Airplane + Conveyor Belt
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nopers, won't fly
- skt0
I'm not sure what the answer is. But under your reasoning Nairn a plane landing at 300Kph onto a converbelt moving at 300kph in the other direction would stop, just like that.
Can't see it.
- ribit0
Yes, you are missing the fact that the extra drag on the wheels (the wheels will spin faster in this scenario) is the only effect that a moving runway will have on this plane.
All that energy used to move the conveyer is,well, moving the conveyer belt, but has little effect on a high powered vehicle with freewheeling wheels.
The forward motion of the plane is only affected by engine thrust, air resistance (big), the initial static wheel spin and tyre deformation resistance (small), and dynamic wheel spin resistance (very small)
- determinedmoth0
I'm not sure what the answer is. But under your reasoning Nairn a plane landing at 300Kph onto a converbelt moving at 300kph in the other direction would stop, just like that.
Can't see it.
skt
(Feb 14 06, 07:03)In space it would work a treat.
- skt0
I'm not sure what the answer is. But under your reasoning Nairn a plane landing at 300Kph onto a converbelt moving at 300kph in the other direction would stop, just like that.
Can't see it.
skt
(Feb 14 06, 07:03)In space it would work a treat.
determinedmoth
(Feb 14 06, 07:06)In space i could fly by farting.
- rupedixon0
lets ask Steve Fossett to answer this question for us once and for all, when he gets back from his latest longest flight attempt. It would seem that he was the only person rich enough and stupid enough, and into planes enough to be bothered to try it out.
This isnt a physics question its a logic question, if the conveyor belt could keep the plane stationary (which it clearly couldnt in the real world), then no, the plane couldnt take off, but its one of those really pedantic questions that relies upon the uber conveyor belt, that managed to nullify the planes thrust. If such a thing were conceivable then it could theoretically stop planes from taking off.
jesus, give me my five minutes back
- ribit0
"In space it would work a treat."
why? Have we rescinded the laws relating to momentum?
- ribit0
"I just asked the guy next to me with a PHD in physics, who pretty much says the same thing. The plane would move forward, but it wouldn't have enough forward thrust and if it tried to lift it would crash."
Could you get him to elaborate on what is altering the thrust/motion situation? Why exactly does it not have enough thrust? Did someone do something to the engines? (Or did he mean it would not have enough speed?)
- shilohous0
the thrust is fighting the negative momentum, like paddling up river
- determinedmoth0
Could you get him to elaborate on what is altering the thrust/motion situation? Why exactly does it not have enough thrust? Did someone do something to the engines? (Or did he mean it would not have enough speed?)
ribit
(Feb 14 06, 07:14)Extra friction = slower plane = less uplift = no take off.
"All that energy used to move the conveyer is,well, moving the conveyer belt, but has little effect on a high powered vehicle"
disagrees. It's quite a drag and planes are very heavy, causing this drag.
- determinedmoth0
"In space it would work a treat."
why? Have we rescinded the laws relating to momentum?
ribit
(Feb 14 06, 07:12)Not at all, but there is no air friction - you dont need lift.
- ribit0
"the thrust is fighting the negative momentum, like paddling up river"
sure, but remember you have big engines with lots of thrust, and this is nothing like the effect on the boat.... the planes only contact with the conveyer is through its freewheeling wheels, which simply have to spin to match the higher relative speed of the conveyer, so you have:
- normal takeoff groundspeed
- normal takeoff airspeed
- wheel rotation double its usual amount (a small amount of extra drag to overcome, but not a problem given the thrust reserves of all aircrraft)
- -scarabin-0
of course it can't take off
- ribit0
"Not at all, but there is no air friction - you dont need lift."
Whats that got to do with stopping?
- joyride0
If the conveyor could keep the plane motionless, the plane will not fly.
But the conveyor will not be able to do this. The thrust will pull the plane forward, the wheels will spin faster trying to keep it still, but they will just spin faster.
If you were to pull the plane with a string forward on the conveyor (=thrust) would it matter how fast the conveyor spins in the opposite direction?
- shilohous0
wrong, if the pull of the conveyor is equal to the thrust of the engine thrust, they cancel each other out and you have 0 ground speed, and 0 airspeed needed for lift.
all it is, is a huge waste of energy.
- ribit0
"Extra friction = slower plane = less uplift = no take off."
Extra friction= pilot puts in a bit more thrust. Easily overcome.
"disagrees. It's quite a drag and planes are very heavy, causing this drag."
The weight of the plane is a constant in both scenarios. All thats changed here is extra drag at the wheels (right?) Or have I missed another area of increased drag?
- ribit0
"wrong, if the pull of the conveyor is equal to the thrust of the engine thrust, they cancel each other out and you have 0 ground speed, and 0 airspeed needed for lift.
all it is, is a huge waste of energy"thats the thing... the pull of the conveyer is way less than the thrust of the engines. They dont cancel out.
- determinedmoth0
Extra friction= pilot puts in a bit more thrust. Easily overcome.
ribit
(Feb 14 06, 07:27)No! Planes aren't built to provide that extra thrust! There's no way it's as tiny as you think it is. It's probably several tonnes worth... A fighter jet maybe, but not an average plane.
- determinedmoth0
"wrong, if the pull of the conveyor is equal to the thrust of the engine thrust, they cancel each other out and you have 0 ground speed, and 0 airspeed needed for lift.
all it is, is a huge waste of energy"thats the thing... the pull of the conveyer is way less than the thrust of the engines. They dont cancel out.
ribit
(Feb 14 06, 07:29)Agreed on that point.