud, your right in saying the engines wont create lift, they dont do that anyway, all they do is propel the craft forwards, once they are doing that then the reulting air flow over the wings creates lift....

regardless of what the wheels are doing.... even if being spun backwards on a conveyor below :)

[selfbuild]

If the planes forward speed is matched by the conveyors backward speed, all forward motion would be lost because the plane in essence is still stationary.

[jaxx]

but the wheels dont drive a plane using frictional force, such as a car does

the engines are working against the air....

if the belt was doing 100mph in reverse, but the engines were pushing at 10mph, the plane would move along at 10mph

but the wheels would be spinning in reverse at 110mph

*EDIT*

ok bear that in mind if we lived in a perfect world! yes there will be drag and it wont be that precise, but the concept is there

[Leeky]

I agree, the plane will move forward.

Doesnt matter how fast the conveyor belt is going, the conveyor belt will make the planes wheels spin but the plane doesnt use the wheels for anything other to sit on.

The thrust from the engines will pull the plane forwards regardless of the speed of the wheels and the directions the wheels are spinning.

[PaulT]

According to the problem as described the plane will of course take off anyway.

However, in real life the tyres will not last doing twice the take-off speed, will pop, the wheels will most likely jam and everything will come to a messy halt in short order.

Paul.

[jaxx]

i think we should send off to Mythbusters for the answer

[Fidgits]

According to the problem as described the plane will of course take off anyway.

However, in real life the tyres will not last doing twice the take-off speed, will pop, the wheels will most likely jam and everything will come to a messy halt in short order.

Paul.

ahhh

that would depend on the exact model of aircraft...

you see, take a Cessna 182 for instance - that has a take-off speed of, 70mph.. BUT, it uses the same aircraft tyres as the Beech King Air's - which have a take off speed of over 120mph..

now, aircraft tyres need a lot of headroom, as the forces they experience during landing is significant (basically they go from stationary to xxxmph in a few feet) so they are very over engineered...

You are correct if the plane was a 747 - due to the take off speed being 400mph - as the tyre could not handle double that - but most light and small aircraft on the other hand, probably could

[jaxx]

400mph take off speed !!!

try about 170ish!

cruising speed is around 600mph (or mach 0.86 to be precise)

[selfbuild]

The only thing i'm getting at is, if you take away the planes forward motion by the use of friction (doesn't matter what the surface is or whether there is a conveyor belt involved :) ), how is it going to get the air movement across the wings to be able to take off?

[jaxx]

but the engines would power the aircraft along the belt as if it was still stationairy, as soon as it gets moving the aerodynamic process will still take place

ill put it in different context (quoting a 'perfect world' aswell)

put a skateboard on the belt, the wheels are not powered... start the belt, the skateboard goes backwards and eventually drops off the end, the board theortically is still but being transported by the belt

now fit a rocket onto the skateboard, again the board would be still and fall of the end

then board on belt, start belt, belt transports skateboard, then fire the rocket.

the board would shoot off the belt and to the other end as if it was not moving at all

give it wings and itll take off!

[Fidgits]

400mph take off speed !!!

try about 170ish!

cruising speed is around 600mph (or mach 0.86 to be precise)

oops, i meant 200 take off, 400 as the double

[GIDDLEPIN]

Lift is the force that directly opposes the weight of an airplane and holds the airplane in the air. Lift is generated by every part of the airplane, but most of the lift on a normal airliner is generated by the wings. Lift is a mechanical aerodynamic force produced by the motion of the airplane through the air. Because lift is a force, it is a vector quantity, having both a magnitude and a direction associated with it. Lift acts through the center of pressure of the object and is directed perpendicular to the flow direction. There are several factors which affect the magnitude of lift.

HOW IS LIFT GENERATED?

There are many explanations for the generation of lift found in encyclopedias, in basic physics textbooks, and on Web sites. Unfortunately, many of the explanations are misleading and incorrect. Theories on the generation of lift have become a source of great controversy and a topic for heated arguments. To help you understand lift and its origins, a series of pages will describe the various theories and how some of the popular theories fail.

Lift occurs when a moving flow of gas is turned by a solid object. The flow is turned in one direction, and the lift is generated in the opposite direction, according to Newton's Third Law of action and reaction. Because air is a gas and the molecules are free to move about, any solid surface can deflect a flow. For an aircraft wing, both the upper and lower surfaces contribute to the flow turning. Neglecting the upper surface's part in turning the flow leads to an incorrect theory of lift.

NO FLUID, NO LIFT

Lift is a mechanical force. It is generated by the interaction and contact of a solid body with a fluid (liquid or gas). It is not generated by a force field, in the sense of a gravitational field,or an electromagnetic field, where one object can affect another object without being in physical contact. For lift to be generated, the solid body must be in contact with the fluid: no fluid, no lift. The Space Shuttle does not stay in space because of lift from its wings but because of orbital mechanics related to its speed. Space is nearly a vacuum. Without air, there is no lift generated by the wings.

NO MOTION, NO LIFT

Lift is generated by the difference in velocity between the solid object and the fluid. There must be motion between the object and the fluid: no motion, no lift. It makes no difference whether the object moves through a static fluid, or the fluid moves past a static solid object. Lift acts perpendicular to the motion. Drag acts in the direction opposed to the motion.

[jaxx]

fidget - got ya ;)

another example...

you stood on the trailer of a truck

the truck is travelling at 60mph

you walk backwards at 4mph to the rear of the truck (as if the truck was working against you as the belt works against the plane)

now are you travelling forwards at 4mph? or backwards at 56mph?

its a similar theory to the einstein one of not being able to travel faster than the speed of light

some may argue that if you were stood on a train for example, doing a pricise speed of light

if you walked along the train at 4mph, would you be tarvelling faster than the speed of light?

[GIDDLEPIN]

If you let a bird free inside your car and accelerated hard would it still fly round or splat on the back window?

[jaxx]

If you let a bird free inside your car and accelerated hard would it still fly round or splat on the back window?

it would hit the back window, in the sense that you are pushed into the seat under acceleration or stuff slides off the dash etc...

[Bibbs]

letting go of an inflated balloon .. doesn't need to be on the floor to move along :)

[GIDDLEPIN]

If you let a bird free inside your car and accelerated hard would it still fly round or splat on the back window?

it would hit the back window, in the sense that you are pushed into the seat under acceleration or stuff slides off the dash etc...

Why don't flies do it then? They still fly round my lug hole while I'm driving

[alanbradley]

Who cares?

:P

A

[GIDDLEPIN]

letting go of an inflated balloon .. doesn't need to be on the floor to move along :)

Or---

[jaxx]

well, a chap at work built a jet engine (complete with afterburner!) so all i need is a conveyor and itll put it to the test :P

[Bibbs]

If you let a bird free inside your car and accelerated hard would it still fly round or splat on the back window?

it would hit the back window, in the sense that you are pushed into the seat under acceleration or stuff slides off the dash etc...

Why don't flies do it then? They still fly round my lug hole while I'm driving

it's the differance between having an inflated baloon in the car, and a ball on the dash.

[jaxx]

yeah the air inside the car would be forced forward under acceleration which has enough force to push the balloon aswell

hence why a fly doesnt get thrown around, as its too light... in fact

thats cos youve got the roof down less!

[GIDDLEPIN]

I take it all back, it will fly if the ground is moving and the plane is stationary....

I HAVE THE PROOF HERE

[Bibbs]