Will it take off?

[TraceZ]

Here we go. Follow me here.

Here is the original proposition just for accurate reference.



Lets split this into 2 parts:



I think that goes without explanation, right?

Ok, second and most important part:



Let's say a given aircraft requires an airspeed of 100.00 MPH across the body and wings of itself to provide enough lift to suspend itself off of the ground for a reasonably sustained period of time (flying). Let's say the conveyor runway is moving in the opposite direction at 50.00 MPH. Let's say the wind speed is mesured at 0.00 MPH in the vicinity of the aircraft and conveyor by a certified weather sensor. Let's also assume that the wheels are free spinning and the brakes are not enagaged and that the friction between the aircraft tires and the surface of the conveyor is identical to that of a conventional plane tire runway relationship.

Now, given this the plane would have to reach and maintain an airspeed (as measured by the aircraft relative to the immediately surrounding air) of 150.00 MPH in order for "lift off" to occur. I feel as if the question incinuates plane speed relative to the conveyor, BUT i am assuming they correctly mean to say actual airspeed as normally measured from a airspeed sensor on the plane for the sake of a "politically correct" argument.




If the conveyor correctly senses (tracks)the actual airspeed of the aircraft measured by the aircraft sensor and then consequently adjusts itself to match that speed, you can see that the energy required to overcome the tire-to-conveyor drag would increase exponentially.

I gotta disagree there. The airspeed indicator on the plane doesnt even know the silly mechanical runway exists. The airplane doesnt care the mechanical runway exists. the wheels on an airplane spin freely.

Go watch the skateboard video again. The answer lies in the skateboard video. The guy can pull the runway out from under the skateboard as fast as he wants, but the skateboard still accelerated forward through the room at the same rate. If it was capable of flight it would be able acheive speed to lift off.

Asuming the air above the runway is unaffected by the spinning runway, the airplane wont even hardly notice it. Its little wheels will just spin twice as fast as normal until it lifts off.

Again, I'm 100% positive this is correct.
Go watch the skateboard video a few more times. It makes my point perfectly.

[Sean 94z28]

If the conveyor correctly senses (tracks)the actual airspeed of the aircraft measured by the aircraft sensor and then consequently adjusts itself to match that speed, you can see that the energy required to overcome the tire-to-conveyor drag would increase exponentially.

the amount of drag would be proportional to the amount of the plane's weight that the wheel bearings are holding. So while the drag might increase exponentially, it would also start to decrease once lift began to reduce the weight on the wheels. It is my opinion that the thrust from modern engines would have no problem overcoming the tire-to-conveyor drag. Speeding up the plane or the conveyor will simply make the wheels go faster with only a marginal "pull" on the momentum of the plane. Will a modern 747 (for example) stay stationary at Full Throttle if the brakes are locked up? I do not know this answer, but my guess is the thrust would oversome locked wheels.

[Jay 02 TA ws6]

Go watch the skateboard video a few more times. It makes my point perfectly.

Actually, the skateboard illustrates my point perfectly - to the bystander (the camera man), the skateboard wasn't stationary it was moving forward, meaning the wheels were moving twice the speed of the treadmill.

[Jeff_in_Atl]

Again, I'm 100% positive this is correct.

Me too.

[Jeff_in_Atl]

Actually, the skateboard illustrates my point perfectly - to the bystander (the camera man), the skateboard wasn't stationary it was moving forward, meaning the wheels were moving twice the speed of the treadmill.

And it flew!

[Jay 02 TA ws6]

Actually, the skateboard illustrates my point perfectly - to the bystander (the camera man), the skateboard wasn't stationary it was moving forward, meaning the wheels were moving twice the speed of the treadmill.

I just realized how bad I f-ed up.

The plane could never be stationary. Assuming zero friction in the bearings of the wheels, the treadmill cannot effect the speed of the plane. LOL... I'm retarded... the plane would always move forward to the person in the control tower, and it would take off as normal. If the propeller began moving the plane 100 mph, the treadmill could adjust its speed to 100 mph, and the wheels of the plane would immediately (assuming no friction) adjust to 200 mph... thus, the plane would continue to move forward.

Yes the plane takes off. It is impossible for it to be stationary to the observer in the control tower because it is the propeller driving the plane and not the wheels.

D'OH!!!!!

[fastTa]

You guys still don't get 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)

The plane will never EVER achieve even enough lift to appear to remove a significant measure of weight from the tires. Every millisecond that is involved in the acceleration of the plane is "tracked" by the conveyor, the plane will NEVER have time to overcome the constantly adjusting speed of the conveyor, laymens terms....the plane will never ever get a jump on the conveyor to build enough speed to lift. Ever.

You cannot momentarily supercede the laws of physics.

[Jay 02 TA ws6]

You guys still don't get it.



The plane will never EVER achieve even enough lift to appear to remove a significant measure of weight from the tires. Every millisecond that is involved in the acceleration of the plane is "tracked" by the conveyor, the plane will NEVER have time to overcome the constantly adjusting speed of the conveyor, laymens terms....the plane will never ever get a jump on the conveyor to build enough speed to lift. Ever.

You cannot momentarily supercede the laws of physics.

The question assumes instant adjustment of the conveyor belt to the speed of the plane - no "time" for the computer to send impulses and adjust speed, no time for acceleration, etc... the wheels are using frictionless bearings and the wheels adjust to counteract the speed of the treadmill instantaneously.

The treadmill - assuming frictionless bearings cannot effect the speed of the plane.

Tracy is right - the skateboard is the perfect illustration of this in action... the treadmill can't make the plane stationary to a bystander no matter how fast it goes.

[fastTa]

The skateboard experiment is a far from a reasonable represenation to the proposed theory. Not even fathomably close.

The skateboard does NOT experience a controlled and "tracked" opposingly moving conveyor. Null from reality.

[Sean 94z28]

Every millisecond that is involved in the acceleration of the plane is "tracked" by the conveyor, the plane will NEVER have time to overcome the constantly adjusting speed of the conveyor, laymens terms....the plane will never ever get a jump on the conveyor to build enough speed to lift. Ever.

You cannot momentarily supercede the laws of physics.

Well you could never make a conveyor that doesn't have some lag in its feedback system.

There is technically no such thing as exactly "at the same time/speed/moment". Either the plane acheives a speed and the conveyor attempts to match it while the plane continues to accelerate further, or the conveyor is active pre-emtively. The wording suggests that the plane speed is monitored then matched. Not that the conveyer "knows" the planes acceleration rate and and matches it perfectly.

Even if the conveyor had 200 mph head start with the plane on it, the plane would still just take off after it overcame the 200mph (with wheels going 350MPH or Ice skids going 150mph).

Trace has nailed it on every post he put up. As usual, he says what I am thinking better than I can.

[TraceZ]

Ok I have an idea that might help get everyone on the same page.

Put a 2' tall steel pole in the ground, one at each end of the runway. Now string a steel cable between the poles, going the entire length of the runway.

This cable represents the air above the runway that is unaffected by the rate at which the runway treadmill spins.

now place youself sitting on a 2' square wooden board with 4 ball bearing casters under it. Hold on tight to that cable and pull youself down to the end of the runway.
The runway will begin to spin as the computer controlling it tries to keep you in one place. If you pull yourself along at 2 mph relative to the cable the runway goes the opposite direction at 2 mph making the casters spin at 4 mph, but you still are able to pull yourself forward at 2 mph without a problem..

Now lets get back to the airplane. The airplane pulls against the air with its propellor in the exact same way you pulled against the steel cable with your hands. When you hit the throttle for takeoff, the airplane will begin going forward, pulling against the air. the computer controlling the runway will make it move to compensate, but will not in any way be able to stop the forward progression of the airplane down the runway.
When you reach takeoff airspeed you will liftoff just the same as you would of on any standard runway.

Does that help?

[fastTa]

I stand firmly by my perspective on this, merely by a formed opinion based on a combination of my intellectual capacity, education, and experience. I could be wrong, those saying it will fly could be wrong. This will be my last post. I feel this thread has the potential to become personal and I don't want that. I love each and every one of the guys that posted in this thread and I intend to keep it that way.

This would make for an interesting experiment though!!

[Sean 94z28]

Kevin,

I do understand what it is you are getting at. And if it were possible to acheive what the question describes (perfectly matched acceleration it opposite directions), the plane would start moving backwards (because all of its weight is on the conveyor) at exactly the same rate it was thrusting forward, esentially zero forward motion. Such a system is in no way possible.

In this way the question is very illogical. It says the system will do something that is not possible. An imperfect human designed system could not accomodate this experiment. At any given moment either the plane or the conveyor would be slightly faster than the other. At that moment the question is invalid because they are no longer exactly the same speed.

Everyone who agrees the plane will fly is reading the question in a way that accomodates the only logical interpretation - that the plane moves first, and the imperfect monitoring system will all be trying to "catch up". Trying to "catch-up" once the plane is moving, would just be spinning the planes wheels and not hurting its forward progrees.

Can we at least agree the question is illogical?

The real question should be: Could you ever built a runway conveyor system (as described in the original question) that could prevent a plane from taking off? This answer is definately no.

[Trash man]

trace nailed it on the head, now i understand it all. thanks trace, u cleared that up, now u wanna help me tune a tbi car?

[fastTa]

Can we at least agree the question is illogical?

Absolutely. Very illogical.