Will the plane takeoff?

[H2 rocks me]

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction) instantly.

Will the plane be able to take off?

[dеiтайожни]

Yes.

[KenP]

No. The plane is "standing".

Or:

No. The plane isn't moving.

[PARAGON]

Originally Posted by KenP

No. The plane is "standing".

Or:

No. The plane isn't moving.

be able to

[BlueTJCO]

it would take off. just think physics, F=m*a. The forward force (from the thrust) in both case is always bigger than the backward force (due to the friction of the wheel and ground, and it's very small compare to the thrust force), therefore the net force is always forward. So the plane will accelerate forward in both cases and take off.


Next Please

[KenP]

Originally Posted by KenP

No. The plane is "standing".

Or:

No. The plane isn't moving.

You're stupid. It will take off.

All the conveyor will do is cause the wheels to spin wildly. Imagine a rocket on wheels on the same conveyor. That rocket is going to take off...with the wheels spinning off.

What the wheels and conveyor do is irrelavent as none of that provides any propulsion. The wheels lower friction and provide for braking.

Theoretically, the conveyor could be moving backwards at double the speed of the plane and it still wouldn't matter. That would only cause the wheels to spin even faster, but the plane will still be getting thrust, moving forward and generating lift.

[SnakeH2]

Originally Posted by KenP

You're stupid. It will take off.

Best arguement yet!!!

[PARAGON]

Originally Posted by KenP

You're stupid. It will take off.

All the conveyor will do is cause the wheels to spin wildly. Imagine a rocket on wheels on the same conveyor. That rocket is going to take off...with the wheels spinning off.

What the wheels and conveyor do is irrelavent as none of that provides any propulsion. The wheels lower friction and provide for braking.

Theoretically, the conveyor could be moving backwards at double the speed of the plane and it still wouldn't matter. That would only cause the wheels to spin even faster, but the plane will still be getting thrust, moving forward and generating lift.

That's not true. Newton's law of motion states that the rocket or plane wants to stay still. As power is applied, as soon as it wants to start to roll, the conveyor moves, sending the motion back to a zero point.

That's where the conundrum lies with this version of the question. The plane can really never get up to any speed because it can't get past zero simply due to the limitations of the question IF you make certain assumptions OR it will take off IF you make other assumptions.

If the speed of the plane will always be instantaneously matched, the forward movement of the plane will never increase relative to it's surroundings.

If the plane starts to move at x MPH and instaneously the belt moves it -X MPH, the body of the plane remains still and actually does not move from a math standpoint.

But, assuming it's not a fictional question and the plane can move past this fictional "barrier of movement" then, as the plane increases it's speed, the plane is moving through the air and the belt is moving beneath and theoretically moving the wheels twice as fast.


That's why there were apparently different versions of the question. The one here was too vague and allowed for the No answer to be argued. The ones Bluehummer posted, that said speed relative to the wheels, changes the whole argument and allows the "body" of the plane to move without respect to the wheels.

[KenP]

I didn't look at his links () so I can't speak for that.

I do know that if I take a bottle rocket and attach it to a Matchbox on a beltsander spinning at full speed, light the rocket, it's going to go. Unless I accidentally sand my fingertips off.

I got my answer by cheating and reading a physics site. No, I didn't read all 15 pages!!!! Just the first and last few.

BTW, when I'm driving down the road and a fly is in the car, why doesn't the fly it the dash when I hit the brakes. And if the fly is flying around from front to back while I'm driving 55, what's the fly's speed in each direction?

[Wisha Haddan H3]

Originally Posted by PARAGON

That's not true. Newton's law of motion states that the rocket or plane wants to stay still. As power is applied, as soon as it wants to start to roll, the conveyor moves, sending the motion back to a zero point.

That's where the conundrum lies with this version of the question. The plane can really never get up to any speed because it can't get past zero simply due to the limitations of the question IF you make certain assumptions OR it will take off IF you make other assumptions.

If the speed of the plane will always be instantaneously matched, the forward movement of the plane will never increase relative to it's surroundings.

If the plane starts to move at x MPH and instaneously the belt moves it -X MPH, the body of the plane remains still and actually does not move from a math standpoint.

But, assuming it's not a fictional question and the plane can move past this fictional "barrier of movement" then, as the plane increases it's speed, the plane is moving through the air and the belt is moving beneath and theoretically moving the wheels twice as fast.

That's why there were apparently different versions of the question. The one here was too vague and allowed for the No answer to be argued. The ones Bluehummer posted, that said speed relative to the wheels, changes the whole argument and allows the "body" of the plane to move without respect to the wheels.

Thank you for the coherent explanation. The only flaw in your evaluation lies in your application of the 3rd law of motion. "For every action there is an equal and opposite reaction".

A car on the conveyor would behave exactly as you describe, since its forward motion is dependent on the force its wheels apply to the conveyor surface. The wheels turn, exerting rearward force on the conveyor belt. The conveyor rolls, absorbing the force and negating forward motion relative to the ground next to the conveyor and the air around it. In other words, although the car moves forward relative to the conveyor, it remains stationary relative to the ground and air.

However, an airplane doesn't have drive wheels. Its forward motion depends the force of the props applied directly to the air. The props turn, exerting force on the air. As air is pushed rearward, the props are pushed in the opposite direction and the plane moves forward through the air, rolling over the conveyor's surface. Meanwhile the conveyor tries to spin, as if to counteract the forward motion of the plane, but the plane's wheels roll freely over it at higher and higher speeds. As the props push air rearward, the wings slice through the static air around the plane until the airflow over the wings produces enough lift for takeoff.

Nothing can stop the plane from taking off unless the tires blow out. Then, the extra friction between the landing gear and the conveyor could crash the plane or slow it down enough to prevent takeoff velocity.

[DURAMAX TIM]

Originally Posted by KenP

You're stupid. It will take off.

All the conveyor will do is cause the wheels to spin wildly. Imagine a rocket on wheels on the same conveyor. That rocket is going to take off...with the wheels spinning off.

What the wheels and conveyor do is irrelavent as none of that provides any propulsion. The wheels lower friction and provide for braking.

Theoretically, the conveyor could be moving backwards at double the speed of the plane and it still wouldn't matter. That would only cause the wheels to spin even faster, but the plane will still be getting thrust, moving forward and generating lift.

same as a float plane or plane w/ skis, wheels don't have to roll to take off.

[PARAGON]

Depends on the plane.

The tires might blow due to the speed.

[BlueTJCO]

Originally Posted by PARAGON

Depends on the plane.

The tires might blow due to the speed.

Thats the correct answer. At 500mph the tires would blow for sure... Aircrafts average take off speed is 120 MPH I think.......

[Mrs.ssippi]

Blue? No, no the answer is yellow. Yes, yellow and that is my final answer. Wait, can I use my phone a friend?

[Wisha Haddan H3]

Yes for self-propelled airplanes but No for gliders towed behind ground vehicles.

In self-propelled airplanes thrust is delivered from the props or jets directly to the air, not to the ground. Since no forward thrust is delivered through the wheels, the conveyor will remain stationary. In fact, the conveyor may even move forward slightly with the plane depending on the amount of friction from the axles and the tire's contact patch. As the plane moves forward through the air, relative airspeed increases, lift is generated on the wings and the plane takes off.

With gliders, thrust is provided by a tow vehicle. If the tow vehicle is a truck on the conveyor, it would deliver its thrust through the wheels to the conveyor. Forward movement would be negated by the conveyor's movement, resulting in zero forward motion. The truck could be going 100 mph (relative to the conveyor) but its airspeed and groundspeed (next to the conveyor) would still be 0. No air would pass over the glider's wings and no lift would be generated for takeoff.

[CO Hummer]

How do you figure the plane can take off when there is no wind moving over the wings to create lift? Can't happen.

[BlueTJCO]

Originally Posted by CO Hummer

How do you figure the plane can take off when there is no wind moving over the wings to create lift? Can't happen.

what do you want to bet?

J/K..........Damn, this question gave me a headache like 3 years ago when it originally popped up on the internet........

[DennisAJC]

Originally Posted by CO Hummer

How do you figure the plane can take off when there is no wind moving over the wings to create lift? Can't happen.

X2 Unless it's a Harrier.

[h2co-pilot]

Originally Posted by CO Hummer

How do you figure the plane can take off when there is no wind moving over the wings to create lift? Can't happen.

X2

[Wisha Haddan H3]

Originally Posted by CO Hummer

How do you figure the plane can take off when there is no wind moving over the wings to create lift? Can't happen.

True that a plane can't take off w/o airflow over the wings to generate lift.

So the underlying question is ... "can a plane generate forward motion (into the wind) on a runway that moves in the opposite direction?"

A car could not, because it generates forward motion by transferring energy to the ground, which would be negated by the conveyor's opposite motion. But a self-propelled plane could still move forward, because it accelerates by pushing the air, irrespective of ground speed or conveyor direction.