ORIGINAL: downunder
A hot plug just means it'll fire the fresh mixture a little easier than a colder plug and that advances the ignition point. Not having a distributor to tweak like in a car we're stuck with trying different heat range plugs but for general flying anything around the medium to hot range will work quite OK.
But Brian, no distributor, but we do have the mixture control, which basically does the same thing...
A hotter plug will ignite the mixture earlier
at any given needle setting.
A leaner mixture will fire earlier
with any given heat-range plug.
You knew I was going to go in and write this...
Paul,
The A3 is one of the hottest glow-plug on the planet, so I suspect that if it does produce such a big drop in RPM, it is probably faulty.
This thought is further accentuated by the fact that another glow-plug that is considered to be of the same heat range, did not suffer from this phenomenon.
The FirePower F7 is just as hot as the A3, or the Enya #3. All three should produce the same RPM drop, or no drop at all, depending on the needle settings and on the engine.
Similarly, all three hot plugs are too hot for this engine. The Irvine .46 needs a medium heat plug, even on 5% nitro.
The needles should be leaned, so there is a minute RPM drop as the glow-driver is removed.
Then you should tweak them for ideal running and transition.
Make sure the engine is fully broken-in (run-in), before investing any time in accurately adjusting it.
Follow [link=http://www.rcuniverse.com/forum/Tapered%2DBore_Engine_Break%2Din_%2D_Upgraded/m_1850473/tm.htm]this RCU thread[/link] for good reference.
If the A3 was used for the engine's initial runs, it may have been compromised. Regard it as the 'break-in plug'...