Will it take off?

[Guest " "]

sputnik

The horizontal force is the belt moving rearward.....gravity keeps the plane on the belt.

Same as a plane on an aircraft carrier.....once in motion....the wheels don't start spinning and the plane takes off.

The carrier turns into the wind, the plane is sent in the same direction as the carrier is going.

If the carrier were to go backwards....and to send the plane in the normal forward direction....you would have to add the rear ward speed to the needed forward speed before the plane will take off.

[bodcaw boy]

Can anyone from the "will not fly" brain trust explain how any horizontal force from the conveyor is transferred to the structure of the aircraft?

If you can't answer that, you can't support your conclusion.

Added: I found this video. It was simply done, but it just might be enough for some disbelievers to see the light.

Amateur Home Video Demonstration

try running on a treadmill. if there were no friction, as soon as you exerted a force on the belt, the belt would move. something about equal and opposing forces or some such nonsense....

engines create thrust....push against "air", makes plane go forward, wheels begin to move, wheels push on conveyor, conveyor moves, plane doesn't, no air goes around wing, wing are cut off, and we have massive buffalo wings....man i'm hungry...........

boy!!

[Guest " "]

There are 28,000 discussions going on right now on the internet about the plane and the conveyor belt. I checked a few threads...and half the folks take the position it wont fly....while the other half takes the position that it will. I'm going to watch Battlestar, mybe the cylons know the answer to this riddle.

http://www.google.com/search?hl=en&safe=off&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=plane+on+conveyor+belt+riddle&spell=1

[DrWho]

Scenario B:

But if you take the frame of reference of a person on the plane - regardless of the force causing it, the wheels are spinning at 10mph (again, as seen by a person on the plane). Then from the perspective of the plane, the treadmill will be moving at 10mph in the other direction causing the plane to be stationary relative to the air. For the plane to move forward on the treadmill, it requires a wheel velocity greater than that on the treadmill, but this isn't allowed because the question says this will never be the case. Basically, the naysayers are arguing that the thrust on the plane is being limited to prevent its wheels from spinning faster than the speed of the conveyor.

Here is the original question, I don't see the restrictions on the wheel speed:

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 major thing that's confusing people is the speed matching thing. I think that's part of the beauty of the question. People get hung up on that. They also get hung up on irrelevant points regarding aerodynamics. There is really nothing wrong with the question - it's very rare in life to encounter clear questions. It's important to able to sift through problems and not get hung up on irrelevancies.

As I've said before, the speed of the conveyor is irrelevant - choose any conveyor speed you want (in the Newtonian sense). Two times faster than the plane, three times faster, or whatever - it just doesn't matter as long the tires don't explode. The action of the conveyor is not transferred to the body of the plane. The planes forward motion is isolated from the action of the conveyor by the wheel bearings. That's why I keep asking anyone to identify and explain how any horizontal force from the conveyor acts on the plane itself.

Scenario B:

Set the wheels on the plane spinning at 10mph as seen by the tachometer on the plane's wheels. This means the treadmill is moving 10mph in the other direction if you use this speed as the determining factor for the treadmill speed. It doesn't matter how you achieve the 10mph on the plane's wheels. You're just not allowed to increase thrust beyond the friction limits of the treadmill as stated in the problem. From an observor on the ground, the plane would be moving 0mph...does this mean the treadmill is also moving 0mph? If that's the case, then the plane will be moving 10mph forward - which then requires the treadmill to be moving 10mph backward and you're back to stationary.

You are trying to apply the speed as measured in scenario A to the speed measured in scenario B. It's a matter of which frame of reference you choose to look at the problem from - people are choosing different frames of reference for their argument because the problem is ambigious in that regard. I personally measure the speed of a plane in relation to the air, but if you want to be annoying (like all the scenario B people) then you are measuring the speed of the plane relative to the conveyor belt.

If you want the plane to move 30mph forward relative to the air, then the plane must be going 30mph faster than the speed of the belt. This is true in every frame of reference.

[sputnik]

try running on a treadmill. if there were no friction, as soon as you exerted a force on the belt, the belt would move. something about equal and opposing forces or some such nonsense....

engines create thrust....push against "air", makes plane go forward, wheels begin to move, wheels push on conveyor, conveyor moves, plane doesn't, no air goes around wing, wing are cut off, and we have massive buffalo wings....man i'm hungry...........

boy!!

The wheels spin freely (like a roller skate). How do they push the conveyor?

speakerfritz: The carrier example is not like the conveyor. Modern carriers launch planes using a catapult system. The vertical forces of the plane's weight (gravity) and the resultant upward force from the conveyor balance each other out until the plane lifts off. You don't need to waste your time with that

[sputnik]

Scenario B:

Set the wheels on the plane spinning at 10mph as seen by the tachometer on the plane's wheels. This means the treadmill is moving 10mph in the other direction if you use this speed as the determining factor for the treadmill speed. It doesn't matter how you achieve the 10mph on the plane's wheels. You're just not allowed to increase thrust beyond the friction limits of the treadmill as stated in the problem. From an observor on the ground, the plane would be moving 0mph...does this mean the treadmill is also moving 0mph? If that's the case, then the plane will be moving 10mph forward - which then requires the treadmill to be moving 10mph backward and you're back to stationary.

You are trying to apply the speed as measured in scenario A to the speed measured in scenario B. It's a matter of which frame of reference you choose to look at the problem from - people are choosing different frames of reference for their argument because the problem is ambigious in that regard. I personally measure the speed of a plane in relation to the air, but if you want to be annoying (like all the scenario B people) then you are measuring the speed of the plane relative to the conveyor belt.

If you want the plane to move 30mph forward relative to the air, then the plane must be going 30mph faster than the speed of the belt. This is true in every frame of reference.

You are reading way too much into the problem and getting confused. There is no "Scenario B". The plane will take off regardless of an observer's frame of reference. You don't "set" the wheels spinning. They spin freely in response to the relative speeds of the plane and conveyor. Once again, the speed of the conveyor (and the wheels) is irrelevant since the plane is isolated from all this action by the wheel bearings.

[bodcaw boy]

try running on a treadmill. if there were no friction, as soon as you exerted a force on the belt, the belt would move. something about equal and opposing forces or some such nonsense....

engines create thrust....push against "air", makes plane go forward, wheels begin to move, wheels push on conveyor, conveyor moves, plane doesn't, no air goes around wing, wing are cut off, and we have massive buffalo wings....man i'm hungry...........

boy!!

The wheels spin freely (like a roller skate). How do they push the conveyor?

speakerfritz: The carrier example is not like the conveyor. Modern carriers launch planes using a catapult system. The vertical forces of the plane's weight (gravity) and the resultant upward force from the conveyor balance each other out until the plane lifts off. You don't need to waste your time with that

grab a fire extinguisher, get a on a skateboard, let er rip, don't you move forward. the fire extinguisher pushes up, you resist so you plant your feet firmly on the board in the opposite direction, that force pushes on board forward, the wheels don't resist so the spin........

boy!!

[sputnik]

grab a fire extinguisher, get a on a skateboard, let er rip, don't you move forward. the fire extinguisher pushes up, you resist so you plant your feet firmly on the board in the opposite direction, that force pushes on board forward, the wheels don't resist so the spin........

boy!!

So far so good. Now put your skateboard on a tread mill and do the same thing - you'll go forward again.

Watch this video again - it's sort of the same thing:

http://videos.streetfire.net/player.aspx?fileid=35E964D9-38DB-4EFD-BE8D-D6BA1A43A06B

[DrWho]

Scenario B:

Set the wheels on the plane spinning at 10mph as seen by the tachometer on the plane's wheels. This means the treadmill is moving 10mph in the other direction if you use this speed as the determining factor for the treadmill speed. It doesn't matter how you achieve the 10mph on the plane's wheels. You're just not allowed to increase thrust beyond the friction limits of the treadmill as stated in the problem. From an observor on the ground, the plane would be moving 0mph...does this mean the treadmill is also moving 0mph? If that's the case, then the plane will be moving 10mph forward - which then requires the treadmill to be moving 10mph backward and you're back to stationary.

You are trying to apply the speed as measured in scenario A to the speed measured in scenario B. It's a matter of which frame of reference you choose to look at the problem from - people are choosing different frames of reference for their argument because the problem is ambigious in that regard. I personally measure the speed of a plane in relation to the air, but if you want to be annoying (like all the scenario B people) then you are measuring the speed of the plane relative to the conveyor belt.

If you want the plane to move 30mph forward relative to the air, then the plane must be going 30mph faster than the speed of the belt. This is true in every frame of reference.

You are reading way too much into the problem and getting confused. There is no "Scenario B". The plane will take off regardless of an observer's frame of reference. You don't "set" the wheels spinning. They spin freely in response to the relative speeds of the plane and conveyor. Once again, the speed of the conveyor (and the wheels) is irrelevant since the plane is isolated from all this action by the wheel bearings.

Sputs, I agree with you, but you're not trying to see the other side of the argument...using whatever force you have to your disposal, propulsion a motor, a wire, whatever - match the speed of the wheels to the speed of the conveyor belt. The naysayers are saying this is a criteria forced by the phrasing of the problem. The fact that you can exert more force to make the wheels spin faster than the conveyor belt is "not allowed". AKA, it's a stupid premise.

[sputnik]

Who,

There is nothing in the problem that constrains the wheels to spin at the same rate as the conveyor. The wheels aren't mentioned at all. The problem just boils down the the question: Does the conveyor inhibit and/or prevent the plane from taking off? Or in the simplest terms: Does the conveyor make any difference?

If there is no thrust from the aircraft, the wheels will spin at a rate to maintain the same tangential velocity as the conveyor. In a frictionless system the plane will remain stationary as the conveyor moves under it when there is no thrust. If we want to account for rolling friction and bearing resistance, it would take very little force to overcome the small frictional components that would comprise a force in the direction of the conveyor motion. You could counter this force with your pinky finger (only a slight exaggeration) and maintain the plane's position. Once the plane applies any thrust, it moves forward regardless of the motion of the conveyor. Thrust or no thrust, the plane is not really affected by the conveyor's motion.

If you want the plane to remain in place once thrust is applied, you must impose an external force to oppose the plane's motion (you correctly mentioned the need for a drive motor or a wire) and this force must be equal to the thrust of the aircraft. There is no mention of such a mechanism in the problem and so no "Option B".

Someone said that gravity somehow pins the plane to the conveyor and it will travel backwards. I can understand how someone might think this. If the conveyor starts up very slowly, there may not be enough force to overcome the static coefficient of the minor frictional forces I mentioned earlier. In a frictionless system, the plane remains in place as the conveyor moves under it (as long as there is no engine thrust). In the real world, it just takes a bit more initial force to overcome the static frictional force and allow the wheels to roll. Think of a magician that swiftly pulls a tablecloth from a table without disturbing the place settings. They must pull quickly and with enough force to overcome the static friction between the plates and the table cloth. If someone tries that slowly, they just drag the dishes off of the table. It's an easier trick with the plane since it's on wheels.

[Guest " "]

"plane spinning at 10mph as seen by the tachometer on the plane's wheels"

Planes do not have tachometers on the wheels, they have airspeed indicators.

[Ray Garrison]

okay, let me take a specific set of circumstances. I'm curious what you think would happen here. This is a restating of the original question, so this is really a different question, I know, but what's the answer to this one?

Suppose the plane was sitting on the belt with its engines off. The belt begins to accelerate at a slow rate, say 1 ft / sec / sec. I'm pretty certain that the plane will move with the belt - I doubt the plane's inertia is sufficient to overcome the static friction of the wheels at such a low rate acceleration. The plane will not move relative to the position on the belt where it started, and it will begin to move backwards relative to the ground at that rate of acceleration.

Now, suppose we set the throttles at a position so the thrust would generate exactly the same amount of acceleration, 1 ft / sec / sec. We start with the plane and belt sitting still. We simultaneously begin moving the belt backwards and start the engines. What happens?

[sputnik]

okay, let me take a specific set of circumstances. I'm curious what you think would happen here. This is a restating of the original question, so this is really a different question, I know, but what's the answer to this one?

Suppose the plane was sitting on the belt with its engines off. The belt begins to accelerate at a slow rate, say 1 ft / sec / sec. I'm pretty certain that the plane will move with the belt - I doubt the plane's inertia is sufficient to overcome the static friction of the wheels at such a low rate acceleration. The plane will not move relative to the position on the belt where it started, and it will begin to move backwards relative to the ground at that rate of acceleration..........

If this is a frictionless system, the plane will not move with the conveyor. If there is friction, as the conveyor accelerates, air resistance would eventually cause the plane to roll forward with respect to the conveyor as the drag force overcomes the minor static frictional force of the wheel bearings.

............Now, suppose we set the throttles at a position so the thrust would generate exactly the same amount of acceleration, 1 ft / sec / sec. We start with the plane and belt sitting still. We simultaneously begin moving the belt backwards and start the engines. What happens?

Once the thrust of the engine exerts enough force to overcome the puny static force of bearing friction (it probably takes a millisecond), the plane rolls, accelerates, and eventually takes off, independent of the motion of the conveyor.

[klipschaholik]

Oh Ray, you've been taken over by the "dark side" of the force. Ray follow your feelings and remember F=ma. (and if that doesn't work go take a class in Statics and Dynamics at your local college)

Come back Ray, it's not to late!

[ZAKO]

The plane will not fly because.......The piolets seat is full of condensed wiled blueberry crap !!!!

[oldenough]

Huh ??????

[Gilbert]

What is there to debate over?

In general, and for the sake of keeping things as simple as possible,.... 2 things are required for a fixed wing aircraft to leave the ground. THRUST (for airspeed) & LIFT (provided by the wings cross sectional geometry).

Neither of these components can occur for the conveyor scenario described, because the engines thrust will be negated by the speed of the conveyor. So all you can do is spin your wheels.

NEXT!

Geeeez, 16 pages of debate for this moronic question,... unfreaking believeable.

[sputnik]

......Neither of these components can occur for the conveyor scenario described, because the engines thrust will be negated by the speed of the conveyor.........

.........Geeeez, 16 pages of debate for this moronic question,... unfreaking believeable.

Gilbert,

How does the speed of the conveyor negate the engine's thrust? I can't wait to hear your answer.

16 pages, because people don't analyze the problem correctly and/or don't bother to read previous posts before they jump in and restate obvious points about thrust and lift.

[Champagne taste beer budget]

Neither of these components can occur for the conveyor scenario described, because the engines thrust will be negated by the speed of the conveyor. So all you can do is spin your wheels.

NEXT!

Oh Boy...

Object: Airplane

Thrust source: Jet Engine

Object weight supported by: Wheels

Wheels resting on: Conveyor

Strap a jetpack on me, tie my feet to a skateboard, stand me on a treadmill.

Object: Me

Thrust source: Jetpack

Object weight supported by: Skateboard wheels

Wheels resting on: Treadmill

You're telling me that if I fire off my jetpack I WILL NOT hit the wall in front of me? Even if we have a Super Duper treadmill with the track surface passing by me at 200 mph, with Super Duper wheel bearings on my skateboard, so I'm just standing on the treadmill going 200, but still holding onto the stationary siderails for support, that firing off the jetpack won't make me hit the wall, or cause me to move forward whatsoever? I thought the jets force was applied directly to the object it was attached to?

The crew of the Space Shuttle are going to be pretty upset to find out this isn't correct the next time they try and use the thrusters to dock up to the space station . Maybe we should call NASA before they do another launch? [H] []

[Ray Garrison]

......Neither of these components can occur for the conveyor scenario described, because the engines thrust will be negated by the speed of the conveyor.........

.........Geeeez, 16 pages of debate for this moronic question,... unfreaking believeable.

Gilbert,

How does the speed of the conveyor negate the engine's thrust? I can't wait to hear your answer.

16 pages, because people don't analyze the problem correctly and/or don't bother to read previous posts before they jump in and restate obvious points about airspeed and lift.

Cool. It just occured to me the Navy's been missing a real opportunity here. These steam catapaults they're using are expensive, dangerous and hard on the planes. *THEY DON'T NEED THEM!!!*

We install a conveyor belt on the flight deck. We put a plane on the belt. We fire up the engines, and start the belt moving backwards. We throttle up the engines and speed up the belt until the belt is going about 500 ft/sec (which ought to be above Vlof for just about any plane I know of), with the plane sitting there furiously burning fuel, stationary on the deck. Then, we *STOP THE BELT!!!* The plane launches forward immediately at 500 ft/sec, safely taking off with a huge safety margin. This is, like, *SO COOL...*

Way to go Klipsch BBS! Making the world safe for technology!