Or, How To Keep Your Belly Clean (Your Plane's, Anyway)
You know what a WHUFFO is, right? It's a guy who asks, "WHUFFO"
do you have a frammis gasket on the plane? Or in this case, an Air
Oil Separator? From time to time we at Aero-News will ask WHUFFO on
behalf of our readers -- or for our writers, who will go fearlessly
to ask these questions, without fear of embarrassment.
So... WHUFFO do you need an air-oil separator on your plane?
"Mostly, people use them for cosmetics," John Kochy, technical
supervisor for Airwolf Filter Corporation explains. "They hate
having oil on the bottom of the plane."
Well, why does oil get all over the bottom of a plane? It turns
out, John tells us, that most aero engines are designed with open
crankcases. The crankcase breather allows the crankcase to out-gas
any excess pressure. (Automotive engines had similar open
breathers, before emissions regulations required positive crankcase
ventilation -- that what the "PCV" in your car's "PCV valve" means
-- first in Californian in 1965, then in the rest of the USA and
the world).
If the pressure in the crankcase is positive relative to the
ambient air in the engine compartment, the gases in the crankcase
will come out. These gases usually contain some oil in
suspension... as the gases join the cooling air out the cooling air
exhaust, some of this breather oil is deposited on the belly of the
plane, or the underside of a twin's nacelles. That's where the
cooling air -- with its cargo of suspended oil -- comes out.
It's not actually the plane scheming with its parts to drive you
mad, it's just the laws of physics doing their thing.
How you fly the plane makes a difference, too. Most
aero-engines, Kochy explains, have wet sumps in which the
lubrication oil pools. This is fine and good if the engine is
operated within limits, but many limits include, for instance,
pitch limits of approximately twenty degrees, plus or minus.
If you exceed those angles, lubricating oil builds up at the
ends of the engine, and this oil can get beaten to froth by
accessory gears -- then go overboard through the breather. This is
one potential culprit when your plane seems to burn a lot of oil
while flying in the traffic pattern, but doesn't burn nearly as
much on a cross- country. Steep pitch attitudes, then, can
contribute to what appears to be excessive oil "burn."
An Air-Oil Separator prevents that by removing the oil from the
crankcase exhaust air, and dumping the air into the cooling
airflow. It doesn't get all the oil out, but Kochy claims that
Airwolf's air- oil separators are 90 percent efficient. That's a
lot of degreasing that owner-pilots are being spared by Airwolf
separators.
Despite this, some owners still complain. "The oil stain is gone
but now there's a thin film on the belly of the plane." Quite
possible, because no separator is 100% effective. But it still adds
up to a substantial reduction in time and effort expended on
keeping the winged chariot clean.
A small air/oil separator, like MiniSep, which Kochy introduced
this year at Sun n Fun (above), can handle either an engine's oil,
or a wet vacuum pump's (Airwolf also makes wet vacuum pumps, a more
reliable technology than the more common OEM dry pump). A larger
separator can handle both.
Installing a separator isn't that hard. It was designed with the
mechanic in mind, and comes complete with all parts for
installation. It can be mounted on the engine, the engine baffle,
or the firewall, with as few as four bolts to hold it in. The upper
and lower parts of the canister can rotate vis-a-vis one another to
make it easy to set it up.
It's affordable, too. The new small filter (or to call it its
proper name, MiniSep, which Airwolf saw as the logical name of the
"baby" of its AirSep line) is just $395 with all equipment required
for installation.
Even the regulatory path has been smoothed -- the part is PMAd
and a blanket STC covers the installation of the device on
literally every single- or twin-engined aircraft ever type
certified. Kochy showed us the master list of aircraft covered by
its STCs, a document called by the FAA an Approved Model List. The
massive document took a year and a half for Airwolf to assemble,
but as a result, Airwolf filters can be installed with just a
logbook entry and the addition of the STC to the aircraft's
permanent maintenance records -- no further STCs, no Form 337, no
hours of flight test.
No grease, no grime, no oily belly. Your plane's, anyway.