Heres another example. I am jogging on a treadmill and I fart...I dont move forward do I ?

Let's assume we put the plane in the 3x3 mode, rear diff locked...

Then we'll solve global warming. Huzzah!

I posed this question to my wife, and told her there was a big debate going on at XOC about this.

Her response was: How many XOC members still live with their moms?

She'd appreciate some prompt replies.

We'd appreciate some pictures

And no I dont live with my mom....she might know the answer though

Have to go ask my mom.

OK, I got the plane, heading to the gym now.

I'm back.
It flew, but very low.

Here's my take on it

In the theoretical description of the question, the end result will be a plane throw off the end of the conveyor-belt-runway and destroyed.

In a real-life attempt at the question, the plane will take off.

Explanation:
If the conveyor belt actually move at a rate exactly the same as the relative speed of the plane on the ground (which at ground level would be the same as its airspeed, as soon as there is enough thrust to move the plane forward, the speed of the conveyor belt (and the rotation of the planes tires) would increase exponentially towards infinity to compensate. This speed would result result in catastrophic failure of the plane's wheel bearings and axles, and the plane would then be violently tossed off the end of the moving runway by the infinitely-fast-moving conveyor belt since there was no longer a spinning wheel to aid in friction loss between the plane and runway.

In real-life, it would not be possible to create a conveyor-belt-runway that could increase in speed to compensate for the thrust of the plane's engines, so the conveyor belt would never get up enough speed to keep the plane in one position, and the plane would takeoff.

You can't-flyers check out that thread that's been linked to about five times and scan for posts by TJ or JeffW. They've got good explanations. I like to think some of my analogies were pretty good, too.

One of my examples-The aircraft is already airborne and on approach to the conveyor/runway for a touch-and-go. The runway is spinning at exactly the same speed in the opposite direction, just like when it took off. Now, when the aircraft touches down (no brakes, remember, doing a touch-and-go) will it immediately come to a complete stop and be unable to take off again (do the "go" part)?

After all this I'm left with wondering how a plane on a movable platform (conveyor/treadmill) can generate enough air over the wings to achieve lift.

But doesn't this whole thing ride on if the plane moves forward on this infinite treadmill? If it sits still because the belt keeps up with its thrust, it will never take off.

If the plane can over come the rolling resistance to move forward eventually it will.

That sound right?

The belt can only spin the wheels, it cannot counteract the thrust of the engines. If someone throws a skateboard at you, can you stop it by touching the bottom of the wheels?

The movement of the conveyor and aircraft are independent of each other. The wheels serve to reduce friction and guarantee independent movement.

Another blast from the past:

There's a car in a northbound lane traveling at 60 mph, and a car in the southbound lane traveling at 60 mph. They have no effect on each other.

Now suppose the highway is perfectly straight and the southbound car has an enormous vertical board attached to the left side, miles long. The northbound car has a set of non-geared, free-spinning wheels on its left side. Supposing that both cars drive straight and the wheels remain in constant contact with the board, what happens

Each car travels at 60 mph, the wheels on the side rotate at a rate of 120 mph. If they have a standing start and accelerate at the same rate, they still would be able to move in opposite directions and the free-spinning wheels would spin at twice the rate of the drive tires.

Hence, the cars are not "equal and opposite forces" because they are not opposing, just like the conveyor is not opposing the plane.

In that case...

Maybe this example could convince people...

A hovercraft is over a conveyor belt. It moves foward as it wishes, regardless of the conveyor belt.

Now instead of air being forced down on the conveyor belt, put wheels (FREESPINNING - that's key) on the hovercraft.

No difference. It will STILL move forward.

Well shit...who am I kidding...that STILL is not going to convince people.

Another reason the original question is worded badly - IF the wheels had enough friction to overcome the engine thrust, then the plane would not take off...but that is NOT going to happen - the wheels are going to fall apart before that happens.

And just for the record, I was one of those who thought it would *not* take off - based on the friction problem.

Here's some other helpful information along those lines..

IF the wheels generated so much friction the plane's engines couldn't overcome it, a plane would NEVER be able to take off... It wouldn't move at all...

The reality of it is, you could lock up the wheels completely so they can't rotate at all, and the plane's engines will STILL generate enough thrust to overcome the friction between the tires and the pavement...

So there's no way in hell the friction of the tires spinning will overcome the thrust of the engine...

And to put two and two together... If the friction of the tires CAN'T overcome the thrust of the engine, than the tires can be spinning in ANY direction for ANY reason (a treadmill, in this hypothetical), and the plane still takes off.

Nope, not buying it.

And the skateboard and cars passing each other are poor analogies.

To me this is no different then being on a bike thats on a treadmill. The treadmill moves backwards at the same speed my wheels move forward.

If you come up behind me and push me, and the treadmill compensates for the added forward motion (as the original problem states), I will stay in the same place.

To me, thats what the plane and its thrust do.

That's a fantastic explanation!
I love this thread more and more!

U N F U C K I N G B E L I E V A B L E !

Explain the hovercraft. Or the example I used on ice skates.

The jet engines' thrust is enough to move the plane relative to earth (regardless of what's under it - a treadmill, a conveyor belt, ice, water, whatever). If it's moving relative to earth, it's also moving relative to the air (assuming a calm day). This moves the wings through the air to create lift.

You're killing me...

Just wait 'til your in town next weekend. I'll take you out to the airfield and let you stand behind a 747-200 as it spools up to break-away thrust... It'll be like flying a Kevin Kite.

I assure you. The plane takes off. NOTHING on the ground, spinning the tires, is going to prevent those engines from moving the plane. The earth below it can move at whatever speed it wants; doesn't matter.

Here's an example:

http://www.youtube.com/watch?v=1qkcVGwhzlY

LOL

The treadmill in your scenario does speed up but has ALMOST NO EFFECT on the bike because the wheels on the bike are free spinning. Apply the brakes and that is another story (and a funny video to be sure)

OK. Had a revelation. This is as simple a logic for explanation as you're ever going to see.

Step 1:

Ask yourself, "What moves a plane?".

Answer: Engines pushing air: called thrust (equal/opposite reaction, blah blah.)

Step 2:

Ask yourself, "Can the tires move a plane?"

Answer: No. There is no connection between an aircraft's engine and it's tires; look all you want; there's no driveshaft...

Step 3:

Ask yourself, "If there is a conveyor belt under a tire, and the conveyor belt moves, do the tires spin?"

Answer: Yes.

Step 4:

Finally make the ONLY logical conclusion, "If the conveyor belt spins the tires (Step 3), but the tires don't move an airplane (Step 2), then the conveyor has no effect on the plane moving."

__________________
There. 4 easy steps to think your way through this thing. If you can't get it with those 4 easy steps, then I suggest you repeat steps 1 and 2 until it finally makes sense to you.

Thank you. Goodnight.

Tires dont move the plane....correct.

Air resistance over the wings give it lift.

An airplane on a treadmill has no wind resistnace.

Chumpmann- your name indicates to me that you're trolling us.

The skateboard and touch-and-go analogies are apt. Those who say the plane won't fly are essentially holding the position that you can stop a thrown skateboard by touching the bottom of its wheels while its in midflight, or that a plane attempting a touch-and-go would stop the instant it hits the conveyor.

Both contentions are patently wrong.

::ETA:: I think I realized Chumpmann's hangup. Here ya go-

Lift is not required for an aircraft to move. Planes can taxi without flying, and they do it without powering the wheels. Because the plane can move forward by propelling air, no force against the bottom of the wheels can stop it.

Lift is not required for a plane to gain horizontal movement. Horizontal movement will lead to lift, not the other way around. The conveyor cannot prevent this, not if it spins at 1000x the speed of an aircraft.

::ETA::: Whoops

You all fail to accept that there is relativity involved here. The speed of the treadmill relative to the plane is different to the speed of the treadmill relative to ground observer. I've said it before. In this example, the plane moves forward on the belt at a given speed. The belt moves backward at the same speed. By definition, the plane isn't going anyplace. If you apply more thrust, the plane moves forward faster than the belt is moving backward. In order to take off, the plane must move faster than the belt, otherwise its place in space doesn't change, only it's position on the belt.

Maybe this will clear things up for everyone. If you put a guy on the treadmill standing still and he shoots a radar gun at the airplane, he shows that it is departing his position at 300mph. The pilot shoots a radar gun down at the runway and shows the runway whizzing past at 300mph. Since by definition the treadmill belt is moving, the plane is stationary in space and thus has no air flowing over the wings and thus creating no lift. The engines are simply maintaining the aircraft's 300mph forward movement along the belt. If you shut off the engines, the airplane would drift backward until its wheels lost their inertia, then it too would begin to move backward at 300 mph.