Plane on a treadmill

MrCreosote · 01-04-2009 09:53PM #1

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 · 01-04-2009 09:54PM

Yes it will

Thomas_S_Hunterson · 01-04-2009 09:56PM

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 · 01-04-2009 09:56PM

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 · 01-04-2009 09:56PM

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 · 01-04-2009 09:59PM

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 · 01-04-2009 10:10PM

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 · 01-04-2009 10:26PM

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

MrCreosote · 01-04-2009 10:32PM

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

tracker-man · 01-04-2009 10:32PM

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 · 01-04-2009 10:51PM

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 · 01-04-2009 11:21PM

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 · 01-04-2009 11:36PM

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 · 01-04-2009 11:41PM

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 · 01-04-2009 11:47PM

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 · 01-04-2009 11:55PM

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 · 02-04-2009 12:11AM

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* · 02-04-2009 12:19AM

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 · 02-04-2009 07:06AM

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 · 02-04-2009 09:46AM

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! · 02-04-2009 10:19AM

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 · 02-04-2009 11:00AM

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 · 02-04-2009 12:05PM

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 · 02-04-2009 12:51PM

B36's used to use treadmills

Fratton Fred · 02-04-2009 01:33PM

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 · 02-04-2009 01:54PM

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 · 02-04-2009 02:30PM

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 · 02-04-2009 03:00PM

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 · 02-04-2009 03:08PM

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 · 02-04-2009 03:38PM

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 · 02-04-2009 03:39PM

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

Plane on a treadmill

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