Downloaded from https://www.everyspec.com ADS-79D-HDBK Reduced Order Algorithm (ROA). ROAs are simplified models of damage accumulation based on the more comprehensive analyses used for life calculations. These models are developed to run in real time to provide life consumption and remaining life predictions either onboard the aircraft or at the ground station after the flight. Safe Life. The number of hours or cycles a component is expected to operate without failure under a nominal mission profile or set of mission profiles. Usage Monitoring. A tracking method utilized for determining the life consumed or the life remaining on a life-limited part in a gas turbine engine.
G.4 DESCRIPTIONS G.4.1 Turboshaft Engine. A turboshaft engine is a class of gas turbine engine designed to produce shaft power rather than thrust power. Thrust power is typical in turbojet and turbofan engines. The majority of turboshaft engines are used in helicopters, but they are also found in tanks, marine applications, and power generation. The GE T700 typifies a turboshaft engine and is shown in Figure G-1. This engine is used in both the H-60 and the H-64 among other aircraft. A cross section of this engine, shown in Figure G-2, illustrates the major components of a turboshaft engine.
A turboshaft engine typically consists of five basic sections; a diffuser or intake, a compressor, a combustor, a turbine(s), and a nozzle or exhaust. In a turboshaft engine, the intake and exhaust are relatively simple components and require little in the way of servicing or monitoring. The basic function of the compressor is to increase the pressure of the incoming air. This is accomplished through a combination of rotating airfoils (rotors) and non rotating airfoils (stators). The work required to operate the compressor is provided by the turbine section which extracts energy from the fluid again using a combination of rotors and stators.
The T700 engine axial and centrifugal compressors generate a 21:1 pressure ratio. The compressor section delivers air to the combustor section as well as bleed air for starting, operability, and pneumatic and heating systems. As shown in Figure G-2, the gas generator turbine is upstream of the power turbine on the T700. On one shaft, the gas generator turbine extracts work from the hot expanding gases to drive the compressor section. On another shaft, the power turbine is used to generate shaft output which drives the main transmission. Depending on the design, the engine accessories may be driven either by the gas generator (T700) or by the power section.
As these working sections contain components rotating at high speeds, they are typically the engine components requiring the most monitoring for both operations and maintenance. A combustor is used with fuel injector nozzles to mix the fuel and the air. The combustor section is where the energy stored in the fuel is extracted through burning (combustion). Higher temperatures in the combustion chamber result in higher energy capable of being extracted, but they also result in lower engine life, thus the combustor is a key component to the engine life. For example, the T700 engine typically has a 5,000 hr service life but this is strongly driven by combustor temperature.
Typical gas generator turbine inlet temperatures are on the order of 1297°C (2367°F) during maximum continuous operation and increases in these temperatures at higher power settings reduce the life of the turbine blades. 114