Sam
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 @ this thread.
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Cosmo
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quote:
Originally posted by LiVe LeE
even though the wheels arnt driven per se - when the aircraft is on the runway/conveyor belt - it is through these wheels that forward propulsion is achieved surely!
If the wheels and hence ground speed is set to zero - as the conveyor belt moves at the same rate as the wheels, the aircraft essentially would be stationary with NO forward propulsion!
When on the conveyor belt, with no coherent wind conditions - there would be no difference between the relative air speed and ground speed, as the two are in contact - the two can only change once the aircraft has taken off
as these two are the same, I dont see that forward propulsion would be gained
Steve using your analogy; the toy car on the tread mill - in order to remain in equilibrium ( ie not move forwards or backwards) the force from your finger and gravity must be equal and opposite to the force generated between the tread mill and wheels - in order to move the car out of a state of equilibrium you will have to overcome the force of the treadmill - by applying and accelerant! this force would in no way be equal to the force required to move the toy car whilst not on the treadmill; it would be equal to the required acceration + the force required to keep the car in equilibrium
as such, if no forward motion (thrust force) is made by the aircraft, no lift will be generated by the wings; the plane wont take off!
thats in my opinion and I've been accepted to read a Masters of Aerodynamics at Southampton University starting Setember 2007 - although what do I know!
any chance you can change that degree to something else before its too late?
The wheels arent driven, so although the converyor belt will speed up as the wheels do the thrust from the engines will still move the plane down the converyor belt. Its just the wheels will be turning alot faster than on a normal run way.
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RichR
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it all hinges on wether or not a forward propulsion will be made - in my opinion and interpretation of the question; the conveyor will act in an equal and opposite capacity to the plane - in which case the forces acting on the aircraft will be in equilibrium - which in turn will give no forward propulsion and would lead to no lift and no take off
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gianluigi
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quote:
Originally posted by LiVe LeE
it all hinges on wether or not a forward propulsion will be made - in my opinion and interpretation of the question; the conveyor will act in an equal and opposite capacity to the plane - in which case the forces acting on the aircraft will be in equilibrium - which in turn will give no forward propulsion and would lead to no lift and no take off
 to that
[Edited on 24-05-2006 by gianluigi]
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RichR
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whilst on the copnveyor - the wheels and the plane are as one, the plane would be in equilibrium; the forces are exerted through the wheels, to the conveyor - hence no forward propulsion
if the plane is in effect in equilibrium - it will also be visually stationary with the wheels spinning faster amd faster with increased ground speed; but will make no headway
the acceleration of the plane is a result of the thrust of the engines proppelling the aircraft forwards via the wheels
the only way that the conveyor idea would work would be if the aircraft was in a permanent state of levitation - in which case it wouldnt need the conveyor or runway
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Cosmo
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quote:
Originally posted by LiVe LeE
it all hinges on wether or not a forward propulsion will be made - in my opinion and interpretation of the question; the conveyor will act in an equal and opposite capacity to the plane - in which case the forces acting on the aircraft will be in equilibrium - which in turn will give no forward propulsion and would lead to no lift and no take off
thats what I was orignally posting (not so technically!) and starting to think I was still correct!
Imagine your driving a car with a rocket on the back on a converyor belt. Obviously the car wheels are driven at first and the conveyor belt matches this speed so it move nowhere. Now what it the rocket kicks in, to achieve forward propulsion the wheels would have to turn faster and if this happened the conveyor belt would speed up and the car would still not move.
The only way it could move is if the wheels didnt speed up, but for this to happen it would have to skid down the conveyor belt.
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RichR
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but it doesnt matter - the wheels are attached to the ground plate - the ground plate moves in an equal and opposite capacity to the thrust in order to maintain equilibrium
the only way it could be overcome would be if there was a limiting factor as to the gyration of the conveyor belt - in which case the plane could essentially increase its thrust to overcome this conveyor speed - however the plane would require so much thrust to overcome this and the length of the conveyor would need to be ridiculously long - the idea is shit - it would never work nor be practical
as I said what would I know - I've only spent four years reading Aero-Hydrodynamics as a part of my course
[Edited on 24-05-2006 by LiVe LeE]
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Brett
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I think Lee speaks sense.
Won't take off. Like I said 
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RichR
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and if the wheels didnt speed up - neither would the conveyor and you'd still be in an equilibrium condition
it all hinges on being able to overcome the effects of the conveyor - as the question is worded so ; I assume this is not possible and so the plane would never overcome this
One way it could have a benefit IMO would be if you could take the planes groundspeed up to say 3/4 take off speed - then shut the conveyor off completely so the plane darts forwards - this would mean that shorter runways could be used as the planes would have a prempted runway speed - would only require the final thrust levels
however - I'd imagine the forces of hitting the solid ground at those sort of speeds would require huge structural improvements to the landing gear
[Edited on 24-05-2006 by LiVe LeE]
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3CorsaMeal
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engines off = plane would move with conveyour
engines on - it will move along conveyour but take more force
sorted 
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Brett
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quote:
Originally posted by 3CorsaMeal
engines off = plane would move with conveyour)
only if the brakes were on
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RichR
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wont move along conveyor regardless, the conveyor moves in an equal and opposite way to the plane - plane wont move; plane wont produce lift; plane wont take off
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Cosmo
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quote:
Originally posted by 3CorsaMeal
engines off = plane would move with conveyour
engines on - it will move along conveyour but take more force
sorted
why would it move forward? If the engines started, the wheels would turn quicker and so would the conveyor.
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Steve
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quote:
Originally posted by LiVe LeE
it all hinges on wether or not a forward propulsion will be made - in my opinion and interpretation of the question; the conveyor will act in an equal and opposite capacity to the plane - in which case the forces acting on the aircraft will be in equilibrium - which in turn will give no forward propulsion and would lead to no lift and no take off
no no no your not correct!!! you say it is through the wheels that there is propulsion? no, its through the jets, how does the plane stay up in the air when the wheels arent even touching the fuckng ground!!
i agree there will be some degree of cancellation of force due to friction and gravity of the weight of the of the aircraft and the conveyor movong backwards, but the plane would still move forwards nad take off
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3CorsaMeal
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no as there is nothing holding the plane in place, like pulling a table cloth out from under stuff.
have to be a really quick movement and eventually the friction would occur
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stuartmitchell
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are we assuming the conveyor belt is at a fixed speed or increasing speed at the same rate of the aircraft? 
My head hurts 
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3CorsaMeal
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quote:
Originally posted by Cosmo
quote:
Originally posted by 3CorsaMeal
engines off = plane would move with conveyour
engines on - it will move along conveyour but take more force
sorted
why would it move forward? If the engines started, the wheels would turn quicker and so would the conveyor.
the plane isn't turning the wheels, its pushing the air
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Steve
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YES 3corsameal understands, the wheels are freewheeling, the air and the jets are making the propulsion the conveyor has NO or VERY LITTLE opposite force on this fixed force
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3CorsaMeal
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the wheels just do what they gotta do to get it done 
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Cosmo
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quote:
Originally posted by 3CorsaMeal
no as there is nothing holding the plane in place, like pulling a table cloth out from under stuff.
have to be a really quick movement and eventually the friction would occur
gravity is keeping it in place, and that wont be cancelled out until their is airflow over the wings, and that wont happen without forward movement, and forward movement wont happen while the wheels are touching the conveyor as that will keep cancelling out any other forward movement.
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RichR
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because the plane ahs two conditions - the condition on the ground is completely diofferent to the condition in the air
the wheels grip to the tarmac and gravitational forces acting myust be overcome to produce lift - if the plane has no forward motion ( as we are lead to believe it is in Equilibrium) then it wont have the airflow over the wings - it wont take off
Its on the ground - the forward motion is exerted through the wheels and to the groundplane - if the ground plane moves equally and opposite (as the question leads to me to believe) then no forward motion will be given
so Steve No, No, No it is you who is wrong
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stuartmitchell
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a plane takes off using the aerofoil shape of the wing to deflect more air under the wing to create upforce, correct?
This process is enhanced using massive jet engines and thrust, The question is:
is the plane displacing enough air to get it off the ground? I think the answer is yes
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Cosmo
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quote:
Originally posted by Steve
YES 3corsameal understands, the wheels are freewheeling, the air and the jets are making the propulsion the conveyor has NO or VERY LITTLE opposite force on this fixed force
but to move along the conveyor the wheels will have to turn as its not in the air yet, yes? Even if they arent driven, gravity is keeping the wheels in contact with the conveyor so no matter what the trust the wheels will have to turn and the conveyor would cancel this out.
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Steve
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quote:
Originally posted by LiVe LeE
because the plane ahs two conditions - the condition on the ground is completely diofferent to the condition in the air
the wheels grip to the tarmac and gravitational forces acting myust be overcome to produce lift - if the plane has no forward motion ( as we are lead to believe it is in Equilibrium) then it wont have the airflow over the wings - it wont take off
Its on the ground - the forward motion is exerted through the wheels and to the groundplane - if the ground plane moves equally and opposite (as the question leads to me to believe) then no forward motion will be given
so Steve No, No, No it is you who is wrong
the wheels do not grip the tarmac, the wheels are free wheeling, yes there is a small amount of frictional force through bearings etc but not much.
the plane is not propelled thru the wheels, if they were then yes it would not move, but the plane is propelled thru the jets
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RichR
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the weight of the plane and friction between the wheels and conveyor mean that the plane would stay in place (assuming no limiter on the conveyor speed)
the wheels are attached to the plane; or are you saying that the plane and wheels move at a completely sepearate rate; ie the two dont move together - and the plane breaks apart, hits its nose on the tarmac, burns and everyone on board dies?
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