Will this plane take off?

[newbrew]

"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."

The question is: Will the plane take off or not?

[JAYROD]

i say no way.

[JAYROD]

why is the plane standing?

[Mealticket]

absolutely not.
Ther's no air speed present

[newbrew]

I say it will.

The wheels are not what propel the airplane, thrust is. I say all the tredmill will do is make the wheels spin faster. The tredmill can spin as fast as it wants or needs to, but the plane will still move forward.

[Mealticket]

then make you question more clear.
You're saying that the point of refrence that the plane starts @ nvr changes becasue the treadmil matches the planes speed so it never moves forward or backward in space, correct?

[Mealticket]

if the treadmill matches the ground speed it wont take off, you have to have airspeed to take off, not ground speed

[newbrew]

I believe the question is clear, but its obviously written in a way to make you think a little...theres no debate if its TOO obvious.

All the question states is that the tredmill matches that of the planes (wheels) speed.

[Schmidty]

no it wont get off the ground

[Kale]

A plane takes off buy virtue of the speed of the air rushing over the wing thus inducing lift, in this scenario the wheels are spinning but there is no air movement so thus no lift. Obvioulsy there is a trick in the question that I am not seeing

[Mealticket]

I believe the question is clear, but its obviously written in a way to make you think a little...theres no debate if its TOO obvious.

All the question states is that the tredmill matches that of the planes (wheels) speed.

First off it's not clear, if you understood principals of aviation you would see that ground speed and air speed are two completly different things.
Your question says, "speed", it doesnt specify which

[newbrew]

If the plane starts to move forward, the tredmill compensates...all this does is make the free spinning (virtually frictionless) wheels spin faster.

[Kale]

"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)."

The question is: Will the plane take off or not?

I am wondering if the trick is here somewhere

[newbrew]

I am wondering if the trick is here somewhere

Im not sure, its just a question that ive seen around on some boards. If there is any 'trick', its in the wording itself like the previous poster here mentioned. However, I do not believe the writer intends for the reader to dig into the wording too much in order to figure out the answer. Its the concept.

Let's attack it this way.....

We start with a tredmill moving at 150mph backwards while plane sits on it stationary. Plane fires up and starts to create thrust.

[SMAN12b]

is this a prop plane or a jet engine?

a prop plane needs forward movement to cause thrust and lift
a jet engine produces its own thrust and thus could possible take off from a stand still

then again.............

if the conveyor counteracts any forward movement, there would still be no air flow over the wings to produce lift.......


I say NO it won't take off

[newbrew]

Here is my final answer:

So long as the wheels can handle the extra stress of spinning 2x as fast, the plane will fly.

[SMAN12b]

Here is my final answer:

So long as the wheels can handle the extra stress of spinning 2x as fast, the plane will fly.

OK, you can't just leave it at that. care to explain why 2x as fast gets it up???

[Kale]

A plane needs air rushing over the wings to create lift. All thrust does is give the plane forward motion and the forward motion allows the air movement to provide lift. No Forward motion = No Lift unless like in a wind tunnel where the air is blown at high speed over the wing which would also create lift. Where is Johan when you need him !!!

[Bojangles69]

**** I gotta actually think about this one for a minute.

[Doc.Sust]

if this would work, dont you think the army,navy and airforce would use this as for a way that planes would be able to take off from air craft carriers and places where there isntenough room for runnways, this idea cant work,if it did, it would be in use today

[Bojangles69]

Ok, NO.
If you had a wind tunnel in addition to the conveyer belt than yes it would lift off. And basically fly midspace w/out actually moving forward.

But yeh, whole point is its got to move through the air to create lift, standing still that plane aint going anywhere.

[Bojangles69]

Certain planes I believe have thrusters that point downwards though and they can lift off without runways so in that case a plane like that (vertical jets) would fly right off the conveyer belt.

[newbrew]

if this would work, dont you think the army,navy and airforce would use this as for a way that planes would be able to take off from air craft carriers and places where there isntenough room for runnways, this idea cant work,if it did, it would be in use today

Im not an engineer, but I imagine a system like that wouldnt be very cost effective compared to the technologies that are currently working just fine.

[newbrew]

Found this on nasioc...

[Doc.Sust]

nope,plane is not moving an inch

[Doc.Sust]

Im not an engineer, but I imagine a system like that wouldnt be very cost effective compared to the technologies that are currently working just fine.

think about this, when did the US govenment ever care about what is cost effective when it comes to military technology?

[newbrew]

Here are a couple answers I found somewhere else:

My answer is it depends on the plane's thrust. If you have for
example, a model plane that weighs 5 oz, and the motor produces 10
oz of thrust the plane should take off. My theory is based on
thefriction formula F=u R, where f= friction force, u is friction
coefficient, and R= weight. With the highest possible coeff. of
1.0, the most force the conveyor could exert is 5 oz, leaving 5 oz of
thrust left over. The plane effectively now has a 1:1
thrust:weight ratio, and applying slip & stick law, should still be able to
move forward. Is this correct?


-----------------------------------------------


Yes, the plane can take off. The key is that the plane's wheels
*freewheel*, they are not driven. the conveyor belt therefore provides
NO force to the plane (OK, there's a little friction in the bearings
which could provide a couple of pounds force to a nomal GA category
airplane, but that's insignificant compared to the thrust. For an RC
plane, the situation should be similar). The prop pushes the plane
through the air until it reaches takeoff AIRspeed, which is the same no
matter how fast the wheels are going. So if you were inside watching
the instruments, you would observe that the wheels are spinning at a
GROUNDspeed different than the indicated AIRspeed, but that does not
matter, since it is AIRspeed you need in order to take off. (Caps
added for emphasis).

Your friction calculation basically assumes you have skids instead of
wheels, and would be basically correct for that case, but notice that
velocity does not appear anywhere in the equation. If you had a plane
with skids, it would take off if it had the power to get sliding with
or without a conveyor runway. It would not matter how fast the
skid-to-runway surface were moving. The friction force F = u * N is
the same at either groundspeed.

Hope this helps!

[Doc.Sust]

well i will be damned!

[newbrew]

odkjofj

[Bojangles69]

Here are a couple answers I found somewhere else:

My answer is it depends on the plane's thrust. If you have for
example, a model plane that weighs 5 oz, and the motor produces 10
oz of thrust the plane should take off. My theory is based on
thefriction formula F=u R, where f= friction force, u is friction
coefficient, and R= weight. With the highest possible coeff. of
1.0, the most force the conveyor could exert is 5 oz, leaving 5 oz of
thrust left over. The plane effectively now has a 1:1
thrust:weight ratio, and applying slip & stick law, should still be able to
move forward. Is this correct?


-----------------------------------------------


Yes, the plane can take off. The key is that the plane's wheels
*freewheel*, they are not driven. the conveyor belt therefore provides
NO force to the plane (OK, there's a little friction in the bearings
which could provide a couple of pounds force to a nomal GA category
airplane, but that's insignificant compared to the thrust. For an RC
plane, the situation should be similar). The prop pushes the plane
through the air until it reaches takeoff AIRspeed, which is the same no
matter how fast the wheels are going. So if you were inside watching
the instruments, you would observe that the wheels are spinning at a
GROUNDspeed different than the indicated AIRspeed, but that does not
matter, since it is AIRspeed you need in order to take off. (Caps
added for emphasis).

Your friction calculation basically assumes you have skids instead of
wheels, and would be basically correct for that case, but notice that
velocity does not appear anywhere in the equation. If you had a plane
with skids, it would take off if it had the power to get sliding with
or without a conveyor runway. It would not matter how fast the
skid-to-runway surface were moving. The friction force F = u * N is
the same at either groundspeed.

Hope this helps!

Totally contradicted himself. The prop aint pushing the plane through shit. Its just spinning which Is moving the wheels forward. If the conveyer belt keeps the wheels spinning BUT theres no FORWARD movement.
The plane aint going anywhere. So mr. f = u * n can lick my ballz imo.

[gixxerboy1]

Totally contradicted himself. The prop aint pushing the plane through shit. Its just spinning which Is moving the wheels forward. If the conveyer belt keeps the wheels spinning BUT theres no FORWARD movement.
The plane aint going anywhere. So mr. f = u * n can lick my ballz imo.

Yes it will. The prop pushes air that moves the plane. The wheels don't. Its not a drive system. they are just rolling on the wheels. If the ground is moving backwards (treadmill) the wheels will just spin twice as fast. The prop is still making it move forward.

[Bojangles69]

Ok you have a plane with a propellar. The prop spins and pulls the plane forwards as it build momentum and reaches flight speed, the point where air pressure above the wings drops (creating a vacuum) and lifts the plane up.

So if the planes on a conveyer belt. The prop is spinning but the plane is stationary. The props job is to pull the wings through the air. If the wheels are on a conveyer the wings are stationary and the only air thats going through the wings is from behind the prop which cancells out forwards movement because the prop is ATTACHED to the plane.

This = stationary wings, which makes it impossible for air pressure above the foils to drop and create lift. Thus again, I stick to my answer 100%.

And where are you getting that the wheels will spin twice as fast? If the conveyer belt is matching the planes speed the wheels are spinning as fast as they would in a normal take off situation.

[gixxerboy1]

Ok you have a plane with a propellar. The prop spins and pulls the plane forwards as it build momentum and reaches flight speed, the point where air pressure above the wings drops (creating a vacuum) and lifts the plane up.

So if the planes on a conveyer belt. The prop is spinning but the plane is stationary. The props job is to pull the wings through the air. If the wheels are on a conveyer the wings are stationary and the only air thats going through the wings is from behind the prop which cancells out forwards movement because the prop is ATTACHED to the plane.

This = stationary wings, which makes it impossible for air pressure above the foils to drop and create lift. Thus again, I stick to my answer 100%.

And where are you getting that the wheels will spin twice as fast? If the conveyer belt is matching the planes speed the wheels are spinning as fast as they would in a normal take off situation.

The wings aren't stationary. Say the plane is moving forward at 50mph. The treadmill moves the opposite direction 50 mph. Since the plane isn't fixed to the treadmill and propulsion from the prop is moving it it will still go forward at 50 mph. The wheels will spin 100 mpg since the ground is moving opposite

[Hoggage_54]

Go to the gym, set the treadmill to a high speed, spread your arms out like you're flying and you will have your answer.

[Bojangles69]

The wings aren't stationary. Say the plane is moving forward at 50mph. The treadmill moves the opposite direction 50 mph. Since the plane isn't fixed to the treadmill and propulsion from the prop is moving it it will still go forward at 50 mph. The wheels will spin 100 mpg since the ground is moving opposite

Ok subtract the wings from the equation for a minute.

The plain is now essentially a car, but instead of having an internal engine its got a jet or propellar. At a certain # of revolutions, the plane will reach a proportional speed depending completely on the weight of the plane.

Say the prop spins at 25,000 rpm. That plane will reach and attain a maximum speed for that # of revolutions. Right?

So you have a car on the conveyor belt. The wheels spin at 50 mph and the conveyor the direct opposite. This is what I mean by "stationary" the car is NOT moving. If there were wings on the car, the wings would NOT be moving, thus being stationary wings.

ANd NO the plane will not STILL move forward. The plane is being held down by gravity where the weight of the plane meets the conveyer belt. The prop can spin at 1 billion revolutions but as long as the conveyer reaches the maximum speed at those revolutions. The only thing moving is the prop, the wheels, and the treadmill.
NOT THE WINGS.

If wings dont move through air, planes dont fly. Simple science.

[newbrew]

First the obvious-but-wrong answer. The unwary tend to reason by analogy to a car on a conveyor belt--if the conveyor moves backward at the same rate that the car's wheels rotate forward, the net result is that the car remains stationary. An aircraft in the same situation, they figure, would stay planted on the ground, since there'd be no air rushing over the wings to give it lift. But of course cars and planes don't work the same way. A car's wheels are its means of propulsion--they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane's wheels aren't motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant. Let me repeat: Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground--and more importantly the air--regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, as you correctly conclude, make the plane's wheels spin madly.

A thought experiment commonly cited in discussions of this question is to imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you'll have to overcome some initial friction tugging you backward, in short order you'll be able to pull yourself forward easily.

As you point out, one problem here is the wording of the question. Your version straightforwardly states that the conveyor moves backward at the same rate that the plane moves forward. If the plane's forward speed is 100 miles per hour, the conveyor rolls 100 MPH backward, and the wheels rotate at 200 MPH. Assuming you've got Indy-car-quality tires and wheel bearings, no problem. However, some versions put matters this way: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way. Everything clear now? Maybe not. But believe this: The plane takes off.

[newbrew]

http://www.straightdope.com/columns/060303.html
http://danbee.wordpress.com/2006/02/...conveyor-belt/

[newbrew]

A riddle was proposed on the Neal Boortz show today:

If an airplane is on a large conveyor belt and is trying to take off by exerting the thrust needed to move it forward at 100 knots, and the conveyor belt starts moving backwards at 100 knots, will the plane be able to take off, or will it just sit stationary relative to the ground, with the backwards speed of the conveyor belt counteracting the forward thrust of the plane?

Astoundingly, Neal and the rest of his crew took the position that the plane would sit there stationary! Good God… this man is a pilot and has a law degree! I could understand a random high school dropout being fooled by this, but a pilot?

Then I googled the riddle, and found a thread on Airliners.net that has been raging on, with the vast majority of people taking Neal’s position… that the plane would not be able to take off.

Their argument is this, to quote one poster:

Thrust acts accordingly to Newtons Third Law of Motion - every action has an equal and opposite reaction. In the case of an aircraft, the reaction of the engines is that of forward motion, against whatever medium it is stationary. But the ground the aircraft is sitting on in this case is NOT stationary, its providing an exactly CANCELLING force pushing the aircraft back.
The problem here, of course, is that the poster (and Neal) cannot disengage themselves from seeing the airplane as a car. The difference between a car and a grounded airplane is that a car uses its wheels to propel itself forward, and an airplane moves itself forward by moving air. They assume that the runway moving backwards would move the plane backwards. This is what would happen with a car (that is in gear), so why not for an airplane? Well, because an airplane’s wheels are free rolling. There is obviously some friction, so there would be some small backwards force, but it would be infinitely small as compared to the forward thrust of the airplane.

You can test this with a piece of paper and a matchbox car (which has free rolling wheels like an airplane… or like a car in neutral.) Place the paper on a table, and place the matchbox car on the paper. Take your hand, and hold the car still with a lightly placed finger on top of the car. At this point you are providing no forward thrust, and the “conveyor belt” is not moving. The car remains stationary. Now, continuing to hold the airplane with a lightly placed finger, and start to pull the paper out from under the car, in the backwards direction. According to Neal’s logic, the car should push back on your finger with the same force that you are exerting on the paper… but this is not what will happen. You will find that your lightly placed finger is not stressed to any noticeable extent. The paper will slide out, and the wheels will spin, but the car will not be propelled backwards. The reason for this is is that the rotation of the wheels is not related to the movement of the matchbox car except by the very small friction component of the axle, which your lightly placed finger can easily control.

So now we have established that movement of the surface beneath a free wheeling object does not exert a noticeable force on the object. Next, we’ll see what happens when the object is trying to move forward. Attach a string to the matchbox car. Place the car at one end of the paper, and use the string to start pulling the car forward with a steady force. As the car moves forward, start pulling the paper out from under the car, backwards. Do you feel increased resistance as you pull the string? Of course not. The wheels are free rolling! Spinning the wheels does not make the object move!

When an airplane takes off, there is one major forward force… the forward thrust. The main rearward force is air resistance. The turning of the wheels provides a small frictional force, but because the wheels are free-rolling, this friction is very small. Unless the wheels are locked, the friction is always going to be less than the thrust, which means that the overall force is still forward, and the plane will still move.

Gah… people are freakin’ stupid.

Update: There is a variation on this riddle that says that the conveyor belt matches the speed of the plane. It doesn’t matter… the plane still takes off. The conveyor belt could be going 5 times as fast as the plane, and the plane would still take off. You’d get into issues about tires blowing out, but assuming that the wheels can take the strain, the airplane would still take off.

[Hoggage_54]

newbrew, could you say its the same thing as with a jet flying off an aircraft carrier? The cable is like the treadmill, it is resisting as much force as the jet is exerting, and once the jet is free of the resistance of the cable, the jet is in flight almost instantaneously.

I'm not sure if it's the same idea... correct me if I am wrong.

[newbrew]

Stand on a tredmill with some rollerblades on. Tie a rope to the handle bar of the tredmill and hold onto it. Turn the tredmill up to 5mph. How much force/strength does it take to not move? Notice next to nothing. Now turn it up to 10mph, notice it requires the same force/strength? Heck, turn it up to 100mph, ill bet it still requires the same strength. While that tredmill is taching along at 100mph, see how much effort it takes to pull yourself forward. Ill bet an infant has enough strength to do it.

The pulling on the rope to move yourself forward on the tredmil is similar to the thrust of an airplane. Even if the speed of the tredmill is continuing to increase in speed, youll still be able to pull yourself forward.

Once you can grasp that concept, it makes a whole lot of sense.