| Can this airplane take off? |
| No |
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| Yes |
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| Total Votes : 72 |
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| nist7 |
 Posted: Tue Dec 11, 2007 2:05 pm Post subject: Can this airplane take-off? |
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Location: KCMO
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okay, so I read this on another forum and it generated some good debate.
There is an airplane on a run way. The run way is like a conveyor belt, and can detect the speed of the wheels of the airplane. When the run way senses the wheels moving, the run way will move match the speed of the airplane's wheels but in the opposite direction.
Can this airplane take off?
Discuss. |
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| (Q) |
| Posted: Tue Dec 11, 2007 2:18 pm Post subject: Re: Can this airplane take-off? |
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Forum Professor
Joined: 12 May 2005
Posts: 1362
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| nist7 wrote: |
okay, so I read this on another forum and it generated some good debate.
There is an airplane on a run way. The run way is like a conveyor belt, and can detect the speed of the wheels of the airplane. When the run way senses the wheels moving, the run way will move match the speed of the airplane's wheels but in the opposite direction.
Can this airplane take off?
Discuss. |
The plane should be able to take off. The conveyor is irrelevant as the turbine engines are pushing the air, not the ground. |
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| Shaderwolf |
| Posted: Tue Dec 11, 2007 3:01 pm Post subject: |
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Joined: 13 Dec 2005
Posts: 312
Location: Las Vegas, Nevada (wanna play?)
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the conveyor belt will move with the wheels of the airplane. no matter how fast the turbine moves, AIR HAS TO BE MOVING OVER THE WINGS FOR LIFT TO OCCUR
Last edited by Shaderwolf on Tue Dec 11, 2007 5:32 pm; edited 1 time in total |
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| william |
| Posted: Tue Dec 11, 2007 4:05 pm Post subject: |
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Joined: 23 Jun 2006
Posts: 910
Location: USA
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Air must move past the wings and along the natural direction that the airplane travels to provide lift.
Now...
If it was the wheels which were driving the airplane, then the conveyor could move in such a way that the plane remains still relative to the ground.
However, it is the turbine that provides the thrust, and the turbine will push the plane relative to the surrounding air. Thus, the plane will have no problem moving down the runway and, hence, will be able to take off.
Good question.
Cheers,
william
N.B. The wheels and conveyor will end up in a runaway-type scenario.
_________________
"... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
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About my avatar: This is a smoothed particle hydrodynamics (SPH) simulation of the merger of two galaxies. The code was written by Volker Springel of the Max Planck Institute for Astrophysics at Garching Germany. This simulation uses 20,000 disk particles (stars) and 40,000 halo particles (dark matter) per galaxy. The three views are, from left to right, the x-y plane, x-z plane, and y-z plane. |
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| Shaderwolf |
| Posted: Tue Dec 11, 2007 5:31 pm Post subject: |
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| Twaaannnggg |
| Posted: Fri Dec 14, 2007 9:12 am Post subject: |
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How the heck does anybody check "NO" in the above question in the first place??? Sheesh...............turbines provide the thrust, not the wheels. The wheel swill rotate way faster than usual, but if they're not destroyed in the process this plane WILL take off of course.
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| SteveF |
| Posted: Fri Dec 14, 2007 10:35 am Post subject: |
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Joined: 28 May 2007
Posts: 464
Location: NC USA
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I say NO.
The problem description is vague but it appears the situation is that the airplane has no forward velocity, relative either to the ground or the air. Thus there is no lift on the wings. No matter how powerful the thrust of the propellers the airpane cannot lift off the belt. |
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| william |
| Posted: Fri Dec 14, 2007 1:08 pm Post subject: |
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Joined: 23 Jun 2006
Posts: 910
Location: USA
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| SteveF wrote: |
I say NO.
The problem description is vague but it appears the situation is that the airplane has no forward velocity, relative either to the ground or the air. Thus there is no lift on the wings. No matter how powerful the thrust of the propellers the airpane cannot lift off the belt. |
Hi Steve,
Take another scenario - that of a wheel-driven car.
Ask: What do the wheels "push" against?
Back to the airplane...
Ask: What does the turbine "push" against?
Cheers,
william
_________________
"... the polhode rolls without slipping on the herpolhode lying in the invariable plane."
~Footnote in Goldstein's Mechanics, 3rd ed. p. 202
About my avatar: This is a smoothed particle hydrodynamics (SPH) simulation of the merger of two galaxies. The code was written by Volker Springel of the Max Planck Institute for Astrophysics at Garching Germany. This simulation uses 20,000 disk particles (stars) and 40,000 halo particles (dark matter) per galaxy. The three views are, from left to right, the x-y plane, x-z plane, and y-z plane. |
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| SteveF |
| Posted: Fri Dec 14, 2007 1:17 pm Post subject: |
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Forum Bachelors Degree
Joined: 28 May 2007
Posts: 464
Location: NC USA
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William, you ask "what does the turbine push against?"
Well, it forces air backwards. And Newton's third law says the airplane is driven forwards.
But the craft is on a conveyor belt that goes just as fast as the airplane but in the opposite direction, neutralizing the plane's forward thrust.
As I said, the description is vague. We are not actually told whether the airplane is able to make forward progress... or not. But my interpretation is that the drag of the belt on the wheels is enough to keep the plane in the same spot (relative to the ground). Frankly, I don't know if this will actually be the case but if it is, there is no forward motion, no lift on the wings, and no takeoff. |
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| gravitywell |
| Posted: Fri Dec 14, 2007 1:38 pm Post subject: |
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Joined: 14 Dec 2007
Posts: 23
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The turbines push the air, right? so, if the mass of the airplane wants to go forward, and the free moving wheels are going backwards, wouldn't it be like pulling a rug from under a wheel that has a turbine on it? wouldn't the wheel just keep going faster and faster and faster, (the rug and wheel racing eachother to catch up as the airplane keeps trying to go faster and faster?) each time the plane moves forwards, the wheels move a little faster and a little faster. The airplane does not stop moving forwards, the turbines push the gigantic body of the plane at a constant rate. finaly, at some point one of a few things will happen.
1) the wheels smash into a million pieces pecause thayer going to fast
2) The friction of the wheels becomes so great that it overpowers the tremendous pushing force of the airplane's turbines
3) the turbine overpowers the friction and accelerates slowly, and in a couple of days and a couple of miles later it reaches take-off speed
- I belive that the wheels would break. If they didn't the ever incresing speed would create enough friction to mess everything up. The wheels would be going realy fast though. |
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| zinjanthropos |
| Posted: Fri Dec 14, 2007 2:33 pm Post subject: |
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| If the conveyor belt reacts to the speed of the wheels then the plane has to be moving forward as speed of wheels increases. If the wheel speed is increasing then the plane must be moving. If the conveyor belt is as long as a runway the plane will take off. |
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| Guest |
| Posted: Fri Dec 14, 2007 2:39 pm Post subject: |
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Are the brakes on or off 
Right, as the engine thrust begins to move the plane forward the runway will move but as the plane is moving the runway will simply accelerate towards infinity or until the friction of the wheel bearings is enough to overcome the thrust and halt the plane, at which point the runway will instantly stop and guess what happens to the plane?
Last edited by Guest on Fri Dec 14, 2007 2:43 pm; edited 1 time in total |
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| zinjanthropos |
| Posted: Fri Dec 14, 2007 2:41 pm Post subject: |
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Location: Driving in my car
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| Megabrain wrote: |
| Are the brakes on or off |
With brakes on the engines take off and the rest of the plane stays where it is. |
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| gravitywell |
| Posted: Fri Dec 14, 2007 5:15 pm Post subject: |
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Joined: 14 Dec 2007
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The friction will slowly slow down the plane, because this question does not allow for mechanical failures (such as melted, seising parts)
as it slows down, the friction drops, and the plane speeds up again.
How fast will the wheels be going?
in mph?
in rpm?
how fast will the plane be going in the small window that the plane speeds up and slows down?
this is realy complicated stuff, so... I'l give you most of the facts you'll need (we might not be able to get them all)
4 engines
Engine thrust is 63,300 pounds (28,710 kg) on the current model.
its maximum takeoff weight is 910,000 pounds (412,770 kg)
16 wheels
unknown radius
unknown wind resistance
(you'll need to find both of those to do the math, obviously)
all aluminum parts
it doesn't need to be perfect, what is a close estiment?
can anyone do the math? |
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| Shaderwolf |
| Posted: Sat Dec 15, 2007 1:41 pm Post subject: |
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Joined: 13 Dec 2005
Posts: 312
Location: Las Vegas, Nevada (wanna play?)
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Will the wheels accelerate indefinately, or will they just move at twice the speed backwords.
Yes, the turbines are pushing air and not ground. however, I belive that the wheels must move (relative to the ground ) for any motion to take place.
If the turbines push the airplane to a speed of 180mph (the take-off speed for one of those airplanes) than the wheels would be moving twice the speed as the airplane, only 360 mph (180 for forward motion, 180 because of the runway) for the plane to experiance any forward motion at all, the wheels must mobe faster than therunway. They can't... the runway will always keep up. they will always be racing eachother. The turbines, however will be pushing the plane forwards. If the plane stops accelerating, it will stand still. If the plane accelerates, the ramp accelerates to. There becomes a physical imposibility. How is it that a plane can move forwards, (a motion that requires the wheels to move faster in one direction than the ramp in another) while the ramp keeps up with him? the movement forwards is what causes the motion of the wheels. As soon as the motion happens, will it not be almost immediately counteracted by the motion of the ramp? The acceleration of the wheels to a tremendous speed would be almost instant. What happens now? The problem is becoming more and more complicated!
Forward motion is made imposible! as infinity is introduced to the equation by the first motion (that motion wich cannot exist) we jump out of the relm of physics, and into the realm of impossibility.
This is a much wordier reitoration of Steve F's last post.
There motion is imossible, because of a variable that depends on motion, there are no possibilities. (unless a 180mph huricane came by and swept the airplane off of it's feet. without desroying it)
Imagine what happens to the wheels as they reach the speed of infinity.. The outside will suddenly move at c. as the inside(still conected to it) tries to reach it. one item now has parts moving at the speed of light and under the speed of light at the same time. they travel in differant dimentions. The outside of the wheel ceases to be matter. another impossibility, but it's fun to imagine, isn't it?
nist7:
I'm interested to know what results other forums produced. could you give us some of their hyperlinks? |
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