Physics question.. can you figure it out?

[TType84]

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?

this is very simple.. do not overcomplicate it.

what do you think tb.com?

 

[disco stu]

With no air speed, the wings cannot generate lift. Nothing will happen.

This has to be some sort of trick question.

 

[jpratt]

With no air speed, the wings cannot generate lift. Nothing will happen.

This has to be some sort of trick question.

Yes it can take off. Think about how a airplane works.

 

[dgreen1069]

Nope, it will sit on the conveyor burning lots of fuel. There needs to be accellerated air passing above and below the wings to produce lift.

 

[JC Turbo]

The plane is driven by engine thrust and not by the wheels. Therefore the plane would accelerate and create enough airspeed to lift off.

 

[TType84]

so we are 50/50 not counting me so far :biggrin:

 

[Buick From Hell]

To expound on JC Turbo's explanation:

The plane is "moving", so it will take off. And the conveyor is only going to spin the planes wheels, so it doesn't matter WHAT it's doing. It can be going 10x as fast as the plane in the opposite direction, all it will do is spin the planes tires.

 

[bishir]

Ok, I agree if there is no airflow over the wings it can't take off, but I think the premisis of the question is misleading. THe airplane is using it's engines to produce thrust and the wheels are not the driving force. Therefore, the speed of the runway will not matter and the plane will still travel down the runway and takeoff the plane is moving through a fluid (air) and that is what is propelling it not th wheels on the runway. That make sense?

 

[mydesigner]

No it cant take off. If the conveyor belt start spinning to the same as the wheels, there is no way it can get airflow, the thrust of the engines will push the plane forward will just push the planes tires. If there were no wheels, it was just sitting on its belly, the conveyor would match the sliding of the plane and it will not move in a forward momentum to cause the lift used by the wings. Unless were talking about a herrier.

 

[justabuickv6]

It will not take off. No air flow over the wings. Ground speed creates air flow over the wings. If the airplane is stationary, there will not be any air speed.

Remove the conveyor belt theory, place the airplane one inch above the ground. Spin the tires as fast as you can.....did it take off?

 

[bishir]

To add what I said... so if the runway speeds up to match the plane's speed it will just spin the wheels of the plane faster, but the plane will accelerate still the friction from the runways on the wheels will not be enough to keep it stationaiy or in other words the runway would just create slightly more drag but not nearly enough.

 

[disco stu]

To add what I said... so if the runway speeds up to match the plane's speed it will just spin the wheels of the plane faster, but the plane will accelerate still the friction from the runways on the wheels will not be enough to keep it stationaiy or in other words the runway would just create slightly more drag but not nearly enough.

OK, yeah, duh. Now I feel dumb. It does not matter how fast the conveyor is moving, thrust will still propel the plane forward.

 

[bishir]

Ha, don't feel bad, the real answer is probably that that the runway/conveyer belt would speed up so fast trying to match the planes acceleration that the wheels would exceed their speed rating and/or create enough frictional heat to catch fire and destroy the plane. Then the only thing they could use that runway for anymore would be the first ever Boston Marathon on a treadmill!

 

[gn85]

Thanks.. now I have something to think about while I'm trying to go to sleep. Right now, I agree with Bishir. When I get up tomorrow I'll post more.

 

[myclone]

Assuming the plane isn’t anything special (vertical take off or similar) my vote is the plane will just sit there with the engines WFO making a lot of racket.

Since a plane has to have air flow over/under the wings to generate lift and the only way that can be generated in a normal air craft is by movement through the air which the conveyer belt going the other way eliminates there is no lift to allow the plane to take off.

 

[PCS74]

This question can be answered by either logical reasoning or physical reasoning. In either case the plane will take off.


Something to consider for those of you still on the fence... Can the aircraft have velocity without motion? If the aircraft has no motion, how can the control system regulate the velocity of the conveyor to match that of the aircraft?

Chris S

 

[corsair231]

The original question states that the airplane moves. If the plane moves then it can takeoff. Once the speed of the wing is sufficient to create lift it can fly. It doesn't matter what the wheel speed is because they freewheel. The runway moving in the opposite direction only increases the wheel speed. Reverse the runway to match the speed of the plane and the wheels will not turn but the plane will still take off when airspeed is sufficient. But if a butterfly flaps his wings in the Rockies......?

 

[salvageV6]

Try walking against an eskitlator going at the same pace you are.

No wind, you don't go nowheres, and hence no lift.

The term motion is for directional movement, if the speeds are matched there won't be any real motion.

Assuming a perfect control system there won't be any movement and no air over the wings.

Now with a catapult and some decent thrust you'd be all set.

If the plane didn't have wheels for takeoff there would be other points of friction for it to overcome to generate lift from moving on the ground and getting air over the wings.

As long as the control system can reverse the wheel speed which is the plane coupled to the ground, the plane sits and it ain't gonna take off.

 

[HighPSI]

No brainer. The plane flies since the wheels are only holding the plane up and not propelling the plane forward (like legs on an escalator).

 

[Epitome]

The plane will take off. Thrust from the engine is independent of the wheels, which can just free wheel. Pretend the jet is a hovercraft over the conveyor belt, just like wheels that can spin freely. Better yet, think of the scenario kind of in reverse. Pretend that the jet is hooked on a strap in the back to a dyno that measures how hard it pulls. the wheels don't move at all but there is tremendous measurable force pushing the jet forward. The friction created by the spinning wheels on the conveyor belt is negligible.