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A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?


/dives for cover

no, as they would have implemented that runway on every airoplane on the world, to get rid of the environment activists

I guess if it was a Harrier jet it would be able to take off, but then you wouldn't be needing the conveyorbelt in the first place
Otherwise it will just sit there spinning it's wheels real fast until the tires go and the plane crashes.

there's no airspeed building up, hence no liftoff
in a gymn people on a treadmill don't have their hair blowing either...

cheers, Tom

The plane's potential and kinetic energy would be converted into "futons" and would *appear* to disappear inside itself.


The conveyer belt would then become quickly over populated with people wanted to try out the "fake skating" illusion.

hmm, im prolly just stupid here but wouldnt the force pushing the plane be relative to the air and not the ground? its not the wheels pushing it forwards , but the engines thrust. i would say it would take off almost as normal, but the wheels would spin more trhan normal beneath it

tracks the plane's speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction)

Since the plane would actually get speed, be it anticipated by the conveyor or not, it doesn't matter in which direction the conveyor moves and the plane would be able to take off normally. As piddi says, the wheels would spin double as fast, true. And as long as the speed limits on the tires aren't exceeded too much so they aren't damaged by centrifugal force, the airplane would take off normally. As another consequence of the conveyor moving below the plane, any pedal movement (steering the nose wheel) would have double directional effect too.

A note, if the belt would start turning with out the plane putting thrust, the plane would remain nearly static to the rest of the world - apart from its wheels that would start spinning (generating some drag/momentum so it would move slightly along in the direction of the conveyor).

As another note, an airplane's speed is measured in 2 ways:
- by GPS or inertial navigation systems, calculating moved distance per time, giving an absolute groundspeed, and
- by a pitot-static system, which uses differential airpressure from pitot and static probes, giving an airspeed. Air impacting the pitot probe would increase the pressure as the plane moves compared to the surrounding air, which pressure is measured by probes which are flush with the side of the plane's body.
Groundspeed is interesting to know when one will arrive at a given point, airspeed is used purely for flight operations. Neither of both would be influenced by the conveyor.

piddi wrote:hmm, im prolly just stupid here but wouldnt the force pushing the plane be relative to the air and not the ground? ...

righty right - you score and Royston can have a laugh at us all

cheers, Tom

piddi wrote:...but the wheels would spin more trhan normal beneath it

Why?

Yet there one thing that keeps me thinking.
Normally, when a plane makes speed, the air (molecules) will 'meet' the wings at the full width of them, passing along the underside of the wings.
This causes the underpressure at the upper side of the wings etc. etc.

Now, when the plane is on the conveyer, the engines just 'suck' the air into them.
The air-movement caused by that activity is in no way comparable to the usual airflow under the whole wings, from full left to full right...
So the uplifting power should be considered as much less than under normal circomstances.
Right or wrong?

Counterparts wrote:This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Tracks the plane's speed or plane's tires rotational speed?
Can you clarify this please?

can't be understood otherwise than that the conveyer's speed compensates for the forward power of the plane, this way keeping the plane exactly on it's location relative to the ground on which the conveyer rests

hubird wrote:Yet there one thing that keeps me thinking.
Normally, when a plane makes speed, the air (molecules) will 'meet' the wings at the full width of them, passing along the underside of the wings.
This causes the underpressure at the upper side of the wings etc. etc.

Now, when the plane is on the conveyer, the engines just 'suck' the air into them.
The air-movement caused by that activity is in no way comparable to the usual airflow under the whole wings, from full left to full right...
So the uplifting power should be considered as much less than under normal circomstances.
Right or wrong?

first of all, sorry for not answering your pm yet hubird, i will

and to put it simple, the wheels of a plane is just there to not have the plane laying directly on the asphalt while being on the ground.

i know i used the phrase "pushing power " in my first phrase. i am sorry for this, as it builds on a common misconception ( i actually thought at0m would punish me for that one ).

its all about PULLING power, not pushing. If the propellers was to push the air backwards it would be on the back of the plane, right?

imagine a plane taking off from an icy lake. there would be very little friction between the planes "skates" and the ice. much less then between asphalt an rubber.

now, how did the plane reach the same takeoff-speed?

it sucks the same amount of air over the wings, regardless off what the ground is doing. if ground speed was at all relevant, what happens when the wheels lift from the ground? does a sudden change of physical laws apply?

the mean part of the riddle is the smart distraction by focussing to the relative ground speed of the 'vehicle', while the 'true' propulsion entirely happens within the static (in this context) 'air' environment.
Even knowing the physical principles of lift regarding airplanes, the association of (omnipresent) 'forward movement' by wheels kind of overruled, even with anticipating there would be a catch... otherwise Counterpart wouldn't have posted it
of course you had a slight advantage Piddi - we have no frozen lakes here where airplanes could lift off

cheers, Tom

you know that trick with a blanket on a table full of dishes and with one fast move you tear the blanket off and all dishes are still at their position ?
that's the conveyor belt ...

cheers, Tom

Does the plane have snakes on it?

Hubird, it's not the engines sucking air over the wing. It's the engines applying forward thrust (disregardless if it's pushing or pulling, piddi, it's just forward force) that gives the airplane forward speed. Then, the speed of the air over the wings generates the lift. In short, engines provide forward force, wings vertical. And the conveyor isn't moving any surrounding air...

braincell: snake? or a bunch of birds that start to fly in the cabin?

a snake for a pet and an amulett - grey green skin, a doll with a pin... ?

Yeah at0m, birds in the cabin, planes on the conveyor

Royston, you are a fly in ointment/cat amongst pigeons/....

at0m wrote:Hubird, it's not the engines sucking air over the wing. It's the engines applying forward thrust [...] that gives the airplane forward speed. Then, the speed of the air over the wings generates the lift.

exactly, therefor I was asking myself how the plane on the conveyer can get lifted when no speed is built up