Airplane / Converyor Belt ... will it take off?

**Epidemic** · October 26th, 2006, 03:27 PM

mr nice guy then I can instantly increase the rotational speed of thousands of pounds of tires to 1000 rpm's. Instantly as in from 0 to 1000 rpm's in 1uS.

personally I would guess that it would take millions of horse power to achieve this.

how many pounds of thrust can you estimate it would take to overcome the belt accellerating 1000 fps^2 if your tires had a radius of 30 inches and weight of 400lbs per tire * 16 tires?

**mrniceguy** · October 26th, 2006, 03:28 PM

yeah, I get agitated by persistant dee dee dee

**mrniceguy** · October 26th, 2006, 03:29 PM

there is no instantaneous acceleration here, it's the normal acceleration of the plane, and double the acceleration of the tires.

**Theophylact** · October 26th, 2006, 03:35 PM

Once again, though: what's the point of arguing about things that are a matter of physics?

I agree that there are physics problems that are hard to analyze easily. One of my favorites is Richard Feynman's sprinkler problem:

You have an S-shaped lawn sprinkler -- an S-shaped pipe on a pivot -- and the water squirts out at right angles to the axis and makes it spin in a certain direction. Everybody knows which way it goes around; it backs away from the outgoing water. Now the question is this: If you had a lake, or swimming pool -- a big supply of water -- and you put the sprinkler completely under water, and sucked water in, instead of squirting it out, which way would it turn? Would it turn the same way as it does when you squirt water out into the air, or would it turn the other way?

For an incredibly full discussion, Google "Feynman sprinkler" and check out some of the references.

**msterzer** · October 26th, 2006, 03:36 PM

I've seen videos of a 747 when it first was being flight tested. Something screwed up and the brakes were locked up. The airplane still moved forward almost as if the brakes were non existant. The engine thrust will win over any stupid conveyor belt. I can't believe there is even any argument here. Thrust trumps. The wheels might as well not even be there for all the difference it would make except to keep the aircraft belly and wings off the ground. The only question there should be is when will the tires disintegrate.

**Epidemic** · October 26th, 2006, 03:37 PM

Originally Posted by butch81385

Epi, take the example in the linke Mrniceguy posted:
if you are on a treadmill with rollerblades, and the treadmill is moving at its highest setting, you will be able to pull yourself forward with just a little extra effort than if the treadmill was off.

I agree with that statement however if you step on to the tredmill moving full speed your feet will jerk backward until you are able to get the wheels up to speed.

The same problem would happen if I suddenly accelerate the treadmill at tremendously high increasing speed. it takes energy to bring the wheels up to speed.

Remember I am dealing in the realm of rediculous acceleration of the belt.

in fractions of seconds I am trying to accelerate wheels from 0 to a new speed.

you know like when you touch down and the wheels skuff for .5 seconds as they achieve speed 180 mph speed. That is tremendous energy released in that burning rubber on landing as the wheels are brought up to speed.

let say they skid for 50 feet as you bring them up to 180 mph 264 feet per second tires skid for approximately .20 seconds. So if I were to accellerate the belt at 264fps ^2 the plane would go backwards or the tires would skid.

**Epidemic** · October 26th, 2006, 03:40 PM

Originally Posted by msterzer

I've seen videos of a 747 when it first was being flight tested. Something screwed up and the brakes were locked up. The airplane still moved forward almost as if the brakes were non existant. The engine thrust will win over any stupid conveyor belt. I can't believe there is even any argument here. Thrust trumps. The wheels might as well not even be there for all the difference it would make except to keep the aircraft belly and wings off the ground. The only question there should be is when will the tires disintegrate.

I am surprised by this but none the less you would never achieve air speed of 150 or what ever take off speed is. and after tire failure the plane is not taking off no matter what.

**butch81385** · October 26th, 2006, 03:44 PM

Originally Posted by Epidemic

Remember I am dealing in the realm of rediculous acceleration of the belt.

But why are you dealing in this realm? That has nothing to do with this problem! The problem says that the conveyor belt moves at the same speed as the plane (would if it were on normal ground). The plane is not producing a ridiculous instantaneous acceleration. If it did you would see the plane just shoot forward off the runway instead of gradually come up to speed. If the conveyor belt is matching the plane for speed, it would have to match it for acceleration.

**FalcomPSX** · October 26th, 2006, 03:44 PM

Originally Posted by Epidemic

mr nice guy then I can instantly increase the rotational speed of thousands of pounds of tires to 1000 rpm's. Instantly as in from 0 to 1000 rpm's in 1uS.

personally I would guess that it would take millions of horse power to achieve this.

how many pounds of thrust can you estimate it would take to overcome the belt accellerating 1000 fps^2 if your tires had a radius of 30 inches and weight of 400lbs per tire * 16 tires?

First question, do you know what THRUST is?

second question, do you know that wheels....spin freely with very little friction?

third question, did you even read the link mrniceguy posted?

fourth question, do you realize you are argueing by 'guessing' against two people who are using actual facts and figures that prove your guess wrong?

**sweeper2** · October 26th, 2006, 03:48 PM

let's take out the TIRE equation here... let's say the tires CAN sustain what ever speed ...

so... my view on this whole thing is... the "thrust" of the planes engines will overcome the conveyor belt... (faster) then the belt will come up to speed.. so the plane would not stay stationary , it would move forward either falling off the conveyor or if it's long enough... it would eventually take off.... (LET"S keep in mind the tires CAN HOLD UP, so take that out of the equation)...

**Epidemic** · October 26th, 2006, 03:51 PM

Originally Posted by mrniceguy

there is no instantaneous acceleration here, it's the normal acceleration of the plane, and double the acceleration of the tires.

who says i can increase the belt speed as fast as I want according the the origial question. So the tires will need to overcome my increase treadmill speed at my 264fps ^2

**FalcomPSX** · October 26th, 2006, 03:53 PM

Originally Posted by Epidemic

who says i can increase the belt speed as fast as I want according the the origial question. So the tires will need to overcome my increase treadmill speed at my 264fps ^2

why would you say this? the original question says it is going as fast as the plane is going, in reverse. you can't make it go at whatever speed you want. read the question again and you will find that yet again, you are wrong.

**FalcomPSX** · October 26th, 2006, 03:55 PM

Originally Posted by sweeper2

You have an airplane on a conveyor belt - when the airplane fires it's engines and begins to move, the conveyor matches its speed in reverse (like on a treadmill).

there's the quote in case you forgot and or dont want to look again.

**sweeper2** · October 26th, 2006, 03:56 PM

Think of a guy on roller skates standing on a backwards rolling conveyor but holding onto a rope that's attached to a wall.. His ground speed measured by the rotation of his roller skate wheels will be whatever speed the conveyor is moving at. Despite this "ground speed" he himself would be stationary relative to the rest of the room. Now take the rope he's holding onto to keep himself still and attach the other end to a rocket instead of a wall....

got this off another forum... and it makes sense.... think about it... hmm just clicked with me... !!

**FalcomPSX** · October 26th, 2006, 04:02 PM

Originally Posted by sweeper2

got this off another forum... and it makes sense.... think about it... hmm just clicked with me... !!

not true, all that's happening is the wheels are spinning at xxx RPM, RPM could be translated into speed but its meaningless, the subject is not actually moving.

**sweeper2** · October 26th, 2006, 04:07 PM

ok.. i get where FalcomPSX is comming from...

there are 2 conclusions i am comming up with... if the conveyor belt moves no matter how fast and it can go as fast as the thrust of the plane... i would say it stands still...

but now.. let's say the conveyor just moves with the wheels ... it just rolls basically...
but the thrust of the engine will move it faster and quicker ...then the conveyor ...

**sweeper2** · October 26th, 2006, 04:12 PM

http://www.kottke.org/06/02/plane-conveyor-belt

or "google" ...

http://www.google.com/search?q=plane...en-US:official

dang... i didn't know this was that popular when i posted it this morning....

still really odd to think about and i would love to see a real life demonstration, of course not of a commercial jet... more a model plane , but it would be cool to see

so my conclusion is... yes.. it would move forward and take off...

**The Real Bingo** · October 26th, 2006, 04:15 PM

I'm with Epi, obviously, on this one. And I give up trying to explain myself. It's like trying to tell a color-blind that the grass is green.

**Toadman** · October 26th, 2006, 04:19 PM

Lift is created by the flow of air over the wings (airfoil). The shape of the wing makes the air go over the top of the wing faster than the air under the wing. This creates lift. If the plane is stationary on the ground it will not lift off - unless the wind is so strong that it picks it up anyway...

Agreed. With a conveyor moving forward, backwards, sideways, 10mph or 1000mph an airfoil will not generate lift without wind over it's leading edge. In hurricane-force or wind tunnel testing it will fly even though it's ground speed is zero, hence airspeed. Ever see Flight of the Phoenix?

Those guys get an F in aerodynamics.

**msterzer** · October 26th, 2006, 04:20 PM

A lot of you people would be right if the airplane was a glider. With thrust the airplane is going to move regardless of what the wheels are doing. I don't care if the wheels are rolling in the forward direction or in a backward direction. Thrust will move the plane. Unless its tied down, as in tail hook.