Liftoff?

Hunter · 12-20-2007, 06:36 PM

I'm late to the party, but here's my two cents. I just finished driving all the way from NH, and for some reason I just read through this whole thing. I blame all of you... fuck you guys.

HAULN-SS Wrote:If The plane needs 88mph to take off, and the treadmill is rolling in reverse at 4mph, then all the plane has to do is give it the same power as if were going to go 92mph, then it takes off.

Here is your problem derek. If the treadmill was going in reverse at 4mph and the plane needed to be 88mph in order to take off, it would not require the extra thrust to get to 92 mph.

In a frictionless world: The engines would still only have to provide enough thrust to get to 88mph because the wind speed is the same.

In the real world: In order to get to the takeoff speed of 88 mph the engines would have to provide the same amount of thrust that would normally get the plane to about 88.1 mph, with that extra 0.1 mph (thats being generous) coming from overcoming the force of friction between the tire/ground and the wheel/bearing.

What you said kinda holds true if you're talking about wind speed. If a 4 mph wind is at the back of the plane, it has to move at 92 mph relative to the ground in order to take off.

The key point: (estimating here) 99% of the friction a plane sees is due to wind resistance while only 1% is due to the friction of the ground.

If a full size plane is sitting on a giant treadmill and you turn it on to 20 mph, the plane will still basically sit still. If you leave it there for ever, eventually the force of friction will make the plane move faster and faster until it's even with the treadmill.

Same physical problem with a different viewpoint: A plane lands at 20 mph, if you apply no brakes or reverse thrust, the plane will keep rolling for a very long time. Actually that example would have wind resistance working against it to slow it down.

Evan · 12-20-2007, 06:58 PM

Evan Wrote:
HAULN-SS Wrote:
asteele2 Wrote:Don't you get it!? The treadmill is irrelevant!

Lol, I really dont think you know how airplanes work. If an airplane has no forward motion, it will not take off. Period. Airplanes don't fly in any other direction than forward. as in the nose always, always, always comes before the tail.
how does an airplane generate forward motion Derek?

1 baby-step at a time...

answer the question Derek

Maengelito · 12-20-2007, 07:53 PM

Hunter Wrote:I'm late to the party, but here's my two cents. I just finished driving all the way from NH, and for some reason I just read through this whole thing. I blame all of you... fuck you guys.

HAULN-SS Wrote:If The plane needs 88mph to take off, and the treadmill is rolling in reverse at 4mph, then all the plane has to do is give it the same power as if were going to go 92mph, then it takes off.

Here is your problem derek. If the treadmill was going in reverse at 4mph and the plane needed to be 88mph in order to take off, it would not require the extra thrust to get to 92 mph.

In a frictionless world: The engines would still only have to provide enough thrust to get to 88mph because the wind speed is the same.

In the real world: In order to get to the takeoff speed of 88 mph the engines would have to provide the same amount of thrust that would normally get the plane to about 88.1 mph, with that extra 0.1 mph (thats being generous) coming from overcoming the force of friction between the tire/ground and the wheel/bearing.

What you said kinda holds true if you're talking about wind speed. If a 4 mph wind is at the back of the plane, it has to move at 92 mph relative to the ground in order to take off.

The key point: (estimating here) 99% of the friction a plane sees is due to wind resistance while only 1% is due to the friction of the ground.

If a full size plane is sitting on a giant treadmill and you turn it on to 20 mph, the plane will still basically sit still. if you leave it there for ever, eventually the force of friction will make the plane more faster and faster until it's even with the treadmill.

Same physical problem with a different viewpoint: A plane lands at 20 mph, if you apply no brakes or reverse thrust, the plane will keep rolling for a very long time. Actually that example would have wind resistance working against it to slow it down.

go back to grad school, hippie!

ScottyB · 12-20-2007, 08:04 PM

i can't believe this has generated 6 pages of debate. this was 2 pages, at best.

.RJ · 12-20-2007, 08:06 PM

10 pages by tomorrow. I'm surprised its not off topic yet!

WRXtranceformed · 12-20-2007, 08:13 PM

Would it take off faster if it had GTR badging on it and was it was being tested by Japanese drift artists on the Nurburgring?

Apoc · 12-20-2007, 09:38 PM

30% are wrong... yay!

I'm glad I modified my answer before voting.

HAULN-SS · 12-20-2007, 11:59 PM

lol, I have a life faggots, I don't have time to post on here 10 seconds after your posts. Anyway, I conceed. I was thinking of this the wrong way, and yes, the wheels for all intents and purposes can spin infinite mph. However, some of the side points that were learned here I don't conceed on, just the main one.

I had something else to write, but I just forgot it.

Evan · 12-21-2007, 12:26 AM

HAULN-SS Wrote:Anyway, I conceed.

Sijray21 · 12-21-2007, 09:51 AM

my god, i feel stupid/confused for just reading all those posts. :-P

the plane will fly due to forward thrust from the jet engines b/c the wheels are free moving. the wheels don't drive the plane, the engines do... friction from the wheel bearings is insignificant. on the other end of the spectrum, picture the treadmill running at 500mph in the 'backwards' direction. the plane will still land, and be able to stop because of the reverse thruster feature of the engine. (assumption: sufficient length of the runway)

completely agree with Hunter

Kaan · 12-21-2007, 10:01 AM

well i'd just like to say that i think friction from the wheel bearings and the mechanical grip of the tires... though in the problem are said to be zero... the 747 weights 91k pounds ... thats got to count for something out side of this theoretical question.

but yes, i'm probably wrong.

Ginger · 12-21-2007, 10:15 AM

Something very, very insignificant compared to the power that the thrusters produce. It can overcome the same force to move along the ground, it's the exact same in the case of the moving treadmill. The point made in the video is that once the frictional forces you're referring to are overcome, it, effectively doesn't matter how fast the treadmill goes in reverse. Rex presents an angular momentum argument, for which the treadmill must be traveling almost infinitely fast in reverse which holds water, but, you know, it outside the realm of possibility.

The model video works great because the proportional forces required are identical on big, real planes. An RC plane follows the exact same principle as a 747. Yes, it's smaller, weighs less, and thereforce produces less frictional resistance... but it's got a tiny freaking motor, too. See what I'm getting at?

Apparently I'm a faggot because I knew this to begin with, though (not a dig at you, Kaan).

HAULN-SS · 12-21-2007, 10:39 AM

asteele2 Wrote:Apparently I'm a faggot because I knew this to begin with, though (not a dig at you, Kaan).

Actually that was a dig at gerald and evan for asking me for a response while i was out doing stuff...but it doesnt bother me if you want it too

CaptainHenreh · 01-30-2008, 10:58 PM

OH LOOK!

Mythbusters proves that a plane on a conveyor belt will take off.

Who owes who beer?

Ginger · 01-30-2008, 10:59 PM

Hunter · 01-30-2008, 11:17 PM

That picture is hilarious. (DJ chopper, not the egg face)

Ginger · 01-31-2008, 12:01 AM

Gosh, Hunter, jerk!

D_Eclipse9916 · 01-31-2008, 12:57 AM

wow I completely missed this thread. A jet has thrust and relies very little on lift until very VERY high speeds. So it doesnt matter anythign, enough thrust will lift the plane.....think space shuttle.

However if we are talking about something like a Cessna 172 or Beechcraft Baron, it is different as these planes rely on lift over "thrust" to get the plane in the air. Therefore they must get sufficient air speed. This is why a lot of private pilots like the idea of a 172 being able to glide a long distance after losing an engine. A jet? Drops like a fucking brick comparatively.

Did they ever air the mythbusters with it? whats the real answer?

CaptainHenreh · 01-31-2008, 08:19 AM

D_Eclipse9916 Wrote:Did they ever air the mythbusters with it? whats the real answer?

CaptainHenreh Wrote:OH LOOK!

Mythbusters proves that a plane on a conveyor belt will take off.

Who owes who beer?

BLINGMW · 01-31-2008, 10:07 AM

Hunter Wrote:That picture is hilarious. (DJ chopper, not the egg face)

:lol: word

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