Airplane on a Conveyor Belt...

[sluggish]

Originally posted by 2bighorn
Do you understand that conveyor is rotating the wheel in the same direction plane would do on the normal runway? By what logic thrust has to overcome that angular momentum?

Normal runway: Planes thrust alone has to overcome wheels inertia

Plane on the conveyor: Plane gets little helper (conveyor)

Nope.  In my little world the conveyor is moving in the oposite direction of the plane to try to stop it.  If the belt is running the same direction as the plane in order to stop the wheels, then of course the plane would take off.  Anyone who doesn't believe the plane would take off under those circumstances is daft.

I'm going to go back and reread the thread. You should do the same...

[2bighorn]

Originally posted by sluggish
Nope.  In my little world the conveyor is moving in the oposite direction of the plane to try to stop it.

Now rotate your 'little world' conveyor 180 degrees so it's on top of the wheel. It will rotate wheel in same direction it did before, yet the conveyor belt goes in the opposite direction.

[Donzo]

Originally posted by 2bighorn
Now rotate your 'little world' conveyor 180 degrees so it's on top of the wheel. It will rotate wheel in same direction it did before, yet the conveyor belt goes in the opposite direction.

What are you talking about?  Who said anything about the conveyor being on TOP of the wheel?

[2bighorn]

Originally posted by Donzo
What are you talking about?  Who said anything about the conveyor being on TOP of the wheel?

It doesn't matter where conveyor is. What matter is direction of wheel rotation and if conveyor is actually opposing force or not.

Some claim because conveyor's belt is running in the opposite direction of the plane, it exercises the opposing force, yet when you rotate that same conveyor to the top, nothing really changes, except the belt touching the wheel is now running in direction of plane movement.

By their logic (or how they place force vectors), bottom, belt would be opposing force and when on top it would be contributing force.


All what this thread proves is, that similarly to religion, you cannot convince believers, just thinkers...

[Yknurd]

I would think drag from the plane trying to move through wind would be greater than anything induced from wheel rotation or friction.

[AKIron]

Originally posted by 2bighorn
OK, the only thing I wanted to know is why Eskimo thinks planes wouldn't have same take off distance, and I wanted to see what kind of logic he applied.

Obviously, we live in the same universe, unless by some internet magic, I actually communicate with the parallel universe Eskimo, the same laws of physics apply.

And whilst we mention laws and physics, I'll remind you and Eskimo about one of the most important, most basic and most known law applicable in this story.

The second law of motion. F=ma

Until the time you guys actually apply that, there's no point going any further.

Eskimo can certainly explain why probably better then me but I have some time to kill. A plane that accelerates down that runway more slowly will use up more of the runway to reach takeoff speed.

[AKIron]

There are a lot of forces involved here.

Here's the simplest way I can explain that given a powerful enough conveyor belt, a normal cessna 172 will not take off.

1. Conveyor belt sits ready for the slightest motion of the plane
2. Full takeoff power applied by the pilot
3. Plane moves forward.
4. Belt counters the speed of the spinning tire.
5. So long as the plane continues to accelerate forward the wheel is increasing it's rate of spin
6. The belt, sensing this, increases it's opposite spin
7. The belt, being enormously powerful, has accelerated to over 10,000 mph in a few seconds
8. The planes tires, wheels, bearings, etc... were not designed to endure these speeds and fail
9. The plane comes to a grinding halt on blown tires and bearings on fire

[2bighorn]

Originally posted by AKIron
Eskimo can certainly explain why probably better then me but I have some time to kill. A plane that accelerates down that runway more slowly will use up more of the runway to reach takeoff speed.

OK, let's see how that would work and if acceleration rate differs among those three planes.

Back to second law of motion: "The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma" (in it's simplest form).

F is actually net sum of all the forces, that is thrust minus drag, minus friction, etc, and we determined that is the same for all three planes, since they are identical in shape and build, according to Eskimo.

mass sum is also identical for all three, the wheel and ballast weight differ though. Lets say, it's 3000lbs total for each

plane 1:  airframe 2950lbs + 50lbs wheel +   0 ballast = 3000lbs
plane 2:  airframe 2950lbs + 25lbs wheel + 25 ballast = 3000lbs
plane 3:  airframe 2950lbs +  0lbs wheel +  50 ballast = 3000lbs

Lets say all three are propelled by electro motor with battery so our mass does not become variable (due to fuel burn), so we can keep formula simple.

Does the acceleration differs?
a = F/m

Since F (net sum of all forces) and m (total mass) are the same for all three planes, so must be acceleration.

If acceleration is the same and they all take off at 50mph, then the length of take off run is the same as well.

[AKIron]

Maybe this will help 2bighorn. Assume that all three planes have an airconditioner but only one has it turned on. Will it use more of the runway than the others? same principle here.

[2bighorn]

Originally posted by AKIron
same principle here.

Yes and no. In Eskimo's story all of the thrust is used (for all three planes) to propel aircraft.

In your example, part of the thrust (energy) is converted to do something completely unrelated and we get differential of usable thrust among planes.

[AKIron]

Originally posted by 2bighorn
Yes and no. In Eskimo's story all of the thrust is used (for all three planes) to propel aircraft.

In your example, part of the thrust (energy) is converted to do something completely unrelated and we get differential of usable thrust among planes.

No, all of thrust is not being used to propel the planes. Some of it is being used to spin those more massive tires. Same as spinning that pump in an A/C.

[2bighorn]

Originally posted by AKIron
No, all of thrust is not being used to propel the planes. Some of it is being used to spin those more massive tires. Same as spinning that pump in an A/C.

For Christ sake, read it again and pay attention to wheel weight.
I did not invent the story. Eskimo is responsible for all the parameters, he defined them. He couldn't give satisfactory answer on his own question.

Whenever you guys get the answer, you redefine the question. Suddenly we got air conditioners, what's next? Ann Coulter in the trunk?

Originally posted by 2bighorn
OK, let's see how that would work and if acceleration rate differs among those three planes.

Back to second law of motion: "The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma" (in it's simplest form).

F is actually net sum of all the forces, that is thrust minus drag, minus friction, etc, and we determined that is the same for all three planes, since they are identical in shape and build, according to Eskimo.

mass sum is also identical for all three, the wheel and ballast weight differ though. Lets say, it's 3000lbs total for each

plane 1: airframe 2950lbs + 50lbs wheel + 0 ballast = 3000lbs
plane 2: airframe 2950lbs + 25lbs wheel + 25 ballast = 3000lbs
plane 3: airframe 2950lbs + 0lbs wheel + 50 ballast = 3000lbs

Lets say all three are propelled by electro motor with battery so our mass does not become variable (due to fuel burn), so we can keep formula simple.

Does the acceleration differs?
a = F/m

Since F (net sum of all forces) and m (total mass) are the same for all three planes, so must be acceleration.

If acceleration is the same and they all take off at 50mph, then the length of take off run is the same as well.

[john9001]

Originally posted by AKIron
8. The planes tires, wheels, bearings, etc... were not designed to endure these speeds and fail
9. The plane comes to a grinding halt on blown tires and bearings on fire

sorry, but my plane doesn't have wheels, it has the same rollers and bearings as the belt, and they are capable of infinite speeds.

[Chairboy]

God forbid someone brings a skiplane to this airport.

[2bighorn]

Originally posted by Chairboy
God forbid someone brings a skiplane to this airport.