Brain teaser

[OldSchoolin86]

There is a debate raging on another board I visit here is the topic:

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?

[LonesomeTriZ]

If it is fom the same forum I saw it on, I think they finally agreed it would fly.

[ATCWRENCH]

I dont think would fly. it doesnt matter how fast the jets are pushing the aircraft if it isnt able to move cuz of the convayer(sp) moving as fast in the opposite direction, the plane essentially is going nowhere. a plane has to move through the air so the wings can create lift with moving air.

[Unclediezel]

Technically---the plane would be traveling at Double its speed because the ground is moving equally in the other direction---it should take off in half the time normally allowed.

[danteross77]

So if we are dealing hypothetically, Is it like lets say:

Your riding your 250r and you top it out at light speed, you turn on your headight, Does it turn on or not?

[slothminx]

So if we are dealing hypothetically, Is it like lets say:

Your riding your 250r and you top it out at light speed, you turn on your headight, Does it turn on or not?


It turns on and your can see the light when your on the bike, but if you were infront watching it come towards you (hypothetically lol) you wouldnt see the light or the R until it had gone past

And on the plane one....... ill let a few more people answer before i chip in lol

[250r'en +TCB]

^^^ yeah I've done that. Went around the world 7 1/2 times in one second....... pretty fast..... When I turned the headlight on it slowed down a bit, but then I just put it in 6th gear and I easily sped up to 1.3 times the speed of light. Those 250R's are pretty fast, couldn't imagine the 500R's!!!! hahahaha

[Howdy]

Avionics 101 here.
1st off the plane is propelled by air. Thus moving the ground wouldn't have much if any effect of it taking off. The only thing moving the ground would do is possibly to cause the wheels to rotate more and wear them out quicker.

So No it wouldn't fly.
Howdy

[slothminx]

So No it wouldn't fly.
Howdy

Sure you meant that Howdy?:beer


The movemnt of the ground has nothing to do with the plane moving or not. the wheels do not drive the plane, the engines do direcly push it with air. so if stil moves.;)

[bigredhead]

exactly.

the wheels can turn as fast as they want.. the plane will still move forward gaining speed and lift and take off .

The engines on the wings push the plane independent of the conveyor and wheels.:lol:

Had me for a minute there tho.

[nouseforaname90]

I was thinking that it wouldn't fly for a minute, too.
But it would fly. That conveyor could be traveling 2x the speed of the plane, and the plane would still take off. The conveyor would not hold the plane back. The wheels would just spin 2x faster than they normally would.

[nouseforaname90]

Now if you were driving your car down this runway, you would get nowhere. But that is because the part that makes it move (the wheels) are contacting the ground and the ground is moving. But the wheels on a plane do nothing. The engines are what push them through the air.

[Unclediezel]

You drive a car forward-- to your destination--2 miles away--
If your destination is moving toward you-you will get there in half the time--
but not half the speed--?
The issue is this--BOTH plane and runway are moving---in opposite directions- but moving none the less.---By this we can assume that air is sucked under the wings and the physical properties of flight have not changed.

[Howdy]

I base my previous post on the assumtion, that when they put it on the conveyor, that they mean the plane basically stays in one place and takes off. Basically a vertical take off. Assuming this the Plane wouldn't fly.

Planes will only fly if they get enough air flowing over the wing to create lift. If it's moving down the runway with the wheels moving 2 times normal speed and it gets enough air flow to create lift, then yes it would fly.
Howdy

[Tri-ZNate]

no not gonna happen. If they conveyer is moving just as fast as the plane and the plane is on the conveyor then the plane isnt moving, there fore it wont fl'y.


Ahh ya got me there for a sec. I didnt read the other posts before I replied.

[Oldshell4481]

its not gonna fly because its just the wheels spinning while the plane is stationary, the jets can push as hard as they want but the plane wont get lift because it is not moving at all, just the wheels, and unless the plane itself is moving along the ground at a speed high enough for it to get lift, it wont take off. get itt??

[nouseforaname90]

No. It will move. I had trouble getting a grasp on it at first, but I figured it out.
The conveyor would only stop a vehicle that uses wheels for movement. The wheels moving and the conveyor moving would cancel eathother out and you would go nowhere. But with the jet, the wheels are not its source of propulsion, the engines are, and they use air. So the plane would still move down the runway, but the wheels would just be moving very fast.

[Billy Golightly]

The wings need the aerodynamics of forward DISTANCE traveled to give the plane lift. I think if the plane is moving 900mph, as long as its not traveled any amount of distance from where it started, it aint going anywheres. This is not taking into effect the possible wind turbulence generated from a conveyor belt turning 900mph. I mean, common now guys. This is the same basic principle as putting a car or truck in a mud hole and stomping on the throttle and making the wheels turn 90mph while the tires sling the surface area under it in the opposite direction the vehicle is traveling (behind it). Does the car or truck go anywheres? Heck no it dont as long as the surface its on is going the opposite direction. And If you put wings on it I dont think its going anywheres either.

[nouseforaname90]

But the tires on a plane have nothing to do with its forward motion, and that is all the conveyor is going to be affecting.

[slothminx]

ok what we are assuming here is that the bearings and tires are causing no real drag and that they can spin free, the jet engines draw air in the front and trust it out the back. so the plane gives it some throttle and starts to move but the conveyor moves the other way at the same speed but because the wheel are idependant the plane move forwards, but the wheels are travelling twice the speed of the plane. Its not going to take off any different from normal and it will fly

[85 250sx]

YES i will fly the belt would not efect it in any way it will just make the wheels spin faster thats it

[Billy Golightly]

The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).




The plane is at a complete stand still distance wise, it is NOT moving across the face of the earth. It is stationairy in relation to the rest of the world. Everytime the plane speeds up, so does the conveyor moving the opposite direction. The conveyor is not just compensating for the wheel speed, but the speed of the entire plane.

Now, if the plane was already off the ground it'd be a different story.

[atctim]

The plane is propelled by jet engines, not it's tires. The plane would take off regardless of wheel speed.

[darrel632]

No way, It must have speed (relative) to get airflow over/under the airfoil. it cant do this if it stands still (forward motion negated by the belt) This aircraft needs forward velocity to break gravitational force (about 145 kt for v2 if its empty) if it doesn't have it, it can't get off the ground., Now if it was a Maule 7c, Storch, or a Pilatus turbo porter PC6 (STOL) it could maybe get off the belt empty using prop wash for lift if they had minimum fuel and weight.

[Banage]

ok ok ok ok ok i got it i got it go to mythbusters fan site and get it on the show.


But if the convayer is moving the same speed as the plane wheels, the plane is not moving thous no air pressure for lift thous the plane is grounded

[nouseforaname90]

Wow. You guys really don't get it.
The plane would move regardless of how fast the belt was moving. The wheels have NOTHING to do with the forward motion of the aircraft. Think about it. The plane is powered by the engines which push air at a high speed to get it to move. The plane would just glide down the conveyor belt as it normally would. Think it through.
Or test it. I would love to see someone test it and prove all of us "It will fly!"'ers right.

[Billy Golightly]

But the danged belt isn't turning the same speed as the wheels, its turning the same speed as the plane! And even if it DID follow the same speed as the wheels, when the plane accelerates teh wheels are going to turn faster and the belt would turn faster with them. As long as the conveyor is going the same speed, and acellerating at the same speed and pace as the plane it aint leaving the ground.

[Tri-ZNate]

ok think about it as if your playing on ice. Your tires just spin but you dont go anywhere, but someone pushes you and even if you speed up your tires your still gonna travel at the speed of the push.

Or lets say the plane is an inch above the conveyer. You can spin the wheels as fast as you want but the engines are still gonna push it.

[Billy Golightly]

if the plane comes off the conveyor it will fly.

As for the ice, thats not accurate because the ice would match the exact speed of your push that you gave the trike, like the conveyor does to the plane.


We're discussing this in chat right now if anyone wants to join in :D

[slothminx]

We're discussing this in chat right now if anyone wants to join in :D


discussing? more like arguing our asses off trying to make you get it billy LMAO

www.3wheelerworld.com/chat

[Garage Boy 34]

? will the 747 take off? I say yes... it has to . its a passenger plane.

[wanta250r]

Are you people saying the conveyor is traveling at the same speed as the plane? If the plane is not moving then how is the conveyor moving?

[slothminx]

Are you people saying the conveyor is traveling at the same speed as the plane? If the plane is not moving then how is the conveyor moving?

me and Billy just got this in chat!! she wont fly

[OldSchoolin86]

me and Billy just got this in chat!! she wont fly
LOL, no it will fly. You didn't get anything.

[wanta250r]

This stuff is tripping me out.

Lets say the caonveyor is not moving, and the plane is not moving. The plane starts its engines and begins to move. Then the conveyor moves too. If the conveyor is moving then the plane would stop right? But how could the conveyor be moving if the plane is stopped? It has to travel at the same speed of the airplane. This is boggling my mind, someone fix this.

[OldSchoolin86]

This stuff is tripping me out.

Lets say the caonveyor is not moving, and the plane is not moving. The plane starts its engines and begins to move. Then the conveyor moves too. If the conveyor is moving then the plane would stop right? But how could the conveyor be moving if the plane is stopped? It has to travel at the same speed of the airplane. This is boggling my mind, someone fix this.
The plane won't stop when the conveyor moves, that's the trick of it.

[Somekindofjerk]

Even if it did take off, keeping the plane from becoming unbalanced and doing a huge incline or some other unwanted effect would be allmost impossible. The plane must be ballanced at the wings to fly level and straight.

[OldSchoolin86]

Even if it did take off, keeping the plane from becoming unbalanced and doing a huge incline or some other unwanted effect would be allmost impossible. The plane must be ballanced at the wings to fly level and straight.
How did we add balance into this?

[Jason Hall]

It won't fly. Without the wings cutting through the air, there will be no lift, so D-plane won't fly.

[Howdy]

Maybe Adam and Jamie can do a experment and we can all watch it on TV. Mythbusters it's up to you now. lmao
Howdy

[OldSchoolin86]

It won't fly. Without the wings cutting through the air, there will be no lift, so D-plane won't fly.
A conveyor won't stop a plane from pushing air and going forward, it will just spin the tires more.

[Jason Hall]

I feel that if you could make a plane lift off on a conveyor than our government would scrap all the air craft carriers in there fleet, & build a 100 foot long conveyor ship & save a butt load of our money.:beer :lol: :lol: :lol:

[OldSchoolin86]

I feel that if you could make a plane lift off on a conveyor than our government would scrap all the air craft carriers in there fleet, & build a 100 foot long conveyor ship & save a butt load of our money.:beer :lol: :lol: :lol:
I agree but that is just impossible. The plane doesn't drive by it's wheels, it pushes air.:lol: The conveyor isn't going to stop it from going forward like normal and taking off.

[Billy Golightly]

The plane has to travel a distance in relation to the earth, and therefore travel the length of the conveyor belt to make lift. It cannot do this because the riddle has the speed of the aircraft and the conveyor belt locked together. No matter what when the plane tries to accelerate via its engines the belts speed is increasing to match it and keep it from moving.


I'm gonna be going on about this until the end of time more then likely :lol:

[bigredhead]

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

The question is:

Will the plane (747 passenger jet) take off or not?

0000000000

If you re-read the question at hand.. the conveyor belt WILL MOVE but at the same speed as the plant.. ie: the plane IS moving.. creating lift.. and the conveyor belt is moving at the same speed as the plane but in oposite direction.

Hence.. the plane moves.. using the engine attached to the wings.. wheels having nothing to do with it.. it will take the plane longer to accelerate than usual due to the forces exerted on the wheels but with enough power from the engines it will overcome the resistance from the wheel bearings going in reverse....

The plane will take off.... Given the rules of the riddle.. it's all in how you word it.


Now...

IF it said that the conveyor somehow could keep the plane at a stand still, realive to it's enviroment, hence not allowing the plance to move an inch forward.. then no.. it would not take off.. but it says that the plane CAN move.. but the wheels will turn in the oposite direction at twice the speed of the planes forward motion..

simple huh.

[Dammit!]

The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The answer is in the question. The plane IS moving.

The wheel speed has nothing to do with anything here. The plane will definitely take off.

Let me make an analogy. Take a trike. Put ONLY the front wheel on a conveyor doing the same thing. The rear wheels are on normal ground. Would the top speed be effected in any substantial way? No. It's the same thing. The mechanism that drives the plane forward (the jets pushing the air is what makes it move) aren't being effected by the conveyor any more than the trikes rear wheels.

[bigredhead]

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

scroll half way down !!! lol....

ding ding ding..

[slothminx]

LOl billy managed to convert me last nigth but the i re read the question and it doesnt say they are directly link as in one moves and the other does, that says that one need to move for the othera and visa versa so the plane is lock by the riddle not to move....... but there is nothing like that there billy! She flies plain and simple, read the page ;)

[Billy Golightly]

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor).

Merriam Webster defines sitting as "10 : to remain inactive or quiescent <the car sits in the garage>"

Ladies and Gentlemen, the plane will not fly. And it will not fly because it cannot travel any amount of forward distance in relation to the earth. This is because of a thing called friction. Let me elaborate and provide a few more hypothetical situations and theories:

Lets say there is a runway like conveyor belt turning 90mph, its the same length of a normal runway whatever that might be (I'm not a pilot so I dont know). Now, lets say that we sat a plane in exactly the middle of the conveyor and did not turn on the jet engines. What happens? Do the "free turning" wheels keep it stationary while the wheels just turn to make up the speed of the conveyor, or does it travel down the conveyor at a speed relative to that which the conveyor belt is turning? The wheels on the airplane are not frictionless. When the plane is sitting still with the engines off and the conveyor belt begins to turn, the whole entire plane is moved down the conveyor belt, without the wheels turning, or at the very most turning but at a much slower speed then the belt. The friction in the wheels, and the bearings transfers to the overal object, the airplane because that energy has to go somewheres.

In a perfect world, the wheels and the bearings would be totally frictionless, and when the plane is set on the conveyor it would maintain its place in relation to the world WITHOUT having to use any engine thrust, the wheels would just turn below it. But they dont, and the plane doesnt stay stationary in relation to the world, it moves on the conveyor belt backwards.

Back to the scenario with friction now, the only way the plane can maintain its posistion static to the rest of the world on the conveyor belt is if some form of something that is off the conveyor belt on static ground is holding it, whether it be a large cable or some sort of clamping device to hold the plane on the belt. Because of the friction in the wheels and bearings, the faster the belt turns the more weight and force there is exerted onto the object holding it because the faster it turns the more friction there is generated.

So now, lets remove the object holding the plane. Lets acclerate the conveyor belt to 15mph. The plane, since it does not have frictionless bearings sits ontop of the belt and travels backwards down the length of the conveyor at a speed of 15mph. The jet engines then come on, and come to a speed that would normally be 10mph on solid ground. The plane, then starts to slow down its backwards travel because it has nearly matched the speed the conveyor is traveling, its still going backwards a little bit though because the speeds are not matched. OK so now the plane is going 10mph, and the conveyor belt 15mph. Lets change the speed of the conveyor belt to 5mph. As the conveyor slows down, the plane slowly stops moving backwards, and begins to slowly move forward on the conveyor belt because the 2 are traveling 2 different speeds. The friction from the speed of the conveyor is transfering from the wheels into the airplane and still putting a backwards momentum onto it, but the plane is over powering it with its engines allow it to travel an amount of DISTANCE forward. If your not traveling any distance forward, then there is no airspeed. UNLESS, there is a very large head wind but we are not talking about that.

Lets take another application. For those of you from the south you should be familiar with airboats. Lets take an airboat and put it in a river. With the engine off, and a strong down river current, the boat floats down the river. Lets crank up the airboat motor, and point the the boat down stream. You give it some throttle and it accelerates on down the river. But, lets turn it around and make it travel UP the current, and you'll find that it requires a little bit more throttle then before to go up the river. This is because the friction between the down river current in the water, and the bottom of the boat is constantly trying to push it the direction the river is going, which happens to be the opposite way. Guess what? The more current there is, the faster the water moves, the more friction there is on the bottom of the boat pushing against it and the more throttle you have to use to keep the boat in a static posistion, and even more to make it travel up river.


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

I demonstrated earlier, that if the plane is sitting still and the conveyor is moving backwards the plane will move across the face of the earth at the same rate the conveyor belt is turning until it reachs the end and falls off. I also explained how if the belt isn't turning, and the plane IS moving the plane will traverse down the length of the belt and take off, because of a lack of friction in the wheels. There is of course still friction, but not as much. But lets turn the conveyor belt on at 50mph now, and set the plane right in the middle of the length of the conveyor and make it accelerate to what would normally be 40mph on solid ground. Its still moving backwards slowly, now at this point on lets imagine the conveyor belt moves 10mph faster then the plane at all times, the plane will still travel backwards down the conveyor belt because it is going slower then the belt. When the speed of the airplane is increased to match that of the conveyor at 15mph, it ceases moving any amount of forward distance in relation to the world. The riddle states the conveyor matches the speed of the airplane exactly, but in the opposite direction. To me, this means that no matter how the plane accelerates and attempts to move whether its via jet engines, wheel driven power, or wind pushed from behind it, the conveyor belt is going to increase its speed (AND FRICTION) backwards onto the plane nullifying any movement it would have had.

Now, I know the first thing you guys are going to do is quote the riddle and say "The plane moves". It also says, like I quoted at the top, that the plane sits on the conveyor, and that the conveyor turns the opposite direction. We can make a couple different things out of those statements. One, is that the plane WAS sitting still on the conveyor and then it accelerated onto the conveyor belt at a different speed, which WOULD allow it to gain lift and move. The only problem with this is, that the riddle also states the conveyor matches the speed of the plane which pretty much cancels out the previous theory. I believe the wording of the riddle is a little bit flawed and that creates most of the conflict over the entire question. The riddle more or less locks itself out of giving an answer either way because of the way its worded. "The plane moves" statement is disputable. I personally believe that its refering to the fact that the plane is keeping pace with the conveyor, as "move" is defined by Merriam "to keep pace". Thats how I read the question, and as such I believe that the plane does not move any amount of forward direction on the conveyor belt or in relation to the world and that it is not able to create any windspeed, and acheive lift.

[Dammit!]

I didn't read all that. :p

Unless something is physically holding the plane in place, it will move forward and fly. What the surface under the wheels is doing is irrelevant.

[Billy Golightly]

Read it, there is something holding it and pushing it backwards, its the friction.

[slothminx]

Lets take another application. For those of you from the south you should be familiar with airboats. Lets take an airboat and put it in a river. With the engine off, and a strong down river current, the boat floats down the river. Lets crank up the airboat motor, and point the the boat down stream. You give it some throttle and it accelerates on down the river. But, lets turn it around and make it travel UP the current, and you'll find that it requires a little bit more throttle then before to go up the river. This is because the friction between the down river current in the water, and the bottom of the boat is constantly trying to push it the direction the river is going, which happens to be the opposite way. Guess what? The more current there is, the faster the water moves, the more friction there is on the bottom of the boat pushing against it and the more throttle you have to use to keep the boat in a static posistion, and even more to make it travel up river.





Billy, your analogy there proves that the pane will be able to move forward and have some air speed.

Yes there is friction on the airboat the same as the plane, yes if you have the engine off the plane will travel with the conveyor and the boat with the river, but fire the engine up and you do need more power to get it moving and keep it the same as the river/conveyor. But the plane has WAY more than enough power to overcome this.

The plane will accelerate from 0-100 in like 10 seconds, it has a HUGE amount of thrust.

The bearings at any speed are never going to be able to stop it. Im will to put a large sum of money on the fact that if you locked the wheels dead on a normal tarmac runway you could throttle the engines and it would move along and probably have enough power to go quite quickly. The point of this is billy that the plane overcomes the friction no problem and then proceed to move forard "across the earth" thus in still air would have a wind speed, eventually although slower taking off.

[Dammit!]

Four jet engines have plenty enough power to overcome what friction those wheels would create. A jet only needs to get up to I think 180mph to take off. The speed the wheels would have to be turning to actually be able to prevent four jumbo jet engines from pushing the plane up to 180mph would have to be a lot greater than 360mph.

[Billy Golightly]

If the surface the plane is running on is standing still, and the friction is not CONSTANTLY INCREASING then yes it would have enough power to overcome it (planes take off and fly all the time from a normal runway) but when you make the amount of friction infinetly variable, especially increasable, it changes things a bit. The friction is increased to the point that the plane and the conveyor (NOT the conveyor belt) do not move. Only the wheels on the plane turning move, and the conveyor belt. And they are moving in a pre-determined spot that does not change.

[Dammit!]

The speed of the conveyor only increases relative to the speed of the plane. Not the level of thrust. This would put the wheels at a top speed of about 360mph.

[slothminx]

If the surface the plane is running on is standing still, and the friction is not CONSTANTLY INCREASING then yes it would have enough power to overcome it (planes take off and fly all the time from a normal runway) but when you make the amount of friction infinetly variable, especially increasable, it changes things a bit. The friction is increased to the point that the plane and the conveyor (NOT the conveyor belt) do not move. Only the wheels on the plane turning move, and the conveyor belt. And they are moving in a pre-determined spot that does not change.

The wheels are never going to have enough friction to stop the plane reaching 180mph. You could have the brakes on full and it would either just overpower the brakes or pushed the locked wheels

A plane lands at about 250 i think maybe more? so billy you are saying that by that it should have enough drag to slow the plane. Not a chance without the reverse thrust and brakes it would roll for ages!.

[Billy Golightly]

The jet engines creating the thrust are hooked onto the airplane, attempting to push it (The entire thing), so I think the conveyor does change. Its constantly changing and perfectly matching the speed, and adding the friction required to keep it from moving.

[Billy Golightly]

The wheels are never going to have enough friction to stop the plane reaching 180mph. You could have the brakes on full and it would either just overpower the brakes or pushed the locked wheels

A plane lands at about 250 i think maybe more? so billy you are saying that by that it should have enough drag to slow the plane. Not a chance without the reverse thrust and brakes it would roll for ages!.


If the plane was landing, and the conveyor was moving towards the plane at a simlar rate of speed yes it would slow it down quicker then normal. Its kind of the same theory has a tailhook on the aircraft carriers.

[Dammit!]

The jet engines creating the thrust are hooked onto the airplane, attempting to push it (The entire thing), so I think the conveyor does change. Its constantly changing and perfectly matching the speed, and adding the friction required to keep it from moving.

Now you're assuming things that are not in the question. It states the conveyor moves in relation to the speed the plane moves. Not relative to the thrust it's producing.

[Billy Golightly]

But...the engines (that are creating the thrust) are one with the airplane right? :(

[slothminx]

Billy, it matches the speed of the plane exactly. This would mean that 40 mph AIRSPEED if the planes had an ATC style speedo attached to the wheel it would read at 80mph. at that speed the rolling resistance would be nothing for the engines to overpower. Up that to say 180 the speedo shows 360 as thats the apparent road speed. the rolling resistance at this speed would be more agreed but the plane would overpower it. Your chainging your mind billy, one minit saying i matches plane speed then sayin i matches it so theres enough friction to stop it

Yep solid connected. You have to remember that the wheels only have rolling resistnace with your friction thing and its nothing.

[Dammit!]

But...the engines (that are creating the thrust) are one with the airplane right? :(

Yes but nowhere in the question is it mentioned that the conveyor is doing anything but moving in the opposite direction of the planes speed. It says nothing about it's power. The way it's worded actually insinuates forward motion.

[atctim]

Think of it this way. Some planes have landing gear made specifically to land on water, be it a river or a lake. I'm sure you have all seen these types of planes. So in theory, if a plane equipped with these boat type landing gear is in a river facing upstream and the water current is 180MPH downstream, than the plane would just sit there (if max thrust speed is 180MPH)????? no - it's not the friction or force holding in place (which they do a little), but rather the thrust force. If that thrust is greater than the friction, it's gonna fly. Does this make any sense????

[atctim]

I have just changed my position, I now agree with billy. The original statement says this:

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

I must assume from this statement, that regardless of the plane being propelled by tire power, or thrust, that conveyor won't let the plane move. It's tracking the speed of the plane, not the speed of the wheels. The plane would remain motionless, thus grounded.

Example of what I mean. you and you friend are sitting in the bed of a moving pickup truck. One facing forward at the back and one facing backward at the fron of the bed. The truck is sitting perfectly level while cruising at 60MPH. You are rolling a golfball back and forth to each other. Does the guy in the back need to push the golf ball 65MPH to have it reach the guy in the fron of the bed at 5mph???? No. The ball has it's own relationship to the truck bed, not the ground.

Once again, the brain teaser states that the conveyor matches the planes speed, not the planes wheel speed

[OldSchoolin86]

Does the guy in the back need to push the golf ball 65MPH to have it reach the guy in the fron of the bed at 5mph???? No. The ball has it's own relationship to the truck bed, not the ground.You may only have to push the ball 5mph on a platform moving at 60mph but that ball is still moving 65mph. The question never mentions that the speed is relative to the conveyor. It just says the conveyor will match the speed ot hte plane.

[atctim]

You may only have to push the ball 5mph on a platform moving at 60mph but that ball is still moving 65mph. The question never mentions that the speed is relative to the conveyor. It just says the conveyor will match the speed ot hte plane.

but the plane is relative to the conveyor.


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

[OldSchoolin86]

but the plane is relative to the conveyor.
Only the speed of the plane is relative, not the planes thrust, the plane moves and the coveyor speeds up. There is nothing holding the plane back, no anchor, no resistance. The wheels can spin as fast as they want on that conveyor, it's still going to push air and move forward.

[slothminx]

Ok, ill go again.


Plane is on a conveyor and speeds up to 2 mph airspeed. the engine is driving the plane over the friction and the force of pushing the plane in gereral. You give the plane more throttle and it speeds up, so does the conveyor but the friction of the wheels turning faster is a TINY amount compared to the force the plane is moving. What im saying is the friction is irelavent. there is never going to be enough to stop the plane moving.

[chris200x]

Ok my eyes and my head hurt after reading through all of this. :rolleyes:

Lets just say the plane takes off and crashes immeditiatly after take off :banned:

[Billy Golightly]

I think you guys are downplaying the friction to much. Dont you agree that the plane DOES NOT sit in place, and the wheels "free roll" under it when its not under power and the conveyor belt is? Why does the plane ride the conveyor when the motors are not producing thrust?

[nouseforaname90]

Oy. Guys. The plane definately takes off. Read the link on the 3rd page that bigredhead found. It says everything that I've been trying to say all along.
The wheels do not propel the aircraft, the engines do. If the wheels propelled it, then no it wouldn't move, but the engines are what propel it and it will move. The friction on the wheels will not be great enough to hold an aircraft back. Just read the link bigredhead gave.

[bigredhead]

another way to explain it.

The conveyer belt won't budge until the plane starts to move....

So.. you aply power to the motor.. and the plane starts to thrust itself forward.. 1 .. 2.. 4. mph...and as it " GOES FORWARD " the wheels turn.. sure.. but the conveyer belt only goes as fast as the motion of the FORWARD MOVING PLANE..

So once the plane goes forward fast enough to take off it takes off.. simple.

The belt is rolling , sure.. at the same speed as the plane and the wheels are FREE ROLLING backwards with the plane MOVING. Air rushing past the wings is what creates lift.. as long as the plane moves in relation to the ground around it.. regardless of the belt.. it will take off.:w00t:

[nouseforaname90]

another way to explain it.

The conveyer belt won't budge until the plane starts to move....

So.. you aply power to the motor.. and the plane starts to thrust itself forward.. 1 .. 2.. 4. mph...and as it " GOES FORWARD " the wheels turn.. sure.. but the conveyer belt only goes as fast as the motion of the FORWARD MOVING PLANE..

So once the plane goes forward fast enough to take off it takes off.. simple.

The belt is rolling , sure.. at the same speed as the plane and the wheels are FREE ROLLING backwards with the plane MOVING. Air rushing past the wings is what creates lift.. as long as the plane moves in relation to the ground around it.. regardless of the belt.. it will take off.:w00t:


One thing wrong with that. The wheels would still move in the direction they usually do.. not backwards.

[bigredhead]

ooops.. yes correct.

But at twice the speed of the forward motion of the plane !! and it still takes off !

[Billy Golightly]

http://forum.physorg.com/index.php?showtopic=2417&st=1155&#entry42611

That is an excellent explanation on a physics forum that pretty much described my thoughts


The thing is if the speed of the plane and the conveyor belt are always matched, the plane ISN"T moving across the face of the earth. Its staying in a static posistion. No matter how much the plane accelerates with thrust or any other type of forward force the conveyor belt is going to match it going the opposite direction therefor cancelling it out and not allowing it to move in across anything in relation to something on the world that isn't moving, like a tree.

[Billy Golightly]

Heres another one, what if we replace the plane with a free rolling jet car that is commonly found at drag races? The conveyor belt still moves in the opposite direction of the car and always matches its acceleration exactly. Does the jet car move down the conveyor (NOT THE CONVEYOR BELT) any, or move any amount of distance closer to a tree that is a 100ft from the end of the conveyor in the direction that the car is attempting to travel?

[slothminx]

Billy, seriously i asked physics teachers at school this and many other people and its flies. IT MOVES FORWARDS! lol, the friction from the belt to teh wheels is f*** all comapared to the 60000 lbs of thrust EACH of those engines put out. you work that billy. for it not to move its like aiming it virtically with 240,000lbs on the nose to stop it moving :crazy: a bit of bearing resistance isnt gonna stop it moving in relation to the earth. Those guys tested it! in the link. From Z owner to Z owner you have to take my word here :lol:

And anyway if the plane was stopped moving by the conveyor the conveyor would stop and the plane would go. Drop the i know im right for a minit and sit down and think it over

[Billy Golightly]

I've already said that the normal friction will not stop the plane from moving forward several posts back. What I also said, is that when the speed of the conveyor increases expotentionally (We're talking into the 100,000's here) the force generated by the friction would be enough to hold the plane back.

Why hasnt anyone said anything about my airboat analogy? How come the faster the river flows the more throttle you have to give it to go up it?

[Lomax]

this is lomaxes brother the plane will take take off because it is not driven by the wheels it has jet engines no matter what direction the wheels turn the plane will go forward if you put legs on a plane the jets will still push it foward. the conveyor is the trick in the ? the only way to stop it from taking off is to not turn on the engines.

[OldSchoolin86]

I've already said that the normal friction will not stop the plane from moving forward several posts back. What I also said, is that when the speed of the conveyor increases expotentionally (We're talking into the 100,000's here) the force generated by the friction would be enough to hold the plane back.

Why hasnt anyone said anything about my airboat analogy? How come the faster the river flows the more throttle you have to give it to go up it?
I haven't read your airboat analogy but an air boat has a huge amount more of friction to overcome then something on wheels. Get moving on an airboat and kill all the drive. Then go get a car moving and stick it in nuetral. You'll coast a lot further in the car because you have a lot less drag. You're compairing apples to oranges here.

You say as the conveyor increases expotentionally (We're talking into the 100,000's here). If you're talking mph, a 747 doesn't move that fast and even if it did it would be long gone. The friction just won't be enough to hold it back. The wheels will never move anthing but exactly twice the speed of the jet.

[slothminx]

Billy, your analogy there proves that the pane will be able to move forward and have some air speed.

Yes there is friction on the airboat the same as the plane, yes if you have the engine off the plane will travel with the conveyor and the boat with the river, but fire the engine up and you do need more power to get it moving and keep it the same as the river/conveyor. But the plane has WAY more than enough power to overcome this.

The plane will accelerate from 0-100 in like 10 seconds, it has a HUGE amount of thrust.

The bearings at any speed are never going to be able to stop it. Im will to put a large sum of money on the fact that if you locked the wheels dead on a normal tarmac runway you could throttle the engines and it would move along and probably have enough power to go quite quickly. The point of this is billy that the plane overcomes the friction no problem and then proceed to move forard "across the earth" thus in still air would have a wind speed, eventually although slower taking off.


I've already said that the normal friction will not stop the plane from moving forward several posts back. What I also said, is that when the speed of the conveyor increases expotentionally (We're talking into the 100,000's here) the force generated by the friction would be enough to hold the plane back.

Why hasnt anyone said anything about my airboat analogy? How come the faster the river flows the more throttle you have to give it to go up it?

the point is billy even if there is friction it will have enough power to carry on forwards. Ohh and if the plane isnt moving in relation to the earth then the belt isnt moving either ;)

[OldSchoolin86]

Lets say there is a runway like conveyor belt turning 90mph, its the same length of a normal runway whatever that might be (I'm not a pilot so I dont know). Now, lets say that we sat a plane in exactly the middle of the conveyor and did not turn on the jet engines. What happens? Do the "free turning" wheels keep it stationary while the wheels just turn to make up the speed of the conveyor, or does it travel down the conveyor at a speed relative to that which the conveyor belt is turning? The wheels on the airplane are not frictionless. When the plane is sitting still with the engines off and the conveyor belt begins to turn, the whole entire plane is moved down the conveyor belt, without the wheels turning, or at the very most turning but at a much slower speed then the belt. The friction in the wheels, and the bearings transfers to the overal object, the airplane because that energy has to go somewheres.

In a perfect world, the wheels and the bearings would be totally frictionless, and when the plane is set on the conveyor it would maintain its place in relation to the world WITHOUT having to use any engine thrust, the wheels would just turn below it. But they dont, and the plane doesnt stay stationary in relation to the world, it moves on the conveyor belt backwards.

Back to the scenario with friction now, the only way the plane can maintain its posistion static to the rest of the world on the conveyor belt is if some form of something that is off the conveyor belt on static ground is holding it, whether it be a large cable or some sort of clamping device to hold the plane on the belt. Because of the friction in the wheels and bearings, the faster the belt turns the more weight and force there is exerted onto the object holding it because the faster it turns the more friction there is generated.

So now, lets remove the object holding the plane. Lets acclerate the conveyor belt to 15mph. The plane, since it does not have frictionless bearings sits ontop of the belt and travels backwards down the length of the conveyor at a speed of 15mph. The jet engines then come on, and come to a speed that would normally be 10mph on solid ground. The plane, then starts to slow down its backwards travel because it has nearly matched the speed the conveyor is traveling, its still going backwards a little bit though because the speeds are not matched. OK so now the plane is going 10mph, and the conveyor belt 15mph. Lets change the speed of the conveyor belt to 5mph. As the conveyor slows down, the plane slowly stops moving backwards, and begins to slowly move forward on the conveyor belt because the 2 are traveling 2 different speeds. The friction from the speed of the conveyor is transfering from the wheels into the airplane and still putting a backwards momentum onto it, but the plane is over powering it with its engines allow it to travel an amount of DISTANCE forward. If your not traveling any distance forward, then there is no airspeed. UNLESS, there is a very large head wind but we are not talking about that.
This is what you're not getting. If a plane is moving at 10mph one way and the belt is moving 15mph the other, the plane is not still going 5mph backwards. This idea only works on something that drives via it's wheels. In this senario the plane would be moving 25mph faster then the belt but still just moving 10mph.

[bigredhead]

BUT.

The conveyer is not attached to the plane itself.. only the wheels.
The wheels do not power the forward movement only the wing's engines.

Remember.. the conditions of this assume there is no wind.. the belt does not create wind resistance.

[tecatecrazy]

i got tired of reading posts so i thought that Id add my own. the plane will definately fly. the plane pushes on air to move itself not the ground therefore the conveyor will have no effect on the jet unless its moving in the same direction, which will just shorten its take off time.

Joe

[Billy Golightly]

A 747 weighs a WHOLE lot more then a normal car or truck and as such is going to have more resistance. Its gonna have even more then the airboat. After a little bit of Googling I've found that depending on the exact model and the cargo a 747 can weigh from 160 to 190 tons, thats nearly 400,000lbs. Thats a whole whole lot of rolling resistance to over come especially when its on a surface thats always pushing it in the opposite direction its trying to go.


This is what you're not getting. If a plane is moving at 10mph one way and the belt is moving 15mph the other, the plane is not still going 5mph backwards. This idea only works on something that drives via it's wheels. In this senario the plane would be moving 25mph faster then the belt but still just moving 10mph.

Explain to me the difference between how the plane is powered from the wheels or the jets? I've read the explanation that it "Doesn't matter because the plane is powered by the airspeed" a 100 times now. The problem is that in order for the jet engine to create thrust (power) it has to have air force inducted into it, which is hard to do when the plane is being pushed backwards by a conveyor belt. If I put wheels under an airboat and put it on a conveyor belt that had a constalty changing rotation speed it wouldn't move either. Just like the 747. THE ONLY WAY its going to accelerate past the conveyor belt and get lift is if its moving at a different speed from the belt and the riddle prevents this from happening.


I'm gonna have to make a giant conveyor belt and put an airboat on it to prove my point arent I? :lol:

[OldSchoolin86]

A 747 weighs a WHOLE lot more then a normal car or truck and as such is going to have more resistance. Its gonna have even more then the airboat. After a little bit of Googling I've found that depending on the exact model and the cargo a 747 can weigh from 160 to 190 tons, thats nearly 400,000lbs. Thats a whole whole lot of rolling resistance to over come especially when its on a surface thats always pushing it in the opposite direction its trying to go.Again over thinking. Simplify and just think of it as a friction to weight ratio.



Explain to me the difference between how the plane is powered from the wheels or the jets? I've read the explanation that it "Doesn't matter because the plane is powered by the airspeed" a 100 times now. The problem is that in order for the jet engine to create thrust (power) it has to have air force inducted into it, which is hard to do when the plane is being pushed backwards by a conveyor belt. If I put wheels under an airboat and put it on a conveyor belt that had a constalty changing rotation speed it wouldn't move either. Just like the 747. THE ONLY WAY its going to accelerate past the conveyor belt and get lift is if its moving at a different speed from the belt and the riddle prevents this from happening.
That's the part you're supposed to realize, the belt won't push the jet back while it's taking off. That's the trick of the riddle. Your mind thinks of a conveyor and how we relate to it most. But then you're supposed to figure out that the jet just uses it's wheels to roll on. Once you realize that then you should pick up on that the only thing abnormal here is that the jet's wheels will be freewheeling at twice thier normal speed. Again, the jet pushes off air, not the ground.


I'm gonna have to make a giant conveyor belt and put an airboat on it to prove my point arent I? :lol:
I would advice against this, it's not going to help your case.;)

[slothminx]

Explain to me the difference between how the plane is powered from the wheels or the jets? I've read the explanation that it "Doesn't matter because the plane is powered by the airspeed" a 100 times now. The problem is that in order for the jet engine to create thrust (power) it has to have air force inducted into it, which is hard to do when the plane is being pushed backwards by a conveyor belt. If I put wheels under an airboat and put it on a conveyor belt that had a constalty changing rotation speed it wouldn't move either. Just like the 747. THE ONLY WAY its going to accelerate past the conveyor belt and get lift is if its moving at a different speed from the belt and the riddle prevents this from happening.


I'm gonna have to make a giant conveyor belt and put an airboat on it to prove my point arent I? :lol:


Illl explain the wheels for you billster:D, think of a person on a tread mill ok. the legs are the wheels and are what drives it. so when the treadmill speeds up the legs have to go exactly the same speed in the opposite direction to im the go in one place. The drive is being transfered to the ground that is moving. Now think of a model plane on the treadmill. the TM(treadmill) starts up and the guy on the plane has to give a little throttle just to hold it there while the mill spins up thats the small amount of friction. But because the drive is air being pushed by the prop in the opposite direction(same as the TM) the plane stands still at the moment but is using a small amount of throttle. The guy on the plane cranks the throttle and the mill speeds but because the force being exerted to drive the plane is greater than the friction from the TM it starts to move forwards, the TM speeds up but beccause the plane has throttle and is moving the wheels just speed up more and the plane carrys on unaffected. You have your car on the mill, the TM is doing 10mph and so are your wheels, your still yes? if you increase your car wheel speed to 15 and the mill stays there the cars is now doing 5 MPH. With the plane tho the engines are not driving onto the moving surface they are sucking the stationary air into the engine and out the back faster, every movemnt has an equal and opposite force, so that push backwards is now trying to push the plane forwards, the cnveyor can now start and the plane will stay stationary as the engines are holding it there. The start up friction is the largest. the plane jacks up the heat a bit and starts to move forward but the belt goes the other way, all that happens now the kinetic energy is in the plane is that the wheels spin faster and theres a small amount more friction in speeding the wheels up but because the engines and pushing air it continues to move forward fatsre and faster and then takes off! because it it moving forward in relation to the rest of the runway thats not conveyor.

If you have points you want to ask about do them as individual questions, its way way easier to answer then :D

[Dammit!]

I seriously thought my trike analogy would have ended this thread when I went to work today. :lol: :lol: :lol: :lol: :lol: :lol:

[Jason Hall]

What about GRAVITY!!! Not only are you overcoming FRICTION!!! How in the world can a jet engine create enough thrust to over come the weight of the plane. I would guess that the plane would weigh alot. If the thrust was aiming straight toward the ground then maybe it would stand a chance. If the plane is not traveling through the air, it will not lift off. The wheels turning has nothing to do with the wings. If the engines pushing the plane forward, then the conveyer would have to be as long as a runway. If a plane could lift off without moving through the air, then there would be no air ports. Don't you think the real estate in N.Y City would be worth more money than the cost of a conveyer? I will never believe that a conveyer could make a plane defi gravity. An air plane wing is desighned to cut through the air & creat lift. The air would not move fast enough over the wing to overcome the gravitational pull of the plane. They call & air plane an air plane for a reason & that reason is air, and lift created by the air, not the wheel speed or ground movment. The ground movment is not the same as air movment. If you had a wind tunnel blowing enough air over the wings, then you might have enough air passing over the wings to create enough lift to overcome gravity.

[Oldshell4481]

The wings need the aerodynamics of forward DISTANCE traveled to give the plane lift. I think if the plane is moving 900mph, as long as its not traveled any amount of distance from where it started, it aint going anywheres. This is not taking into effect the possible wind turbulence generated from a conveyor belt turning 900mph. I mean, common now guys. This is the same basic principle as putting a car or truck in a mud hole and stomping on the throttle and making the wheels turn 90mph while the tires sling the surface area under it in the opposite direction the vehicle is traveling (behind it). Does the car or truck go anywheres? Heck no it dont as long as the surface its on is going the opposite direction. And If you put wings on it I dont think its going anywheres either.
100% correct, jets dont propel it to give it forward motion so that the aerdoynamics give the plane lift. by saying it just needs the jets to move than why are wings put on jets hmmmmmmmm?

[OldSchoolin86]

If the plane is not traveling through the air, it will not lift off. The wheels turning has nothing to do with the wings. If the engines pushing the plane forward, then the conveyer would have to be as long as a runway.
The plane is moving, that's why it lifts. The whole runway is a conveyor. All the conveyor will do is spin the tires, the plane will go forwad and take off as normal.


100% correct, jets dont propel it to give it forward motion so that the aerdoynamics give the plane lift. by saying it just needs the jets to move than why are wings put on jets hmmmmmmmm?The plane isn't stuck in one spot, that's the trick of the question. There's no anchor and no resitance to keep it back. It goes down the runway, uses those wings and lifts off the ground as normal. All the conveyor does is spin the tires. Since a plane doesn't use it's tires to push forward there is no problem.

[Lomax]

I was agreeing with Billy on the situation after i thought about it, now im so damn confused :rolleyes: . Hell with that plane.........

[CorbinKale]

I've already said that the normal friction will not stop the plane from moving forward several posts back. What I also said, is that when the speed of the conveyor increases expotentionally (We're talking into the 100,000's here) the force generated by the friction would be enough to hold the plane back.

Why hasnt anyone said anything about my airboat analogy? How come the faster the river flows the more throttle you have to give it to go up it?

I don't see how we could be talking 100,000s. The fastest these planes can fly is less than 700 mph. You have stated several times 'in relationship to the earth', when referring to the conveyor belt. Planes don't fly in relationship to the earth, they fly in relation to the air passing over the wings, creating a vacuum above them to generate lift. If the plane has to reach a certain speed to take off, the conveyor will be going in the opposite direction up to the same speed, far less than 700 mph, and certainly not in the 100,000s. :) The wheels will be spinning at twice the speed as the airspeed of the plane, and wheel-to-conveyor friction is not an issue. The belt only goes as fast as the plane is going. If the wheels were the source of propultion, you would be correct, but in this case, they only serve to allow the plane and conveyor belt to travel in opposite directions.

When the plane reaches takeoff speed, the conveyor belt will be travelling at the same speed in the opposite direction, while the wheels act as the bearings, allowing these two forces to move in opposite directions.

As far as your airboat analogy goes, the plane is not rolling on a surface. It is actually sunken into the surface of its runway. Friction would be a definite factor here due to the amount of surface area contact. In that case the float plane would seem to remain stationary, but this would change as the plane gained speed and the water gained speed in the opposite direction. The moving water would begin to push the plane out of the water the same as a boat does as the speed increased, lessening the surface contact and friction, allowing more speed to be gained. Eventually, the float plane would fly, too, but it would take longer than in the first scenario with the conveyor belt.

[Oldshell4481]

the plane wont move along the conveyor because the conveyor moves as fast as the plane is trying to move, but in the opposite direction. it matches the speed and moves the opposite direction. the planes jets need to push the plane along the runway, which makes the wheels spin, now the jets can push as hard as they want they need the wheels to roll it on down the runway to give it lift, and if the wheels are spinning the same speed as the conveyor in the opposite direction the jets will just make the wheels spin and spin but it wont move. the jets push, the wheels spin making the plane move forward at a high rate of speed(to give the plane lift through aerodynamics), but the conveyor moves in the opposite direction of the wheels spin at the same rate of speed in which the plane is traveling, this cancels the movement of the plane out so it is going nowhere and hence wont get any lift no matter how hard the jets push the plane.
the jets can push the plane as hard as it wants, but to get any lift the plane needs to be moving at a high enough velocity for the air to lift the plane. without the jets pushing the plane ALONG THE GROUND fast enough for it to get lift its going no where.. the conveyor would be acting against the jets to move the plane in the opposite direction... you guys dont get it, its a canceling effect.

[freewheel3]

There is a debate raging on another board I visit here is the topic:

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?
Thrust makes the jet move forward.
Friction holds it where it is.
As the thrust increases, so does the friction from the wheels created by the conveyor moving in the opposite direction.
The conveyor will not be running at twice the air speed or anything like that, it will be running as fast as it needs to, to keep the jet where it is.
The control system will regulate the speed of the conveyor in relation to the thrust created by the jet. The conveyor speed (and wheel speed) would be phenominal to counteract the thrust.
Maybe repack the bearings & check the tires 'cause this baby isn't gonna fly but the wheels are sure gonna be spinning.:lol: .

[slothminx]

Im pulling my hair out and the close minded people who are replying. Lets say the friction force is like it haveing to drag 2000lb weight. Well those jets on takeoff throttle are producing 240,000 lbs of thrust! the conveyor is matching planes speed across the non conveyor ground anyway so even IF the conveyor was magically holding back 240,000lbs of thrust the conveyor would then stop again as it stopped the plane :rolleyes: the plane will move 100% as the drive is by pushing air not by pushing on the ground.

[Billy Golightly]

Well I'm done arguin but I still think I'm right and everyone that says it'll fly is wrong :D

[slothminx]

LOL billy i gotta agree im done arguing, if i ever meet you we will continue then! :lol:

Ohh and everyone who thinks it wont fly is wrong;)

[CorbinKale]

the plane wont move along the conveyor because the conveyor moves as fast as the plane is trying to move, but in the opposite direction. it matches the speed and moves the opposite direction. the planes jets need to push the plane along the runway, which makes the wheels spin, now the jets can push as hard as they want they need the wheels to roll it on down the runway to give it lift, and if the wheels are spinning the same speed as the conveyor in the opposite direction the jets will just make the wheels spin and spin but it wont move. the jets push, the wheels spin making the plane move forward at a high rate of speed(to give the plane lift through aerodynamics), but the conveyor moves in the opposite direction of the wheels spin at the same rate of speed in which the plane is traveling, this cancels the movement of the plane out so it is going nowhere and hence wont get any lift no matter how hard the jets push the plane.
the jets can push the plane as hard as it wants, but to get any lift the plane needs to be moving at a high enough velocity for the air to lift the plane. without the jets pushing the plane ALONG THE GROUND fast enough for it to get lift its going no where.. the conveyor would be acting against the jets to move the plane in the opposite direction... you guys dont get it, its a canceling effect.

This problem is so funny! I love watching the thought process of a diverse group. Read the problem again. The plane and conveyor will move at the same speed in opposite directions. No plane speed = no conveyor speed. Plane 5 mph = conveyor 5 mph, and you have a 10 mph relative speed difference. This continues until the plane reaches takeoff speed. If the plane never moved forward, the conveyor would be at rest, as well. For the conveyor belt to begin turning, the plane must be moving. You are imagining the plane at rest and the wheels spinning like crazy trying to cancel out the conveyor speed.

If the wheels were the source of propulsion, you would be correct, and the wheels and conveyor would cancel each other out, keeping any forward movement to nil. With the plane, the source of propulsion is insulated from the conveyor belt by the wheels, which can spin freely when force is applied. The problem does not state that the belt will spin at a speed required to keep the plane in place, but instead, it says it will travel at the same speed in the opposite direction. The plane will gain speed, as will the conveyor belt, but the plane will have no difficulty in flying.

[Blown 331]

Ohh and everyone who thinks it wont fly is wrong;)

This is my first reply to this thread but I don't think it would fly. Correct me if I'm wrong but I believe air flow over the shape of the wing causes low pressure above the wing and causes the plan to lift. In this senerio the plane is technically not moving (in relation to earth and atmosphere). No movement = no air flow over the wing = no low pressure above the wing = no lift.

[Dammit!]

I give up too. :lol: :welcome:

[Blown 331]

The plane isn't stuck in one spot, that's the trick of the question. There's no anchor and no resitance to keep it back. It goes down the runway, uses those wings and lifts off the ground as normal. All the conveyor does is spin the tires. Since a plane doesn't use it's tires to push forward there is no problem.

I put in my .02 then came back and read everyone elses response. This does make sense but I still can't see how the plane would move in relationship to the ground. Just to look at some numbers lets say the conveyor is moving 100mph one direction and the plane is moving 100 mph in the other. Lets stop the planes forward thrust. Now what? Does the plane just sit there and not move (in relation the the ground?) No it move 100mph with the conveyor. Yeah I give up, I don't think what I said made sense. lol

[CorbinKale]

This is my first reply to this thread but I don't think it would fly. Correct me if I'm wrong but I believe air flow over the shape of the wing causes low pressure above the wing and causes the plan to lift. In this senerio the plane is technically not moving (in relation to earth and atmosphere). No movement = no air flow over the wing = no low pressure above the wing = no lift.

Why would the conveyor belt be moving while the plane is standing still? The belt will only move as fast as the plane is going. The plane will fly.

[Blown 331]

Why would the conveyor belt be moving while the plane is standing still? The belt will only move as fast as the plane is going. The plane will fly.


OK I got it now, makes total sense. By as fast as the plane is going you mean as fast as it is going in relation to the earth not as fast as the tires are spinning. I got it. It will most definitely take off.

Just the way it's worded makes is sound like the belt keeps the plane from moving in relation to the ground but that is not the case.

[Blown 331]

My next question is why would a runway be made of a conveyor belt? lol.

[CorbinKale]

I put in my .02 then came back and read everyone elses response. This does make sense but I still can't see how the plane would move in relationship to the ground. Just to look at some numbers lets say the conveyor is moving 100mph one direction and the plane is moving 100 mph in the other. Lets stop the planes forward thrust. Now what? Does the plane just sit there and not move (in relation the the ground?) No it move 100mph with the conveyor. Yeah I give up, I don't think what I said made sense. lol

If the takeoff speed was 90 mph, then the plane would be flying already and no longer in contact with the conveyor. :) For the belt to be moving 100 mph in one direction, it requires the plane to be moving 100 mph in the opposite direction. There will be a 200 mph relative speed difference between them, but assuming that the conveyor belt is attached to the earth and the winds are calm, the airspeed over the wings will be 100 mph.

[MyMistress86R]

Wow

Right now, I'd just love to throw another, as of yet undiscussed, concept into the mix for this arguement, but I don't think the board would survive...lol.

It's been quite a ride so far though...

[Jason Hall]

Well I finally got it (duh). The planes wheels act like an idler wheel. They are just a spinning link between the ground & the plane. The plane moves forward according to the earth, because of the thrust from the engines. If you think about it with the conveyor turning the opposite way of the plane, the wheels are turning twice the speed of the planes movement to earth. If the conveyor were turning forward, the wheels could be made to stop & the plane would still lift off. The planes body is being pushed by the engines thrust, while the wheel bearings get spun blistering fast. The engine will easily spin the wheels, if they will push a 160,000 pound plane.:lol: :lol: :lol: :crazy:

[Lomax]

Well I finally got it (duh). The planes wheels act like an idler wheel. They are just a spinning link between the ground & the plane. The plane moves forward according to the earth, because of the thrust from the engines. If you think about it with the conveyor turning the opposite way of the plane, the wheels are turning twice the speed of the planes movement to earth. If the conveyor were turning forward, the wheels could be made to stop & the plane would still lift off. The planes body is being pushed by the engines thrust, while the wheel bearings get spun blistering fast. The engine will easily spin the wheels, if they will push a 160,000 pound plane.:lol: :lol: :lol: :crazy:

Exactly, also meaning that regardless of how fast the wheels or the conveyor are moving, the plane still lifts off. Thats the part of this that messes with everyone. It doesnt matter what the Conveyor and the wheels are doing because there affect will have no overall result on what the Jet engine is doing which is pushing air to lift off, not wheel/ground contact like a car needs to move.

[eh_tee_see]

I havent read many of the other posts. This is retarded. Imagine the plane is bolted into the ground which is essentially whats going on here. The engines are there to pull the plane forward not to blow air under the wings although they do do that to some degree. If the plane can not move forward then there is not enough air moving under the wings to lift the plane. Or just figure that the pilot is holding the brakes which by some crazy law of physics can hold the plane in place. By letting go of the brakes at peak RPM the plane would just go straight up. Same exact thing. No the plane won't fly. I want to imprison and sterilize anybody that beleives it will.

[nouseforaname90]

Wow man. You shouldn't have rekindled it. And you are wrong, too.. which makes it worse. We had all (mostly) just agreed that it would fly, and then you butt in.. read the rest of the posts and you'll understand.

[bigredhead]

*Gets in line for sterilization.

hey Ooldschoolin.. get the life jackets and bring the boat !!

lmfao..

[eh_tee_see]

Realize that air speed and ground speed are not related at all. If a plane is facing a 30 knot headwind but not moving anywhere on the ground its ground speed is zero but its airspeed is 30 knots. If a plane is traveling along the ground at 90 knots and it has a 90 knot tailwind its airspeed is zero and its groundspeed is 90. I have no idea what the take off speed for a 747 is so I'm going to use a Cessna 180. The "safe" take off speed of a Cessna 180 is no less than 75 knots. If the plane is moving along the ground on a converor belt at 75 knots its ground speed is obviously 75 knots yet its airspeed is zero. And now back to the 747 deal. If the plane for some reason did get off of the ground on the conveyor, its airspeed would have to jump from zero to probably 180 in tenths of a second or else it would not stay in the air. Nouseforaname90 you apparently have no use for a vas deferens either.------------- I'm just kidding on that one.

[kernalklink]

There is a debate raging on another board I visit here is the topic:

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?

now there is a debate raging on this forum! :crazy:

this is simple really, a plane sitting on a conveyor with the conveyor moving in opposite direction with relative speed control to the plane. The plane will not move at all, thus no lift will be created. you would hit the gas and nothing.

consider a dyno machine the wheels on the car spin very fast and the rollers do the same but the wind over the car does nothing. if the car wasn't strapped down it would zoom off of the machine, the speed control works like the straps on a dyno keeping the motor from pushing the wheels faster than the belt can turn!

assuming that it was a prop plane; it would only make wind behind the plane, not lift from reaction with the wind.

the plane simply would not take off!

Its only chance for take off would be to lose the speed control relation and hopefully you would have enough power and fuel to make it to a take off speed. The wheel bearings would also have to hold out at twice the speed, and then some, that they normally operate. Shouldn't be an issue but it is going to take a very long time to get up to speed with that kind of resistance.

what makes this confusing is that a machine of the calibur to move at the same speed as a jet is just a dream, and it is had to imagine it actually working because there would be alot of other factors to involve to be successful in creating such a device.

[Jason Hall]

If you look at it in this way, you will understand. The air is the air, the ground is the ground. They are two seprate things. An AIR plane will move through the air, with the force of the thrust coming out the back of the engines. That thrust is pushing the plane through the AIR. The wheels of the plane are along for a super spinning ride. The body moves very easily through the air & will easily overcome the slight drag of the bearings. The drag from the bearings would probly slow the plane slightly. Like instead of it taking off in 5,899' it would take off in 5,915 ':lol: :lol: