Dick Sanders wrote,
>An article in the Sunbeam Alpine Owners Club "Horn" a few months ago
claimed
>NINE horsepower saved. Both 5 and 9 sound like way, way too much. There
>just isn't a lot of mass to keep in motion here. If a little fan takes 5-9
>hp to turn, then the crankshaft must take about what....75-100 hp?
>
>If it takes five horsepower to turn that fan, then someone's using some
mighty
>puny ponies.
>
>Dick Sanders
>Seattle
Dick,
You are confusing inertia with friction.
The mass of the components has nothing to do with horsepower. Only the rate
at which a given torque will cause acceleration of the component.
Steady state a massive component provides nor uses power unless it is not
balanced.
The difference in HP figures relates to the amount of energy and friction
lost to the fan pushing the air it is pumping.
In fact an electric fan is less efficient in moving air per engine HP due to
mechanical to electrical conversion losses (gen/alt) to actual motion, which
is
mechanical to electrical to mechanical.
Becuase of this, the electric setup consumes more engine HP at low RPMs,
where the mechanical system is not robbing too much power from the engine.
Where the electric scheme pays off is where at higher RPMs where the
mechanical
fan is spinning full tilt, and is robbing the most power from the engine,
the
electric fan motor is either off, or still using the same amount of energy
that it needs at low RPMs.
An electic fan need only produce the amount of airflow needed to cool it
at low RPMs and standing still. If a mechanical fan consumes 5HP at 5000
RPM,
then one could assume it would be about 1HP at 1000 RPM.
A typical 14 inch electric fan consumes around 100 to 200 (~.3HP) watts of
electrical energy, but after the conversion inefficiencies, the actual HP
load
on the engine is about 1HP.
I believe the 5 HP savings figures, but the 9 HP figure is probably pushing
it.
Jarrid Gross
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