Wren 44 TurboProp Users Manual. Copyright Wren Turbines Ltd February 2008 Page 23
Installation – System Components
The airframe should be one in which an I/C engine was the intended powerplant as the engine
needs a secure firewall to attach to. It is difficult to be specific as the exact procedure for
mounting but a good place to start is to examine the original intended I/C engine install for any
information on the requirements for positioning the thrust line. If you are converting an aircraft
which had an I/C engine already then you may need to install a sub-firewall to take the engine.
See the full-size view at the end of the manual for positioning of the unit with respect to a known
propellor backplate point.
Using the fuselage plan (if available) or from your own judgement, mark the engine centre point
on the firewall with a line top to bottom and side to side. Cut out one of the mounting templates
from the back of this manual and align the template to the cross lines already marked in. Use
some double-sided sticky tape or simply glue the template in place and use a drill and narrow
saw to cut out the opening for the main body and the two “ears” to clear the glowplug and
lubrication fitting on the engine.
Offer up the engine unit to the hole and mark any tight
spots. Remove the engine and with a coarse file or
modelling knife ease the opening. Be careful not to injure
the delicate lubrication fitting on the engine or damage the
lubrication pipe – the clear 3mm tube that connects to the
gearbox whilst offering up and removing the engine.
Once the engine is fitting well, you can now drill the six
3mm (1/8”) mounting holes marked on the template and fit
captive nuts to the reverse side of the firewall.
An opening needs to be cut into the bottom of the fuselage
or the lower half of the firewall where a plane has a chin
inlet (see left), to allow cool air to reach the engine intake.
This should be an absolute minimum of 2500
2
mm - 50mm
(2”) square, more is better for the engine.
If you have made the opening in the lower firewall then it
must be isolated from the exhaust and gearbox section
using a false bottom. This is ideally positioned in the lower
section of the cowl, where this is removeable.
This is by far the preferred option as it is easy to position
and mark the exhaust cutouts.
The chin inlet allows easy
passage for cooling air to
reach the engine intake by
passing
under
the
partition.
In flight a degree of ram
effect may help the engine
too!
