The VP prop will adjust itself within the limitations of the propellor pitch
adjustment
to maintain the rpm setting although if the throttle is not open sufficient
there will be insufficient power to even maintain the set rpm on full fine
and the rpm will drop at lower throttle settings. Therefore power is related
to the throttle setting and this will adjust the MP until Wide Open Throttle
is achieved. Full consumption will rise as you open the throttle and therefore
produce more power.
Not sure where you have obtained the 18.7 number from but the Power/Fuel
Consumption
performance graphs in the ROTAX Operating manual should be your guide and
more important I suggest a MP Guage to provide you with the performance settings
you want to achieve and also measurement of the fuel consumption for your
aircraft at chosen cruise altitudes so you best able to determine the
performance
and range of your aircraft. Relying on someone else's figures is never wise.
Alan
Sent from my iPad
> On 4 Jul 2016, at 20:58, jonathanmilbank <jdmilbank@yahoo.co.uk> wrote:
>
>
> Guys, thanks for the replies. Firstly I don't have a manifold pressure guage,
but only an old car economy guage to give warning of carburettor ice build-up.
Permission was given for this and it works very well, although the needle moves
in the opposite sense. Because my 912 ULS engine isn't turbo boosted, there's
no chance of "overboosting".
>
> Now to my puzzlement about the consequence of using a constant speed Airmaster
propeller and changes in horsepower without changing rpm. In my simple brain,
if I have 5000 rpm selected for cruise and move the throttle within the governed
range, then the horsepower MUST increase as I move the throttle from lowest
position at which 5000 rpm can be maintained to the fully forward position.
>
> Therefore the tables provided in the engine manual become nonsensical
> regarding
RPM vs horsepower. It's more likely to me that the only remaining approximation
to horsepower being produced must be manifold pressure.
>
> So assuming I generally cruise at 4700 RPM for aural comfort, indicating 115
to 120 KIAS and at a fixed throttle position, what remains for me to have an
idea
of what % power I'm using is fuel consumption. Somehow I've acquired the idea
that 18.5 litres/hour indicates about 75% power.
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=457721#457721
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