Plane Problem

[Mr.Russian]

Moz.. your video rocked!!!

 

[Tak]

If there was a blimp above a treadmill, and I was on the treadmill holding a rope tied to the blimp, and the blimp decided to continually apply thrust, I would get dragged along and scream and cry right off the treadmill, possibly even make a poopie.


I didn't grab it either at first, but it'll click. Coming from a fellow 'no fly' this might help


Get a skateboard, and stand up next to a wall. Push yourself away from the wall, just using your hands with both feet on the skateboard (or your butt, if you can't stand on a board). Got the feel for how that works? You are not involving the ground in anything other than holding you up.

Now lets get on a treadmill with the skateboard, with a wall behind you. Get up to a nice speed. Now push yourself forward off the wall. You still moved forward. Why? Because again, just like when the ground wasn't moving, the ground didn't do anything other than hold you up. The only difference is the skateboard wheels are moving super fast.

Now in all likelyhood, if you turned the treadmill up too fast, you'll just hurt yourself, because I imagine the average human can only push themselves so far with one good shove.

But imagine if you were Mr Stretchy Arms Guy, and your arm continued to press forward at the same rate, or even faster. Even with the treadmill trying to continually match your speed, you'd just keep moving forward until you die, or in the case of the airplane, take off.


It completely goes against the 'gut feeling', and I completely agree that it *shouldn't* work. And in the real world we couldn't GET it to work just because of the expense and the phucking uber wheels it would take.

Fellow no-flyers, it's ok. I was one once too. The flying side cares and loves all! And...well, makes you feel like a dunce for not seeing it once it finally clicks
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[Silky_Slim]

No matter how much logic or rational thinking is involved, i will stay undecieded untill a fullscale treadmill/testing facility is built.
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[WickedPenguin]

@Moz: Dude, that video kicked ass. Great way of explaining it. "Feeel my brain. Feeeeeeel my brain."

What I mean is, if a 25,000 pound thrust jet is running full throttle, you are gointg to have a micro climate around the plane were air is being ****ed into the engine and out the back at such a high speed, winds are created.

The JSF can take off without lift with thrust vectoring.

Microclimate? WTF? The air is being pulled directly into the engine and has no effect along the wings whatsoever. That "high speed wind" you're talking about that's created by the engine...well, that's called "thrust".

As for the F-35 JSF, Harrier, Yak-141, Yak-38, etc., their vertical flight capabilty has nothing to do with airfoil lift and is simply a matter of thrust to weight ratio.

 

[BuddyLee]

@Moz: Dude, that video kicked ass. Great way of explaining it. "Feeel my brain. Feeeeeeel my brain."



Microclimate? WTF? The air is being pulled directly into the engine and has no effect along the wings whatsoever. That "high speed wind" you're talking about that's created by the engine...well, that's called "thrust".

As for the F-35 JSF, Harrier, Yak-141, Yak-38, etc., their vertical flight capabilty has nothing to do with airfoil lift and is simply a matter of thrust to weight ratio.

Then what do you call the highspeed air flowing into the front of the engine? the engines effect the environment around them, but not enough to effect lift... which is what I said in the first place... the air flowing INTO the engine is NOT thrust... the air out the back IS. fail.

I never said the vtol was achived by lift, I said high-powered jets can take off without lift... like the JSF. With thrust alone, like a rocket. you fail at nitpicking.

 

[Moz]

Then what do you call the highspeed air flowing into the front of the engine? the engines effect the environment around them, but not enough to effect lift... which is what I said in the first place... the air flowing INTO the engine is NOT thrust... the air out the back IS. fail.

I never said the vtol was achived by lift, I said high-powered jets can take off without lift... like the JSF. With thrust alone, like a rocket. you fail at nitpicking.

You are arguing my wording, because I am tired, and I decided to make that stupid video instead of working on a few essays, which I am paying for right now.

(zzZzzZZzzzZzzzz)

congratulations, you are irrelevant, just like the groundspeed.

PS.

Youtube video is FINALLY up

http://www.youtube.com/watch?v=iLCCFeOWozw

 

[BuddyLee]

Good Video, I guess now the only question would be...

Would the wheel bearings fail and cause the wheels to freeze up?

 

[melipone]

This has had me scratching my head a bit but i've come to this conclusion in the end (that video helped Moz ). Now is this the final answer or am I still wrong.

Edit..I was being stupid

OK now i've thought about it some more..would the wheels not just spin on the spot if the conveyor is always moving at the same speed as the plane? Bah i'm not so sure now.

 

[Nestor Makhno]

Guess what! The engines = wind making machine! Since they cause the airplane to move relative to the air around it thereby creating wind, and LIFT!

So yes, there is a windmaking machine involved in this scenario.

The air chucked out of the back of the engines does not pass over and under the wings therefore it provides no lift.

 

[Ruprecht]

WeelSpeed = PlaneSpeed + PlaneSpeed

WeelCircumferential = 0,1

WeelSpin = WeelSpeed / WeelCircumferential

WeelFriction = (0,0001 * WeelSpin) * AmountWeels

PlaneThrust = 10000

PlaneAcceleration = PlaneThrust - WeelFriction

if(PlaneAcceleration!=10001){PlaneActualSpeed=PlaneAcceleration}

PlaneMinTakeOffSpeed = 600

if (PlaneActualSpeed == PlaneMinTakeOffSpeed) PlaneTakeOff(1)


lol..

 

[Grobut]

The argument isn't so much the lift. The argument is if the plane could move forward.

if the plane could move forward and reach its take off speed, it would be take off. (with no wind)

Nothing else matters.

Jet engines do not create flow. They create thrust, that is all they do. Plane moving into air creates airflow (this is how player airplanes work)

The real question is:

if a plane was on a treadmill, that moved backwards, would that be enough drag to prevent it from taking off?

The physics say no. The plane would still be able to take off because the drag transfered from the treadmill to the plane from the wheels would not ever be enough to prevent it from taking off anywhere near the speeds it would take to take off.

You are not answering the question though, just poininting out that the question is flawed.

And it is, no argument there.

However, the question does state that we have this magical treadmill that can prevent the plane from just accelerating off of the treadmill, and we have to work with that if we are to answer the question posed, as it is posed.

Its a stupid question, yes, and the treadmill would not work in real life, agreed! but there it is anyway, that magical treadmill, and it is the whole point of the question, and to simply state "the treadmill would not work, the plane would just drive off-of it and take off normally" is not answering the hypothetical situation created.


It would be the same as answering thouse typical math questions like "Train X drives 50 Mph, train Y 40 Mph, where do they collide?" with = They dont! in real life there are side tracks to prevent such stupid collisions!

Its true, but you'd get an F anyway, now woulden't you?


Yes the treadmill is stupid, and woulden't really work, but this hypothetical forces us to pretend that it does, its magic dude! woohoo! good, so what would happen?

 

[Nestor Makhno]

Moz - ur video went all high speed and Minnie Mouse halfway thru - was that deliberate? Anyway I too am getting wound up by people who have no real knowledge of physics talking about, "erm..maybe the wheels would jam" or "Man - that's like a zillion pounds of thrust -are you trying to tell me it gets no where?"

Some of the arguments you put forward aren't very enlightening although you are, of course, right about the bottom line. The plane will not take off. (I guess that's what you were saying - I was too busy laughing towards the end.)

The wording of the inital problem says that the speed of the treadmill magically matches that of the plane. Unlikely though this setup may be, that is what we are given. Therefore the plane is not moving forwards. Arguments about friction of the wheels are spurious as the forward speed of the (untreadmilled) plane is also affected by wheel friction. Any net forward force (resulting in speed) is counteracted by the treadmill - that's what the problem says.

The only force that has any impact on whether a plane takes off is the only upwards force, the lift. Once the lift is greater than the downwards force, the weight, the plane will take off. Wings are a device for converting forward motion relative to the surrounding atmosphere (which can also be considered airflow depending on your point of reference) into upwards force. If there is no nett forward motion, and the initial problem exactly states that there is none, then there is no lift. The plane will never take off.

All other arguments about wheels and so on are red herrings. Once more for the hard of thinking...

1 - No forward motion (not up for debate - term was defined in initial problem)

2 - No forward motion = no lift on wings

3 - No lift = no takeoff

 

[User Name]

Newton's third law.

For every action there is an equal and opposite reaction.

Both the jet's engines, and the belt are actions[FONT=helvetica,geneva,arial]. [/FONT]The are equal, yet opposite. Therefore they neutralize each other. The jet doesn't move. It's that simple.

 

[Conscript]

What if the VTEC kicks in, yo?

 

[radix]

IAS <- indicated air speed. the relevant speed to get lift off.

- this speed is measured by the Pitot tube and indicate the relative AIR speed of the plane at 0m.

IAS = 0 -> no take off.

 

[melipone]

1 - No forward motion (not up for debate - term was defined in initial problem)

2 - No forward motion = no lift on wings

3 - No lift = no takeoff

I agree without air moving over the wings at a certain speed then it won't take off, but the question doesn't really state that the net forward velocity of the plane is 0, only that the speed of the conveyor matches the speed that the plane would be going at without the conveyor, but does the conveyor actually add speed to the wheels and result in speeding the plane up? I don't know i'm starting to think it stays in the same spot but i'm still not totally sure

 

[Grobut]

I agree without air moving over the wings at a certain speed then it won't take off, but the question doesn't really state that the net forward velocity of the plane is 0, only that the speed of the conveyor matches the speed that the plane would be going at without the conveyor, but does the conveyor actually add speed to the wheels and result in speeding the plane up? I don't know i'm starting to think it stays in the same spot but i'm still not totally sure

As i read it, the problem states that we are dealing with a ground speed, but 0 air speed.

In other words, its driving at high speed, but since its on the treadmill, its not actually moving, so our air speed is 0, which gies us 0 lift.


Now in reality its not possible, because the wheels aren't powered, the treadmill would do jack-all-anything, but the problem does state that the treadmill somehow works, so we'll have accept that to answer the question (even though its not really correct).

Its a poorly thought out question, really, but to answer it as the author seems to have intended, the answer would be: No takeoff, as there is no airspeed.

If we answer it by real life physics only, the answer will be: The treadmill doesen't work... and i doubt that is what the author was fishing for.

 

[O'Shannon]

here is a pic(modell) i have made.

so pulling the rope allows you too get the same speed for Plane and treadmill at every time. (the pope represents the forces that are

when you pull the ropes, the plane will move forward and the treadmill will move backward at the same speed right? and the plane will start to fly at a certain speed.

EVERYONE that says the plane wont fly is terribly mistaken

hopefully i could help you guys

 

[Nestor Makhno]

when you pull the ropes, the plande will move forward and the treadmill will move backward at the same speed right? and the plane will start to fly at a certain speed.

You contradict yourself in one paragraph here. The Plane will not reach 'a certain speed' in fact, it will not reach any speed at all 'cos of what you are saying in the first sentence of this paragraph. When the plane is sitting on the ground the source of its forward motion is the fact that its wheels (or skis or whatever) are, as a solid part of the whole plane, trying to move forward relative to the treadmill. This is it does. But the treadmill is moving backwards resulting in nett movement of zero with respect to the ground.

The only way the situation you illustrate would be analogous to the actual problem would be if the top rope were infinitely elastic or the friction of the wheels on the treadmill were zero. A treadmill with zero friction kinda defeats the object as does trying to pull something with an infinitely elastic rope.

Next!

 

[Grobut]

here is a pic i have made.

so pulling the rope allows you too get the same speed for Plane and treadmill at every time

when you pull the ropes, the plande will move forward and the treadmill will move backward at the same speed right? and the plane will start to fly at a certain speed.

EVERYONE that says the plane wont fly is terribly mistaken

hopefully i could help you guys

No, it wont fly if it stays on the treadmill, its wheels would move quite fast, but that does not give it lift, infact it woulden't even lift its tailwheel off the ground such as your picture shows, how could it? theres no air flow there to make it lift.

However, in reallity it would not stay on the treadmill, you'd be pulling it straight off the mill and on to the ground, where it can accelerate and then it would take off.


If we read the problem as "the plane DOES stay on the treadmill somehow", then it cannot possibly lift off, since it has 0 airspeed flowing over the wings.

But if we stick to hard-arse real life physics, it can't stay on the treadmill in the first place, and the whole experiment is debunked, the plane would just drive off the treadmill and onto solid ground, and then accelerate to takeoff speed as usual.