Airplane on Conveyor Belt Mythbusters 12/12

[7xray]

So if the airplane takes off and falls into a forest and there is nobody on the plane, does it make a sound?

 

[BobG]

If you are talking about myth busters, the one screw up they did was to say that Carlos Hathcock could not have killed another sniper by shooting them through the other snipers scope. The idiots used a .308 instead of the same 30-06 that Hathcock used. It is small details like this they omit and come up with different conclusions.

They may be entertainment but I wouldn't bet my life on their findings.

As for the question about the conveyor belt and the plane. Where is the whole question?

Because A lot of answers are based on assumptions I don't see in the question.

These guys could show you the answer.



Bob

 

[ionbeam]

So if the airplane takes off and falls into a forest and there is nobody on the plane, does it make a sound?

The correct quote is: If a Man is talking in the forest and there is no woman there to hear him, is he still wrong?

 

[Checkswrecks]

So if the airplane takes off and falls into a forest and there is nobody on the plane, does it make a sound?

Sure. Just listen to the cockpit voice recorder.

 

[kansas transit]

JMHO, but I think you guys have to many available opitions to answer the question, If you narrow it down to jet vs prop vs is the conveyor canceling ground speed vs air speed? to many variables. But here is my take on what I think is being asked, If the plane is setting on a belt that is going to turn at WHATEVER speed the plane would normally attain going down the runway, effectively cancelling ANY lift that the wings would get from ground speed then, No i don't think the plane will takeoff, simply put it has no lift. Now think about this, what if the takeoff speed of a certain plane was let's say 150mph before it had enough lift to fly, now lets say you had a 150mph tailwind, would it takeoff, because I would think the wings would have zero lift. I always thought that this is way planes take off into the wind to aid them with lift. If you had a 300mph wind behind the plane, it would roll along the ground but I don't think it would take off. Now if you turn the plane into the wind i think it would have lift and raise. JMO. I'm not a pilot or an aeronautical engineer, BUT I did stay at a holiday inn exp. last night Stan

 

[Randy]

I hesitate in doing this, but, for clarification, the conveyor belt is spinning in the opposite direction at the same speed as the wheels are turning. There was never any mention of ground speed.

 

[feejer222]

I've seen an airplane take off in as little as 18ft.

This plane is obviously taking off into a very strong headwind, you can see tha the guys are all holding on tight to the ground.

 

[xviper]

I always get sucked into these things.

The premise of the conveyer belt is that the plane is held stationary relative to the ground the conveyer is bolted to. As more thrust is applied the conveyer belt speeds up so the plane remains in the exact same place relative the ground the belt mechanism is anchored to.

1. The plane stays fixed in space, with no forward movement relative to the ground.

2. Given (1), there is no air movement over the wings.

2.1 If it's a jet, the effect of the thrust is out the back and has no direct effect on the lifting surfaces of the plane

2.2 If it's a prop driven plane, the props must provide enough air movement over the lifting surfaces to more than counter the weight of the plane in order for it to leave the conveyer belt. If the plane weighs 1000 lbs. lift must be just over 1000 lbs. Can a prop generate that kind of wind over that small portion of the wing? I suppose if you had a big enough engine and big enough prop, it's possible. The average prop driven plane? I doubt it.

3. Thrust is NOT vectored. It is acting only on a horizontal vector. A rocket has its thrust vectored opposite to the weight of the craft and thus, the craft can lift off. A JATO rocket pack is also "vectored" about 45 degrees from horizontal. It is assisting in lifting the craft by acting directly against the craft's weight and only partially by pushing the craft faster forward (increasing air speed).

Even if you have a jet or rocket propulsion system that has double the thrust of the craft's weight, as long as it is NOT vectored and IS pushing horizontally, a 1000 lb craft on a conveyer belt that is keeping it stationary, will still weigh 1000 lbs as there is no air movement over the wings to counter that weight. It takes air movement over the lifting surfaces to counteract gravity that makes the plane weigh 1000 lbs. No air movement over the wings, no lift. The plane will not leave the conveyer belt. It'll still be a 1000 lb weight with its wheels spinning ferociously and thus, would be relatively stationary.

That video of the fixed wing prop plane took off in that short distance because it had a very strong headwind (notice the flag?). A plane like that can likely lift off the ground with an airspeed of about 50 to 60 mph. If that wind was 40 mph, the plane would only need another 10 mph or so of ground speed before it could lift off.

One must assume that on a conveyer belt, there is no wind acting on the experiment.

The scenario of the earth spinning is invalid. Except for cases of wind movement due to heating and cooling of the atmosphere, the atmosphere spins with the earth and thus, remains relatively stationary. To relate this with the conveyer belt, the air above the belt would also have to move with the belt and it doesn't.

 

[feejer222]

Looks like this kid decided to see for herself.

2 YEAR OLD GETS LOST ON CONVEYOR BELT AT MANCHESTER AIRPORT

 

[kansas transit]

I hesitate in doing this, but, for clarification, the conveyor belt is spinning in the opposite direction at the same speed as the wheels are turning. There was never any mention of ground speed.

Exactly my point if there is no ground speed, plane sitting on a rotating belt, there is no lift. Besides if you think about it, IF THE WHEELS ARE NOT GEAR DRIVEN, THEY WILL ALWAYS TURN THE SAME SPEED AS THE BELT, THE BELT SPEED IS DICTATING WHEEL SPEED, and the wheels will always turn the opposite direction of the belt. Randy, if I'm missing a component please explain. Thanks Stan

 

[kansas transit]

I always get sucked into these things.The premise of the conveyer belt is that the plane is held stationary relative to the ground the conveyer is bolted to. As more thrust is applied the conveyer belt speeds up so the plane remains in the exact same place relative the ground the belt mechanism is anchored to.

1. The plane stays fixed in space, with no forward movement relative to the ground.

2. Given (1), there is no air movement over the wings.

2.1 If it's a jet, the effect of the thrust is out the back and has no direct effect on the lifting surfaces of the plane

2.2 If it's a prop driven plane, the props must provide enough air movement over the lifting surfaces to more than counter the weight of the plane in order for it to leave the conveyer belt. If the plane weighs 1000 lbs. lift must be just over 1000 lbs. Can a prop generate that kind of wind over that small portion of the wing? I suppose if you had a big enough engine and big enough prop, it's possible. The average prop driven plane? I doubt it.

3. Thrust is NOT vectored. It is acting only on a horizontal vector. A rocket has its thrust vectored opposite to the weight of the craft and thus, the craft can lift off. A JATO rocket pack is also "vectored" about 45 degrees from horizontal. It is assisting in lifting the craft by acting directly against the craft's weight and only partially by pushing the craft faster forward (increasing air speed).

Even if you have a jet or rocket propulsion system that has double the thrust of the craft's weight, as long as it is NOT vectored and IS pushing horizontally, a 1000 lb craft on a conveyer belt that is keeping it stationary, will still weigh 1000 lbs as there is no air movement over the wings to counter that weight. It takes air movement over the lifting surfaces to counteract gravity that makes the plane weigh 1000 lbs. No air movement over the wings, no lift. The plane will not leave the conveyer belt. It'll still be a 1000 lb weight with its wheels spinning ferociously and thus, would be relatively stationary.

That video of the fixed wing prop plane took off in that short distance because it had a very strong headwind (notice the flag?). A plane like that can likely lift off the ground with an airspeed of about 50 to 60 mph. If that wind was 40 mph, the plane would only need another 10 mph or so of ground speed before it could lift off.

One must assume that on a conveyer belt, there is no wind acting on the experiment.

The scenario of the earth spinning is invalid. Except for cases of wind movement due to heating and cooling of the atmosphere, the atmosphere spins with the earth and thus, remains relatively stationary. To relate this with the conveyer belt, the air above the belt would also have to move with the belt and it doesn't.

Xviper, Thanks, that's what I was trying to say but you did a much better job of it, That's why I said it depends on the variables in the equation. Stan

 

[xviper]

Xviper, Thanks, that's what I was trying to say but you did a much better job of it, That's why I said it depends on the variables in the equation. Stan

These things always intrique me, not so much the physics of it, but rather, the types of responses and beliefs that arise from it. In my view, the whole point of the conveyer belt is to negate airspeed. If it wasn't for that, why do it at all? It's just like if you put an airplane in a wind tunnel. Given just the right amount of wind and the right amount of thrust, the plane would simply lift off but go nowhere. It would just hang there, completely stationary relative to the ground the wind tunnel is built on. It's an excercise in "airspeed" (or the lack thereof), not what's directly under the plane and one has to eliminate thrust vectoring.

 

[kansas transit]

Xviper, Thanks, that's what I was trying to say but you did a much better job of it, That's why I said it depends on the variables in the equation. Stan

These things always intrique me, not so much the physics of it, but rather, the types of responses and beliefs that arise from it. In my view, the whole point of the conveyer belt is to negate airspeed. If it wasn't for that, why do it at all? It's just like if you put an airplane in a wind tunnel. Given just the right amount of wind and the right amount of thrust, the plane would simply lift off but go nowhere. It would just hang there, completely stationary relative to the ground the wind tunnel is built on. It's an excercise in "airspeed" (or the lack thereof), not what's directly under the plane and one has to eliminate thrust vectoring.

So, what did you think of my solution to getting the ping pong ball outta the hole???? Stan

 

[xviper]

So, what did you think of my solution to getting the ping pong ball outta the hole???? Stan

Didn't see that one. Can you point me to that discussion?

 

[feejer222]

I am totally lost as to why there is any question here.

Planes fly because they travel fast enough through the air for the air to cause lift because of the shape of the wings.

If the plane is stood still it cant fly. If a plane slows whilst in flight it drops like a stone. Thats why it has a run up on a runway to get up to the speed at which it will lift.

Otherwise all airports would be much smaller and just have a line of heavy duty conveyor belts.

Its like saying if you stand with your feet in 2 buckets and pull up on the handles you will lift yourself up....doesn't take much working out does it?

 

[xviper]

I am totally lost as to why there is any question here.
Planes fly because they travel fast enough through the air for the air to cause lift because of the shape of the wings.

If the plane is stood still it cant fly. If a plane slows whilst in flight it drops like a stone. Thats why it has a run up on a runway to get up to the speed at which it will lift.

Otherwise all airports would be much smaller and just have a line of heavy duty conveyor belts.

Its like saying if you stand with your feet in 2 buckets and pull up on the handles you will lift yourself up....doesn't take much working out does it?

I totally agree. But then, it's these sorts of goofy myths that "Mythbusters" love. It makes good press and it's entertaining for the guys who do the show and for the people who watch them.

BTW, I can lift myself off the ground in your example. I've got Pixie Dust in the buckets. :bleh:

 

[kansas transit]

So, what did you think of my solution to getting the ping pong ball outta the hole???? Stan

Didn't see that one. Can you point me to that discussion?

POST# 30 this thread.

 

[sonicspeed]

i think Kari is HOT

clearly this is not a thread hijack because it is about mythbusters

 

[Scythian]

I believe the theory is that if the treadmill is driven so that the wheel speed matches the airspeed at which the thrust would be driving the aircraft, the effective groundspeed would be zero and thus the aircraft would be relying solely on the thrust produced by the engine(s).
There qre some very powerful military aircraft that might be able to fly relying completely on the thrust produced by the engines, but....

So what do planes use to "fly" other than thrust produced by the engines? (which provides velocity to the airframe which causes the wings to create lift)

How could a ski-plane take off on snow if an airplane needs wheels driving it?

 

[Coyote]

Otherwise all airports would be much smaller and just have a line of heavy duty conveyor belts.

Which is exaclty how it would be, if not for a well funded lobby of runway builders and sweepers.