Tech Engine Question?

What mechanisms are in effect that will cause glow-plug-attributed differences in engine runs? Does the heat range of the plug effectively alter the cumbustion timing?

Other than starting, what other symptoms would appear or should be attributed to plug selection?

Thanks

I am not a glow plug Guru. We "use what works" and smile. Since we don't scream our engines, but run them rich, a hot plug is in order. As a general rule, the hotter the better. Or, putting it another way, I have never heard of a plug that was too hot.

Good plugs (and they don't have to be expensive to be good) should last a long time--maybe 100 or 200 flights Maybe even longer. Plugs are sneaky, however. Sometimes a brand new one won't work. And they deteriorate slowly. But a going bad plug will stil start your engine. If, when you take the battery off, the rpm drops significantly, try a new plug. If you start getting some "goofys" along the way, try a new plug. If your fuel mileage begins to change, try a new plug. If the new plug changes things, get rid of the old one. If the new plug is "just the same" put the old one back in and put the new one on your wrench as a "tested" new plug. Then the next time you suspect something you are ready to go.

Leonard --

>Plugs are sneaky, however.
>Sometimes a brand new one
>won't work.

>. . . If
>the new plug is "just
>the same" put the old
>one back in and put
>the new one on your
>wrench as a "tested" new
>plug. Then the next
>time you suspect something you
>are ready to go.

That is about as clever "simple" idea out there. Pre-testing plugs for one run means you have a few plugs that are "proven", and will keep one from chasing ghosts.

>What mechanisms are in effect that
>will cause glow-plug-attributed differences in
>engine runs? Does the
>heat range of the plug
>effectively alter the cumbustion timing?
>
>
>Other than starting, what other symptoms
>would appear or should be
>attributed to plug selection?
>
>Thanks
>
>Curt

My basic criteria is that the engine should show no loss of RPM when the battery is disconnected. The temperature of the plug helps determine the spark "advance" or "timing" of a glow engine. Other factors are fuel volitility, compression, and atmospheric considerations. If the engine loses revs when the battery is disconnected this indicates a need for either a hotter plug (to retain more heat and thus start the fuel burn sooner), higher compression (to increase the "heat of compression" which advances the burn, or more nitro (to make the mixture more volatile at a lower pressure.

Generally speaking we like to run comparatively low compression ratios to mitigate power surges with two/four breaks thus requiring a hotter plug to keep the fires lit at the proper time. Juggling nitro percentages then becomes a handy way to balance the changes due to atmospherics...density altitude, humidity, etc.

>My basic criteria is that the
>engine should show no loss
>of RPM when the battery
>is disconnected.

This is why I am partial to Fireball (Swanson) Hots. Guy named pakrattt sells them Dutch on ebay for $18 for 12, which is the price you usually can get them for. This is a Deal for plugs.

I've had engines "running" blubberingly, slobberingly, rich (a human equivalent would be the late actor Robert Morley, Hepburn's Preacher bro in The African Queen, in your face), and, when you yank off the McDaniel glow stick...no drop in rpm.

Currell (movie buff too)

Yep:

On your rec, I bought a card of the Swansons from Pakratt. The seem to work well--havent had a failure yet but was wondering about the differences between these and the THunderbolt plugs I've heard others recommend?

My understanding is that the type of filament, normally platinum, reacts with methonal, and that keeps it hot enough to cause combustion of the fuel/air mixture. Not all plugs are the same, which is a given. A hot plug reamins lit and is less suseptiple (sp?) to being quenched by the oil in the fuel. Thus the r/c hot plug with the idle bar is used a lot. The idle bar keeps oil off the wire filament. Nitro percentage will affect timing and starting ease, assuming all else it equal. If you make any changes to your engine, such as type of plug, fuel mixtures, etc, do it one thing at a time and make a quick note. Each thing will cause a change in the performance of the engine, good or not so good, on the ground or in the air. If you dind a plug that seems to work for you, stick with ut and buy a bunch. It never fails, I buy four or six and a month later, they are out of stock, just when I need them.

One comment on the engine revs dropping or not dropping when you remove the plug lead.

A couple of years back, I picked up a power board - one of those critters the radio fliers like that drives plugs, starters, air craft carriers, etc. Mine is real nifty in that it feeds 12v to your plug, but in pulses. You adjust the pulse rate to avoid frying your plug. The beauty of this is that it will dry a wet plug in no time.

When I first started using it, I hooked up a plug and fiddled with the settings. The better the glow the better the start right? Hah! I set the thing so my plug was incandescant - no flooding issues there. However, my ST 46 got nasty (!) and when you removed the clip, the revs dropped heaps. It took a while and some whacked fingers to twig (slow learner - too much nitro in my coffee). The plug was getting too much power. I backed of my glo-driver until the plug was a nice cherry red. The engine immediately started nicely and the engine rev drop when removing the lead lessened.

Hence the lesson - thou shalt not have your plug glowing too brightly