Will The Plane Fly? - Page 4

Hightower · 24 November 2007, 01:29

Quote:

Originally Posted by jwalker

A good bevvy tonight was it, Andy?

Yeh, my spelling actually gets better

kitten · 24 November 2007, 11:30

Oh this could run and run,
Wait till we get into boundary layers surface friction inertia and the like.
But personally I stand by the second post on this thread, it's a wheel bearing issue.

shthpnz · 26 November 2007, 21:44

OK OK, I smacked my forehead twice.

Andy Moore · 26 November 2007, 21:51

Quote:

Originally Posted by shthpnz

So now to the situation where a plane wants to encounter enough headwind to get a lift off, but where it stays at the same spot. Either because it is placed on a reverse moving belt or because the rear of the plane is attached to an anchor. No matter how much motorpower you use, the minimum of headwind is not reached as you stay at the same spot. And without a minimum of headwind no lift off.

Motorpower gives no headwind, speed does.

So the anwer is: no.

My €0,01

But in this scenario, the plane will not be stationary. It will be moving forward along the conveyor belt at its normal takeoff velocity.

So it will fly.

shthpnz · 26 November 2007, 22:01

Quote:

Originally Posted by Andy Moore

But in this scenario, the plane will not be stationary. It will be moving forward along the conveyor belt at its normal takeoff velocity.

So it will fly.

Yes so right. I removed my elaborate reasoning why it would not fly after discovering that the topic had already two pages wheron the second one was the clear explanation why the plane would fly. I thought to be smart to quickly delete my own reasoning why the plane would NOT fly , but I was not swift enough I discovered

Andy Moore · 26 November 2007, 22:04

Quote:

Originally Posted by shthpnz

Yes so right. I removed my elaborate reasoning why it would not fly after discovering that the topic had already two pages wheron the second one was the clear explanation why the plane would fly. I thought to be smart to quickly delete my own reasoning why the plane would NOT fly , but I was not swift enough I discovered

It took me a while to understand that it would fly too.

visualpecepts · 27 November 2007, 07:49

The question is impossible to answer correctly because it is impossible to have the conveyor locked to the same speed of the aircraft and not break the rules of the question. If with no conveyor the plane was moving forward at 100mph, you then put a conveyor under it moving backward at 100mph, the plane would come to halt relative to the ground. And if the plane has zero forward speed over the ground, then the question says the conveyor must have the same speed which is also zero. Therefore, for the plane to take off you have to break the rules of the question which means the question is unanswerable. Its a trick question.

kitten · 27 November 2007, 09:34

Quote:

Originally Posted by visualpecepts

the plane would come to halt relative to the ground.

why

visualpecepts · 27 November 2007, 09:42

Oops, I didn't consider the rotational speed of the wheels doubling.

kitten · 27 November 2007, 10:02

Most people are missing the point that almost all aircraft have free spinning wheels. In this case, ground(conveyor ) speed and air speed are not relative

jyasaki · 29 November 2007, 17:05

Quote:

Originally Posted by visualpecepts

If with no conveyor the plane was moving forward at 100mph, you then put a conveyor under it moving backward at 100mph, the plane would come to halt relative to the ground.

Only if the thrust was coming from the plane's wheels. It's not. The thrust is directed into the air, and it's that effect that creates the forward motion. The planes motion is created by the difference between the still air and the jet exhaust. Putting a treadmill at the same 100mph underneath just gets the wheels doing 200mph, with the plane still going forwards. To get the plane sitting still, you have to remove the recipient of thrust, i.e. the air; it has to be moving rearward at the 100 mph to get the plane to stand still. At that point, you've got airflow over the wings, which generates lift, and, well... see ya.

jky

Nos4r2 · 05 February 2008, 02:16

Finally! The definitive answer!

[YOUTUBE]0ul_5DtMLhc[/YOUTUBE]

Told ya so....

Richard Selman · 05 February 2008, 07:01

That proved nothing. The plane was moving relative to the ground all the time. He was overcoming the slight backward motion of the belt by gunning the engine a bit harder to get ground speed = air speed = lift = flight.

It would have been more scientific if they had measured the air speed at takeoff with and without the belt.

One thing that has not been mentioned as far as I can see is the boundary layer effect (all fluids tend to stick to surfaces). The belt would tend to drag air along with it and provide lift to a plane maintaining its velocity over the belt in the opposite direction (whether still relative to the ground or not). The effect would probably be insignificant for the plane in the clip but it might be non-negligible on a small scale. The effect would quickly diminish as the plane lifted away from the belt but it is possible that flight might be maintainable just above it.

Richard

Nos4r2 · 05 February 2008, 09:55

limeydal · 06 February 2008, 00:18

Way over complicated

Pulling that "conveyor belt" leads to all discrepencies in co-efficent of friction between the wheels and the canvas and the ground beneath.
You would need a frictionless system (impossible) and computerised matching of belt and plane belt speed to get true effect.
Boils down to this.

Plane needs increased airflow over wings to provide lift.
So get on your 5 speed on a roller bearing.
Pedal slow and then pedal fast.
Do you feel the wind in your face

Nuff said

Nos4r2 · 06 February 2008, 00:30

Quote:

Originally Posted by limeydal

Way over complicated

Pulling that "conveyor belt" leads to all discrepencies in co-efficent of friction between the wheels and the canvas and the ground beneath.
You would need a frictionless system (impossible) and computerised matching of belt and plane belt speed to get true effect.
Boils down to this.

Plane needs increased airflow over wings to provide lift.
So get on your 5 speed on a roller bearing.
Pedal slow and then pedal fast.
Do you feel the wind in your face

Nuff said

It's NOT THE WHEELS THAT ARE POWERED ON A PLANE AND THATS WHY IT TAKES OFF!!!!!!!!!

DJL · 06 February 2008, 01:38

Quote:

Originally Posted by Nos4r2

It's NOT THE WHEELS THAT ARE POWERED ON A PLANE AND THATS WHY IT TAKES OFF!!!!!!!!!

I don't think your going to convince them.

Nos4r2 · 06 February 2008, 02:08

Quote:

Originally Posted by DJL

I don't think your going to convince them.

I tend to agree. Maybe I'll have more luck at this:-

Although you can see it's green,this grass is actually red.

limeydal · 06 February 2008, 04:33

The propellor provides the "pull" to increase the wings speed relative to the air
around it. No forward movement " relative to the air " ,so no decrease in pressure above the wing ,so no increase in lift on the areofoil , hence no flight.
Think someones pulling our plonkers

codprawn · 06 February 2008, 12:35

I have had RC planes in the past that will takeoff from a complete standing start just using thrust from the prop - will also take off vertically like a helicopter - it's all about power to weight ratio.