Will it take off?

[Coytee]

I saw this on another forum I frequent and found some of the commentary interesting. I don't know the answer although I've got an opinion. It WAS interesting seeing the answers/thoughts some people gave (2 pages worth).

I'm copying it exactly like he had it there

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.

the question is

will the plane take off or not?

(ps its been debated to death on other forums, its always fun to see how people present the theory behind there answer)

[Guest " "]

[

It won't take off.

Under a conveyor belt senerio, the propellor, jet thrust, etc, would be the only source of lift over the top of the wings.

During the take off process, the propeller or jet thrust, begins the lift process by setting the plane into forward motion, as the plane moves forward, the area of the planes wings beyond the direct path of the propellor or jet thrust creates lift as air moves across the top surface of the wings. This would occur even if the plane was being towed by a truck. It's the forward motion of the wings that generates the lift needed for flight. The propellor or jet engine, just begines the process, thru intiating the forward motion.

[Daddy Dee]

Coytee,

From the title, "will it take off"... I was expecting a post asking if the Jubilee for home use will take off.

I would say, yeh. I think so. Word of mouth will be the biggest seller. It's a huge value, IMO. for the price.

the airplane,

nah. I don't think it would take off. If I'm understanding the conveyor thing right, the airspeed flow over the wings wouldn't have lift unless the plane is rolling down the runway.

[Champagne taste beer budget]

When I was in trade school, one of our classes in business required us to give a presentation in front of the class on an automotive subject. A lot of people did things like hopping up an engine, how camshafts differ, etc. I did mine of the aero effect of an F1 race car. Although I don't remember the details, the "wing" shape of the body would develop a low pressure system under the vehicle, while airflow over the top would create a high pressure area. The pressure differential is measurable in lbs, and once you exceded the weight of the vehicle, it could literally drive on the top of a tunnel, or upside down, in theory. I'm not sure, but I believe I read somewhere that MB or a similar European manufacturer has proven it in real time somewhere.

All that being said, if the ground moves, and the plane moves, but the air doesn't move, you just have a silly looking experiment with no real outcome other than the plane just rolling along.

[dtel]

Well the people on this forum must be smarter than the people on the forum you speak of ? That's a much harder question to answer.

[Ray Garrison]

Courtesy of Richard Feinman, from his book "Surely you're joking, Mr. Feinman?"

Take one of those sprinklers everyone

has seen before, the kind that has three pipes sticking out with the ends

slightly bent to the side in opposite directions. When you connect it to a hose and turn it on, the head spins around (force of water begin accelerated at an angle imparts force to head) and waters your lawn.

Now, uncouple the hose from the spickot (?spell?) and connect the hose to a pump. Submerge

the sprinkler in some water, so now when you turn on the pump the

sprinkler is drawing water in through the pipes. What happens to the

sprinkler? How does it move, if at all?

Be advised that if you do a Google search on this, you'll find that legions of grad students at Cal Tech, MIT and various Polytechnic Institutes have been debating this for, like, 30 years.

[Champagne taste beer budget]

OK, so I have a small wading pool 30' long and 6' wide, with an electric pump (sump pump) on one end, with it's output to a hose 20' long terminated to a common sprinkler head. I turn on the pump, the sprinkler emits water, though not far since it's underwater, and the water ends up being recirculated through the pump at some point. Am I missing something, or are college boys just that dense? (No offense to those of your with 4/5/6/7/8 year degrees.) I must have missed something in the experiment, sounds too easy to me.

[DrWho]

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.

the question is

will the plane take off or not?

(ps its been debated to death on other forums, its always fun to see how people present the theory behind there answer)

I think the question is worded very poorly because it imples that the

plane is motionless from the perspective an observor not on the plane

nor moving runway (basically the perspective of the iar). The plane is

going to move forward just like normal....the only thing that will be

different is that the wheels of the plane are going to sping twice as

fast while the wheels are still touching the runway.

Now if you blew wind at the plane such that the plane is motionless

from the perspective of an obersvor in the same spot, then the plane

would actually take off. In fact, this is why planes always take off

"into the wind" because they don't need as much ground speed to achieve

lift-off.

[Coytee]

Well, a couple observations so far.. (perhaps this hasn't been up long enough)

1. There are far more off topic responses here than I noticed in the other forum (attention deficit disorder amongst Klipscheads?)

2. The answers here seem to be universal so far, in that the plane will NOT take off (consistency shows perhaps a singular point of view mindset? Just like a bunch of myopic Klipscheads to be focused??)

3. I happen to AGREE with the flavor of answer (no, the plane won't take off). On the other website there are in fact, some yes answers. (since all answer no, which I happen to believe, perhaps we're collectively smarter than the other website? Hmm... just like a bunch of myopic bookworm Klipschheads?)

So, I wonder if this has changed the question a bit from the plane question to "If you're a myopic bookworm Klipschead, it must mean you're unable to focus on anything except Klipsch stuff, your mindset will be made quickly and heartfelt and evidently, it takes a pretty smart individual to have these quirks?

[8-)]

I suddenly feel like Lucy (Peanuts, pshycho-analyst)

[Coytee]

Interestingly enough, here's a guys response, I've deleted his name but otherwise, a direct copy of his comments. Seems he's one of them smart ones and his answer is the plane WILL take off. [:$]

This is a very simple dynamics problem. Draw a free-body or force diagram of the airplane and you will see that the only horizontal force applied to the airplane by the conveyor is through the almost freely spinning wheels. That force resolves itself into a force applied to the a/c via the rolling resistance of the wheels. The only other horizontal force (neglecting aerodynamic drag) felt by the airplane is thrust from the engine.

Now, the engine thrust must greatly exceed the rolling resistance of the wheels or the airplane couldn't move even if the conveyor were dead still. Since the engine thrust pulling the airplane is much greater than the force of the wheels retarding the airplane, the airplane must accelerate in response to those unbalanced forces. Sir Isaac Newton taught us that back in the 1600's. F=MA where F is the unbalanced forces acting on the object, M is the Mass (or in very loose terms, the weight) of the object, and A is the acceleration of the object.

Don't confuse displacement with force. The conveyor can be "displacing" at a phenomenal rate, but the only force it can exert on the airplane is through those freely spinning wheels. It is FORCE which accelerates and moves unrestrained objects.

Said it before, and I'll say it again. The airplane doesn't care one iota what that conveyor is doing, anymore than if the airplane were flying with the wheels .001 inch above the conveyor.

If the engine is producing, say, 1000 lb of thrust, the airplane would act just like a stationary winch was attached to the airplane and pulling with a constant 1000 lb force. That 1000 lb force, reduced by the drag of the wheels, will accelerate the airplane forward regardless of what the conveyor is doing. Neither the a/c engine nor that imaginary winch cares about, or is even aware, of the existence of the conveyor, they just continue to apply that 1000 lbs of motivating force - and that a/c motivates!

But, since the wheels spin as if the a/c is moving at twice its actual speed (relative to a stationary observer) and a/c tires are rated for a specific maximum speed (RPM) you may ruin your tires or wear out the wheel bearings, but you will fly the a/c- if the tires/wheels last long enough.

I was an aeronautical engineer in the aviation industry for going on 40 years (MSAE), and a rated a/c pilot (Private, ASEL, Instrument) longer than that. I can categorically state that this is one of those logic problems in which your intuition leads you to a dead wrong conclusion. The key is to identify the forces acting on the a/c. Everything else is totally irrelevant.

If anyone cares to read that thread it's here:

http://www.tractorbynet.com/forums/owning-operating/90325-will-take-off.html

[jacksonbart]

I saw this on another forum I frequent and found some of the commentary interesting. I don't know the answer although I've got an opinion. It WAS interesting seeing the answers/thoughts some people gave (2 pages worth).

I'm copying it exactly like he had it there

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.

the question is

will the plane take off or not?

(ps its been debated to death on other forums, its always fun to see how people present the theory behind there answer)

Well first if the conveyor would need to match the pace of the plane indefinatly/ till it ran out offuel as it accelerated. If it did not, then I believe it would take off, its not the wheels moving the plane but the jet engines, which will over come resistance if the conveyor if the speed were level off at some point.

[Coytee]

I still can't see how it would take off.

I keep picturing a Cessna and NOT a Space shuttle... so maybe that's one weakpoint of the scenario... perhaps it should be better clarified.

Seems to me a plan can not take off until the airspeed over the wings is sufficient to lift the plane, regardless of groundspeed. (what if takeoff was 100mph, plan is rolling at 100 mph but there's a 100 mph TAIL wind?? would it still take off?)

I don't know, but I'd guess the propwash of a Cessna would NOT generate enough airflow over the wings to lift the plane (perhaps I'm wrong)

So, if a Cessna won't do that, then I simply can't see how it would allow take off.

Put it this way, if the planes engine were STOPPED and the conveyor moved, the plane would move 'backwards' so to say. Now, if we did that at 10 mph (or maybe even take off speed) but cranked the engine up, all the engine would do would be to counteract the backward motion of the plane and NOW, allow it to be stationary (with respect to a point on the ground)

Once the plane is stationary with respect to a point on the ground, the only real airflow over the wings is from the propeller. Not enough to take off (IMHO)

Perhaps a different plane (F-14, F-16 with afterburners) would be different?

I just can't see how it can happen. Anyone got a BIG treadmill you can loan out?

[Champagne taste beer budget]

I swear, I must have been drinking last night when I wrote my first reply. (Oh, wait, I was)[:$]

Somehow it slipped my mind that the plane has a jet or prop engine providing the forward thrust. It could care less what the wheels are doing. They are not used for traction and propulsion as in a car. If my initial answer were correct, then a plane couldn't take off on ice, which I think we all agree happens.

Yes the plane will fly. The tires may not appreciate the 2x wear due to the conveyor, but planes take off without tires, too, don't they?

[oldenough]

Yes.

[PhilMays]

I feel as long as the plane maintains the same exact longitude and latitude then it cannot take of. A plane takes off due to lift under the wing that is designed for such. The prop or jet is simply a propelling device to allow the wing to attain a lift.

One could accelorate to say 500MPH and not take off (fly).

[PhilMays]

I feel as long as the plane maintains the same exact longitude and latitude then it cannot take of. A plane takes off due to lift under the wing that is designed for such. The prop or jet is simply a propelling device to allow the wing to attain a lift.

One could accelorate to say 500MPH and not take off (fly).

I guess a good head wind could make a plane take off in the same longitude and latitude.

[Champagne taste beer budget]

The force exerted by the prop is against the air surrounding the plane, which is static, NOT against the ground, which is moving. It's not the propwash moving over the wings that provide the lift, but the air it passes through as the plane is forced forward by the prop.

Jet would be the same.

[Andy W]

I saw this on another forum too and the debate rages for months.

Simple answer is that the plane will take off, but it's wheels will be turning twice as fast when it does.

Some people get hung up on the conveyor, thinking that it is like a treadmill.

When you walk your legs exert force on the ground that pushes your body forward. If you are on a treadmill you push the conveyor belt backward instead (which is on low friction rollers). Your acceleration and speed is relative to the amount of force you exert on the ground

An airplane engine doesn't exert force on the ground it exerts force on the air and its resulting acceleration and speed is relative to the air. It could care less what the conveyor is doing. It will only add a small amount of drag based on the friction in the bearings of the wheels and the tires' rolling resistance.

[Ray Garrison]

Champagne,

guess I should have been clearer. We connect the hose from the sprinkler to a pump, and *SUCK* the water in *THROUGH* the sprinkler. The dynamics are reversed. What happens to the sprinkler as a result of sucking water in through it?

See this link:

http://www.physics.umd.edu/lecdem/outreach/QOTW/arch4/q061.htm

[Doc Robin]

What movie will be showing to the passengers? Will there be food served? Since they are not actually flying the passengers dont get frequent flyer miles. Sounds to me like they are only going to be turning fuel into noise!!!!!!!! Bill