Plane on a treadmill argument...

[Drew Dowdell]

I think I worded it wrong...that should be "speed of the plane" not "wheel speed"

Nick worded the question incorrectly the first time... this is his update.

[Drew Dowdell]

So if I get on my mom's treadmill and the speedometer says 6 mph, I'm really running at 12 mph?  Uh...

if you get on your mom's treadmill and the speedometer say 6 mph, but relative to the ground under the treadmill you are moving at 6 mph, then your legs are running at 12mph.

[Drew Dowdell]

I can't believe we're debating the "Theory of Relativity" on C&G.

[the_yellow_dart]

OK, that is a completely different situation then what I was picturing then. If the treadmill is only going as fast as the plane's speed, in reverse, then the plane would just need to get the wheels going twice as fast as normal and it would take off. We were arguing different situations.

[ocnblu]

But I don't have a treadmill under my wheels to counteract the thrust of the rocket which would turn my wheels, but no faster than the treadmill could turn. Or do I?

Isn't a rocket a different principle than a winged aircraft? Doesn't a rocket primarily fly on thrust? When it runs out of fuel, doesn't it plummet to the ground?

[Drew Dowdell]

But I don't have a treadmill under my wheels to counteract the thrust of the rocket which would turn my wheels, but no faster than the treadmill could turn.  Or do I?

Isn't a rocket a different principle than a winged aircraft?  Doesn't a rocket primarily fly on thrust?  When it runs out of fuel, doesn't it plummet to the ground?

I feel like I need to 'splain this in person lucy.

[Drew Dowdell]

But I don't have a treadmill under my wheels to counteract the thrust of the rocket which would turn my wheels, but no faster than the treadmill could turn.  Or do I?

Does the tread mill really counter act the thrust of the rocket if your truck is in neutral and the brakes are off?

Edited June 26, 2006 by Oldsmoboi

[Drew Dowdell]

But I don't have a treadmill under my wheels to counteract the thrust of the rocket which would turn my wheels, but no faster than the treadmill could turn.  Or do I?

Isn't a rocket a different principle than a winged aircraft?  Doesn't a rocket primarily fly on thrust?  When it runs out of fuel, doesn't it plummet to the ground?

the difference between winged aircraft and the rockets you are thinking of is the direction you aim them.

Rockets can <and have> been used on fixed wing aircraft.

Jet engines can't operate out of the atmosphere, that's why they don't use them in space.

[ocnblu]

Too much thrusting for the wheel bearings to handle? It would pull the truck off the treadmill and into like 4 houses here in the neighborhood because I can't steer it? Edited June 26, 2006 by ocnblu

[Drew Dowdell]

Too much thrusting for the wheel bearings to handle?  It would pull the truck off the treadmill and into like 4 houses here in the neighborhood because I can't steer it?

Now add wings and a rear stabilizer and rudder.... see if that helps...

[Flybrian]

Rockets do indeed work on thrust. You can strap a rocket onto a maytag dryer and make it 'fly.' The principle is different because what keeps a rocket in the air is thrust while a fixed-wing aircraft is kept aloft by lift generated from the airfoil. Thrust is used to create that lift.

That is why when a rocket motor quits in the atmosphere, it enters a parabolic trajectory and falls back to earth. If a plane's source of thrust quits in the air, it can remain aloft simply with lift generated from its wings until the airflow slows to the point where the wings cannot support the airfoil. This is how gliders stay up.

[Drew Dowdell]

You can strap a rocket onto a matag dryer and make it 'fly.'

that caused a bit of an office disturbence here Fly.

[NOS2006]

So, you guys are saying that the wheels serve no purpose but to hold the belly of the plane off the dirt?  The treadmill would not counteract anything because the wheels do not contribute to the plane rolling along the runway as it gains the air speed to lift off?

Yes! But the treadmill will be countering the wheel's speed because the wheels are spinning, but they don't have any significance.

[Cory Wolfe]

Heh... let's put it this way, shall we? Are the plane's engines powering the wheels? No. If they were, the plane would remain still. However, the engines suck in air and over the airfoil and such. Regardless of what the wheels are doing, they are just there to let it move over ground and to be stopped. They are not powered in this example. The plane's engines are what makes a plane move. It creates thrust and lift, which makes it fly. Once in the sky, it's all lift. The main thing some of you guys aren't getting is that the wheels are not powered and are not what gets a plane up to the speed in which it lifts off a ground. If the power of the engine was sourced to the wheels... Then yes, it wouldn't move. But it's not... The engines create moving air which will essentially move it along the treadmill until it takes off.

[Sixty8panther]

If you tied a cable to one end of the plane to hold it in place, then ran the treadmill up to 160 knots, would the plane take off?

You keep missing the point dude...

In this HYPOTHETICAL scenario even as the speed of the wheels approaches

infiniti the treadmill keeps up with the wheels so that the forward motion of

the plane as relative to the stationary ground and air is counteracted. Yes...

it's not realistic but neither is a treadmill the size of manhatan!

The plane can NOT move forward because the treadmil counteracts any

forward movemetn by the plane via the frictioin of the wheel bearings as its

wheels start spinning at infinitesimal speeds.

Yes, theoretically IF the plane was just on a plain treadmill spinning at some

crazy speed like mach 3 (2200mph) and say to keep math simple the plane

needs to accelerate to 100mph in order to reach enough wind speed velocity

to take off, then (remmeber no speed sensors on wheels) the plane would

push itself to 100mph a lot slower than normal as it's wheels would have to

be spinning at 2300 mph in order of it to be able to take off.

Theoreticaly even this scenario has a boat load of problems like the relative

traction of the wheels to the runway etc... the wheels would probably melt &

or break off.

But back to our example: the plane's wheels are touching the ground and so

as long as traction exists the reverse movement of the treadmill negates any

forward movement generated by the engines.

All these "solid rocket strapped to a car roof on a dyno" examples lack the

element of the speed sensors hooked up to a MOTORIZED treadmill.

[the_yellow_dart]

Heh... let's put it this way, shall we? Are the plane's engines powering the wheels? No. If they were, the plane would remain still. However, the engines suck in air and over the airfoil and such. Regardless of what the wheels are doing, they are just there to let it move over ground and to be stopped. They are not powered in this example. The plane's engines are what makes a plane move. It creates thrust and lift, which makes it fly. Once in the sky, it's all lift. The main thing some of you guys aren't getting is that the wheels are not powered and are not what gets a plane up to the speed in which it lifts off a ground. If the power of the engine was sourced to the wheels... Then yes, it wouldn't move. But it's not... The engines create moving air which will essentially move it along the treadmill until it takes off.

BV: Where the power comes from makes no difference.

[scharmer05]

it does not matter what is happening to the wheels. This is not a car, there is VERY minimal forces being applied to the wheels (unless you applied the brakes). The thrust forward is from the jet engines. Nick said that he had worded it wrong as was pointed out earlier. He meant to say that the treadmill at the same speed (but in the opposite direction) as the plane as moving, so the speed of the wheel does not matter at all. If the plane is moving forward (relative to the ground) at 100mph, then the treadmill is moving in the rearward direction at 100mph, and the wheels are spinning at 200mph. If all these speeds increase, the plain would eventually take off.

[scharmer05]

BV: Where the power comes from makes no difference.

where the power comes from makes EVERY BIT of difference. If this were a car, then it would not be going anywhere, because the thrust is applied THROUGH the wheels. In a plane, that is not so. The thrust comes from the jet engines, which are COMPLETELY independant from the wheels.

[CaddyXLR-V]

Would the friction of the wheels be enough to counter the forward thrust of the engine?

[scharmer05]

Would the friction of the wheels be enough to counter the forward thrust of the engine?

nope

[CaddyXLR-V]

nope

So then the plane would move forward, and would be able to fly.

[scharmer05]

So then the plane would move forward, and would be able to fly.

yep, nowhere did Nick say that the plane couldn't move forward on the treadmill

[Drew Dowdell]

You keep missing the point dude...

In this HYPOTHETICAL scenario even as the speed of the wheels approaches

infiniti the treadmill keeps up with the wheels so that the forward motion of

the plane as relative to the stationary ground and air is counteracted. Yes...

it's not realistic but neither is a treadmill the size of manhatan!

as I've pointed out... the speed of the wheels is irrelevent. That was a miss wording in the original problem.

[the_yellow_dart]

scharmer - I disagree.

If the situation is as Nick corrected it, we could have the following situation:

Car/plane going 50 mph forwards relative to ground.

Treadmill from hell going 50 mph backwards to "counter".

Wheels on car/plane are going 100 mph. It doesn't matter if you are powering the wheels or have a jet engine - if you can get the wheels going 100 mph, you can go 50 mph relative to the ground.

If you look at the situation as I originally understood it, we have the following:

Car/plane's wheels going x mph (doesn't matter how fast)

Treadmill from hell going x mph backwards to "counter".

Actual car/plane going nowhere, since the wheels are completely being countered. Again, where the power is coming from doesn't matter.

The only time it matters where in the object the force is being exerted from is when the object can rotate. I'm assuming the plane stays right side up whether being driven by wheels or jet, so both situations would be the same.

[Drew Dowdell]

scharmer - I disagree.

If the situation is as Nick corrected it, we could have the following situation:

Car/plane going 50 mph forwards relative to ground.

Treadmill from hell going 50 mph backwards to "counter".

Wheels on car/plane are going 100 mph. It doesn't matter if you are powering the wheels or have a jet engine - if you can get the wheels going 100 mph, you can go 50 mph relative to the ground.

If you look at the situation as I originally understood it, we have the following:

Car/plane's wheels going x mph (doesn't matter how fast)

Treadmill from hell going x mph backwards to "counter".

Actual car/plane going nowhere, since the wheels are completely being countered. Again, where the power is coming from doesn't matter.

The only time it matters where in the object the force is being exerted from is when the object can rotate. I'm assuming the plane stays right side up whether being driven by wheels or jet, so both situations would be the same.

You are correct in the case of a car.

On a jet plane, the wheels aren't the source of the forward motion.

The jet engine can push the body of the plane forward regardlessof the rearward force on the wheels because the bearing in the wheels negate this rearward force.

[scharmer05]

You are correct in the case of a car.

On a jet plane, the wheels aren't the source of the forward motion.

The jet engine can push the body of the plane forward regardlessof the rearward force on the wheels because the bearing in the wheels negate this rearward force.

my point

[Sixty8panther]

here are some interesting threads on the topic...

http://answers.google.com/answers/threadview?id=428718

or better yet, here (way long though):

http://forum.physorg.com/index.php?showtopic=2417&st=0

I think you guys need to check what the experts are saying,

as in look in the links Nick posted!

There's inteligent people on BOTH ends of the argument but

I think the majority are right: The plane is NOT going

anywhere unless you impose the concept of mechanical

limitations of the landing gear,treadmill etc. but even then

it begs the question what about the mechanical limits of the

engines? It takes a lot a power to roll rubber & steel at near

infiniti!

At any rate here's a few inteligent explanations:

PhysOrg.com Forum 

Atl5p

So we agree on the final outcomes of our equations....

So sure;

Wheelspeed = Groundspeed - (-Beltspeed)

...I was already assuming that we already knew the belt was going backwards, so I finished off the equation (without showing my work)...

WS = GS + BS

So I guess we don't really disagree there...I thought you were using the above to somehow 'force' the IAS to remain at 0.

From your following post, I believe I can see where we differ.

You seem to think that the above equation (wheelspeed theory) somehow predisposes the GS/IAS to remain at 0. I'm not really sure I follow...

You see, most of the flyboys here will tell you that the plane 'moves' forward because the question 'says it does'. By that measure, they simply 'double the wheelspeed' when the treadmill turns on.

Look, this is the way I solve the equation:

(Given IAS = GS)

WS = GS - (-BS)

'The plane moves 50mph against a treadbelt matching the plane's wheelspeed'

50mph = ?x - (-50)

50mph - (- (-50)) = ?

50mph - 50 = 0mph!!

GS = 0mph

thus

IAS = 0mph

***

This is the way the 'fly Boys' solve the problem, when they assume 'move' means 'airspeed'. This is how they solve for IAS.

'The plane moves 50mph against a treadbelt matching the plane's Airspeed'

Given IAS = GS (calm air, remember?)

WS = GS - (-BS).....waitasecond...who cares? I just said IAS = GS, right? duh!

IAS = GS

GS = 50 (right?)

so,

IAS = 50!!! (yeahhhhhhhh,, I'm sooooo smart...!!!!)

Now, c'mon....you tell ME which one is pre-disposing an answer, and which one is SOLVING for an answer...and which one is just plane DUMB!!!!

It's this simple...if the treadbelt's SURFACE only FEELS 12hp, then it only needs to RETURN 12hp, in order to stop the plane!

The other 88hp from the plane is making the plane 'move over the treadbelt'.

The other 88hp from the treadbelt is making the treadbelt 'go at 50mph under the plane' (...eq's, sic, whatev')

So in order for the treadbelt to RETURN 12hp through those wheels, it must actually SEND 100hp...(because it's loosing 88hp to the wheels)....

I dunno...it may take a bit more vectoring to figure out....

One final note...for all those who want to see the plane 'Move'...

The question dosn't mention the ground or the tower or 'outside observers'...if you really want to get inside this experiment, you need to do 1 thing, and 1 thing only:

GET OFF THE GROUND!!

Get ONTO the Treadbelt, beside the plane! Or get INTO the plane and paint some lines on the treadbelt...

Got it?

NOW, make the plane "MOVE". And at the same time, turn on the treadbelt (remember, now YOU are on the treadbelt).

What say ye, Stu?

Yup... that's pretty self explanitory to me.

PhysOrg.com Forum 

Boeing Engineer

For Your Information,

The question is poorly worded.

However the plane will not take off.

A plane is merely a motor vehicle with wings, powered not by a drive shaft connected to the wheels but by an engine mounted on the chasis/fuselage.

As the engine, suppose on the back of a ute powers the 'plane' the plane tries to move forward. The conveyor moves backwards and stops the plane moving forward. A car or a plane on a conveyor (in neutral) will move in the direction of the conveyor. A person on rollerblades will move in the direction of the conveyor.

The only argument against this happening is the wheels are free spinning or there is not enough force exerted on the plane. But the question states that the conveyor matches the planes 'speed' (A Bad Word)

The thrust approaches infinity as does the conveyor, however there is not any air passing over the wings, only an infinite amount going through the jet engine.

Unless the plane can move relative to the groun and hence the air around the ground/conveyor it can not take off.

This is an elementary problem posed to 1st year aerospace engineers and a clear answer was given. The plane can not take off!

If you are going to disagree with this, please state clearly why and I will give a clear response.

Exactly!

It does NOT say it matches the plane's speed as relative

to the conveyor belt or air speed or wahtever, it just

says "speed"which means ANY speed or velocity.

Therefore any engineer would assume that ANY and all

forward motion is negated by the belt!

PhysOrg.com Forum 

egnorant:

Welcome back!

While we "fly guys" have been drawn into investigating your "wheelspeed theory",

it still remains a very limited and subjective theory.

A more appropriate term should be "simulated speed theory" in that it contains many of the aspects of speed, but lacks others.

One item it is lacking is actual movement!

The plane is very limited in that it is applying the "simulated speed" to the wheels of the plane only.

A car gets the "simulated speed" applied to more components involved including its drive components.

A man on a treadmill has "simulated speed".....much of the body is used to keep it from being moved backwards by the treadmill.

As applied to your pet theory, these are not movement in a direction.

They are applications of energy to PREVENT movement!

I have been watching to see if you veered off into a man going up the down escalator in order to add up and down to the discussion.

I watched a show with a free fall simulator where skydivers jumped into a wind blast created by a huge fan in the floor. This was the one that lead me to the "simulated speed" application.

This example, like your "wheelspeed theory" are just one element that has movement (distanceA X durationB = speedBELT) while the other interacting element is balanced with no movement (distanceC = 0) (distanceC X duration B= speedPLANE).

Last time I looked anything times 0 = 0.

Did you ever think that possibly this is a very simple question with a very simple answer?

Bruce

The people that really crack me up ar the ones on that Physics Forum

that say the plane would take off FASTER if it was on the

"treadmill runway" now that's funny! Extra friction = MORE speed? I'll

have to put my parking brake on in the Datsun next time I race at

New England Dragway, maybe I'll run 10.9 in the 1/4 mile!!!

[NOS2006]

Sixty8, you and those others you quoted clearly don't get it.

Put a vehicle in neutral. Will it move forward or backward if you put it on a treadmill?

[scharmer05]

ok well we have 2 seperate arguments here. If the wheels can't spin faster than the belt is turning, then no it can't go anywhere, but Nick changed it halfway and said that the belt is only going as fast as the plane and that the wheels could go faster. If that is the case, then the plane takes off, because the plane can move forward on the "treadmill from hell" (funny yellow dart) and take off, its just that the ground would be moving underneath it.

[Drew Dowdell]

Ok, how about we think of it this way:

On the front of the plane attach a rope, on the other end of the rope, attach a high speed winch, something that would operate much like the launching mechanism on an aircraft carrier.

Place the plane on the same treadmill we've been talking about

Activate the winch.

which way will the plane move?

[Cory Wolfe]

How about this, then... What affect does the treadmill have on the air? As noted, the plane moves via air being thrusted by its engines. The wheels are free moving... they aren't being powered or stopped. In essense... the engines thrusting air would make the plane move. Let's say a certain plane generates enough lift to take off at 80mph. Unless the wheels velocity is being slown down by a brake or something... No matter how the treadmill matches the planes speed, the wheels are free spinning. The plane will move down the threadmill with the treadmill spinning impossibly fast.. backwards, but it has no effect on the air, therefore no effect on the plane flying. Get it?

[NOS2006]

How about this, then... What affect does the treadmill have on the air? As noted, the plane moves via air being thrusted by its engines. The wheels are free moving... they aren't being powered or stopped. In essense... the engines thrusting air would make the plane move. Let's say a certain plane generates enough lift to take off at 80mph. Unless the wheels velocity is being slown down by a brake or something... No matter how the treadmill matches the planes speed, the wheels are free spinning. The plane will move down the threadmill with the treadmill spinning impossibly fast.. backwards, but it has no effect on the air, therefore no effect on the plane flying. Get it?

That's the best, easiest way to put it.

[Flybrian]

Exactly. Without the air moving, it doesn't matter. Differences in air pressure with an airfoil is what actually, physically, really makes an airplane (or helicopter) fly. Not propellers, not jet engines, not rocket motors, nothing else.

[CaddyXLR-V]

Lets say the wheels are spinning at 50mph, and the conveyor is spinning 50mph the opposite direction. It would take a certain amount of force(in this case thrust from the engines) to keep the plane from moving backwards-the direction of the conveyor, so the plane remains stationary. Now, if you increase the speed of both to 100mph, it would still take the same amount of force to keep the plane stationary. So what happens if you increase the thrust past the amount of force needed to keep the plane stationary? The plane will move forward.

[aaaantoine]

I have come to the conclusion that you are all crazy.

It's good that I'm not a moderator because I would have locked this thread for the sake of everyone's sanity.

[Drew Dowdell]

Can you push a rollerskate along a grocery checkout belt even if the belt inversely matches your speed?

[NOS2006]

Can you push a rollerskate along a grocery checkout belt even if the belt inversely matches your speed?

Good one.

[Newbiewar]

No.

Assuming it takes a speed of 150mph for the plane to take off. The wheels will be turning an equivilant of 300 mph because the treadmill is running backwards at 150mph.

no thats not exactly correct...

the wheels will see a much higher speed then 300mph.... the wheels speed will go up expedentially while the plane trys to start getting forward inirtia

this is why i suggest, that while the turbine engines might hit max rpm after the wheels hit there maximum rotational speed

[Newbiewar]

How about this, then... What affect does the treadmill have on the air? As noted, the plane moves via air being thrusted by its engines. The wheels are free moving... they aren't being powered or stopped. In essense... the engines thrusting air would make the plane move. Let's say a certain plane generates enough lift to take off at 80mph. Unless the wheels velocity is being slown down by a brake or something... No matter how the treadmill matches the planes speed, the wheels are free spinning. The plane will move down the threadmill with the treadmill spinning impossibly fast.. backwards, but it has no effect on the air, therefore no effect on the plane flying. Get it?

although that is in a perfect world where the wheels are moving free... but there is a tremendous amount of friction that will add up on those wheels as they spin... enough so that, it might, limit the thrust from propelling the plane...

now it would be impossible to tell imho without knowing the bearings on the wheels... but friction doubles as a brake regaurdless of the engines thrust... if the plane can not attain enough volocity to support the wieght of the plane under the wings, the plane will never be able to take off...

[CaddyXLR-V]

although that is in a perfect world where the wheels are moving free... but there is a tremendous amount of friction that will add up on those wheels as they spin... enough so that, it might, limit the thrust from propelling the plane...

now it would be impossible to tell imho without knowing the bearings on the wheels... but friction doubles as a brake regaurdless of the engines thrust... if the plane can not attain enough volocity to support the wieght of the plane under the wings, the plane will never be able to take off...

But, if the treadmill was spinning that fast to overcome the engine thrust, there would also be friction between the moving conveyor, and the air around it, causing a headwind for the plane.

[Drew Dowdell]

you're all over thinking the problem.

I say again

"Can you push a rollerskate along a grocery checkout belt even if the belt inversely matches your speed?"

[CaddyXLR-V]

you're all over thinking the problem.

I say again

"Can you push a rollerskate along a grocery checkout belt even if the belt inversely matches your speed?"

But what if the belt inversely matches the rollerskates speed?

[NOS2006]

But what if the belt inversely matches the rollerskates speed?

It doesn't matter.

[Drew Dowdell]

But what if the belt inversely matches the rollerskates speed?

then the wheels will spin at a rate equal to ground speed or twice belt speed, but the rollerskate will still be moving forward

Edited June 26, 2006 by Oldsmoboi

[Newbiewar]

you're all over thinking the problem.

I say again

"Can you push a rollerskate along a grocery checkout belt even if the belt inversely matches your speed?"

the answer to that is no...

[CaddyXLR-V]

It doesn't matter.

But it does, because the only way for the rollerskates to go faster, is for the wheels to slide or go faster than the belt. Since the belt matches the rollerskate speed, the wheels would have to slide in order for the rollerskates to actually move forward.

[Drew Dowdell]

the answer to that is no...

you're trying to tell me, that if you move a rollerskate forward with your hand on a belt moving the same speed in the opposite direction, the rollerskate will stay in place relative to the earth?

You need to go to the grocery store and try it.

i'm going to have to get a video camera I see....

[Drew Dowdell]

But it does, because the only way for the rollerskates to go faster, is for the wheels to slide or go faster than the belt. Since the belt matches the rollerskate speed, the wheels would have to slide in order for the rollerskates to actually move forward.

No! That is only the case if the rollerskate wheels are providing the forward motion. in this case your hand is providing the forward motion. the wheels are just along for the ride.

[CaddyXLR-V]

then the wheels will spin at a rate equal to ground speed or twice belt speed, but the rollerskate will still be moving forward

But the wheels cant spin faster than the belt speed, because they must always be the same values, but in opposite directions.

[Sixty8panther]

But what if the belt inversely matches the rollerskates speed?

We're over analyzing the problem???

Are you kidding me? You guys are talking about all

kinds of math here. Check this out:

CB = conveyor belt

AS = air speed

WS = wheel speed

P = aircraft

P pushes itself down the CB... it accelerates using the

thrust of its engines, we all know a plane does not

push itslef down a runway using wheels & axles, I

hope all of us knew that fropm the begining otherwise

how would it sustain air speed once airborne.

Anyway....

AS = 0mph when treadmill is stationary. Other than a

10mph wind or what have you, not relevant to AS.

WS = 100mph

(sensors in the wheel tell the CB to accelerate to 100mph)

AS= 0 since 100mph -100mph = 0 (zero)

so now the plane only has the friction of the wheels

preventing it from pushing itself down the runway &

accelerating to an AS high enough for takeoff...

the force of 2/3/4 turbines easily negates the 100mph

of the CB...

so the plane accelerates to 200 (on the CB not relative to the ground)

(sensors in the wheel tell the CB to accelerate to 200mph)

and this goes on and on and on untill (in theory) infinity.

Either way the plane CAN NOT fly even if the treadmill is

going light speed so long as the aircraft is stationary.

Ropes, rockets, cars in neutral, roller skates and all the

other things yoy can throw at this problem do NOT

change the fact that the CB is preventing AS from

reaching even 1mph nevermind the 120 required for flight.