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The LHTEC T800 turboshaft engine is part of the newest generation of highly advanced gas turbine engines, integrating the newest technology and thinking along with new materials to bring unseen levels of power, reliability, and fuel economy in a light, compact, and easy to maintain package. LHTEC, which stands for Light Helicopter Turbine Engine Company, was put together as a partnership between Rolls-Royce and Honeywell International, with the intention of developing a state of the art turboshaft engine for military and commercial helicopters. The T800 was developed specifically for use in pairs on the Boeing/Sikorsky RAH-66 Comanche helicopter, though other versions are slated for use in future commercial helicopter applications.
Because the T800 is a very new engine, not very much information is readily available on it, but from what can be found, the T800 is a free shaft turbine engine with a two stage compressor driven by a two stage turbine, and the load is driven by a two stage free power turbine. Air enters at the front of the engine through an annular duct that surrounds the engine output. At the front of the engine is an integrated vaneless inlet particle separator. The particle separator is similar to the unit found on the General Electric T700, except that instead of using fixed inlet guide vanes to impart a rotational force on the air, the IPS on the T800 uses a spiral shaped duct. As the air passes through this duct, a natural rotation is imparted. Foreign objects in the air stream tend to have more mass than the air molecules themselves, so the foreign objects are thrown toward the outside where they are drawn up and expelled by an engine-driven blower, while the cleaned intake air gets drawn in toward the center by the first compressor stage.
The engine features a very simple yet efficient two stage centrifugal compressor, to effect a high compression ratio without the need for a delicate, complex, and heavy multi-stage axial arrangement. Because of the inherent stall-free nature of a centrifugal compressor, there is no need for variable inlet guide vanes or variable stators. Air from the first centrifugal compressor stage is turned 180 degrees to feed the eye of the second stage impeller. The second centrifugal compressor stage feeds the compressed airflow to an annular reverse flow, machined ring combustor which features a design based on previous Honeywell and Allison engines, with the latest in high temperature materials technology for maximum efficiciency and reliability. Combustion gas is turned 180 degrees before it is fed to the two stage axial gas producer turbine, which drives the compressor and the accessory geartrain. The first stage turbine is transpiration cooled for higher turbine inlet temperatures. The second stage is uncooled. The load is driven by a two stage axial free power turbine. The turbine turns a shaft which runs coaxially through the center of the gas producer shaft. The power takeoff is at the front of the engine. The standard engine features a high speed output at 23,000 rpm power turbine speed, although the engine can be fitted with a compact output reduction gearbox that weighs 60 lbs. and reduces output speed to either 9,000 rpm or 6,000 rpm. Engine exhaust gas escapes through a large diameter axial flow exhaust duct for maximum efficiency. On the Comanche helicopter, the exhaust outlets are fitted with a special diffuser duct which collects the exhaust from both engines, mixes it with fresh air to cool it, slows the airflow down, and then expels the gas through special louvered vents to minimize the aircraft's infra-red signature.
All engine accessories are driven by the accessory gearbox mounted on top of the engine for easy accessibility in the field. The accessory gearbox is driven by a bevel gear and jackshaft arrangement off of the gas producer shaft. Engine systems include a fully self contained oil system with integral reservoir, pressure pump and scavenge pumps, fuel system with low pressure and high pressure engine driven pumps and an electronic fuel controller and governor, and an electric starter and generator. Spare drive pads are provided for hydraulic pumps and other additional accessories.
Engine control is fully electronic, using a state of the art FADEC system. The electronic control system provides N1 speed control, N2 governing, overspeed and overtemp protection, surge control and acceleration limiting. The engine features a one touch automated starting procedure for ease of use, and engine acceleration is extremely rapid. The engine requires less than three seconds to accelerate from ground idle speed to 100% N1 for takeoff. The electronic control system also monitors engine condition, records engine usage, diagnoses engine problems, and schedules maintenance intervals. There is no set time between overhaul, but TBO is expected to be at least 6,000 hours.
LHTEC T800-LHT-801 Turboshaft Engine
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