Constant speed prop question

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.

Terence Wilson wrote:

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.


It's engine rpm, but in direct drive engines prop rpm and engine rpm are the
same.

On 2008-07-20, Steven P. McNicoll wrote:
Terence Wilson wrote:
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?
It's engine rpm, but in direct drive engines prop rpm and engine rpm are the
same.

....and in geared engines, or engines with some other propeller speed
reduction unit (such as the Rotax 912), they're directly proportional. Thus,
it doesn't matter whether it's engine or prop rpm.
--
Jay Maynard, K5ZC http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
Fairmont, MN (FRM) (Yes, that's me!)
AMD Zodiac CH601XLi N55ZC (got it!)

Jay Maynard wrote:
...and in geared engines, or engines with some other propeller speed
reduction unit (such as the Rotax 912), they're directly proportional. Thus,
it doesn't matter whether it's engine or prop rpm.

Yes, unless there is a torque converter between the crank and the prop.

On Sun, 20 Jul 2008 08:31:45 -0500, "Steven P. McNicoll"
wrote:

Terence Wilson wrote:

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.


It's engine rpm

Just to clarify, it's engine rpm for all the blanks?

Thanks.

Terence Wilson wrote:
On Sun, 20 Jul 2008 08:31:45 -0500, "Steven P. McNicoll"
wrote:

Terence Wilson wrote:

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.


It's engine rpm

Just to clarify, it's engine rpm for all the blanks?


Yes. Or propeller. Either would be correct as there is a fixed ratio
between engine rpm and prop rpm. In a direct drive engine that ratio is 1.

Terence,

Just to clarify, it's engine rpm for all the blanks?


There is no difference between the two. Change one, and the other
changes in the same way.

--
Thomas Borchert (EDDH)

"Terence Wilson" wrote in message
...
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. I run oversquare as
much as possible simply because it's more efficient. Many turbo engined
pilots routinely run 12" oversquare with no ill effects.

Here's an excellent group of articles that explains the principles involved
in easy to understand language:

http://www.advancedpilot.com/downloads/prep.pdf

Mike,

originated
out of military teachings that applied to very different pilots doing very
different things while flying very different aircraft.


Actually, it couldn't have been all of the military. Many major cities in my
home country of Germany would contain many more historic buildings today, if
those B-17s hadn't run oversquare and lean of peak. The B-17s would never
have reached them.

--
Thomas Borchert (EDDH)

In article ,
Thomas Borchert wrote:

originated out of military teachings that applied to very different
pilots doing very different things while flying very different aircraft.

Actually, it couldn't have been all of the military. Many major cities in my
home country of Germany would contain many more historic buildings today, if
those B-17s hadn't run oversquare and lean of peak. The B-17s would never
have reached them.

We can all say thank you Charles Lindberg for teaching us this technique.