Riddle Me This.........

big_pete · 29-11-2005, 10:26 PM

ok, ive seen this on a couple of forums now, and i dont think a conclusion has been reached for this little problem........

Quote:

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?

so what do you think????

EBFalcs · 29-11-2005, 10:28 PM

No. the plane won't take off. it's just like you being on a treadmill you are not moving but your legs are. in a planes perspectivr it would be your wheels if the plane isn't moving the wind can't lift it

LTDHO · 29-11-2005, 10:33 PM

No it can't.

It needs speed relative to the world not the ground!

It'll probbly run very hot and blow up!!

Bluefreak · 29-11-2005, 10:35 PM

No... The planes wheels will be rolling at(pluck a figure out of my butt)100mph but there would be no air flow over the wings... Without the airflow, you lose the pressure differential required to generate lift.

GT595 · 29-11-2005, 10:41 PM

Confusious asks - Does your car Drive you from A to B when your on the Dyno????
Wheres Newton when you need him - Id say No - the plane would not fly....

EBFalcs · 29-11-2005, 10:42 PM

damn! your right, i must have fallen asleep during that part of physics ;

EBFalcs · 29-11-2005, 10:43 PM

who cares

29-11-2005, 10:49 PM

It will take off.. A plane uses air for displacement to move forward. The wheels of it would just be spinning like crazy tho...

GT595 · 29-11-2005, 10:49 PM

Quote:

Originally Posted by Malakai

Of course it can take off. The wheels of the plane do not provide any force to move it. The engines do. So it is of no consequence that the ground below the plane is moving the opposite way. All it means is that the wheels of the plane will be spinning twice as fast as they would during a take off from solid ground.

Just a thought - wouldnt the friction of high speed (from a normal take off) cause the lift under the wings. If the aircraft is stationary at all times this wouldnt be available.....

Quote:

Originally Posted by ArgonEF

It will take off.. A plane uses air for displacement, whereas a car uses rolling contact.

twas a joke.... :Reverend:

EBFalcs · 29-11-2005, 10:51 PM

the air craft won't be stationary. it's propelling itself by the wind

EBFalcs · 29-11-2005, 10:52 PM

the air craft won't be stationary. it's propelling itself by the air

Walkinshaw · 29-11-2005, 10:59 PM

the aircraft will take off.

IF the aircraft used its wheels to provide thrust then no it wouldn't.
Seing it uses air displacment then yes it will take off. The aircrafts wheels will be turning at 2x the speed of the aircraft relitave to the air.

DOC · 29-11-2005, 11:05 PM

My Call = NO

It would not matter how fast / slow the tread mill / plane was going i could stand in front of the wing ( away from the jet ) and there would be no further air rushing past me than there would be if the plane was stationary, it would need the air travelling over the wings to create a lower pressure on top of the wing to lift it off the ground and it wouldnt be there.

Blue Oval Mopar Man · 29-11-2005, 11:06 PM

the plane will take off as the wheels dont have any effect on the plane momentum other than to keep it off the ground by being a very low friction point of contact when the plane is not flying !

zetec · 29-11-2005, 11:06 PM

If the conveyor can track the plane's speed on a moving road, it would track that of the plane and not the wheels. Regardless of wheel speed, if it is on a moving road/conveyor, the plane's fuselage speed is always going to be zero relative to the stationary environment around it, thus the conveyor itself will never move if dependent upon the fuselage speed.

Moral of the story, the conveyor will never move, nor will the plane.

OR

It will take off at regular speed with the wheels spinning twice as fast as normal ground speed.

I'm leaning more toward the second one... can't decide.

GT595 · 29-11-2005, 11:07 PM

It isnt moving - stationary in the sense it is not shifting a cm from its starting point because of the conveyors equal travel speed in the reverse direction. Surely even with air displacement you would need extra force to fight gravity - hence the flap direction changes on the wings etc during takeoff to maximise this air change against the plane and under the body of the plane to get it off the ground...
This is one for the Myth Busters - not me.....

EA_Bender · 29-11-2005, 11:09 PM

No it wont take off, there is no pressure difference over the top of the wind and below it. yes there is air passing thru the engines but there is nothing near the wings.

If the engines blew the air over the wings then yes it is a posibility

LUXO_8 · 29-11-2005, 11:12 PM

someone go get a plane and put it on a treadmill

flappist · 29-11-2005, 11:18 PM

Ok guys.....

Conveyor in opposite direction.
Aircraft (for sake of fact rather than hypothesis) Cessna C172R
Nil wind, nil gradient, standard friction surface.

Throttle applied, aircraft accellerates to, say, 30 kts indicated air speed.
Conveyor senses 30kts and applies 30kts in opposite direction which has negligable effect on aircraft other than spin wheels at 60 kts.
Conveyor notices that aircraft is still going 30kts so increases its speed to 90 kts compensate.
Conveyor notices that aircraft is still going 30kts so increases its speed to 120 kts compensate.
During this time aircraft is still accellerating....

This continues to happen until:

a) The aircraft accellerates faster than the conveyor can compenstate and reaches 60kts IAS before the wheels rip off due to friction. Aircraft rotates and commits aviation.

b) The aircraft accellerates at the same speed that the conveyor can compensate and either the conveyor blows up or the gear collapses as they would be doing infinity kts. (actually this would happen immediately because as soon as the aircraft moved the conveyor would constantly increase speed because it has no effect on IAS).

Conveyer in same direction.
Aircraft accellerates to 60kts IAS, rotates and pilot is happy as there in no wear on landing gear as it is not moving.

Wheels on aircraft are just there to reduce friction, some come with skis or floats....

Capt Flappist ARN 540335 (guess where my name came from)

zetec · 29-11-2005, 11:19 PM

Quote:

Originally Posted by MADNC_8

someone go get a plane and put it on a treadmill

duaned · 29-11-2005, 11:28 PM

Quote:

Originally Posted by zetec

You legend!

**Captain Stubing** · 29-11-2005, 11:29 PM

The aircraft is in contact with the conveyor belt. Any forward motion attempted by the aircraft to get up to speed is NEGATED by the conveyor belt.

Therefore, no actual movement of the aircraft, so no airflow over the wings.

The aircraft will sit there, engines going redline, till there's a theoretical meltdown, and then the conveyor belt will slow down...

DOC · 29-11-2005, 11:32 PM

if it was a harrier jet ( S ) it could take off.

**Charliewool** · 29-11-2005, 11:32 PM

Ohhhhhh F**K... zetec... surely ONLY a bent Maribyrnongnite could come up with that.........You ARE a nut! (Photo shop lessons to the right)

rodderz · 29-11-2005, 11:41 PM

I'm with others here, how the hell can the plane lift off with no foreward movement, whereby air speed is needed to create the pressure differences on the top and bottom of the wings which lift it up? If you're not moving through the air, it will be like standing still with zero air speed!

zetec · 29-11-2005, 11:42 PM

The man asked for a plane on a treadmill.

:

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

:

**Charliewool** · 29-11-2005, 11:55 PM

Quote:

Originally Posted by zetec

The man asked for a plane on a treadmill.

:

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

:

And Magnificently presentated too zetec!...
To a "layman" like me... The thrust, wheelspeed, AND LACK of forward underwing air pressure is made perfectly obvious now!... (how many people are on the plane BTW?)

**Captain Stubing** · 30-11-2005, 12:07 AM

It's an impressive read, but I can't buy it. He says it's all about air speed, but this plane doesn't seem to get any, the way I see it.

zetec · 30-11-2005, 12:20 AM

Put it this way. Imagine running on a treadmill, the faster it goes, the faster you run, you still go nowehere. That's like a car on a treadmill.

Imagine you running but you're holding onto a rope tied to a wall in front of you. No matter how fast you're running, all you have to do it pull the rope and you'll move forward off the treadmil as fast as you pull your arms. This is like a plane. It get's it's propulsion by pushing the air through the engines regardless of how fast the wheels are going.

Therefore, even with the wheels spinning at 300km/h on the dyno, increasing the thrust of the engines will simply roll it forward as per normal like nothing has happened.

The only strange thing is when it rolls off the dyno, onto solid ground, it'll be doing a 300km/h burnout under momentum of the wheels and might slightly lurch forward a metre until the wheels grip and return almost instantly to airplane speed.

Makes sense to me.

THORNSPAWN · 30-11-2005, 03:17 AM

I agree with everyone who thinks it WILL take off.
It's a plane not a car it doesn't use the wheels to accelerate it uses thrust, air, gasses
to push it forwards, the conveyor can be travelling as fast as it wants in the other
direction the thrust will still be pushing the plane forward. The only way you could prevent it from taking off would be a huge fan moving the air in the opposite direction
matching the engines thrust. wheel speed has nothing to do with it.