Under those fancy cowlings is a pretty amazing little engine. The Pratt and Whitney Canada PT6A-42, producing 850 lbs of shaft horsepower, 2230 lbs of torque and approximately 135 lbs of jet thrust through the engine exhaust. To protect the engine from damage, those smart engineer people at Beechcraft invented a number of systems.
One of those protection systems is called the Engine Air Inlet Lip Heat, the heated engine inlet gets its heat source from engine exhaust, the engine inlet is always heated and cannot be turned on or off.
The engine exhaust is fitted with a small pipe (scupper) that pulls some of the exhaust gases away from the main exhaust stream. The scupper is connected with heat resistant clamps and heat-resistant pipes to the engine inlet cowling (see next photo)
The heat-resistant pipe is mounted to semi-flexible pipes to allow for fitting of the lower inlet cowling
Here is another view of the inlet cowling and the inlet lip heating system.
The next invention is the engine inertial separator system or Engine Anti-Ice, pilot controlled electrically actuated, preventing ice or other foreign objects (sand, dust) from entering the engine inlet plenum and prevents ice from forming on the engine inlet screen. This system is generally turned on before engine start, left open during taxi and turned off just prior to entering the runway (unless conditions dictate otherwise, i.e. gravel strip take-off, winter operations including snow-covered runway). Remember this is a reverse flow engine, the air is drawn from the back of the engine. The air moves through the inlet cowling, some of the air is forced over the oil cooler and some of the air is directed to the engine inlet screen (see below)
The engine inlet screen is the very last protection you have before FOD enters your million dollar engine. If you look closely, the screen is not designed to prevent ice or snow from entering the engine, that is the inertial separator’s/ice vane’s job. But when do you turn the inertial separator/ice vanes on? The Beechcraft manual is very implicit and directs you to deploy the vanes when in icing conditions, plus +5 deg C or lower, or in visible moisture. When the temperature is 15 deg C or greater, close the vanes to ensure adequate airflow through the oil cooler.
Engine inertial separator/Ice vanes not deployed
Engine inertial separator/Ice vanes deployed
As ice particles or water droplets enter the inlet, they accelerate rapidly by the venturi effect of the extended vane. Due to their greater mass and greater momentum, the moisture particles or ice accelerate past the screen and discharge overboard through the ice vane’s bypass door as the airstream makes a sudden turn before entering the engine through the air inlet screen.
Engine inertial separator/Ice vane bypass door in the open position
Many wise King Air pilots have a policy, if they see any visible moisture with an OAT of 5 deg C or less (ice crystals at night can be seen with the strobe lights, if you see snow or ice crystals, then turn on your ice vanes immediately), if they are descending into cloud (turn on the vanes), when you do turn them on (they take about 6 seconds to deploy in each engine) you should expect a greater fuel burn. If your entire trip is requiring the vanes to be left open, you might want to consider the extra fuel you might need
My last word of caution, if you wait to see a buildup of ice on your aircraft before you turn on your ice vanes, you are probably already damaging your PT6 engine. How? ice builds up underneath the inlet screen and when you descend into warmer air, a piece can break off and FOD your engine!
This is a PT6 engine compressor wheel, damaged by ice ingestion during the descent into a convective cloud in the summertime. It is painted red and left in the ground school classroom to remind everyone that forgetting to turn on Engine Anti Ice is a really expensive, possibly career limiting move.
I hope you enjoyed the quick look at aircraft systems and the walk-around of the King Air 200. There are so many systems to look at and are beyond the focus of this blog. As a turboprop pilot, you need to know how your aircraft systems work for your PPC ride, you could be asked almost anything with regards to aircraft systems.