Will the plane fly?

[the other pc]

Originally posted by Jeff Smith
I spoke with 1 of our flight test engineers this morning before I left work. His thoughts were the aircraft cannot fly. He pointed out something we had not looked at. With the aircraft not being able to develop any ground speed there would not be enough airflow over the aircraft control surfaces (Flaps) to be able to get the aircraft up into the air....

We have discussed this. As he points out airfow is needed over the control surfaces, i.e. air speed. We totally agree on this.

The mistake is equating ground speed with air speed or implying that the conveyor somehow affects the air speed. On a normal runway, in dead calm air, they are equal. In this artificial scenario ground speed is not air speed. They happen to be opposite. But ground speed doesn't matter since the ground exerts no drag force on the aircraft.

It doesn't matter that the ground is moving backward or forward, fast or slow, tracking the plane or moving randomly. It doesn't matter at all. It simply has no effect on the motion of the airframe. All of the airframe motion is due to propulsion thrust.


PC.

[Jeff Smith]

Originally posted by the other pc
As I said before, the motion of the conveyor has no effect (in this simplified example). The take off roll is exactly the same distance with or without it.

Your comment above is the point at where I lose you and start leaning in the other direction. I'll explain my thuoghts as best as my feable mind can.

It is my understanding that the point of the conveyor is to stop the possibilty of "ANY" distance being covered during a take off roll. In other word's long as the aircrafts wheels are in contact with the is conveyor there is not chance of it moving foreward. The wheels are spinning but there is no foreward movement of the aircraft itself. At least this is my understanding of the Conveyors purpose. To thwart "any" foreward motion while the wheels are in contact with the ground.

This aircraft, while not moving foreward while its wheel are on the ground is running it's engines up to full throttle to take off, still with weight on wheels and wheels on ground. So with no foreward motion this arcraft instantly acheives enough airspeed to simply lift off of it's wheels while standing still and flies away.

So this aircraft from a stationary position, goes 1 MPH then 2 then 3 then 4 and so on. up to it's given speed. This is all without the lift being generated form the air passing over the surface of the wings and this happens without air passing over the surface of the control surfaces.

Thats is where I lose your train of thought. This aircraft is sitting stationary as long as it's wheels are in contact with this conveyor. So from my understanding you re stating this aircraft is going to take off and fly from a stationary positon with no lift.

All this without the mementum built up from doing a ground rolla dn developing inital speed. As long as the aircraft is stationary I don't see this.

Even when one thinks in terms of airspeed as opposed to groundspeed, Those wheels are still in contact the the ground until that aircraft can generate enough thrust . In the meantime there is not enough lift being generated because of the lack of foreward movement and there can't be any foreward movement until the aircraft is off the ground and can't do this without lift.

[the other pc]

Originally posted by gb387
Would you get any "product sling" if you applied Endurance to the tires? If so, how do I prevent it, to further explain my thoughts on this subject?

Well, if you were getting sling on a regular runway you'll get a lot more on the conveyor.

The inertial force that slings tire dressing, holds NASCAR stockers on the high banks of Daytona and make the carnival whirl-n-puke so, um, entertaining, follows the equation:

Force=mw^2r

where:
m is the mass of the object (glob of dressing, Dale Jr., your kid and a stomach full of corn dogs)
w is the angular velocity of rotation (how fast it's spinning)
r is the radius from the center of rotation to the mass.

In the case of our aircraft tires, the conveyor is forcing them to spin twice as fast as they would on a fixed runway. Twice the speed means twice the angular velocity.

The force depends directly on mass and radius but it's dependent on the square of angular velocity. So twice as fast means four times the sling force!

I'd go with #40 since it soaks in and doesn't sling.

Side note; this massive increase in inertial force with rpms is the big reason engines fly apart when over revved, especially poorly balanced engines.


PC.

[the other pc]

Originally posted by Jeff Smith
..It is my understanding that the point of the conveyor is to stop the possibilty of "ANY" distance being covered during a take off roll....

This would only be true for a wheel driven vehicle. Any time the wheels are torqued to rotate the conveyor would move to cancel it. Our aircraft is not wheel driven. As engine thrust pushes the airframe the conveyor merely spins the tires beneath it.

Imagine you're towing the plane by walking along next to the conveyor and pulling the plane with a rope. As you take a step the plane moves with you and the conveyor moves the opposite direction under the tires. You keep walking and pulling the rope and as long as the wheels are free to spin (no brakes or chocks) the plane follows you. The tires have to turn faster because the conveyor is moving under them but the plane still follows you.

Now, replace the rope with prop thrust.

Originally posted by Jeff Smith
...In other word's long as the aircrafts wheels are in contact with the is conveyor there is not chance of it moving foreward....

Only if the brakes are on or the wheels are chocked. Otherwise, they roll freely.

Originally posted by Jeff Smith
... The wheels are spinning but there is no foreward movement of the aircraft itself. At least this is my understanding of the Conveyors purpose. To thwart "any" foreward motion while the wheels are in contact with the ground....

There is forward motion because it comes from engine thrust, not wheel torque. Whoever concocted this devilish little problem threw the conveyor in to try and trick us. The physicists I know can be very fiendish that way.

Originally posted by Jeff Smith
...This aircraft, while not moving foreward while its wheel are on the ground is running it's engines up to full throttle to take off, still with weight on wheels and wheels on ground...

If the brakes and chocks are off it will move forward.

Originally posted by Jeff Smith
... So with no foreward motion this arcraft instantly acheives enough airspeed to simply lift off of it's wheels while standing still and flies away...

Since the wheels spin freely there is forward motion from engine thrust and the plane will roll out, accelerate to speed and lift off normally.

Originally posted by Jeff Smith
...So this aircraft from a stationary position, goes 1 MPH then 2 then 3 then 4 and so on. up to it's given speed. ...

Yes, relative to the air and the earth, not the conveyor belt. The speed relative to the conveyor belt is double.

Originally posted by Jeff Smith
... This is all without the lift being generated form the air passing over the surface of the wings and this happens without air passing over the surface of the control surfaces....

As it rolls up to speed relative to the earth and air (the conveyor is irrelevant) there will be airflow over the wings and control surfaces. The wings will generate lift and the control surfaces will stabilize and control the airframe.

Originally posted by Jeff Smith
...Thats is where I lose your train of thought. This aircraft is sitting stationary as long as it's wheels are in contact with this conveyor....

No, it's moving as long as there is engine thrust and the tires can roll freely.

Originally posted by Jeff Smith
...So from my understanding you re stating this aircraft is going to take off and fly from a stationary positon with no lift...

As you said earlier "this aircraft from a stationary position, goes 1 MPH then 2 then 3 then 4 and so on. up to it's given speed" (relative to the earth and air, not the conveyor). It has air speed and therefore lift.

Originally posted by Jeff Smith
...All this without the mementum built up from doing a ground rolla dn developing inital speed. As long as the aircraft is stationary I don't see this. ...

The aircraft is not stationary. Engine thrust is moving it relative to the earth and air. It will roll out and gain speed.

Originally posted by Jeff Smith
...Even when one thinks in terms of airspeed as opposed to groundspeed, Those wheels are still in contact the the ground until that aircraft can generate enough thrust...

Thrust is generated the instant you fire up the engine and spin the prop. This will push the plane forward. Even though the plane is still in contact with the conveyor belt it will roll forward, pick up speed and generate lift.

Originally posted by Jeff Smith
...Those wheels are still in contact the the ground ...

And they are rolling.

Originally posted by Jeff Smith
... there can't be any foreward movement until the aircraft is off the ground and can't do this without lift.

The aircraft is not "stuck" to the belt, merely sitting on it, rolling along. It will keep rolling relative to the air and the earth, building air speed and consequently lift. When lift exceeds weight; lift off.


PC.

[Mosca]

Originally posted by the other pc
the wheels would spin freely, at double the speed they would on a fixed runway. Since they're free spinning they have no effect on air speed.


PC.

OK, I see what you mean, but go back to the original parameters, because we read the question differently.

In the original posit, I understand it to say that the conveyor ACTIVELY speeds up to prevent forward motion of the wheels (IOW, not relying on the wheels to turn it).

"This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."

SO, regardless of how fast the plane goes, the conveyor speeds up to prevent forward motion. If the wheel speed doubles, the conveyor speed doubles. The conveyor inputs energy to exactly negate the energy added by the engine.

Yes, at some point there will be mechanical failure, but will it be the wheel bearings or the conveyor motor? If wheel bearings, no flight. If conveyor motor, flight.



Tom

[Mosca]

OK, I went and looked it up on the internet; I figured that this COULDN'T be the only place that the problem came up.

I am wrong. The airplane WILL fly.

Explanation of why:

http://www.avweb.com/news/columns/191034-1.html

"It was an interesting argument, but as things progressed, more rational heads prevailed, pointing out that the airplanes do not apply their thrust via their wheels, so the conveyor belt is irrelevant to whether the airplane will takeoff. One guy even got one of those rubber band powered wood and plastic airplane that sell for about a buck, put it on the treadmill someone foolishly donated to the Lounge years ago, thinking that pilots might actually exercise. He wound up the rubber band, set the treadmill to be level, and at its highest speed. Then he simultaneously set the airplane on the treadmill and let the prop start to turn. It took off without moving the slightest bit backwards."

[Bedinabox]

my opinion. There is no way the plane will be able to take off. In order for that to occur, wind needs to be pushed over the wings to create lift. If the plane is on a belt and the belt is matching the speed, the plane is effectively standing still with no air movement over the lifting surfaces. No air over the wings at 70 + MPH = no lift. No lift, no flight.

[Bedinabox]

The only problem with the rubber band plane is that the speed of the plane and the speed of the treadmill were not matched, thusly it would not have the same parameters and this question does.

[SVT Lightning]

[QUOTE]Originally posted by the other pc
[B]This would only be true for a wheel driven vehicle. Any time the wheels are torqued to rotate the conveyor would move to cancel it. Our aircraft is not wheel driven. As engine thrust pushes the airframe the conveyor merely spins the tires beneath it.

Imagine you're towing the plane by walking along next to the conveyor and pulling the plane with a rope. As you take a step the plane moves with you and the conveyor moves the opposite direction under the tires. You keep walking and pulling the rope and as long as the wheels are free to spin (no brakes or chocks) the plane follows you. The tires have to turn faster because the conveyor is moving under them but the plane still follows you.

Now, replace the rope with prop thrust.

AH HA! I get it now. Best explanation in laymans terms so far. I have changed my mind. Thanks 'other PC'

[Bedinabox]

"This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."

it says that the conveyer belt speeds up with the plain, no matter how fast the plain thrusts its self to. The belt matches the same speed in the opposite direction so it is impossible for it to move. Or so I think.....

[gb387]

[QUOTE]Originally posted by SVT Lightning
[B]

Originally posted by the other pc
This would only be true for a wheel driven vehicle. Any time the wheels are torqued to rotate the conveyor would move to cancel it. Our aircraft is not wheel driven. As engine thrust pushes the airframe the conveyor merely spins the tires beneath it.

Imagine you're towing the plane by walking along next to the conveyor and pulling the plane with a rope. As you take a step the plane moves with you and the conveyor moves the opposite direction under the tires. You keep walking and pulling the rope and as long as the wheels are free to spin (no brakes or chocks) the plane follows you. The tires have to turn faster because the conveyor is moving under them but the plane still follows you.

Now, replace the rope with prop thrust.

AH HA! I get it now. Best explanation in laymans terms so far. I have changed my mind. Thanks 'other PC'

Very simple explination....

[Beercan31]

I would like to Thank Jngrbrdman From detail city for this link and an end to this Thread.

You might want to get your reading Glasses and a beverage before reading further
Case in Piont

[the other pc]

Originally posted by Mosca
... but go back to the original parameters, because we read the question differently. ...

Here are the original parameters:

Originally posted by Scottwax
...The plane moves in one direction, ...

Says right there, the plane is moving. It doesn't say the plane is stationary with the belt moving under it.

Originally posted by Scottwax
... This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)....

If the plane was stationary the belt would "track" that "speed" and be stationary too. But the plane does move and the belt also moves under it.

Originally posted by Scottwax
... tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)....

So the plane has speed (relative to the earth and air) and the belt is traveling in the opposite direction.

When the plane is going zero knots airspeed the belt is stopped at zero knots and the plane's tires are stopped at zero knots.

Now we add engine thrust.

When the plane is going 1 knot airspeed the belt is moving at -1 knot and the plane's tires are rotating at 2 knots.

When the plane is going 2 knots airspeed the belt is moving at -2 knots and the plane's tires are rotating at 4 knots.

When the plane is going 10 knots airspeed the belt is moving at -10 knots and the plane's tires are rotating at 20 knots.

All the while we are building airspeed and consequently lift.

Eventually the plane will move at its lift off airspeed and become airborne. Meanwhile the belt is moving at -1x (lift off airspeed) and the tires are rolling at 2x (lift off airspeed).

Originally posted by Mosca
..SO, regardless of how fast the plane goes, the conveyor speeds up ...

Yes, we agree there.

Originally posted by Mosca
... to prevent forward motion. ...

No, it does not prevent forward motion. The tires spin freely so they can spin at whatever speed the belt moves without having any effect on the airframe.

Originally posted by Mosca
...If the wheel speed doubles, the conveyor speed doubles. The conveyor inputs energy to exactly negate the energy added by the engine...

The belt does not input kinetic energy to the airframe, only to the tires and only rotational. (If rotational inertia of the tires is negligible there will no effect on the airframe energy. If you specify some particular inertia for the tires then that will subtract from the airframe energy and cause the roll out to lengthen, but it will not prevent it.)

Originally posted by Mosca
...Yes, at some point there will be mechanical failure, but will it be the wheel bearings or the conveyor motor? If wheel bearings, no flight. If conveyor motor, flight...

I sure hope nobody builds a "runway" that can't the load of a takeoff. (I hope nobody builds this "runway" at all. )

The loads generated by real world aircraft making normal landings (tires must accelerate from zero to landing airspeed almost instantly) are probably far higher than simply spinning the tires and bearings a 2x takeoff airspeed anyway.

Plus, they have to be designed to withstand emergency landings like you'd get with hydraulics failed "flaps up" so they can take speeds much greater than a standard takeoff.



PC.

[teterd]

The whole tire/convayor belt portion if the equation is thrown in to confuse the solvers. The tire/convayor belt has no real function in this problem but to confuse people. That's why it is a fun conundrum.
The plane will fly as so eloquently stated above by "The Other PC"....

[Jeff Smith]

Well I have spent the last hour mulling this over and I found my thought error. Then of course I bring up the thread and you guys have already figured it out as well. But I am still going to lay out where I lost it at now that I have spent all this cotton pickin' time on it!

1. The aircraft is sitting still.

2. The aircraft moves forward while the conveyor "duplicates speed but in the opposite direction". (Per the explanation). At this point the wheels are turning at a rate in proportion to the conveyor.

3. In order for the aircraft to roll forward, the speed of the wheels would have to change in relation to the conveyor which is countering the "speed and direction" of the aircraft, "not the wheels".

4. So as these wheels are rotating, their rotation needs to either speed up or slow down, albeit a small amount, on a conveyor that is countering the the speed and direction of the aircraft and not the wheels.

5. So we now have wheels that "need to keep surface contact" trying to roll at a slightly different rate while the conveyor maintains another.

There was were error showed up. My thoughts were that in order for it to move the rotation of the wheels would have to be at a different rate in proportion to the aircrafts foreward speed and with the conveyor countering the foreward speed of the aircraft and not the rate of wheel turn that the wheels would skip. I had forgotten the conveyor would increase in speed in proportion to the aicrafts foreward speed and the wheels turning rate would also be adjusted accordingly as a result.

I probably didn;t explain that last part very well but I think you get the message. Plus, I am tired of thinking about it now.

P.C. I tip my hat Sir