Max RPM for constant speed

My IO360 with CS prop is rated full power at 2700 rpm.
Actual RPM on takeoff is usually around 2615. Should I have the
governor adjusted, or is this appropriate margin to prevent overspeed?

Static RPM at runup or dynamic RPM in flight?

I didn't realize there is a different? What would cause a prop to turn
at a different speed in flight vs. during run up when set to high?

50 rpm here or there are irrelavant.

Except for the extra centrifugal forces on the propeller. Some prop
manufacturers demand a visual inspection of a prop when overspeeded
(typically under 10% overspeed), and that the prop be removed and sent
in for NDI when more than 10% overspeed. A 10% overspeed translates
into 21% higher forces on those blades, and cracking can start.
The real danger is the aging tachometers; they tend to under-read,
and if it's indicating 50 RPM higher it might actually be 200 RPM
higher. Here in Canada we have to check them yearly, and any more than
4% error in the centre of the cruise RPM range means the tach gets
replaced.

Dan

It can be less if the blades hit the fine pitch stop when in
the static condition. As you start your roll, the rpm quickly
comes up and regulates at the redline.

Depends on how the thing is set up originally.

Do check the tach... then the governor is about 25 rpm/screw
turn... more would be ccw. The prop control should be limited
by the stop screw on the governor, not by the position of the
prop control relative to the panel.

Bill Hale

On 1 Nov 2005 16:32:38 -0800, wrote:

50 rpm here or there are irrelavant.

Except for the extra centrifugal forces on the propeller. Some prop
manufacturers demand a visual inspection of a prop when overspeeded
(typically under 10% overspeed), and that the prop be removed and sent
in for NDI when more than 10% overspeed. A 10% overspeed translates
into 21% higher forces on those blades, and cracking can start.
The real danger is the aging tachometers; they tend to under-read,
and if it's indicating 50 RPM higher it might actually be 200 RPM
higher. Here in Canada we have to check them yearly, and any more than
4% error in the centre of the cruise RPM range means the tach gets
replaced.

Dan

This is also true of the engines. I forget the details, but when I
had an overspeed a few years ago I researched it and Lycoming had
parameters for 10% or less above rated power and over 10%. I do
remember that the over 10% is a very expensive "prop"osition and I
think required some sort of tear down for the engine. You can find
the info on their site.

z

"Robert M. Gary" wrote:

Somebody at the Mooney factory is smoking some powerful stuff.

Not at all. There is a mountain of engineering data concluding that
reducing RPM reduces fuel flow and cooling. In fact, I just spoke with
one of the test pilot the other day who talked about flying the
instrumention for that. Its too bad Cessna doesn't do the same level
of
engineering.

This is not making sense, to me. Of course increasing fuel flow by
richening the mixture results in cooler CHT's, but how does increasing
fuel flow by increasing RPM give cooler CHT's? My engine runs hotter at
higher RPM.

--
Dan
C172RG at BFM

Confusion reigns, Dan... Lets assume a 2700 rpm continuous engine...
Extra fuel for cooling the exhaust valves comes when the throttle is
firewalled.... Pull it back a quarter inch and you lose the cooling...
Prop speed control comes from the setting of the prop governor
adjustment screw and/or the prop lever position... This also controls
the engines power...

So, if a 2700 rpm engine is adjusted to run 2700 at full throttle and
full prop lever then you climb at full throttle and full prop lever,
gaining the benefits of fuel cooling at max continuous power...
If the engine governer is set at 2750 and the pilot pulls the throttle
back to reduce power to max continuous, then he loses the benefits of
extra fuel flow for valve cooling... He would do less damage by letting
the engine overspeed 50 rpm at full throttle and get the extra fuel...
What he should do to control the max continuous power is leave the
throttle full forward and pull the prop rpm back to 2700 - which is
where it would have been if the governor screw was set up properly in
the first place...
For bush pilots, setting the 2700 prop adjustment to 2800 is the thing
to do for short field takeoffs... They, being smarter than the average
urban pilot, know that after takeoff they reduce the propellor RPM to
the 2700 continuous setting and LEAVE the throttle full forward to gain
the extra cooling the engineers intended...

Recently I flew a C-180 for a biennial... The owner is an API and
CFI... As is usual he had extra rpm adjusted into his airplane and was
alwyas proud of how short it will takeoff... After takeoff I would
reduce the prop to max continuous RPM... Each time he would grimace and
glare at me and reach over and pull the throttle back a half inch...
"Never reduce the prop without reducing the throttle or you will ruin
the engine.", he would thunder... I would just shrug and do it the same
way on the next takeoff... He gave me heck but signed off the
biennial... He just had to change two jugs on a mid time engine...
Coincidence? I don't think so...

denny...

Dynamic RPM on takeoff, digital tach.

Paul kgyy wrote:
My IO360 with CS prop is rated full power at 2700 rpm.

Actual RPM on takeoff is usually around 2615. Should I have the
governor adjusted, or is this appropriate margin to prevent overspeed?


A constant speed prop should go to the redline. The governor is
supposed to take care of flattening the pitch as necessary (and
at the high end of the range that's not hard).

Paul kgyy wrote:

My IO360 with CS prop is rated full power at 2700 rpm.

Actual RPM on takeoff is usually around 2615.

Around xx rpm is as good as you can do. No way, no how with an aircraft
engine do you set any one particular rpm and the governor keeps it
precisely there. You will always have a minimum 15 rpm variance.