Lets see the BRAINS of RME

[BioNuke1]

if the plane is moving forward at the same rate the conveyor is moving backward, the plane is still sitting in the same point in space, and the air around the plain is still basically sitting there too (assuming there isnt a 60mph headwind) same thing as a car on a dyno or a fat chick on a treadmill, the speeds cancel each other out and you stay in one spot

The plane will go nowhere
since the plane relies on air moving around the airfoil to creat lift (weater by the plane moving through stationary air, or air moving past the stationary plane)

 

[Meat_]

...same thing as a car on a dyno...

Is that why they have to chain the car to the ground on the dyno?

 

[BioNuke1]

Is that why they have to chain the car to the ground on the dyno?

the rollers move at the same surface speed as the tire, they cancel each other out- thats the whole point, so the car doesnt go anywhere. The chain is mostly for safety, so the car doesnt move sideways as you slam it through the gears or jump the rollers going 150mph, ive seen a car idle on one w/o a chain and it dint take flight or stay in a holiday inn express

its the acceleration/deceleration that causes it to want to 'derail', the rollers wanting to remain at 'rest' and not accelerate and all that scientific bs

 

[way2nosty]

Is that why they have to chain the car to the ground on the dyno?

Not even! they strap the car down just in case that big metal drum full of water under the tires accellerates and decellearates at a different rate then that nice neat aluminum wheel that only weighs 20#s.

the answer to the question is No, it won't here is the formula to calculate lift. The lifting force must be greater then the weight of the aircraft.

L=CL*p*V^2/2*A


where:

CL is the coefficient of lift,
ρ is the density of air (1.225 kg/m3 at sea level)*
V is the airspeed
A is the surface area of the lifting surface
L is the lift force produced.

Obviously, we are ignoring the complexity of vorticity, viscosity and compressibilty of the air, but this demonstrates the point and it's easier then solving or explaining Bernoulli's.

set V to 0 see what happens. the L becomes undef=0

 

[Meat_]

Not a good comparison, a car on a dyno isn't driven by the air it's driven by the wheels, and a chick on a tread mill is driven by her feet.

And my point was that even if it was a good comparison you'd still be wrong because something with good acceleration will drive right off of a dyno if it's not chained down.

Not even! they strap the car down just in case that big metal drum full of water under the tires accellerates and decellearates at a different rate then that nice neat aluminum wheel that only weighs 20#s.

the answer to the question is No, it won't here is the formula to calculate lift. The lifting force must be greater then the weight of the aircraft.

L=CL*p*V^2/2*A


where:

CL is the coefficient of lift,
ρ is the density of air (1.225 kg/m3 at sea level)*
V is the airspeed
A is the surface area of the lifting surface
L is the lift force produced.

Obviously, we are ignoring the complexity of vorticity, viscosity and compressibilty of the air, but this demonstrates the point and it's easier then solving or explaining Bernoulli's.

set V to 0 see what happens. the L becomes undef=0

You missed the sarcasm in that post.

 

[BioNuke1]

Not a good comparison, a car on a dyno isn't driven by the air it's driven by the wheels, and a chick on a tread mill is driven by her feet.

And my point was that even if it was a good comparison you'd still be wrong because something with good acceleration will drive right off of a dyno if it's not chained down.

My comparison was about the opposite speeds canceling eachother out so that you are stationary. Fat chick sprinting at 3mph, treadmill holding her back at 3mph means she is still just beyond arms reach of the TV remote in the living room.

and acceleration is not relevant, as stated in the question, there is a control device that will exactly match the planes speed, canceling out any acceleration/deceleration

 

[waynehartwig]

This caused a thread of more than 200 pages on another board due to people being idiots....lets see who's smart on here. :greg:


A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

The question is:

Will the plane take off or not? Will it be able to run up and take off?

I know the answer!
A plane can't stand!

 

[Brad]

Under the conditions of the question and no assumptions, the plane will fly. What really simplified it for me was to quit regarding the conveyor runway as the airplane's medium of movement. The plane's thrust is never transferred to the runway, therefore the runway's counter-thrust is of little influence to the plane's forward motion.

 

[Meat_]

I'm done with this thread before I start saying something rude.

 

[Brad]

http://www.avweb.com/news/columns/191034-1.html

 

[BioNuke1]

Under the conditions of the question and no assumptions, the plane will fly. What really simplified it for me was to quit regarding the conveyor runway as the airplane's medium of movement.

Isn't that the whole point though? that the conveyor is holding the plane back at the same speed the plane is going forward?

if the plane is not moving forward through the air, obviously it wont lift off, is the plane IS moving forward (fast enough) it will lift off

 

[way2nosty]

http://www.avweb.com/news/columns/191034-1.html

doesn't mean he's right. If you take an airplane hold it up with a crane and let it get to 30 Knots or whatever the stall speed is then turn it loose, it will hit the ground! no ifs ands or buts about it, the answer is no, it wont fly. Look a the math, the moment you set the airspeed to nill the function becomes nill.

 

[Brad]

Under the conditions of the question and no assumptions, the plane will fly. What really simplified it for me was to quit regarding the conveyor runway as the airplane's medium of movement. QUOTE]

Isn't that the whole point though? that the conveyor is holding the plane back at the same speed the plane is going forward?

if the plane is not moving forward through the air, obviously it wont lift off, is the plane IS moving forward (fast enough) it will lift off

It's tough, which is why I initially suggested that the plane was going nowhere. But the link posted does a MUCH better job of explaining than I ever could. Simply put, because the runway is not the medium of acceleration and velocity so it has no effect to counter the plane's movement.

 

[way2nosty]

It's tough, which is why I initially suggested that the plane was going nowhere. But the link posted does a MUCH better job of explaining than I ever could. Simply put, because the runway is not the medium of acceleration and velocity so it has no effect to counter the plane's movement.

The airplane is on wheels, without them the plane can't acheive any airspeed at all, because it would be scraping it's belly on the ground the whole time, and the prop would hit the ground. DO THE MATH! unless the airplane the entire airfoil can make 30Knots of forward progress or come agains a 30 Knot wind it isn't going to lift off, the prop or jet or whatever produce thrust which moves the airfoil which in turn produces lift, otherwise, why doesn't an air craft carrier have a giant treadmill on the front of it to catipult jets into the air.

 

[Brad]

The airplane is on wheels, without them the plane can't acheive any airspeed at all, because it would be scraping it's belly on the ground the whole time, and the prop would hit the ground. DO THE MATH! unless the airplane the entire airfoil can make 30Knots of forward progress or come agains a 30 Knot wind it isn't going to lift off, the prop or jet or whatever produce thrust which moves the airfoil which in turn produces lift, otherwise, why doesn't an air craft carrier have a giant treadmill on the front of it to catipult jets into the air.

The wheels under the plane are essentially free-spinning, a conveyor running equal to a 30 knot wind eastbound is not going to prevent the plane, pulling air aft, reaching the 30knot westbound needed to lift. The wheels will be spinning equivalent to 60knots but the plane will take off.

 

[James K]

I'm done with this thread before I start saying something rude.

wuss

 

[Badger]

i can't believe that people don't understand that priciples of thrust.its not that frigin hard .the motion of the ground has nothing to do with airspeed.air speed is produced by thrust .thrust is produced by the movement of air through a prop or jet.no matter how fast the ground moves its not affecting the air which is what the airplane is using to move not the ground.

its very simple a plane moves air not the ground so the ground is irrelivent

 

[ZUKEYPR]

Not a good comparison, a car on a dyno isn't driven by the air it's driven by the wheels, and a chick on a tread mill is driven by her feet.

Wrong, a fat chick on a tread mill is driven by bon-bons , not her feet!

 

[Greg]

http://www.avweb.com/news/columns/191034-1.html

Good link, it sums it all up at the end-

Here the propeller is pushing against the air, as it does every time an airplane takes off. How fast the airplane is moving over the surface on which its wheels rest is irrelevant; the medium is the magic. On a normal takeoff -- no conveyor involved -- if there is a 20 mph headwind, Manfred and the J-3 will lift off at 45 mph indicated airspeed; but relative to the ground, it is only 25 mph. Should the wind increase to 45 mph and if Manfred can get to the runway, he can take off without rolling an inch. His airspeed is 45 and groundspeed is zero. It is not necessary to have any groundspeed to fly, just airspeed. Conversely, if Manfred has a lot of runway and nothing to hit, and takes off downwind in a 25 mph tailwind, the propeller will have to accelerate the airplane to a zero airspeed, which will be a 25 mph groundspeed, and then on to a 45 mph airspeed, which will have him humming across the ground at 70 mph. The speed over the ground, or a conveyor belt, when an airplane takes off is irrelevant; all that matters is its speed through the air, and unless the pilot sets the brakes, a moving conveyor belt -- under the freely turning wheels -- cannot stop the process of acceleration.

 

[BioNuke1]

ok i'm going to try to break this down the way i am imagining it.

ok image first thing you put the plane on the conveyor and turn the converyor to 30mph.

the plane is going backwards at 30mph.

now slowly throttle the plane until it is stationary to a single point on the ground.

this is the equalibrium.

at this point the plane obviously will NOT lift off cuz the air isnt moving around the wing at all.

now if you throttle the engine hard, the plane will overcome the conveyor because the acceleration if coming from the air being pushed by the prop and not through the wheels. the plane will slowly gain speed and eventuallly take off.


the question is kinda vague and there is alot to be considered, but theres my solution for each view