Constant speed props

On Thu, 24 Jun 2004 08:55:30 -0700, "C J Campbell"
wrote:

I think Deakin is worth reading, but some of what he says should be taken
with a grain of salt. His columns are mostly based on experiments with his
own highly modified Bonanza, a few high performance radial engines, and some
theory. In fact, a careful reading of his columns will show no test data for
the most common engine and propeller combinations in use today. The reasons
for this are fairly simple -- few airplanes have the instrumentation that
Deakin needs to test his theories. This is why Deakin's theories for running
lean of peak remain a minority view. Granted, it is a very noisy minority,
but remember that it is also a small minority. I think they have a point.
They may even be right. But they don't have nearly the evidence that they
think they have.

Deakin's Bonanza is highly modified? I thought it had an ordinary
Continental TIO-550. Or is that engine considered highly modified?

Far as I know, from what I've read, the only extra instrument he has
on his instrument panel is the JPI EGT analyzer. He has said
repeatedly that in order to take advantage of running the engine lean
of peak, you really have to have a multi cylinder EGT guage, otherwise
you do not know if you are truly running all the cylinders lean of
peak. One or two may still be on the rich side or at peak which would
cause them to run a lot hotter than the lean ones.

Deakin's remarks are mostly pertinent to running TCM engines, which are much
different than engines from other manufacturers. Not to put too fine a point
on it, some TCM engines are the only ones I know of that so consistently
develop cracks that the most part of an annual inspection basically consists
of measuring and cataloging the spread of these cracks. The engine used in
the early 70's Cessna T206 rarely made it to its 1400 hour TBO, for example.

Barring solid data to the contrary (and Deakin, remember, does not give you
solid data -- he only appears to do that), your airplane should be operated
in accordance with the manufacturer's recommendations. This will ensure that
you maintain your insurance coverage, if nothing else.

I guess I'll have to ask why you think Deakin does not give solid
evidence for his recommendations. The GAMI folks (who's testing he
repeatedly cites) have been testing different types of engines for
years, and developed their precision injectors and proved them with
more testing before marketing them.

In addition, running engines lean of peak isn't new. When radial
engines were what powered most commercial aircraft, cruising them lean
of peak is what just about every pilot was trained to do. My father,
who flew PB4Y-1's and -2's and P2V Neptunes used to tell me about
flying them and how he set up for cruise and he mentioned the leaning
process. Ernest Gann talked about it. There were even percentage of
horsepower instruments in the big engined airliners that pilots were
required to adjust the engines to using the lean of peak setting. It
was the only way to get maximum range out of the airplane, at
reasonable speed.

Charles A. Lindbergh rather famously demonstrated to pilots in the
South Pacific during WWII how to greatly extend their range using lean
of peak operation. The technique worked for the F4U Corsair, the P-47
Thunderbolt, and most famously, the P-38 Lightning. The Lightning's
range was extended to such a degree that it permitted the large twin
engined fighter to accompany a bombing raid on a northern New Guinea
Japanese airbase, which had previously been out of range for fighters.
The Japanese were totally unprepared for the attack as they had
believed no bombing force would dare attack without fighter escort,
and they believed no American fighter had the range to make the trip
from Port Moresby. The attack is sometimes cited as perhaps the single
most effective raid of it's type in the Pacific War. How did
Lindbergh learn about lean of peak operation? I have no idea when he
first learned it or who taught him, but he knew about it when he made
his sort of well known solo trip across the Atlantic Ocean. He leaned
the engine visually, by leaning out the window and watching the
exhaust flame change color as he leaned the engine.

Deakin, as he stated several times in several different articles,
isn't introducing something new. He's re-intruducing a technique that
is old and well proven. It just did not work well with horizontally
opposed aircraft engines until now. It worked very well for radials
because the big ones all had impellers and equal length intake
manifold runners. The impellers distributed exactly the same fuel/air
mixture to each and every cylinder, every time it was ready to fire.
Horizontally opposed engines don't have the benefit of equal fuel/air
mixture being distributed to each cylinder. The GAMI people fix this
by taking your EGT readings which you give them when you install a
multi cylinder EGT guage and record the temperatures for each
cylinder. Then they send you a set of injectors calibrated for each
specific cylinder. If you install them properly (in the correct
cylinders, which is very important), the rich cylinders will be leaned
and the lean cylinders richened. The cylinder to cylinder
distribution now becomes equal enough that leaning should not produce
any rough engine operation. Some people had to return an injector to
be recalibrated, sometimes several times, but eventually the EGT's
reach relative uniformity.

If you can run the engine lean of peak without engine roughness, which
creates less heat in the engine, why would you not want to do that?
Less heat, less fuel burned, nearly the same speed at cruise (a little
less), what's wrong with this picture, anything? Can anyone explain
how this could possibly hurt the engine? It can't burn valves because
they are running cooler than they would if the mixture were set to
rich of peak operation. You can't cause detonation because that's a
result of heat and high power settings. The lean of peak setting is
normally used at or above 7,000 to 8,000 feet where no normally
aspirated engine is producing more than 60 or 65% power. With that
percentage of power, it's impossible to cause detonation. Even
Lycoming agrees with this.

Unless you really need to get somewhere at maximum possible speed, in
which case you would run the engine for best power which is a setting
on the rich side of peak, I don't understand why everyone would not
want to set for lean of peak cruise, when possible, if they have the
right instrumentation and the engine tolerates it.

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

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.

Dave

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