A Strange and Thought-provoking riddle
Sat, 12/10/2005 - 10:35 — mJaber
Here's the scenario...
An airplane is on a conveyor. The conveyor is set to match the speed of the airplane in the backwards direction. However fast the plane moves, the conveyor moves just as fast.
Can the plane take off?
Re: A Strange and Thought-provoking riddle
I know the answer I believe but I don't know if I should type it in here or see what the next person gets. OK I will PM you MJABAR.
Re: A Strange and Thought-provoking riddle
Not if you don't turn the plane "on."
Re: A Strange and Thought-provoking riddle
Only from a woman! =D>
That is a compliment by the way.
Re: A Strange and Thought-provoking riddle
I am assuming the plane is on and the conveyor is working in the opposite direction and this isn't a trick question.
The plane can never leave the ground becuase lift isn't generated. There is no lift becuase there is no change in air speed or pressure around the plane because despite the work being done by the plane, the conveyor is exerting and equal and opposite amount of work to zero out any actual displacement of the plane.
The plane isn't going anywhere.
Now if they put a huge fan in front of the plane and it increased it's power in proportion to the speed of the plane. Lift would be generated and the plane would lift off the conveyor, then what?
Re: A Strange and Thought-provoking riddle
Wrong.
If MJaber permits I have the perfect example of the explanation already saved in a email I sent a friend. Or should we let more people guess?
Yes the aircraft is running as if it were trying to take off and the conveyer is running backwards. As if you were on a people mover going the wrong way.
Re: A Strange and Thought-provoking riddle
Go ahead, George...
Re: A Strange and Thought-provoking riddle
Yes it will.
Your answer:
The aircraft has engines that through action/reaction principles cause it to accelerate in relation to the AIR not the belt.As the aircraft starts to move the belt will move in the opposite direction, the only effect this will have is to increase the speed of rotation of the tires, the plane will continue to accelerate in relation to the air and the ground beside the moving belt no matter how fast the belt moves. This may have detrimental effects on the tires but will not detrimentally affect the AIRSPEED of the plane. In fact, air entrained by laminar boundary layers on the belt may actually enhance the airflow to the wings, shortening the takeoff run. Depends on how long the landing gear legs are. In the 60's a plane was built with a hovercraft type skirt instead of regular gear, this plane wouldn't even notice the increasing speed of the belt.
If you need another example I have a few.
Re: A Strange and Thought-provoking riddle
I'm sorry to controdict you George, but your conclusion would only apply to a limited number of aircraft. The conditions you quote would depend upon the type of aircraft, amount of power produced, and wing configuration. While some aircraft might be able to take off, most will never get airborne. Also, you are not taking into consideration of the disruption in the airflow caused by the movement of the belt. While it may work for some craft in theory, it would more than likely not work in practice.
Re: A Strange and Thought-provoking riddle
It took me quite some time to understand the answer as well.
You have to remember that the wheels of the plane (the only contact with the conveyor) have nothing to do with propelling the plane. The wheels of an airplane are not powered in any way. The forward motion of the plane is created by the thrust of the engine(s). Regardless of how fast the conveyor moves in the opposite direction of the plane, there will be little to no affect of the movement of the plane. The only part of the plane that would be affected would be the speed of the wheels.
Re: A Strange and Thought-provoking riddle
:?
Not sure what you mean by "limited number of aircraft", but I cannot think of any airplane (other than ones that cannot fly in the first place) that would not be able to take off.
I am assuming that the wheels are free rolling.
As long as the plane's engine provided enough forward thrust to exceed the drag (and a little rolling friction) the plane would move forward. When the forward velocity generated enough lift to exceed the weight of the plane, it would lift off the ground.
Check out more info on how a plane flies here:
http://travel.howstuffworks.com/airplane.htm
Initially, there would be some (relatively very little) rolling friction that the thrust would have to overcome as well, but most would agree this is negligible as all planes have to and do overcome this rolling friction in order to take off every day.
If anyone is thinking in terms of a runner on a treadmill, you have to disconnect the physics behind a plane flying from that of a runner. The plane pushes forward independently of the ground while a runner is dependent on the ground in order to push him or herself forward.
The conveyor and the wheels are a red herring here and would have no bearing (pun intended :) ) on whether or not the plane could take off.
Finally, for the win, I am writing this from inside an airplane where I asked the pilot and first officer this very question (through the flight attendant) and they both assured me that the airplane would take off citing most of the items I mentioned above. These are Continental Airlines pilots in case it make a difference to you.
:)
Some other sites who are discussing this as well:
http://www.physicsforums.com/showthread.php?t=101259
http://txfx.net/2005/12/08/airplane-on-a-conveyor-belt/
http://www.airliners.net/discussions/tech_ops/read.main/136068/
http://www.ar15.com/forums/topic.html?b=1&f=5&t=413254&page=2
Re: A Strange and Thought-provoking riddle
The way I explained it to my kids is this:
OK, I am on a bike with no chain (because the air craft does not power it wheels either.) on a people mover at an airport. I am tied to the end of it. the people mover starts to move in the direction opposite the way I am tied off too. What happens to me and the bike? Right, I stay still. What happens if I start to pull on that rope? Right I move towards the end. The pulling of the rope is like the jets/engine. It is in fact the only source the air craft uses to move. It never uses it's wheels.
As far as OneArmBandit, what type of aircraft might that be. I can't think of one. Maybe you are right I just don't know one that uses it's wheels.