Aircraft and conveyor belt (again)

[noseall]

when i spoke about the plane needing a cable restraint to keep it from going backwards, once the conveyor was switched on and before the engines were powered up, it was stated that a restraint would not be necessary due to zero friction at the wheels.

in a made-up world where you can have zero friction that is.

in other words the plane would remain in the same place even though the conveyor was switched on, with or without cable restraint, engine thrust etc.

status quo.

cue the engines and you have forward movement.

end of.

 

[markie]

Not this debate again

 

[megawatt]

Any pilot will tell you that, to calculate safe takeoff distance you must take into account rolling resistance which is derived as a factor of the coefficient of friction of the runway surface multiplied by the laden weight of the aicraft.

Nowadays all commercial runways meet coefficient standards thus rendering it obsolete in the calculations.

No mention of speed, wind or anything else in the rolling resistance calcs guys.

On your holiday flight you'll notice that sometimes you need to taxi right to the end of the runway past the piano keys and this will be because the aircraft will be close to its fully laden weight limit ... And more prevalent in hot climes where engine thrust is reduced and runway surfaces are softer (and thus provide more friction).

Its good to see that sanity is more prominent in this incarnation of this thread ... Cue TractorFred or his oppo's and let's watch it deteriorate

MW

 

[Softus]

Not this debate again

They say we're young and we don't know
We won't find out until we grow...

 

[megawatt]

Softus ... I got you babe ....

 

[Trazor]

Thank God that this thread is now dead.

Now that everyone understands and knows that the plane will take off, their is no more room for debate.............

 

[blondini]

It's not dead.


It's just stunned.

 

[securespark]

Like a baby goat just before it has its jugular & carotid severed...

 

[Softus]

I though it was just resting.

Beautiful plumage.

 

[ColJack]

I missed the original problem, would someone care to sum up the theory for us?

in this theoretical world you are working in, the bearings and tyres etc have zero friction?

what about rotational inertia?

 

[Softus]

what about rotational inertia?

Could that be what doitall has?

 

[blondini]

The original OP states.

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?

I would have to presume that it would be a real aircraft, so no zero friction, and that if the if the conveyor were able to ****** the acceleration of the aircraft, it would still be long enough to allow the aircraft time to reach sufficient speed for take off.

For Softus. You had a right go at me about the double wheel speed thing. Similar threads are easy to find but the wording of the OP is sometimes different. I have only looked at a couple and noted that one stated that the runway will match the speed of the aircraft. This would mean that the wheel speed would simply be double the speed of the aircraft and there is no argument for me. The aircraft would easily take off. The OP here is different, but I think you know that.

If the plane were real and the conveyor runway were real, the runway would try and match the wheel speed of the aircraft and as has been pointed out, as soon as the aircraft starts to move forward, the runway will react and the wheelspeed will increase very rapidly.

What happens then is where the disagreements really start to er fly.

 

[blondini]

what about rotational inertia?

That's something I hadn't considered.

Thinking it through, the power to accelerate the wheel rotation to exceptional speeds would have to come from somewhere, but it's the runway thats doing it. Whatever the runway does to the wheels, the net input from the aircraft to the wheel speed is only that which would be needed for a regular takeoff. Maybe...

 

[Softus]

For Softus. You had a right go at me about the double wheel speed thing.

On the contrary - I credited you with the intelligence to understand what I was explaining, which is why I was incredulous that you didn't [seem to].

I asked you for your working, and no point was I abusive towards you.

In what way was that "having a go"?

The OP here is different, but I think you know that.

I do indeed, but I take the view that the OP here is just badly worded. The reasonable thing to do in that situation is to take the most likely interpretation, which is what I did, and is what I explained that I'd done.

...the runway would try and match the wheel speed of the aircraft and as has been pointed out, as soon as the aircraft starts to move forward, the runway will react and the wheelspeed will increase very rapidly.

I concur.

What happens then is where the disagreements really start to er fly.

I don't remember any disagreement about what happens when the wheel speed increases to infinite. IMHO the bearings would break up, or the tyres would explode, before the aircraft reached take-off velocity.

 

[Trazor]

I don't remember any disagreement about what happens when the wheel speed increases to infinite. IMHO the bearings would break up, or the tyres would explode, before the aircraft reached take-off velocity.

If you accept that the aircraft does take off, then the maximum wheel speed attainable is twice that of take off speed, no greater speed than that needs to be considered.