Wren 44 TurboProp Users Manual. Copyright Wren Turbines Ltd February 2008 Page 9
Detail description of the Wren 44 two-shaft drive system
Gas Generator
The gas generator used in the system is the well proven
Wren 44 GOLD engine which has the standard Wren FOD
guard fitted – this is no place for a tea strainer. A lubrication
port in the outer casing has been added and this connects
through a stainless tube to the gearbox. Other than the lube
outlet there are no other changes to the engine and the full
throughput has been utilised to generate shaft power.
This TurboProp engine has been fully run and tested
It is important to stress the unit has been fully tested with all the components supplied with it
before it left the factory at Wren Turbines Ltd. There should be no need to make adjustments
other than setting the radio to the ecu. Please refrain from jumping in and changing things just
because you or a friend have another Wren 44. The settings match the components used and
may not be the same as you are used to.
Hot Section
A specially designed and manufactured miniature
interstage and guide vane assembly, cast from high
temperature stainless steel is bolted to the engine.
A purpose made 66mm power turbine – not just
taken from a thrust engine, is cast in Inconel 713c
and is fitted and running on a fully hardened and
ground shaft in a pair of preloaded high speed
ceramic angular contact bearings. The shaft tunnel
they run in is made from low expansion stainless
steel.
These components define what is called the hot
section. Nothing has been left to chance.
Gearbox
The front of the turbine shaft is contoured with a hardened and ground gear profile and supplies
the shaft power into a specially design high speed planetary gearbox. This heavy duty assembly
utilising fully ballraced support shafts and the planet carrier has been ground and bored as an
assembly to retain great strength and accuracy.
The
housings
are
anodised
to
resist
corrosion and maintain
their lustre. The gears
are fully hardened and
are able to run with
long life using just a
small amount of engine
fuel bled off the gas generator fuel system. To keep the flow
to a low level the oil percentage is maintained at 5% to
ensure satisfactory lubrication.
The lubrication reaches the gearbox by a small pipe in the gearbox front wall and is fed from a
special fitting mounted on the engine. The gearbox is designed to retain much of the lubrication
and only release what is surplus via the power turbine bearing.
