Will it take off?

[jacksonbart]

No I did not. If you pass the right guy $1500 you can do it though.

[sputnik]

I'd shop around (and always haggle in Mexico), I think you could get it done for less.

[Ray Garrison]

Tom,

Pretty simple. As the plane flys, the wings are furiously throwing air down toward the ground like a rabid gorilla sittingin a tree throwing bananas at bystanders. Just as the gorilla can lift the tree off the ground by throwing a sufficiently massive amount of high carbohydrate fruit towards the crowd with sufficient velocity, the plane remains in the air through the same mechanism.

[jacksonbart]

I like bananas and nice Monkeys and really good music.

[oldenough]

Sputnik wrote: If the plane is "loaded" with both Canadians and Americans and crashes on the border between the US and Canada, where do you bury the survivors?

Sputnik this really is an old one, i'm not gonna spoil your fun.

[PhilMays]

If I could get $1,500 a head, I would bury all the survivors anywhere I could.

Let's see, $1,500 x 147 survivors = $220,500 - customs fee's. Not a bad take!

Reminds me of a Monty Python film...Bring out your dead...E's not dead yet!

[sheltie dave]

Here's one from the admiral...

Stop the Enterprise dead in the water. Don't use the catapault. Have the jet on the runway rev its engines to the max with brakes on(a hypothetical), and then release the brakes. Will it fly?

Nope. It'll make a big splash, because you need BOTH the thrust vector(creating travel from the origin) AND the lift vector to work together over a long distance to get up in any type of non-VTOL craft.

If you don't have sufficient travel vector, the jet on the treadmill might bunny hop before it crashes. The object is to have a controlled flight vector within the designed engineered stress limits.

THIS is what the Boeing engineers and the admiral understood to be the crux of the paradigm. It is also why airport runways have certain minimum runway lengths for both takeoff and landings, and why all pilots will be aware of the minimum travel distance with which they can successfully achieve sustained takeoff.

It's also why the aircraft carriers will answer a launching flank into a headwind, to provide jets with the maximum possible additional lift. They have to cheat because there is not an adequate travel vector from the origin, UNLESS they factor in the ramp, flank speed into a headwing, and throwing the bird off the deck on top of the jet's thrust + lift vector. Even then there are problems.

[Champagne taste beer budget]

How is the thrust from our airplane tied to the movement of the treadmill?

[oldenough]

Champagne, therein lies the crux of understanding the problem... In short it is'nt...once you can get your head around that part of it you have to realize the plane will fly...

[Champagne taste beer budget]

Thank You.

I had that on page one. Or two. I think page one was my beer induced page.

[sheltie dave]

An F-15 is about what, 65 feet long? Get an 80 foot treadmill that freewills, raise it fifteen feet above and parallel to the ground, put the jet on it, and pray it flies.

If you take the absolute horizontal displacement from the origin out of the equation, it won't fly. The planes launched off the Enterprise, with all possible cheating added, still take 300 feet to get up and mostly stay up. I think 1200 feet is the briefest distance for the F-series on a normal runway. It takes distance, acceleration, and time for the combined vector forces to beat gravity.

A plane does not accelerate if it does not move from the origin. It will not sustain flight if it does not accelerate and achieve sufficient lift at a combined vector.

Sorry to beat the horse, but it is a different horse with specific rules.

[oldenough]

Sheltie, forget everything about aircraft carriers, etc, go back to the original question. So much has been introduced into the problem that you are able to set up your own scenario, and thus make it impractical for the plane to fly, but not impossible.

[Champagne taste beer budget]

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)

A plane is standing on a movable runway...

It may be sitting, resting, standing, but it is located there.

As the plane moves...

We have motion, hopefully safe to assume in a forward direction, which is being caused by some forward thusting agent, be it a propellor or jet engine. Certainly not caused by the wheels. It's NOT a car.

The conveyor moves but in the opposite direction...

It (the conveyor) has to be self driven, since there is no rotational force acting on the wheels of the plane other than the friction from moving forward against said conveyor.

The conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction.

How else could the conveyor match the speed of the plane other than to have it's own driving force?

So what do we have? A conveyor that has ability to match the rotational speed of the tires of the plane. How did the plane start to move in the first place? CERTAINLY not by anything that had to do with the conveyor or the wheels. Come on, I just KNOW some of you guys were the same ones that were in on the treadmill threads a month ago, go down, fire that puppy up to a 5 minute mile speed, and tell me you can't reach out and throw a paper airplane out in front of you as you run on it.

[sputnik]

This is a dangerous topic. Here is a link to another forum where this topic has been beaten to death for over 400 pages. Yep, over 400 pages (over 6,000 replies and over 210,000 views)! Maybe someone is trying to take over the world while the internet is preoccupied by the plane on a conveyor.

http://forum.physorg.com/index.php?showtopic=2417&st=0

[jacksonbart]

!

[sputnik]

Here is my last attempt to put the topic to rest:

Although a couple of the analogies that have been given don't really apply, the plane will take off. The aircraft carrier is not the same as the conveyor problem - the

carrier is actually more of a slingshot. The rotating earth example is

also not really the same as the conveyor problem since everything is in

the same inertial frame - the earths rotation is not really felt as an

external force to an observer on the earths surface.

Again,

the problem is not aerodynamics but simple mechanics. Bernoulli's

equation, laminar flow, boundry layer effects, etc., etc., are just not

relevant to solving the question. The pilots, admirals, and

aeronautical engineers can take a break for a while. It's about

forces, moments, and how wheel bearings transmit certain forces but not

others.

I drew up a diagram that I hope helps and I'm going to

try to put concepts into terms for non-engineers. We have an aircraft

landing gear wheel on a yellow conveyor. The gray part of the wheel is

the rubber tire, the blue part is the pin, or axle, of the wheel and

the red ring is the wheel bearing.

I've shown the horizontal

forces acting on the wheel. F(t) is the thrust from the plane's engine

that is transmitted to the axle of the wheel. F© is the force from

the conveyor that acts tangentially on the surface of the tire - so it

creates a shear force on the surface of the tire perpendicular to the

contact patch between the tire and the conveyor. As you might expect,

the shear force results in tire rotation (as shown). The tire contact

patch is shown as line A-A' on the figure (to make things easy we'll

assume there is no tire deformation so the contact patch will be a line

and not a rectangle). Remember, this is the only point of contact

between the tire and the conveyor and so it is the only place a force

from the conveyor can act on the wheel assembly. Also for simplicity,

I've not shown the vertical forces acting on the wheel, consisting of

the plane's weight on the axle or the resultant, or normal, force

counteracting it from the conveyor to the tire - they will cancel each

other out. We only need to focus on the horizontal forces (engine

thrust and shear force from the conveyor).

The function of a

wheel bearing (shown in red on the diagram) is to eliminate frictional

forces between a wheel and an axle. Let's say this wheel bearing is

truely frictionless (again for simplicity). As a frictionless ring, it

is not affected at all by shear forces. The spinning tire does not

twist (apply a torque) to the axle - again, the bearing prevents that

by not transferring the shear force from the tire surface. If the red

ring is a rigid connection such as a weld, brake, or drive gear instead

of a wheel bearing, then the force, F©, from the conveyor will apply

a moment (or torque) to the axle and affect the planes forward motion.

The

only horizontal force acting on the axle is the result of the thrust of

the plane's engine, F(t), so the tire (and the rest of the plane)

accelerates in response to that force. The force, F©, from the

conveyor does not oppose this force - it only spins the tire.

To

convince yourself, try the following experiement. Take one of your

kid's skateboards, turn it upside down (wheels up) and lay it on the

floor of your garage. Fire up your belt sander and run the sanding

belt on the wheels of the skateboard. I've never done this, but I know

that the skateboard will not go shooting across your garage but will

just sit there while your sander spins the wheels. There might be some

movement since the skateboard wheel bearings are not truely

frictionless, but you'll get the idea. Just as the plane's forward

motion is not affected by the conveyor, the skateboard is not affected

by the shear force you are applying to the wheels (unless you slip and

drop the sander on the board).

[Ray Garrison]

This has got to be one of the most depressing threads I've been involved with in at least 6 years. I really can't believe there's any argument about it. Of course the plane takes off. What the ground under the plane is doing while the plane is moving forward through the air has nothing whatsoever to do with the forces acting on the plane. I don't know how many other ways to express this. The fact that there's even any question about it shows how little basic physics understanding there is. I'm gonna go to bed and hope that when I wake up Dorothy has found her shoes.

[jacksonbart]

That is it. If Ray is depressed, then I am going to strap on a GE90 to my back wearing a rain coat. I mean come on, I will fly and the GE90 is designed for the Boeing 777 will create 127900 lbs of thrust. Thats is a Guiness book of World Records for the most powerfull commercial Jet engine, for giving 123,000lbs of steady thrust during testing. Dang! That is a lot of thrust. I have actually gained some weight recently and my conveyer belt run way is running faster now, but I have no wings and I still expect to fly given that with a heavy rain coat and rollor skates I am under 220lbs. Wing lift be damned,I am flying. Peace out. Landing may be a slight problem, but I will recover. Cheers.

[Ray Garrison]

Sorry about the car battery, but science marches on, etc...

[sheltie dave]

Why does this question get recycled so often?

The admiral has taught using this example at Nevada. Two of the Boeing engineers cut their teeth on it. It is used, in varying forms in military flight schools, to reinforce the concepts of stall, operating limits, and the physics involved during the transition from ground to flight physics.

The transition is not instantaneous, an unchanging calculated number, nor hardfast. It also shows that engineers communicate and listen differently, just as the example back in the early days of jet design when the US flight engineers had to tell the Brit engineers NOT to use frozen chickens to test the jet engines' ability to withstand passage of avian bodies.