willhaney's blog
Posted by willhaney | Jul 03, 2009 @ 10:01 PM | 4,179 Views
Conditions:
Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.

Question:
Can the plane take off?

Obviosly, no. The plane cannot take off.

Nothing can even move while it's on something that matches its speed in the moving opposite direction at all times.

End of story.

Will
Posted by willhaney | Jul 03, 2009 @ 08:02 PM | 4,051 Views
Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the plane at any given time, moving in the opposite direction.
There is no wind.

Can the plane take off?

Our question:
Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.

Can the plane take off?

In the first question (belt matches plane), the plane can take off.

In the second (belt matches wheels) the plane can't move.

Will
Posted by willhaney | Jul 02, 2009 @ 08:21 PM | 4,156 Views
Can we attribute the poll results to the quality of “no” posts or the inferior posts of the “yes” posts? Probably both.

However, it may be more likely that in general, the members on RCGroups understand the question as written and have voted accordingly.

Just an observation.

Will
Posted by willhaney | Jul 02, 2009 @ 03:19 PM | 4,045 Views
Circular reasoning:

Posted by willhaney | Jul 02, 2009 @ 12:40 PM | 4,067 Views
Quote:
 Originally Posted by gnofliwr I like the VTOL solution. It is the only one that gets the plane into the air within the stated conditions. I'm still not sure it can move horizontally with respect to the belt without violating the conditions, but if you consider hanging on the prop as taking off, then it can. Barring the VTOL solution, the theoretical plane will never take off from the theoretical belt. - Roger
Precisely.
Posted by willhaney | Jun 30, 2009 @ 10:11 PM | 3,972 Views
The wheels have mass. As long as the belt accelerates there is a force produced.

f=ma

A force equal and opposite to the thrust of the plane.

No, the plane cannot take off, it cannot move.

Will
Posted by willhaney | Jun 27, 2009 @ 12:38 AM | 4,130 Views
Tachometer:
Quote:
 Originally Posted by theKM Say the diameter of the wheels are the same as the diameter of the belt axis at one end. If you put a tachometer on them they will read the same as long as the plane doesn't move. Now if the wheels move forward on the belt relative to something that is not on the belt (as what is needed for the plane to fly), the tachometer on the wheels will need to measure rotation higher than that of the belt. Therefore... the wheels need to rotate faster than the belt in order for the plane to take off. But because condition of the question states that the belt matches the speed of the wheels, the plane cannot move while this condition is true.

Posted by willhaney | Jun 24, 2009 @ 01:51 AM | 4,084 Views
The wheels act like flywheels on the accelerating belt.
Posted by willhaney | Jun 24, 2009 @ 12:56 AM | 4,088 Views
One of the fundamental aspects of physics is conservation of energy.

A plane transforms the potential energy of its fuel into a force commonly know as thrust. Nothing is lost in this conversion.

Heat, sound, electromagnetic radiation and force manifested.

Nothing is lost.

An accelerating belt is under the same laws of physics as the fuel and propulsion system of a plane.

Nothing is loss only transformed.

Conservation of energy dictates that the accelerating belt will transfer a force to the wheels and subsequently the plane.

Like it…or not.

f=ma
Isaac Newton

Will
Posted by willhaney | Jun 22, 2009 @ 01:06 AM | 4,422 Views
Posted by willhaney | Jun 20, 2009 @ 12:22 AM | 4,343 Views
Acceleration ≠ speed

Speed = ft/sec
Acceleration = ft/sec˛

A speeding belt, a belt at a constant speed, would produce very little force against the wheels.

An accelerating belt, that is a belt whose speed increases over time, would produce a significant amount of force on the wheels proportional to the rate of acceleration.

Earths gravity near the surface has an acceleration rate of 32.2 ft/sec˛ or 9.8 meters/sec˛.

This seems to be a significant stumbling block for those who believe the belt cannot produce a force on the wheels.

One needs to understand the difference between speed and acceleration.

Once firmly grasped the solution will becomes clear.

No, the plane cannot take off, it cannot move.

Will
Posted by willhaney | Jun 19, 2009 @ 02:24 PM | 4,179 Views
An accelerating belt will produce a lateral force on a wheel:

inertia

Wheel Pull

Will
Posted by willhaney | Jun 16, 2009 @ 06:06 PM | 4,647 Views
Force formula:
Quote:
 Originally Posted by Montag DP Let's do a little dynamics problem. Say you have a wheel with frictionless bearings on a conveyor belt. The wheel has diameter d and moment of inertia I. You apply a force F on the axle of the wheel to get the wheel to accelerate at a rate A. The belt is accelerating backwards at a rate A1. What is the value of the force F in terms of all the other parameters? I worked through it and got a value F = 4I(A+A1)/d^2. On the other hand, if the belt is not accelerating, the force is just 4IA/d^2 (obviously). If A is 0, then the force (the "thrust") is 4IA1/d^2 (in this case, the wheel is stationary or moving at constant speed). So clearly, the accelerating belt produces a force on the wheel, pulling it backwards. The same could go for a plane, so in theory a belt could hold a plane in place by accelerating at a high enough rate. This is just one example that shows that the accelerating belt imparts a linear force to the axle of the wheel, even in the absence of bearing friction.

Posted by willhaney | Apr 12, 2009 @ 11:30 PM | 4,703 Views
I don't believe this is to be a trick question.

At its very core it is a simple question with a simple answer. Given the belt the plane cannot move any more than any other vehicle on a treadmill that matches its speed despite its locomotion.

Where it gets dicey is when a new question is introduced: "How can the belt perform as designed?"

For this, one must understand principles of physics that are not intuitive to the untrained. Wheels have mass/inertia. They can have forces applied to them just like any other object with mass. The fact that the spin as well as are pushed confuses a little less than half of the members.

Trying to prove this thought experiment is futile as no belt could be made with current technology.

This is a thought experiment.

Given the belt, can the plane take off?

Obviously the plane cannot take off, it cannot move, forward or backward.

Will
Posted by willhaney | Apr 10, 2009 @ 11:27 PM | 4,401 Views
Quote:
 Originally Posted by scaredsilly If the speeds of the belt and the wheels do not match, than the preconditions of the question are not met. The question is if the plane can take off if the speeds do match. The answer is no.
Well put and right on.

Will
Posted by willhaney | Apr 10, 2009 @ 01:13 PM | 4,400 Views
Quote:
 Originally Posted by willhaney Here’s the question the “yes” voters are answering: Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. There is no wind. Can the plane take off?
Quote:
 Originally Posted by gnofliwr Will, You are correct. The "Yes" answers have answered a different question that the one posed in the problem. It is difficult for most people to think abstractly when the problem they are solving is outside of - or more importantly - contrary to common experience. The problem as stated is defilitely outside the box of common experience. On the other hand, the "Yes" solutions are outside the box of the problem. I don't know which side is thinking outside of the right box. - Roger
What roger said.
Posted by willhaney | Mar 08, 2009 @ 11:26 PM | 4,257 Views
Here’s the question the “yes” voters are answering:

Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. There is no wind.

Can the plane take off?

Posted by willhaney | Feb 02, 2008 @ 09:54 PM | 7,049 Views
fractal wrongness

The state of being wrong at every conceivable scale of resolution. That is, from a distance, a fractally wrong person's worldview is incorrect; and furthermore, if you zoom in on any small part of that person's worldview, that part is just as wrong as the whole worldview.

Debating with a person who is fractally wrong leads to infinite regress, as every refutation you make of that person's opinions will lead to a rejoinder, full of half-truths, leaps of logic, and outright lies, that requires just as much refutation to debunk as the first one. It is as impossible to convince a fractally wrong person of anything as it is to walk around the edge of the Mandelbrot set in finite time.

If you ever get embroiled in a discussion with a fractally wrong person on the Internet--in mailing lists, newsgroups, or website forums--your best bet is to say your piece once and ignore any replies, thus saving yourself time.
Posted by willhaney | Nov 08, 2007 @ 01:09 PM | 7,571 Views
Axle friction and rolling resistance are too small to account for a force large enough to match the thrust from the plane, IMHO.

It is the accelerating belt which produces a force on the mass of the wheels that counters the thrust.

The accelerating belt transfers a force to the wheels in two ways.
1. Spins the wheels increating their angular momentum.
2. Pushes the wheels in the direction of the belt(F=ma).

How much of the force is distributed to the wheels as spin or push depends on
1. Belts rate of acceleration
2. Mass of the wheels
3. Distribution of the wheels mass within the wheels (the wheels moment of inertia)
Will