On Jul 23, 1:08*am, Frank Olson
wrote:
Bertie the Bunyip wrote:
Terence Wilson wrote in
:

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

I'm not surprised. It's a **** poor explanation and actually misleading,
not to say wildly inaccurate in some places. "High internal manifold
pressures" WTF is that? The author has no understanding whatsoever ofwhat
he's talking about.

Bertie

I've yet to see a normally aspirated horizontally opposed engine "blow
up" due to "high manifold pressure". *I've seen governors fail (which
caused an engine overspeed), but all things being "normal", there is no
way you're going to damage your engine running with the throttle wide
open and your prop on "fine"... *One of my engine checks (pre-flight) is
to cycle the prop. *Is the idiot that wrote this article saying that I'm
damaging the engine when I do that???

Unless there's a good reason to do otherwise, it would be good
practice to stay within the limits of the POH. Ours lists many
manifold pressures, (measured in inches of Hg) greater than RPM. Most
times in cruise at 5000 to 12000 feet we have rpms cranked pretty far
down with the throttle at max. 1950 rpm with our IO 360 is pretty
common.