Airplane on a Conveyor Belt...

[sluggish]

Originally posted by john9001
that does not answer the question, why do you want the wheels locked when a wench cable is attached to the plane?

lets try this, put a sail plane on the belt and the tow plane off the belt, when the tow plane takes off will the sailplane take off or will the belt hold both planes at 0 mph ground speed.

If you'll look you'll see I went back and edited the post to make it more easily understood.  The planes wheels aren't locked.  The winch will be able to pull the plane forward if it were powerful enough to drag the plane when it's wheels are locked.

If the tow plane has enough thrust to drag the sail plane with it's wheel locked then it will move.  If not, it won't move.

[eskimo2]

Originally posted by john9001
that does not answer the question, why do you want the wheels locked when a wench cable is attached to the plane?

lets try this, put a sail plane on the belt and the tow plane off the belt, when the tow plane takes off will the sailplane take off or will the belt hold both planes at 0 mph ground speed.

I’m sorry.  I think we are talking about two different things.  My wheels locked example was addressing whether there would be sufficient traction for the treadmill to keep the plane in place through loading rotational inertia into the wheels.  Your talking about the cable illustration.

[AKIron]

Here's an argument to say the guys that did this on TV did it wrong. Obviously they ran the belt at the same speed but opposite direction of the plane. If the original poser of the question intended for the belt to match the speed of the plane then why were "wheels" specifically mentioned instead of just saying the belt must match the speed of the plane?

[eskimo2]

Originally posted by AKIron
Here's an argument to say the guys that did this on TV did it wrong. Obviously they ran the belt at the same speed but opposite direction of the plane. If the original poser of the question intended for the belt to match the speed of the plane then why were "wheels" specifically mentioned instead of just saying the belt must match the speed of the plane?

The original AH BBS question last year by rabbidrabbit specified wheel speed.  We found out in that thread that this question has been around the Internet, but specified the treadmill matches the plane’s speed.

[SaburoS]

Originally posted by eskimo2
Suppose the wheel is only rolling 2 mph on the treadmill, but its center/axle is not moving down the runway.  The treadmill also must be going 2 mph…  In this case the treadmill is matching the wheel’s speed.


Now imagine the wheel is only rolling 2 mph on the treadmill, and its center/axle is moving down the runway at 1 mph.  The treadmill must be going only 1 mph…  In this case the treadmill is not matching the wheel’s speed.

Now imagine the wheel is rolling 1,002 mph on the treadmill, and its center/axle is moving down the runway at 1 mph.  The treadmill must be going only 1,001 mph…  In this case also, the treadmill is not matching the wheel’s speed.

When the treadmill is matching the wheel’s speed, the plane is stationary.

Hmmm. I think the question has to do with the wheel's rotational speed, not the ground speed of the plane.
If the wheels were powered by the vehicle then one can say that wheel speed and ground speed are the same (provided traction isn't lost).

In this case the wheel speed is independent of the ground speed.
The conveyor must react and try to match the wheel's rotational speed, not have the conveyor set up the speed(s) to which the wheel has to match.

As it stands in real life, the runway and the wheel speed is the same as it is the plane that is moving forward and taking off.

Now think of this sample:

The magic conveyor has little to no rotational inertia (very little mass) so it takes practically no force to get it to accelerate. Now we line up our Cesna but it has very poor bearings in its wheels (the wheels are hard to turn). Pilot guns the throttle on the Cesna on this conveyor. The plane goes down the runway and takes off with zero wheel speed (remember that the conveyor has to match the wheel speed in our example) at 100knts ground speed.

In my sample (extreme, I know) the conveyor fulfills the matching wheel speed as it has to react to the wheel speed.
In your extreme example, the conveyor is setting and controlling the wheel speed, not the plane.

Therefore it does not meet the criteria (as I've interpreted the question).

[SaburoS]

Originally posted by eskimo2
The original AH BBS question last year by rabbidrabbit specified wheel speed.  We found out in that thread that this question has been around the Internet, but specified the treadmill matches the plane’s speed.

If that's the case then the plane that takes off at 100knts then the conveyor matches that speed in the other direction.
The conveyor doesn't add additional speed to other than to match.

Now if the question was that 'is it possible to have a magic conveyor runway go so fast as to keep the plane from taking off', then yes, you would be right.
But that's not the puzzle/question.
Plane still takes off.

[AKIron]

Originally posted by eskimo2
The original AH BBS question last year by rabbidrabbit specified wheel speed.  We found out in that thread that this question has been around the Internet, but specified the treadmill matches the plane’s speed.

Ah, well, there ya have it.

It should be fairly obvious to all that matching the plane's speed will have little effect on the outcome. Matching the spinning wheel speed is a much more interesting question.

[AKIron]

Some may wonder how many angels can dance on the head of a pin  but I'm sure you're wondering how many:

[VERTEX]

This issue has become unnecessarily confused and complex.

The conveyor can do three things.
1)
Rotate in the same direction the aircraft moves, which if the speed matches the forward speed of the aircraft the wheels rotation will be zero rpm.
2)
Rotate on the opposite direction the aircraft moves, which will impart an rpm higher than normal to the wheels.
3)
Rotate in the direction the aircraft moves but at a greater rate, which will cause the wheels to rotate backwards.

In all cases the aircraft will take off as normal because the direction and speed of rotation of the wheels has nothing to do with the forward motion of the aircraft. The propeller, spun by the engine pulls the aircraft forward as the propeller, "screws" itself through the air. The aircraft will fly at the point the wings generate enough lift as the aircraft travels forward trough the air which surrounds it. The wheels could be accelerating in a backwards rpm direction and the aircraft would still fly.

Granted, the takeoff roll would be slightly greater but it would be a small difference.

Note, I have assumed the conveyor has its own power source to drive the belt.

It really is this simple.

Thanks for reading

Vertex.

[SD67]

This is getting out of hand.
An aircrafts' engine moves air, period. This air generates thrust and it is the thrust that moves the aircraft forward. If the belt is started only once the aircraft starts to move, the aircraft will continue to move forward regardless whether the belt is going faster or slower, speeding up or slowing down. The airflow will build until sufficient lift is generated and the aircraft will fly. The only thing that will be affected is the relative rolling resistance due to the speed of the belt.
Only if the belt is started before the aircraft starts to move, the aircraft will move backwards initially until the level of thrust reaches a level sufficient to overcome the backwards motion of the belt. In this case if the speed of the belt is increased (exponentially?) to prevent parity will the aircraft fail to build sufficient airflow to generate lift.

[WWhiskey]

Originally posted by AKIron
Here's an argument to say the guys that did this on TV did it wrong. Obviously they ran the belt at the same speed but opposite direction of the plane. If the original poser of the question intended for the belt to match the speed of the plane then why were "wheels" specifically mentioned instead of just saying the belt must match the speed of the plane?

the original question did state that the speed of the belt would be equal to the take off speed of the plane I.E. 100 knots! the belt would be moving in the opposite direction of the plane! most planes differ in takeoff speed so whatever plane you use, if its take off speed is 50 or 60 or 75 then that is the speed of the belt! no more no less!

[eskimo2]

Originally posted by SaburoS
Hmmm. I think the question has to do with the wheel's rotational speed, not the ground speed of the plane.
If the wheels were powered by the vehicle then one can say that wheel speed and ground speed are the same (provided traction isn't lost).

In this case the wheel speed is independent of the ground speed.
The conveyor must react and try to match the wheel's rotational speed, not have the conveyor set up the speed(s) to which the wheel has to match.

As it stands in real life, the runway and the wheel speed is the same as it is the plane that is moving forward and taking off.

Now think of this sample:

The magic conveyor has little to no rotational inertia (very little mass) so it takes practically no force to get it to accelerate. Now we line up our Cesna but it has very poor bearings in its wheels (the wheels are hard to turn). Pilot guns the throttle on the Cesna on this conveyor. The plane goes down the runway and takes off with zero wheel speed (remember that the conveyor has to match the wheel speed in our example) at 100knts ground speed.

In my sample (extreme, I know) the conveyor fulfills the matching wheel speed as it has to react to the wheel speed.
In your extreme example, the conveyor is setting and controlling the wheel speed, not the plane.

Therefore it does not meet the criteria (as I've interpreted the question).

SaburoS,

Think about this: imagine the wheel is only rolling 2 mph on the treadmill, and its center/axle is moving down the runway at 1 mph. The treadmill must be going only 1 mph… In this case the treadmill is not matching the wheel’s speed.

Do you see this?

[eskimo2]

Originally posted by SaburoS
If that's the case then the plane that takes off at 100knts then the conveyor matches that speed in the other direction.
The conveyor doesn't add additional speed to other than to match.

Now if the question was that 'is it possible to have a magic conveyor runway go so fast as to keep the plane from taking off', then yes, you would be right.
But that's not the puzzle/question.
Plane still takes off.

Why would the conveyor be satisfied with 100knts?  Why choose to have the conveyor fail at that particular speed?  

If you were asked to match the speed a hare and a turtle also happened to be running along as well, would you just all of a sudden decide to match the turtle's speed as soon as the hare got a tad ahead of you?  No, you would do you best to keep up with the hare.

[eskimo2]

Originally posted by VERTEX


Granted, the takeoff roll would be slightly greater but it would be a small difference.

Vertex.

So, you do recognize that there would be a difference...  Now imagine that the acceleration rate of the conveyor is doubled.  That “slightly greater takeoff roll” would now be “slightly greater” times 2… Right?  Now imagine that the acceleration rate of the conveyor is 10,000 times what you were initially imagining…  It is a very big force now.

Imagine a question that asks, “Could a team of mice be as strong as a team of men?”  If you assume that there are the same number of mice as men, then clearly the answer is no, the men are stronger.  But “team” is not defined.  “Team” for men could be two, and “Team” for mice could be 200,000.

In the question where the conveyor must match the plane’s speed, an analogy could be: pitting men against the same number of mice.  In the question where the conveyor must match the plane’s wheel speed, however, an analogy could be: pitting men against a much larger number of mice.  Don’t assume that they have to be the same number!

[eskimo2]

To see this force watch these AVI's:


http://hallbuzz.com/movies/wheel_on_sander_250th.AVI



http://hallbuzz.com/movies/paper_treadmill.AVI [/B][/QUOTE]

Argue all you want; here is proof that the force exists.