There's been a lot of discussion this year on the Cessna Pilot's Association
Forums about lean of peak operation in carb engines with simple
instrumentation. I've been experimenting with it and flying this way a lot.

LOP is actually easier than the "find peak and the enrich 50 - 75 degree"
method that I was taught. CHT's are no higher than running at the same power
output ROP and sometimes slightly lower.

Here is 3 meg Windows Media video file showing our O-320 H2AD being leaned
from peak to 75 LOP and then back to 25 LOP. The operation is repeated to
show the knob movement.

Note how smooth the engine sounds with carb heat on when leaned to about a
100 RPM drop. Throttle was full open and CHT were right where they are shown
20 minutes later. This video was taken at 5500 feet.

http://baldeagleflyingclub.org/LOP.wmv


--

Roger Long

Roger Long wrote:

> Note how smooth the engine sounds with carb heat on when leaned to about a
> 100 RPM drop. Throttle was full open and CHT were right where they are shown
> 20 minutes later. This video was taken at 5500 feet.

I did this on a recent cross country flight, 100+ miles each leg. The
oil temps ran higher than normal, as well as EGT's. I wasn't running WOT
and was only at 3500' ASL. We don't have CHT instrumentation and what we
do have is analog...

A 25 LOP EGT will be 50 degrees higher than 75 ROP but changes the mixture
creates in the combustion timing offset this so that CHT is usually the same
or slightly lower. This small difference in EGT has no effect on the engine
or exhaust system whatever. Hard to say what was going on without at least
one cylinder of CHT data.

None of this should effect your oil tempearature. Ours runs the same in the
winter as the summer because the thermostat just sends more or less through
the oil cooler.

An important part of operating an engine without an all cylinder analyzer
this way is to keep power settings at or below 60%. You should make up a
table from your POH for reference but flying with carb heat on will make the
engines like the O-320 pretty much self limiting. It also improves the
mixture distribution so that the engine will run leaner with acceptable
smoothness. The drop off in RPM and onset of roughness is less abrupt and
more predictable with carb heat on.

I now use WOT for almost all cruise above 3000 feet.

You can read more here: http://baldeagleflyingclub.org/Manual.htm

--

Roger Long



"Darrel Toepfer" > wrote in message
. ..
> Roger Long wrote:
>
> > Note how smooth the engine sounds with carb heat on when leaned to about
a
> > 100 RPM drop. Throttle was full open and CHT were right where they are
shown
> > 20 minutes later. This video was taken at 5500 feet.
>
> I did this on a recent cross country flight, 100+ miles each leg. The
> oil temps ran higher than normal, as well as EGT's. I wasn't running WOT
> and was only at 3500' ASL. We don't have CHT instrumentation and what we
> do have is analog...

Roger Long wrote:

> A 25 LOP EGT will be 50 degrees higher than 75 ROP but changes the mixture
> creates in the combustion timing offset this so that CHT is usually the same
> or slightly lower. This small difference in EGT has no effect on the engine
> or exhaust system whatever. Hard to say what was going on without at least
> one cylinder of CHT data.

I'd like to add one of those digital wonders one day. Next project is to
replace the baffle gasketing, they're getting limp...

> None of this should effect your oil tempearature. Ours runs the same in the
> winter as the summer because the thermostat just sends more or less through
> the oil cooler.

It went up, just under the redline...

> An important part of operating an engine without an all cylinder analyzer
> this way is to keep power settings at or below 60%. You should make up a
> table from your POH for reference but flying with carb heat on will make the
> engines like the O-320 pretty much self limiting. It also improves the
> mixture distribution so that the engine will run leaner with acceptable
> smoothness. The drop off in RPM and onset of roughness is less abrupt and
> more predictable with carb heat on.

Cont. 0-300D '65 C172F

> I now use WOT for almost all cruise above 3000 feet.

Our concern is not to overrev the engine, or limit WOT to less than 5
minutes...

> You can read more here: http://baldeagleflyingclub.org/Manual.htm

Thanks...

On Mon, 23 Aug 2004 10:21:37 -0500, Darrel Toepfer
> wrote:

>Our concern is not to overrev the engine, or limit WOT to less than 5
>minutes...

Do you understand that under leaned conditions and above a certain
altitude, say, 7,000 feet, that you cannot achieve engine redline?
The altitude limits the engine output due to the lowered oxygen
content in the air.

WOT cannot harm the engine under this condition because the engine can
only produce around 65% to 60% power at that altitude. You might as
well run WOT or you may be limiting the engine even more.

Corky Scott

Woah! It sounds like something may be wrong with this engine. Bad baffling
could be it if it is running very hot. Nothing you do with the mixture
should make that much difference in oil temperature. If your prop (fixed I
assume) conforms to the type certificate, over speed should not be a problem
unless you descend without pulling power.

That engine should run fine WOT for hours. If you are pulling power after
five minutes on a 10 - 20 minute climb, you are making the engine work
harder and get hotter.

Fix your baffle problems immediately. Make sure you don't have any
induction leaks and the engine is set up properly.

If you are not a member of the Cessna Pilots Association, join. The $40.00
dues has saved us literally thousands. Read Deakin's articles on engine
management at Avweb.com. They are mostly about larger and more complicated
engines but you'll learn some good stuff about yours. Search the CPA fourms
for threads on leaning and engine operation.

--

Roger Long



"Darrel Toepfer" > wrote in message
.. .
> Roger Long wrote:
>
> > A 25 LOP EGT will be 50 degrees higher than 75 ROP but changes the
mixture
> > creates in the combustion timing offset this so that CHT is usually the
same
> > or slightly lower. This small difference in EGT has no effect on the
engine
> > or exhaust system whatever. Hard to say what was going on without at
least
> > one cylinder of CHT data.
>
> I'd like to add one of those digital wonders one day. Next project is to
> replace the baffle gasketing, they're getting limp...
>
> > None of this should effect your oil tempearature. Ours runs the same in
the
> > winter as the summer because the thermostat just sends more or less
through
> > the oil cooler.
>
> It went up, just under the redline...
>
> > An important part of operating an engine without an all cylinder
analyzer
> > this way is to keep power settings at or below 60%. You should make up
a
> > table from your POH for reference but flying with carb heat on will make
the
> > engines like the O-320 pretty much self limiting. It also improves the
> > mixture distribution so that the engine will run leaner with acceptable
> > smoothness. The drop off in RPM and onset of roughness is less abrupt
and
> > more predictable with carb heat on.
>
> Cont. 0-300D '65 C172F
>
> > I now use WOT for almost all cruise above 3000 feet.
>
> Our concern is not to overrev the engine, or limit WOT to less than 5
> minutes...
>
> > You can read more here: http://baldeagleflyingclub.org/Manual.htm
>
> Thanks...

Roger Long wrote:

> Woah! It sounds like something may be wrong with this engine. Bad baffling
> could be it if it is running very hot. Nothing you do with the mixture
> should make that much difference in oil temperature. If your prop (fixed I
> assume) conforms to the type certificate, over speed should not be a problem
> unless you descend without pulling power.

It was the use of carb heat during leaning that raised the oil temp...

> That engine should run fine WOT for hours. If you are pulling power after
> five minutes on a 10 - 20 minute climb, you are making the engine work
> harder and get hotter.

We haven't flown it very high yet...

> Fix your baffle problems immediately. Make sure you don't have any
> induction leaks and the engine is set up properly.

Yep...

> If you are not a member of the Cessna Pilots Association, join. The $40.00
> dues has saved us literally thousands. Read Deakin's articles on engine
> management at Avweb.com. They are mostly about larger and more complicated
> engines but you'll learn some good stuff about yours. Search the CPA fourms
> for threads on leaning and engine operation.

Yep...

Corky Scott wrote:

> Do you understand that under leaned conditions and above a certain
> altitude, say, 7,000 feet, that you cannot achieve engine redline?
> The altitude limits the engine output due to the lowered oxygen
> content in the air.

I do... However I live 44' asl and have never been that high in any of
the 5 types I've flown sofar...

> WOT cannot harm the engine under this condition because the engine can
> only produce around 65% to 60% power at that altitude. You might as
> well run WOT or you may be limiting the engine even more.

Typically we're at 2000' or below, but this plane is a recent purchase
and will see more crosscountry time than what we've done previously...