running over-square

[Dan Luke[_2_]]

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

[Matt Barrow[_4_]]

"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.

[Maxwell]

"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.

[Thomas Borchert]

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)

[[email protected]]

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

[Dan Luke[_2_]]

"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

[Dan Luke[_2_]]

"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

[Roy Smith]

"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.

[Roy Smith]

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.

[Dan Luke[_2_]]

"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

[Mortimer Schnerd, RN[_2_]]

Dan Luke wrote:
> 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."


Your quotation refers to a turbocharged engine which by definition would always
be operated oversquare in cruise anyway. I doubt you will ever see 31" of
manifold pressure in a normally aspirated engine. They just can't do it.

That being said, I have been a long time fan of using the lowest RPM I can get
away with for cruise flight mostly because of my experience with bigger twins.
The slower they turn, the quieter they are, and the less tired everybody in
earshot becomes.

I look for whatever combination of low RPM and manifold pressure can give me
65-75% power. I still want the speed but don't need the extra noise trying to
get an extra 7 knots out of the beast. All things in moderation...



--
Mortimer Schnerd, RN
mschnerdatcarolina.rr.com

[Blueskies]

"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.
>
> --
> Dan
> T-182T at BFM
>

That was one of the 'tricks' Lindbergh taught the P-38 pilots to increase their range in the Pacific...

[Dan Luke[_2_]]

"Mortimer Schnerd, RN" wrote:

>> "A power setting of 2200 RPM and 31" Hg manifold pressure is recommended
>> for
>> all cruise flight."
>
>
> Your quotation refers to a turbocharged engine which by definition would
> always be operated oversquare in cruise anyway. I doubt you will ever see
> 31" of manifold pressure in a normally aspirated engine. They just can't do
> it.

My engine is a turbocharged engine.

http://tinyurl.com/2jskz7


> That being said, I have been a long time fan of using the lowest RPM I can
> get away with for cruise flight mostly because of my experience with bigger
> twins. The slower they turn, the quieter they are, and the less tired
> everybody in earshot becomes.

Yep.

--
Dan
T-182T at BFM

[Andrew Sarangan]

On Sep 17, 7:36 pm, Roy Smith > wrote:
> 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.

Where did the term "square" come from? I mean, we are not squaring a
number, and there is nothing square as in a four-sided thingy.

[Doug[_1_]]

The same is true in an automobile. If you go up a hill, stay in high
gear and floor it as opposed to shifting down and NOT having to floor
it. It is not intuitive. For maximum fuel economy and least engine
wear go for the least revolutions per MILE.

It's a bit different in a plane, because you are dealing with a
constant speed prop instead of transmission with gears, but the
principles are the same.

There is one other caveat, and it can be a big one. That is to run the
engine where it is smoothest. You can feel it.Vibration shakes thiings
apart, and the less the vibration the better off your aircraft is
going to be. So keep that one in mind too.

[Matt Whiting]

Andrew Sarangan wrote:
> On Sep 17, 7:36 pm, Roy Smith > wrote:
>> 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.
>
> Where did the term "square" come from? I mean, we are not squaring a
> number, and there is nothing square as in a four-sided thingy.

Well, if you have a 4" square you might say it is 4" x 4" or 4" square.

The analogy is that 24" and 24 hundred RPM are the same number (yes,
different units, but the same raw number) and thus the 24 square
nomenclature. Seems to make some sense to me.

Matt

[Matt Whiting]

Doug wrote:
> The same is true in an automobile. If you go up a hill, stay in high
> gear and floor it as opposed to shifting down and NOT having to floor
> it. It is not intuitive. For maximum fuel economy and least engine
> wear go for the least revolutions per MILE.

The trouble is that is isn't true in either an airplane or an
automobile. Jay is correct that the tach records less time, but you
can't be sure that you are using either less fuel or incurring less
engine wear. If you run too slow with cylinder pressures to high, you
will run hotter, often much hotter in a water cooled engine that depends
on the water pump speed to circulate coolant. And running way below the
torque peak is not efficient fuel-wise at some point either.


> It's a bit different in a plane, because you are dealing with a
> constant speed prop instead of transmission with gears, but the
> principles are the same.

To a degree. There is an optimum point and running too slow with
cylinder pressures too high is not the most efficient at some point.


> There is one other caveat, and it can be a big one. That is to run the
> engine where it is smoothest. You can feel it.Vibration shakes thiings
> apart, and the less the vibration the better off your aircraft is
> going to be. So keep that one in mind too.

That is generally too, but there are exceptions here as well. Some
frequencies of vibration are much more damaging to certain instruments
and components that are others. What feels good to a human may be
killing a sensitive instrument.

Matt

[[email protected]]

On Sep 17, 5:36 pm, Roy Smith > wrote:
> 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.

No, there's nothing magic about it. Just that the old guys
often avoided oversquare operation unless they could find
manufacturer's data recommending it. Some of these old practices get
carried forward into newer engines where they make no sense. Old
engines often had to run on low-octane fuels that suffered detonation
at low RPM and high MP, and the accident of RPM vs. MP was a handy way
to avoid it. Detonation was a sure way to end up on foot miles from
anywhere hospitable, and since fuel was cheap and the boss was paying
for it anyway, it was safer to use more and get home.
I have the cylinder from an IO-520 here that had been
detonating. The head is blown clean off the cylinder; the aluminum
fractured at the top of the cylinder threads. Things would get very
noisy, shaky, smoky and scary if that happened. Cylinder pressures go
out of sight during detonation, as do CHTs.

Dan

[Newps]

wrote:


> I have the cylinder from an IO-520 here that had been
> detonating. The head is blown clean off the cylinder; the aluminum
> fractured at the top of the cylinder threads. Things would get very
> noisy, shaky, smoky and scary if that happened. Cylinder pressures go
> out of sight during detonation, as do CHTs.


That sounds like preignition, not detonation. Detonation is rarly fatal
to an engine.

[Thomas Borchert]

Blueskies,

> That was one of the 'tricks' Lindbergh taught the P-38 pilots to increase their range in the Pacific...
>

And the B-36. Berlin and Dresden never would have been bombed without running oversquare...

--
Thomas Borchert (EDDH)

[Bertie the Bunyip[_19_]]

wrote in
oups.com:

> On Sep 17, 5:36 pm, Roy Smith > wrote:
>> 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.
>
> No, there's nothing magic about it. Just that the old guys
> often avoided oversquare operation unless they could find
> manufacturer's data recommending it.

Some of these old practices get
> carried forward into newer engines where they make no sense. Old
> engines often had to run on low-octane fuels that suffered detonation
> at low RPM and high MP, and the accident of RPM vs. MP was a handy way
> to avoid it. Detonation was a sure way to end up on foot miles from
> anywhere hospitable, and since fuel was cheap and the boss was paying
> for it anyway, it was safer to use more and get home.

It's not an old practice. Many prewar engines were run over square and
100 octane fuels were commonly available immediatly after the war, not
to mention 115/145.
The only time I ever ran an engine like that was in training, and that
was only for ease of operation as a quick rule of thumb. never during
actual revenue operation.


IMO it's a practice that crept in over the years out of ignorance of the
way engines operate and ignorance of the loads and forces at play when a
piston is whizzing up and down.


bertie

[Bertie the Bunyip[_19_]]

Newps > wrote in news:
:

>
>
> wrote:
>
>
>> I have the cylinder from an IO-520 here that had been
>> detonating. The head is blown clean off the cylinder; the aluminum
>> fractured at the top of the cylinder threads. Things would get very
>> noisy, shaky, smoky and scary if that happened. Cylinder pressures go
>> out of sight during detonation, as do CHTs.
>
>
> That sounds like preignition, not detonation. Detonation is rarly fatal
> to an engine.


No, he's right about that,definitely. High BMEP's will cause the fuel to
burn so that it gives insanely high peak pressures and that will trash an
engine pretty quickly. That's the definition of detonation and it's the
quickest way to blow a hole through the top of a piston.


Bertie

[Morgans[_2_]]

"Thomas Borchert"> wrote

> And the B-36. Berlin and Dresden never would have been bombed without
> running oversquare...

Berlin and Dresden were bombed with B-36's?
--
Jim in NC

[Bertie the Bunyip[_19_]]

Thomas Borchert > wrote in
:

> Blueskies,
>
>> That was one of the 'tricks' Lindbergh taught the P-38 pilots to
>> increase their range in the Pacific...
>>
>
> And the B-36. Berlin and Dresden never would have been bombed without
> running oversquare...
>

A, the B36 was only a pipedream in WW2, and running oversquare in a
supercharged airplane is not relevant to the discussion anyway. For one
thing, the engines were geared, for another, the MP pressures for takeoff
for even the lowest boosted airplanes were in the order of 32 inches, with
some running well over 40 inches.
IOW you're comparing apples with oranges.

Bertie

[Morgans[_2_]]

"Clark" < wrote

> Right after the Germans bombed Pearl Harbor.

<chuckle> Yeah, that's the ticket! The German's bombing Pearl Harbor;
that's the ticket!

What I would give, to see a real, full sized B-36 flying overhead, and doing
a few takeoffs and landings and fly-bys, just one time!

Think it will ever happen again?
--
Jim in NC

[Dan Luke[_2_]]

"Morgans" wrote:

> What I would give, to see a real, full sized B-36 flying overhead, and doing
> a few takeoffs and landings and fly-bys, just one time!

When I was a 6-year old Air Force brat on Williams AFB ca. 1953, some B-36s
went overhead at low altitude and were so loud I peed my pants. The sound was
so overwhelming I didn't even realize what had happened until I went back in
the house.

What an airplane!

--
Dan
T-182T at BFM

[Morgans[_2_]]

"Dan Luke" > wrote

> When I was a 6-year old Air Force brat on Williams AFB ca. 1953, some
> B-36s went overhead at low altitude and were so loud I peed my pants. The
> sound was so overwhelming I didn't even realize what had happened until I
> went back in the house.
>
> What an airplane!

Yeah!

I've heard that they were so loud that the sound pressure could rupture your
spleen! ;-))
--
Jim in NC

[[email protected]]

On Sep 18, 1:40 pm, Newps > wrote:
> wrote:
> > I have the cylinder from an IO-520 here that had been
> > detonating. The head is blown clean off the cylinder; the aluminum
> > fractured at the top of the cylinder threads. Things would get very
> > noisy, shaky, smoky and scary if that happened. Cylinder pressures go
> > out of sight during detonation, as do CHTs.
>
> That sounds like preignition, not detonation. Detonation is rarly fatal
> to an engine.

http://en.wikipedia.org/wiki/Engine_knocking
http://www.streetrodstuff.com/Articles/Engine/Detonation/
http://www.sacskyranch.com/deton.htm
http://www.americanaviationinc.com/effectsNavajo.html

Dan

[Thomas Borchert]

Clark,

> Right after the Germans bombed Pearl Harbor.
>

Uhm, not really. Not that Hitler wouldn't have liked to. ;-)

I meant the 17s...

--
Thomas Borchert (EDDH)

[Ross]

wrote:
> On Sep 18, 1:40 pm, Newps > wrote:
>
wrote:
>>
>>> I have the cylinder from an IO-520 here that had been
>>>detonating. The head is blown clean off the cylinder; the aluminum
>>>fractured at the top of the cylinder threads. Things would get very
>>>noisy, shaky, smoky and scary if that happened. Cylinder pressures go
>>>out of sight during detonation, as do CHTs.
>>
>>That sounds like preignition, not detonation. Detonation is rarly fatal
>>to an engine.
>
>
> http://en.wikipedia.org/wiki/Engine_knocking
> http://www.streetrodstuff.com/Articles/Engine/Detonation/
> http://www.sacskyranch.com/deton.htm
> http://www.americanaviationinc.com/effectsNavajo.html
>
> Dan
>

Back to the original post somewhat... I knew about the over squared and
my Lycoming O-360 manual has a chart that shows conditions acceptable to
over square for the same % hp. I tried it last night and set the two
conditions for 65% and leaned. I noticed that the CHT were lower in the
over squared condition rather than the "under squared?". I have a C/S
prop with a redline condition between 2000 and 2250 RPM. Really limits
my choices. Do you folks see the same?

--

Regards, Ross
C-172F 180HP
KSWI

[[email protected]]

On Sep 18, 6:15 pm, "Dan Luke" > wrote:
> "Morgans" wrote:
> > What I would give, to see a real, full sized B-36 flying overhead, and doing
> > a few takeoffs and landings and fly-bys, just one time!
>
> When I was a 6-year old Air Force brat on Williams AFB ca. 1953, some B-36s
> went overhead at low altitude and were so loud I peed my pants. The sound was
> so overwhelming I didn't even realize what had happened until I went back in
> the house.

As you get older, peeing your pants might recur. Without the
B-17 to trigger it.

Two old guys are sitting on a park bench. One is complaining
long and loudly about his aches and pains and dysfunctional body
parts; the other finally says, "I feel like a newborn babe."
"Huh!" says the complainer. "How's that?"
"Well, says the other, "No hair, no teeth, and I think I just
wet my pants."

Dan

[Matt Barrow[_4_]]

> wrote in message
ps.com...
> On Sep 18, 1:40 pm, Newps > wrote:
>> wrote:
>> > I have the cylinder from an IO-520 here that had been
>> > detonating. The head is blown clean off the cylinder; the aluminum
>> > fractured at the top of the cylinder threads. Things would get very
>> > noisy, shaky, smoky and scary if that happened. Cylinder pressures go
>> > out of sight during detonation, as do CHTs.
>>
>> That sounds like preignition, not detonation. Detonation is rarly fatal
>> to an engine.
>
> http://en.wikipedia.org/wiki/Engine_knocking
> http://www.streetrodstuff.com/Articles/Engine/Detonation/
> http://www.sacskyranch.com/deton.htm
> http://www.americanaviationinc.com/effectsNavajo.html
>
http://www.avweb.com/news/pelican/182132-1.html (Detonation Myths)