Will the plane fly?

[Billy Golightly]

Actually, the scenario depicted by TwoHundredEX is both correct and incorrect at the same time. The only way the conveyor will move in the opposite direction is if the wheels produce a rotational moment. This is assuming the conveyor is unpowered. Newton's Third Law of Motion: For every action, there is an equal and opposite reaction. The only appreciable force is applied to the airframe of the plane, which causes the plane to move forward. If the wheels provided a rotational moment, the belt would react by moving in the opposite direction. The wheels of an airplane are not driven by any force, therefore, they cannot deliver any rotational force to the surface below them. Rolling resistance is the only force seen between the wheel and ground. This rolling resistance, in a perfect scenario, would actually cause the belt to move in the same direction as the airplane, but at a slower rate due to the difference in friction between the belt and the conveyor and the airplane and the air. Confused yet?

Do this experiment if you can. Find a conveyor with rollers instead of a rubber belt. The rollers make it much easier to do this because you won't be able to produce enough force manually to overcome the friction of a rubber belt. Take a bicycle and roll it across the conveyor, increasing speed with distance traveled, without using the pedals. This simulates the force the engines inflict on the plane and its resultant acceleration. Remember, no force goes to the wheels. Guess what? The rollers will roll in the same direction as the bike, but at a slower rate. Amazing, huh?

Now what Billy is talking about actually would happen. If an airplane is on a conveyor belt that can accelerate fast enough to keep the airplane relatively still, the airplane will not take off, no matter how much throttle is applied. The thing to remember here is that the belt is powered by an outside source and is not driven by the airplane. Airplanes only take off when the relative wind across their wings is enough to produce a resultant lift greater than the weight of the airplane. If the airplane doesn't move fast enough relative to the air it is passing through, the wings will never produce the force necessary for flight. The wheels might be spinning at 100 knots, but if the wings are only moving 5 knots and the minimum takeoff speed (V1) is 75, the plane will not leave the ground.

Now are you confused?

Whoa, I didn't think anyone would agree with me! Haha. I wish I could remember the exact wording of the question, I think that has a lot to do with whether it can or not. It seems like it was worded sort of tricky, like it made you think one thing but was actually talking about another. Maybe I can remember to check out this episode of mythbusters coming up...

Oh yeah, I forgot about this: http://www.3wheelerworldforums.com/s...ad.php?t=44770

[Jason Hall]

Wow I fell for this once. Yes the plane will fly. The thrust from the engine pushes the plane forward. The wheeles have nothing to do with the forward motion of the plane. It really plays games with your mind, but It WILL fly. The only reason a plane needs wheels Is so It will have something to roll on, otherwise It would shoot sparks off the belly. It also needs the wheels to help It STOP, once It lands back on the ground.

[Dammit!]

There is now way for any conveyor belt to keep the plain relatively still. Plane engines (be them props or jets) push against the air. What the wheels are doing has no effect. None. Zero. Nadda. Especially when you look at the wording of the original riddle. I'll have to paraphrase since I don't remember it exactly but it asks "if the conveyor belt moves in the opposite direction of the plane" which insinuates the plane IS moving forward and that the conveyor belt matches this forward speed in the opposite direction. So if the plane is moving 250mph, the belt is going 500mph. This would have no effect on the plane reaching take off speed. Some people want to take it further than the original question goes and crank up the treadmill to be equal to the force of the engines. The question never says anything about doing that and even then the plane would still move forward because the engines push against the air and not the ground.

Now, I think where people get confused here is they think the plane will be sitting still with it's engines cranked and no air running across the wings to create lift. Like if the plane were chained to a stationary object and unable to move. In that case it wouldn't take off. The thrust of the engines pushes against the air and makes the plane move forward (nothing to do with the wheels spinning), the air running across the wings as a result of it's forward movement is what makes it take off.

[Jason Hall]

Here Is another way to look at It. How does a plane with pontoons lift off. It has thrust from the engines/prop moving the plane forward. It very easily over powers the drag of the pontoons In the water and creates lift and fly's away.

[Dammit!]

God I can't wait until Wednesday.

[Jason Hall]

Me neither . This will be funny

[The Goat]

it really all depends on how you look at it.

if the belt is doing 500...and the wheels are freespinning, the plane can take off.

if the belt is doing 500...but the wheels are not spinning, and the plane is doing 500 mph in reverse, the plane likely won't be able to take off.

if the belt is freerolling...the plane takes off.

if the belt doesn't move at all...the plant takes off.

if the second option is tried...it's likely a few people will die.

[Red Rider]

Actually, the scenario depicted by TwoHundredEX is both correct and incorrect at the same time. The only way the conveyor will move in the opposite direction is if the wheels produce a rotational moment. This is assuming the conveyor is unpowered. Newton's Third Law of Motion: For every action, there is an equal and opposite reaction. The only appreciable force is applied to the airframe of the plane, which causes the plane to move forward. If the wheels provided a rotational moment, the belt would react by moving in the opposite direction. The wheels of an airplane are not driven by any force, therefore, they cannot deliver any rotational force to the surface below them. Rolling resistance is the only force seen between the wheel and ground. This rolling resistance, in a perfect scenario, would actually cause the belt to move in the same direction as the airplane, but at a slower rate due to the difference in friction between the belt and the conveyor and the airplane and the air. Confused yet?

Do this experiment if you can. Find a conveyor with rollers instead of a rubber belt. The rollers make it much easier to do this because you won't be able to produce enough force manually to overcome the friction of a rubber belt. Take a bicycle and roll it across the conveyor, increasing speed with distance traveled, without using the pedals. This simulates the force the engines inflict on the plane and its resultant acceleration. Remember, no force goes to the wheels. Guess what? The rollers will roll in the same direction as the bike, but at a slower rate. Amazing, huh?

Now what Billy is talking about actually would happen. If an airplane is on a conveyor belt that can accelerate fast enough to keep the airplane relatively still, the airplane will not take off, no matter how much throttle is applied. The thing to remember here is that the belt is powered by an outside source and is not driven by the airplane. Airplanes only take off when the relative wind across their wings is enough to produce a resultant lift greater than the weight of the airplane. If the airplane doesn't move fast enough relative to the air it is passing through, the wings will never produce the force necessary for flight. The wheels might be spinning at 100 knots, but if the wings are only moving 5 knots and the minimum takeoff speed (V1) is 75, the plane will not leave the ground.

Without hearing the original scenario put forth by the Mythbusters, I don't know if it will fly or not, but everything that 69Hemi said above is correct. On takeoff, the wheels of an airplane only need to provide friction to keep it going straight down the runway until it has enough airflow that the control surfaces become effective.

[Jim mac]

you need air speed over and under the wings to get the plane to lift. the conveyer belt can be spinning 2000mph but the air above the belt is not moving. so you put a plane on the conveyor, power up the conveyor and plane, if the conveyor is going 200mph and the plane, jet or prop, powers up for the plane to move so its sitting stationary. there is no airflow over the wings. so no lift, no fly. If you hooked a speedometer to the wheels it would be showing you 200mph ground speed. but air speed will read 0. There is a guage that sticks out of the front of the plane, basically a tube that reads how fast the plane is moving through the air. Now if you get the plane to power up to 400mph ground speed. that would be 200mph air speed. then you would have a plane capable of flying. I work with a guy thats got a pilots liscense and tried to get a simplified explanation. jim

[Jason Hall]

The wheels could be spinning 9000 mph and the plane will still have lift because the thrust pushing air Is moving the plane, not the wheels. The wheels are like an Idler pully on the belt that turns your accesories on the front of you engine In your car. If you unhook the belt, the Idler just spinns, It has no drive at all. The only time the wheels of the plane do anything besides roll Is when the brakes are on. There Is no driveshaft that Is connected to the plane at all. How do the tires propell a plane when It Is In flight. They don't, the THRUST from the engines propell the plane with AIR. If you guys were right, then you would be able to stop a plane from going forward by holding a rope tied to the plane. Do you think you could over power the thrust of a plane with a rope tied to It?

[Billy Golightly]

If the ropes tensile strength increased at the same rate of the thrust.....

[Jason Hall]

Ok I'll try this one more time. Do we all agree that air/ thrust moves a plane? If air/thrust moves a plane then why would the ground have anything to do with forward motion? Forward motion will happen no matter what the conveyor Is doing under the plane, because the thrust from the engines Is pushing the plane. The wings will create lift. The plane will not just lift straight up, It will cover the same distance with or without the conveyor until the forward motion of the plane (because of Air/thrust) creates enough lift for the plane to lift off.

If the plane was tied to the ground with a cable behind the conveyor, It would not lift off. If the plane Is moving forward because of thrust then It all the sudden reached the end of the conveyor, the tires would Instantly change speed, but the plane would still move forward because the wheels have no drive to connect them to the plane just free wheeling bearings. What I just explained works the oposite way when a plane lands. The wheels are stopped, when they touch down on the ground they Instantly start to spinn the same speed the plane Is moving through the air. If there was drive or alot of resistance between the wheels and the plane, as soon as the plane touched down It would Instantly nose dive and crash.

[Billy Golightly]

The riddle says the planes speed and the conveyor are linked, not the wheels. So yes, I do agree, wheel speed is irrelevant.

[Jim mac]

dont forget its the "airspeed" over the wings that give it lift. so if the conveyor is going 200mph and the plane if sitting there it would be traveling backwards 200mph. Say you have a cessna 172 that needs 75mph to take off. turn it so the conveyor is going to get the plane moving forward, then at 75 mph the plane will start to lift. even without the engine running. But turn it around, and the plane is going backwards 75mph, turn on the motor. spin it up so you get 0 air speed and the motor is spinning away and the plane is going nowhere, no air over the wings. so its just sitting there. its like taking the same cessna and taking it off into a 20mph headwind. the actual ground speed is only 55mph when it lifts off, but the windspeed is 75mph so it flys. But if the wind stalls just after takeoff, and you dont have a true 75mph the plane comes down. My freind at work knows of a guy that did just that, unfortunately he and the plane didnt make it. Jim

[smokinwrench]

You guys just cast your VOTE that way we will know who was wrong and who was right.