Airplane on a Conveyor Belt...

[hitech]

Also on a trivia note, what did HiTech do for 10 years before writing flight sims?

[2bighorn]

Originally posted by hitech
Also on a trivia note, what did HiTech do for 10 years before writing flight sims?

IIRC, you were designing conveyors or something like that, no?

[eskimo2]

Originally posted by hitech
Eskimo: It still does not make any sense. When the conveyor speeds up the wheel speeds up, hence once the plane starts to move a system can never do what is stated to make the speeds exactly match. By definition the wheel speed = Plane speed + Conveyor speed. So Conveyor speed only = P + C when P = 0.

It has nothing to do with a delay, every thing to do with definition.

Also how you state the original question of plane speed also does not make any sense if the belt was to ever hold the plane, because it would mean the belt had to not move for the plane to not move. Once again a bad question with out an answerer.

Notice how the Myth Buster avoided this problem by stating conveyor at Take off speed.

Imagine it works like an automobile’s cruise control as a car changes from level ground to an uphill.

In a car, when the speed drops a bit, the cruise control “steps” on the gas, it keeps pressing harder until the car stops decelerating and starts accelerating.  As the speed nears the set speed, the cruise control backs off and tries to ease it into the set speed.  If the car goes faster than the set speed as it crests the hill, the cruise control backs off on the gas.

The conveyor control could work the same way; the plane moves forward so the control speeds up the conveyor to “catch up” with the wheel.  When the conveyor acceleration rate passes 910 ft per second per second, the RV-4 starts backing up.  The conveyor control eases back to an acceleration rate of 910 ft per second per second.  When the pilot give up and chops the throttle, the acceleration rate also drops.  

When the pilot kills the engine the acceleration rate drops to 0.  The belt, however, is still moving at a zillion mph.  The pilot does not notice this and steps out onto the moving belt and is instantly turned into a long smear!

[VERTEX]

Originally posted by hitech
Also on a trivia note, what did HiTech do for 10 years before writing flight sims?

Hmm let me see,

He studied physics at the undergraduate level as a minor while working on a computer science degree???

[hitech]

Eskimo: But what you imagine is not what the problem states. It states "Exactly matches wheel speed"

Your version states Accelerates constantly until the desired speed is obtained.

2 very very different requirements.

HiTech

[john9001]

what means "wheel speed"?

[eskimo2]

Originally posted by hitech
Eskimo: But what you imagine is not what the problem states. It states "Exactly matches wheel speed"

Your version states Accelerates constantly until the desired speed is obtained.

2 very very different requirements.

HiTech

How would you answer this version:

A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off.  This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.

The question is:

Will the plane take off or not?

[VERTEX]

Ya it still takes off.

[hitech]

By definition of the question it will take off.

[eskimo2]

I agree…

But wait a minute, the question is bogus because the conveyor could never match the plane’s speed “exactly”…   Right?

[eskimo2]

Note that the point of this question isn’t to debate how such a conveyor could be built, what materials the belt could be made of, how wide or long it must be, what the power source might be.  It also does not matter HOW the conveyor matches the plan’s speed “exactly”.  

We naturally accept that the conveyor somehow works: power, size, controls and all.  

The point is that the question brings to light how many people misunderstand the forces at work; that the thrust of the prop is counteracted by the acceleration rate of the plane diminishing into the air drag on the wings and airframe.  The extra energy loaded into the wheels at these speed is negligible, not even worth mentioning in this question, the plane takes off.  For many people, studying this question opens up a new level of understanding not-so-obvious forces.

In the wheel speed question, if we also just accept that the conveyor exists as described, it opens up a new level of understanding not-so-obvious forces.  It’s a great question because it fools so many people and has such a counter-intuitive solution/answer that most people cannot even comprehend.

[VERTEX]

Often when engaging in thought experiments like these, one must first separate the relevant from the non relevant, and concentrate on the spirit of the question rather than get bogged down with small details.

Anyway, its been fun.

Hitech, are you going to tell us what you did for 10 years before writing sim games?

[eskimo2]

P.S.
Be sure to note that the paradox of the conveyor matching the plane’s speed is the same paradox as matching the wheel’s speed.  The conveyor must react to the plane in the plane-speed question; it will constantly adjusting to the increasing speed and decreasing acceleration rate of the plane.

[eskimo2]

Originally posted by VERTEX
Often when engaging in thought experiments like these, one must first separate the relevant from the non relevant, and concentrate on the spirit of the question rather than get bogged down with small details.

Anyway, its been fun.

Hitech, are you going to tell us what you did for 10 years before writing sim games?

I'll second both of these statements and the question!

[hitech]

Vertex: I developed and designed electrical control systems for conveyors.


Eskimo: Different then the wheel speed question, the change of speed of the conveyor will effect the acceleration of the plane, but not change its current speed.
You could even integrate the acceleration back in to the controller to remove all conveyor delay.

Hence the theoretical system is valid.


HiTech