Author Topic: Airplane on a Conveyor Belt... (Read 30702 times)

eskimo2 · « **Reply #180 on:** February 01, 2008, 04:33:25 PM »

OK, I'm back.

Argue all you want. These AVI's show the force we are talking about in RL action:

http://hallbuzz.com/movies/wheel_on_sander_250th.AVI

Note that the sander accelerates for only an instant. When it gets up to speed after that split second the lateral force on the wheel becomes nil and the wheel drifts back.

I like this one too:

http://hallbuzz.com/movies/paper_treadmill.AVI

eskimo2 · « **Reply #181 on:** February 01, 2008, 04:35:51 PM »

Quote

Originally posted by Chairboy
The problem w/ the 910^2 answer is that it implicitly seems to assume that the power is being transferred through the tires. The diagram doesn't explain how this overcomes the u*N friction co-efficient math that shows the bearing friction as linear and constant. A wheel spinning at 5 rpm induces as much bearing drag (the relevant figure here) as one at 100rpm.

Bearing friction is not the force we are talking about.

2bighorn · « **Reply #182 on:** February 01, 2008, 04:37:01 PM »

Quote

Originally posted by sluggish
I WIN!!

No you don't.

All Hitech calculated is, how much conveyor has to accelerate in order to create wheel/belt friction torque to match the plane thrust.

How much of that torque is transfered through bearings to the airframe is another story...

Chairboy · « **Reply #183 on:** February 01, 2008, 04:38:27 PM »

That's the only way the treadmill can impart backwards force on an airplane. The rest is rotational energy with zero impact on the actual acceleration of the aircraft. Sure, the bottom of the wheel is pushed back, but then the top goes the other way, and back and forth.

If rotational force could be converted to a 'push' the way y'all keep assuming, then the Dean Drive would have revolutionized everything from flying cars to spaceships.

It just doesn't work that way.

2bighorn · « **Reply #184 on:** February 01, 2008, 04:42:16 PM »

Quote

Originally posted by eskimo2
Bearing friction is not the force we are talking about.

Yes we are, since bearings are the force transfer bridge.

If you have a car and put in bearings instead of gears, it'll take helluva time before you start moving, no mother how big your engine is.

eskimo2 · « **Reply #185 on:** February 01, 2008, 04:44:20 PM »

Chairboy,

Think about what happens when you land you plane. Even if you grease it in there’s a chirp when the wheels touch and a lateral “bump”. Some of your forward speed gets scrubbed off in an instant to get those non spinning wheels up to speed in an instant. It’s only slight if the plane’s tires/wheel are small and light. If you’ve ever landed in a bush plane with big tundra tires you’d note that the force is pretty significant. Now imagine that the “instant” becomes a constant. At the end of say, ¼ second the wheels go from stopped to 50 mph, at ½ sec = 100 mph, 1 second 200 mph, 10 seconds 2,000 mph… We are talking about a real force here.

sluggish · « **Reply #186 on:** February 01, 2008, 04:44:39 PM »

Wow. I give up. HiTech agrees with us, Eskimo films elaborate videos that prove it, we give you mind-numbingly simplistic explanations and yet you refuse to see...

there is no hope for mankind.

hitech · « **Reply #187 on:** February 01, 2008, 04:47:15 PM »

Chairboy: I am not speaking of friction of the bearing. I agree with you that bearing friction is a constant. Think of the force needed to simply accelerate the spin of the wheel.

If there was not a force of the prop I assume you do not the the wheel would stay at one point in space but would start rolling and move backwards like it does in the sample on the Belt sander?

Chairboy: It does work as I described. If you look at some of the basic physics I posted in the old thread, I did scans of how to do this analysis as my proof.

Chairboy. Spin a wheel on a axle that you are holding in your hands. Drop the spinning wheel on the ground, does it roll forward?

If you believe it moves forward, then think of the entire process in reverse. That is where the translation force comes from.

HiTech

eskimo2 · « **Reply #188 on:** February 01, 2008, 04:48:14 PM »

OK guys,

Please explain what's happening in these AVI's:

http://hallbuzz.com/movies/wheel_on_sander_250th.AVI

http://hallbuzz.com/movies/paper_treadmill.AVI [/B][/QUOTE]

Why does the wheel move back as it starts to spin?

Why are the balls pulled off the table? They should just stay in one place and spin as long as the paper is accelerating under them, from how you describe things. Be sure to watch in slo-mo.

2bighorn · « **Reply #189 on:** February 01, 2008, 05:15:34 PM »

Quote

Originally posted by hitech
If there was not a force of the prop I assume you do not the the wheel would stay at one point in space but would start rolling and move backwards like it does in the sample on the Belt sander?

Only until initial inertia is overcome. And that's only wheels. You'd have to account for the plane's inertia as well. If you include thrust, and you'd still want to keep it back you'd have to accelerate at such rate you'd need quite a traction between belt and tire. Pretty soon we'd approach insane numbers close to infinity and we know what happens then.

SaburoS · « **Reply #190 on:** February 01, 2008, 05:33:51 PM »

Interesting...

From what I understand of the question is that magical the conveyor belt matches the speed of the wheel.

What forces the plane's wheel to rotate in the first place?

The forward movement of the plane.

The conveyor belt has to react to the wheel's speed, not the other way around.

The only way the wheel's speed changes is through the forward motion of the plane.

Plane takes off.

Just a hunch.

... or put wheels made of glass and the plane will just slide forward and take off

eskimo2 · « **Reply #191 on:** February 01, 2008, 05:41:20 PM »

Quote

Originally posted by 2bighorn
Only until initial inertia is overcome. And that's only wheels. You'd have to account for the plane's inertia as well. If you include thrust, and you'd still want to keep it back you'd have to accelerate at such rate you'd need quite a traction between belt and tire. Pretty soon we'd approach insane numbers close to infinity and we know what happens then.

2bighorn,

That “initial inertia” that you are talking about is acceleration. It’s important to understand the difference between acceleration and speed. Acceleration is a force that is constantly applied; such as speed increasing regularly.

“And that's only wheels.” Yes it’s only the wheels because it makes it easier to see the force. Suppose the plane were to weigh 1,000 times the weight of the wheel; just increase the acceleration rate by 1,000 fold and you have the same result as the wheel alone at 1X acceleration.

Believe it or not, the traction requirements for this scenario are no greater than the traction needed to hold a plane on a tarmac with its engines on full power and it brakes on full – locked.

eskimo2 · « **Reply #192 on:** February 01, 2008, 05:44:30 PM »

Quote

Originally posted by SaburoS
Interesting...

From what I understand of the question is that magical the conveyor belt matches the speed of the wheel.

What forces the plane's wheel to rotate in the first place?

The forward movement of the plane.

The conveyor belt has to react to the wheel's speed, not the other way around.

The only way the wheel's speed changes is through the forward motion of the plane.

Plane takes off.

Just a hunch.

... or put wheels made of glass and the plane will just slide forward and take off

Imagine that “exactly matches” really means that YOU have a big acceleration control dial for the conveyor and your job is to keep it in place. The plane fires up and begins to inch forward; you see this and crank the acceleration dial. (Or are you going to say, "I give up" the instant you see the plane budge?) You go too far, however, so the plane drifts back behind its starting point. Seeing this you back off on the acceleration dial and adjust it to keep the plane pretty much where it started.

Look at the concept; don’t get caught up in the semantics of the word “exactly”.

eskimo2 · « **Reply #193 on:** February 01, 2008, 05:49:01 PM »

Quote

Originally posted by sluggish
Thank you sir. I consider this case closed.

I WIN!!

Sluggish,

I hate to break it to you, but you already knew that you knew the answer, as did many others here. The point/challenge of a BBS argument like this is to explain your point so that others can see/get it. You’re failing until they get it bro!

vorticon · « **Reply #194 on:** February 01, 2008, 05:52:32 PM »

Quote

Originally posted by eskimo2
Sluggish,

I hate to break it to you, but you already knew that you knew the answer, as did many others here. The point/challenge of a BBS argument like this is to explain your point so that others can see/get it. You’re failing until they get it bro!

or just repeat yourself until they grow weary and leave, which is more common.