6
INSTALLATION
With any single-cylinder engine, it is preferable to bolt the
engine firmly to a body that has as much mass as
possible, in order to minimize loss of power due to engine
movement through vibration. However, the vibration that is
transmitted through the fuselage of an aircraft may,
dependent on the airframe construction, generate
considerable resonant sound.
For F3A competition purposes, in order to reduce this
vibration induced extra noise, it is now common to use a
so-called "soft mount", e.g. to isolate the engine mounting
from the actual fuselage structure with a resilient
material(e.g. rubber) in the form of grommets, bushes or
buffers.
Power loss
When a soft mount is used, full-throttle power output
may be reduced by the equivalent of 300 to 500 r.p.m.
under load, depending on the flexibility of the mounting.
Therefore, it is desirable to select a degree of rigidity
that will provide a reasonable compromise. The softer
the mount used, the better the noise reduction achieved
-
but at the expense of greater power loss.
Throttle linkage
When the engine is throttled down to idling speed,
vibration amplitude, with a soft mount, is considerably
increased and this can result in fluctuation in the throttle
opening and erratic operation if the idle position of the
throttle rotor depends solely on the linkage to the servo.
Therefore, it may be advisable to use the throttle stop
screw on the carburetor, to positively fix the idling
position.
Note: Fixing the idling setting with the throttle stop
screw, will also mean that the engine cannot be
stopped by retarding the throttle control trim
lever on the transmitter.
Installation of tuned silencer and exhaust header pipe
When a tuned silencer is firmly secured to the fuselage,
engine vibration will impose considerable strain on the
exhaust header pipe and, in extreme cases, the header
pipe may be damaged. It is advisable, therefore, to
insert some resilient material in the mountings for the
exhaust system, also.
Installation of cowling, etc.
When a soft mount is used, the engine may vibrate more
than expected. Make sure that the engine and spinner
do not touch the fuselage or cowling, otherwise,
overheating, additional noises and unreliable idling etc.,
may be caused.
Securing the engine
Be sure to secure the engine to the mount firmly, using'
4.5 - 5.0mm steel screws, such as Allen type, with
locknuts.
Remember to allow for some light spring compression in
the throttle linkage travel, so as to avoid stalling the servo
at the end of the throttle movement.
7
If the fitting of the "klunk" type fuel pick-up weight in the
fuel tank is incorrect, the weight may stick to the tank wall,
resulting in an irregular fuel flow to the carburettor, or,
alternatively, in the fuel flow being cut off during the course
of sharp aerobatic manoeuvres. Therefore, it is advisable
to make slots in the end of the weight, with a file or
hacksaw blade. Thoroughly wash out the weight to remove
any minute particles of metal before reinstalling it in the
tank.
FUEL TANK
Alternatively, a 'NON-BUBBLE WEIGHT' FUEL PICK-
UP(Code No.71531000) may be used. This is an improved
type of fuel pick-up weight which prevents air bubbles,
generated by engine vibration, from reaching the
carburettor and causing the engine to malfunction or stop.
It is available from O.S. stockists as an optional extra
part. A silicone-rubber O-ring surrounds the 'Bubbless'
pick-up weight to prevent internal damage to the fuel tank.
Use thick silicone tubing
10mm
For piping, use heavy duty silicone tubing of approximately
2.5mm bore and 5mm outer diameter. It is advisable to
secure connections with commercially available tube clips.
Tube lengths should be kept as short as possible. Take
care not to cause any kinks in the "plumbing".
PIPING
Connect to fuel tank
IN
OUT
PD-06
8
Below is an example of a typical installation. A muffler
pressurized fuel feed is not required.
It may be convenient to lead the pipes outside the fuselage
and connect with approx. 35mm(1-1/2") length of silicone
tubing, as shown.
When filling the tank from any position other than that
shown in the sketch, be sure to pinch the silicone tube with
a clip on the pump side to prevent fuel entering the pump.
Overflow
L-shaped nipple or
aluminum tubing
Silicone tubing
Disconnect here when filing the tank
Connect to "IN" nipple
of the pump
GLOWPLUGS
Since the compatibility of glowplug and fuel may have a
marked effect on performance and reliability, it would be
worthwhile to try different heat range glowplugs.
Recommended O.S. plugs are A5, No8 and TYPE F.
Carefully install the plug finger-tight, before final tightening
with the correct size plug wrench.
The role of the glowplug
With a glowplug engine, ignition is initiated by the
application of a 1.5-volt power source. When the battery is
disconnected, the heat retained within the combustion
chamber remains sufficient to keep the plug filament
glowing, thereby continuing to keep the engine running.
Ignition timing is 'automatic' : under reduced load, allowing
higher rpm, the plug becomes hotter and, appropriately,
fires the fuel/air charge earlier; conversely, at reduced rpm,
the plug become cooler and ignition is retarded.
Glowplug life
Particularly in the case of very high performance engines,
glowplugs must be regarded as expendable items.
Fit a plug suitable for the engine.
Use fuel containing a moderate percentage of
nitromethane unless more is essential for racing events.
Do not run the engine too lean and do not leave the
battery connected while adjusting the needle.
However, plug life can be extended and engine
performance maintained by careful use, i.e.: