Bristol Siddeley/SNECMA M45H
The Rolls-Royce/SNECMA M45H was a medium bypass ratio turbofan produced specifically for the twin-engined VFW-Fokker 614 aircraft in the early 1970s. The design was started as a collaborative effort between Bristol Siddeley and SNECMA.
The single-stage fan, together with a five-stage LP compressor, was driven by a three-stage LP turbine, whilst the seven-stage HP compressor was driven by a single-stage, air-cooled, HP turbine. An annular combustor and an unmixed exhaust, with a plug-type primary nozzle, were other design features.
The M45SD-02 or RB.410 was a derivative of the M45H-01 turbofan, designed to demonstrate ultra-quiet engine technologies, needed for STOL aircraft operating from city centre airports.
A geared, variable pitch, fan replaced the first stage of the low pressure (LP) compressor. A modest fan pressure ratio, consistent with the high bypass ratio, meant a low fan tip speed could be employed. A low hot jet velocity was another major design feature.
In reverse thrust, intake air entered the bypass duct, via a gap in the cold nozzle outer wall, and went through the fan, to be expelled through the intake. A small proportion of the bypass duct air entered the IP compressor, via a special diverter valve, to sustain the gas generator. Reverse thrust was obtained by the fan going through fine (rather than feather) pitch. Engine testing took place in the mid 1970s.