Max RPM for constant speed

[Paul kgyy]

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?

[Jim Burns]

First, I'd get an optical tach and see how fast it's actually turning
compared to what the mechanical tach indicates.

Jim

"Paul kgyy" > wrote in message
oups.com...
> 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?
>

[Kobra]

Jim's advice is wise and just to compare, my plane always shows 2710 to 2730
on take-off and it is an IO360 200 HP.

Kobra


"Paul kgyy" > wrote in message
oups.com...
> 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?
>

[Paul kgyy]

Sorry, I should have mentioned that I have a digital tach.

[mikem]

Yes, have the gov adjusted. You should be able to get 2700+-25Rpm. The
extra 85 RPM translates to much higher takeoff engine power.

[Doug]

You can check the accuracy of your tach at 1800 rpm by doing a runup at
night with a street light in back of you. Due to the strobe effect, the
prop should appear to stop at 1800 rpm (for a two blade prop). For a 3
blade prop, it should appear to stop at 1200 and 2400 rpm. Good
inexpensive accurate double check on tach accuracy.

[Robert M. Gary]

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?

Its not unusual for tachs to read wrong, but assuming its a correct
reading, I would have it adjusted. In the Mooney community we often try
to get the A&Ps to adjust it to 2800 RPM max. For a normal take off we
pull the blue lever back just a bit to keep it at 2700. But for a short
field take off (especially for Mexico operations) we'll push 2800 for
short periods of time. Also, the Mooney factory tells us that climbing
out at 2600 is very hard on the engine. Much of the cooling an IO-360
receives is from fuel and having the prop turn at 2600 reduces fuel
burn, which increases climb out temps interally. My IO-360 pulls 19
gal/hr in climb out and about 10 gal/hr in cruise.
The IO-360 engine is a bit unusual because Lycoming actually certified
it to run 2000 hours at sea level at 2700 RPM. There is no reason to
pull power back.

-Robert, M20F

[Newps]

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?

Max rpm on my IO-520 is 2700. Actual rpm during takeoff, which I know
because I have a Horizon digital tach, 2725-2750. I would never let the
rpm stay on the low side, you're just ****ing away HP. When I had my
182 the governor was set at about 2650 when the redline was 2600. 50
rpm here or there are irrelavant.

[Dan Luke]

"Robert M. Gary" wrote:
> Also, the Mooney factory tells us that climbing
> out at 2600 is very hard on the engine. Much of the cooling an IO-360
> receives is from fuel and having the prop turn at 2600 reduces fuel
> burn, which increases climb out temps interally.

Somebody at the Mooney factory is smoking some powerful stuff.

--
Dan
C-172RG at BFM

[Robert M. Gary]

> 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.

-Robert

[john smith]

> 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?

[Robert M. Gary]

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?

[[email protected]]

>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

[[email protected]]

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

[zatatime]

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

[Dan Luke]

"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

[Denny]

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...

[Paul kgyy]

Dynamic RPM on takeoff, digital tach.

[Ron Natalie]

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).

[Newps]

> 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.

[Dan Luke]

"Denny" > wrote in message
ps.com...
> 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...

It's really got nothing to do with the RPM setting, per se, which
Robert's post implied. It's purely a matter of throttle and/or mixture
setting: one can run max rich at lower RPM.

--
Dan
C172RG at BFM

[Denny]

Dan, either we are miscommunicating or there is confusion...
At full throttle you cut in an extra X% of fuel flow, beyond 'max
rich'... It is for cooling the exhaust valves at take-off power...
Pull the throttle back, even a small amount, from full forward and you
lose that extra X% of cooling... It is the same for carburetor and
injected engines...
The RPM at which you can run full throttle continuously is in the
POH... Reduce power in climb by reducing the prop to that RPM and leave
the throttle full forward and your engine will be a happy camper with
cool valves... My API / CFI buddy still hasn't figured it out...

On my Super Viking Take-Off RPM was limited to 5 minutes... But you can
pull the RPM back to Max-Continuous power, still at full throttle, and
run it all day and have the benefits of the valve cooling - hard on the
fuel supply though... It is a separate metering circuit on the
injector body for full throttle cooling... Pull the throttle back as
little as a quarter inch and the valve cooling metering circuit shuts
off... Leave the throttle retarded slightly in a long hot climb and you
will likely have valve damage...

Same thing applies to fixed pitch propellprs... Leave the throttle
firewalled in climb for the cooling - assuming the POH allows it... As
soon as you pull the throttle you lose the cooling... Now, be aware
that as you climb at full throttle you are losing manifold pressure
with each thousand feet gained, which is automatically reducing the
engines output power, reducing the strain, and improving the cooling by
allowing the mixture to go even richer than it was a thousand feet
lower... Airplanes, at lower altitudes, are best climbed at full
throttle... Funny how those dumb engineers at the tractor engine
factory figured that out all on their own without any help from us god
like pilots...

cheers .../ denny

[[email protected]]

Denny > wrote:
: soon as you pull the throttle you lose the cooling... Now, be aware
: that as you climb at full throttle you are losing manifold pressure
: with each thousand feet gained, which is automatically reducing the
: engines output power, reducing the strain, and improving the cooling by
: allowing the mixture to go even richer than it was a thousand feet
: lower...

... so leaning to a constant EGT in a climb is a great way to keep the *same*
overrich mixture without going too rich.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[Dan Luke]

"Denny" wrote:

> Dan, either we are miscommunicating or there is confusion...
> At full throttle you cut in an extra X% of fuel flow, beyond 'max
> rich'... It is for cooling the exhaust valves at take-off power...
> Pull the throttle back, even a small amount, from full forward and you
> lose that extra X% of cooling... It is the same for carburetor and
> injected engines...
> The RPM at which you can run full throttle continuously is in the
> POH... Reduce power in climb by reducing the prop to that RPM and leave
> the throttle full forward and your engine will be a happy camper with
> cool valves...

That's what I'm saying. It really has nothing to do with the RPM setting.
In fact, the higher the RPM, the higher the horsepower and the higher the
CHT.

--
Dan
C-172RG at BFM

[Stan Prevost]

"Denny" > wrote in message
oups.com...

> At full throttle you cut in an extra X% of fuel flow, beyond 'max
> rich'... It is for cooling the exhaust valves at take-off power...
> Pull the throttle back, even a small amount, from full forward and you
> lose that extra X% of cooling... It is the same for carburetor and
> injected engines...

On our Turbo Saratoga's TIO540S1AD, the throttle is nowhere near full
forward at takeoff when we set max manifold pressure. Full forward will
significantly overboost. The throttle has to be continually moved forward
as altitude increases, reaching full forward at critical altitude.
Throttle-linked wastegate, no turbocharger governor.

Stan

[Aaron Coolidge]

Newps > wrote:

: 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.

A friend with an Arrow has a electronic tach. It has a red light that
comes on at 2701 RPM. When he starts the takeoff roll he takes at least
5 seconds to push in full throttle to "prevent the engine overspeed
light from coming on". He also chases the tach constantly during the
takeoff and while flying. "I want 25"/2500, not 2505!" This is why I don't
have an electronic tach....
--
Aaron C.

[Thomas Borchert]

Aaron,

> This is why I don't
> have an electronic tach....
>

The problem you describe is not at all caused by the electronic tach...

--
Thomas Borchert (EDDH)

[Denny]

That's true and it is because the cheap sob's who built your plane
refused to spend the money for proper boost control... That's a
business decision unrelated to proper engine management... Assuming tha
tthe fuel engineer knew his business you should have adequate fuel flow
for valve cooling built into the fuel controller at part throttle...
However, my experience is that turbo airplanes are hard on exhaust
valve...

denny