Just wondering how many flights to expect out of a glow plug before it fails.

I am using the following McCoy No 9
OS 91
Ramtec fan
Trim aircraft pipe
Fuel 22% castor & 5 % nitro
No inflight mixture control but set on rich side

Is their a warning sign the plug is going to fail or can you tell by looking at the element?
I have had about thirty flights changing the plug about every ten with no problems but
am just wondering how many I can reasonably expect without risking a deadstick.

sounds like you have a good setup if you getting 10. I used to typically limit myself to 7 or 8 flights. I'd keep swapping them out at 10 as it seems to be working for you.

I've gotten as many as 25-30+ on a MC-9 plug with the engine tuned correctly. If you've gotten to 10 you should be able to continue on with it. You could pull it out once in awhile and see if the element is getting beat out of shape. Should look normal, else change it. Generally, the only indications I've seen for a plug going south is the idle starts to act up or it won't start due to a broken element wire. Many folks like to change them just to be safe but I've found more often than not, something will happen and the plug will get blown whether its new or not. By "something will happen" I mean you got it too lean for any number of reasons: the head bolts loosen, filter gets clogged, or something like a flake of exhaust o-ring goes thru the engine, etc. BTW, I've had flakes of exhaust o-ring end up in in the tanks from going thru the pipe pressure tap to the tanks and then back to the mixture control. So make sure you use filters.

Is the McCoy No 9 recommended for this setup ? Better than an OS 8 ?

I wouldn't use nothing other then a MC-9 for Ducted Fan application.[sm=thumbup.gif]

BVM also recommends the K&B HP which I've also used. I prefer the MC-9 but it's a push. Both have a heavier (thicker) element wire than the others.

I've always used the Hangar 9 - Ducted Fan Plug (which I believe is the same as McCoy) with good luck. Averaging 15 to 20 flights. But I normally would change the plug out once per month. I figured a $5 plug was just part of the cost of flying jets.

JR

Thanks for your input. What to do with the remaining plugs ? May I use them on std engines ? Do u simply throw them away ?

Just wanted to put in another vote for McCoy #9 plugs. They have been ultra reliable for me. I change them out about every ten flights or so. Usually by flight #10 on a plug, the engine isn't runnig quite as well as when the plug was new, so it's time for a change.

BTW, for some reason, my plugs seem to go bad sooner on a pusher fan than a tractor fan.

b/r,
DFF

I just replaced an MC-9 plug that had about 35 flights on it. The OS .91 still ran, but it was hard to start. I'm running PowerMaster 5% ducted fan.

On a related note; I intent to use an onboard 1 cell battery connected with a manual switch to start the engine and keep it lighted the whole flight (dead afraid of a deadstick since my fleld is short with no great emergency landing areas)
Any impact on glow plug life?
Thinking on using 3000mah NIMH I have on hand.

Thanks