Airplane Riddle (This one will stump you.)
By ryante
@ryante (14)
United States
November 10, 2006 11:27am CST
Here is a riddle, or in fact, a real theoretical question that is very difficult to answer. Have fun with it.
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 the opposite direction). Can the plane take off?
2 people like this
9 responses
@owlwings (43915)
• Cambridge, England
10 Nov 06
I think it might lift off eventually but it would need something extra to give it the 'bounce' into the air. While there was enough friction between the wheels and the moving runway, it couldn't ever have enough air speed to give it the lift (unless the props were so designed as to thrust air efficiently over the wings). However, any slight bump in the conveyor or a gust of wind towards the plane might be enough to break the physical contact between the plane and the 'ground'. The props would then be generating enough thrust to pull the plane into the air.
It sounds as if it might be a very unstable and dangerous system!
@owlwings (43915)
• Cambridge, England
10 Nov 06
The critical thing is the air speed OVER THE WINGS. If the plane were a jet, it would probably never happen, because a jet depends on pushing the plane through the air. If it were an aircraft with props forward of the wings, so that the airflow generated by the props passed over the wings, then there is a remote possibility, as I say, IF the props (acting as fans) were able to pass air (without too much turbulence, of course) over the wings to generate the necessary difference in air pressure to provide the lift.
I can see the thinking behind such a crazy idea (- lookie! a shorter runway! -) but there are better and safer solutions, in tilt wing aircraft design, for example.
@owlwings (43915)
• Cambridge, England
10 Nov 06
Professors' minds are usually just too full of theory and double integration calculus to be able to think practically!
One could test it quite cheaply - with a model aircraft!
@redyellowblackdog (10629)
• United States
10 Nov 06
Yes, the plane will take off. As the conveyer belt moves, the plane's engine has to move air fast enough to pull the plane forward as fast as the conveyer belt is moving. The air that the engine is moving goes over the airplane's wings at the speed of the conveyer belt as the airplane stays in one place. When the speed of the conveyer belt reaches the airplane's take off speed the air is moving over the airplane's wing at its take off speed. The airplane will then lift off and fly away.
@redyellowblackdog (10629)
• United States
11 Nov 06
What is important for the airplane to take off is the speed of the air going over and under the wings of the airplane. The speed of the conveyer by itself is unimportant. The speed of the aircraft relative to the earth, by itself is unimportant. When the air moves over and under the wings fast enough the plane will lift off. Then instead of remaining stationary to the earth because the conveyer was going just as fast as the plane was pulling itself forward, the plane will move in what would be ordinary flight.
@srhelmer (7029)
• Beaver Dam, Wisconsin
10 Nov 06
Since planes pull themselves through the air, the direction the runway is moving shouldn't have any bearing on whether it can take off or not.
So yes, it can.
@srhelmer (7029)
• Beaver Dam, Wisconsin
10 Nov 06
The plane isn't counting on the wheels for take off, it's counting on the air under it's wings, which will still be there since the treadmill is still simulating movement. The wheels themselves would still be spinning too.
@RAMPersona (2033)
• Philippines
11 Nov 06
yes, it can.
e.g. RAF Harrier jet
catapult-like system in an aircraft carrier
@forfein (2507)
•
10 Nov 06
It would lift off.
It is the air moving over the wings that makes planes fly.
Notice the next time you are sat next to the wing what happens to the leading or trailing edge.
This is why it takes off. It needs speed to get the air moving over the wing.
It would not stay in the air long however if the engines were not working! Unless it was a Glider!
@Jetdanet (1025)
• Portugal
10 Nov 06
i think it cant.
because what matters is the axis between the plane and the earth.
The plane needs more speed in comparission with the earh movement.
The conveyer moving dont change his relative speed to earh.
This is an Newton's Law :) I answered well?
@ryante (14)
• United States
10 Nov 06
I still don't know. I've never found a true answer for it and it has never been tested.
Every answer given is in theory, yet even a professor I read about it stumped on it. First saying it couldn't then saying it could, and then going back to his first answer and still questioning himself. lol
@RAMPersona (2033)
• Philippines
11 Nov 06
yes, it can.
e.g. RAF Harrier jet
catapult-like system in an aircraft carrier
