Turbine installation
The Sabre is designed for turbines of between 4.5 and
6.5kg thrust. We flew the prototype with a PST600,
which is quite a heavy motor, and even though the com-
pleted plane weighted about 6.7kg (dry) it flew very well
indeed.The current production Sabres are considerably
lighter than our original prototype, and several cus-
tomers have flown the Sabre with the excellent little
Wren MW44, and it has sparkling performance as the
weight is reduced considerably.
IMPORTANT:
The Sabre is designed to have a turbine
of
maximum
90mm diameter installed. If you fit a larger
diameter motor the turbine will be too close to the top
surface of the wing, which could cause insufficient air-
flow around the turbine, and may even cause structural
damage to the wing due to the heat. You must maintain a minimum 10mm gap between the outer
case of the turbine and the top surface of the wing in all circumstances.
If you are fitting a heavier turbine towards the upper end of the thrust range, we recommend that
you position it as far forward on the rails as possible to prevent CG problems later. The weight of
your thrust-tube (exhaust duct) can also have a considerable affect on CG. We used a lightweight
Wren tube, with a short s/s ejector tube and a fibreglass outer tube, and did not have to add any
lead at all in the nose. We have also made some useful weight savings in the stabiliser section of
the current production kits that will help here.
The turbine is mounted on the 2 milled plywood mounting rails provided, working through the wing
opening. Fit your motor onto the rails with it’s mounting strap, mark the holes carefully and then
remove the mounting rails for drilling the bolt holes. M3 allen bolts and can be used with T-nuts on
the other side of the rails. Fit the rails back into the slots in the fuselage bulkhead and bolt your
turbine in place. View from the
back of the fuselage to check
alignment.
Note that with the fuselage up-
side down, the upper surface of
the mounting rails is about
3mm below the centerline of
the fuselage and, therefore, de-
pending on your chosen turbine
you might need to add plywood
packers under the mount to
center it in the fuselage. When
the mounting position of the tur-
bine is finalised, glue the rails
into the slots in both bulkheads
with slow epoxy. You may be
able to make some lightening
holes in the rails, against the
side of the fuselage.
Fox Composites Co., Ltd.
23
The composite plywood turbine rails
mounting are removable, for ease of
installation. Glue in place with epoxy
and milled-fibre when completed.
If fitting a turbine at the heavier end of the thrust range,
mount it as far forward as possible for easy CG location. Full
auto-start PST600 shown here.
