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Interesting Debate for the Physics Savy

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Topic: Interesting Debate for the Physics Savy

Posted By: carl_the_sniper
Subject: Interesting Debate for the Physics Savy
Date Posted: 29 January 2008 at 10:21pm

I'm not sure if this will work on this forum but...

This is a hypothetical situation that has been going around a lot of aviation and RC aviation forums. There has been a lot of debate as to what would happen and I'd like to know what you guys think.

The story goes:

An airplane is on a large treadmill pointing in a reverse direction of the treadmill.

The treadmill has been engineered to match the exact speed of the airplane but backwards. This will mean that in relation to the ground, the airplane will not move and will be moving at 0 miles per hour in relation to the ground)

The question is, will the airplane fly?

Replies:

Posted By: Hysteria
Date Posted: 29 January 2008 at 10:24pm

No.

Lift is created when air is displaced by the wings. If there is no air being displaced by the wings there is no lift, thus the airplane will not fly.

At least, that is my uneducated guess. I did, after all, drop out of Physics after a month or two last semester.

Posted By: usafpilot07
Date Posted: 29 January 2008 at 10:25pm

LOLMYTHBUSTERS?

Posted By: Snake6
Date Posted: 29 January 2008 at 10:26pm

usafpilot07 wrote:

LOLMYTHBUSTERS?

And as far as I see it will not fly...

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Posted By: carl_the_sniper
Date Posted: 29 January 2008 at 10:28pm

Hysteria wrote:

No.Lift is created when air is displaced by the wings. If there is no air being displaced by the wings there is no lift, thus the airplane will not fly.At least, that is my uneducated guess. I did, after all, drop out of Physics after a month or two last semester.

What about the air displaced by the propeller?

usafpilot07 wrote:

LOLMYTHBUSTERS?

Mystbusters is crap. They half ass and screw up so many things.

Posted By: Susan Storm
Date Posted: 29 January 2008 at 10:29pm

Generally speaking, no. Lift is created by the upward suction of the air above the wings, which is created by airspeed.

No airspeed = no lift = no fly.

Some turbine placements might themselves create some lift, but that would be cheating.

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"No society can surely be flourishing and happy, of which the far greater part of the members are poor and miserable."

Posted By: Tolgak
Date Posted: 29 January 2008 at 10:34pm

You explanations are flawed.

The wheels do not generate the power, the prop/jet/rocket/fan does. The only thing you'll accomplish is making the wheels rotate twice as fast. The plane will take off a bit slower than normal, only because the wheels will be contacting the runway which will create considerable drag.

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Posted By: Styro Folme
Date Posted: 29 January 2008 at 10:36pm

carl_the_sniper wrote:

What about the air displaced by the propeller?

usafpilot07 wrote:

LOLMYTHBUSTERS?

Mystbusters is crap. They half ass and screw up so many things.

i dare you to make a better show.

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X

Posted By: Susan Storm
Date Posted: 29 January 2008 at 10:36pm

Tolga is smarter than us.

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"No society can surely be flourishing and happy, of which the far greater part of the members are poor and miserable."

Posted By: Glassjaw
Date Posted: 29 January 2008 at 10:47pm

Tolgak wrote:

You explanations are flawed.

The wheels do not generate the power, the prop/jet/rocket/fan does. The only thing you'll accomplish is making the wheels rotate twice as fast. The plane will take off a bit slower than normal, only because the wheels will be contacting the runway which will create considerable drag.

I was going to say this.

tl:dr, the plane will take off.

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The desire for polyester is just to powerful.

Posted By: Snake6
Date Posted: 29 January 2008 at 10:58pm

Styro Folme wrote:

carl_the_sniper wrote:

What about the air displaced by the propeller?

usafpilot07 wrote:

LOLMYTHBUSTERS?

Mystbusters is crap. They half ass and screw up so many things.

i dare you to make a better show.

Agreed. Mythbusters is very entertaining. That show with Bear Grylls is crap.

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Posted By: Tolgak
Date Posted: 29 January 2008 at 10:59pm

Glassjaw wrote:

I was going to say this.

tl:dr, the plane will take off.

Well, there's no guarantee. It will take considerably more power because of the drag that takes place. However, as more thrust is put out, you will start to overcome that drag and there's a good chance you'll be able to get up (unless your wheels explode or the plane tips the wrong way).

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Posted By: Jack Carver
Date Posted: 29 January 2008 at 11:02pm

Read it again:

carl_the_sniper wrote:

The treadmill has been engineered to match the exact speed of the airplane but backwards. This will mean that in relation to the ground, the airplane will not move

The airplane never moves, so no high-speed air past the wings (other than maybe a little bit if you've got propellers), no lift, no takeoff.

Posted By: carl_the_sniper
Date Posted: 29 January 2008 at 11:04pm

Susan Storm wrote:

Generally speaking, no. Lift is created by the upward suction of the air above the wings, which is created by airspeed.

No airspeed = no lift = no fly.

Some turbine placements might themselves create some lift, but that would be cheating.

Tolgak wrote:

You explanations are flawed.The wheels do not generate the power, the prop/jet/rocket/fan does. The only thing you'll accomplish is making the wheels rotate twice as fast. The plane will take off a bit slower than normal, only because the wheels will be contacting the runway which will create considerable drag.

Exactly, you can't think of it like a car because the wheels don't produce thrust.

My personaly opinion is that it is possible but only on certain aircraft designs with certain engine types. A front mounted prop would work. A rear mounted prop or jet engine would not.

Styro Folme wrote:

carl_the_sniper wrote:

What about the air displaced by the propeller?

usafpilot07 wrote:

LOLMYTHBUSTERS?

Mystbusters is crap. They half ass and screw up so many things.

i dare you to make a better show.

It's not hard to make a show that actually does proper experiments instead of taking short cuts.

Posted By: carl_the_sniper
Date Posted: 29 January 2008 at 11:05pm

Jack Carver wrote:

Read it again:

carl_the_sniper wrote:

The treadmill has been engineered to match the exact speed of the airplane but backwards. This will mean that in relation to the ground, the airplane will not move

The airplane never moves, so no high-speed air past the wings (other than maybe a little bit if you've got propellers), no lift, no takeoff.

The propeller moves more than a little air.

Posted By: Jack Carver
Date Posted: 29 January 2008 at 11:07pm

Ok, so since the jets/prop will continue to give thrust, the plane's speed on the treadmill will rise until the wheels overheat, explode and everybody inside dies as the plane goes belly-down onto a 700 mph giant treadmill.

/hugemanatee

edit: but it only moves a lot of air over a small part of the wing. The plane works because the entire wing causes lift. Your props would have to be spinning like a mofo to cause enough lift to get it in the air.

Posted By: DeTrevni
Date Posted: 29 January 2008 at 11:07pm

Hit the stop button on the treadmill when the plane is going at full tilt. Make that sucker fly. Problem solved.

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Evil Elvis: "Detrevni is definally like a hillbilly hippy from hell"

Posted By: Gatyr
Date Posted: 29 January 2008 at 11:09pm

:(

I was hoping to post it.

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Posted By: carl_the_sniper
Date Posted: 29 January 2008 at 11:14pm

Jack Carver wrote:

edit: but it only moves a lot of air over a small part of the wing. The plane works because the entire wing causes lift. Your props would have to be spinning like a mofo to cause enough lift to get it in the air.

Thus my point though, that it could take off but only if the right aircraft was used.

Posted By: choopie911
Date Posted: 29 January 2008 at 11:20pm

I went over this before: yes it will.

The treadmill matches the tires, yes. No thrust is coming from the tires, it's all in the engines. Yeah the tires will spin hella fast, but it will take off regardless.

Posted By: Jack Carver
Date Posted: 29 January 2008 at 11:28pm

How will it take off? The thrust of the engines is there to provide forward motion, which does not happen in this case. Unless you're also talking about the propellers putting air over the wings, which I don't think is an assumption you can make.

It's like taking a plane and tying the tail to an unmovable building with an unbreakable chain, and gunning the engines. Why would it leave the ground?

Posted By: carl_the_sniper
Date Posted: 29 January 2008 at 11:36pm

Jack Carver wrote:

How will it take off? The thrust of the engines is there to provide forward motion, which does not happen in this case. Unless you're also talking about the propellers putting air over the wings, which I don't think is an assumption you can make.

That is the assumption that I am making.

Why couldn't I make it?

Forward motion is not required for lift.

Jack Carver wrote:

It's like taking a plane and tying the tail to an unmovable building with an unbreakable chain, and gunning the engines. Why would it leave the ground?

That definately would fly.

I am willing to do that with one of my rc airplanes, and youtube it.

Posted By: Benjichang
Date Posted: 29 January 2008 at 11:39pm

Mmmm. Forum theorycrafting.

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irc.esper.net
#paintball

Posted By: Jack Carver
Date Posted: 29 January 2008 at 11:42pm

You can make that assumption, but in my opinion it is not realistic.

My comment was more directed at Choop, who seemed to imply that forward thrust alone was enough. All it will be doing however is overcoming the friction of the wheels, because in the original problem it is stated that the plane will not move.

About the R/C
If you have the cable tied higher than the plane, and your weight to power ratio is low enough, it will definitely leave the ground.
If you tie the cable at the same level as the plane, actually it might still work because of the whole "prop putting air over the styrofoam wings" thing, but I don't think that would work with a cessna.

Posted By: carl_the_sniper
Date Posted: 29 January 2008 at 11:47pm

Jack Carver wrote:

You can make that assumption, but in my opinion it is not realistic.My comment was more directed at Choop, who seemed to imply that forward thrust alone was enough. All it will be doing however is overcoming the friction of the wheels, because in the original problem it is stated that the plane will not move.

I don't see how it isn't realistic under the correct conditions. What about a biplane with a small wingspan and a large, powerfull prop?

That's not what I understood from choop's statement but if that is what he meant, than you are correct with that.

Jack Carver wrote:

About the R/CIf you have the cable tied higher than the plane, and your weight to power ratio is low enough, it will definitely leave the ground.If you tie the cable at the same level as the plane, actually it might still work because of the whole "prop putting air over the styrofoam wings" thing, but I don't think that would work with a cessna.

So then yes, It is possible depending on the aircraft.

Posted By: Jack Carver
Date Posted: 29 January 2008 at 11:57pm

Well, I don't have the knowledge to do any kind of calculations with a small biplane with a big prop, but it would be interesting to find out just how light it'd have to be and how much power you would need.
I would still like to see the video some time :)

Posted By: scotchyscotch
Date Posted: 29 January 2008 at 11:58pm

If as you said the speed relating to the ground is 0 then assuming the air around the plane is still (excluding that created by the prop) Then the air speed will be 0.
I don't think that the prop could generate enough "wind" to provide more than negligable lift. On this assumption the plane will not fly.

Basicly until the plane goes faster than the treadmill and moves through the air then no lift will come about.

Don't argue accept it.

Posted By: TippmannBro
Date Posted: 29 January 2008 at 11:59pm

carl_the_sniper wrote:

IThis will mean that in relation to the ground, the airplane will not move and will be moving at 0 miles per hour in relation to the ground)

If the airplane is not moving in relation to the ground, then it isn't moving in relation to the air, either. The airplane will not fly.

Any thrust from any engine is exerted in a horizontal direction, not a vertical direction. Thrust from an engine alone is not enough to make the airplane fly- it must have lift from the wings (exception: high performance aircraft such as the F-15 or F-22).

The lift that makes an airplane fly comes from air moving over the wings. If the wings aren't moving in relation to the ground or the air, then how does it fly?

Side note- the propwash coming from the propeller and flowing over the wing is not enough to make the plane fly. There isn't enough moving air, and it is not fast enough.

The airplane will not fly at all.

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WAR EAGLE!!!

Posted By: Jack Carver
Date Posted: 30 January 2008 at 12:00am

scotchyscotch wrote:

Don't argue accept it.

Not exactly a popular motto around here. They want double integrals, pressure gradients, differential equations, tests for every value of altitude you could try this at until you prove that the lift is negligible.

Posted By: scotchyscotch
Date Posted: 30 January 2008 at 12:03am

carl_the_sniper wrote:

That is the assumption that I am making.

Why couldn't I make it?

Forward motion is not required for lift.

It's all relative. Relative to the ground forward motion is not needed for lift. But the ground is irrelevent in this question, planes don't seem to need it to fly.
All you need is air moving over the wings. Wich in this example you don't have.

Im surprised that people who fly planes frequently would even think this would work.

Posted By: Tolgak
Date Posted: 30 January 2008 at 12:03am

Jack Carver wrote:

How will it take off? The thrust of the engines is there to provide forward motion, which does not happen in this case.

It will. Think of it this way:

Let's say that the wheels are perfect, in that there is no friction in their axles, but there is friction between the ground and the tires.

With a car, when those wheels are rotated, it is done by the engine. On a treadmill with frictionless axles, this will pull the belt in the opposite direction, and the car will go nowhere.

In a plane, no thrust is given by the wheels. In a system of frictionless axles, a treadmill without a motor will not rotate backwards. The force of the air on the propellers is what pushes a plane forwards; and is, in effect, independent of the treadmill.

So, add a motor and add friction.

The car will not change, because the speed of the belt is adjusting for the speed of the car. With or without a motor, the car will stay in its place.

A plane will, at first, be fighting the treadmill. But once it's up to power, the friction will slowly be overcome, and the weight will be much less on the tires as speed slowly increases. Thus, the friction between the belt is reduced and the plane will be less and less affected by the backwards motion of the belt. The right plane will then be able to take off.

If you want to take this one step further, we can add the belt's effect on the air around it. A belt moving fast enough will certainly move the air in the plane's favor. It wont be much, but it'll definitely take a load off the plane.

If the belt theory was entirely true, it would mean that in order a plane to fly, its wheels would have to be in contact with a stationary surface. That's not flying. That's called driving.

Unless you're also talking about the propellers putting air over the wings, which I don't think is an assumption you can make.

In pretty much every plane with a puller prop (prop in front of the engine), the prop blows air over the wings. Even with the engine in back, it sucks air over the entire surface of the vehicle. This creates a little bit of lift.

It's like taking a plane and tying the tail to an unmovable building with an unbreakable chain, and gunning the engines.

I see no such constraints here. Even so, and even with powerful enough full-size planes, lift can still be created here.

Why would it leave the ground?

1) It has an engine that is independent from the ground.
2) It has wings.

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Posted By: carl_the_sniper
Date Posted: 30 January 2008 at 12:11am

Jack Carver wrote:

Well, I don't have the knowledge to do any kind of calculations with a small biplane with a big prop, but it would be interesting to find out just how light it'd have to be and how much power you would need. I would still like to see the video some time :)

The point is, you could do it.

The rc airplane that I am building would definately be powerfull enough to do that. My current built ones may not.

scotchyscotch wrote:

carl_the_sniper wrote:

That is the assumption that I am making. Why couldn't I make it? Forward motion is not required for lift.

It's all relative. Relative to the ground forward motion is not needed for lift. But the ground is irrelevent in this question, planes don't seem to need it to fly.All you need is air moving over the wings. Wich in this example you don't have.

Im surprised that people who fly planes frequently would even think this would work.

Yes you do, you have a propellor (assuming that a prop plane is being used) that blows air across the wing.

You say that forward motion is not required to fly but that without it, there is no air over the wings to produce lift. This means that no plane would ever fly, make up your mind as to which it is.

Posted By: Jack Carver
Date Posted: 30 January 2008 at 12:17am

Yes, I'll admit you could do it, but for all we know the numbers might work out so you'd need a power to weight ratio that is just not available today.

Tolgak wrote:

It's like taking a plane and tying the tail to an unmovable building with an unbreakable chain, and gunning the engines.

I see no such constraints here.

That's where we're just having a different interpretation of the situation. In anticipation for precipitation, ya know...

Posted By: carl_the_sniper
Date Posted: 30 January 2008 at 12:19am

TippmannBro wrote:

If the airplane is not moving in relation to the ground, then it isn't moving in relation to the air, either.

No, it is moving in relation to the air as well as in relation to the treadmill. This is a non-issue and isn't up for debate here as it is basic physics.

TippmannBro wrote:

The airplane will not fly.Any thrust from any engine is exerted in a horizontal direction, not a vertical direction. Thrust from an engine alone is not enough to make the airplane fly- it must have lift from the wings (exception: high performance aircraft such as the F-15 or F-22).

Thrust is exerted in a horizontal direction, yes. However, we are no talking about thrust, we are talking about lift.

Lift is produced from air blowing over the wings... thus the propellor.

TippmannBro wrote:

The lift that makes an airplane fly comes from air moving over the wings. If the wings aren't moving in relation to the ground or the air, then how does it fly?Side note- the propwash coming from the propeller and flowing over the wing is not enough to make the plane fly. There isn't enough moving air, and it is not fast enough.The airplane will not fly at all.

But they are moving in relation to the air.

The air from the propellor being strong enough depends on the plane and engine.

Posted By: carl_the_sniper
Date Posted: 30 January 2008 at 12:22am

Jack Carver wrote:

Yes, I'll admit you could do it, but for all we know the numbers might work out so you'd need a power to weight ratio that is just not available today.

Tolgak wrote:

It's like taking a plane and tying the tail to an unmovable building with an unbreakable chain, and gunning the engines.I see no such constraints here.

That's where we're just having a different interpretation of the situation. In anticipation for precipitation, ya know...

Posted By: Tolgak
Date Posted: 30 January 2008 at 12:23am

Jack Carver wrote:

Yes, I'll admit you could do it, but for all we know the numbers might work out so you'd need a power to weight ratio that is just not available today.

An F-22 has enough power to take off vertically.

It's not that we can't make more planes that have the power to take off without lift, it's that they often aren't needed/are too expensive to make.

Tolgak wrote:

It's like taking a plane and tying the tail to an unmovable building with an unbreakable chain, and gunning the engines.

I see no such constraints here.

That's where we're just having a different interpretation of the situation. In anticipation for precipitation, ya know...

It's not up to interpretation. There is nothing forcing the plane to be stationary. All the treadmill is doing is making it harder, not impossible.

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Posted By: Tolgak
Date Posted: 30 January 2008 at 12:26am

carl_the_sniper wrote:

Jack Carver wrote:

Yes, I'll admit you could do it, but for all we know the numbers might work out so you'd need a power to weight ratio that is just not available today.

I bet this could:

http://www.turbinetoucan.com/ - http://www.turbinetoucan.com/

That is a biplane that has over a 1:1 thrust to weight ratio. This means that it can do things that no other aircraft can. Mainly, the ability to hover vertically.

A few other aircraft have that capability. But I made that point in an earlier post.

It is absolutely orgasmic to a pilot.

I just started flight training today

YOU GET IT, I FLY

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Posted By: Jack Carver
Date Posted: 30 January 2008 at 12:27am

Yes there was. Original post:

The treadmill has been engineered to match the exact speed of the airplane but backwards. This will mean that in relation to the ground, the airplane will not move and will be moving at 0 miles per hour in relation to the ground)

And about the F-22, that's a case where the thrust is all contributing to lift. In the case we are talking about, the thrust pushes air over a wing, which provides lift. Energy is lost, because air will be going over the top and bottom of the plane, and over and under the wings at a distance where it can not contribute to the lift. It's a separate situation.

Posted By: carl_the_sniper
Date Posted: 30 January 2008 at 12:29am

Tolgak wrote:

carl_the_sniper wrote:

Jack Carver wrote:

Yes, I'll admit you could do it, but for all we know the numbers might work out so you'd need a power to weight ratio that is just not available today.

I bet this could:

http://www.turbinetoucan.com/ - http://www.turbinetoucan.com/

That is a biplane that has over a 1:1 thrust to weight ratio. This means that it can do things that no other aircraft can. Mainly, the ability to hover vertically. A few other aircraft have that capability. But I made that point in an earlier post.
It is absolutely orgasmic to a pilot. I just started flight training today

YOU GET IT, I FLY

An F-22 could never attain a hover. It is too unstable.

What kind of flight training?

I will be starting training for my commerical pilot's license next year.

Posted By: scotchyscotch
Date Posted: 30 January 2008 at 12:37am

carl_the_sniper wrote:

The point is, you could do it.

The rc airplane that I am building would definately be powerfull enough to do that. My current built ones may not.

scotchyscotch wrote:

carl_the_sniper wrote:

That is the assumption that I am making. Why couldn't I make it? Forward motion is not required for lift.

It's all relative. Relative to the ground forward motion is not needed for lift. But the ground is irrelevent in this question, planes don't seem to need it to fly.All you need is air moving over the wings. Wich in this example you don't have.

Im surprised that people who fly planes frequently would even think this would work.

If you were to blow air at a stationary plane then it could produce lift with now forward motion. All i am saying is that in the circumstances given the plane would not fly as there is no movement of the plane relative to the air. (disregarding that from the prop or whatever)

It's basic physics for a reason.

The model plane you suggested can only attain a hover whilst pointing verticly upwards. The plane in the aforementioned scenario is not. So, whats your point?

Posted By: Tolgak
Date Posted: 30 January 2008 at 12:38am

carl_the_sniper wrote:

An F-22 could never attain a hover. It is too unstable.

It can still accelerate in an upwards direction.

What kind of flight training?

PPL

I will be starting training for my commerical pilot's license next year.

Jack Carver wrote:

Yes there was. Original post:

The treadmill has been engineered to match the exact speed of the airplane but backwards. This will mean that in relation to the ground, the airplane will not move and will be moving at 0 miles per hour in relation to the ground)

Correct, but what you are saying does NOT hold the plane back indefinitely. I think I need to post a diagram to illustrate my point.

And about the F-22, that's a case where the thrust is all contributing to lift. In the case we are talking about, the thrust pushes air over a wing, which provides lift. Energy is lost, because air will be going over the top and bottom of the plane, and over and under the wings at a distance where it can not contribute to the lift. It's a separate situation.

Just saying that there are a few planes out there with a power to weight ratio enough to lift a plane that's tied down, either by pure engine power or by blowing air over the wings.

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Posted By: carl_the_sniper
Date Posted: 30 January 2008 at 12:45am

scotchyscotch wrote:

It's basic physics for a reason.

The model plane you suggested can only attain a hover whilst pointing verticly upwards. The plane in the aforementioned scenario is not. So, whats your point?

Yes, there is movement of the plane relative to the air. That means nothing to this situation though.

The plane I suggested was not a model. My point was that it has and over 1:1 thrust to weight ratio and that it could probably attain flight in this instance.

Posted By: scotchyscotch
Date Posted: 30 January 2008 at 1:04am

I still don't follow.
I might be missing something because i'm seriously tired

It doesn't matter what thrust to wieght ratio a plane has if you stick to the scenario given then I don't see how it could fly.

Posted By: carl_the_sniper
Date Posted: 30 January 2008 at 1:09am

scotchyscotch wrote:

I still don't follow. I might be missing something because i'm seriously tired

It doesn't matter what thrust to wieght ratio a plane has if you stick to the scenario given then I don't see how it could fly.

We have allready concluded that it is possible with the right aircraft.

I was merely providing an aircraft that I guessed could possibly do it. More of an example than anything.

Posted By: Tolgak
Date Posted: 30 January 2008 at 1:44am

I'm missing an "=0" after Force of Gear on Treadmill.

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Posted By: Hysteria
Date Posted: 30 January 2008 at 1:56am

Shouldn't F(system on plane) = 0?

According to Newton's third law, F(prop on air) and F(air on prop) cancel each other out.

I think (See: dropped out of Physics

Posted By: carl_the_sniper
Date Posted: 30 January 2008 at 2:01am

Tolgak:

Forgive me if I misunderstoof that but that doesn't seem to account for lift.

The plane will not move in the direction that the air is pushing it (in relation to the ground). The plane will not move horizontally at all. The idea is if it will move vertically or not, we know that it won't move horizontally at all.

From what I saw (though I could have misread) you provided an incorrect explanation as to why you think the plane would move horizontally forward. Furthermore, that is not even the topic at all. The topic is whenever or not lift will be attained.

Posted By: Tolgak
Date Posted: 30 January 2008 at 2:11am

Hysteria wrote:

Shouldn't F(system on plane) = 0?

No.

According to Newton's third law, F(prop on air) and F(air on prop) cancel each other out.

Think of it this way. You are at a wall, standing on a skateboard. In accordance with the 3rd law, when you put a force on the wall, the wall puts a force on you. Since you are not bound to anything, the force the wall exerts on you is what pushes you away from it.

The same applies when you're pushing another person on a skateboard. In this case, the forces you exert on each other separate you, even if you're the only one doing the pushing.

The same concept transfers over to propellers and air.

I think (See: dropped out of Physics

carl_the_sniper wrote:

Tolgak:

Forgive me if I misunderstoof that but that doesn't seem to account for lift.

The plane will not move in the direction that the air is pushing it (in relation to the ground). The plane will not move horizontally at all. The idea is if it will move vertically or not, we know that it won't move horizontally at all.

Most planes get their lift when moving horizontally, and the treadmill idea is to counter that horizontal movement. The example definitely applies.

From what I saw (though I could have misread) you provided an incorrect explanation as to why you think the plane would move horizontally forward.

The Force of the air on the plane will make it move forward, that's how propulsion works in the case of flight.

Furthermore, that is not even the topic at all.

It absolutely is the topic.

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Posted By: carl_the_sniper
Date Posted: 30 January 2008 at 2:21am

"Most planes get their lift when moving horizontally, and the treadmill idea is to counter that horizontal movement. The example definitely applies.

The Force of the air on the plane will make it move forward, that's how propulsion works in the case of flight.

Yes, but I have already said that we are not talking about thrust, we are talking about lift.

It absolutely is the topic.

From the last point, it seems that you aren't grasping the topic properly. We are talking about resultant lift, not thrust and therefore, it is not the topic.

Posted By: scotchyscotch
Date Posted: 30 January 2008 at 2:56am

Tolgak,The diagram did'nt do much for me. I know what you mean.

However, Read the question you were asked. "The treadmill has been engineered so that the plane will not move relative
to the ground" or words to that effect. I see your logic but in this case the plane will not fly. (maybe a fault in the scenario)

I may be mistaken but i think you've missed the point.

Posted By: WGP guy2
Date Posted: 30 January 2008 at 6:21am

Sorry I skipped all the post because I don't have time.

The answer is that the airplane WILL move forward and it WILL takeoff provided the wheels can take the stress of a speed equal to or greater than 2 * Vr. That the airplane will not move forward is absurd and you don't deserve a pilot's license if you think that, it's the fundamentals.

Posted By: Tolgak
Date Posted: 30 January 2008 at 8:22am

scotchyscotch wrote:

Tolgak,The diagram did'nt do much for me. I know what you mean.

However, Read the question you were asked. "The treadmill has been engineered so that the plane will not move relative
to the ground" or words to that effect.

My whole purpose in my posts above is to show that you cannot engineer such a treadmill because the force of propulsion, unlike land vehicles, has nothing to do with the ground. The only way to keep a powered plane at zero ground speed is to either literally tie it to the ground, or provide enough AIR flow in the opposite direction. Even so, it will have lift and be able to take off.

I see your logic but in this case the plane will not fly. (maybe a fault in the scenario)

I may be mistaken but i think you've missed the point.

I understand the point entirely. You (and the others) are just not understanding the physics of flight and the idea of relative motion.

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Posted By: Tolgak
Date Posted: 30 January 2008 at 8:34am

carl_the_sniper wrote:

"Most planes get their lift when moving horizontally, and the treadmill idea is to counter that horizontal movement. The example definitely applies.

What I understood is that you said that basically, the plane would have resultant forward movement even with the treadmill acting the other way. Isin't that basically what you said? If I understood it correctly, than not only does the example not apply, but it is also wrong.

That's what I'm saying, and that's what the Mythbusters are going to test. Because the resultant force of the system is independent of the ground, the plane will achieve forward motion despite the treadmill going the other way.

To say the treadmill will keep the plane on the ground is to think that the wheels are what propels airplanes.

The Force of the air on the plane will make it move forward, that's how propulsion works in the case of flight.

Yes, but I have already said that we are not talking about thrust, we are talking about lift.

Taking off in an airplane has to do with both. Without thrust you've got a glider, and without lift you've got a car; neither of which can take off without help. A car on the runway will stay put relative to the earth. A glider on the runway will move backwards.

It absolutely is the topic.

From the last point, it seems that you aren't grasping the topic properly. We are talking about resultant lift, not thrust and therefore, it is not the topic.

In conditions of zero windspeed (the conditions required for such a test), you will not get lift without forward motion, which requires thrust. Lift doesn't apply until after you begin moving forward relative to the air, and that can't be explained without explaining why an engine that propels through contact with the air is independent of whatever is happening on the ground below it.

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Posted By: Jack Carver
Date Posted: 30 January 2008 at 9:38am

WGP guy2 wrote:

Sorry I skipped all the post because I don't have time.

The answer is that the airplane WILL move forward and it WILL takeoff provided the wheels can take the stress of a speed equal to or greater than 2 * Vr. That the airplane will not move forward is absurd and you don't deserve a pilot's license if you think that, it's the fundamentals.

Dude, read the friggin question. The treadmill is not stuck at speed 10, it's

"engineered to match the exact speed of the airplane but backwards. This will mean that in relation to the ground, the airplane will not move and will be moving at 0 miles per hour in relation to the ground"

The friction from the wheels is stopping the plane from going forward. It's an absurd experiment anyway, those puppies are gonna be cruisin.

Posted By: Tolgak
Date Posted: 30 January 2008 at 9:45am

Jack Carver wrote:

Dude, read the friggin question. The treadmill is not stuck at speed 10, it's

He's not saying that.

"engineered to match the exact speed of the airplane but backwards. This will mean that in relation to the ground, the airplane will not move and will be moving at 0 miles per hour in relation to the ground"

This is wrong. Only land vehicles can be completely stopped from movement in this manner.

The friction from the wheels is stopping the plane from going forward. It's an absurd experiment anyway, those puppies are gonna be cruisin.

The friction of the tires will hold back the plane but will not always prevent it from taking off. If the wheels don't fail, the plan can and should take off.

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Posted By: carl_the_sniper
Date Posted: 30 January 2008 at 11:45am

Crap sorry.

It was late last night and I actually did miss your point.

It depends on how you look at it and what conditions are factored in.

If it is under enough friction than no, it will not move forward but it will still fly.

If it is not under enough friction, than it will move forward.

It all depends on the engineering of the wheels.

For the purposes of this, let's follow the rules of the situation from now on. Meaning that the plane will not go forward because the wheels under enough friction. not to.

Also, mythbusters is a far from reliable show. Take the results with a grain of salt.

Posted By: Tolgak
Date Posted: 30 January 2008 at 12:08pm

carl_the_sniper wrote:

Crap sorry.

It was late last night and I actually did miss your point.

It depends on how you look at it and what conditions are factored in.

If it is under enough friction than no, it will not move forward but it will still fly.

Wings need proper air flow over them to produce lift. The air flow provided by an engine is pretty much never enough on manned planes. A plane has to be moving in relation to the air in order for this flow to happen. It takes a wind tunnel or a hurricane to achieve this.

Because the wind is static in this situation, the only moving environment being the treadmill and the air being moved by the engine, it will not take off.

If it is not under enough friction, than it will move forward.

Correct.

It all depends on the engineering of the wheels.

And the thrust of the engine, lightness of the airplane, and stall speed.

For the purposes of this, let's follow the rules of the situation from now on. Meaning that the plane will not go forward because the wheels under enough friction. not to.

It wouldn't take off. This is because the rules are unrealistic.

Also, mythbusters is a far from reliable show. Take the results with a grain of salt.

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Posted By: carl_the_sniper
Date Posted: 30 January 2008 at 12:41pm

Tolgak wrote:

carl_the_sniper wrote:

Crap sorry.

It was late last night and I actually did miss your point.

It depends on how you look at it and what conditions are factored in.

If it is under enough friction than no, it will not move forward but it will still fly.
Wings need proper air flow over them to produce lift. The air flow provided by an engine is pretty much never enough on manned planes. A plane has to be moving in relation to the air in order for this flow to happen. It takes a wind tunnel or a hurricane to achieve this. Because the wind is static in this situation, the only moving environment being the treadmill and the air being moved by the engine, it will not take off.
If it is not under enough friction, than it will move forward.
 Correct.
It all depends on the engineering of the wheels.
And the thrust of the engine, lightness of the airplane, and stall speed.
For the purposes of this, let's follow the rules of the situation from now on. Meaning that the plane will not go forward because the wheels under enough friction. not to.
It wouldn't take off. This is because the rules are unrealistic.
Also, mythbusters is a far from reliable show. Take the results with a grain of salt.

But can we admit that is technically possible though doubtable with any of today's aircraft?

Posted By: Tolgak
Date Posted: 30 January 2008 at 12:49pm

Yes.

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Posted By: Bunkered
Date Posted: 30 January 2008 at 1:21pm

/me lifts off vertically in a Harrier jet.

What was the problem again?

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Posted By: Glassjaw
Date Posted: 30 January 2008 at 2:56pm

http://www.straightdope.com/columns/060203.html

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The desire for polyester is just to powerful.

Posted By: Project Irene
Date Posted: 30 January 2008 at 4:13pm

I've read the articles, read this thread, and I say the plane does not fly.

IF you believe that you were an observer of the plane on the treadmill and you notice the plane staying still, it WILL NOT fly.

IF you believe that you were an observer of the plane on the treadmill and you notice the plane move forward relative to the ground, it WILL fly, barring a suitable flight speed for sufficient lift.

What influences what you believe is the problem statement. It states that the conveyor matches the speed of the plane. Say the speed of the plane relative to the treadmill is 200 mph. The treadmill matches this, the speed of the treadmill is 200 mph relative to the plane, in the opposite direction. So the speed of the plane relative to the ground AND THE FREESTREAM VELOCITY of the air is 0. No airflow over the wing means no lift (barring special case thrust systems where air could be forced over the wing creating lift).

Posted By: Pezzer
Date Posted: 30 January 2008 at 5:14pm

Projene, you are wrong man. The plane moves FOWARD relative to the ground the treadmill is on. There is NOTHING THAT WILL KEEP THE PLANE FROM MOVING FORWARD. STOP THINKING LIKE YOU ARE DRIVING A CAR, THE FORCES ARE NOT THE SAME.

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Suck, sqeeze, bang, blow, and GO!

Posted By: Hairball!!!
Date Posted: 30 January 2008 at 5:17pm

The way I see it, nothing is really stopping the plane from moving forward, except drag from the wheels. Assuming such an absurd experiment, I'm assuming they are frictionless, and don't matter. Depending on the length of the treadmill, it'll either drive right off the end or gather enough speed to take off.

Posted By: Ilford Rule
Date Posted: 30 January 2008 at 5:19pm

The plane will take off, but only because the experiment is flawed. If the plane were held in place in the forward-back plane, but free in the up-down, it would not take off simply because the air moved by the prop is not nearly enough to generate lift. This is why planes have a wingspan larger than the prop diameter. However, because the plane will move forward, it will take off. Because the force moving the plane forward is completely unrelated to the wheels (whose only purpose is to allow the plane to move on the ground), the body of the aircraft will still be moving forward, its wheels rotating twice as fast. The treadmill will have no effect whatsoever in a frictionless system.

EDIT: I now realize that others have said this. Oh well.

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CPro (w/ polished internals)
14" Bigshot
BT SBS
Various Rails
NcSTAR D4B
Macro
AA 68/45

CCI Phantom
45 Grips

Posted By: carl_the_sniper
Date Posted: 30 January 2008 at 5:21pm

Pezzer wrote:

Projene, you are wrong man. The plane moves FOWARD relative to the ground the treadmill is on. There is NOTHING THAT WILL KEEP THE PLANE FROM MOVING FORWARD. STOP THINKING LIKE YOU ARE DRIVING A CAR, THE FORCES ARE NOT THE SAME.

Unless there is enough friction produced from the wheels.

Possible though definately not likely.

Posted By: Project Irene
Date Posted: 30 January 2008 at 5:23pm

carl_the_sniper wrote:

I'm not sure if this will work on this forum but...

This is a hypothetical situation that has been going around a lot of aviation and RC aviation forums. There has been a lot of debate as to what would happen and I'd like to know what you guys think.

The story goes:

An airplane is on a large treadmill pointing in a reverse direction of the treadmill.

The treadmill has been engineered to match the exact speed of the airplane but backwards. This will mean that in relation to the ground, the airplane will not move and will be moving at 0 miles per hour in relation to the ground)

The question is, will the airplane fly?

If the statement in bold is true for the problem statement, then the freestream air velocity is 0, and barring any special propulsion generating lift via induced airflow, the plane will not lift off of the ground. I'm a senior in aerospace engineering at Auburn, I'll see if I can speak to one of my professors about this tomorrow. I will come back and tell you how stupid I am if he proves to me it will take off.

Oh, and pezzer, thanks for typing in bold caps. I wouldn't be able to read that without it.

Posted By: Jack Carver
Date Posted: 30 January 2008 at 5:23pm

Yeah nothing will keep the plane from moving forward except the statement in the first post that says this is a given for the problem. I think we've pretty much beat this horse to death and back.

Posted By: Pezzer
Date Posted: 30 January 2008 at 5:25pm

carl_the_sniper wrote:

Unless there is enough friction produced from the wheels.

Possible though definately not likely.

In that case the plane wouldn't take off on the ground anyway and wouldn't really be a plane, would it?

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Suck, sqeeze, bang, blow, and GO!

Posted By: Ilford Rule
Date Posted: 30 January 2008 at 5:28pm

Pezzer wrote:

In that case the plane wouldn't take off on the ground anyway and wouldn't really be a plane, would it?

Tomato tomahto

My plane is SO good, it's not even a plane! BEAT THAT!

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CPro (w/ polished internals)
14" Bigshot
BT SBS
Various Rails
NcSTAR D4B
Macro
AA 68/45

CCI Phantom
45 Grips

Posted By: WGP guy2
Date Posted: 30 January 2008 at 5:31pm

Ilford Rule wrote:

Pezzer wrote:

In that case the plane wouldn't take off on the ground anyway and wouldn't really be a plane, would it?

Tomato tomahto

My plane is SO good, it's not even a plane! BEAT THAT!

Uhh...what?

Posted By: Ilford Rule
Date Posted: 30 January 2008 at 5:32pm

YOUR FACE!

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CPro (w/ polished internals)
14" Bigshot
BT SBS
Various Rails
NcSTAR D4B
Macro
AA 68/45

CCI Phantom
45 Grips

Posted By: Reb Cpl
Date Posted: 30 January 2008 at 5:40pm

I'm going to wait for the Mythbusters special to see for myself.

The fact that carl doesn't like them raises my respect for them.

Posted By: Ilford Rule
Date Posted: 30 January 2008 at 5:41pm

I like that show. It's a TV show, nothing more, but it's very entertaining I find. Are they actually testing this or is it just something people want to see tested?

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CPro (w/ polished internals)
14" Bigshot
BT SBS
Various Rails
NcSTAR D4B
Macro
AA 68/45

CCI Phantom
45 Grips

Posted By: carl_the_sniper
Date Posted: 30 January 2008 at 6:01pm

Reb Cpl wrote:

I'm going to wait for the Mythbusters special to see for myself. The fact that carl doesn't like them raises my respect for them.

Carl likes accurate data and properly done experiments.

Posted By: Ilford Rule
Date Posted: 30 January 2008 at 6:07pm

... it's a TV show mang...

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CPro (w/ polished internals)
14" Bigshot
BT SBS
Various Rails
NcSTAR D4B
Macro
AA 68/45

CCI Phantom
45 Grips

Posted By: Reb Cpl
Date Posted: 30 January 2008 at 6:07pm

carl_the_sniper wrote:

Reb Cpl wrote:

I'm going to wait for the Mythbusters special to see for myself. The fact that carl doesn't like them raises my respect for them.

Carl likes accurate data and properly done experiments.

Quote in PM several instances of poorly done experiments, as well as cite for me data taken from other tests which have produced results different than those on MB. THEN I'll have a bit of respect for apparently the only guy on the forum with serious complaints about them.

I say do it in PM so I'm not responsible for derailing an interesting thread.

Posted By: carl_the_sniper
Date Posted: 30 January 2008 at 6:22pm

I'll do it later, I have noticed a few myself as well as many noticed online.

I will be watching tonight though. What channel/time is mythbusters on?

Posted By: Bunkered
Date Posted: 31 January 2008 at 7:34am

I'll go one further to say that I used to be of the opinion that Mythbusters is a sham, until Carl agreed with me.

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Posted By: FROG MAN
Date Posted: 31 January 2008 at 8:54am

any one who thinks the plane wont take off, either doesn't understand, or is a retard

watch the new the mythbusters, surprisingly they do a good job.

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<1 meg sig = bad>

Posted By: Jack Carver
Date Posted: 31 January 2008 at 9:13am

It depends on the episode for me. Also, sometimes it seems they just don't have the time/budget to explore every option, so they have to settle for what they think would be the most likely. It's not 100% thorough every time.

And thanks for that unsupported opinion FM.

Posted By: Tolgak
Date Posted: 31 January 2008 at 9:16am

Jack Carver wrote:

It depends on the episode for me. Also, sometimes it seems they just don't have the time/budget to explore every option, so they have to settle for what they think would be the most likely. It's not 100% thorough every time.

And thanks for that unsupported opinion FM.

I support his opinion.

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Posted By: usafpilot07
Date Posted: 31 January 2008 at 10:46am

It worked on mythbusters...sorta

Posted By: Man Bites Dog
Date Posted: 31 January 2008 at 10:46am

carl_the_sniper wrote:

Reb Cpl wrote:

I'm going to wait for the Mythbusters special to see for myself. The fact that carl doesn't like them raises my respect for them.

Carl likes accurate data and properly done experiments.

If only they realized when they did mess up data or the experiment, and would go back and do a series of correction episodes each season.

Oh wait, they do.

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Posted By: reifidom
Date Posted: 31 January 2008 at 10:51am

I'm beginning to understand. My issue was this:

The situation is worded in such a way that I was thinking the plane was somehow held stationary by the motion of the conveyor in relation to the surrounding air and the ground around the conveyor. Therefore I couldn't see how it could possibly fly. I have a creeping feeling this was intentional in the wording.

The actual case is that the conveyor or whatever is incapable of making the plane stand still in relation to the ground, and thus the air relative to the ground, and incapable of preventing it from gaining enough forward movement to achieve lift-off. The wheels spin freely and in an ideal situation cannot unduely affect the acceleration of the plane.

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Posted By: Tolgak
Date Posted: 31 January 2008 at 11:01am

reifidom wrote:

I'm beginning to understand. My issue was this:

The situation is worded in such a way that I was thinking the plane was somehow held stationary by the motion of the conveyor in relation to the surrounding air and the ground around the conveyor. Therefore I couldn't see how it could possibly fly. I have a creeping feeling this was intentional in the wording.

The actual case is that the conveyor or whatever is incapable of making the plane stand still in relation to the ground, and thus the air relative to the ground, and incapable of preventing it from gaining enough forward movement to achieve lift-off. The wheels spin freely and in an ideal situation cannot unduely affect the acceleration of the plane.

HOORAY! RATIONALITY STRIKES AGAIN!!!

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Posted By: reifidom
Date Posted: 31 January 2008 at 11:08am

I knew something wasn't quite right as I was thinking it over, and I wanted to piece out just what it was before I spoke.

I hope the way I put it might shine a light for somebody else.

And maybe not quite so many

's.

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Posted By: Project Irene
Date Posted: 31 January 2008 at 4:35pm

Yeah, my problem was the problem statement saying that speed relative to the ground is 0. It can not fly with speed relative to the ground equaling 0. The plane obviously moved down the runway and took off normally, with the wheels spinning something fierce.

Posted By: scotchyscotch
Date Posted: 31 January 2008 at 6:21pm

Thats what I have been saying.

The question is flawed.