running over-square

This weekend the Cessna Pilots Ass'n put on one of their 2-day Systems &
Procedures classes at Sporty's in Batavia Ohio. This one was for 182S, 182T
and T182S/T owners. About 20 owners attended, and it was well worth the trip
and cost.

Anyhow, one of the best tips I picked up from John Frank was to cruise my
engine more over-square than I usually do, i.e., instead of 26"/2400 RPM or
25"/2300 RPM, run it 27"/2200 RPM or 26"/2100 RPM.

I tried this on the way home and found I got the same performance, maybe a
hair better, by trying to get the same % horsepower with more MAP and less
RPM. It was quieter and the fuel flow was down a smidgen, too. According to
John, most of the advantage comes from less internal mechanical horsepower
loss at the lower RPM settings.

This is probably not news to a lot of you folks, but it was to me, and it's
the way I'm going to run from now on.

--
Dan
T-182T at BFM

"Dan Luke" wrote in message
...
This weekend the Cessna Pilots Ass'n put on one of their 2-day Systems &
Procedures classes at Sporty's in Batavia Ohio. This one was for 182S,
182T and T182S/T owners. About 20 owners attended, and it was well worth
the trip and cost.

Anyhow, one of the best tips I picked up from John Frank was to cruise my
engine more over-square than I usually do, i.e., instead of 26"/2400 RPM
or 25"/2300 RPM, run it 27"/2200 RPM or 26"/2100 RPM.

I tried this on the way home and found I got the same performance, maybe a
hair better, by trying to get the same % horsepower with more MAP and less
RPM. It was quieter and the fuel flow was down a smidgen, too. According
to John, most of the advantage comes from less internal mechanical
horsepower loss at the lower RPM settings.

This is probably not news to a lot of you folks, but it was to me, and
it's the way I'm going to run from now on.


WOTLOPSOP.

"Dan Luke" wrote in message
...
This weekend the Cessna Pilots Ass'n put on one of their 2-day Systems &
Procedures classes at Sporty's in Batavia Ohio. This one was for 182S,
182T and T182S/T owners. About 20 owners attended, and it was well worth
the trip and cost.

Anyhow, one of the best tips I picked up from John Frank was to cruise my
engine more over-square than I usually do, i.e., instead of 26"/2400 RPM
or 25"/2300 RPM, run it 27"/2200 RPM or 26"/2100 RPM.

I tried this on the way home and found I got the same performance, maybe a
hair better, by trying to get the same % horsepower with more MAP and less
RPM. It was quieter and the fuel flow was down a smidgen, too. According
to John, most of the advantage comes from less internal mechanical
horsepower loss at the lower RPM settings.

This is probably not news to a lot of you folks, but it was to me, and
it's the way I'm going to run from now on.


Is John with the CPA or Lycoming? Just wondering what Lycoming thinks of the
recommendations.

Dan,

This is probably not news to a lot of you folks, but it was to me, and it's
the way I'm going to run from now on.


Just like the book (POH) says...

You might want to read the engine management columns by John Deakin over at
avweb.com.

--
Thomas Borchert (EDDH)

On Sep 17, 10:13 am, "Maxwell" wrote:
"Dan Luke" wrote in message

...





This weekend the Cessna Pilots Ass'n put on one of their 2-day Systems &
Procedures classes at Sporty's in Batavia Ohio. This one was for 182S,
182T and T182S/T owners. About 20 owners attended, and it was well worth
the trip and cost.

Anyhow, one of the best tips I picked up from John Frank was to cruise my
engine more over-square than I usually do, i.e., instead of 26"/2400 RPM
or 25"/2300 RPM, run it 27"/2200 RPM or 26"/2100 RPM.

I tried this on the way home and found I got the same performance, maybe a
hair better, by trying to get the same % horsepower with more MAP and less
RPM. It was quieter and the fuel flow was down a smidgen, too. According
to John, most of the advantage comes from less internal mechanical
horsepower loss at the lower RPM settings.

This is probably not news to a lot of you folks, but it was to me, and
it's the way I'm going to run from now on.

Is John with the CPA or Lycoming? Just wondering what Lycoming thinks of the
recommendations.- Hide quoted text -

- Show quoted text -

Go by what the POH says. If it says you can do it, then do
it. The old no-more-than-square thing was a rule of thumb for pilots
who flew engines that had little or no operating instructions,
especially higher-compression engines that would detonate easily. The
POH will have a cruise chart, along with a lot of other advice, that
is often ignored or overlooked. Lycoming will have worked with Cessna
to establish those limits.
Dan

"Maxwell" wrote:


Is John with the CPA or Lycoming? Just wondering what Lycoming thinks of the
recommendations.

CPA

The settings I mentioned, and some that are even more over-square, are listed
as permissable in the POH.

Here's what I found in a Lycoming flyer for a higher-power version of the
TIO-540:

"A power setting of 2200 RPM and 31" Hg manifold pressure is recommended for
all cruise flight."


--
Dan
T-182T at BFM

"Thomas Borchert" wrote:

Just like the book (POH) says...

Yep; it's all in the POH.

You might want to read the engine management columns by John Deakin over at
avweb.com.

I'm sure I've read Deakin's thoughts on this and not paid much attention. I
was always concentrating on the LOP/ROP stuff.

--
Dan
T-182T at BFM

"Dan Luke" wrote:
Anyhow, one of the best tips I picked up from John Frank was to cruise my
engine more over-square than I usually do, i.e., instead of 26"/2400 RPM or
25"/2300 RPM, run it 27"/2200 RPM or 26"/2100 RPM.

In general, I recommend running at the highest MP and lowest RPM
combination in the engine manufacturer's power setting table for the %HP
you want to achieve. This will give you the lowest noise, lowest
vibration, and best efficiency.

On top of that, the tach runs slower too, so if you're paying by tach time,
you save money. If you're a commercial operator watching the hours tick
down to an obligatory engine overhaul or inspection, it's good for you too.

wrote:
The old no-more-than-square thing was a rule of thumb for pilots
who flew engines that had little or no operating instructions,

Keep in mind that there's nothing magic about "square" operation. Square
means "the manifold pressure is that same as the prop speed". That's
hogwash; the numbers only work out the same because of an accident of what
units we use.

There's nothing that says we have to measure prop speed in RPM; we could
just as easily measure it in radians per second or Mega-degrees per
fortnight. There's also nothing that says we need to measure manifold
pressure in inches of mercury. It could be in mm/Hg, torr, atmospheres,
PSI, Pascals, etc.

"Roy Smith" wrote:

On top of that, the tach runs slower too, so if you're paying by tach time,
you save money. If you're a commercial operator watching the hours tick
down to an obligatory engine overhaul or inspection, it's good for you too.

I hadn't thought about that angle. Even if you're a part 91 owner, it saves
you money.


--
Dan
T-182T at BFM