Mythbusters tackles the plane/treadmill

[TurboTnZ06]

Only 10 more "It won't fly" votes needed! C'mon!

 

[Pitbozz]

Ummm.. I don't know. Maybe catapults are more EFFICIENT than a treadmill would ever be, and by turning into the wind, MAXIMUM AIRFLOW can be achieved....

Let's keep going with this. Do you think if they did place a plane on a treadmill and ran it in the same direction as the plane that it would take off a hell of alot quicker and in a much shorter distance?

 

[Pitbozz]

The question is slightly unclear: if the conveyor "tracks the plane's speed" and keeps it exactly zero, then obviously, no, the plane would not take off as it would be stationary with respect to the air. I don't see what could possibly be difficult to understand about that.

The way the question is worded though, it could mean to say that the plane moves forward at 150kts, while the conveyor belt moves backwards at 150kts, for a rotational speed of 300kts for the wheels. In that case, as long as the wheels don't burn off, the plane would take off.

Perhaps the wording is all that is causing the problem there...



Looking only at friction, and assuming the aircraft could take off if unhindered the cases are as follows:

Case 1: If the treadmill is frictionless and the wheel bearings have any amount of friction, the treadmill will move (in the direction of flight), the wheels will not turn, and the plane will lift off.

Case 2: If the treadmill has any friction and the wheel bearings do not, the treadmill will not turn, the wheels will turn, and the plane will lift off as if on a conventional runway.

Case 3: If the treadmill and wheel bearings have infinite friction, the aircraft will sit there under maximum power and not move, unless maximum power overcomes the friction between the wheel and the treadmill, then all hell breaks loose.

Case 4: If the treadmill and wheel bearings both have some friction, but not enough to stop the plane from reaching takeoff velocity, either the treadmill or wheels will turn, or both the treadmill and wheels will turn, and the plane will take off (albeit with a longer takeoff roll than in Cases 1 & 2)

Case 4 is what actually happens and has a few subcases to it:

Case 4a: There is a threshold of treadmill friction where, if the wheel bearings have a much smaller friction, the wheels will turn and the treadmill will not.

Case 4b: Conversely, it's possible for the wheel bearings to have a relatively high friction compared to the treadmill where the treadmill turns and the wheels do not.

Case 4c: It is also possible for combinations of treadmill/wheel bearing friction to have both the treadmill turning AND the wheels turning during the takeoff roll.

The question is pretty clear. People get it wrong by thinking the treadmill will keep the plane stationary and it won't. They confuse the fact that a plane is NOT wheel driven but their logic thinks it is.

 

[87GNSteve]

I don't know how else to tell ya' man. The plane will take off just like it normally would. Re-read the posts here about why it will move and take off just like it would on a normal runway. Maybe it will click. If it does click, come back and save a little face.

I absolutley understand what you are saying:
that since the wheels arent driven by gear, and are free rolling they would just be spinning at double the speed they normally do at take off speed since the 'jet' is pushing it.

BUT my interpretation of the question is that the conveyor halts any forward motion by counteracting with the exact opposite power. and therefore since no forward progress is achieved no take off is achieved.

Now do you see my point?
What exacly is the conveyors job? that is the reason for the divide here.

 

[Pitbozz]

I absolutley understand what you are saying:
that since the wheels arent driven by gear, and are free rolling they would just be spinning at double the speed they normally do at take off speed since the 'jet' is pushing it.

BUT my interpretation of the question is that the conveyor halts any forward motion by counteracting with the exact opposite power. and therefore since no forward progress is achieved no take off is achieved.

Now do you see my point?
What exacly is the conveyors job? that is the reason for the divide here.

There it is! You have all the aspects of it correct, EXCEPT for thinking the treadmill will halt the forward motion. It can't and won't stop the plane from rolling out and taking off.

 

[Pitbozz]

Let's see if this works.

 

[Geoff87]

Let's keep going with this. Do you think if they did place a plane on a treadmill and ran it in the same direction as the plane that it would take off a hell of alot quicker and in a much shorter distance?

It would, and it should. Hence the reason for the catapult on the aircraft carrier.

Am I missing something here? - I'm assuming the the plane will remain stationary while moving, like a runner on a treadmill. That is, I'm assuming that like a runner, the plane does NOT move forward on the treadmill.

Now if the plane moves forward fast enough on the treadmill to go forward, AND pass enough air over its wings, then it MAY fly. But what would be the point of that experiment?

If it remains stationary it WILL NOT FLY, in my opinion.

If it does, I'll buy a parachute as an additional safety device the next time I run on a dyno. I'll also install a rear wing for the additional downforce on the rollers.

 

[ITSNOTAGN]

I absolutley understand what you are saying:
that since the wheels arent driven by gear, and are free rolling they would just be spinning at double the speed they normally do at take off speed since the 'jet' is pushing it.

BUT my interpretation of the question is that the conveyor halts any forward motion by counteracting with the exact opposite power. and therefore since no forward progress is achieved no take off is achieved.

Now do you see my point?
What exacly is the conveyors job? that is the reason for the divide here.

This is where people are DEAD wrong in thinking it would not take off. For this to happen the plane would have to be attached to the treadmill somehow, or be in some sort of enclosed vaccuum chamber that would surround the plane and also control the air. A treadmill cannot control air, it can only control what it is (the ground) and what is immediately attached to it.
To think a treadmill is in any way going to effect the air going over the wings is just plain wrong, and thus, the treadmill has no effect on whether the plane will fly or not

Case has been made with the pontoon plane. If a plane only requires 30mph to leave the ground, and it is on a river that has a 30mph current, it still only has to reach 30mph relative to the space around it, the water itself has no effect on the plane. Just that the pontoons would see 60mph, a 30mph vector of the plane, and a opposite 30mph vector of the water. Fact is the plane is still going 30mph and will still take off.

Really the river principle is the best way to look at this, and is alot easier to see than the treadmill, and is 100% equal in application. the water is precisely matching and opposing the speed of the airplane, but the plane is still moving forward relative to someone that is on dry ground.

Gary

 

[Pitbozz]

It would, and it should. Hence the reason for the catapult on the aircraft carrier.

Am I missing something here? - I'm assuming the the plane will remain stationary while moving, like a runner on a treadmill. That is, I'm assuming that like a runner, the plane does NOT move forward on the treadmill.

Now if the plane moves forward fast enough on the treadmill to go forward, AND pass enough air over its wings, then it MAY fly. But what would be the point of that experiment?

If it remains stationary it WILL NOT FLY, in my opinion.

If it does, I'll buy a parachute as an additional safety device the next time I run on a dyno. I'll also install a rear wing for the additional downforce on the rollers.

Okay. The catapault isn't attached to the wheels. It is attached to the structural body of the plane. Just like the engines are. If the plane were put on a treadmill running in the same direction, it would be akin to pulling the tablecloth out from under some dishes. And your runner on the treadmill comparison is incorrect also. The runner is using his legs for power. Attach a rocket to the back of your runner and what happens?

It will NOT stay stationary and it WILL fly.

 

[Geoff87]

If the plane doesn't remain stationary, then what is the point of the experiment?

 

[ITSNOTAGN]

If the plane doesn't remain stationary, then what is the point of the experiment?

Exactly, the treadmill has no effect on the plane does it???

 

[GullsGN]

There is the key. The question relates the speed of the treadmill to the speed of the AIRPLANE, not the speed of the tires. The treadmill cannot match the speed of the tires. If the tires are going 10mph as soon as the treadmill is going 10mph then the tires are instantly going 20mph, as soon as the tires are going 20, the treadmill goes 20, now the tires are going 40. You can match the treadmill to the planes speed. If the plane is going down the runway at 20 you can speed the treadmill to 20 but the wheels will be going 40 You cannot have the wheels and treadmill match speeds.

 

[Pitbozz]

If the plane doesn't remain stationary, then what is the point of the experiment?

That's the whole point of the question.

 

[Pitbozz]

There is the key. The question relates the speed of the treadmill to the speed of the AIRPLANE, not the speed of the tires. The treadmill cannot match the speed of the tires. If the tires are going 10mph as soon as the treadmill is going 10mph then the tires are instantly going 20mph, as soon as the tires are going 20, the treadmill goes 20, now the tires are going 40. You can match the treadmill to the planes speed. If the plane is going down the runway at 20 you can speed the treadmill to 20 but the wheels will be going 40 You cannot have the wheels and treadmill match speeds.

But the thing is, the speed of the treadmill doesn't really matter. The plane will roll out and take off no matter what the speed is.

Because......













wait for it.......












almost.........












The treadmill is irrelevant.
The treadmill is irrelevant.
The treadmill is irrelevant.
The treadmill is irrelevant.
The treadmill is irrelevant.

 

[Pablo]

An altimeter not only tells you the distance from the ground. It can also tell you how fast the aircraft is approaching the ground. Probably the most important cockpit instrument there is in my opinion.


I understand what most are arguing in the pro argument. Thrust will over come the speed of the treadmill, creating forward motion. The treadmill in turn would speed up negating the effect of thrust.

Thrust alone will pull SOME air across the wings, it would take an enormous amount of thrust, spread out over an enormous airsurface for this to occur.

Your knowledge of aviation is lacking.

An altimeter does not tell you how fast an aircraft is approaching the ground. An altimeter only tells you how far you are from sea level. It makes this assumption based upon barometric pressure. Every time you take off you have to calibrate an altimeter to atmospheric conditions in order for it to give you a relatively accurate measure of altitude.

Altitude is not a measure of distance from the ground it is a measure of your distance from sea level. (I told you this before, apparently you did not read it) For every 1000 feet you go up you lose 1"HG of pressure. An altimeter is nothing more than a fancy barometer.

Repeat after me, Altimeters Do NOT tell you where the ground is!

There is an instrument that measures how fast you are changing in altitude, and that is the vertical speed indicator. An altimeter does not tell you how quickly you are changing altitude unless you have a supercomputer for a brain. Most people don't and thats why most aircraft have a VSI. It too operates based upon pressure changes. I could tell you how it works but I'd be wasting my breath.

Neither of these instruments have anything to do with where the ground is in an airplane. For that you need maps and navigation equipment to know what the terrain is like around you.

The treadmill is irrelevant. Nothing the treadmill could do can counteract anything the airplane is doing. Airplanes move air to fly, not ground.

 

[GNandGS]

 

[imjoesnuffy]

Your knowledge of aviation is lacking.

An altimeter does not tell you how fast an aircraft is approaching the ground. An altimeter only tells you how far you are from sea level. It makes this assumption based upon barometric pressure. Every time you take off you have to calibrate an altimeter to atmospheric conditions in order for it to give you a relatively accurate measure of altitude.

Altitude is not a measure of distance from the ground it is a measure of your distance from sea level. (I told you this before, apparently you did not read it) For every 1000 feet you go up you lose 1"HG of pressure. An altimeter is nothing more than a fancy barometer.

Repeat after me, Altimeters Do NOT tell you where the ground is!

There is an instrument that measures how fast you are changing in altitude, and that is the vertical speed indicator. An altimeter does not tell you how quickly you are changing altitude unless you have a supercomputer for a brain. Most people don't and thats why most aircraft have a VSI. It too operates based upon pressure changes. I could tell you how it works but I'd be wasting my breath.

Neither of these instruments have anything to do with where the ground is in an airplane. For that you need maps and navigation equipment to know what the terrain is like around you.

The treadmill is irrelevant. Nothing the treadmill could do can counteract anything the airplane is doing. Airplanes move air to fly, not ground.

Pablo,

You seem like a pretty fart smeller. You are correct, but you asked for an instrument that would tell you what the ground is doing. In the most simplest of terms, it can tell you how fast it is approaching the aircraft or vice versa. I also understand how it works through pressure.

If I am flying an aircraft, and I run out of gas or the engine stalls and I lose forward motion and I roll into a dive. Now would that altimeter tell me anything?

I know it has nothing to do with ground speed, but you asked for an instrument that would tell you something about what the ground was doing. Now repeat after me. An altimeter can tell you how long you have to kiss your a$$ goodbye :biggrin: in that scenario.

You are correct also that airplanes use air for travel. Where will that air come from if forward motion is negated?

 

[87GNSteve]

You are correct also that airplanes use air for travel. Where will that air come from if forward motion is negated?

They are ignoring this concept.

Most contend that the conveyor is limited to counteracting the speed of the planes wheels; sort of like a shortened runway idea.

BUT if the conveyor counteracts the speed of the plane AKA the velocity of which it travels forward,then the plane is limited to a stationary area.

Like I said this experiment would be hard to duplicate in real life. You would need a super high speed, low friction conveyor and willing to risk destruction of a plane (and conveyor) when the wheels/bearings hit critical limits.
One can't use a model plane on an exercise treadmill and call it an accurate scientific experimentation, since the speed control is way off, and it doesnt have the capability to keep up.

 

[Madcat455]

One can't use a model plane on an exercise treadmill and call it an accurate scientific experimentation, since the speed control is way off, and it doesnt have the capability to keep up.

I disagree... a treadmill and model airplane will prove the concept. As long as the take off speed of the plane is less than the belt speed of the Treadmill, then the treadmill has the advantage since it can over compensate.

It's basically a Cause and effect thing...

The airplane starts to move forward, causing the belt to rotate equally in the opposite direction, but the belt can ONLY effect the tires that contact it. Since the tires have NO control over the speed of the plane, other than to lessen rolling friction, the plane will take off as it would any other day.

Simply because the belt only touches the tires, and the tires only spin... nothing else.

The only purpose of the "speed matching" part of the question, it to trick people into thinking it has importance. When it is not important, that belt could be rotating 1000mph in reverse, and the only thing that will be effected is the rotation of the tires. Which can't keep the plane still.


If TU24 doesn't kill us all on the 29th , Mythbusters will put this to bed on the 30th.

 

[Pitbozz]

They are ignoring this concept.

Most contend that the conveyor is limited to counteracting the speed of the planes wheels; sort of like a shortened runway idea.

BUT if the conveyor counteracts the speed of the plane AKA the velocity of which it travels forward,then the plane is limited to a stationary area.

Like I said this experiment would be hard to duplicate in real life. You would need a super high speed, low friction conveyor and willing to risk destruction of a plane (and conveyor) when the wheels/bearings hit critical limits.
One can't use a model plane on an exercise treadmill and call it an accurate scientific experimentation, since the speed control is way off, and it doesnt have the capability to keep up.

Obviously IF the treadmill kept the plane stationary it could not take off. Unless it was a Harrier. But the treadmill WON'T keep the plane stationary.

They tested it by using an ultralight and a bigass piece of tarp attached to a truck and under the airplane. Airplane starts to accelerate and truck accelerates in the opposite direction. Effectively it is the exact same as a treadmill.