Planes fly due to the difference in velocity created by the planes wings. The jets simply keep the plane moving while in the air. They have nothing to do with the air surrounding the wings and producing the lift. Am I missing something?

1/28/2008 12:11:08 PM

hey i'll be the guy on roller skates with a rocket strapped to my ass.

1/28/2008 12:13:43 PM

Quote :

"Planes fly due to the difference in velocity created by the planes wings. The jets simply keep the plane moving while in the air. They have nothing to do with the air surrounding the wings and producing the lift. Am I missing something?"

no you are correct

Quote :

"you neglect the friction between the wheels and the treadmill."

then its a hovercraft and not an airplane so the myth doesn't matter.

1/28/2008 12:16:12 PM

^You can neglect the friction between the wheels and the treadmill because the friction force is so much smaller than the thrust.

Quote :

"The jets simply keep the plane moving while in the air. They have nothing to do with the air surrounding the wings and producing the lift."

Without the engines pushing the plane forward, there is no air moving over the wings to create the difference in velocity. They have everything to do with the air around the wings.

1/28/2008 12:21:35 PM

haha. I hope they just blow up the plane instead and laugh at everyone who thought they were actually going to see if it would fly.

[Edited on January 28, 2008 at 12:23 PM. Reason : ]

1/28/2008 12:22:55 PM

Quote :

"Without the engines pushing the plane forward, there is no air moving over the wings to create the difference in velocity. They have everything to do with the air around the wings. "

Ever seen a glider fly? Oh thats right they dont have engines so they must not be able to fly.

1/28/2008 12:30:48 PM

i was always under the impression that the engines were off during the treadmill run, which obviously meant that it wouldn't take off.....if the engines are on though, it would take off eventually

1/28/2008 12:38:49 PM

why is it always a jet?

[Edited on January 28, 2008 at 12:41 PM. Reason : ^^ you are right, they don't fly. They freaking glide.]

1/28/2008 12:40:43 PM

Quote :

" was always under the impression that the engines were off during the treadmill run, which obviously meant that it wouldn't take off.....if the engines are on though, it would take off eventually "

Nope, Still no wind over the wings to create lift.

1/28/2008 12:42:46 PM

Quote :

"hey i'll be the guy on roller skates with a rocket strapped to my ass."

Lets hook this up.

1/28/2008 12:43:09 PM

Quote :

"This still won't quell the discussion,"

because people are retards

1/28/2008 1:00:07 PM

Quote :

"Ever seen a glider fly? Oh thats right they dont have engines so they must not be able to fly."

Gliders glide, they dont fly. They eventually lose energy (both potential and kinetic) once they land. Planes do not lose energy due to the engine.

This is retarded. The only way the plane will fly is if enough air velocity is created around the wings. Engines or not, it wont work unless Bernulli's principle produces an upward force greater than gravity. And for those wondering, things always go to lower pressure. The hump in a wing reduces the pressure above the wing (due to that air flows increased velocity), forcing the plane body upward.

I have a better experiment to test. If you mount huge fans infront of a plane, creating very high turbulent air flow, would the plane then fly?

1/28/2008 1:09:05 PM

so carriers point into the wind for no reason when launching aircraft huh?

1/28/2008 1:18:24 PM

^^ Your beliefs are flawed on multiple fronts there, just like your politics.

1/28/2008 1:29:08 PM

Quote :

" Ever seen a glider fly? Oh thats right they dont have engines so they must not be able to fly."

Ever seen a glider take off by itself?

1/28/2008 1:30:37 PM

Quote :

" Ever seen a glider fly? Oh thats right they dont have engines so they must not be able to fly"

1/28/2008 1:32:05 PM

Quote :

"I have a better experiment to test. If you mount huge fans infront of a plane, creating very high turbulent air flow, would the plane then fly?"

once again, we have people describing a wind tunnel, as if they don't already exist and work.

1/28/2008 1:33:27 PM

Quote :

"whether the myth is true or not depends largely on how it is worded, and if it's worded such that the treadmill is generating the same force as the engines, or that the treadmill is moving the same speed in the opposite direction of the plane,"

The treadmill CAN move at the same speed of the PLANE but it can't move at the same speed (by that I mean angular velocity) as the wheels. Because the (speed of wheels)=(speed of the plane)+(speed of the treadmill)

where (speed of the plane)=(speed generated by the engines)

For others...
So you can see by those simplified equations, at no point is the actual speed of the plane itself affected by the treadmill, it's just the speed of the wheels which are affected. So the plane takes off as usual (maybe a tiny bit longer depending on friction).

1/28/2008 1:38:45 PM

Quote :

"Ever seen a glider fly? Oh thats right they dont have engines so they must not be able to fly"

any flying machine has to have an energy source to remain in flight.

Planes use engines to take off from the ground and remain in flight.

Gliders don't have engines, so they cannot take off from the ground. They are dragged into the sky by a plane, then released. Now remember back to your 6th grade science class.... now that the gliders are thousands of feet in the air with nothing under them, what do they have? Potential Energy! They use gravity as their energy source, but instead of falling like a rock to disperse the energy, they use wings to slow their descent. While it is possible for gliders to move up and down slightly based on the prevailing winds and fancy flying, it is impossible for them to remain aloft indefinitely without an additional external supply of energy, like and engine.

1/28/2008 1:43:09 PM

gk2004 is such a fucking troll

1/28/2008 1:56:24 PM

Quote :

"^^ Your beliefs are flawed on multiple fronts there, just like your politics. "

Actually thats an example a professor used in my first transport phenomina class 4 years ago....

And Im not talking about a wind tunnel. I am talking about an actual apparatus that mounts to the plane. Would it be able to actually go up and down with no forward motion?

1/28/2008 2:05:16 PM

jet engines move the plane relative to the air, not the ground./parodoxical ever increasing treadmill speed.

1/28/2008 2:09:37 PM

It says the treadmill moves at the same speed of the wheels in the opposite direction. If the plane is not moving, then the connected wheels are ALSO NOT MOVING (spinning = 0 net displacement) and the treadmill therefore does not move either.

[/troll]

1/28/2008 2:19:23 PM

IMPOSSIBLE.

now whats this about a helicopter turntable?

1/28/2008 2:22:46 PM

WE'RE GOING TO NEED MORE TREADMILL!!!!!!!111oneoneoneeleven

1/28/2008 2:23:38 PM

Quote :

"WHAT ABOUT A HELICOPTER ON A GIANT TURNTABLE????"

1/28/2008 2:27:20 PM

Quote :

"Actually thats an example a professor used in my first transport phenomina class 4 years ago.... "

The plane will fly. The treadmill won't affect it.

The process that keeps gliders in the air is the same one that causes planes to fly.

And in the case of your theoretical plane with fans mounted on it, assuming that the fans were light enough and positioned not the throw the balance of the plane off, it would fly (although the fans would also be giving it forward motion).

1/28/2008 2:39:46 PM

^AKA a twin-engined propeller aircraft with the engines mounted on the wings, where the engines provide thrust, but also move air over the wing surfaces.

1/28/2008 2:55:34 PM

my coworker is trying to argue with me about a goddamned helicoptor on a turntable now.

1/28/2008 3:08:35 PM

Quote :

"And Im not talking about a wind tunnel. I am talking about an actual apparatus that mounts to the plane. Would it be able to actually go up and down with no forward motion? "

well something would have to fix the plane in position to avoid forward or backward motion. If you mount fans or jets to blow air over the surface of the wing, unless the plane was fixed on a vertical axis, then the force from the fans/jets would blow the whole plane forward, just like normal jet/prop engines do. Instead of fixing it to a vertical pole/axis, i guess you could take the wheels off or use another method to create more friction between the ground and the plane, but in that case I suspect that if the wings are able to generate lift before the thrust overcomes the horizontal friction, then the plane would hop or jump briefly, relieving it of the horizontal friction, but would soon fall right back down again. Fact remains that if the plane is left free to move horizontally, the fans/jets/props have to be able to provide enough thrust to generate the lift on the wings.

If, however, you fix the plane on a vertical axis and blow air across the wings, then yes, it will generate lift, which is not coincidentally, exactly how a wind tunnel works.

Quote :

"^AKA a twin-engined propeller aircraft with the engines mounted on the wings, where the engines provide thrust, but also move air over the wing surfaces."

I would double check this with an AE, but I suspect that the air that is blown directly from behind the props over the wing produce very little of the plane's lift, compared to the rest of the air that flows over the wing because of the motion of the plane (as a result of the thrust from the props)

1/28/2008 3:11:33 PM

Quote :

"So the plane takes off as usual (maybe a tiny bit longer depending on friction)."

yes.

1/28/2008 3:21:12 PM

Quote :

"It will take off. I used to think it wouldn't, but after watching that video, and thinking about it more it will take off. Imagine it this way.... You have a friend wearing rollerskates and he is standing on one of the moving sidewalks. You are standing to the side on stationary ground. You have your hand against his back and the moving sidewalk is going 5mph. Right now he is not going anywhere. He is staying in one spot and the wheels of the skates are rotating. If you walk forward pushing him with your hand, he is going to move forward also. Imagine at this time you are the jet engines. If the sidewalk increases to 15mph you are still going to be able to move him forward with the same amount of energy and you are also free to push him as fast as you want no matter if the moving sidewalk was even going 100mph. Does this make more sense to those who think the plane will not take off? "

Let me post that on page 3 for those of you still thinking it won't take off.

1/28/2008 3:23:29 PM

Quote :

"I would double check this with an AE, but I suspect that the air that is blown directly from behind the props over the wing produce very little of the plane's lift, compared to the rest of the air that flows over the wing because of the motion of the plane "

Yeah, you are right. If you could somehow cause the fan on the front to push air over the wings without pulling the plane forward, provided the fan was large enough and pushed enough air, it would theoretically lift the plane off the ground. But it would be ridiculously impractical.

1/28/2008 3:46:11 PM

yeah, not to mention, the air coming off the props is horribly turbulent and probably has all kinds of swirls and vortexes and whatnot, which is why wind tunnels go to extreme lengths to get the air as smooth as possible before going over the plane in question (many wind tunnels actually operate on "suction", where the fan is placed behind the plane, then air is blown forward through a closed loop and makes several turns before coming back to the front of the plane, so the plane is not directly exposed to the air coming off the propeller)
The air flowing around the rest of the wing outside of the props, through, would be relatively smooth and would create much more uniform lift.

1/28/2008 4:00:40 PM

What about a hot air balloon in a freezer??

1/28/2008 4:20:09 PM

^^That is how our subsonic wind tunnel in Broughton is set up.

[Edited on January 28, 2008 at 8:00 PM. Reason : ]

1/28/2008 8:00:47 PM

Quote :

"What about a hot air balloon in a freezer??"

I find your ideas intriguing and wish to subscribe to your newsletter.

1/28/2008 8:36:24 PM

I haven't read the whole thing, nor have I read the other thread...so I have no clue if this has been said yet or not...and I don't care...however this is what my dad said (he graduated from state in aerospace engineering)

To the question can a plane take off from a treadmill when the plane remains motionless and the ground is what is moving...
his answer "No, someone has to be a complete idiot to think that's possible"

He did say however that it might could be possible if you have a small enough plane on a big enough treadmill that is producing a strong enough wind that can cause lift.


But like I said, I'm sure some of y'all have already figured that out and already knew that and you've already moved on to the next subject about girls with perfect tits.

[Edited on January 28, 2008 at 8:54 PM. Reason : gk]

1/28/2008 8:54:25 PM

he's right

but you asked the wrong question

1/28/2008 8:55:23 PM

^^To clarify, you're thinking of a myth in which the treadmill is moving the plane forward.

The myth in this thread involves a treadmill running in the opposite direction of the thrust from the plane engines.

^Indeed.

[Edited on January 28, 2008 at 8:56 PM. Reason : ^]

1/28/2008 8:56:26 PM

haha see I told you that I didn't read the thread. I just assumed that was the question that was being asked. But you know what happens when someone assumes something


I'll go ask him that question now and see what he says...bbl with an update




Okay this is what he said....

If the plane is on a long enough treadmill and when the tredmill starts it makes the plane go backwards, then the plane turns on it's engine to produce thrust and is able to get up to the speed that it needs to be at and is moving fowards (not just the wheels turning) then a plane can take off from a treadmill.
I think I worded it the same as he did.

[Edited on January 28, 2008 at 9:02 PM. Reason : ]

1/28/2008 8:58:09 PM

the wording of the myth is what it so weird. i've heard it about 50 different ways.

if it is worded that the treadmill matches the wheel speed, then the plane takes off

it is worded that the treadmill matches the speed of the wings, the plane is stationary and will not take off.

it can be worded different ways to make each way correct, or incorrect.
the right answer does not always have to be right to make the situation correct, but the wrong answer can only be wrong if the right answer is said differently.
It all depends on how it works.

1/28/2008 9:11:22 PM

^ you have those 2 wordings backwards.

1/28/2008 9:12:26 PM

This thread is filled with people that fail physics.

Quote :

"which is impossible, because the treadmill is generating force against the wheels, and the plane engines are generating force against the air, which is completely decoupled from the treadmill and wheels. "

HURRR HURRRRR I DONT UNDERSTAND HOW FORCE AND PROPULSION WORK HURRR

1/28/2008 9:15:50 PM

^^No, he's got it right. His second one is saying that the treadmill is moving against the plane with such an immense speed that the rolling friction generated would overcome the force of the engines, resulting in an immobile plane... which is NOT the proposed myth, but a mistaken interpretation.

He also forgot the third explanation: The treadmill is moving the plane forward rapidly, would the plane take off? It would "fly" similar to a glider being thrown (if it is flung by the treadmill fast enough), but would not actually fly by the definition of the word... this one is also basically assuming the plane's wheels aren't rotating and friction is present.

Also, the first one isn't actually possible, it results in a paradox of A=A+A. The practical and logically possible version is that the treadmill's speed in reverse matches the plane's forward speed (not the forward speed of the wheels, the forward speed of the plane), which obviously results in a plane taking off.



[Edited on January 28, 2008 at 9:23 PM. Reason : correction (v Yeah, I corrected that.)]

1/28/2008 9:20:25 PM

he said the one where the treadmill matches the speed of the wheels though

Edit:

Also since "fly" has a first definition of "to move in or pass through the air with wings", it would fly if it were thrown. Apart from this, since it is a powered plane and not a glider, the engine would sustain it's flight after takeoff.

[Edited on January 28, 2008 at 9:24 PM. Reason : . ]

1/28/2008 9:22:19 PM

1/28/2008 9:23:00 PM

Quote :

"No, he's got it right. His second one is saying that the treadmill is moving against the plane with such an immense speed that the rolling friction generated would overcome the force of the engines, resulting in an immobile plane... which is NOT the proposed myth, but a mistaken interpretation."

The second one doesn't mention anything about friction, he just has the conclusion wrong. And the first one, as you noted, is the paradoxical situation, but he said the plane DOES take off where you (and I) are saying it WON'T.

So, he has the 2 scenarios backwards.

treadmill matches wheel speed -> paradox

treadmill matches plane speed -> plane will take off

1/28/2008 9:27:03 PM

^I concur with that.

I kept reading his post wrong and/or forgetting what I had wrote and/or forgetting what he had wrote.

1/28/2008 9:28:14 PM

This whole discussion is retarded. I don't care about how the myth is worded. The whole idea of the myth is to see if a plane can take off while staying in one place, hence the treadmill. Its the theoretical plane taking off without a runway.

And the answer? Nothing happens because the myth's scenario cannot occur (unless we were to create a wheel propelled plane).

In the end, it all boils down to this: the people who say that it will fly are more wrong than those who say it won't fly. Why? Because . . . if you are smart enough to realize that the treadmill won't actually stop the plane from moving forward, you should be smart enough to realize that this is an invalid scenario.

Stationary planes do not fly . . . are we really even having this discussion?

1/28/2008 9:33:11 PM