Will it take off?

reply to post by billybob


Yes..... an Ultralight can take off without the wheels exploding... but, can a 747 at MTOW?

[edit on 22/2/2008 by C0bzz]

1/2 of the plane takign off, if not more, is the lift from the wind. If the plane remains stationary...is it going to get lift? That is unlikely..but i do not thinkn it impossible. her eyou go, when you run on a treadmill, do you feel wind like you are runng outside?

lol, technically speaking, a plane could be on a treadmill at all times...considering the earth is spinning and all :0 though the ration is much different...

Originally posted by billybob
in the real world, the tired can EASILY take the double speed rotation, and the plane takes off, like it did in the real world.

No commerical airliner has a tyre rating of double its rotation speed.


At most its around 1.5x Vrot.

oh dear....even when a video showing a real life practical test is shown people still don't get it!

I imagine it this way. Lets forget about wheels, imagine a hovercraft on the conveyor. Start up the lift fans and it floats, it's air cushion is in effect it's wheels using ultra efficient bearings, it provides no thrust at all.
Start the conveyor and the hovercraft will not move....agreed? Now, start up the thrust fan (ie jet engine or prop in the plane scenario) and the hovercraft would begin to move forward....agreed? No matter how fast the conveyor runs it will have no, or negligable affect on the hovercraft.
It's exactly the same priciple....taking it one step further, if you then stuck a glider on the hovercraft and your airspeed got high enough you could release the glider and it would fly....(until it's airspeed dropped and it stalled)

Another way of thinking would be to park the aircraft at the beginning of the conveyor, with it's tail hanging out over the end. Stand behind the aircraft and push, it will roll forward. Ok, start the conveyor and hold the tail, the conveyor will run under the wheels and the only force you will feel is that caused by the friction of the bearings in the wheel hubs. Give the aircraft a big push and it will roll forward, agreed? Now imagine the pilot starts the engines and you try and stop the aircraft moving forward, regardless of how fast the conveyor runs you'll not be able to keep hold of it!!

Cheers

Robbie

Originally posted by kilcoo316

Originally posted by billybob
in the real world, the tired can EASILY take the double speed rotation, and the plane takes off, like it did in the real world.

No commerical airliner has a tyre rating of double its rotation speed.


At most its around 1.5x Vrot.

the OP question makes no mention of what type of plane it is. so, the answer to the question is still yes. the plane will take off, as shown in the video.

wow I love mythbusters, looks like my theory was dead wrong. The plane does in fact take off. Regardless of the speed in the opposite direction of the ground.

Originally posted by kilcoo316

Originally posted by billybob
in the real world, the tired can EASILY take the double speed rotation, and the plane takes off, like it did in the real world.

No commerical airliner has a tyre rating of double its rotation speed.


At most its around 1.5x Vrot.

mythbusters were drooling about trying it with a jumbojet. i think it does make a difference to the experiment, ie. wheel temperature/failure, but this could be compensated for by using stronger wheels. wheel strength is not part of the OP. assume there are made of adamantium on a jumbo jet.

the jumbo jet takes off.

Oy... the problem is in a few assumptions that people are making about the problem.

Some assume that the concept is, literally, a plane on a treadmill.

Others look at it from a more abstract point of view - to mean that the net velocity of the plane is zero relative to the observer (and assumed to be relative to the air, as well).

And others are just flat-out confused.

Now - to the first one, if we, literally, place a plane on a treadmill, it will be capable of taking off. Real life says that our wheels will create friction, which will slow the plane down a tad - but the friction will likely never be able to overcome the power of the engines (for jets, at least). So, yes, you might have a slightly longer strip of runway needed to take off, but it will be negligable (the difference of a hundred yards or so with larger aircraft, I'd guess).

However, the thought-question states that the velocity of the treadmill is equal to and opposite of the velocity of the plane. Which - as stated above and a hundred times before - yes, the plane will be able to take off under such circumstances because the propulsion of the plane is not coming from torque applied to the wheels, but rather, pushing/pulling on the air.

However, if, somehow, one were to place a plane in a situation where the velocity of the air was equal and opposite to the velocity of the aircraft - then there would be no lift generated (unless you're talking about the YF-23 - the engine intake ducting up over the wings gave it a source of 'static' lift - though it would not be great enough to really lift the plane anywhere).

Are we following? The literal experiment with the treadmill does not present a situation where the airflow over the wings will be equal to and opposite of the velocity of the aircraft... but if we were to create a scenario where that did happen (under any circumstances) - then the plane would not be able to take off.....

Oh, and I saw the AC rating symbol on someone's profile a little bit ago. Good to meet another Airdale - I'm and AT(I-level)!

Without looking at the answer or any other replies... I would say yes!

The engines on the plane are pushing against the air, the power is not going to the runway like on a car etc. So the plane will still move forward..

However.. i'm not sure what will happen to the wheels lol... ooooh the more i think about it....

But i think it will due to the fact I said, the power is in the air not on the tarmac.

Edit - I was right wooo! of course the wheels will just have to rotate twice as fast... i knew that

[edit on 29-2-2008 by fiftyfifty]

Originally posted by Aim64C
(unless you're talking about the YF-23 - the engine intake ducting up over the wings gave it a source of 'static' lift - though it would not be great enough to really lift the plane anywhere).

Run that by me again...



I don't see a way the black widow's engines generate lift.

The intakes are below the engine, so the engine is pulling air up and in - thats a net downforce on the plane.

The jet will be underexpanded, the pressures will be above ambient - this will again produce a downforce on the aircraft surfaces downstream of the nozzle exit plane.

reply to post by Aim64C


close!

the friction actually SHORTENS the length on the runaway before takeoff because the plane is being pulled backwards slightly by belt (due to the (negligible) friction).

(i didn't figure that out. it's a result of the experiment, and i see now why)

No. It will not fly.

Lift is needed. Lift is produced by the speed of air over and under the wings.

www.salon.com...

See the above link if it has not already been posted.

reply to post by masawa


oh, come on, you've seen video proof... why do you still think it doesn't?

i've now tried it myself and even with a $50 model the thing takes off from my gym treadmill (boy, i had to do some persuading to get that done!)

reply to post by maldives01



2006! time sure as hell flies on a conveyor belt.

holy crap.
even when it's over, it ain't over, apparently...

plane push air.
conveyors depend on friction to move things.
wheels and wheel bearings negate friction between belt and plane very efficiently.
therefore, belt cannot transfer force to counteract force of plane engines.

dill holes. LOL! (i'm not calling anyone here that, i called a physorg poster that, where more abuse is allowed, lol)




[edit on 1-3-2008 by billybob]

Well this question is now no more as mythbusters last night just had a plane take off on a conveyer belt of sorts both in miniture and full scale with a ultralight.

There is different versions of this myth so the one they set out to test was as follows:

If a power conveyer belt is spun in the oposite direction that a airplane is facing will the airplane be able to accerlerate and take off?

The answer is yes as they proved but the science as they explained behind this version of the myth is that the planes wheels are not like that of a cars. A cars wheels are powered and are what push the car forward throught the traction with the belt. But a plane whos power is through the prop or jet creates its movement through moving the air around the plane. So with freely moving wheels the plane is still able to accelerate and take off due to no significant friction with the belt.

This subject was trated through all depth possible in a thread in a very famous spotters site for months. (I don`t know if I`m allowed to say which). But let me just say that both positions take off/no take off can be refuted and therefore there still is no conclusion at that thread which is immense.

[edit on 21-3-2008 by Camilo1]

reply to post by Camilo1


i think i may have read the thread you mentioned but to my understanding the question outlined as the mythbusters had it will result in the aircraft taking off.

reply to post by Camilo1


please read this thread for the answer. there is an answer.
the plane takes off, and it was proven in a real life test with a plane and a conveyor belt.

strangely, the pilot was surprised.

reply to post by billybob


yeah i was surprised by that too BB. Makes you question what exactly he was thinkin the plane was powered by? Probably wondered what that big fan was used for at the front of the plane and how it lifted his plane into the air lol.