Nick check your PMs

This horse is dead. I'm done playing Mr. Wizard. Somebody else give it a shot.

Lets just say that the conveyer does not have the force to stop the airplane, if the airplane descided to move.

When you apply brakes on the aircraft, you are literally, what (I may be wrong in this) but applying several tons of force on those wheels. The conveyor would have to apply the same amount of force on the wheels to stop the forward movement of the aircraft.

It wouldn't have the mass and speed to do it.

Required reading - and proof!:

http://www.avweb.com/news/columns/191034-1.html

The plane will definitly take off. The force of the prop /jet engine is against the surrounding air,and NOT the ground. Therefore, the plane will accelerate in forward direction untill air speed over wings provides lift.
Speed and direction of conveyer belt (ground speed) is not in the equation.

Try this: suspend an electric fan above the floor with a length of string, so air flow will be parrallel to the floor.
turn on the fan,it will try to move ( forward ) . Now place a large flat piece of cardboard on floor under fan.
With fan still turned on move the cardboard around ,forward ,back,sideways, at different speeds.
Notice what effect this had on the fan.
I'll guarantee there was no effect

Re-cap, lift is produced by air moving over wing/ or wing moving through air.
speed of air over wing,not ,speed of air,or wing over ground produce lift !

fierosteve

quote Originally posted by Gary W: Required reading - and proof!: http://www.avweb.com/news/columns/191034-1.html

Good link. This is a great example of misdirection.

And the misdirection was?

Nick Nick Nick. Imagine a toy plane with wheels that can rotate, sitting on a moving conveyor. You are preventing the plane from rolling backwards down the conveyor with your finger--the wheels are rotating, and the plane is stationary in relation to everything else but the conveyor belt. Now, push forward with your finger. In relation to everything else, the plane has now moved forward. Air has passed over the wings, and lift is generated. The conveyor may indeed have sped up to match the movement of your finger, but the rest of the world did not, including the air around the wings. Your finger is the thrust of the propellor. You WILL be able to just push that toy plane right off the end of the conveyor belt regardless of how fast the belt moves below the plane.

Speeding the conveyor belt up only means the wheels rotated at a faster rate. The only thing that matters is how fast you moved your finger.

quote Originally posted by maryjane: Nick Nick Nick. Imagine a toy plane with wheels that can rotate, sitting on a moving conveyor.

don't imagine! DO!

get a rubber band plane and some butcher paper, and a helper. We'll put a stop to this once and for all

hey there you go -

"One guy even got one of those rubber band powered wood and plastic airplane that sell for about a buck, put it on the treadmill someone foolishly donated to the Lounge years ago, thinking that pilots might actually exercise. He wound up the rubber band, set the treadmill to be level, and at its highest speed. Then he simultaneously set the airplane on the treadmill and let the prop start to turn. It took off without moving the slightest bit backwards."

[This message has been edited by ryan.hess (edited 12-03-2005).]

Simple questions for the doubters:

If the relative speed of the plane vs. the earth is zero, even at full thrust, what is the magical force holding the plane back?
The engine pushes it forward.
The belt does not push it backward - the wheels are rolling and friction is negligible. The air does not push it backward. If you think that they do, please explain the forces involved.
In order to remain stationary, the FORCES on the plane must be equal. The speed of the belt vs. the plane is irrelevant, unless the belt can somehow create a backward force on the plane equal to the force of the engines. How does the belt do this?

If the forward force on the plane exceeds the backward force, the plane will accelerate forward. Since there is no force mentioned in the original question holding the plane back, it moves forward freely relative to a stationary point on the earth. You cannot break physical laws to simplify the question.

quote Originally posted by fierofetish: Sorry...!!! The inference is that the belt matches EXACTLY the speed etc of the plane. If the plane accelerates at 0-500mph in 2 seconds...so too does the belt..and so it won't shoot off the end of the paper!!! The belt doesn't have an end!!! The plane stays static in relation to the air that surrounds it..so no lift!!! Night!! Time for bed!!! Nick

Again, you are missing the difference. The plane accelerates from 0 to 500 mph relative to the air. It does not accelerate relative to the conveyor belt. This is the critical difference. It is pushing on the air and the air is pushing it forwards. It is not pushing on the conveyor belt.

Lets try another example. You are on a skateboard. You have a winch that is pulling you and the skateboard forward at the rate of 10 mph. Now this is a strong winch that has 1,000 of lbs of pulling power. So yo move forward at the rate of 10 mph. But your skateboard is on an exercise treadmill and someone turns the treadmill on 10 mph the other way. Do you stop? No, because the winch is still pulling you forward.

The winch is the engine of the plane, and the winch cable is the air. The winch and cable pull you forward no matter what is happening to the skateboard wheels.

I can think of several things that this difference of opinion is based on. One is that you think the engine of the plane is only strong enough to make the wheels of the plane go 120 mph. This is simply not true. The engine on almost any aircraft is much stronger than required to get the wheels turning at a higher rate of speed. The second is that you think the speed of the wheels or the speed of aircraft relative to the surface it is on is important to this question. It is not. The speed over the surface means nothing to an airplane. The third thing is what I think is most likely, but it is most complex. I'll see if I can describe it.

There are basically four speeds in this question. Ground speed. The speed of the aircraft relative to the ground (not the belt). Belt speed, the apparant speed of the belt compared to the ground. Air speed, the speed of the relative wind passing over the aircraft wings. Wheel speed, the speed the wheels are turning on the belt.

As the wind isn't mentioned, we'll assume the air be still. Since the ground doesn't move, and we assumed that the air isn't moving, then anything moving along the ground must also be moving through the air at the same speed.

We'll assume the drag from the wheels reduces the speed of the aircraft by 10% of the wheel speed. We'll assume the aircraft has enough thrust to pull the aircraft 120 mph through the air. And we'll assume that it can take off at 100 mph air speed. These are good numbers as you only are supposed to take off when you have more engine power than you need.

Our take on this is that the belt speed of the conveyor belt is set to the ground speed in the other direction. Say we take the aircraft engine up to 10% power. That would give us 12 mph. When out speed gets to 10 mph compared to the ground the belt must move 10 mph compared to the ground in the other direction. Ground speed is 10 mph and belt speed is 10 mph, so we've got the part where the belt is moving opposite of the aircraft at the same speed. So wheel speed is 20 mph (10 mph forward plus 10 mph backwards). 10% of that is 2 mph, but we have 2 mph more in the engine. So the extra thrust of the engine balances the extra drag from the belt. If we take the engine up to 100% power, we would get a speed of 120 mph. When we hit 100 mph ground speed, the belt is going 100 mph the other way. 10% of the 200 mph wheel speed is 20 mph. Since our aircraft has the extra power to overcome that 20 mph, we are heading along with a ground speed of 100 mph. Since air speed and ground speed are the same, our air speed is 100 mph and we can take off.

Your take on this is that the belt speed is set to the wheel speed. Using this idea, the aircraft is moving 10 mph over the belt with the engine set to give us 12 mph. So the belt increases to 10 mph in the other direction. This gives us a wheel speed of 20 mph. Since the belt speed matches the wheel speed, the belt speeds up to 20 mph. That gives us a wheel speed of 40 mph. 10% of that is 4 mph plus the 10 mph ground speed is more than the engine is producing, so the airplane slows down.

The problem with the second take is two fold. One, it creates a positive feedback look. An increase in A will increase B. An increase in B will increase A. Scientists and engineers never, ever use positive feedback as whatever it is will go out of control. If you get the mike to close to the speaker, you get feedback because the sound of the speaker is picked up by the mike and the amplifier amplifies this and plays it out the speaker, which is picked up by the mike, amplified, and played out the speaker again. So the scientific minds here automatically dismissed this interpretation of the problem. Two, this take involved an invented vairable, wheel speed. Aviation is only concerned with airspeed for flight and groundspeed for navigation. They don't care about wheel speed. So the aviation minds here didn't think about this critiria.

Yeah, yeesh! Nick, you have a point in that the weels help the plane take off, but lets look at why. If you were to draw an FBD of the plane's wheels, they, because they are bearings, provide no resistive moment, and no horizontal resistance. They only provide a force normal to the surface they are on, the conveyer in this case. The only force the wheels can apply to the plane is in the verticle direction (of course this is all assuming that there is no friction, which you stated that you were assuming). So, why do we have wheels? They provide an upward force on the airplane to keep it in static equilibrium the 2 feet or so it sits off the ground when parked. Why not take away the wheels? now we have a plane sitting on the ground. ok, the only force here is the equal and opposite forces of the plane on the ground and the ground on the plane. Can the plane still take off? not really because in this case, the friction would be way to large to neglect. while probably isn't enough to stop the plane from taking off, it would be enough to rip whatever material is on the bottom of the plane off therefore wrecking the structural integrity. So back on track. the wheels on the plane really only provide an upward force on the plane, no horizontal forces. this means that the plane is free to move forward or backward from any outside force. The treadmill will not provide this force as it is acting on the wheels which will rotate and not transfer any of the horizontal motion to the plane. same would happen in a car if you disengaged the engine from the trans and neglected all friction in the wheel assembly, which you are. turn on the treadmill and the car, plane, whatever on wheels will not turn. Next time you are at a gerocery store try this. it is fun. put a grape on their conveyer belts and it will remain stationary and rotate freely, provided you give it a little umph to overcome initial static friction, and that the grape is fairly round. So the treadmill cannot transfer any horizontal force to the plane. it only causes rotational force to the wheels, and this rotational motion is not transfered to the plane as the wheels are just on bearings, not hooked up to an engine of any sort. So the plane could be off and the treadmill speed wont affect it. Turn the engine on in the plane and now you have greated a force to give it horizontal motion. the propeller pushes against air around it pushing the air backward and the plane forward. the treadmill is helpless against this motion as it can transfer no horizontal movement to the plane. ok so..once the plane gets going to a significant speed due to the interaction between the props or what ever method of propulsion and the air (or exhaust if a rocket), the force of the moving air over the wings will give lift. The moving air occures because the plane is moving forward from the prop and the treadmill is helpless to impeed it. And then the plane can take off. Ok. Still don't believe me? get one of those gas powered model airplanes. hold it by your hand in the air. turn on the engine and rev it up. Feel that strong force? That is from the prop. now the plane is stationary because your hand provides the force to equalize gravity and the force to counteract the prop. if you let go the plane will go forward and start to drop in altitude untill it has reached enough forward momentum to gain lift (all from the props, not from wheels) and then it willl fly, unless it hits the ground first before it gained enough forward momentum. So there!

And just so you all know, I talked with one of the lead engineers of the "Stealth Bomber" project, who worked on the design while it was still top secret. And he said that no matter what, the question is flawed. It's all illrelevant unless we know certain facts about things such as the atmosphere, wind speeds, the plane's weight, etc.

Think about it, if we're 7,000 feet above sea level, it'll be a little harder to get the thing off the ground then being at sea level.

And thus, I end this entire stupid debate because there's not enough information to solve the problem. There's too many dependencies, and a lack of information.

In theory it could work both ways.

[This message has been edited by Scythe (edited 12-03-2005).]

What if you were on "Let's Make a Deal" and you had to choose between three doors.

One of the doors has a new plane (good) and two have conveyor belts (bad).

You pick one door. Without opening that door, Monty Hall opens a different door that has a conveyor belt.

If you switch doors from the one you picked will you have a better chance of having the plane fly off that if you stick with the existing door?

quote Originally posted by Gary W: OK. That would be like saying that the plane were nailed to the ground. No amount of thrust would get it to move relative to the ground or the air. It would not move, and it would not fly. But the question was not about pretending it was NOT on a conveyor belt. This is a Physics test question we actually debated in college. It's meant to challenge the way you look at the problem, and the question is asked in a very specific way for a specific reason. As put forth in the original question, making no assumptions or interpretations of what you think somebody was asking, the plane will accelerate down the moving runway and take off.

In our aero course, we used REAL scenarios with numbers.. But seriously, no, as the question reads, yes, of of course it would take off. But I'm assuming thats not what he meant.. It doesn't really matter, whatever way he meant has a quick and easy response. If he meant plane stands still, groundspeed 0, plane doesn't take off. If he meant giant treadmill but everything else works as should, then plane takes off.

quote Originally posted by Gary W: the wheels are rolling and friction is negligible.

I see. So therefore none of us would have any trouble attaching a rope to the front of a 747 and pulling it down a runway by hand.

Although the whole scenario is of course impossible because the magical "conveyor belt" would never spin fast enough, that doesn't make it fair game to conveniently ignore known factors (in the real world) such as friction and/or rolling resistance. But then some of you seem to be ignoring gravity as well.

Using examples such as toy cars on moving pieces of paper is comparing apples to oranges to say the least.

We need to get Stephen Hawking in on this discussion!

[This message has been edited by Patrick (edited 12-03-2005).]

My God I love the human race. After reading the entire thread, it is refreshing to see men (and maybe some women) arguing about a theoretical system.

This thread is not about religion or politics, it is about an idea. An idea that by its very nature suggests that man is capable of flight. An astounding assumption from the very get-go.

Yes, man can fly given the thrust, lift, and control vectors of a defined technology. I spent 5 years of my life learning 7th degree differential equations, and complex coefficient non-linear equations defining the parameters of a flight system. Mathematics is just a language folks. Its not an end all, be all, end in its self. It just allows us puny humans to communicate to each other ideas. of what the universe behaves like.

Given that, I love this thread. You all are pulling out all the stops, with whatever language skills you have, to justify an idea. An idea, that only a couple of hundred years ago would have put you in the stocks, or the nut house. Now, you spend 4 pages on an internet forum arguing if a set of flight parameters can end with a flight result. You folks are great.

What do I know? ..........Nothing............... Only that what you see here in front of your eyes are pixels forming letters on a computer screen. It is making you thing, and think hard. Your position is where it is. You will fly your fingers over the keys to put what you think is correct, into little pixel lights on a screen that someone a thousand miles away will see.

It gives me hope. I would much rather see a thread like this get a hundred pages, rather than a thread about a some political or economic system difference. At least on this one, we could build the belt............build the plane........and find out the truth in the end............without killing each other in the process.

Hehehe great discussion.

It looks like, as JohnnyK stated, there are just different interpretations of the question causing the diaggrozzlements on the result....perhaps the question was worded as it is to create this split in opinions?

Cheers
PK

Very nice comments, zardoz. I couldn't agree more.
I have to be honest, and say this thread has given me probably more pleasure than any other.It gets the brain working positively.It brings out a desire to communicate verbally.I doubt the Spanish or Italians would be able to communicate as successfully, because they rely so much on body expression, hand and arm gestures, and facial expressions to convey at least 50% of their meaning. We are doing it through two planes only (no pun intended!!)..vision and words. No diagrams, no visual aids, just words. We strive to communicate to the best of our ability, using words. Nothing else. That is truly remarkable.Irrespective of whether we agree at the end. We have discussed an idea.We have expressed our thoughts, ideas and opinions. And nobody has been slammed, insulted or emotionally hurt. Wonderful. And that is the beauty of this Forum. Whatever the subject, in the main, we listen.We understand, or try to. We are keen to impart our ideas, feelings and aspirations. Long may it continue.
Nick

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fierofetish.PFF'S self-confessed Snowbird!!

Responsibility: the solution for our World's Dilemmas..
Yahoo messenger:nickcannspain
MSN Messenger-nicholascann@hotmail.com

Johnny, this is an accurate statemen. Well, except for the one about groundspeed 0, that's BS, it is quite possible to take off with a groundspeed of 0 as long as you have sufficient airspeed.

John Stricker

quote Originally posted by JohnnyK: In our aero course, we used REAL scenarios with numbers.. But seriously, no, as the question reads, yes, of of course it would take off. But I'm assuming thats not what he meant.. It doesn't really matter, whatever way he meant has a quick and easy response. If he meant plane stands still, groundspeed 0, plane doesn't take off. If he meant giant treadmill but everything else works as should, then plane takes off.

quote Originally posted by zardoz: At least on this one, we could build the belt............build the plane........and find out the truth in the end............without killing each other in the process.

I love you too

quote Originally posted by ryan.hess: I love you too

Bear Claw: Whats on the spit?

Jeremiah Johnson: Grown particular?

Bear Claw: Thank ya' kindly.

Just want to get one thing straight in my head, Roger. This is my definition of airspeed in relation to groundspeed.

An aeroplane is flying at 20.000 feet, in totally 'still' air. Its groundspeed is 450 mph (I know it is really in knots, but just to keep it simple ). As the air it is flying through is 'stationary', I assume its airspeed and groundspeed are equal. If, however, that air starts moving, in the form of a 100mph headwind, and the pilot applies more power to keep its groundspeed the same, the actual airspeed will be 450 mph groundspeed, plus the 100 mph headwind, making its actual airspeed 550mph?
Thanks in advance for a reply, yay or nay, and if the latter, enlighten me please!!
Nick

http://www.allstar.fiu.edu/aero/airspeed.htm

Thanks JohnnyK..should have just Googled it, I know!! I think I wasn't too far off the mark, though, for a novice?
Nick
(ps..just got "smells like teen spirit" backing track!!! !!)

Nope, plane WILL NOT fly. Remember the song a few years ago "Wind Beneath My Wings" ? Well, wind beneath the wings has nothing to do with flight. Air flowing OVER the top curved surface of the wing makes it fly. The lift is caused by the difference in air pressure; less above the wing and more below, that creates lift. The plane in question will remain on the ground until it runs out of gas, then fly off the back of the conveyor like someone running on a treadmill who suddenly stops running forward. CRASH!!!!!!!!!!!!!!! Ed

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I cannot believe this thread has 4 pages The airplane will be able to fly. The propeller creates the force to move the aircraft forward. The conveyor belt cannot stop the aircraft from accelorating forward because it will just spin the aircraft "WHEELS" faster, big whoop. If there is no force physically holding the aircrafts feusalage from accelorating ( the conveyer does not ) it WILL accelorate. When the aircraft reaches it's determined minimum takeoff airspeed ( with flaps or with out) The aircraft will fly . The conveyor belt is doing nothing but spinning the tires, the tires DO NOT drive the aircraft forward the propellor does . The conveyor affects the speed of the tires which it turn has NO effect on the forward motion of the aircraft (unless brakes are applied).

In short the aircraft will accelorate like normal and it will fly in normal fashion.

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HARDCORE SBC CRONIE AND PROUD OF IT ! GOT TQ ?

[This message has been edited by FIEROPHREK (edited 12-03-2005).]

The plane will fly.

Here's why.

The plane is pushed forward through thrust in the air, not torque on the wheels. The wheels are basically "lubrication" between the fuselage and the ground.

When the plane accelerates, it pushes its body forward. The conveyor belt will begin to move in the opposite direction, but the only effect that will have is that the wheels of the plane will spin faster than it would normally be spinning... twice as fast as the apparent plane-to-ground speed, in fact. All the while, the plane is still travelling forward and accelerating as usual (minus a miniscule amount of drag that the conveyor belt manages to transmit through the wheels to the fuselage).

Because the plane is travelling forward, it still develops lift under the wings and flies.

At the point of takeoff, the wheels will be spinning twice as fast as the fuselage is moving forward... that is the only effect of this system.

[This message has been edited by VoicesInMyHead (edited 12-03-2005).]

VoicesInMyHead-exactly. AND, assuming the horsepower of both the conveyor and the AC are unlimited, it won't be all that hard. IF, as stated elsewhere in this thread, the conveyor belt's speed actually begins to drag air along in it's rearward motion, this will actually aid in lift off.
The plane does move. It's even stated so in the initial post.

quote The plane moves in one direction, while the conveyer moves in the opposite direction.

Ding!! Round 2? Nah.....I'm punch-drunk enough already!!!

OK.....errr..no!! !! Pulls fingers away from keyboard....

Just one thing...more!!!!!

Assuming the conveyor belt is moving backwards at the same speed as the plane is trying to move forward.Therefore, it would be travelling at for example 120 mph in relation to the belt surface, but stationary in relation to its surroundings.Two scenarios that have been buzzing around my head all day!!
1.The belt suddenly stops..instantly. What would happen? I think the plane would scream down the belt at the speed, or near enough, that it was being propelled by the plane's motive power, to keep it stationary, in relation to the static ground around the belt, on the belt.And take off.Mainly because the inherent inertia caused by the tyre resistance and wheelbearings has been overcome already, because the wheels are rotating at 120 mph.
2. The planes engines cut out, instantly , but the belt keeps going at the same speed. Momentum of the plane moving on the belt would decrease ,due to tyre/ bearing friction building up; and sooner or later, the plane would loose speed in relation to the belt surface, and fall off the end of the belt.
Any takers ??? I am assuming that the theory that the plane would NOT be able to fly is correct. Next we can look at the same question, assuming that the plane WOULD take off. I just want opinions as to the 2 options I have given above for now!!
If nobody wants to indulge my whim, I will most certainly understand!!
Nick

Ever driven your car on a ferry? The ferry is moving forward. CAN you put your car in forward and move forward both in relation to your previously parked spot on the deck, and in relation to all the rest of the world, without even accelerating to the same speed the ferry is moving? Yes you can. Yes, even at idle, you can drive right off the front of the ferry if the bow door is open. If your car had an air thruster on it, instead of wheel driven propulsion, you would still be able to drive off the end of the boat, no matter how fast the boat sped up.

Of course the plane will fly! There is no doubt about it, and there are no ambiguities involved. Remember ... we are talking about a real airplane taking off from a real conveyor belt.

If the opportunity ever presents itself, I will fly with jstricker, Wolfhound, GaryW, maryjane, and anyone else who has correctly stated that movement of the runway (or movement of the Earth, for that matter) has no significant effect on the plane's takeoff, flight, and landing behavior. They are all correct. The rest of you guys scare me ... especially those of you who claim some background in aviation or aeronautical engineering!

Some points to ponder:

1) Every runway in North America is already moving east at a speed significantly faster than the takeoff speed of any aircraft using it.

2) How does the runway affect the airplane ten seconds after takeoff? How about one millisecond after takeoff, when the tires are less than an inch off the surface? How is this different than a millisecond before the tires break contact with the runway? How is it different than ten seconds before takeoff? How is it different than at the very beginning of the takeoff roll?

I'm at least relieved that no one has (yet) proposed "Intelligent Flying" as a philosophical alternative to the laws of physics.

[This message has been edited by Marvin McInnis (edited 12-04-2005).]

quote ??? I am assuming that the theory that the plane would NOT be able to fly is correct.

The assumption is wrong. But, in the inetrest of interest, we have a variable speed conveyor system at work. I'll see what I can do with a cam corder and a wheeled vehicle of some sort.

I will set the conveyor at 1/2 it's maximum speed. I will tie a string to the vehicle, place it on the moving conveyor belt and hold the vehicle stationary with the string. I will make some kind of external marker as a real world reference point. Then, I will pull the vehicle as slow as is humanly possible via the string, which is a simulated propellor. It WILL move against the conveyor in reference to the externally mounted reference point (and the air). I will then speed the conveyor up to it's maximum speed and again pull the string as slowly as possible. Again, it will move in refernce to the rest of the world--including the air. Remember, I will be sitting on the conveyor belt as well, just as the propellor on the plane would be. Unfortunately, it would have to attain a tremendous belt travel velocity for me to get enough lift to fly, so I will probably go off the end of the conveyor.
(I'm off to go buy a little toy plane)

[This message has been edited by maryjane (edited 12-03-2005).]

MJ..don't do anything to hurt yourself!!
Your control project is flawed.. I believe. You would have to be standing on the aeroplane, for it to be correct. The motive power of the real plane is mounted on the plane, not the floor. You would be exerting the string-pulling force against the floor, or whatever you would be standing on. The motive force of the plane is only exerted against the surrounding air. It is using the body of the aeroplane, and its weight, to provide a platform for the motive force to push against the air.You would have to be suspended in mid-air , and transferring your resistance against said air, to provide a motive force through the string, to pull the plane along.Impossible!! You, like the engine, need the support of the plane to stop you falling to the ground!!
It ain't over, til the aeroplane flies !!
Nick
I am going to try to draw some theoretical diagrams to explain this, if nobody else gets what I am trying to say..

quote Originally posted by maryjane: [QUOTE]??? I am assuming that the theory that the plane would NOT be able to fly is correct.

The assumption is wrong. But, in the inetrest of interest, we have a variable speed conveyor system at work. I'll see what I can do with a cam corder and a wheeled vehicle of some sort.

I will set the conveyor at 1/2 it's maximum speed. I will tie a string to the vehicle, place it on the moving conveyor belt and hold the vehicle stationary with the string. I will make some kind of external marker as a real world reference point. Then, I will pull the vehicle as slow as is humanly possible via the string, which is a simulated propellor. It WILL move against the conveyor in reference to the externally mounted reference point (and the air). I will then speed the conveyor up to it's maximum speed and again pull the string as slowly as possible. Again, it will move in refernce to the rest of the world--including the air. Remember, I will be sitting on the conveyor belt as well, just as the propellor on the plane would be. Unfortunately, it would have to attain a tremendous belt travel velocity for me to get enough lift to fly, so I will probably go off the end of the conveyor.
(I'm off to go buy a little toy plane)

[/QUOTE]

[This message has been edited by fierofetish (edited 12-03-2005).]

quote Originally posted by Wolfhound: And the misdirection was?

The misdirection is the conveyor belt. It makes you think the conveyor will counter the planes forward movement. It seems intuitive at first, but it's not. If the plane was sitting on the conveyer and held in place by tie downs that weren't on the conveyor - starting the belt wouldn't move the plane, right? The tie downs are holding it in place, so the wheels just start turning as the belt speeds up.

By the same token, the thrust of the propeller moves the plan forward. As the plane moves forward the belt speeds up in the opposite direction. But all that does is spin the wheels even faster. It doesn't affect the forward speed of the plane.

If you used a car instead of a plane - it would stay stationary, because the car gets it's forward thrust through the contact between the wheels and the belt. But the plane's thrust is from the propeller and is therefore independant of what's happening on the ground. All you need is airspeed over the wings, and that has nothing to do with ground speed at the wheels. The plane could take off standing still - if the head wind were fast enough.

quote Originally posted by Formula88: No. That's part of the assumption. If the plane accelerates to 10mph and the belt accelerates to 10mph in the opposite direction, you're assuming they cancel out and the plane remains stationary. That's the misdirection. Say the plane is moving at 10mph. If you move the belt at 10mph opposit (i.e. -10mph) will the plane slow down to a stop? No, it won't. It will continue to go forward at 10mph, but the wheels will now be rotating as if it was travelling 20mph. You'll have a 10mph air speed, but a 20 mph ground speed. The motionless assumption only works if the plane gets it's propulsion thorugh contact with the belt - like a car's tires on the road.

No, i get it.. Aerodynamics was my thing in school, remember? But I mean, I am assuming the original poster of the question MEANT that the plane remains motionless, know what i mean?

According to the original premise, forward motion of the plane produces rearward motion of the conveyor.
So if the plane is stationary so is the conveyor. In that case it,s just parked.