Airplane and Belt Conveyor

[Bob Denman]

Let me see if this is the right way of looking at this... :banghead:
The Turbines are providing their thrust against the atmosphere...
The conveyor is working against the speed attained by the wheels...

While there are opposing forces working hard; they're not opposing each other...
It should (might, maybe, sort of, could...) take off; once the wings are providing enough lift...

I need some Aspirin, and a handgun! :shocked:

 

[ARtraveler]

Let me see if this is the right way of looking at this... :banghead:
The Turbines are providing their thrust against the atmosphere...
The conveyor is working against the speed attained by the wheels...

While there are opposing forces working hard; they're not opposing each other...
It should (might, maybe, sort of, could...) take off; once the wings are providing enough lift...

I need some Aspirin, and a handgun! :shocked:

Please fax me some Aspirin. I will see what else I can find. :roflblack:

 

[Yazz]

A plane is standing on a runway that can move (some sort of belt 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 the opposite direction). Can the plane take off?"

No or yes...

The conveyer belt is moving as fast backwards as the plane is moving forwards, which means the plane has it's engines spooled up but it's going nowhere.

The plane has to reach the proper airspeed to take off, not how fast the wheels are going, or the thrust output, but how much air is flowing over the wings.

Refer back to blowing on a piece of paper, make sure you have parental guidance.

This may be a trick question. Something about a light plane and strong headwinds, in that case, it can be done.

 

[BajaRon]

I wish I'd gotten in on this earlier. But you guys have it nailed as it is airspeed, not ground speed that creates lift.

If takeoff speed is reached at 100 mph AIR SPEED, the plane could actually achieve liftoff at zero ground speed in a 100 mph wind. Of course it could not maintain it without forward thrust because once it left the ground the wind would begin to push it backwards (ground speed) which would reduce air speed to below the needed 100 mph to maintain sufficient lift to keep the plane in the air.

Very clever though. Pointing the reader to a ground speed question when the answer lies in the arena of air speed. I love it! :thumbup:

 

[jcthorne]

No or yes...

The conveyer belt is moving as fast backwards as the plane is moving forwards, which means the plane has it's engines spooled up but it's going nowhere.

The plane has to reach the proper airspeed to take off, not how fast the wheels are going, or the thrust output, but how much air is flowing over the wings.

Refer back to blowing on a piece of paper, make sure you have parental guidance.

This may be a trick question. Something about a light plane and strong headwinds, in that case, it can be done.

Your first sentence contradicted itself. Either you say the plane is moving forward under power (correct) or you say it is NOT moving forward (incorrect for this scenario).

The air is flowing over the wings based on the aircraft's speed relative to the earth. And that is the same as without the conveyor. The conveyor is detached from the plane and does not act on it. Makes no difference HOW fast the conveyor belt is moving, it does not affect the speed of the plane.

 

[bruiser]

F=ma

Basic physics. If the aircraft is static, that is, no forward motion, then it remains static. However, if you add thrust or acceleration as a constant, then the aircraft will move forward because force is overcoming mass creating velocity. If that force is great enough and constant to overcome the mass (aircraft) then lift will be achieved. The only constant force acting to keep mass in place is gravity. Gravity acts in only one direction, down. By providing rearward thrust, the mass has to move forward, overcoming the downward acceleration of gravity.

If you are running on a treadmill, your mass is constant to the speed of the treadmill because the downward force of gravity is holding you in position so you don't move forward. Now, if someone comes from behind and pushes you forward with enough force to overcome gravity you will move forward (probably falling on your face) regardless of the speed of the treadmill. If you increase the speed of the treadmill, but don't increase your pace relative, force from the treadmill will propel you backwards because that force is great enough to overcome mass.

 

[Magdave]

Turn the plane around on the runway. It will take off in half the time. Assuming the runway rolling direction is 1 way of course.:thumbup:

 

[Magdave]

Your first sentence contradicted itself. Either you say the plane is moving forward under power (correct) or you say it is NOT moving forward (incorrect for this scenario).

The air is flowing over the wings based on the aircraft's speed relative to the earth. And that is the same as without the conveyor. The conveyor is detached from the plane and does not act on it. Makes no difference HOW fast the conveyor belt is moving, it does not affect the speed of the plane.

In the original scenario the plane speed = 0. The relative motion to the earth below the wing tips is 0

 

[ARCTIC]

In the original scenario the plane speed = 0. The relative motion to the earth below the wing tips is 0

The treadmill would instantly go to Infiniti mph as the plane pulled itself forward by the propeller as it overcame the initial pullback of the friction created by the wheel bearings beginning to spin. Not sure what kind of drag a greased axle could create but the treadmill would probably break at some point less than infinity and the tires and bearings on the plane might last longer than the treadmill. If BRP manufactured the treadmill it would overheat and go into limp mode long before it created issues for the airplanes tires:roflblack:

 

[Explorer]

1. The plane will take off.
2. The air speed and true ground speed will be the same.
3. The conveyor will have to be almost as long as a runway.
4. At lift off the conveyor will be moving at the lift off speed, of the plane, but the wheels will be spinning at 2X that speed.
5. Of course the tires may blow or the wheel bearings seize, due to the heat generated by 2X normal rotation of the wheels. In which case, "Houston We Have A Problem".
Roger

 

[jcthorne]

In the original scenario the plane speed = 0. The relative motion to the earth below the wing tips is 0

In the original question the plane moves, not zero, and the conveyer belt moves at the same speed in the opposite direction. Both are moving relative to the earth and in opposite directions. None the less, the plane is moving as a result of its engines providing thrust and thus air flow over the wing and lift.

I think i liked Arctic's explanation best though.

 

[Magdave]

In the original question the plane moves, not zero, and the conveyer belt moves at the same speed in the opposite direction. Both are moving relative to the earth and in opposite directions. None the less, the plane is moving as a result of its engines providing thrust and thus air flow over the wing and lift.

I think i liked Arctic's explanation best though.

There is no lift, no air going over the wing the plane is stationary relative to the earth. If the wing tips are wider that the belt you would see no positional difference relative to the ground. Engine speed has nothing to do with it. It is like a car being Dyno tuned. Is it moving?

 

[ARCTIC]

There is no lift, no air going over the wing the plane is stationary relative to the earth. If the wing tips are wider that the belt you would see no positional difference relative to the ground. Engine speed has nothing to do with it. It is like a car being Dyno tuned. Is it moving?

I'll anchor a plane stationary to the ground, pitch the props to full dig and bring the engine up to full RPM's. You walk around back behind the wings and tell me if you feel any wind :roflblack::roflblack::roflblack:

 

[aeroshots]

pps:thought I was done posting here
I can't control my typing thumb. Since the trend seems to be that lift is related to the aircraft movement relative to the ground/earth, I must interject. The aircraft movement relative to the ground has nothing to do with producing lift. The cord line of the wings angle of attack to the relative wind produces lift. An airplane can fly controlled backwards over the ground and I assure you if it is below the critical angle of attack it remains airborne and it's producing lift.

 

[BajaRon]

pps:thought I was done posting here
I can't control my typing thumb. Since the trend seems to be that lift is related to the aircraft movement relative to the ground/earth, I must interject. The aircraft movement relative to the ground has nothing to do with producing lift. The cord line of the wings angle of attack to the relative wind produces lift. An airplane can fly controlled backwards over the ground and I assure you if it is below the critical angle of attack it remains airborne and it's producing lift.

Very true! In the right conditions an airplane can fly with a negative ground speed. Especially smaller airplanes that need less airspeed to maintain flight.

The stall warning device has no idea what your ground speed is. That should tell you something!

 

[Bob Denman]

:gaah: Okay...

...It's time to decide this; once and for all! :banghead:

We'll need an airplane, a BIG conveyor belt, and...

 

[ursamajor35126]

This ought to answer the question!

 

[Bob Denman]

Thanks!

:clap::clap::clap::clap::clap::clap: :2thumbs:

 

[ThreeWheels]

This ought to answer the question!

Sorry, no.

 

[Magdave]

That will only work on a forward prop plane pushing wind over the wings. Not a jet. It sure seemed to me it was moving faster than the belt was pulled. Look at the pylons move as the belt is pulled:dontknow: