Can Plane Take Off

TheWand said:

this is a rather crude example, but yeah same principal
the conveyor dont even slow the skateboard

http://videos.streetfire.net/player....D-D6BA1A43A06B

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That one has more to do with the friction between the skateboard and the paper. Paper has a very low coefficient of friction, thus there was not enough grip on the wheels to match their movement. edit: He should try that again using a thick, coarse cloth.

That"s a good observation, though. For the airplane experiment to go over right, there would need to be a high force of friction between the tires of the landing gear and the conveyor belt, otherwise the plane would just roll slowly off of the belt.

The Wand said:

I begged to differ and said "think ratings"

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Those guys forget sometimes that not everybody is an aeronautical engineer. I admittedly couldn"t draw the free body diagram to show how the air"s reactive force lifts the plane. That principle is key to why the plane would lift, which does make this a worthy experiment.

This question is pissing me off. I asked my cousin, a Marine jet/helicopter mechanic, and my mom"s friend, who works as a pilot flying commercial jets. My cousin says the plane could not take off, because for example, if a plane needed to go 100 mph to take off, and the belt is going 100mph, the plane is doing nothing but sitting there. He says it wouldn"t be able to lift off because it doesn"t matter how much thrust the engines are producing, they are still equal to the power the belts behind it are pulling.

However, the pilot says that it wouldn"t matter at all. The wheels are just a free rotation to make sure the plane doesn"t scrape the ground. He says the plane would take off with no trouble.

Problem is, I"m not a professional. This one of those questions where you"d have people argue about for an hour and a half at thanksgiving dinner, and then argue another hour during the football game.

the pilot is right.

the wheels are in free motion in the sense that they are not what propels the airplane. they act as a friction source to stop it while on the ground though. most people think of wheels and relate it to cars, so they believe the wheels act as a driving force when in fact the wind generated by the propeler is the real force. a better comparison is take a railroad track and put a cart on it. the cart is attached to a string that pulls it. the string and the break system are the only thing affecting its speed, not how fast the rail underneath it is or isnt moving.

basically wheels will only stop a plane on the ground if the breaks are applied as it creates an immense amount of friction for the engine to overcome. otherwise it doesnt matter if the wheels are spinning at negligable speeds(in air) or at 2x normal takeoff(in this scenario).

The plane takes off, the conveyor belt may as well not be there.

I had an uncle who tried this and the plane didn"t not take off. He made the conveyor belt out of adamantium.

So that proves it.

Zeste said:

I had an uncle who tried this and the plane didn"t not take off. He made the conveyor belt out of adamantium.

So that proves it.

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Adamantium molecules are packed extremely close together. As such, the surface of an adamantium conveyor belt is very, very smooth, and has a very, very low coefficient of friction.

Thus, the question is... When your uncle"s plane slid off the conveyor belt in an uncontrolled manner, did he get hurt?

<3 physics

This is getting stupidly complex, as a hundred different people wave around scientific e-penises.

The only thing that matters is that the wheels on a plane aren"t powered. The conveyor belt does nothing but make them spin faster, which doesn"t matter, as they serve no role in a plane"s speed. Unless the pilot decides to put on the brakes, the wheels will just be spinning twice as fast while the plane takes off normally.

It"s a simple fucking trick question. You"re led to focus on the wrong thing, and the answer is obvious once you see it. Unless of course you"re the sort of person who had a hardon during Chemistry class; then you"ll write seven paragraphs about friction or something.

This is just a plain stupid question, especially as it was originally stated in this thread. It was hard to even understand what the fuck was being asked. And once you clearly understand what"s being asked, the answer is incredibly obvious to anyone but those with incredibly low intelligence.

The plane takes off because the CIA has secretly hidden a nuclear device in the tail section and explodes it on cue in order to launch the plane into orbit. Once in orbit Vin Diesel ejects from his cyrogenic regeneration chamber and flies Superman-style straight into the heart of North Korea. His impact with the ground instantly kills everyone within a 79mile radius, and the resulting fall out cloud from him taking a shit in the blast crater will wipe out the remaining people in the country. China will get pissed off cause the cloud will come their way but Vin will say "Deal with it chink faces" and then bite the heads off of their leaders.

Really doesnt matter what the belt is made of.. according to the laws of friction, cirlces are the only exception. Wheels have no friction, they are replaced by rotation.

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There"s friction inside the wheels, the bearings etc. And for practicality"s sake, if the belt was moving as fast as the plane"s minimum takeoff speed (say 250mph) then the wheels would have to be rotating as fast as they would if the plane was moving 500mph on firm ground. No idea what kind of tolerances they have on aircraft wheels, but I have a feeling that if you exceed a reasonable speed on them, they"ll either burn out (the bearings) or disintegrate (the tires).

So again, depending how complicated you want to get, the answer can go either way. If you just look at it in the simplest way, then yes it can take off. But you can complicate the situation and the answer becomes a matter of "if."

The Ward said:

Really doesnt matter what the belt is made of.. according to the laws of friction, cirlces are the only exception. Wheels have no friction, they are replaced by rotation.

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Rotational movement is subject to friction when said motion is surrounded by a surface in contact with another surface.

If it were true that all rotational motion has no friction, then cars wouldn"t move.

You"re confusing the motion of a pendulum with the motion of a wheel.

Actually, the motion of a pendulum or physical pendulum is also subjected to friction with the surrounding medium. The fact that the motion is broken up into both rotational and translational math doesn"t make friction cease to exist.

We just tend to ignore it in our calculations because that makes the difference between a fourth degree differential equation and a first degree differential equation.

The video with the paper and skateboard is excellent proof of this.

DJ3 said:

This is getting stupidly complex, as a hundred different people wave around scientific e-penises.

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My scientific e-penis has some real life balls beneath it. This sort of shit is right up my alley.

Of course, you are perhaps right about over-analysing it. On the other hand, that is exactly what scientists do, especially physicists.

OK, I"m just going to throw in my two cents since I skipped a lot of the science being laid down as I"m just not educated enough in physics or airplanes to make a lot of use of the higher-end shit.

Lift is created by air moving over the wings due to the shape of the wing, the design that stopped man from being able to achieve flight for so long. I think most people who even enter this conversation should understand that basic fact. That said, most of us DO NOT understand how liftoff actually functions. That includes me. The only way I could concieve of an airplane being able to fly under these circumstances is if a pilot is able to make it leave the ground momentarily without any vertical lift from the wings, something I can"t understand how they would do, but this seems to be 100% necessary to even go to step two of the physics required.

The next requirement is, does the plane have momentum despite the fact that it is not moving in space? I think yes. Can it create enough momentum that it achieves the appropriate airspeed for lift once the pilot has made the plane lose contact with the conveyor, however that would occur? Dunno, I would think yes also. So in my mind it comes back to point one, can you make the plane leave the ground without lift from the wings. This seems to be entirely a pilot question.

the propeller "pulls" the plane forward by pushing the wind backwards. it basically works like a wind screw, once it grabs it is driven forward due to the curvature. the resulting wind over the wing causes the lift. and then you have flight.

while you can argue the bearings friction may superheat and only chuck norris could turnback time enough to cool it down, the case wont happen. the speed at which planes lift off the ground is a lot lower then you might expect. in smaller single engine cessna"s its only around 50-60 miles, sometimes lower(seen em lift off at around 30, depends on nosewind). i know, i used to get bored and race them with my prelude for shits n giggles.


and when you take off you tend to angle the wings so that you are slightly pointing down(increasing speed), until at which point you feel safe to take off and then pull back to angle the wings at such a degree that the air causes you to lift.

Plane would take off. The engine"s create the thrust to move it forward. The conveyor belt is moot. The wheels would just be spinning twice as fast.

Ok, if I understand this shit correctly, doesn"t this mean that the plane is sitting still relative to the ground AND the air? So that would mean shit can"t take off, right?

potam said:

Ok, if I understand this shit correctly, doesn"t this mean that the plane is sitting still relative to the ground AND the air? So that would mean shit can"t take off, right?

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It"s still relative to the ground, but not to the air. The big quote with the first scientific explanation was a little iffy on this point.

It would be better to say that the air is not still with relation to the plane.

What happens is you end up with static conditions for horizontal movement, but not for vertical movement. The statics here are fairly simple, but the vertical lift isn"t, at least at this moment for me.

brekk said:

Along with Newton"s Law of Physics you need Bernouli"s principle. Its the basis for lift. Air moving fast has lower pressure. The air flowing over the top of a wing must move faster then the air underneath. This causes low pressure over the wing. Literally the higher pressure air under the wing pushing up is the lift of a plane.

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Awesome! You"ve given me something to read about on the break between this semester and the spring.

Thank you very much Much, much respect goes to those who I can learn from.

I"ve wanted to fully understand how this works (that is, in more than colloquial terms) for a long time now.