T56-A-14 Turboprop Aircraft Engine

The Allison T56-A-14 Turboprop Aircraft Engine

Power Section

The power section is where the air is compressed, fuel injected, ignited, and pushed through a turbine in order to turn fuel, air, and heat into mechanical rotation. It operates at 13820 RPM, and is controlled via a power lever in the flight station. The compressor has 14 stages which are described as single spool, axial flow. This means the air flows more or less in a straight manner backwards through the compressor, which has only one route the air can take. The diffuser is the highest point of pressure, and is where the air is prepared for entranace into the combustion cans. There are 6 "cans," two of which have igniters. Each has a fuel nozzle which delivers a stream and/or fine spray of atomized fuel. The hot gases are expelled through the 4 stage air cooled turbine and directed through the tailpipe, which provides a small amount of thrust.

The power section also includes the air inlet scoop and accessory drive section, which contains an oil pump and filter, engine control components, fuel control and fuel pump

Reduction Gearbox (RGB)

Provides an overall reduction ratio of 13.54:1, in order to convert the high speed, low torque operation of the engine into the low speed, high torque required for the optimum performance of the propeller. The gearbox uses two stages of reduction to keep the size to a minimum. Stage 1 has a reduction ratio of 3.125:1 and stage 2 has a reduction ratio of 4.333:1

Gearbox accessories include the starter,

torquemeter, oil pump & filter, generator,

engine driven compressor (EDC), and

tachometer generator.

Operation

When power levers in the flight station are moved, a cable connected to the fuel control adds or subtracts fuel flow. This will increase or decrease air temperature flowing into the turbine, which will in turn cause an increase or decrease in power. The actual change in power is achieved by the propeller, which operates at a constant speed. In order to avoid speeding up and slowing down every time fuel flow is changed, the propeller reacts by increasing/decreasing blade angle, which results in a change in the amount of thrust generated by the propeller blades. This is how power is adjusted in a constant speed, variable pitch turboprop engine.

Glossary of Terms

Turboprop: Turbine-Propeller. A type of engine which uses a turbine in order to extract power from heat and rotate a propeller.

SHP: Shaft Horse-Power. A measurement of power used in machines such as aircraft and ships. Denotes usable power at the prop shaft.

Turbine Inlet Temperature: A measure of the air temperature entering the turbine. Temperature is an indicator of output power.

Axial Flow: Indicates manner in which air flows through compressor. Axial means straight, as opposed to centrifugal or radial.

Single spool: Indicates that the compressor has only one path for air to take; there are no concentric rings as in some turbofan engines.

Reduction Gear Ratio: A ratio which describes input rotations in relation to output rotations (of gears or a shaft.)

Torquemeter: The output shaft joining the engine to the reduction gearbox. Serves to transmit power, and as a rigid connection which also provides a means for power measurement.

Reduction Gearbox: Synonymous to a transmission on a car.

Engine Driven Compressor, EDC: An engine accessory which provides compressed air for cabin pressurization, equipment cooling and air conditioning.

Power Lever: Synonymous to a gas pedal on a car. Each P-3C has 4 power levers, one for each engine, in order to indivudually control their thrust by manipulating fuel flow.

General Characteristics

• 4600 SHP* (Airframe limit), 5300 (Engine limit) max output
• 14 stage axial flow, single spool compressor
• 13820 RPM (power section)
• 1020 RPM (Propeller)
• Reduction gear ratio of 13.54:1
• Max Turbine Inlet Temperature of 1077 plus or minus 6 degrees celsius
• Hamilton Standard 54H60-77 Propeller (4 blades, 13 foot diameter)
• Each P-3C has 4 engines, 3 of which have generators, and 2 with EDCs