Hi,

Am currently flying my WOT4 with a Irvine .46 and an OS A3 glow plug. When I remove the glow starter after starting there is quite a drop in RPM. I also have a firepower F7 from a while ago, and when I trying using this plug there is no drop in RPM.

Am quite new to modelling so should I be using the A3, and maybe buy a new one, or stick to the F7?

Any help greatly appreciated!

Thanks guys, Paul

Stay with the F7

A decrease in RPM when the glow lighter is removed usually means a too-rich mix or a bad plug. Replace the plug (with the same type) and lean out the engine.

Dr.1

That's great guys. Thanks. Am also a little confused about the hot and cold ratings given to plugs, what do they mean?

A big drop in RPM when the ignitor is removed usually indicates that the idle mixture is set rich. IF the F7 is working fine though I would just stick with it and fly. Your A3 plug may have gone bad or the engine design may just work better with the F7 (I am not familiar with it but it sounds like the F7 may be a "hotter" plug).

FYI, other symptoms of a rich idle setting are if the engine wants to load up at idle, and/or stumble as you increase the power from idle. If you are seeing this even with the F7 then you definitely should try leaning the idle mixture a bit.

Walt

Mixture should be tad rich on the ground because it will lean in the air. Nitro content will also effect rpm drop whem plug is removed.

The F7 is their hottest plug and should be fairly similar to the OS A3 except probably that the OS plug is slightly shorter in length although that shouldn't make any real difference. I'd suspect the A3 is on the way out so just use the F7.

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'...

Just my thoughts on plugs:

Always clean the threads of a new plug. Most every plug has either a plating or an oxide put on it's base metal, and is not always "clean". If you use a small wire brush and scrub the threads, it will help preserve the glow plug threads in the head. Just be carefull you don't snag the element. Just a gentle brushing a couple times around the thread will do it. Be sure to wash with fluid and blow out the plug with air from a small squeeze bulb.

Another good tip is to "heat temper" the new element a few times by charging it with the glow driver orange hot for five or ten seconds, and let it cool completely. Repeat five or six times. You don't have to do this procedure, and it does not hurt it if you do, but it will add a few more flights to the plug. It will heat temper by itself in the motor with each run, but this gets a start on it before the intake charge gives it a pounding.

Jetpack, I suggest one step further in this glow plug discussion. It was pointed out to me some time ago that you cannot trust the plug mfg's in producing perfectly formed threads all the time. The recommendations to prevent cylinder head thread damage was to run all plugs through a 1/4-32 die using a light machine oil. So far I have found all plug threads leaving a great deal of metal in the die indicating the threads were not a perfect 32 threads per inch. I am hoping this is old information to everyone.

Rich S.