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General Electric T700-GE-401 Turboshaft
The General Electric T700 Turboshaft engine is a part of the next generation of gas turbine engines beyond the likes of the Lycoming T53 and the GE T58. Due to an advanced design and better materials, the T700 has commensurately higher performance levels in terms of specific power, power density, and thermodynamic efficiency. The T700 is used in a variety of modern military helicopters, including the AH-1 Cobra attack chopper and the AH-64 Apache Helicopter Gunship.
The T700 is a lightweight and compact free shaft gas turbine engine, with a power output exceeding 2,500 horsepower in some of the newest models. The engine is made up of four modules, the accessory gearbox, the cold section, the hot section, and the power turbine. The engine features its own active inlet particle separator, designed to protect the compressor from FOD, particularly from sand particles that get drawn up into the intake. The particle seperator first separates the particles from the air by forcing the intake air through a stator type swirl inducing set of vanes. This imparts a rotation to the intake air. The particles, with more mass and thus more inertia, tend to move to the outside of the separator, while the clean air is drawn into the engine compressor at the center. The particles are collected in a plenum, and then drawn up and expelled by an engine driven blower.
The intake air passes through a set of inlet guide vanes, which straighten out the airflow before it is admitted to the mixed flow compressor. The engine features an ultra efficient compressor with 5 axial stages followed by a single centrifugal stage. The wide chord axial compressor blades combined with swept back impeller vanes of the centrifugal compressor provide an incredibly high 21:1 pressure ratio for such a relatively simple compressor. This high compression results in very high turbine inlet temperatures, and very high cycle efficiency. The airflow is admitted to the through flow annular combustor, where twelve fuel nozzles mix fuel with the air. The combustion gases exit the burner via the high pressure turbine nozzle, to drive the two stage axial gas producer turbine. The turbine is cooled via transpiration and convection cooling. Air is bled off of the compressor, and circulated to the interior of the gas producer turbine blades and nozzle vanes, and then allowed to exit via small holes in the skin of the blades. This cooling allows for higher turbine inlet temperatures for greater thermodynamic efficiency.
The power turbine is a two stage axial, uncooled, and shrouded turbine which turns at a maximum speed of 24,000 rpm. The power turbine drives a shaft that travels forward through the center of the gas producer shaft. The shaft fetures an electronic torquemeter, which measures the relationship of two sensors on opposite ends of a calibrated twisting shaft to determine the amount of torque being generated. The engine output is taken off of the front of the engine at direct speed; there is no output reduction gearbox. Exhaust is removed from the rear of the engine through an annular duct. The gas producer drives the accesssory gearbox which is situated at the top of the engine for easier access, and also so that the engine can be mounted lower. Accessories include fuel and oil pumps, and an electric starter/generator. Fuel control is via FADEC. The engine features a patented lubrication system that allows the engine to run for at least six minutes after losing all of the oil.
The T700 has been such a success in a both military and commercial applications because of its high efficiency, reliability, power, and maintainability. It is a clear example of the current state of the art of smaller gas turbine technology, even if it has already been around for a long time. The newest generation of gas turbines should be even more impressive.
General Electric T700-GE-401 Turboshaft Engine
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