"Bertie the Bunyip" wrote in message
...
"Mike" wrote in news:WPHgk.144$DS3.119@trnddc01:

"Terence Wilson" wrote in message
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In the course of trying to understand how a constant speed prop works
I came across the following passage in one of the Jeppesen books:

"If the throttle is advanced without decreasing the pitch of the prop
blades to increase ___ rpm, the manifold pressure increases as the
prop mechanism attempts to keep ___ rpm constant by increasing the
blade angle. The combination of high manifold pressure and low ___
rpm can cause damage due to high internal manifold pressures."

I found this paragraph to be confusing because it makes several
references to rpm but doesn't clarify whether it is engine or prop
rpm. The blanks were inserted by me. Can someone help me out?

Thanks in advance.

As others have said, unless you have a gearbox (not many planes do),
they are one and the same.

You may also want to ditch your Jepp book as the "theory" they are
describing really doesn't apply to most small piston aircraft. The
old "don't run oversquare" mentality which has been taught for years
originated out of military teachings that applied to very different
pilots doing very different things while flying very different
aircraft.


Actually, they dont, since most military aircraft,even smaller ones,
were supercharged and they ran well oversquare.. A 985, for instance, is
around 37 inches max and a typical cruise MP might be in the order of
25 inches with a cruise rpm of something like 1850, depending on how
fast you want to go and how much you want to burn.
The geared engines were even less relevant to this argument, since
almost everything larger than about 1500 c.i.d. was geared. The
indicated RPM was usually engine rpm and max for somthing like an 1830
was around 2400 and max MP for takeoff was about 43 IIRC and cruise was
around 30/2,000.
The practice originates from a perceived need to simplify for light
aircraft pilots new to variable pitch props.

And that need is even more of a necessity in military trainers which have
considerably more power and are much more easily red lined. That's why I
always assumed the mentality came primarily from military instructors giving
instruction in training aircraft. At any rate the myth still persists to
this day even with instructors who should know better.