Constant speed props

On Thu, 24 Jun 2004 20:16:30 GMT, Dave S
wrote:

It's possible that the POH's specify rich of peak operation because
that produces the highest cruise speeds, which is often what sells the
airplane.

Corky Scott



The POH (provided by the airframe manufacturer) is not the same as an
operating manual provided by the engine manufacturer.

In regards whether to lean past peak or not and people following
proper procedures, here's what the Cessna Pilot Center Training manual
says:

"In order to lean, you pull back the mixture control knob until the
EGT guage reaches its highest temperature reading (called peak EGT)
and then starts to decrease. At this point enrich the mixture until
it's 50 degrees cooler than peak EGT. You can also lean by pulling
back the mixture control until the RPM just starts to decrease, then
continue leaning until it drops 25-50 rpm." Both instructions are
describing how to adjust the mixture to below peak EGT.

I've seen in Deakin's columns a response from Lycoming (response to
his mixture control columns) to the effect that "we would not
recommend lean of peak to our worst enemy". In light of the Cessna
Training Manual's instructions, I wonder if the two entities (Cessna
and Lycoming) should communicate a bit better?

Corky Scott

On Fri, 25 Jun 2004 10:35:14 +0200, Thomas Borchert wrote:

Greg,

It bothered me how
lean he was suggesting the engine should be run.


I am really interested: What exactly bothered you? What points in his
line of reasoning could you not follow? What part of his data did you
find lacking?

Well, keep in mind that it was the first article of his that I read. It
presumed that I had already been introduced to the LOP concept. I had
not. In fact, for some engines that I used (r/c nitro and car engines),
too lean is a great way to completely destroy an engine. Thusly, it did
bother me to see him talking about leaning an engine beyond where I would
normally expect it be richened back up.

Since that comment, I have continued to read many more of his articles. I
Think he makes many excellent points and has a powerful argument. Am I
completely sold on the notion? Nope. Am I interested enough to learn
more about it? Absoluetely. In fact, I pushed a pointer of his articles
to a pilot friend of mine (my father). It should make for some
interesting conversations. I'll be interested to find out if he's
even heard of the concept before, as he's been flying before I was born.

Cheers!

Greg

On Fri, 25 Jun 2004 11:44:30 -0500, Greg Copeland
wrote:

Well, keep in mind that it was the first article of his that I read. It
presumed that I had already been introduced to the LOP concept. I had
not. In fact, for some engines that I used (r/c nitro and car engines),
too lean is a great way to completely destroy an engine.

But Greg, you just described a situation worlds apart from what Deakin
advocates. Running a race engine, any race engine, at full power and
too lean is not anywhere near the LOP description for aviation
engines. Yup, running an engine like that probably would blow it up.

Deakin is talking about cruising, with the engine producing no more
than 60% power. At 60% power virtually all experts agree that there
is no way to hurt the engine no matter where you decide to set the
mixture. Full rich, lean to the point where it's stumbling, it won't
matter, the engine can't hurt itself while making only 60% power.

For takeoff, his recommendation is to use FULL RICH. Not only full
rich, he recommends those who are flying behind the large 6 bangers
check out the mixture setup to make sure that it is reaching the
proper full fuel pressure. If it's set a little too low, something
below the specified maximum pressure, *THAT* situation is worrisome
and could cause engine problems. That's because the engine needs to
have the full rich mixture at takeoff power to stay cool. Having the
mixture on the rich side of ideal slows the burning down enough to
keep the Peak Pressure Point at around 16 degrees past top dead
center.

If the mixture isn't rich enough to achieve this, in other words if
it's a bit leaner, it may burn fast enough to cause the PPP to occur
with the piston closer to top dead center. The closer to top dead
center the PPP occurs, the higher the pressures and the more heat
produced, and THAT is why running rich keeps the engine cool.

This only happens, of course, because aircraft engines are stuck using
fixed timing. If they had automatically adjusted variable timing, the
mixture could be set for best power and left there (saving gas) with
no need to worry about whether the engine will overheat or not because
the timing would adjust to the proper 16 degrees ATDC regardless the
conditions or power setting.

And you thought "cooling the engine with fuel" literally meant that
the rich mixture hosed down the cylinder? Big smile

Corky Scott

"C J Campbell" wrote
I merely point out that his theories are controversial -- they are hardly
universally accepted, as even this thread amply demonstrates.

A thread on usenet demonstrates no such thing. Evolution is hardly
controversial within the scientific community, yet it is debated ad
nauseam on usenet. Deakin's theories (which are really not his at
all, and not really theories) are really no more controversial - in
fact, they formed the basis of normal operating practice for piston
fighter and airliners for as long as there were piston fighters and
airliners.

As I said, I
think he has a point, but I have to consider that the engine manufacturers
and aircraft manufacturers might know at least as much about their products
as GAMI does.

That was true once, but is true no longer. For all practical
purposes, there hasn't been any progress made in piston aircraft
engines for decades. Neither Lycoming nor Continental have a design
engineering staff anymore. Most of the knowledge has been lost.

It's actually fairly common for knowledge to be lost that way. Doing
development is fun; documenting it isn't. When the people who did the
development move on, a lot is lost. Corporate-mandated processes
generally don't help much - they just cause the brightest people to
move on sooner.

Michael

On Fri, 25 Jun 2004 14:09:20 -0400, charles.k.scott wrote:

On Fri, 25 Jun 2004 11:44:30 -0500, Greg Copeland
wrote:

Well, keep in mind that it was the first article of his that I read. It
presumed that I had already been introduced to the LOP concept. I had
not. In fact, for some engines that I used (r/c nitro and car engines),
too lean is a great way to completely destroy an engine.

But Greg, you just described a situation worlds apart from what Deakin
advocates.

I know that. But, when you're ignorant of the details of what he's
prescribing and know only the scary details of your own universe, it's a
natural reaction. I'm not saying it's justified. I'm just saying, that
was my reaction.

Running a race engine, any race engine, at full power and
too lean is not anywhere near the LOP description for aviation
engines. Yup, running an engine like that probably would blow it up.

Yep. That's certainly a good point.


For takeoff, his recommendation is to use FULL RICH. Not only full
rich, he recommends those who are flying behind the large 6 bangers
check out the mixture setup to make sure that it is reaching the
proper full fuel pressure. If it's set a little too low, something
below the specified maximum pressure, *THAT* situation is worrisome
and could cause engine problems. That's because the engine needs to
have the full rich mixture at takeoff power to stay cool. Having the
mixture on the rich side of ideal slows the burning down enough to
keep the Peak Pressure Point at around 16 degrees past top dead
center.

I have read that article since my ignorant gut reaction was made known.
I think he makes a lot of sense! I think he makes a powerful argument. I
think he goes to lengths to describe when, what, why, and how. That's all
excellent. But, if it's my $20k+ engine on the line, that's a long hard
thought before I'd commit to it. After all, he makes it perfectly clear
that you have to have an engine monitor, which makes it a
hole-in-your-wallet type of commitment for many. Not to mention,
irrational whispers in your head can sometimes just be a bitch to get
past, no matter what data is telling you.

Needless to say, I'll certaily be looking more into it. It sounds very
interesting and it does seem to be well reseached, both presently and
historically. Just the same, I'd still like to be more educated on the
topic.


Cheers!

Greg

Greg,

After all, he makes it perfectly clear
that you have to have an engine monitor, which makes it a
hole-in-your-wallet type of commitment for many.


One could (succesfully) make the argument that the information gleaned
from an engine monitor will save you more in money than it costs.

--
Thomas Borchert (EDDH)

On Sat, 26 Jun 2004 09:58:44 +0200, Thomas Borchert wrote:

Greg,

After all, he makes it perfectly clear
that you have to have an engine monitor, which makes it a
hole-in-your-wallet type of commitment for many.


One could (succesfully) make the argument that the information gleaned
from an engine monitor will save you more in money than it costs.

This is true. I read one such example where he had an 18gph engine
running at 15gph. Anyone have any idea what can be done with some of the
smaller engines? Say, something in the 9-11gph range? If we assume the
same ratio of savings, that puts us at 7.5 - 9.2 gph, right? At a savings
(unsupported assumptions here) of 1.65gph, on average, at $2.40/g, that's
$3.96 saved per hour. At, say, 100hr/year, that's $396 saved per year.
If we assume the 700 series JP Instrument, installed, that's something
like $1700 - $2000 installed (right?). So, that means we can recoup our
investment in 4.3 to a little over 5 years. Ouch.

Granted, the more you fly and the bigger the fuel rate of your engine, the
quicker it's going to pay off, but I think it's hard to justify it across
the board on a economy savings basis.

If we run with the demoed 3gph savings, at $2.40g, that's $7.20/hr
savings. If we assume 200hr/yr, that's $1440 savings a year, which makes
the cheap JPI monitor paid for in about 1 1/4 years. And that is still
assuming that it's a four cylinder. Realistically, it's probably going to
be a 6-cylinder, which is going to raise the price again. So, again, even
with 200hr/yr, we're looking at something about two years for a return on
our investment.

So, it doesn't look like quite the sweatheart deal after all. Now, if
there are some supporting numbers which indicate a return on TBO, then we
might have something to sing about.

Just some fun numbers for food for thought.

Cheers!

Greg

"Thomas Borchert" wrote in message
...

One could (succesfully) make the argument that the information gleaned
from an engine monitor will save you more in money than it costs.

It's not really an economic issue; an engine monitor can help diagnose
impending mechanical problems either on the ground or in the air before they
become more serious -- that's all the justification needed to install one.

---------------------
Richard Kaplan, CFII

www.flyimc.com

On Sat, 26 Jun 2004 10:53:43 -0500, Greg Copeland
wrote:

So, again, even
with 200hr/yr, we're looking at something about two years for a return on
our investment.

So, it doesn't look like quite the sweatheart deal after all. Now, if
there are some supporting numbers which indicate a return on TBO, then we
might have something to sing about.

Just some fun numbers for food for thought.

Cheers!

Ok, it may take two years to get your investment back in money saved
from fuel not burned. Isn't that better than not getting any
realization of savings ever?

Also, Deakin doesn't say you must have the JPI instrument, there are
at least three other multicylinder EGT guages that show you what's
happening in each cylinder, including one that is NOT a digital LED
type. That one costs less than $1,000.

Corky Scott

wrote in message
...
On Sat, 26 Jun 2004 10:53:43 -0500, Greg Copeland
wrote:

So, again, even
with 200hr/yr, we're looking at something about two years for a return on
our investment.

So, it doesn't look like quite the sweatheart deal after all. Now, if
there are some supporting numbers which indicate a return on TBO, then we
might have something to sing about.

Just some fun numbers for food for thought.

Cheers!

Ok, it may take two years to get your investment back in money saved
from fuel not burned.

And that's just fuel; it doesn't even take into account wear and tear due to
higher CHT temps.

Isn't that better than not getting any
realization of savings ever?

Let's see: About 40 cents a gallon time 15 gph = $6.00 and hour * 200 horus
a year = $1200 per year.

Figure in the amortized cost of a early TOH (two F33's I looked at had two
and three before they hit the 1700 TBO...one as early as 380 hours TTSN)
from running ROP (at least these two admitted such).


Also, Deakin doesn't say you must have the JPI instrument, there are
at least three other multicylinder EGT guages that show you what's
happening in each cylinder, including one that is NOT a digital LED
type. That one costs less than $1,000.

Quite. He merely says the JPI is _his_ favorite.