will it take off?

[RobJ]

Yes it will take off!!!

Planes takeoff and land, with, against, perpendicular and any angle in between for that matter, from a naturally occurring conveyor every day and it doesn't matter what the wind speed or wind direction is. It's called the rotation of the earth. At the equator, the earth rotates just over 1000 mph and decreases to zero at the north and south poles.

Keep trying. That's like saying if I jump off the ground when I land I'll be 10 blocks away. Or if I toss a frenchfry to my son in the back seat it'll put an eye out(just a toss, not a fast fry!!).

And only Superman can stop, speed up, reverse the earth rotation! So please lets use facts we can verify!

 

[NorthwestBlue]

Sorry I missed the beginning of this thread. Schmism, you devil you. Anyway, I was on vacation, and when I got back I was out on my tractor. Well, I finally came in and turned on the computer and saw this thread. You wouldn’t have had such passionate responses to the question: Blue, green, or orange gear or hydro synthetic. Tractors are still kinda new to me but I do know a thing or two about airplanes. So here are some analogies that might get you non-believers over on the side of truth, freedom, and the TBN way.

I’m not going to debate the interpretation of the wording of the question. I think it’s pretty clear, but then again, others don’t always see things the way I do. Therefore, this is mainly for those who see the “Magic Conveyor Belt” (or MCB) as the stumbling block to this airplane’s eventual stabilized departure. I will use real world materials for my ideal airplane which will help you envision the reality a little easier. I will also use real world physics, with the exception of the movement of said conveyor belt. Here goes…

The Plane: The ideal plane would have a very large aspect ratio (think glider wing) and a very large thrust to weight ratio (powerful engine, light plane). The one that jumps to mind is the U2 (that Kelly Johnson was amazing). Change out the engine with say an F100 (F15, F16 engine… gobs of power) or something similar. The tires would need to be very hard and smooth, almost slick with very high air pressure. Oh, I know how about this… solid Teflon. Then we’ll change out the wheel bearings and axles. New super-high speed, high temp, roller bearings and axles. No holds barred when you’re dealing with magic.

The Set Up: Now the next thing you need to understand is that there is no mechanical connection between the conveyor belt and the airplane. There is friction (mass, gravity, coefficients and all that garbage), but that’s it. Also, there is no mechanical connection between the wheels and the airplane. Now it’s getting good. The wheels spin freely. Spin em’ forward, backwards, stop them, the plane doesn’t care.

The Analogies: What happens when an airliner touches down during landing? It doesn’t stop immediately does it? When the wheels first touch the runway their rotation is zero even though they are moving through the air at say 140 knots. As the wheels contact the ground friction comes into play. There is a puff of smoke as the rubber boils and vaporizes due to the friction between the ground and the tires. It sometimes takes over a hundred feet for the tires to spin up to a speed where there is no longer slippage and… friction increases. This is key. Friction decreases as the speed between the objects increase. More on this in a second. The airliner hasn’t slowed down a bit from this violent impact. Ground spoilers and thrust reversers are deployed to reduce the lift from the wings and increase friction between the tires and runway to allow the brakes to stop the plane.

The next analogy for you ground bound folks. Take an older car or truck i.e. no anti-skid brakes. You’re cruisin’ at highway speeds, say 80-90 mph… err… I mean 55-65 mph and slam on the brakes. Smoke rubber on pavement, but you don’t stop for a couple of hundred feet.

The Flight Test: With our souped up U2 on the MCB runway with just enough fuel for a short flight and all unneeded instrumentation removed, we’re ready. Now if the MCB wanted to maximize friction it would spin up slowly to maintain an equal speed between the wheels and the belt, but if it did that, the U2 would be 1000 ft in the air before you could blink. Instead the MCB will spin up instantaneously to a thousand, a million, a billion revolutions per second, faster than the speed of light. At witch point the MCB will disappear into the space/time continuum. The U2 will then fall to the ground and takeoff normally.

Sorry, I couldn’t resist. So, as the U2 pilot applies full afterburner and full nose up pitch, the MCB will try to rotate the wheels to restrict the airplanes forward movement. It won’t be able to, remember the analogies? The MCB can accelerate instantly (remember it’s magic) but the wheels have mass and only friction can come into play. The MCB will begin to move the wheels, but by then the U2 will move forward gliding on its super-slick bearings increasing lift and in turn decreasing friction between the tires and belt even more. Lots of smoke and some burned up Teflon tires, but the plane will be flying.

I know I said that I wasn’t going to debate semantics, but…

“a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction. the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction”

Where is the magic conveyor belt?

Now pardon me I’ve got some work to do… on my TRACTOR.

 

[RobJ]

WOW Blue...that was certainly a lot of typing.

The MCB is sort of a hypothical thing and I think everyone gets hung up on it. The MCB doesn't need to go up to light speed or anything. Our fastest plane is only capible of Mach 3 or so. Plus that plane..SR-71 doesn't go 0-mach 3 in .0025 seconds. The initial roll out of a jet or prop is pretty slow...generally speaking.

 

[NorthwestBlue]

RobJ,

Yea, I know its a lot of typing, but I kinda felt like I missed out on something.

"The MCB is sort of a hypothical thing and I think everyone gets hung up on it. The MCB doesn't need to go up to light speed or anything. Our fastest plane is only capible of Mach 3 or so. Plus that plane..SR-71 doesn't go 0-mach 3 in .0025 seconds. The initial roll out of a jet or prop is pretty slow...generally speaking."

And thats my point the plane does not have to be fast. The MCB only has the relatively small tire ground contact patch to apply any force to the plane and then only to the tire, not to the airframe. The U2 in my example was not meant to be fast, but to have a very short ground roll and power to overcome any drag the MCB could possibly apply. It can't possibly stop the plane from moving. Another analogy, put a weight on a piece of paper on a table and pull the paper slowly across the table. Friction keeps the weight on the paper. Now pull the paper quickly. Friction is overcome and the weight remains stationary. The paper is the conveyor, the weight is the plane. The plane will take off.

 

[SPYDERLK]

RobJ,

Yea, I know its a lot of typing, but I kinda felt like I missed out on something.

"The MCB is sort of a hypothical thing and I think everyone gets hung up on it. The MCB doesn't need to go up to light speed or anything. Our fastest plane is only capible of Mach 3 or so. Plus that plane..SR-71 doesn't go 0-mach 3 in .0025 seconds. The initial roll out of a jet or prop is pretty slow...generally speaking."

And thats my point the plane does not have to be fast. The MCB only has the relatively small tire ground contact patch to apply any force to the plane and then only to the tire, not to the airframe. The U2 in my example was not meant to be fast, but to have a very short ground roll and power to overcome any drag the MCB could possibly apply. It can't possibly stop the plane from moving. Another analogy, put a weight on a piece of paper on a table and pull the paper slowly across the table. Friction keeps the weight on the paper. Now pull the paper quickly. Friction is overcome and the weight remains stationary. The paper is the conveyor, the weight is the plane. The plane will take off.

No. If the tires have enuf traction to overcome engine thrust the magical conveyor could hold the plane stationary by applying a force, equal&opposite to engine thrust, to the tires. This thrust would rotationally accelerate the mass of the wheels. As long as the wheels, tires and bearings could withstand the increasing rpm the plane would not move.

 

[NorthwestBlue]

No. If the tires have enuf traction to overcome engine thrust the magical conveyor could hold the plane stationary by applying a force, equal&opposite to engine thrust, to the tires. This thrust would rotationally accelerate the mass of the wheels. As long as the wheels, tires and bearings could withstand the increasing rpm the plane would not move.

SPYDERLK: Don't need and don't want traction in this scenario. Try this... go get a small toy with free moving wheels (Hot Wheels car, train, or the like). Put a sheet of paper on a smooth surface. Place the vehicle on the paper so that you are looking at the side of it. Now move the paper back and forth rapidly in the direction of the wheels (make them roll). What happens? Now push the vehicle with your finger at the same time as you pull the paper out in the opposite direction. What happens? Same theory, same physics, just a smaller scale (like wind tunnel testing).

 

[MossRoad]

Anyone here know how a treadmill works?

Nope. Mine is sitting in the basement gathering dust.

 

[patrick_g]

Tom, I don't know why but my browser or some limitation doesn't let me insert smilies.

As to the response I gave. If you knew me better you'd know it was tongue in cheek, mostly. Some of the hypersonic stuff, I thought, was particularly inspired.

Aircraft like sailboats (sound familiiar?) operate on relative wind. Unless a conveyor belt made the plane go backward before it developed enough thrust to move forward it would have little effect on the takeoff. Sure there might be more rolling resistance of the tires and bearing resistance if anything made the wheels rotate faster that the air speed.

Once the plane developed enough thrust to overcome static friction and start rolling forward the conveyor belt is just about as involved as the color of the tie worn by the third onlooker. The aircraft would take off pretty much as if there were no conveyor belt.

Now, if we have a sealed opaque box with a bird in it, can we use a sensitive scales to determine if the bird is perching or airborn knowing the weight of the box and bird separately?

Pat (//INSERT SMILING FACE ICON//)

 

[RayH]

Sometimes it helps to work these problems backwards. Lets expand on the original question to gain a better understanding.

A plane from another airport is visiting our airport with the magical conveyor belt to do touch and goes. As the airplane does his approach for landing, the magic conveyor belt automatically matches the planes speed, because thats what it does. It magically matches the speed of any plane either taking off or landing. The planes landing speed is 60knots, so the conveyor is doing 60 knots backwards as the plane lands.
Does it:
A). immediately come to a stop
B). land normally
C). The plane lands nomally but the wheels are doing 120 knots.

The correct answer is C.

Now the second part of the touch and go. The plane needs a takeoff speed of 100 knots, so once the plane is down and going 60 knots, the pilot gives it full throttle and accelerates up to 100 knots. The MCB does what it does and accelerates up to 100 knots as the plane does.
Does the plane:
A). immediately come to a stop
B). takeoff normally
C). Takeoff normally but the wheels are doing 200 knots.

The correct answer is C.

If you dont agree with these answers you need to explain why because it seems very basic to me.

 

[joerocker]

Some of you guys just don't get HOW a plane takes off/flies!

A plane doesn't take off the way a car moves. It doesn't transfer anything to the ground in order to move or to take off. It takes off INDEPENDENT of the ground! The ground just happens to be the thing it's RESTING on before it takes off. As the plane applied power, it WILL move forward irregardless of how fast the "conveyor" moves. Unless this "magic conveyor" can CAPTURE the surrounding air and move it in the OPPOSITE direction keeping the plane from achieving any air speed, the plane WILL move forward. The ONLY thing that will be affected are the tires that will be spinning REALLY fast.

As long as you don't affect the surrounding AIR, The plane will take off as normal with REALLY fast spinning tires...