A plane on a runway, how smart is r3vlimited?

[chucko]

Ok, I will yield my position.

Justin and others, If your plane is as light as a feather and can produce the thrust of a space shuttle, then yes the plane will take off even if the belt is moving at infinity because the thrust can overcome any frictional forces keeping the planes wheels on the conveyor belt. There I've said it, are you bitches happy?

[tonytony]

i'm emailing myth busters

[e30fiend]

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.

[Mike325]

i'm emailing myth busters

I already did.

[tonytony]

I already did.

i couldn't figure out how to email them but i signed up and posted a thread, hopefully both our threads and maybe others will make them do a show on it!

[DEV0 E30]

I say this to the all of you...

[RobertK]

FUCK PLANES!

I'm going to Buffalo Wild Wings. They gots Mango Habanera = mmmmmmmm

[DarkWing6]

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.

[Justin B]

No you are wrong. You, like Justin, are trying to reference speed from outside of the system and applying that to the system. That's like standing on the moon and measuring the speed of a car on the earth while the earth is spinning 1700 km/hr and saying that the car is moving at 1720km/hr when on the earth the car is only moving at 20km/hr. The conveyor belt can not measure the speed of the plane from outside of the system, it measures the speed of the plane from within the system.

Ok, I'm back and you're logged out. Thats perfect actually. You are interpreting the problem all wrong, the plane needs speed to take off, but it isn't going anywhere if its just spinning its wheels on the belt. Even then, with a tiny bit of thrust, its going to need to belt to go a zillion mph to keep it in one spot via the drag on the wheels and their supports. Eric posted right below yours and explained it perfectly, the plane must be moving through the air itself, aka airspeed, even though its stilll on the ground, to take off. Obviously. However, the only way the conveyor belt can go at the same speed the airplane is going, is by going backwards while the plane ROLLS FREELY fowards. Both the plane and belt gain speed, and it takes off. The problems wording and exacting standards are supposed to be confusing, and obviously they are confusing you.

[Brew]

I'm quoting myself again because there are still jackasses arguing this:

Forget the plane, picture a missile sitting on the same runway with a few casters on it. Someone try and tell me that it wont accelerate, I dare you.

And yes, a sailboat with a fan mounted in front of sail will move also. Sails work exactly like wings.

[Justin B]

OK, let me start this post by saying that I seriously doubt most of you that don't think it will fly area even attempting to 1) think hard and interpret confusing problems literally, and 2) reading and taking a little bit of time to even think about my posts. You guys are posting so fast after I do, all you're doing is quoting me and going off on some tangent that only halfway relates to the problem and that I already explained a million times before in 100% clear detail. Now...

How do you know that isn't happening? The problem does allow for that possibility. In fact I'd say the problem suggests that.

Here I will provide to you how the problem literally asks for this to be achieved. The drag on the wheels is irrelevant. Seriously man, just look a few posts back, you're back peddling worse than a chronic liar that SUCKS at lying. You JUST said that we should assume that there was no drag, I agreed, but then of course told you that regardless of drag, given a planes maximum speed on tarmac, not taking into account for any wind resistance, it will move at maximum (if wind resistance is not factored in, ie, if the plane can only top out at a few mph with brakes on the wheels or glue in the bearings) speed of half that, on a belt. Forward on the belt at half, and the belt reverse at half. Of course, if the wheels create so much drag that the plane cannot move at all on tarmac, neither the plane nor the belt will move at all regardless of how hard the engines push.

I noticed you "yielded" your position sarcastically if the plane was a spec of dust or whatever and had the thrust of a space shuttle, but you're still not thinking the way the problem WANTS you to think.

You don't DRIVE an airplane as much as a car, of course there is drag, and of course it is POSSIBLE that the wheels have their brakes on or something of that sort preventing it from moving forward too well. Even if the plane can move forward at 1mph (air and wheel speed) on a normal tarmac runway, that would equate to half a mph forward, and half a mph backwards (from the belt going backwards at a half mph). Thats MAXIMUM speed on a normal tarmac and maximum speed in this scenario on a belt, but it can only advance forward at a half mph since the wheels are creating such a great amount of drag. This however satisfies the "same speed" riddle.

Look at it this way, really any other way, for the given thrust of a plane to move at 10mph, a belt underneath the plane will have to move at 30mph, lets just make it a small number to keep it simple, assuming there really is a considerable amount of drag on the bearings. I get to that later though. First of all, the plane isnt moving anywhere, and even if it was (it would have to be on solid ground by your thought) it would only be doing 10mph. The bel tis doing 30, and theres no way any of that matches up. Its GOT to be moving equal and opposite. Ever hear of that? You're an engineer or something for criminy sakes. Equal and opposite speeds here, we're not talking about equal and opposite drag to keep the plane in one location. In THAT case, you'd be right, but its not.

Of course it will not take off if this is the case, but for the love of sanity, which way are you going with the drag vs no drag? The problem, ourselves, and logic tells us that the problem implies there is no drag on the wheels. Ive said it before, that if you want to factor in drag, you're going ot have to know how much drag, you'll need to know how much speed the plane needs to take off, you'll need to know how much thrust the plane has, the weight of the plane, and even wind speed and air density. Give me a break, its a physics problem. If it is not expressed, it is not implied.

All of you that still believe the plane will not take off with even minimal drag on the wheels, a real world scenario of wind over the body, and anything else, are too set into your ways to even think outside the box. I feel sorry for any engineers that are like this. Really. You need to think and understand all of the possibilities, and the relative drag vs thrust in ANY sort of plane, AND interpret problems correctly. You are doing none of them, as well as anybody else that feels the same way.

Do I need to draw up an animated gif for you guys? You're seriously killing me.

For you WA people, I like you guys and all, but did the PNW get a dose of stupid pills? :p

[Justin B]

I'm quoting myself again because there are still jackasses arguing this:

Forget the plane, picture a missile sitting on the same runway with a few casters on it. Someone try and tell me that it wont accelerate, I dare you..

An EXTREME example of the same exact problem. THINK a little bit people!!

[Justin B]

I really need to go back to school and finish up my engineering degree. I cant believe I can see this so much easier than a lot of people.

The missile and casters example is really really close, just a hell of a lot more thrust and a hell of a lot less resistance rolling, but it has all of the same properties. Stick a wing on it and once it reaches a certain speed it'll flip and go out of control, but it'll fly.

A plane is the same, exact thing. Just more resistance and less thrust, the same thing will happen but at less acceleration and less overall top speed.

The belt will move backwards to meet the (air) speed (if its the wheel speed, like in a car going off its speedometer, the plane isn't going anywhere, I just feel it necessary to keep repeating this) of the missile/plane traveling forward.

The same problem will work with a car too, really. The car's speedometer will just read 80mph if the car is traveling at 40mph (from point A to point B) while the belt is moving backwards at 40mph. It all still works, again, the wheels are the only ting going twice as fast as they should.

[matte30is]

The FAA would never allow a plane to take off on a conveyor belt any ways, so this topic is really a wash.

[Justin B]

lol