All
I'll stand being corrected if I am wrong but if I remember correctly what I
learned over 30 years ago when I did my commercial subjects, the power of an
engine is proportional to Manifold Pressure (controlled by the throttle
and/or altitude in the case of a normally aspirated engine) and is also
proportional to Revs per minute (RPM)
Given that the RPM remains constant, less throttle (MP) = Less Power, more
throttle (MP) = More Power
also
Given that the MP (throttle setting) remains constant, less RPM = Less
Power, more RPM = More Power
It therefore follows that for a given power setting, there are many
combinations of MP and RPM that will do the trick.
Also if I remember correctly, for a given power setting, best economy is
achieved with the combination of maximum MP (allowable) with the minimum RPM
for that power setting. This may only be the case for radials ...... I'm
not sure.
With a normally aspirated engine, if you are cruising at say 8,000 ft on
full throttle and wish to climb to say 10,000 ft, the only way extra power
can be attained is to INCREASE the RPM assuming you were already cruising at
less than Max RPM and ignoring mixture settings.
I note John Wigney has already covered what Rotax has to say so I would like
to make the comment that with a 912 as in my case, I cannot see why a MP
gauge should be mandatory but it is certainly desirable if one wishes to get
the best out of the engine both in performance and economy otherwise one is
just guessing.
Since power is proportional to mp AND rpm, what would be the point in having
one gauge and not the other?
Just my two bobs worth. I think manifold pressure may be abbreviated as MAP
nowadays but I'm sure it was MP once upon a time!!
Regards
Kingsley
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