Plane on a treadmill

MrCreosote

This was one from my brother and it's getting on my nerves...
Suppose you've got a runway sized treadmill. You pop a plane on it, and as the plane accelerates the treadmill accelerates to match the speed. Let's say there is no wind blowing. Will the plane take off?
This makes my head explode thinking about it!

Pacifico

Yes it will

Thomas_S_Hunterson

Without air moving across the wings, there is no lift.

/ah but of course the plane will accelerate beyond the treadmill regardless since the power is not through the wheels... carry on

Alanstrainor

Yes it will. The plane is driven by it's propeller, not it's wheels, therefore the speed of the wheel spinning in the opposite direction will make no difference.

A320-200

Yes, because unlike a car the wheels on an aircraft are free spinning.
The thrust is coming from the engines which have nothing to do with the treadmill, and will still push the aircraft forward.

mrDerek

as sean said theres no lift the plane would not take off.its basically staying in the same place if its on a threadmill.Airflow is essential in flight the speed at which the tires go is not if your on a threadmill you wont get sufficient speed for enough airflow going under the wing to produce "lift"

A320-200

mrDerek wrote: »

as sean said theres no lift the plane would not take off.its basically staying in the same place if its on a threadmill.Airflow is essential in flight the speed at which the tires go is not if your on a threadmill you wont get sufficient speed for enough airflow going under the wing to produce "lift"

You're thinking of a car being on a treadmill, in which a car translates it energy into forward momentum through the wheels, which the treadmill cancels out. An aircraft uses the thrust from the engines, which have no relationship with the treadmill, observe:

http://www.youtube.com/watch?v=IbRcg3ji_Pc

mrDerek

thats an incredibly light aircraft.you wont get a a380 off the runway on a threadmill.

MrCreosote

Ah good old youtube! Nice one. I was making the mistake of thinking like a car...

tracker-man

Mythbusters did this.... but they did it WRONG. They used a microlight but it was clearly not stationary on their "treadmill", it was moving, air was flowing over the wings, lift was produced and he took off. On a single engine aircraft or an A380, the airflow over the wings produced by the engine alone is not enough to get the plane airborne. Simple as. The engines PULL the plane through the air, generating lift as the air and wind move around the wing at speed.

Hope this answers your question.

View Profile

The aircraft will not takeoff because it requires lift to do so.

Since there is no airflow over the wings there is no lift, irrespective of how fast the wheels may be rotating or how much thrust the engine were producing.

However, if you had a light aircraft with a rotate speed of lets say 50 knots parked on a ramp. If a steady 50 knot wind was to blow head on at the aircraft then it would "technically" get airborne and kind of hover.

Flyer1

Right, some sensible and not so sensible answers here.

The airplane will fly off a treadmill. Throttle up and you'll get forward airspeed, regardless of how fast the wheels turn. Once you've enough airspeed any plane will fly.

View Profile

Okay we need to examine the difference between thrust and lift in this case.

No lift will be created as the aircraft on the treadmill is not moving relative to its surroundings. It's stationary!

It is however producing thrust but only enough to remain at the same point on the treadmill.
Now you could argue that a rocket can "fly" by thrust alone, it dosen't really produce lift then you could maybe say the aircraft could get airborne. This however would require a huge amount of thrust.
Eg. If you cut the wings off an F-18 it may have thrust from the engines but without wings (i.e. lift) it wont fly.

View Profile

Just rewatched the Mythbusters clip.

In that, the microlight was also moving forwards through the air thus creating lift. That's why it got airborne.

Flyer1

But is the original question not, will it fly off a treadmill ? i.e. on full power... Airplane being dragged forward by the prop, air moving over the wings, lift being created, h'up she goes.

Pacifico's answer is the best on the thread so far

View Profile

The original question stated:

You pop a plane on it, and as the plane accelerates the treadmill accelerates to match the speed. Let's say there is no wind blowing. Will the plane take off?

So if the airplane is matching the treadmill speed, as a runner does on a treadmill, then it is not moving. Right?

So no air is passing over the wings.


Mythbusters asked a different question.

Thomas_S_Hunterson

View Profile wrote: »

The original question stated:



So if the airplane is matching the treadmill speed, as a runner does on a treadmill, then it is not moving. Right?

So no air is passing over the wings.


Mythbusters asked a different question.

The fact that the treadmill is running is largely irrelevant to the actual velocity of the plane, it just means the wheels have to spin twice as fast.

*Kol*

https://www.youtube.com/watch?v=4owlyCOzDiE

It wont take off it has no forward motion to move air over the wings. That answers the original question. As long as the aircraft cant accelerate away from the treadmill there will be no lift and it wont take off.

Davidth88

I agree with the people that say there would be no lift.


The air moving over the wings causes the lift , in the scene descibed by the OP the air is not moving over the wings , therefore no lift



Nice question OP !

Fratton Fred

thrust, velocity, momentum etc has nothing to do with it surely.

The engines drag/push the plane along the ground until there is enough air passing over the wings to create lift. If the ground is moving in the opposite direction then this counteracts the forward momentum of the plane and the actual speed of the plane is zero, therefore no lift.

If this scenario worked (Which it wont) then every aircraft carrier would have a rolling road type setup instead of catapaults.

Danbo!

Fratton Fred wrote: »

hrust, velocity, momentum etc has nothing to do with it surely.

The engines drag/push the plane along the ground until there is enough air passing over the wings to create lift. If the ground is moving in the opposite direction then this counteracts the forward momentum of the plane and the actual speed of the plane is zero, therefore no lift.

If this scenario worked (Which it wont) then every aircraft carrier would have a rolling road type setup instead of catapaults.

As I was reading the thread I was trying to think of how to explain what I was thinking, but fred's done a perfect job.

If the engines thrust matches the speed of the treadmill, basically the engines are keeping the plane in place. Any slower, and it will be pulled backwards off the belt, and faster and the plane will move forward along the belt, and then it depends on exact speeds as to whether it will take off

Biro

Fratton Fred wrote: »

hrust, velocity, momentum etc has nothing to do with it surely.

The engines drag/push the plane along the ground until there is enough air passing over the wings to create lift. If the ground is moving in the opposite direction then this counteracts the forward momentum of the plane and the actual speed of the plane is zero, therefore no lift.

If this scenario worked (Which it wont) then every aircraft carrier would have a rolling road type setup instead of catapaults.

You're not thinking of it correctly. The treadmill won't actually keep the plane stationary. You have a plane, with an engine trying to drag the plane forward from 0mph to 100mph for example. In a normal situation the ground stays stationary, the plane goes forward lets say one mile and reaches 100mph airspeed and groundspeed.
Now the same situation with a mile long treadmill, the engine pulls the plane forward in the exact same manner. The treadmill turns the other direction, but because the plane is being dragged by the engine and not the wheels, the result is the plane still accellerates at the same rate as it was before, except this time that as the plane reaches 20mph forward airspeed, the treadmill rotates 20mph backwards ground speed, so the planes wheels are doing 40mph. At 100mph airspeed the planes wheels are doing 200mph ground speed because of the treadmill, but the aircraft is still accellerating at the same rate forward!

Muppet Man

For whats it worth, I get it... and IMHO, the plane wont take off due to the lack of airflow over the wings, because the relative speed of the airplane is zero. Its not actually moving forward...

(all assuming as the OP States that the threadmill / converyer is moving at the exact same speed as the plane is accelerating forward).

I think Fred put it best...

If this scenario worked (Which it wont) then every aircraft carrier would have a rolling road type setup instead of catapaults.

Muppet Man.

Capt'n Midnight

B36's used to use treadmills

Fratton Fred

Biro wrote: »

You're not thinking of it correctly. The treadmill won't actually keep the plane stationary. You have a plane, with an engine trying to drag the plane forward from 0mph to 100mph for example. In a normal situation the ground stays stationary, the plane goes forward lets say one mile and reaches 100mph airspeed and groundspeed.
Now the same situation with a mile long treadmill, the engine pulls the plane forward in the exact same manner. The treadmill turns the other direction, but because the plane is being dragged by the engine and not the wheels, the result is the plane still accellerates at the same rate as it was before, except this time that as the plane reaches 20mph forward airspeed, the treadmill rotates 20mph backwards ground speed, so the planes wheels are doing 40mph. At 100mph airspeed the planes wheels are doing 200mph ground speed because of the treadmill, but the aircraft is still accellerating at the same rate forward!

this is the important bit.

MrCreosote wrote: »

as the plane accelerates the treadmill accelerates to match the speed.

it doesn't matter how fast the wheels or engines are going, it is how fast the wings are moving through the air. if the treadmill matches the speed of the wheels then the plane will stay in the same place.

Jip

tracker-man wrote: »

Mythbusters did this.... but they did it WRONG. They used a microlight but it was clearly not stationary on their "treadmill", it was moving, air was flowing over the wings, lift was produced and he took off.

Was thinking that myself when I watched it, I'm sure it will be on one of its Myths revisited shows.

Biro

Fratton Fred wrote: »

this is the important bit.



it doesn't matter how fast the wheels or engines are going, it is how fast the wings are moving through the air. if the treadmill matches the speed of the wheels then the plane will stay in the same place.

Nope, you're wrong, read my post again. The treadmill can match the speed of the wheels all it wants, all it will do is speed the wheels up because the wheels turn freely.
Think of it another way. You put yourself on a treadmill. I tie a rope around you and stand in front of the treadmill. I tell you that the faster I pull the rope, the faster the treadmill will turn below your feet. Once I start pulling (remember, I'm not on the treadmill) you'll start moving forward on the treadmill, no matter what the treadmill does to try to stop you.

Capt'n Midnight

IAS , indicated air speed is what's important.

This tells you how much wind you have in your sails.

examples
B29's over Japan before they figured out the effects of the jet stream.
In one example they flew over the target so fast they couldn't aim properly.
In another they were flying at about 250mph into the head wind, plenty of air speed and plenty of lift, but ground speed was 3mph backwards so getting a lot of flack

U2 spy plane looks like a glider but flies at a mach number than most subsonic planes , it's the original sonic cruiser. the air is so thin up there that you can use big wings to get lift without having much of a drag penalty.


There are quite a few STOL planes that will take off vertically into a head wind because the air speed is high enough. Thats with the threadmill off.

Fratton Fred

Biro wrote: »

Nope, you're wrong, read my post again. The treadmill can match the speed of the wheels all it wants, all it will do is speed the wheels up because the wheels turn freely.
Think of it another way. You put yourself on a treadmill. I tie a rope around you and stand in front of the treadmill. I tell you that the faster I pull the rope, the faster the treadmill will turn below your feet. Once I start pulling (remember, I'm not on the treadmill) you'll start moving forward on the treadmill, no matter what the treadmill does to try to stop you.

But you would be fixed to the ground. If you were (Unattractive as it may sound) sat on my shoulders pulling the rope (Which is what the engine would be in relation to the plane), it would make no difference at all. The plane has nothing to gain traction with.

Biro

Fratton Fred wrote: »

But you would be fixed to the ground. If you were (Unattractive as it may sound) sat on my shoulders pulling the rope (Which is what the engine would be in relation to the plane), it would make no difference at all. The plane has nothing to gain traction with.

But it has! The air! The same air that it would have if the treadmill weren't there. The air doesn't move no matter what the treadmill is doing. So for example, if I tied the rope to a wall, a fixed object, and sat on your shoulders, you on the treadmill, and pulled the rope, I'd bring you forward at what ever rate I pulled on the rope, regardless of whether the treadmill was switched on or not. The only difference the treadmill would make is to how fast your legs would be moving.
Seeing as the air is independent of the treadmill, and the engines pull on the air to bring the plane forward, once they start pulling the plane forward then it doesn't matter what the treadmill does, it'll only speed up the wheels, the plane will continue being pulled forward by the engines, which will still be pulling themselves through the air regardless of whether the treadmill is on or off.

Flyer1

I dunno about ye, but it's a nice day out, i'm goin' flyin

Fratton Fred

The engines don't make it fly though, the wings do. I get your point, but the plane has to trundle forward on the wheels before there is enough air passing over the wings to create lift.

What I think you are talking about, is the plane effectively outrunning the treadmill which it needs to do if it is dragged off. Don't forget, the plane still weighs the same until the wings start to lift it off the ground, which they will not do until the reach a certain velocity. Until this happens, the plane may as well not have wings at all.

Biro

Fratton Fred wrote: »

The engines don't make it fly though, the wings do. I get your point, but the plane has to trundle forward on the wheels before there is enough air passing over the wings to create lift.

What I think you are talking about, is the plane effectively outrunning the treadmill which it needs to do if it is dragged off. Don't forget, the plane still weighs the same until the wings start to lift it off the ground, which they will not do until the reach a certain velocity. Until this happens, the plane may as well not have wings at all.

I know the engines don't make it fly. What I'm saying is the engines will bring it forward at the same rate as they would regardless of the treadmill. The plane doesn't have to outrun the treadmill at all. The wheels do, but they're free spinning anyway, and therefore not part of the equation.

A320-200

I know the engines don't make it fly. What I'm saying is the engines will bring it forward at the same rate as they would regardless of the treadmill. The plane doesn't have to outrun the treadmill at all. The wheels do, but they're free spinning anyway, and therefore not part of the equation.

Exactly. For example, B777 roll's down the treadmill, Vr of 140KIAS, at Vr the wheels will be at a rotational speed of 280Kts.

Fratton Fred

Biro wrote: »

I know the engines don't make it fly. What I'm saying is the engines will bring it forward at the same rate as they would regardless of the treadmill. The plane doesn't have to outrun the treadmill at all. The wheels do, but they're free spinning anyway, and therefore not part of the equation.

This is a really good question, I see why the OP was so confused now.

I get what you mean and I can see that happening.

Does it not depend on how how fast you win up the engines? if you start off slowly and slowly increase the power, the plane will think it is moving forward and eventually not go anywhere, but if you increase the power quickly, I can see the power dragging it forward.

It was a long time ago i did my physics exams, but is there not something about initial momentum, initial velocity etc? if it can achieve that then it will go forward I guess. Newton would know the answer.

Jesus, my head hurts.:D

civdef

Won't the plane just roll off the treadmill and take off normally? Even if the treadmill was infinitely long, the plane would move fiorward along the treadmill at close to normal takeoff speed- allowing for a bit of extra friction.

The treadmill won't keep the plane fixed in place wrt the air around it since the aircraft wheels freewheel.

Fratton Fred

I got ye,

What you are saying is that rather than trundling down the runway on the wheels, the plane is dragging them along the ground behind it (Effectively anyway).

I'm still pretty sure that if you wound it up slowly, it would stay where it was, the plane needs to generate enough power to overcome the forces holding it down, a bit like the initial effort required to push a box along the floor, so the plane would use a load of fuel to take off, but it would eventually.

mikedragon32

The quick answer is yes it will.

The threadmill is "runway length" so there is no issue about the plane falling off. As some have stated, the jets/props provide the forward motion, not the wheels. The wheels are just there to keep the belly of the plane off the ground. So the plane will be moving through the air.

So, if the plane needs to be doing 200kph to take off, it's speed through the air will be 200kph. The speed of the threadmill will be 200kph, so the speed of the wheels will be 400kph. The plane is still moving through the air and it's the that speed that counts!

Tazzle

Hi, I just wandered into this forum by spotting it on the front page. Here's my two cents. Don't think of it in speed. Think of it as force. The force pulling the plane forward is the thrust from its propellors. Some forces resisting it are its drag from the air and its drag from the ground. The drag from the ground is reduced using wheels, you move the ground backward all you do is increase the drag on the wheels. I think it's a fair bet that considering a plane can take off from water that a Boeing on a ginormous treadmill is going to take off, unless the speed is so great the wheels ignite and make the plane splode.

Biro

Fratton Fred wrote: »

I got ye,

What you are saying is that rather than trundling down the runway on the wheels, the plane is dragging them along the ground behind it (Effectively anyway).

I'm still pretty sure that if you wound it up slowly, it would stay where it was, the plane needs to generate enough power to overcome the forces holding it down, a bit like the initial effort required to push a box along the floor, so the plane would use a load of fuel to take off, but it would eventually.

Yep, now you're on board!
I see what you're saying about the initial movement, but what would likely happen is that at lets say 5% thrust under normal circumstances the plane would start rolling forward to lets say 10mph, if it were moving backwards on a treadmill before you applied 5% thrust it would probably slow down from minus 10mph to zero then accelerate to 10mph, but after that point accleration from then on would be the same, minus the extra friction from the wheels, which probably would be negligable enough.

Biro

tracker-man wrote: »

Mythbusters did this.... but they did it WRONG. They used a microlight but it was clearly not stationary on their "treadmill", it was moving, air was flowing over the wings, lift was produced and he took off. On a single engine aircraft or an A380, the airflow over the wings produced by the engine alone is not enough to get the plane airborne. Simple as. The engines PULL the plane through the air, generating lift as the air and wind move around the wing at speed.

Hope this answers your question.

They actually did it right. No one said the plane had to be stationary, and we know that the engines don't even come close to providing any lift.

Fratton Fred

My old Mech Science lecturer would have been hard reading this thread. I can just see him doing diagrams etc on the board and scribbling all sorts of equations.

Thinking of the wheels keeping the belly of the plane off the ground rather than the plane moving on its wheels makes it a lot clearer.

cormy

I can't believe this debate is still going on. The plane will take off regardless of the treadmill speed. The reason this gets confusing is because the wiring in our brains seems to make us attribute too much significance to the speed of the wheels. The engines are pushing against the surrounding air and so the craft *will* move forward/accelerate ... simple as that ... (forget about the wheels - they are irrelvant). Think about it another way: imagine landing a plane on this notional treadmill, or performing a touch-and-go on it. Would the plane stop dead as soon as it touched the treadmill? Nope. The wheels would spin at the speed of the craft but this is completely irrelevant, the engine(s) are providing thrust against the surrounding air and this is keeping the craft moving forward - just as would be the case when initial takeoff began.

MrCreosote

cormy wrote: »

I can't believe this debate is still going on. The plane will take off regardless of the treadmill speed. The reason this gets confusing is because the wiring in our brains seems to make us attribute too much significance to the speed of the wheels. The engines are pushing against the surrounding air and so the craft *will* move forward/accelerate ... simple as that ... (forget about the wheels - they are irrelvant). Think about it another way: imagine landing a plane on this notional treadmill, or performing a touch-and-go on it. Would the plane stop dead as soon as it touched the treadmill? Nope. The wheels would spin at the speed of the craft but this is completely irrelevant, the engine(s) are providing thrust against the surrounding air and this is keeping the craft moving forward - just as would be the case when initial takeoff began.

Maybe this is a good way of thinking about it- thinking about what would happen in the opposite situation i.e. a plane landing? Thanks for all the replies! It's been getting on my nerves for a few days now...

asdasd

Good thread. Well done biro.

youtheman

I thought this was a simple problem, but the more I thought about it, the more I realised it was a little more difficult.

I've applied my superior engineering brain to come up with the following logic (and I welcome it being shot out of the air):

Assume the plane has a take off speed of 10 mph.

Step 1
Put the model plane on the threadmill. Leave the engine off. Turn on the threadmill. The plane will move backwards. No argument there.

Step 2.
Put the model plane on the threadmill. Leave the engine off. Turn on the threadmill to 8 mph. Keep a push on the back of the plan with a force 'F' to keep it stationary (i.e. to balance the friction in the undercarriage).

Step 3.
Put the model plane on the threadmill. Turn the engine on. Turn off the threadmill. If the engine applies a force of 'F' then the plane will reach 8 mph (as confirmed by Step 2). This assumes no friction in the air. In reality you will have to apply a force of 'F' plus a % to reach the 8 mph (the extra allowing for the air friction). You will have to apply a force of 'F' plus %% to reach the take off speed of 10 mph (to overcome the total air friction and the undercarriage friction). The action/reaction is between the aircraft engine and the surrounding air.

Step 4
Now to the original query. Turn on the threadmill to 10 mph. As long as the engine can develop a thrust of 'F' plus %% then the aircraft will reach 10 mph and take off ('F' will get it to 8 mph allowing for the undercarriage friction, the extra % will allow for the air friction and the extra %% will allow for 8 mph to 10 mph).

So its not about the threadmill speed, the power is not being applied throuh the threadmill. It's about having enough power to get the plane to the take off speed (allowing for the various frictions involved).

asdasd

If the engine applies a force of 'F' then the plane will reach 8 mph (as confirmed by Step 2)

Thats not quite right. The only force you are acting against when the treadmill is going backwards is the friction force on the wheels, going forward at the same speed you need to accelerate the large object to eight miles an hour which needs the equivalent thrust backwards.

If in fact you applied that force instead of just holding the plane when the treadmill was going backwards at 8 miles ah hour, the plane would go forward at 8 miles an hour and the wheels spin as if they were going forward at 16 miles an hour.

In the grand scheme of things the wheel friction in negligible.

FOGOFUNK

I cant believe this thread lasted so long.

Basically take off speed has no relation to the undercarriage or surface the plane is sitting on.

Think of seaplanes, if a current is flowing the opposite direction, the take off speed doesnt change.

Takeoff speed is only relative to airflow over the wings.

asdasd

I can't believe you didn't understand any of the thread.

FlutterinBantam

FOGOFUNK wrote: »

I cant believe this thread lasted so long.

Basically take off speed has no relation to the undercarriage or surface the plane is sitting on.

Takeoff speed is only relative to airflow over the wings.

Weeeeeey.:D:D:D:D:D


One shiny new Euron to the man with the Phil Lynott haircut.

Manic Moran

Also depends on the airplane.

Harriers, Forgers and Freestyles will be able to take off with little trouble regardless of what the treadmill is doing, for example.

There are also fixed-wing aircraft designed to have the airflow from the engine pass directly over the wing, thereby creating lift even without forward movement. Usually you need to get a little forward motion, but if the engine is strong enough and the aircraft light enough, you will get lift without forward velocity of the fuselage compared to the ground.

NTM