Frank Olson wrote in
news:F1zhk.23979$nD.19490@pd7urf1no:

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???



Well, you will do damage with a low rpm and high enough MP to raise the
BMEP to the point where knocking occurs. Knocking will apply loads that
will exceed the ability of the oil to keep the metal parts seperated and
wear the engine or even overstress parts to the point of breaking.
Observing manufacturer's limitations should ensure that knocking doesn't
occur and while there is obviously a margin included in those to account
for conditions instrument error and so forth, I know i would take care
if it were my engine!

Bertie