ach generator (Nf)
Identify the type of engine oil system utilized in the 250C – 20J.
Pressurized, circulating, dry-sump system (Dry sump, meaning oil reservoir is located separately from the oil pump.)
State the function and location of each component of the engine oil system.
: Holds engine oil and provides mount for the oil temp bulb.
: Located inside the accessory gear box, driven by same shaft which drives the Ng tach generator. Spur gear oil pump with 1 pressure and 4 scavenge elements. Delivers oil under pressure the Internal Oil Filter Assembly.
: Contains Pressure Regulating Valve, Filter Element, and Differential Pressure bypass valve.
Delivers signal via wet line to the Oil Pressure Gauge.
10 micron pleated paper, bypass type filter.
Located near the Airframe External Oil Filter. Cool oil is sent back to the reservoir. At 71oC 160oF valve begins to open and allow hot oil to flow through the radiator type cooler.
Cooled by air from the squirrel cage fan, which is driven off of the tail rotor shaft. This same air is ducted and sent forward to cool the transmission oil and hydraulic fluid.
Identify how to determine the engine oil level and why it is important to know the exact level.
Sight gauge: Located on the Stbd. side of the Oil Tank.
Dipstick / Filler Cap: Located on Port side of the Oil Tank. This is the only way to know the exact amount. This is important because if freewheeling unit oil seal fails, transmission oil under pressure will enter the accessory gear box (which is not under pressure) and cause and overfill condition.
State how engine oil temperature and pressure information is transmitted to the cockpit.
Temperature: 28 v DC oil temp bulb located in the oil tank.
Pressure: Wet line from pressure sensing port (downstream of internal filter)
State why fuel metering is important for a turbo shaft engine by identifying the problems which can occur if fuel is not metered correctly.
Excessive temperature, Compressor Stall, Rich or Lean Blowout
Identify the type of fuel control used in the 250C–20J engine and state how it controls engine power.
Ng Fuel Control Unit: Ng gear train drives flyweights which meters fuel. During Start compressor discharge pressure is used to meter fuel.
Nf Governor: Varies bleed air control line air pressure which goes to the Ng Fuel Control which in turn varies fuel to the engine.