On 31/03/16 11:47, Thomas Prufer wrote:
On Thu, 31 Mar 2016 11:15:39 +0100, The Natural Philosopher
wrote:

Consider: at a given speed you want to maximise thrust. Thrust is
linearly related to torque, so what you want is to maximise the product
of torque and the speed, which happens to be the dimension of POWER.

Eh?

Consider: at a given speed you want to maximise thrust.

Ok...

Thrust is linearly related to torque,

ok...

so what you want is to maximise the product
of torque and the speed, which happens to be the dimension of POWER.

Why don't you want to maximize the torque --hence the thrust-- anymore, like you
did above?


Because torque does not stay constant with SPEED.

So to get the best torque at any given speed, you need the most power
out of the engine.

If that's too hard, think of energy and power and the relationship of
rate of change of kinetic energy to them

I.e to move from say 50 mph to 70 mph requires an *energy* input of 1/2
mass x (70^2-50^2) (excluding drag)

The faster that energy goes in, the faster you get that job done, and
the rate of energy is POWER.


Consider a water wheel which gives as much torque as a formula one
engine, but rotates once every 10 seconds. Which do you think would
accelerate a block of whatever the fastest?

You want torque? How about a worm drive. Given a couple of worm drives I
can by hand generate more torque than a car engine.

Does that mean I can out accelerate the car on a bike?

At anything faster than 1/10 mph?

You are not alone in the confusion. I spent years patiently explaining
that 'static thrust' on a model aeroplane propellor is only useful if
you want it to emulate a helicopter, because static thrust drops away at
speed.

Power delivery at the speed you want is what you want.





Thomas Prufer



--
Those who want slavery should have the grace to name it by its proper
name. They must face the full meaning of that which they are advocating
or condoning; the full, exact, specific meaning of collectivism, of its
logical implications, of the principles upon which it is based, and of
the ultimate consequences to which these principles will lead. They must
face it, then decide whether this is what they want or not.

Ayn Rand.