Thanx for that good info, Shaun. If I were World Commander, it would
be law to spec these things at typical RPM on an instrument approach.
In analyzing my electrical sys, it seems I can put only the single
strobe (3.4A) and landing lite on the SD-8, hoping to get away with
one that draws 4.5A. The light will dim during landing (aux battery),
but most planes do that, and it's bad manners to use strobes on the
ground. Else the SD-8 is backup power for key items, via a panic
switch. I found that on all the electrical items I have, the actual
current draw is less than what they say, so it works out so far on
paper -- only 11.5A continuous/night on the Rotax.
Also, on your 914 amp figures, I wonder if the actual output is a bit
less, given the power wasted in heating the regulator. I note in the
Rotax manuals, beyond the bad translation, they appear oversold on the
concept that brevity is clarity.
Regards,
Fred F., A063
Shaun Simpkins wrote:
>
> Not exactly. I was making my remarks with reference to economy cruise
> settings of around 4800-5000 RPM. Check out www.bandcspecialty.com. By their
> own documentation, and confirmed by Bill, the SD-8, SD-20, and 914 internal
> generator perform so:
> SD-8/SD-20 Rotax 914 Generator
> PTO RPM Output Engine RPM Output
> 2000 2.3 2000 7
> 2500 4.7 2500 11
> 3000 6.8 12 3000 14
> 3500 8.4 20 3500 16
> 4000 9.4 26 4000 19
> 4500 10.2 31 4500 19.5
> 5000 10.7 33 5000 20
> 5500 20.5
> 6000 21
>
> Note the clear knee in the output curves. The SD-8 and 20 are clearly
> designed for the Lycoming, and, perhaps conveniently, the 912, but on the
> 914 the SD-8 is down 40% or so at economy cruise, and down 15% at max RPM.
> The SD-20 is no better than 50% of rating! Note also that at most cruise
> power settings the Rotax internal generator is producing full output!
> The 914 PTO needs to have about a 0.7:1 ratio, not 0.54:1.
>
> Shaun
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