202: Propulsion System

202.1 System components and component parts Referring to a standard print of this system or the actual equipment, identify the following system component parts and discuss the designated items for each:

202.1.1 State the function of the Propeller system

Comprises that portion of the powerplant that converts engine torque into usable thrust.

202.1.2 State what part of the propeller system has electrical anti/de-ice components.

Spinner and blades – embedded in the plastic material of the front and rear spinners and in rubber heater pads adhered to the leading edges of the blade.

202.1.3 The six major (components) subassemblies of the propeller.
* Hub
* Dome
* Four blades
* Electrical contact ring assembly
* Low pitch stop assembly
* Pitch lock regulator assembly.

202.1.4 State the function of the following major engine components

a. Reduction gearbox – The reduction gear assembly reduces the high-speed, low torque energy of the propeller section. The energy is reduced to the low-speed and high-torque required for efficient propeller operation. The speed-reduction is accomplished in two stages. The first stage reduction is accomplished by a spur gear set in a ratio of 2.882 to 1. The second stage reduction is accomplished by a planetary gear set in a ratio of 4.333 to 1. The overall reduction is 12.490 to 1. When the engine rpm is 100%, reduction gear rpm is 1,106, power section rotor rpm is 13,820 and propeller shaft is 1,106.

b. Torquemeter – The torque-meter assembly measures the shaft horsepower output of the power section assembly. Two concentric shafts make up the drive shaft between the power section assembly and the reduction gear assembly. The inner (torque) shaft carries the load and produces the twist to be measured. The outer (reference) shaft is rigidly connected to the torque shaft at the drive-input end. The drive output end transfers the output for measuring purpose.

c. Compressor assembly – Compresses air, air then passes through the successive stages of the compressor toward the combustion section. Under certain operating conditions, such as starting and rpm accelerations/decelerations below 94 percent, this pressure buildup in the compressor can reach a value sufficient to cause compressor stall. To prevent compressor stall, bleed air valves are installed at the 5th and 10th stages to unload the compressor, thereby greatly improving airflow characteristics at critical engine speeds.

d. Accessory drive housing – The accessory drive housing assembly is mounted on the bottom of the compressor air inlet housing. Mounting pads for the fuel control fuel pump and external scavenge oil pump are on the rear face of the housing. Mounting pads for the speed-sensitive control and speed-sensitive valve and main oil pump and filter are on the front face of the housing. The housing has gear trains for driving all the power section gear-driven accessories at their proper speed. Power for driving the gear trains is taken from the compressor extension shaft by a vertical accessories main drive gear shaft.

e. Combustion section - As compressor air passes into the combustion section, it is mixed with fuel supplied by the engine fuel system. Igniter plugs in No. 2 and No. 5 combustion liners fire the fuel-air mixture. The fuel-air mixture in the other 4 liners is ignited through crossover tubes

f. Turbine section -. The hot gases from the combustion section impinge on the four-stage turbine that converts the heat energy to torque and transmits torque back to the compressor and through the interconnecting Torquemeter shaft to the reduction gear assembly.

202.1.5 State the function of the following fuel system components

a. Boost pumps – Two electrically operated boost pumps are submerged in each tank: one mounted forward and one aft. The boost pumps provide uninterrupted fuel flow to both engines, down to 1 % fuel remaining, at all normal landing altitudes. The aft pump is a dual impeller pump in a separate chamber within the tank. It provides a sustaining fuel flow during limited period of negative-g flight. Each of the four boost pumps can sustain two-engine operation at military power up to the service ceiling of the aircraft. Below 6,000 feet with all tank boost pumps inoperative, the engine-driven fuel pumps can provide the fuel necessary to operate the engines.

b. Fuel tank vent – The tanks are vented through a common vent line that is open to the atmosphere, on the right side of the aircraft. The vent valves are float-type that close to prevent fuel spillage out of the vent line.

c. Fuel quantity probes – Four probes are in each tank in positions that provide maximum probe submergence for all fuel loads and aircraft attitudes. One probe in each tank supports a compensator that compensates for fuel density fluctuations because of temperature changes or to the use of different types of fuel. The probes transmit signals to the fuel quantity indicators.

d. Fuel jettison (dump) – A gravity fuel dump system permits emergency in-flight weight reduction. The system permits jettisoning fuel from both tanks to approximately 20 percent fuel remaining (1,212 pounds per tank), depending on the aircraft attitude. With the fuel tanks full, jettisoning to the 20 percent fuel-remaining level is accomplished at approximately 1,300 pounds per minute.

202.1.6 State the maximum fuel capacity

a. 1,824 gallons, 12,400 lbs. Note: weights are based on 6.8 pounds per gallon of JP-5 fuel for standard day conditions.