[Science Question] Will a plane take off?

Mr.B.ThatsMe · Nov 29, 2005

Originally posted by Joe
Thats childs play

a real quote:

"Rolls Royce RB.211 engine produces 140-270 kilonewtons of thrust.

900,000 pound aircraft = about 4000 kN.

For the wheels of the aircraft, let's assume teflon on steel (which would be a higher coefficient of friction then something that's lubricated properly, or that uses ball-bearings)

4000 kN x 0.04 = 160 kN friction.

Which means there is at least 400 kN left over to propel an airplane. (A 747 has four of these engines) 400,000N / 400,000kg = 1 m/s^2 Not much, but it's a start. And that's all it needs.

We're all familiar with acceleration, but how many of us have heard of "Jerk". Just like acceleration is a change of speed, Jerk is a change of acceration. most moving object usually experience negative jerk because of the increase of air friction at higher speeds, and this might suggest that the airplane might not be able to take off because it will reach a terminal velocity. A 747 with 1 MN can travel at about 950 km/h. So let's say the drag is 1MN @ 950 km/h. Usually if we cut the speed in half, then the drag would be divided by four. But for the sake of over-exaggerating the number to try and stop this plane from flying, i'll cut the numbers proportionally. so 1MN = 950km/h then 400 kN = 380 km/h

A MiG has an unusually fast take-off speed of 340 km/h. Still below this artificially low terminal velocity.

But,
As soon as the airplane starts moving in generates lift. This lift reduces the Normal force acting on the plane, and thus reduces the force of friction acting on the plane, which increase acceleration. Therefore increasing lift, reducing friction, increasing velocity, increasing lift, reducing friction etc."

The plane flew.
Click to expand...

Thanks joe, you just confirmed everything i was thinking.

Micky-Owens · Nov 29, 2005

Re: Re: [Science Question] Will a plane take off?

Originally posted by andy_rocks

I don't understand how there was an arguemnt
Click to expand...

we he must of thought there was a big fan infront of the plane as well ??

*edit as i never relised this one was 7 pages long
*

Phil Mitchell · Nov 29, 2005

Was it a harrier jump jet?

andy_rocks · Nov 29, 2005

Re: Re: Re: [Science Question] Will a plane take off?

Originally posted by Micky-Owens

we he must of thought there was a big fan infront of the plane as well ??

*edit as i never relised this one was 7 pages long
*
Click to expand...

I'll accept I was wrong insofar as there was an argument

But there is still no way the plane can take off, if the conveyor belt is moving at the same speed as its wheels! If you switch the engines on though, then the wheels move at a different speed and you do get relative velocity between air and plane and take-off ensues

Rob · Nov 29, 2005

Originally posted by sj_js
Was it a harrier jump jet?
Click to expand...

Lee · Nov 29, 2005

Re: Re: Re: Re: [Science Question] Will a plane take off?

Originally posted by andy_rocks
I'll accept I was wrong insofar as there was an argument

But there is still no way the plane can take off, if the conveyor belt is moving at the same speed as its wheels! If you switch the engines on though, then the wheels move at a different speed and you do get relative velocity between air and plane and take-off ensues
Click to expand...

obviously the engines were on, because if they werent on and the plane was on a runway it wouldnt take off anyway.

SeniorChem Si · Nov 29, 2005

Originally posted by Lee
im im walking at 5mph on a treadmill then the mill itself is going round at 5mph and im not going forwards or backwards im staying in the middle. same with the plane
Click to expand...

nah you've got it wrong, the treadmill thing is right as far as it goes, but try this....

If it was a car with wings that could fly (stay with me) it would stand still and never take off cos it's air speed it still 0 whatever it's wheel speed is, but this only applies because it's drive comes from it's wheels, or in your case your feet on a treadmill.

The plane gets its speed from it's jets which are gonna accelerate the plane even if the conveyor is going at 1000mph

I'm right and evryone who doesn't think so is wrong

SeniorChem Si · Nov 29, 2005

Originally posted by Joe
If our jet is moving at 40mph in one direction and the conveyor is moving 40mph in the other, then our jet will still go forwards at 40mph, but the wheels will rotate at 80mph.

If this were a car then it would be different as the car would be pushing on the conveyor belt, however this isn't a car - its a plane and its pushing against the air.
Click to expand...

didn't see this, but you've figured it the same as me, so that definitely seals it

Mr.B.ThatsMe · Nov 30, 2005

Another bit of confusion has kicked off.

Is it even possible to match the speed of the wheels and the conveyor at ALL times? Acceleration requires that either the wheel or the conveyor moves first, no?

So at the end of all of this could the answer be that the plane does not move, does not take off and the wheels/conveyor stay at 0mph?

I'd have left this topic for the rest of time if I hadn't just spent over 2 hours discussing it with someone on msn who obviously didn't have the pleasure of going through it since this morning

I suppose this technicality groups together with all the other factors such as friction though so maybe it's best that nobody answers this.

Log in or Sign up

[Science Question] Will a plane take off?

Users Viewing Thread (Users: 0, Guests: 0)

Mr.B.ThatsMe 'yi raji puff

Micky-Owens Registered User

Phil Mitchell check me a dollar brer?

andy_rocks Registered User

Rob Registered User

Lee original gowans artwork

SeniorChem Si Registered User

SeniorChem Si Registered User

Mr.B.ThatsMe 'yi raji puff

Share This Page

Log in or Sign up

[Science Question] Will a plane take off?

Users Viewing Thread (Users: 0, Guests: 0)

Mr.B.ThatsMe 'yi raji puff

Micky-Owens Registered User

Phil Mitchell check me a dollar brer?

andy_rocks Registered User

Rob Registered User

Lee original gowans artwork

SeniorChem Si Registered User

SeniorChem Si Registered User

Mr.B.ThatsMe 'yi raji puff

Share This Page

Useful Searches