Plane on a treadmill argument...

[Nick]

A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

Will the plane be able to take off?

[Flybrian]

The ability for a fixed-wing aircraft to fly is based on the speed (and pressure) of the air travelling over its airfoil(s). Therein lies your answer.

[76ChevyTrucker]

Yeah, its Bernoulli's (sp?) Principle. As speed increases over an airfoil (see, wing) shaped section, the air coming over the top of the wing has to speed up to meet the air coming under the wing. That creates a pressure difference, lower pressure being on the top, higher pressure on the bottom, and in an effort to equalize pressure, you generate lift. So theoretically, yes, the aircraft should be able to fly.

Edited: By the way, that's aerodynamics 101 for me, as a previous Aerospace Engineer and Certified Private Pilot.

Edited June 25, 2006 by 76ChevyTrucker

[Flybrian]

Are you current on your license/medical, 76?

[76ChevyTrucker]

Lost my medical in May 2004, didn't have the money to renew it, still don't, so no, I'm not current.

[PurdueGuy]

I was under the impression that most aircraft wheels were not powered, but that the engines provided the power, so the moving runway would just make the wheels spin faster and the plane would move pretty much as usual?

[76ChevyTrucker]

The only power directed to the wheels of an aircraft is braking power, which would provide a negative reaction. But the idea is that no matter how hard you jam the throttles ahead, you would be "negating" the forward motion provided from engine thurst.

[Drew Dowdell]

A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

Will the plane be able to take off?

yes.

forward motion is provided by the thrust of the engines, not the spining of the wheels.

All the belt will do is stop the spinning of the wheels completely and match the forward speed of the aircraft.

[ocnblu]

Help a retard here. I don't understand how the plane can take off if it is on a treadmill. It cannot gain any forward motion if it's on a treadmill, so how can it generate speed enough to achieve lift?

[Nick]

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

...

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

[Drew Dowdell]

ok... so I was right... either way it's worded.

If the belt is moving in the opposite direction of the plane at a speed equal to, but opposite direction of the plane, the plane will still take off. Any speedometer attached to the wheels will report a speed double the actual speed.

[Sixty8panther]

No... not even a fat chance.

The ability for a fixed-wing aircraft to fly is based on the speed (and pressure) of the air travelling over its airfoil(s). Therein lies your answer.

exactly & the air under the wing is not moving...

This is like putting a Lamborghini Countach on

free-moving rollers and strapping it down, then

accelerating to 200mph. The car still aint going

anywhere!

"Wheah you goin'? That's right NO-wheah!" [boondocksaints]

[Sixty8panther]

A plane is standing on a runway that can move (like a giant conveyor belt). This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

Will the plane be able to take off?

You guys need to re-read it... the plane is NOT

moving relative to the air or ground. Only

relative to the treadmill & therefore air speed

is 0.0000 mph.

[Drew Dowdell]

You guys need to re-read it... the plane is NOT

moving relative to the air or ground. Only

relative to the treadmill & therefore air speed

is 0.0000 mph.

Sly, consider this:

1. Put your maxima in neutral

2. Strap a solid fuel rocket to the top

3. place on magic treadmill

4. light rocket

5. stay off the brakes.

What happens next?

You want to try and tell me that you're not going anywhere?

[scharmer05]

yes....the plane takes off, but the wheels are just spinning twice as fast

[NOS2006]

Okay, I get it, but it took me awhile. Yes, the plane takes off.

Why does the plane take off? Well, the plane is going at whatever speed.. It wouldn't take off if it didn't have wings. However, since it has wings, it takes off because it's going that fast no matter what. The wheels are just free-spinning and don't matter.

It's hard to explain, but I get it.

[scharmer05]

Okay, I get it, but it took me awhile. Yes, the plane takes off.

Why does the plane take off? Well, the plane is going at whatever speed.. It wouldn't take off if it didn't have wings. However, since it has wings, it takes off because it's going that fast no matter what. The wheels are just free-spinning and don't matter.

It's hard to explain, but I get it.

yep, the plane is still going forward its just that the ground is moving under it

[Sixty8panther]

Oh $hit yeah, the Maxima would jump off the treadmill and into a tree

or other stationary object in that scenario.

From the way it was written it sounds like no matter how much thrust

the plane generates the tread mill keeps up so that the plane does

not actually move relative ot the stationary ground. In other words,

with the friction of the wheels spinning at XXX mph the plane is still

standing still even though such a treadmill does not exist that is the

way I read it.

[the_yellow_dart]

Sorry guys, but I'm pretty good at physics, and I'm quite sure the plane would NOT take off.

Unless your plane tires are greased and are going to slide along the treadmill, they will rotate no matter where the power is coming from. So, no matter if the power was coming from the jets or the wheels, the plane wouldn't move, because the treadmill would counteract the speed.

It would probably be VERY fast though! Jets have enough power to push the large plane through the air against all that friction. If the plane was standing still and all the jets were really doing was pushing the wheels faster and faster against the backwards force of the treadmill, the wheels could get going much faster than the plane normally could, since the air would be standing still and offering much less friction then normal. Of course, that same dead air would generate no lift.

[zhawk]

Sorry guys but this plane isn't going anywhere.

It only has motion relative to the treadmill as the problem is written.

The aircraft is stationary in respect to all other elements and that includes the air that is required to flow around the wing.

The treadmill removes the ability to move forward in relation to the surrounding air and create the lift necessary.

[Drew Dowdell]

Consider:

The plane's movement relative to the ground is irrelevant.

The plane's movement to the air is what allows it to take off.

The jet engine provides thrust through the air.

The tread mill provides a counter acting thrust on the wheels.

The wheel bearings remove the effect of the thrust from the treadmill.

The average speed of a loaded 747 take off is around 120 knots <so I've read>.

All the treadmill will do is spin the hell out of the wheels while the jet is taking off.

[z28luvr01]

The real question is: does the thrust generated by the engines somehow increase the speed of the air moving over the wings? Tire speed really means zilch. The engines take in air and throw it out the back at a much higher speed. However, this has no effect on the air that traveling over the wing, and if it's on a treadmill the plane's speed relative to the air around it is still zero, so I'm saying that nothing happens to the plane other than getting a good workout.

[Drew Dowdell]

The real question is: does the thrust generated by the engines somehow increase the speed of the air moving over the wings? Tire speed really means zilch. However, the plane's speed relative to the air around it is still zero, so I'm saying the plane gets nothing more than a good workout.

Does the engine push the plane forward?

If not, why?

[ocnblu]

The engine pushes the plane forward on its wheels initially, it has to gain enough ground speed via the wheels before it can gain lift to fly. If the speed of the treadmill is the exact speed of the wheels, it will never gain speed for lift. Edited June 26, 2006 by ocnblu

[z28luvr01]

Oldsmoboi...check my edited post

[the_yellow_dart]

The engine doesn't push the plane forward because for that to happen, the wheels have to either:

a. slide along (not going to happen) or

b. go faster than the treadmill (which violates the question)

The jets probably would create SOME wind across the wings, but not enough for takeoff.

This raises another interesting question though: If a strong enough backwards wind hit a parked plane with the flaps in the right position, would it take off?

Edited June 26, 2006 by the_yellow_dart

[ocnblu]

We've seen airports after hurricanes. Pretty messed up.

[Flybrian]

The engine itself doesn't push the plane forward by any means of traction like an automobile engine would. Aircraft propulsion systems are intended to create lift by pushing the plane forward through air, moving air past the airfoil, etc.

This raises another interesting question though: If a strong enough backwards wind hit a parked plane with the flaps in the right position, would it take off?

If by backwards you mean a wind coming from behind the plane, then no. The airfoil wouldn't be generating any positive lift, though the stabilizer may simply have enough air pushing under it to kick the plane onto its nose.

Here's another one - can a plane gain lift if it remains perfectly stationary in realtion to the ground? Absolutely. Not only in wind tunnels, but I've seen this happen during storms. Your typical single-engine 4-seat plane weighs about 2200-2700lbs and has a rotation speed of about 45-60kts. If the plane isn't tied down too tautly on the ramp, it will actually partially or completely lift off the ground and settle back down because the wind passing under/over the airfoil generates the lift. Its groundspeed would be 0kts though the airspeed indicator would display whatever the windspeed is.

[Drew Dowdell]

Let me phrase it this way....

what force is being exerted on the body of the plane by the treadmill?

or another way.....

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?

The engines provide thrust on the body of the plane

the treadmill provides the thrust on the wheels of the plane

the bearings in the wheels neutralize the opposing forces

[Drew Dowdell]

Want to see an Aveo fly?

1. Place Aveo on dynometer

2. Run Aveo up to 70mph in reverse.

3. Light the solid fuel rocket attached to it's roof.

which way will the Aveo travel?

[Newbiewar]

The average speed of a loaded 747 take off is around 120 knots <so I've read>.

All the treadmill will do is spin the hell out of the wheels while the jet is taking off.

okay spin the hell out of the wheels...

but what is the maximum speed those wheels will turn?

every wheel has a maximum volocity under a certain force, there comes a point when there is too much road friction, to much friction on the ball bearings such that the wheels are incapable of increasing speed... if the treadmill can match that speed, i find it difficult that the plane will ever take off...

anyone who has ever ridden a skate board knows what i mean... the wheels although you can purchase higher quality bearings and wheels... they have an eventaul top speed...

[Flybrian]

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?

Assuming that you're in realtively calm conditons (i.e., no gale-force winds), then no. And it never would, even if you ran it up to 1000kts. All you'd do is burn up the bearings at some point.

[ocnblu]

Are we throwing wind speed into this equation? Now I'm getting more confused. The plane without a treadmill gains speed initially by pulling itself along on its wheels until it achieves enough ground speed to generate lift. If the wheels are on a treadmill, the plane cannot move or gain enough speed to generate lift, true or false? This thread is gonna go on and on like a treadmill. Someone unplug it please! :AH-HA_wink:

[the_yellow_dart]

Let me phrase it this way....

what force is being exerted on the body of the plane by the treadmill?

or another way.....

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?

The engines provide thrust on the body of the plane

the treadmill provides the thrust on the wheels of the plane

the bearings in the wheels neutralize the opposing forces

Exactly. No net force = no acceleration -> no movement. No movement means no wind speed over the wings.

[ocnblu]

Correct me if I'm wrong here, an airplane lifts off horizontally, not vertically like a helicopter. It needs ground speed to lift off.

[Drew Dowdell]

okay spin the hell out of the wheels...

but what is the maximum speed those wheels will turn?

every wheel has a maximum volocity under a certain force, there comes a point when there is too much road friction, to much friction on the ball bearings such that the wheels are incapable of increasing speed... if the treadmill can match that speed, i find it difficult that the plane will ever take off...

anyone who has ever ridden a skate board knows what i mean... the wheels although you can purchase higher quality bearings and wheels... they have an eventaul top speed...

I assume that Boeing uses slightly higher quality bearings then what one might find on a skateboard.

[Drew Dowdell]

Exactly. No net force = no acceleration -> no movement. No movement means no wind speed over the wings.

there are plenty of net forces...

the bearings of the wheels ensure that there are no forces from the treadmill effecting the body of the aircraft

If the aircraft moves forward, the treadmill moves backwards. The force of the treadmill is rendered irrelevant because of the bearing in the wheel hubs. Because there is no backwards force pushing on the body of the aircraft, the plane continues to move forward.

[Flybrian]

Correct me if I'm wrong here, an airplane lifts off horizontally, not vertically like a helicopter.  It needs ground speed to lift off.  

No.

It needs lift and the motion of air passing over/under the airfoil, either generated artifically (wind tunnel) or by the plane moving itself through the air. This is speed relative to the air its travelling though, i.e. airspeed. Groundspeed is derived from your indicated airspeed and timing how long it takes you to fly over a certain distance and using one of these fun little guys...

...and indicated your motion relative to the earth's surface. If you have a tailwind, your groundspeed will be higher than your indicated airspeed. If you have a headwind, the opposite. Groundspeed is useful in calculating about how long it'll take you to arrive at your destination (navigation).

Oh, and for the record, these are the different 'speeds'...

Indicated airspeed

Calibrated airspeed

True airspeed

Equivalent airspeed

Groundspeed

And, yes, we have to learn all those...except equivalent...because I'm not flying that high or that fast...yet.

[Drew Dowdell]

Correct me if I'm wrong here, an airplane lifts off horizontally, not vertically like a helicopter.  It needs ground speed to lift off.  

it needs air speed.

again, look at my solid fuel rocket examples.

which way do you think an Aveo in neutral is going to travel if you put it on the same treadmill with a rocket strapped to the roof?

[ocnblu]

Sorry Brian and Drew, now we're arguing semantics. I used the wrong term. If the plane cannot gain air speed it will not take off, correct? Edited June 26, 2006 by ocnblu

[Flybrian]

Sorry Brian, now we're arguing semantics.  I used the wrong term.  If the plane cannot gain air speed it will not take off, correct?

In layman's terms, yes.

Technically-speaking, its lift that's needed and lift and airflow themselves is not something that can be directly measured, hence why airplanes can stall (not enough positive lift) at any airspeed.

Believe me, I don't know all of it myself and I'm probably not explaining it the best either. I really haven't yet met a person who can really explain every facet of lift and how it works in a way that everyone can understand. I've read a book that says that Bernoulli's Principle as its commonly explained isn't exactly right. Lift is just generally something pilots accept as 'being'...and we always, always want lift.

[the_yellow_dart]

it needs air speed.

again, look at my solid fuel rocket examples.

which way do you think an Aveo in neutral is going to travel if you put it on the same treadmill with a rocket strapped to the roof?

You're missing a very simple piece of my argument though. How can it possibly move forward if the wheels can't go faster than the treadmill? The wheels don't slide, and the plane doesn't lift without moving forward. Hence, no movement.

[ocnblu]

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?

[the_yellow_dart]

Remember though - even if we ignore friction entirely, it still takes energy to make mass (like in the wheels) rotate. So all the energy from the jets will go to making the wheels spin faster and faster until they melt off.

[Drew Dowdell]

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?

You've got it!

[ocnblu]

I don't think I do, Drew. Give it to me straight.

[Drew Dowdell]

Remember though - even if we ignore friction entirely, it still takes energy to make mass (like in the wheels) rotate. So all the energy from the jets will go to making the wheels spin faster and faster until they melt off. 

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.

[ocnblu]

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

[the_yellow_dart]

You just violated the original stipulations with your example. If the wheels are going 300 mph, the treadmill should be going 300 mph too. Otherwise we just threw out the original question.

[Drew Dowdell]

I don't think I do, Drew.  Give it to me straight.

Put a jet engine in the bed of your colorado.

Put the colorado in neutral.

Light up the jet engine and see what happens with 30,000 lbs of rearward thrust.

tell me what happens....