Plane on a Conveyor Belt

[Hmbre97]

Yes, it will take off

[choran]

The plane DOES take off.

[golfchief]

no. If it could take off we don't need miles of runways for taking off, all planes could take off that way?

[golfrnut]

Nope...last time I checked, planes weren't dependent on wheels to takeoff.

[g-funk13]

Dude, it totally takes off!

[iacas]

Here is the Answer: The plane flies.

To an observer standing on the ground, the takeoff appears perfectly normal except that the wheels will be spinning twice as fast.

A plane with locked brakes could take off from a sheet of pure ice, too.

The reason? Unlike a car, planes don't push against the ground - they pull themselves through the air. Since the air isn't moving (only the conveyor belt is), the plane pulls itself through the air, reaches takeoff speed, and takes off.

In my experience, those who said "no" either:
a) forgot that planes don't push against the ground like cars do
b) misread the question and/or assume things that don't make sense at all or which aren't in the question, like "the plane is stationary."

The plane isn't stationary, and in fact the very question says the plane moves (or else the conveyor belt would just sit there and not move either).

[lamebums]

That makes no sense. Planes make lift by air moving over the wings. Whether the wind is blowing, or the engines pushing the plane forward, air is moving over the wings to provide lift.

If you are stationary on a conveyor belt, there is absolutely no wind moving over the wings, and hence no lift. You're going to spin the wheels a lot, but unless you've got vectored thrust or a rocket engine you're not going anywhere.

In effect, the plane is running on a giant treadmill.

Edit: Now I get it - the wheels aren't connected in the same way a car is, a la gears and such.

[iacas]

Edit: Now I get it - the wheels aren't connected in the same way a car is, a la gears and such.

Right, they're free-spinning wheels. So do you see now why all of what you wrote at first is wrong?

As I said, the plane moves forward and takes off normally. It isn't stationary relative to anything - not an observer on the ground and obviously not the conveyor belt, nor the air.

[Shindig]

In my experience, those who said "no" either:

Guilty! Except for the "forgot" portion, since I'm not sure I knew it in the first place. In any case, good brainteaser.

[srjorion]

For those of you who said "No", don't feel too bad. I'm a pilot and frequent a professional pilot forum where this same question was asked last year. A lot of pilots, many of them airline pilots, also answered "No".

[neudi]

OK, I have been waiting a while to do this, if this is based on mythbusters I do not believe that it is true, because for a plane to take off the airflow under the wing has to be slower than that of the air going above the wing, hence the curve on top of the wing that is more significant than the air flow under the wing. When a plane is standing still how is air moving under the wing? This gets me to the mythbusters question: When you watch the mythbusters the plane is NOT standing still on the conveyor belt, the plane is still moving forward even though not as fast as normal. So until the plane is actually standing still on the conveyor belt, as in i mean wheels are moving, but plane isn't, then I will believe it, but for now I still say no.

[srjorion]

When a plane is standing still how is air moving under the wing?

That's the problem in your thinking. The plane

IS moving. Reread this part of the question: A plane is standing on a runway that can move (some sort of large conveyer belt). The plane moves in one direction, while the conveyer moves in the opposite direction. Many people get this question wrong because they assume that the plane does not move due to the conveyer belt. The plane is definitely moving. Think of it this way, for the conveyer belt to move, the plane must move. Remember, the conveyer belt moves as fast as the aircraft in the opposite direction. If the plane were to remain stationary then the conveyer belt would not be moving. The only difference between a takeoff on a runway and a takeoff on a conveyer belt is the speed of the tires spinning.

[neudi]

If the plane is standing still while moving on the conveyor belt, meaning it is stationary, how is the wind going under the wing....the conveyor belt is moving, the wheels are moving on the plane, but the air is not moving and the plane is not being pushed through the air, I just don't agree with what mythbusters did b/c the plane actually moved forward if you watched the background. I would have to talk to someone who is a genius at physics and aeronautics because I still don't think it's possible.

[neudi]

k, now I understand, thank you for the logical explanation vancortlandtgc

[iacas]

I see you've had your question answered in the time it took me to write my response, so I'll leave my post up in case anyone else falls into the same trap as you.

If the plane is standing still while moving on the conveyor belt, meaning it is stationary,

How can something be "standing still while moving"?

As the question says, the plane is standing on the conveyor belt... then starts moving. Most planes are sitting there prior to takeoff - this one's no different. Other ways of saying it would be that "you set a plane on a conveyor belt" or "a plane moves onto a conveyor belt, stops, and then tries to take off as planes do." As I said above, the plane takes off 100% normally... except the wheels are spinning twice as fast as normal.

the conveyor belt is moving

Right

the wheels are moving on the plane

Right

but the air is not moving

Right

and the plane is not being pushed through the air

Wrong. The plane is moving through the air (and relative to the ground, and also relative to the conveyor belt).

I just don't agree with what mythbusters did b/c the plane actually moved forward if you watched the background.

You need to read what I said above. You have fallen prey to one of the two flaws most people seem to succumb to. The conveyor belt can do nothing to stop the plane's prop (or jet engines) from pulling the plane forward through the air.

Nowhere is it stated that the plane REMAINS stationary. In fact, the very question says the plane moves - and that the conveyor matches its speed. Objects just sitting there have no speed.

I would have to talk to someone who is a genius at physics and aeronautics because I still don't think it's possible.

I assure you it doesn't take a genius to figure this one out.

Here's another way I've seen it explained: the conveyor belt's only real force is applied upwards. It holds up the plane. A teeny, teeny, teeny bit of friction (force) in the wheels themselves resist their turning, but the source is the wheel's bearings, which are pretty close (99.99%) to frictionless. This force is negligible and obviously exists on normal takeoffs too. The weight of the plane pushes down, canceling the force of the conveyor belt (or ground normally) pushing up. The engine of the plane applies a force that moves the plane forward. This force is thousands (or more) times greater than the force of friction in the wheels. Where there are misbalanced forces, you see acceleration. Nothing abnormal here. The plane takes off normally. You're putting "stationary" into the question when it isn't there except to state where the plane is positioned. You have to say the plane is "sitting" on the conveyor belt because the only other options are that it's "hovering above," "beside," etc. The very question goes on to state that the plane then moves, as does the conveyor belt.

[tcarter]

A plane only takes off because of the air over the top of the wings takes longer than the air underneath the wings. This causes lift. As the plane will not be moving this lift will not occur - the plane will never take off.

[iacas]

A plane only takes off because of the air over the top of the wings takes longer than the air underneath the wings. This causes lift. As the plane will not be moving this lift will not occur - the plane will never take off.

Please see the above. You're wrong about the plane not moving and thus about the plane not taking off.

The answer's already been given.

[Staff-Bag]

No!

Why would the plane take off?

In order for a plane to take off there must be lift from the flow of air past the wings. The plane isn't going any where, so there is no lift! No lift.... no takeoff!

(Must be Northwest Airlines!)