The old airplane on a conveyor...

[lilcoop03]

I googled it and wow! It is basically a crappy question and it depends how and in relation to what the treadmill is spun. I view it as the treadmill magically allows the 747 to be stationary with zero ground speed. Zero ground speed means zero lift and hence the plane will not takeoff. F22 would take off, it has greater than 1 to 1 power to weight ratio. That would be something to see.

EXACTLY what Ive always thought about this question...I think a small prop plane will easily take off.. A 747...not so much. Could definitely see an F22 doing it. Makes sense

 

[08mojo]

I googled it and wow! It is basically a crappy question and it depends how and in relation to what the treadmill is spun. I view it as the treadmill magically allows the 747 to be stationary with zero ground speed. Zero ground speed means zero lift and hence the plane will not takeoff. F22 would take off, it has greater than 1 to 1 power to weight ratio. That would be something to see.

EXACTLY what Ive always thought about this question...I think a small prop plane will easily take off.. A 747...not so much. Could definitely see an F22 doing it. Makes sense

Guys, it has nothing to do with ground speed. It has everything to do with air speed. Air moving over the wings is what causes an air plane fly. The lift of the plane has absolutely nothing to do with ground speed, only air speed. It doesn't matter if it's a ultralight plane, 747 or fighter jet.

The treadmill could move forwards, backwards or not at all. The wheels are independent, completely, from the plane generating air speed. There is no propulsion coming from the wheels--only the prop, ducted fan, or jet engine.

Ever seen a water plane? Did you know they don't even have wheels and can take off from a moving river or stationary body of water?

 

[blk02edge]

I knew this topic would prove some still confused lol

 

[Weather Man]

Guys, it has nothing to do with ground speed. It has everything to do with air speed. Air moving over the wings is what causes an air plane fly. The lift of the plane has absolutely nothing to do with ground speed, only air speed. It doesn't matter if it's a ultralight plane, 747 or fighter jet.

The treadmill could move forwards, backwards or not at all. The wheels are independent, completely, from the plane generating air speed. There is no propulsion coming from the wheels--only the prop, ducted fan, or jet engine.

Ever seen a water plane? Did you know they don't even have wheels and can take off from a moving river or stationary body of water?

The plane on water moves faster than any current.

Again, it depends on what the relationship between the conveyor and plane. When I hear the question I imagine the conveyor spins as fast as needed so that i could touch and hold the wing tip. There is no lift on the wings, only engine thrust. A 747 could run of of gas and NEVER generate enough engine thrust to lift the plane on thrust alone.

 

[Coiled03]

The plane on water moves faster than any current.

Again, it depends on what the relationship between the conveyor and plane. When I hear the question I imagine the conveyor spins as fast as needed so that i could touch and hold the wing tip. There is no lift on the wings, only engine thrust. A 747 could run of of gas and NEVER generate enough engine thrust to lift the plane on thrust alone.

Apparently you don't understand:

1) It doesn't matter how fast the conveyor spins, it's producing essentially zero force in the direction opposite the plane's thrust. The ONLY force produced indirectly by the conveyor is rolling resistance from the wheels. A 747 can clearly generate enough thrust to overcome that, and get moving forward.

2) Airplanes generate lift through relative air velocity between the top and bottom of the wing. Thrust doesn't create lift by itself, unless the power to weight ratio is greater than 1. Thrust is just a means to get the plane moving through the air, thereby leading to lift.

 

[DHG1078]

The plane on water moves faster than any current.

Again, it depends on what the relationship between the conveyor and plane. When I hear the question I imagine the conveyor spins as fast as needed so that i could touch and hold the wing tip. There is no lift on the wings, only engine thrust. A 747 could run of of gas and NEVER generate enough engine thrust to lift the plane on thrust alone.

The current still increases drag, much in the same way a treadmill would.

In order for the plane to not take off, you have to make a HUGE assumption that the frictional forces are large enough to prevent forward motion. In this thought experiment you have to explicitly state that is somehow true.

The reality is, the frictional forces aren't large enough to prevent forward motion. It would likely take a little more thrust to overcome the added friction in wheel bearings due to increased rotational speed, but it wouldn't be significant enough to prevent the plane from reaching take off speeds.

 

[AustinSN]

The plane on water moves faster than any current.

Again, it depends on what the relationship between the conveyor and plane. When I hear the question I imagine the conveyor spins as fast as needed so that i could touch and hold the wing tip. There is no lift on the wings, only engine thrust. A 747 could run of of gas and NEVER generate enough engine thrust to lift the plane on thrust alone.

This might be difficult to explain but I'll give a shot.

The airplane wheels are moving freely, think of it like a wagon but instead of a prop, we will have a handle that is being pulled by something that isn't on the treadmill. Like if you put a wagon on a regular sized treadmill and held the handle as the treadmill increased speed. Regardless of the speed, you would still be able to pull the wagon towards you (assuming the friction of the wheels wasn't too great to overcome, it's not). In this situation, you are the prop that is moving through the air (unaffected by the treadmill).

The ultimate goal is to get the airplane moving, because airflow creates lift.

"Pulling" the handle of the wagon would create that lift.

Does that make sense?

 

[Weather Man]

The current still increases drag, much in the same way a treadmill would.

In order for the plane to not take off, you have to make a HUGE assumption that the frictional forces are large enough to prevent forward motion. In this thought experiment you have to explicitly state that is somehow true.

The reality is, the frictional forces aren't large enough to prevent forward motion. It would likely take a little more thrust to overcome the added friction in wheel bearings due to increased rotational speed, but it wouldn't be significant enough to prevent the plane from reaching take off speeds.

Are you are saying the magical 747 treadmill cannot spin fast enough for me to hold onto the wingtip? Silly question that can be interpreted several ways, hence the many interpretations. If the plane is allowed to move on a runway size treadmill, it takes off.

 

[08mojo]

Are you are saying the magical 747 treadmill cannot spin fast enough for me to hold onto the wingtip? Silly question that can be interpreted several ways, hence the many interpretations. If the plane is allowed to move on a runway size treadmill, it takes off.

You are going to feel silly when it finally clicks in your head. I think you're close on your last statement--and that's the key, they plane will move. If you stood off to the side of the treadmill on normal, solid earth, you'd be able to 'hold on' to the wingtip as much as you would if you went down to your local airport right now.

If you were standing off to the side of the plane, say like viewing planes take off from a termial at the airport. It's takeoff from your vantage would look the same with or without the treadmill.