6 Sep 2006 10:56
You are talking about zero airflow overthe wings, it wouldn't take off.
If the system was setup so that the plane ws first fixed by some giant imaginary hand, than the conveyer would simple rotate the wheels (imagine the planes mass is not pressing on the conveyer surface, the hand is holding it up and resisting the parallel force being applied to the wheels)
remove the horizontal force of the hand and replace it with the engines thrust, which in this assumption is perfectly parallel to the conveyer force, the hand is still holding the plane resisitn gits mass pull down on the conveyer, if the forces where balanced the wheels would resmeble the wheels of a car on a bhp testing thingy, going really fast, the conveyer and thrust act in the same direction on the rotation of the wheel but in opposite directions on the body (plane) it would remian motionless but the wheels would be going like hell.
However in reality, without the magic hand holding the mass of plane it would be more likely the wheels would skid along the moving surface due to the mass of the plane pushing down on the wheels generating huge fiction, due to forces invloved the wheels would last a couple of seconds before blowing out. look at how much smoke is gnerated when the wheels are forced to spin up to an instant couple of hundred mph on the non moving runway..
SOS
6483 posts since 12/10/04
6 Sep 2006 11:16
hmmm so your saying that despite the jet engines thrust, in theory the plane would stay still and not move? Would the jets engines not still push the plane along in the air, be it on the ground.
For exmaple, I am on a scateboard on a treadmill, but not moving, however if someone in front of me had rope around my wasit and pulled me and i would in fact move forward despite the moving converor belt on the wheels?
6 Sep 2006 12:23
If the thrust force is greater than the force generated by the treadmill in the opposite direction then of course some small acceration in the direction of the thrust force would occur, however in the friction less wheel situation the wheel would be spinning very fast due velocity of the treadmill
eg treadmill = -10 mph
thrust = 11mph
velocity of 1 mph in the thrust direction
wheel spinning at 10mph (approx)
6 Sep 2006 12:32
If where talking the plane, complicated, gravity is strong enough to keep the plane driving and around on the surface, it couldn't fly as there is no atmosphere so no lift. If would be like a mental big car.
On the tread mill there is less force pushing down on it so more likely to have the spinning wheel senario.
SOS
6483 posts since 12/10/04
6 Sep 2006 12:38
do doodle, if a plane was to be flying already, and approached a conveyor belt to land that matched its speed what would happen?
6 Sep 2006 12:49
I typed along one out but it crashed.
F = ma, so if the convey was producing force in the direction of the plane travel it would land then be rolling on it and appear to be travelling twice as fast to a reference bystander, this is like a flat escalator in airports
Opposite direction on the conveyer, would be a very rapid de-accelaration, like hitting a wall of wheel friction was strong enough.
poof
116 posts since 29/4/06
6 Sep 2006 18:29
its 0130 for me here.
what about the majority?
SOS
6483 posts since 12/10/04
6 Sep 2006 18:42
doodle i stil ldont get your reply mate
in theroy , assuming the wheels dont break etc, where is this wall on landing then? I mean if i ran and jumped onto a treadmill running against me i woul dcarry on running but not move right? So what about the plane landing? the wheeels would turn with the ground speed, but the the movement of the treadmill would compensdate for the momentum no? SO it would just stop dead on landing correct?
6 Sep 2006 18:43
18:42 - Is the clock on here correct ?
6 Sep 2006 18:47
thought i was going mad
6 Sep 2006 18:48
its not…change it in your otions you loons.
Posted: Wed, 06/09/2006 - 6:47pm
6 Sep 2006 18:57
i think it would fly as the energy is not being forced form the ground up, as in the wheels are not the source of power.
the power lies within the engines which have no connection to the travelling ground.
so wouldnt the plane just roll over the ground as the force is generated from the wings to push the weight from on top of the wheels to behind???
also on a side note, if you let a bird loose on a plane say the plane is big enough for it fly aorund in, would it eventually be drawn to the back of the plane?
or better yet, an open top bus, if you throw a ball in the air on the bottom floor it will go in a stright vertical line.
if you thrown the ball up in a vertical line say 5 feet on top of the bus, how far will it go back, if at all.
if you're sitting at the back of the bus on the top open deck and throw the ball forward but diaginally upwards, can you throw it hard enough with the right amount of speed for it land in your lap????
6 Sep 2006 19:01
also (sorry to drag on), what would happen if a car is in the back of a moving truck which is say half a mile long.
if the car is facing the opposite direction as the truck and the back door opens, the car builds up speed and drives out the back of the truck while it is moving, what direction would the car end up going??????
stoney
16709 posts since 22/1/05
6 Sep 2006 19:07
need to start digesting this thread after a couple more glasses of red
6 Sep 2006 19:07
Ok the read mill is moving in the opposite way to your movement. Put a stationary object onto it, it sticks to it the travels in the direction of the treadmill. Its energy is absorbed by friction in the horizontal and by the treadmill pushing back up on it in the vertical. Becasue it sticks it then travels in the direction of the treamill, the wall is the deacceralting force the treadmill applies to the object to get it to stop then stick (in combination with friction) obviosuly with a wheeled device friction is less as the wheels spin.
As the plane lands normally it has a speed say constant 100mph the ground applies a force vertical to stop the plane sinking inot the floor and friction on the wheels slows it down. The rate of negative accelartion is small, so hence the force felt by the plane . passengers is small.
you feel a bump upwards but you are not pinned in your seat on landing like you are on take off, this is horizontal not vertical force.
If the runway was a treadmill, you would feel the force like when you break hard in a car, that is becasue the ground is now producing a horizontal force to slow the plane down, if the speed was the same, it would deaccerate the plane from high speed to low speed very quickly.
By F = ma with m and a being very large you have a massive force on the plane, hence the wall effect.
Crashing the car inot a wall is the same type of rapid deacceration.
