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<< Lancair Builders' Mail List >>
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My 360A1A is equipped with a “Skinny Dipper” that
provides a constant indication of crankcase oil
level using a capacitance probe mounted inside
the filler tube, which extends to the bottom of
the crankcase. It provides a visual and audible
low level or high temperature alarm.
While the engine is running oil level drops about
1.5 – 2 quarts. My guess is it needs about two
quarts in the bottom of the pan to avoid sucking
air, so that adds up to 3.5 – 4 quarts stone cold
to avoid oil pressure (and cardiac) palpitations.
Of course you need that much at the end of flight
so add the amount consumed which depends on the
rate of consumption and duration of the leg.
I normally use low power settings and drain about
two quarts less than I had put in at 40hr change
intervals. An oil separator is not required
unless the acro gets too exuberant, and the belly
is easily cleaned (small area and no rivets or
antennas). I use a dishwashing detergent water
mix to cut the grease followed by Simple Green in
a spray bottle which works great on exhaust
stains, wear rubber gloves and long sleeves to
avoid lead exposure.
The oil sump contains the fuel/air distribution
spider which provides a substantial amount of oil
cooling, especially in carbureted engines since
the evaporating fuel absorbs heat from the air
and spider. As the oil level goes down less of
the spider is submerged resulting in less heat
transfer and higher oil temps. I generally run
5.5-6 quarts in the winter for warmer temps and
6.5-7 in the summer.
Several years ago I decided to replace the cork
rocker box gaskets with silicone rubber gaskets.
It just happened to be winter and when the covers
were removed there were hundreds of small water
droplets covering all the surfaces including the
valve springs. The previous flight had been a
high altitude cross country ending with a cruise
descent to landing, and the engine never warmed
up enough to dry out. Now I finish cold weather
flights by slowing down 20 miles out and dropping
the gear and 15-20 degrees of flap. The CHT time
constant is short and the oil temp time constant
is long so if you drop down to pattern altitude
and grind in at a high power setting it wastes
fuel, subjects people on the ground to
unnecessary noise and the cylinders will cook
before the oil heats up. The trick is to lower
the gear up high on a normal decent profile, 6-7
miles per thousand feet, and motor in using a low
power setting (1700 at 12-14” leaned to peak EGT)
at 80-90 MPH. The CHT levels off at a
comfortable 160-180C, and the oil temp slowly
ramps up to the desired 80-90C range. The noise
level and fuel flow are quite low, the only down
side is a few extra minutes of flying which can
be quite beautiful at the end of a good day.
I haven’t seen the Skinny Dipper advertised in
several years, the last I heard the gentleman was
moving into high end boating applications for
more bucks and less liability.
My 1.8 cents worth.
=====
BILL HANNAHAN
WFHANNAHAN@YAHOO.COM
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Please send your photos and drawings to marvkaye@olsusa.com.
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