A plane on a runway, how smart is r3vlimited?

[Justin B]

I wont even try to give my own answer again. I'll just post two quotes together here.

This is where you are wrong. The plane is on the Conveyor Belt Runway from the start and the belt speeds up as the plane does. So, it is not already going 50 onto a runway going 50 the other way.

I see where you are going and if I thought about it that way I believe I would agree with you, but the plane will never get to 50 because the converyor belt is always under it.

LOL I can't believe you guys. It's practically a trick question. It's designed to lead you to believe that the plane is stationary. THE PLANE IS ACTUALLY MOVING FORWARD.

As others have stated, if the engines are providing 200mph thrust it doesn't matter whether the plane is on a conveyor or not; the forward thrust actually pushes the airplane, it doesn't just spin the wheels. If the conveyor is moving backwards at 200mph, the wheels on the plane will simply spin at 400mph. That's 200mph forward velocity, plus the 200mph the conveyor is spinning the wheels.

On Edit - This is exactly the problem that I was pointing out with you people. You dont even read any of the most recent posts, you might skim them, quote them, then write out your own bs. I am not post whoring, almost every one of my posts either makes more logical sense or has more information in it than most of the other posts combined. I am setting people straight myself because the people who know better tired of hearing it and don't want to reiterate everything for however many times its been said already +1. Do yourselves a favor and read the last few pages, if even only my posts, and really actually READ them, dont just "Read them". I mean seriously read them and understand them as you should be as the words enter your head. I hope that makes sense itself.

[NC325iC]

i didnt read all of the thread but, it all depends, it says the plane is moving, does this mean it has air speed or does this mean it has speed relative to the conveyer(by this i mean that the wheels are spinning but relative to the ground the plane is still). if the plane gets enough air speed hell yes it will take off, since planes do not get their speed from the wheels ie the wheels dont move the plane, if the engines are on in the plane even though the conveyer is goin the other way it will more than likely have positive air speed, and if theres enough runway the plane will take off. all the conveyer is doing is making the wheels spin really fast

sorry thats so long, thats pretty much the train of thought i went through

[Justin B]

Do yourself a favor and at least just pick up the last 3 or so pages. It will be explained in detail more than once in that area.

[Digitalwave]

[benDASHDASH]

Once and for all:

"This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."

The plane cannot move faster than the belt, no matter what is powering it.

[E30 Wagen]

Once and for all:

"This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."

The plane cannot move faster than the belt, no matter what is powering it.

The plane CAN move faster than the belt.

If the plane was traveling 200 mph in the air, and touches down on the belt travelling an equal 200mph in the opposite direction, the plane would not stop but continue to move forward, just not as fast because of the resistance of the wheels contacting the belt and the wheel bearings, etc. The only way the plane would stand still is if the belt was sped up so fast that the friction of the wheels and wheel bearings became too great for the thrust of the jet engines to overcome, assuming the jet engines have mainted a throttle position of 200mph. However, by doing this the actual speed of the plane and the actual speed of the belt are no longer the same.

In the matchbox car on the treadmill example where you putting your finger behind the car to hold it in place, the pressure you feel against your finger represents the force of the jet engine at a constant throttle position. If you speed up the treadmill, then the jet engines can throttle up to match it, and this is represented by the increased pressure you feel as the car pushes against your finger. The point that people are trying to make is that no matter how fast you speed up that treadmill, you can still take your finger and push the car forward, albiet with an increased effort of the engines (but minuscule to you).

As to whether or not the plane will be able to lift off, that is where information like the coefficient of friction of the wheels and the maximum thrust of the engines become imporant. If the friction is low enough, the plane will easily take off.

[DarkWing6]

I think I am starting to see it.....

[Ray Smoodiver]

I live with 2 flight instructors, both with over 1000hrs each, one teaches met, the other teaches aircraft tech. I'm going to go ahead and say that they know what they're talking about.

They have simplified the problem thus - the conveyor is EXACTLY like taking off with a tail wind - the plane doesn't get airborn with a tailwind, and neither does it when its sitting on the conveyor belt.

[Justin B]

Once and for all:

"This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."

The plane cannot move faster than the belt, no matter what is powering it.

I have decided not to answer every single post form now on. Just the easy shit because I've already explained it a million times.


Here's what it is, and the only way it is, and the only way it will ever be -

The belt moves, and by your logic, if the wheels spin under the plane, the plane is technically moving too. It is not. The plane is stationary in space. Debunked. I'm sure you can see why. That is a really simple way to explain it. The belt is moving, the wheels are moving, but the plane is not moving through space (air, forward).

Now, it IS possible, and all of us have agreed on this at one point or another I believe, for the plane to use its thrust to overcome the resistance of the wheels and roll forward on the belt in relation to the ground beside it. The plane can move forward, the belt can still go backwards, but the plane per unit of effort, is only going half the distance it would on tarmac. The wheels are spinning twice as fast as the plane is moving through space.

AGain,

Yours -
Conveyor belt 10mph
Wheels 10mph
Plane as a whole in SPACE 0mph. The plane must move, not just the wheels, which are what you are suggesting

Mine, and everybody else that knows whats going on :P
Conveyor belt 10mph
Wheels 20mph (plane's thrust thinks its going 20mph)
Plane as a whole in space is only 10mph.
The plane is going at the same speed as the belt. Problem solved.


========REAL WORLD EXAMPLE========
Take a conveyor belt. Stand on it and set it to half of your walking speed. Start walking. Your feet are the wheels going twice the speed as the conveyor belt and the rest of your body (from your starting point, something beside the belt) but it solves it as the belt and your body are moving in opposite directions at the same speed from the point of origin.
================================

This problem will work with a jet, which just so happens to throw into the mix whether or not it will be able to take off or not, of course. It will work witha car, but the car's speedo will have to read twice the speed of the belt going underneath it, to match the cars forward speed to the speed of the belt going backwards. It will also work with you standing on a conveyor belt in a grocery store and walking on it.

I don't mean to confuse you more, but this is just how it would work for anything from a dead stop whether its a plane, a car, a bicycle, your feet etc. Its the belt vs the wheel(foot etc) speed, as they speed up, lets have a table, 0mph wheels 0mph belt. .5mph wheels, .25mph belt. 10 mph wheels, 5mph belt. The belt will always accelerate exactly at half the wheel speed, but that will allow the belt and whatever happens to be riding,walking, taxiing down it, to be at exactly the same speed, through space as the belt is. What you have always wanted was to keep the belt at the same speed as the wheels, but like I proved above, that adds up to 0 net speed through space of what is riding on the belt, so its really not going anywhere.

It really is that simple people, you're over thinking it.

[E30 Wagen]

They have simplified the problem thus - the conveyor is EXACTLY like taking off with a tail wind - the plane doesn't get airborn with a tailwind, and neither does it when its sitting on the conveyor belt.

You can't equivocate those two. The issue here is the friction of the wheels and whether or not the jet engines could overcome it and pull the plane forward with sufficient speed to lift off. With the lack of information regarding the whether conditions, we can assume that the windspeed is 0.

However, if the plane is travelling 200mph and the belt 200mph in the opposite direction, if the plane touches down on the belt, the wheels will not then be spinning 400mph. It will be less than 400mph because of the friction of the wheels and the wheel bearings slowing it down, but not stopping, the plane. THe plane will still be moving, just not as fast. If we knew the coefficent of friction, we could calculate the speed of the plane. But, just to illustrate it, let's say that the extra friction of the wheels slows the plane down 50mph. The plane would then be moving 150mph down the belt. 200mph belt speed +150mph plane speed = 350mph wheel speed.

If a plane needed to be going 200mph to take off, it could throttle it's engines up to 300mph, and likewise the belt to at 300mph in the opposite direction. If the plane, by the thrust of the jet engines, could overcome the extra friction of the wheels to move forward at 200mph, then the plane could lift off.

[Justin B]

Yay my army is building.

[dirty30]

16 pages guys? come on now

[Justin B]

Its hard to convince kindergarteners :) come on now.

lol. I'm just messing with you guys, I just hope my latest large post explains that I do understand exactly where you're coming from, but also understand exactly how it is possible to satisfy the question, and let anything that is riding on the belt to gain air speed, through space.

[benDASHDASH]

so it loses traction

[Justin B]

el oh el. You're grabbing at straws now Ben, admit it. It will not lose traction :P The jet is pushing it, hell, if it loses traction that helps my point, because then there's less rolling resistance.


I proved you wrong in a way that a 5 year old could understand if I used Tonka toys as examples, and seriously no offense, but I hope you're kidding.