Erfahrungsberich Leanen
- From: "Walter Diefenthal" <w.diefenthal@xxxxxxxx>
- Date: Thu, 17 Dec 2009 12:38:55 +0100
Hallo zusammen,
hier ein interessanter Erfahrungsbericht von Albin F. Meske,
MAPA #10045, mit dem Titel "THE LEANER (AND SAFER)
MACHINE"
MAPA ist die Abkürzung von Mooney Aircraft Pilots Association.
"In 1985 I bought a 1975 Mooney M2OF with a 200 HP fuel injected
10-360-A 1 A Lycoming and 1100 hours total time. I felt that its
64 gallon fuel capacity would give me the range I needed to cover
most of the sixteen or so Midwestem states in my service territory.
Shortly thereafter, I became aware of Lycoming Service Instruction
1094D, entitled "Fuel Mixture Leaning Procedures." In essence, it
states that a fuel mixture on the lean side of peak EGT is accept-
able within power ranges (75% or lower) that keep cylinder head
temperatures below the recommended limits. On the basis of these
recommendations, as well as a confirming conversation with the
Lycoming factory man at '85 Oshkosh, I started to experiment with
the procedures outlined in this bulletin. Although they result in
3-5% loss of airspeed, the range I get is well beyond the valves
listed in the Pilot Operating Manual for this airplane. Since then,
I have flown more than 1800 hours in this mode. Here are
representative examples of the performance that I am getting:
A winter trip from my home base in Wisconsin to Luflcin, TX,
took 6.1 hours at altitudes of between 4,000' and 8,000', using
just 44 of the 64 galions that were available. My endurance would
have been 8.9 hours. The retum trip was much slower due to
headwinds.I held it at 5,000' except for a short climb to 11,000'
needed to cross a front. I was airbome for 8 hours but I still had
1.4 hours of fuel left when I landed. These were low altitude flights
in cold, high density air. More typical was a flight from Santa Fe,
NM, to Wisconsin which took 7.4 hours at airspeeds of 131-137
knots and at altitudes of 13,000' and 15,000'. I had more than 3
hours of fuel left at touchdown. Overall, my fuel consumption is 7.58
gallons per tachometer hour for the 1,800 plus hours that I have flown
this plane. For longer hops at more moderate temperatures, I plan on
a fuel bum of about 6.5 gallons per hour. As a practical matter, I
almost never complete a flight with less than 3-4 hours of fuel reserve.
Because I fly alone, the plane is always well below gross weight. I
always fly on IFR flight plans at altitudes of 8,000' to 13,000', unless
weather or strong headwinds aloft dictate otherwise. Here is how I
fly the plane: Within 3 minutes of takeoff, and with power at 65-75%,
the engine is leaned to peak EGT. Cylinder temperatures will be well
below red line. I maintain 23-25" manifold pressure on climb out.
At 6,000' to 7,000', the mixture is further leaned past peak EGT
into the "economy range" described in the Lycoming bulletin. It
gives me a fuel bum of about 7.3 gph at 9,000', 6.3 gph at 12,000',
and under 6 gph at 13,000'. There is reduction in climb rate and a
modest speed penalty at low altitudes which disappears -at -about
7,000' or 8,000', all of which adds around 12 minutes to a cross
country flight of 4 hours. It is a small price to pay for the
additional range. When flying into 25-30 knot headwinds at 4,000',
I will use 22-23 inches of manifold pressure and lean past peak
EGT, which costs about 5 knots of airspeed. Normal operation at
75% power would result in a 120 knot ground speed for my plane
model and a 300 NM flight would take 2.5 hours. My reduced power
settings add about 7 minutes to this time, but I use 17.5 gallons
while the cowboy burns 24 or more gallons.
When headwinds approach 50 knots, I use more power, but never so
much that the mixture needs to be on the rich side of peak EGT.
In all cases, my range is optimized. While safety is improved by
having a huge fuel reserve at landing, it would be a hollow victory
if the engine reliability was adversely affected. It turns out that
I need not have worried. I have always questioned the wisdom of 100%
power takeoffs with the mixture at full rich from runways which
(for me) are usually 4-10 times longer than needed. Avgas is an
oil solvent which is being supplied in excess quantities just when
cylinder forces and velocities are at their greatest. Although
aircraft engines are well configured for cruise operation, climbs
and descents appear to have a greater potential for problems. We
hear about these catastrophic failures - engines that seize at
the first power reduction following takeoff or at power reduction for let
down. But what about all the other engines that do not fail? Is excessive
wear taking place at these times and might it be minimized? I wondered
if takeoffs could be performed with power low enough to allow some
leaning while reducing temperature differentials and forces on
cylinders, pistons, valves and valve guides at this same critical
time. Here is what I ended up with: Starting, taxi and run up is
all done with a lean mixture. It idles beautifully with no evidence
of sticking valves. With my low takeoff weight and the extra thrust
of a constant speed Propeller, I use about 2,000' of (a long) runway
to smoothly raise the manifold pressure to 20". The plane is at
liftoff speed by this time and, thanks to the more relaxed pace,
it provides great experience in crosswinds and gusts. I continue
increasing the manifold pressure to my usual climb out setting
of 23-25". The mixture is never at full rich. It will be about
50-75 degrees rich of peak EGT. Further leaning is done as described
above and the remarkable efficiency of a Mooney kicks in with a
vengeance.My 7435V has neither speed brakes nor altitude hold,
so that from en route altitudes of 10,000' or higher, I begin
letdowns from about 60 miles out. From a point slightly above
the assigned altitude, manifold pressure is reduced .5".
If trim is left alone, about 5 minutes later the
plane will be about 100' below the assigned altitude. Unless
it is a busy sector, the controller usually get the drift and
assigns a descent. Where traffic conditions permit, I try to
emulate a parabolic curve, decreasing the power to where 1,500
fpm can be attained with no danger of shock cooling. The mixture
is not changed until approach altitude is reached and, even there,
it is still kept lean in order to keep the engine warm, especially
in cold weather. After I began leaning aggressively, the oil stayed
amber much longer and the engine always ran wen with very low oil
consumption and excellent compression. However, I was curious about
the effects that these techniques might have an the engine. And
considering the amount of hard IFR that I fly, I had it overhauled
at 2,913 hours.The engine tear down told an interesting story. The
cylinder bores had .001" to .002" wear except for the choke area,
here maximum wear was .007". The exhaust valves, seats and guides
were in excellent shape, and Tom Guntly of Guntly Aircraft Repair
commented that the exhaust valve stems had less deposit on them
than he had encountered on engines with much lower time. There
was little wear on the cam shaft and lifters. The crankshaft
journals were highly polished, smooth and round, and wear was
not quite halfway to service limits. No grinding was done and
only bearings were replaced. No problems were expected with the
case, and none were encountered. I opted for new Lycoming cylinder
assemblies, and someone now has a beautiful set of first run
cylinders with a heat and stress historv that is modest by any
conceivable standard.
The takeoff procedures that I describe are
only for experienced owner-pilots who are extremely familiar
with the performance of their aircraft and are best used with
constant speed propellers because of their increased thrust at
takeoff. There are many circumstances where full power takeoffs
are necessary.
You should have a couple of hundred hours of cross
country experience, flying to a variety of airports, before trying
this.The economies from this kind of operation are impressive. The
fuel savings for my 1,800 hours of use are at least 3,600 gallons
- worth $7,200. engine TBO increased 62% - worth $4,500,
and the overhaul costs less. If costs were prorated from day
one of the aircraft, the savings would easily exceed $20,000.
More importantly, the low engine stress levels, especially at
takeoff, affords a peace of mind that far transcends the monetary
savings.When a Hobbs meter is the basis for flying charges, it
encourages short runups and operation at full power from
takeoffuntil the last second when reduction to zero power
will get the plane down in time to make the runway. It begs
for engine abuse and I often hear aircraft from a nearby airport
flying overhead at "rental speed." Tachometer time does not
penalize longer warmups, slower taxiing and run up with moderate
engine operation nearly as much. I would think twice about buying
or renting a high hour plane with a Hobbs meter. Careful Engine
and fuel management helps to reduce the boredom of flying alone
for long periods of time. A database Loran coupled to the autopilot
greatly reduces cockpit workload, and a storm scope relieves me of
preoccupation with weather ahead. Personal comfort is an important
safety consideration for long flights. My liquid intake is reduced
before flying. A cup of coffee, taken at least an hour before
departure, takes care of itself by takeoff time. During climb out,
I eat a couple handfuls of a salty snack to lock in body fluids.
Cheese flavored styrofood seems to work best. I am sure that my
low salt diet increases the effect of the snack in extending my
personal range. On long flights, one or more pieces of fruit
seem to work best to assuage thirst and provide energy. It
appears to be mildly antidiuretic as well. For me, these
procedures totally eliminate discomfort and distraction, even
on 7 and 8 hour flights, and the restroom is no longer a first
priority upon landing. If unexpected weather is encountered en route,
there is less possibility that the choice of a longer and safer
route (or a decision to go around at landing) would be affected
because of personal discomfort. I appreciate the efflciency and
speed of the Mooney. It has a strong, stable and comfortable
instrument platform with very few bad habits, and an operating
cost about as low as one could hope for, onsidering the number
of systems that must be maintained. I don't know if any other
airframe would respond to this type of low power operation
with so slight a reduction in cruise performance.Best of all is
the peace of mind and safety that comes from the humongous endurance
and range that both I and my plane enjoy. I still remember the surprise
and respect of an approach controller who knew that I had departed
more than 4 hours earlier. During a 35 minute holding pattern at night, in
IMC while the airport was being plowed, he called to ask how much
fuel I had left. I replied, "Three and three-quarter hours." In a relieve
tone, he answered, "That's great, Three Five Victory."
It made his job much easier, as well as mine."
Wahrscheinlich wird dieses Thema nur wenige hier interessieren.
Ich habe den Artikel trotzdem geposted und hoffe auf Meinungs-
äußerungen.
Gruß Walter
.
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