Aircraft and conveyor belt (again)

[Trazor]

If you disagree, read the original question and tell me what you think the belt speed is, with a plane moving relative to a fixed point at a speed of 1mph.

With the plane moving forward at 1 mph, the conveyor reacts by moving backwards at what ever speed it needs to, to match the rotational speed of the wheel.

The plane still moves forward, and the wheels as a UNIT will move forward at 1mph as well. The rotational speed of the wheels will depend on their diameter( large wheels spin slower than small wheels for the same distance moved. )

Assuming a take off time of about 15 to 20 seconds, the wheels would only need to survive this time for lift off.

Wheel rotational speed and aircraft speed must be considered separately.
The conveyor only reacts to wheel speed , it does not know the speed of the aircraft.

Remember its the forward thrust only of the aircraft which creates wheel speed, if the aircraft is doing 50 mph the conveyor will only match this speed, through the wheels.

 

[JohnD]

read the original question and tell me what you think the belt speed is, with a plane moving relative to a fixed point at a speed of 1mph.

I see you didn't

 

[Trazor]

read the original question and tell me what you think the belt speed is, with a plane moving relative to a fixed point at a speed of 1mph.

I see you didn't

That is not possible to determine, as I did explain, it will depend on the Diameter of the wheels

 

[JohnD]

you're telling me you can't work out the belt speed, when the aircraft is moving forward at 1mph?????????t

 

[joe-90]

....and what does the wheel diameter have to do with it?

 

[megawatt]

Belt speed and wheel speed matter not a jot in answer to the original question which was ... Will the aircraft take off?

The only thing which has any bearing on the answer to that question is airspeed.

Perhaps someone would care to explain why the aircraft will not move forward in relation to a fixed point not on the belt ... Let's say immediately to the right of the nose of the aircraft.

When you realise that you can't do this and that the aircraft will in fact move forward in exactly the same manner as it would normally you've cracked it.

MW

 

[megawatt]

I wrote:

The aircraft engines will accelerate until the point at which the thrust they produce overcomes the mass of the aircraft at which point it will begin to move

Blondini Wrote:

Did you really mean to say that?

Yes, why the question?

MW

 

[megawatt]

A couple of diagrams may help ...

1. Thrust applied with no belt

For force (F) equivalent to 1knot of airspeed (for example) the aircraft will move distance (d) as a result of a single rotation of the wheels.

2. Thrust applied with belt

For the same force (F) the aircraft will still move distance (d) as a result of a double rotation of the wheels.

Thrust is relative to airspace not the conveyor chaps.

(Sorry the pictures are so big BTW)

MW

 

[blondini]

you're telling me you can't work out the belt speed, when the aircraft is moving forward at 1mph?????????t

How about infinity + 1mph.

 

[JohnD]

correct except that infinity + 1mph is still infinity

 

[blondini]

I wrote:

The aircraft engines will accelerate until the point at which the thrust they produce overcomes the mass of the aircraft at which point it will begin to move

Blondini Wrote:

Did you really mean to say that?

Yes, why the question?

MW

I'd rather duck that one because I don't want to appear overly pedantic. Yet if I just say that I'll look like I'm trying to be a smartarse. So it's about thrust, mass, and drag. But it's not relevant to the topic so Il''l duck.

Back on topic, can I assume that you consider the aircraft to be a real one?
If so what sort of ground speed would you consider to be unsafe for it to exceed? There has to be a limit.

 

[blondini]

correct except that infinity + 1mph is still infinity

 

[Trazor]

you're telling me you can't work out the belt speed, when the aircraft is moving forward at 1mph?????????t

Your original question was wheel and belt speed, I simply mixed them up when replying to your previous post......

In answer,the belt will be moving backwards at 2 mph. the reasoning is as follows...
The plane will move forward at 1 mph, the conveyor will counter this by going backward at 1 mph, this will double the wheel speed, so the conveyor must increase to 2 mph as it has to match the wheel speed.

Provided the planes speed stabilizes at 1 mph the conveyor can go no faster than 2 mph.

Lets say take off speed is 100 mph then the conveyor will be doing 200mph at this point.

 

[JohnD]

ha ha got you!

it doesn't work because the question is defective and it is impossible to achieve what it says within its own terms.

the question says:

An aircraft is standing on a very long runway that can move (a conveyor belt). The aircraft moves in one direction, while the conveyor belt moves in the opposite direction. This conveyor belt has a control system that tracks the aircraft's wheels speed and tunes the speed of the conveyor belt to be exactly the same as the wheels, but in the opposite direction. There is no wind. The pilot begins to add thrust to the engines...

Will the plane ever take off?

if the conveyor and the wheels are both moving at the same speed but in opposite directs, the plane must be stationary. It cannot be moving forward at 1 mph

 

[AtoZ]

john D

if the belt controlled the speed of the wheels backwards, forwards or in a samba rhythm. the thrust will still make the plane move forward.

i know thats not what the question said but if you think of it in the ^^above^^ way, it may help.