1200 RPM sounds awfully fast. Most CDI ignitions do require more speed
than an old magneto, but even then it's usually 600 RPM or a little
less. I don't think even the starter motor can crank the engine that
fast!
The trick is that if your battery is flat, you need to get enough RPM
to allow the alternator to generate electricity to make a spark. But,
if your batt. is low enough to not crank, it still may have enough
juice to make a spark if you hand prop.
Interesting.
Chris
A159
ef.com>
>
> Something is suspicious here.
>
> According to Rotax the engine must be up to 1200 RPM in order to
start, so
> let's do some math. 1200 RPM divided by 2.43 (the gearbox ratio) is
494 RPM
> at the prop. If we assume a 72 inch diameter prop, then the tip
speed is
> 494 rev/min times 3.1416 times 72 in/rev divided by 12 in/ft equals
9312
> ft/minute or 155 ft/sec. Hmmm, that's about 120 knots, and I don't
think
> any human can move a hand that fast let alone actually turn a prop
against
> the engine's compression.
>
> So.... either Rotax is wrong or...well, draw your own conclusion.
>
>
> Best regards,
>
> Rob Housman
|