Airplane + Conveyor Belt
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- ribit0
The Pilot's Lounge #94: It's The Medium, Manfred:
http://www.avweb.com/news/column…
- ribit0
another point to consider:
Air flow induced by the moving belt may slightly increase the planes airspeed, which may shorten the takeoff run (a bit)
- determinedmoth0
That's where we differ then ;)
- ribit0
"No, but it's obvious. If I parked a plane on your head, you'd die under several tonnes of pressure. The friction that causes between plane and ground, and I am guessing, is HUGE, and not insignificant "wheel drag". It's very significant."
Yes I would die under the weight of the plane.
But planes seem to deal very nicely every day with this weight (due to big wings and big engines) , and a bit more drag on the wheels due to a doubling of their rotation speed isnt going to be such a big deal in percentage terms..
- ribit0
"so ribit - you are saying the plane has airspeed?
if i'm running on a treadmill my hair doesn't blow in the wind..."
Thats because you arent moving relative to the air in the room. You are running forward at the same speed as the belt moves backwards. The plane has abit more power than you do, and it doesnt push against the ground (or against the air to any great extent for that matter).
- determinedmoth0
Do you have any references for this 'several tonnes' amount? We're only talking increased wheel drag here...remember airspeed for takeoff is not increased.
ribit
(Feb 14 06, 07:34)No, but it's obvious. If I parked a plane on your head, you'd die under several tonnes of pressure. The friction that causes between plane and ground, and I am guessing, is HUGE, and not insignificant "wheel drag". It's very significant.
- Nairn0
no, what ribit's envisaging is a state where thrust and belt are expending so much energy, that the focus (the wheels) turn into an electromagnetic plasma, creating a frictionless interface between plane and belt, at which point the infinitely-thrusting plane will be able to overcome the belt's limitations and begin accelerating to air take-off speed.
i think.
I concede.
but I'm still right. :)
- joyride0
it would if you sat on a turbine engine with wheels on it... =)
If you put a plane on a conveyor belt with a string attached. Pull the plane forward... what happens to the wheels as the conveyor tries to go faster. they go faster. The only way to negate the pull of the string forward is to have something pulling it in the opposite direction. Freewheeling wheels do not achieve this.
- jakeyj0
so ribit - you are saying the plane has airspeed?
if i'm running on a treadmill my hair doesn't blow in the wind...
- ribit0
"well, it is supposed to be a kickss conveyer that can match the speed right?"
we've already established that the conveyer is matching the aircrafts speed...the question is how much of a drag component does that apply to the plane through its wheels.
- joyride0
wheels are freespinning right, then you will get a little friction. but the thrust will easily overcome that. the 2 forces are independent, thrust pulls the plane forward no matter how fast the conveyor is spinning
- ribit0
"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."
Do you have any references for this 'several tonnes' amount? We're only talking increased wheel drag here...remember airspeed for takeoff is not increased.
- Nairn0
this is going no further than the innumerate ID threads..
- shilohous0
well, it is supposed to be a kickss conveyer that can match the speed right?
- 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.
- 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.
- 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.
- 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?
- 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.
- 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?