Carl Pattinson wrote:
> <carl@flyers.freeserve.co.uk>
>
> I am just filling in the LAA form to change our propeller (from a fixed
> pitch to a CS version - Woodcomp/ Smart Avionics controller). The engine
> is a Rotax 912 UL 80hp.
>
> The LAA form says that the installation of a manifold pressure gauge is
> mandatory. Anyone know why?
A CS prop keeps the rotation speed constant (hence the name Constant
Speed prop). The RMP gauge doesn't tell you the engine power anymore, it
shows just the prop setting. If you fly with a certain rpm, and throttle
back, nothing will change on your rpm gauge as the prop will keep the
rpm constant. Hence you won't notice anything as the engine looses power
for whatever reason. However, engine power can be determined by looking
at the manifold pressure. It is close to ambient pressure if the
throttle is wide open, and it will be showing a vacuum at idle, and of
course anything in between.
Frans
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