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.

FMI; www.airwolf.com