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FUEL
The role of the glowplug
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.:
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.
Apart from when actually burned out, a plug may need to be
replaced because it no longer delivers its best performance,
such as when:
When to replace the glowplug
Filament surface has roughened and turned white.
Filament coil has become distorted.
Foreign matter has adhered to filament or plug body has
corroded.
Engine tends to cut out when idling.
Starting qualities deteriorate.
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Model engine fuel is poisonous. Do not allow it to
come into contact with the eyes or mouth. Always
store it in a clearly marked container and out of
the reach of children.
Model engine fuel is also highly flammable. Keep it
away from open flame, excessive heat, sources of
sparks, or anything else which might ignite it.
Do not smoke, or allow anyone else to smoke,
near to it.
Select, by practical tests, the most suitable fuel from among
the best quality fuels available in your country for model use.
For the best performance, a fuel containing 5% to 20% nitro-
methane is preferable. Lubricants may be either castor-oil or a
suitable synthetic oil ( or a blend of both ) provided that they
are always of top quality.
For consistent performance and long engine life, it is essential
to use fuel containing AT LEAST 18% lubricant by volume.
Some fuels containing coloring additives tend to deteriorate
and may adversely affect running qualities.
Once a satisfactory fuel has been selected and used for a
while, it may be unwise to needlessly change the brand or
type. In any engine, a change of fuel may cause carbon de-
posits in the combustion chamber or on the piston head to be-
come detached and lodged elsewhere, with the risk of this
causing unreliable operation for a while. If, however, the
adoption of a different fuel is unavoidable, check the engine
for the first few flights on the new fuel, by temporarily reverting
to the running-in procedure.
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