Wren 44 Gold Helicopter Owners Manual
Page 12
gasoline engine but with very low weight levels allows the operator a level of dial-in
performance previously enjoyed by only those operating high performance specialist engines
with tuned pipes etc, with all the attendant noise, extreme vibration and operational issues
associated with such equipment. Scale fliers will really enjoy the smooth and quiet response
and operation coupled with high power reserve to get out of those difficult situations that
scale helicopters with multiple long rotors and lots of fine surface detail, can find themselves
in. The high torque ability of the engine allows it to cope well with a wide range of helicopter
reduction ratios, so there is no need to swap away from the standard ratios supplied for the
airframe. The emphasis on small and compact lends itself more clearly to sport than scale
but users will find the engine at home in either role.
What about smoke?
The engine itself is a clean burning gas turbine that makes very little smoke in normal
operation. However the gearbox bearings are lubricated with a very small amount of fuel,
which at low rpms or throttling down can sometimes be seen as a small puff of smoke, but
this is normal, there is none of the typical smoke trail of the I/C engine. The oil percentage
used in the fuel helps to minimize pollution from unburnt fuel, although the gas turbine does
produce a very distinguishable smell which for many is the "
raison detre
" for this type of
model flying. On shutdown, excess remaining fuel in the gearbox will be blown into the
exhaust area and can make quite a lot of smoke but treat this as a confirmation of lube
present.
Can I use the transmission supplied with my heli
kit?
Yes. In all cases we have looked at so far the
transmission components are modelled around
the standard 0.90cu in (15cc) heli engine and
there is a high degree of standardisation in the
shaft size and arrangements of such i/c engines.
We have continued this standard to our gearbox
and output shaft enabling the fitting of standard
collet and clutch/fan arrangements supplied with
most airframes.
Don’t forget to fit the black washer first!
Some cutting around of the fan shroud may be
needed to clear exhausts etc but modellers with
normal hand skills should encounter no difficulties in making these modifications using
standard hand tools.
Do I need to change the standard ratio?
No. In the cases we have looked and compared the torque curve to, we see very little gain
but users will no doubt experiment and may find optimum selections than best suit their
particular airframe and flying style. But we would emphasize that for initial flying and testing
the standard ratios supplied for use with 2-cycle glow engines will be perfectly adequate.
How do I go about my installation?
There are literally dozens of different helicopter
kits currently available for the 90’ size i/c engine
and all would need some degree of modification
to enable the install of the Wren Heli Unit. For
this reason it is difficult to give specifics but to
show what we have done in the installing on the
two prototypes done so far.
