Will it take off?

[oldenough]

Could this not be regarded the same as the conveyor belt?? Seems to work for them.

[sheltie dave]

Oldenough, the admiral has flown on/off these conveyor belts. Some people will recognize the plane starts toward the rear of the deck, and with full military power applied, is catapaulted forward, off the inclined ramp, and into the air.

Now remove the displacement vector, in any direction, and watch the jet in this case run its jet engines without physically changing from its point of origin. The finite conveyor is the same thing as the jet sitting on a patch of ice. It takes both the air movement over/under the wings creating the differential pressure, and physical displacement from the point of origin at an accelerating rate, to get the going in the sky deal.

If it didn't take the going forward trick, all jet and prop planes could just turn on their engines, cycle them up to "go fly" speed, and they would be off. Kinda like helicopters and Harriers, ya know.

Even these guys jumping off the Enterprise have problems once in a while and go for a swim. []

[Andy W]

Could this not be regarded the same as the conveyor belt?? Seems to work for them.

LOL!

Good One!

[Ray Garrison]

The following is from http://www.classontheweb.com/hWhyWhy.asp

(see here)

The Physics of Airplanes:

Why We Go Up

An old, lofty theory of how airplanes fly

Year 2005 witnessed the 300th birth anniversary of Daniel Bernoulli, the Swiss Mathematician and Polymath, born in 1700, Bernoulli never had a lot to say about airplanes while he was alive, and yet these days he is widely credited with keeping every one of them in the air. In an article on insect flight it was almost off-handedly maintained that an airplane wing diverts air downward and that this "downward flow lowers the air pressure above the wing, lifting it ..."

Air flows faster over the top surface of the wing than below (underneath) the bottom. Bernoulli's principle says that when any fluid moves faster for instance as it passes a bottleneck in a pipe the static pressure in it decreases. Therefore, borrowing Bernoulli's logic, the air above the wing must be at lower pressure than the air below that lifts the wing.

The air flowing over the curved upper surface of the wing travels farther than the air traveling under the bottom, and so it has to travel faster to get to the trailing edge at the same time. The problem is, there is no earthly reason why the air should get there at the same time. In fact, it doesn't. Someone, somewhere (and let's hope it wasn't a science journalist) made up the "principle of equal transit times." The air on top actually gets to the trailing edge sooner than the air on the bottom, because it really does travel faster.

'What makes a wing fly?' Lift is a reaction force. The wing pushes the air down, so the air pushes the wing up. To understand lift you need only Newton's three laws and something called the Coanda effect. The Coanda effect is just the tendency of air or any even slightly viscous fluid to stick to a surface it is flowing over, and thus to follow the surface as it bends. As air follows the upper surface of a wing, it gets bent downward because the surface is curved but also because the leading edge is tilted up (especially when ascending) at what is called the angle of attack. The air that is bent downward pulls on the air above it, distending it and creating a low-pressure zone above the wing. To bend the air downward, the wing has to exert a force on it (air). That action inevitably elicits an equal and opposite reaction (Newton's third law). By means of the low-pressure zone above the wing and the higher pressure below it, the air exerts an upward force on the wing: That's lift. The size of the force is equal to the mass of air the wing has diverted downward multiplied by the acceleration of that air (Newton's second law). A pilot can increase the lift by flying faster (adding power) or by increasing the angle of attack (pulling back on the stick); either way the wing diverts more air down and behind the plane. The wings of a 250-ton airliner pump down about 250 tons of air every second. It holds itself up by brute force.

In this quick illustration we find that air flows to the right, such as in a wind tunnel. Inside the air stream is a wing diverting the molecular flow.

At the front edge, molecules of air are diverted upward, compressing the atmosphere above. Incoming molecules, which may not strike this object, are also caused to move upward because of the compressional effect of the molecules below them and already moving upward, low pressure is formed above and behind the wing. Beneath the wing, the molecules have not undergone deflection, and standard air pressure exists, pushing the wing upwards.

Once compressed, the airflow above begins to return downward to fill this low pressure, its momentum carrying its molecules below their initial position, building pressure below, which then pushes them back up in a progressively dampened process.

A wind tunnel clearly reveals low pressure formed as a boundary layer flow becomes dispersed.

[jacksonbart]

"What would happen if I where wearing roller skates standing on a tread mill going full tilt with a GE F110 jet engine strapped to my back..."

You'd set your a$$ on fire and appear on America's Funniest Home Videos, thus ensuring fame and fortune beyond your wildest dreams.

Was jemals Sie Kapitän sagen

[jacksonbart]

What would happen if I where wearing roller skates standing on a tread mill going full tilt with a GE F110 jet engine strapped to my back, that would produce any where between 27,000 to 32,000 lbs of thrust? Would I fly? Now mind you that tread mill is going full speed.

I saw Wyle E. Coyote try that in a Road Runner cartoon...........It didn't turn out well.

Ich liebe W. E. Coyote

[Jay481985]

Oldenough, the admiral has flown on/off these conveyor belts. Some people will recognize the plane starts toward the rear of the deck, and with full military power applied, is catapaulted forward, off the inclined ramp, and into the air.

uhh.... the aircraft carrier is split into two parts the back is for landing and is skewed and not straight so that if the plane cannot land and catch the one of five guidewires it will not crash into other planes that are parked in the front or taking off. The front half has two - three catapults run by steam

Now remove the displacement vector, in any direction, and watch the jet in this case run its jet engines without physically changing from its point of origin. The finite conveyor is the same thing as the jet sitting on a patch of ice. It takes both the air movement over/under the wings creating the differential pressure, and physical displacement from the point of origin at an accelerating rate, to get the going in the sky deal.

If it didn't take the going forward trick, all jet and prop planes could just turn on their engines, cycle them up to "go fly" speed, and they would be off. Kinda like helicopters and Harriers, ya know.

It might depend. I believe the American F-15 was the first plane to have more thrust then weight. Meaning it could climb vertically without stalling. Most commercial airliners do not. Again no particular plane was stated so it is still possible. So technically with a F-15 if we were to hold it in place like a NASA space shuttle it would be able to fly and climb.

Even these guys jumping off the Enterprise have problems once in a while and go for a swim. []

[Champagne taste beer budget]

Sticking my head out of my cave just long enough to state I can not believe that such seemingly rational, logical folks believe that airplanes move forward by applying force to the ground through their wheels.

Cars/trucks/trains/lawnmowers/ATV's/buses/snowmobiles/earthmovers/motorcycles and tractors all do that. Airplanes do not.

If airplanes depended on some interaction with the ground do move forward, would they not stop moving as soon as that interaction were lost? Lift off, land, lift off, land, repeat. The end of that aircraft carrier would come up pretty fast, you'd better have a plan B to apply some force to besides the ground (or whatever the wheels are in contact with) if you don't want to get wet.

Based on the opposing view, a plane without wheels, just sticks jutting down from the fuselage, could never take off, regardless of how large an engine it had? What if you pointed it straight up?

What if we took said shuttle and placed it on this treadmill? You don't think the thrust that will propell it STRAIGHT UPWARD would be able to overcome some silly force applied by your treadmill?

[sputnik]

The nose of the plane will never advance beyond the 50 yard line, hence there is no displacement vector in this example, and thus the plane will not get off the ground. In this model the admiral is correct.

Other models obviously lead to other results. It all depends on the paradigms of the model you use.

I asked you to explain why the plane does not move - not just restate an unsupported conclusion. You might want to consult another "expert" - I'd recommend you talk to an engineer. As we know, a US Navy admiral can never be wrong but in this case he's short of being right.

.......The finite conveyor is the same thing as the jet sitting on a patch of ice..........

Please explain why. Are you trying to say that a plane can't take off from an icy runway??

[PhilMays]

I believe you can take off from any surface with out wheels. You simply need more thrust than resistance to obtain the nessassary airflow for the lift. Heck, you could sit a plane on plows and lift off. You may plow some long potato rows while doing it though.

My father is an engineer. I posed this question to him a little while ago. Keep in mind he had surgery yesterday and is 70 years young. His initial thought was that it would not take off. It really was not fair for me to pick on him while he was down. Oh well. I did ask for graphs and equations to back up his thought and visual props would be helpful. He told me it wasn't going to happen and where I could put it.......He told me he does have some graphs on exploding buildings his team had done recently. Perhaps that would help Wile E. Coyotee[]

[Rockets]

Champagne, you beat me to it, LOL!

I have to admit, when I first heard the question I was thinking the

plane would indeed be static, given the equal but opposite forces. It

should be the same as connecting a dead weight, of weight equal to the

thrust to the plane. No way, no how it's going to fly Orville.

Then I started thinking what would happen if one were to lay the

Shuttle over on it's side and attached roller skates to the external

tank. Placing this on a treadmill traveling in the opposite direction

of equal air speed should result in a static display. Yeah, the

conveyor belt would be running it's *** off compared to the ground, but

the Shuttle would be doing the same in the opposite direction. Remove the skates,

and the two would still be running equal but opposite speeds to one

another, but not to the ground. The reality of it sunk in at that

point. Standing the Shuttle on its tail, and conveyor belt

vertically sealed the deal.

Granted the Shuttle really only uses its wings when it's landing like a

brick, but I think overall the comparison is close enough for

government work...of course I could still be wrong[]

[klipschaholik]

Let me try this 1 more time. Regardless of the fact that the runway is moving in the opposite direciton of the aircraft (regardless of speed) the only effect the wheels have on the airplane is to reduce the frictional component between the aircraft and the ground since the wheels are free spinning, in other words the wheels aren't driven by a motor. Given this fact you could put 2X4 skids on the ground in place of the landing gear and wheels to support the weight of the aircraft and the only difference is going to be the increased frictional force created from dragging the 2X4 across the ground. (try this at home and see for yourself. It's easier to move a load in a wheelbarrow than it is to drag it acrooss the ground). That's the frictional force working against you. Now if all other conditions are typical of the aircraft, ie thrust from the engines, lift generated by the wings and ample runway to achieve minimal airspeed for takeoff, THIS PUPPY'S GONNA FLY! Regardless of the speed of the spinning wheels the thrust of the engines is going to exceed the frictional forces of the spinning wheels and allow the aircraft to accelerate to a velocity needed for takeoff, no matter how fast they are turning, you just might wear out the wheel bearings a little sooner.

And if you need a more detailed explanation read the following;

Newton described how an object at rest will stay at rest unless a force acts on it. This really means an unbalanced force. In other words, while you sit there in your chair, you are not moving. But there are two forces acting on you ... the force of gravity is pulling you downwards, and the chair is pushing back with the same force. The net result is zero, so there is no net force, and you don't move.

Similarly, when an object is moving at constant velocity, there is no net force acting on it. But that doesn't mean there is no force ... just that the forces are equal and opposite.

In the diagram above, the object is moving. But it is moving at a constant velocity. There is no acceleration. This is because there is no net force on it. There are two forces acting on the object, both the applied force and the frictional force, but they are equal and opposite, so they cancel each other out.

In order to maintain the object's motion at a constant velocity, you must continue to pull with this applied force. The moment you pull less hard, or stop pulling, the frictional force will be stronger and the object will slow or stop.

In order to maintaining this constant velocity, you will have to pull hard enough to counteract the frictional force, which for a moving object is sliding friction. To get the object moving in the first place, you will have had to apply a slightly larger force, to overcome static friction (which is generally bigger than sliding friction), and to cause some acceleration. But once the object is moving at constant velocity, you only need to pull hard enough to balance the force of sliding friction.

If you want to accelerate the object, however, your applied force must be bigger than the frictional force.

Here's what happens when you apply a force to an object that is bigger than the frictional force.

The frictional force always acts in the opposite direction to the motion, so the applied force will be reduced by an amount equal to the frictional force. The resulting force that can actually be used to accelerate the mass is smaller than it was. This reduced force is called the net force, and it is the force responsible for accelerating the object.

That's worth saying again, because it's important. When you apply a force to an object where there is friction, some of the force gets used to overcome the friction. Then, whatever is left can be used to accelerate the object.

Let's stick with our 20 kg mass, which weighed 196 N, and look at what happens when we apply a force.

Suppose we apply a force of 300 newtons to the object.
The frictional force F_f can be found using:

F_f = 0.4 · 196 = 78.4 N

This means that the net force acting on the obect is only 300 - 78.4 = 221.6 N.

F_net = 221.6 N

Now we can find out its acceleration. Using F = m · a, where F is the net force:

What we've just done is to calculate the acceleration on an object by applying a force, where there is friction.
In order to do this, we needed to find the frictional force first, and subtract it from the applied force.
The remaining net force was used to calculate the acceleration.

Let's look at a real problem. We'll use our 20 kg mass again, with a coefficient of friction of 0.4, and apply a force to it that causes it to accelerate at 5 m/s².

The question is this: "What force must you apply to cause this acceleration?"

This is not a trivial problem, because friction is involved. Some of your applied force must be used to overcome that friction.
Step 1: Calculate the net force


The acceleration of 5 m/s² is the result of whatever force is left over after friction is subtracted. So if we use that acceleration to calculate a force, it will be the net force.

The result of this calculation is shown on the left. The net force that resulted in an acceleration of 5 m/s² must have been 100 N.


Step 2: Calculate the frictional force

We'll need to work out the normal force first.
We've already done this for our 20 kg mass, but here's the calculation again. We'll ignore the negative sign.

The normal force is 196 N.
The frictional force is given by the equation

So the friction force works out to be: F_f = 0.4 · 196 = 78.4 N


Step 3: Calculate the applied force

Here's what we have so far.
The net force is only 100 N.
It's what's left, after overcoming a 78.4 N frictional force.
How much was the force that was applied?

This is clearly just an addition problem.
The original force applied must have been 178.4 N.

In order to do force calculations at an angle, you'll have to understand vector components and vector addition.


Here is our 20 kg mass again. This time we're pulling on it in an upwards direction, at the angle shown. The applied force is no longer pulling entirely in a forwards direction; one component pulls up, and another component pulls forwards.

The horizontal component of the force, F_H, can be used to balance or overcome the frictional force.
The vertical component of the force, F_V, can be used to lessen the normal force, and thus reduce the frictional force.

The size of the components of F can be calculated using these equations:

In practice, questions involving forces at an angle, friction, and acceleration, all in the same question, would be a little too complicated for Physics 20. Instead, you'll see problems like the following:


An object is moving at constant velocity. This velocity is being maintained by a force of 400 N that is pulling on the 20 kg mass at an angle of 30°.

What is the force of friction?

Because there is no acceleration, the force of friction is exactly balanced by the forward horizontal component of the applied force.
Work that out, and you'll know what the frictional force is.
F_H = F · cos 30 = 400 x cos30 = 346.4 N so the frictional force is -346.4 N.

---

Here's a similar problem. With several forces that are horizontal and vertical, we won't need to use components, but we will have to be able to add vectors.


Two people are pulling on an object, with forces of 120 N vertically, and 100 N horizontally.
Ignoring friction, at what force and angle must you pull in order to keep the object from moving?

This is an 'equilibrium' question. In order to prevent movement, you must pull with a force that is the same size as the sum of the two other vectors, and at an angle 180° in the opposite direction.

We'll have to calculate the sum of the forces, and the angle this sum vector makes with the horizontal.
Here's a diagram of what we must do.

First we'll have to find the size of the resultant force, which is the vector sum of the two red forces.

Then we'll have to find the angle this sum vector makes with the horizontal.

The final step will be to state the size and direction of the equilibrant.

The vector sum diagram is shown at the right. We'll leave the vectors 'tail to tail', and redraw the diagram.
Here is the right triangle we'll need in order to solve for the length of the sum vector (x) and the angle with the horizontal.

Using the Pythagorean Theorem, the value of x turns out to be 156.2 m.

Using simple trigonometry, the value of the angle works out to be about 50°.

(You've used both of these methods in Math 9 and Math 10, so we won't show the work)

Here's the original diagram, with our answers added.

The size of the equilibrant force is 156.2 N.

Its angle is measured from the positive x-axis, and simple geometry gives an angle of 180 + 50 = 230°.

So you must pull at 156.2 N at an angle of 230°, in order to balance the two applied forces.

And that's all I have to say about that...

[]

[mas]

First question; HOW DID YOU POST THAT? What editor did you use????????

I NEED that capability!

Second...Folks you are making this far too complex! The initial system as posited is in equilibrium. The wheels are simply rotating with a small enough frictional coefficient regards to bearing and air resistance allowing the plane to remain stationary be it unpowered or under power. It doesn't matter. It is just one more level of abstraction similar to the fact that the earth is rotating at ~67,000 mph and the conveyor is moving at an equal rate relative to the earth! The net difference in their relative velocities is 0! In this system, this is the starting point!

Here is the ONLY important issue:

The air flow around the wing has a speed of 0 mph because it is 'sitting on the wing' and has no motion relative to the wing!! (or conversely, the wing has no motion relative to the air!!)

All you need is to apply an additional force (& I don't care what kind or source of the additional force is employed; prop, jet, donkey, a fart...whatever!) sufficient to accelerate the plane (and its wings) to a velocity relative to the air sufficient to satisfy the specific conditions of Bernoulli's principle pertinent to generating the minimum required lift necessary to 'fly' the plane!

The given initial conditions, being in equilibrium, effectively 'cancel' each other. And like equal variables on both sides of any equation, can be 'cancelled'. Thus what remains is the need for an additional force to accelerate the plane relative to the air.

But how did you post that 'rich text' environment? THAT is the real question !!!!!![][]

[bodcaw boy]

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)

OKAY!! so i read it again. if the plane increases thrust then the conveyor goes faster right? and if it slows down the conveyor slows down, correct? it doesn't say the conveyor goes faster or the plane can thrust harder, it says in the exactly the opposite direction. so again, i say, no air over the wings, no lift!!

okay coyotee-o, what did i win? ribs and ice cream??[:^)]

boy!!

one more time!!

[sheltie dave]

Sputnik, as the followup posts indicate, the combination of thrust and physical displacement help create the goes up part of flying. For the last time, confirmed by three aero engineers at Boeing today(and they do use their masters and PhDs, unlike the derelict admiral[:^)]) if you are not piloting a VTOL craft or rocket, unless you satisfy both conditions, you only burn fuel. Driven wheels on a treadmill/conveyor satisfy the zero displacement vector the admiral stated.

I don't care about whether the wheels are driven or freewheeling. The paradigm was stated, and the constraints are what drive the answer. It's just like the question "is this a running car?"

Put a car with bald tires in an icy parking lot in Chicago, floor the speedo until it hits 70mph, how soon will you reach Rockford, which is 70 miles away?

You have two trains on train tracks, 60 miles away from each other. If one train goes 100 mph, the other goes 80 mph, how far way from each other will they be in 30 minutes?

All three questions are poorly structured, and can have a multitude of right /wrong answers depending on the constraints you apply to answer. Have fun.

[Champagne taste beer budget]

Nice post, klipschaholik, very impressive use of the computers capabilities. I agree wholeheartardly.

If I were a stationary object, though in motion, (right here, picture, if you will, me on a treadmill, running at a fair clip to maintain my verticalness) and then, in my right hand, I have a paper airplane.

My feet (the airplanes wheels) are moving at a speed equal to the treadmill (the conveyor belt). No matter how fast the treadmill goes, my body can keep up. (Because I am a stellar example of the male human form, and all that, and a bag of chips.)

Now, as I do rthymic breathing so as to not over do my ex-smokers lungs, I suddenly decide to TOSS MY RIGHT HAND FORWARD, with enough thrust to allow the paper airplane in my hand to achieve a velocity sufficient to impart flight. The paper plane IS going to fly forward.

I'm sure one of you nay-sayers has a treadmill. Go try this for yourself. A force not related to the ground (my hand) will certainly allow that paper airplane to move forward/fly,(dependant on weight and speed, I could certainly not throw a real airplane, heck, I could barely lean against one to impart forward motion), the same as the plane on our hypothetical treadmill, but it's the same forces and theories.

Oh yeah.... I have a BIG bag of feathers waiting for someone... unless they invite me to a Jubilee audition...

[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)

OKAY!! so i read it again. if the plane increases thrust then the conveyor goes faster right? and if it slows down the conveyor slows down, correct? it doesn't say the conveyor goes faster or the plane can thrust harder, it says in the exactly the opposite direction. so again, i say, no air over the wings, no lift!!

okay coyotee-o, what did i win? ribs and ice cream??[:^)]

boy!!

one more time!!

Roy-Boy... maybe you can draw a parallel with fishing... perhaps something like, if you hook a bass and it's swimming against the current, can you reel it in?

[8-)]

[Champagne taste beer budget]

Sputnik, as the followup posts indicate, the combination of thrust and physical displacement help create the goes up part of flying. For the last time, confirmed by three aero engineers at Boeing today(and they do use their masters and PhDs, unlike the derelict admiral[:^)]) if you are not piloting a VTOL craft or rocket, unless you satisfy both conditions, you only burn fuel. Driven wheels on a treadmill/conveyor satisfy the zero displacement vector the admiral stated.

Put a car with bald tires in an icy parking lot in Chicago, floor the speedo until it hits 70mph, how soon will you reach Rockford, which is 70 miles away?

How many Boeing engineers does it take to answer a simple question?

Too Many.

If You take the above mentioned car with bald tires on ice (which I believe I brought up 2 or 3 pages ago) and then strap on the rocket propellant used on the space shuttle, I have to guess we get to Rockford before our take out order is ready.

Smaller rocket, it's still cooking, but we get there.

No rocket, just a propellor, we get there and complain that the food's cold.

I jest fix cars, I en't thet smrt.

[klipschaholik]

Why am I doing this?

Go get your little boys toy truck. You know the little plastic thing with 4 wheels that spin. Go downstairs to the basement (or where ever your wife's treadmill is stuck away collecting dust until the next time she looks into the mirror, asks you if you think she's fat, you know not to answer but somehow that look you give her gives away your thought to which she storms off saying something to the effect you need to get the treadmill out of the basement and bring it back upstairs to the bedroom cause you think she's fat) and turn the thing on. Now as you and your son (who followed you downstairs to the basement asking what you were going to do with his truck) sit next to the running treadmill hold the truck with one hand on the rolling mat. Observe that while you hold onto the truck keeping it in a stationary position the mat continues to roll and the wheels on the truck do to. (Pay very close attention to this part) With the treadmill still running and the mat turning push (this is the thrust part) the truck forward. Did you notice that the truck moved even though the mat turned in the opposite direction? Now repeat this one more time but this time turn up the speed on the treadmill. Same thing happens the truck moves forward with respect to the ground you are sitting on which if you were to do this fast enough would create a movement of air over the truck.

This is the same principal as provided for in the original question.

a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves

In this comparison the truck(plane) is standing on a movable runway(treadmill) and as you push the truck (plane engines provide thrust) the truck moves forward with respect to the ground you are sitting on (plane moves forward with respect to the earth not the movable runway) accelerating to whatever velocity your arm can shove the truck off the treadmill with (plane accelerates to takeoff speed with respect to the earth), your son goes running after the truck (plane takes off into the wild blue yonder) Question answered, again. (Son get's bored says you're crazy and takes his truck back upstairs leaving you behind)

And it's no fancy computer program. It's (Edit Copy), (Edit Paste).

[Ray Garrison]

All I can say is no wonder our collective a$$es are getting kicked in high school math by just about every other country. Any first year physics high school student should be able to look at the question, think about it for a second, and say "uh, of course it will take off??? I'm not sure why you think there's a question..."