Page 20 - Volume 11 Number 4

Ask the Expert Auto-Ignition –
History and Usage
by Tom Clements
If you were to gather a group of King
Air pilots together and ask them
their understanding of and usage of
the Engine Auto-Ignition system, I will
wager that you would receive a wide
variety of responses. Some will arm
it on every takeoff and leave it armed
until after landing, while others will
use it only when in icing conditions.
Some will say it prevents an engine
flameout, while others will say its
purpose is to provide a relight after
the flameout has already occurred.
Let me see if I can add some historical oil cooler scoop. context to this system and describe
its purpose in detail.
The very first King Air models did not have an auto- ignition system. In fact, they did not have an ice vane system! “But, Tom, last month you wrote how important ice vane usage is for engine ice protection, and now you are telling me inertial separators weren’t even installed on the King Air initially?! How did they fly in ice?!”
As surprising as it is today, after ice vanes have existed for so long, the first model 65-90s (also known as “Straight 90s”) used alcohol spray nozzles in the cowling. Similar to alcohol windshield or prop anti-icing, a pump forced the alcohol mixture from a storage tank out through the ejectors. The spray very effectively eliminated the ability for ice to form on the engine intake screen. The system worked quite well ... until the alcohol tank went dry. It could sometimes be quite a hassle to find an FBO that could readily refill the tank so complaints were received by Beech’s Customer Service department that this alcohol method certainly had its drawbacks.
Before continuing with our main discussion, allow me to add a couple of interesting tidbits. If you look closely at a picture of the prototype King Air or one of its first progeny, you will notice that the cowling is different. It is missing the oil cooler housing, or scoop, on the bottom. Due to the absence of the scoop, the cowling is noticeably cleaner in design. So where is the oil cooler and where is it getting its airflow? It was located near the back of the cowling, below and behind the location where the inlet air turned the corner to reach the engine’s inlet
18 • KING AIR MAGAZINE
King Air 90 (LJ-1) on its maiden flight. Notice the original clean cowling without the
plenum. (Its location, in fact, was quite similar to how the oil cooler is housed in the entire 200-series.) Some of the air entering the cowling inlet continues aft to flow across the fins of the cooler instead of being ingested by the engine.
The second interesting tidbit is to point out that it was a good thing that the early King Airs did not use engine bleed air as the pressurization air source! Since that air would be mixed with alcohol when the anti-icing system was in use, the pilots and passengers might be getting a bit higher than the airplane as the alcohol affected their brains! Instead of bleed air, the pressurization source was from a roots blower type of supercharger driven by the left engine. Its intake was located in a place such that no alcohol found its way in.
Back to our main story: In response to the complaints about the inconvenience of refilling the alcohol tank, the Beech engineers came up with an inertial separator system, the first ice vane design. Instead of the well- known T-handles that operate the vanes mechanically via a push-pull cable, the first system deployed the vanes via an air-operated piston/cylinder arrangement. Yes, this air was engine bleed air. All King Airs, even those with superchargers, still utilize “Little P3” bleed air for things like deice boots and, in this case, the ice vane actuators. By the way, the engineers were smart enough to design the system such that if all electric power were lost, the pneumatic actuator would default to the extended position, thus protecting the engine in the event that icing conditions were encountered.
APRIL 2017