Airplane on Conveyor Belt Mythbusters 12/12

[xviper]

Wrong. You are using the example of the running man and it's a bad example. A running man develops forward thrust from pusjing off against the treadmills belt. A plane, whether Jet drive or Prop drive, develops forward thrust by pushing against the air. Actually in a Jet is the displacement of air, but that is the same thing for our purposes. Therefore a conveyor belt will not have any effect on the thrust or the forward movement of the plane.
Oh, sorry, you are right, this has nothing to do with vectoring.

I think this Mythbusters is on tonight at 9PM

Your "running on the tread mill" comparison is wrong. As stated earlier in this thread its not the wheels of the airplane pushing on the ground thats creating the forward movement (like our feet do, or a motorcycle). It's the pushing by thrust. The only thing the wheels are for is to reduce the friction with the ground, so the airplane can achieve enough velocity to achieve lift (a plane can not depart off a concrete runway, on its belly, too much friction).

In this scenario, it's purely semantics, but I'll leave you with your opinion.

Thrust is thrust in this experiment. It doesn't matter if you are pushing against the surface you're on to move along that surface or if you're using the air to move along the surface. You are merely providing the ability to keep up with the treadmill. Only once the object leaves the ground (or treadmill) does the propulsion system come into play. As presented, it is my contention that the plane will not leave the surface of the treadmill. There is no AIRspeed.

 

[Rondo777]

As a pilot and aircraft owner for almost 30 years I can attest to the fact that: An airplanes ability to fly is 100% dependent on AIR SPEED (The measured speed of the air over the wing) Unless the tread mill is on the back of a truck moving at the appropriate speed for flight of the plane in question, that plane aint going any where. GROUND SPEED (The measured speed the aircraft is moving along the ground) is completely irrelevent flight. If your in a plane that can fly at 40 knots and the wind is blowing 40 knots directly at the plane then you can fly with no power and have no forward motion(ground speed) The airspeed indicator in the plane will show 40 knots. I used to live in Daytona Bch and on really windy days I would take my plane along the beach and fly backwards. Head wind of 50knots and my plane was capable of flight at 33 knots. I was actually moving backwards at a ground speed of 17 knots, really trippy to people watching from the beach.

 

[xviper]

As a pilot and aircraft owner for almost 30 years I can attest to the fact that: An airplanes ability to fly is 100% dependent on AIR SPEED (The measured speed of the air over the wing) Unless the tread mill is on the back of a truck moving at the appropriate speed for flight of the plane in question, that plane aint going any where. GROUND SPEED (The measured speed the aircraft is moving along the ground) is completely irrelevent flight. If your in a plane that can fly at 40 knots and the wind is blowing 40 knots directly at the plane then you can fly with no power and have no forward motion(ground speed) The airspeed indicator in the plane will show 40 knots. I used to live in Daytona Bch and on really windy days I would take my plane along the beach and fly backwards. Head wind of 50knots and my plane was capable of flight at 33 knots. I was actually moving backwards at a ground speed of 17 knots, really trippy to people watching from the beach.

I'm not even a pilot (I tried but ran out of money) and I can understand what you just said. It's totally correct. Physics doesn't lie.

(Damn, I hope it's on tonight in Canada.)

 

[tinpusher]

As a pilot and aircraft owner for almost 30 years I can attest to the fact that: An airplanes ability to fly is 100% dependent on AIR SPEED (The measured speed of the air over the wing) Unless the tread mill is on the back of a truck moving at the appropriate speed for flight of the plane in question, that plane aint going any where. GROUND SPEED (The measured speed the aircraft is moving along the ground) is completely irrelevent flight. If your in a plane that can fly at 40 knots and the wind is blowing 40 knots directly at the plane then you can fly with no power and have no forward motion(ground speed) The airspeed indicator in the plane will show 40 knots. I used to live in Daytona Bch and on really windy days I would take my plane along the beach and fly backwards. Head wind of 50knots and my plane was capable of flight at 33 knots. I was actually moving backwards at a ground speed of 17 knots, really trippy to people watching from the beach.

I'm not even a pilot (I tried but ran out of money) and I can understand what you just said. It's totally correct. Physics doesn't lie.

(Damn, I hope it's on tonight in Canada.)

Agreed, except for the Canada part, that doesn't affect me.

 

[twowheelnut]

OK. You can stop now. The answer is: Who gives a shit?

 

[Fred W]

OK, let's look at it this way. An airplane with perfect wheel bearings is sitting still on top of a conveyor belt. Turn on the conveyor belt. Big lump of an airplane being stationary it will not want to move backwards and the tires will begin to rotate. Plane continues to stand perfectly still with the engine off, wheels are spinning proportional to the belt speed. No thrust. No airspeed. No lift.

So I guess what you are saying is that you would turn on the engine and only provide enough forward thrust to make up for the friction of the wheel bearings? Is that the deal? If so, then obviously there will still be no airspeed, no lift, nada.

Any amount of forward thrust applied beyond the amount of drag from the bearings and that puppy's gonna start moving forward no matter how fast you run that belt backwards.

 

[feejer222]

I used to live in Daytona Bch and on really windy days I would take my plane along the beach and fly backwards. Head wind of 50knots and my plane was capable of flight at 33 knots. I was actually moving backwards at a ground speed of 17 knots, really trippy to people watching from the beach.

love the flying backwards bit. lol

You missed the show guys, the conveyor was faulty so they couldnt do the test.

 

[Fred W]

You missed the show guys, the conveyor was faulty so they couldnt do the test.

Are you serious? That would be too funny. I suppose they left it plausible then...

 

[Scythian]

It wont, but the original question assumes it would stop forward movement (otherwise there would be no point to having the treadmill). In reality, it would drive off the treadmill, or nose dive into the ground.

EXACTLY! Thank you!

If the plane is allowed to make forward motion, there is absolutely no point to this whole excercise.

Let's say a plane needs 60 mph to lift off. Put it on a treadmill running at 60 mph, with the propulsion system keeping up with that treadmill. Do you actually think that plane will lift off? It won't. There isn't 60 mph worth of AIR going over it's lifting surfaces (wings) to make the plane weightless. It will still need 60 mph of AIRspeed before it will fly. On a 60 mph treadmill, the AIRspeed is still ZERO. Therefore, NO lift. It would require the equivalence of 120 mph RELATIVE to the treadmill, thus RELATIVE to the ground the treadmill is bolted to, in order to get 60 mph of AIRspeed to take off. If a typical airplane that lifts off at 60 mph airspeed requires (and I'm guessing here) 300 feet of stationary runway to take off (no natural winds), on a treadmill operating at 60 mph, it would need that treadmill to be 300 feet. There goes the idea of building a bunch of giant treadmills at airports so you can get rid of runways.

How does the treadmill affect the airspeed if it is only rolling under the wheels? In that case, we could just roll the treadmill spinning the airplane wheels in the opposite direction and the plane will take off.

What effect does the speed of the aircraft wheels have on airspeed?

 

[xviper]

OK, let's look at it this way. An airplane with perfect wheel bearings is sitting still on top of a conveyor belt. Turn on the conveyor belt. Big lump of an airplane being stationary it will not want to move backwards and the tires will begin to rotate. Plane continues to stand perfectly still with the engine off, wheels are spinning proportional to the belt speed. No thrust. No airspeed. No lift.
So I guess what you are saying is that you would turn on the engine and only provide enough forward thrust to make up for the friction of the wheel bearings? Is that the deal? If so, then obviously there will still be no airspeed, no lift, nada.

Any amount of forward thrust applied beyond the amount of drag from the bearings and that puppy's gonna start moving forward no matter how fast you run that belt backwards.

That's exactly what I'm talking about. There is no point to putting the plane on a treadmill if it's allowed to move forward. The whole idea behind the treadmill is to keep it stationary relative to the ground the treadmill is on. (I think I've said that a few times.)

 

[IndianaTom]

Anyone here fly RC airplanes? I used to, and a light plane with a big prop and deep grass on the run way CAN cause a plane to just lift off with no forward motion. The prop wash over the high lift wings of a balsa wood and cellophane air frame will certainly cause enough lift for the plane to get off the ground with no forward motion.

This is not likely with a Boeing 747, but when the thrust to weight ratio is high enough, and enough air is passed over the airfoil of the plane, lift will over power gravity. With or without forward motion.

 

[xviper]

How does the treadmill affect the airspeed if it is only rolling under the wheels? In that case, we could just roll the treadmill spinning the airplane wheels in the opposite direction and the plane will take off.
What effect does the speed of the aircraft wheels have on airspeed?

I think either we have a misunderstanding or you've missed the point. The treadmill (or the speed of the aircraft wheels) has absolutely no affect on airspeed. It only serves to keep the plane stationary relative to the rest of the world around it. THAT'S the point to the whole exercise.

As for "spinning the airplane wheels in the opposite direction", that would defeat the purpose of the treadmill. You would now be simply adding another form of propulsion and move the plane through the air. In this case, you'd need a pretty long treadmill to get enough airspeed to lift off.

I think we need to look at the precise wording of the original myth. I don't think the airplane is meant to move relative to the ground, only relative to the moving conveyer belt and the whole conveyer belt system is stationary to the ground.

 

[xviper]

Anyone here fly RC airplanes? I used to, and a light plane with a big prop and deep grass on the run way CAN cause a plane to just lift off with no forward motion. The prop wash over the high lift wings of a balsa wood and cellophane air frame will certainly cause enough lift for the plane to get off the ground with no forward motion.
This is not likely with a Boeing 747, but when the thrust to weight ratio is high enough, and enough air is passed over the airfoil of the plane, lift will over power gravity. With or without forward motion.

But now you're talking about vectoring again and you are providing some airspeed over the wings from the prop. The "prop-wash" for a model airplane is HUGE when you compare it to that of a full size "real" airplane.

 

[Rondo777]

Anyone here fly RC airplanes? I used to, and a light plane with a big prop and deep grass on the run way CAN cause a plane to just lift off with no forward motion. The prop wash over the high lift wings of a balsa wood and cellophane air frame will certainly cause enough lift for the plane to get off the ground with no forward motion.
This is not likely with a Boeing 747, but when the thrust to weight ratio is high enough, and enough air is passed over the airfoil of the plane, lift will over power gravity. With or without forward motion.

I fly r/c, both airplanes and Helis. I'm still trying to figure out a way to transport some rc toys on my Feejer

 

[xviper]

I fly r/c, both airplanes and Helis. I'm still trying to figure out a way to transport some rc toys on my Feejer

Enclosed trailer?

 

[Scythian]

I think we need to look at the precise wording of the original myth. I don't think the airplane is meant to move relative to the ground, only relative to the moving conveyer belt and the whole conveyer belt system is stationary to the ground.

So how does the treadmill do that?

 

[IndianaTom]

I fly r/c, both airplanes and Helis. I'm still trying to figure out a way to transport some rc toys on my Feejer

You got a passenger that can run the controller while you drive to the airfield and the plane flys there? Why do I always have to figure this stuff out! sheesh!

 

[Rondo777]

Anyone here fly RC airplanes? I used to, and a light plane with a big prop and deep grass on the run way CAN cause a plane to just lift off with no forward motion. The prop wash over the high lift wings of a balsa wood and cellophane air frame will certainly cause enough lift for the plane to get off the ground with no forward motion.
This is not likely with a Boeing 747, but when the thrust to weight ratio is high enough, and enough air is passed over the airfoil of the plane, lift will over power gravity. With or without forward motion.

But now you're talking about vectoring again and you are providing some airspeed over the wings from the prop. The "prop-wash" for a model airplane is HUGE when you compare it to that of a full size "real" airplane.

Its probably not lift created by the wing getting the rc off the ground. All of my r/c planes have what us r/c guys refer to as UNLIMITED VERTICLE. This means that if you hold the plane in front of you pointing straight up, give it throttle, let it go it will climb. Thats not flying, thats the prop creating more lbs of thrust then the plane weighs. Even an r/c aircraft needs to have a predetermined airspeed before it is "flying". The Elevator on the back of the plane is also a wing, chances are INDIANATOM'S propwash was affecting the elevator enough to get it pointing up and the thrust of the prop was enough to drag it off the ground. With R/C, unless very big it would take very little forward motion before TOM was able to control the plane and take off safely.

 

[Scythian]

Anyone here fly RC airplanes? I used to, and a light plane with a big prop and deep grass on the run way CAN cause a plane to just lift off with no forward motion. The prop wash over the high lift wings of a balsa wood and cellophane air frame will certainly cause enough lift for the plane to get off the ground with no forward motion.

Oh my....

And if you are going fast enough you can turn the engine off and let the wind spin the propellers to stay in the air!

 

[Rondo777]

I fly r/c, both airplanes and Helis. I'm still trying to figure out a way to transport some rc toys on my Feejer

You got a passenger that can run the controller while you drive to the airfield and the plane flys there? Why do I always have to figure this stuff out! sheesh!

DAm, I should have posted this problem to this forum months ago. 2 minutes and bang, problem solved. Thank you!