On 30/03/16 23:01, newshound wrote:
On 3/30/2016 8:03 PM, The Natural Philosopher wrote:
On 30/03/16 19:53, bert wrote:
In article , Roger Mills
writes
On 30/03/2016 00:37, Dave Plowman (News) wrote:
In ,
Roger wrote:
This clearly shows you get more force by choosing peak power in a
low
gear over peak torque in a higher one.


That's a no-brainer, anyway. Just as you can express engine power in
terms of engine speed (times) engine torque (divided by) a suitable
constant, you can also express propulsive power as road speed (times)
thrust at the contact patch (divided by) a different constant - but
they
should equate to the same thing apart from transmission losses. So
when
the engine is developing its peak power, you'll get peak thrust at
the
wheels.

Are you at it too? ;-)

Peak torque at the wheels happens when the engine is at peak torque -
not
peak BHP, unless the two coincide. Regardless of which gear you
choose.


See my previous post. At any given road speed the max available thrust
at the wheels occurs when the engine is developing its max *power* not
its max *torque*. You choose the gearing to suit.
If you chose the correct gearing would the car achieve maximum seed at
maximum power output? In which instant the acceleration would be zero.

Peak power is always the place of maximum speed and maximum
acceleration, given suitable choices of gears



Not convinced. Peak power is certainly the place of max speed, I would
have said that peak torque is the place of max acceleration.

Well you are simply WRONG.

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.


In order to get the best acceleration you set the engine at peak POWER
and use a particular gear ratio to match its RPM to the desired road speed.

Knowing when to stop thinking in terms of force and or torque, and start
thinking in terms of power and energy, is actually a key thing you learn
as an engineer.

Acceleration is adding kinetic energy, to get best acceleration you need
to deploy the best deployment of energy with time, that's power.

The mere mechanical detail of whether that energy is being deployed at a
wholly inappropriate crankshaft speed is why you employ mechanical
engineers to design gearboxes.



--
"In our post-modern world, climate science is not powerful because it is
true: it is true because it is powerful."

Lucas Bergkamp