ORIGINAL: Gidusko
hey guys,
I have a 60lx on a weston magnum and it totally rips the sky apart, but i cant seem to keep a glow plug more than one or two flights. The plug usually deforms and is useless i have tried os-8, fox plugs, mc-9, various os plugs i had in my box. they all have the same fate of black and melted or blown out elements. The mc-9 actually starts to fall apart! the pin in the center seems to be getting blown out. I am using 15% omega and a APC 9-9 cut to 8-9 and static on a new os-8 is about 18500 to 19000 rpm. I set it by leaning to max rpm and then backing off about 500 rpm. It seems if i go richer it doesnt get on pipe. Do you all have any ideas for plugs that will not fail each flight cause i am at a loss. i love the engine and it has amazing power but it is damn expensive to put a new plug in after each flight. oh, i have run about 3/4 of a gallon or so.
The prop and RPM are fine. No issue there. Maybe back off more like 600-700 - might help. You may want to try an APC 8.8x9.25 prop, and clip that to 8" diameter.
The engine should stage and stay on the pipe at any rpm over 17,500 (60LX with the SS muffler). The SS muffler also re-stages and re-peaks near 20,000 rpm but it looks like you are a bit short of that yet.
However....
If you are not using either a Tetra or Jett fuel tank, install one very soon, or you
will toast the engine.
Blowing plugs comes from the engine going lean. Blowing insulators/posts out means its getting VERY hot. A head shim might help as dave noted, but lets evalue the fuel system first.
(if the head shim is the problem, fire up the engine with your 8x9, a new plug and full tank of fuel. Let it run full throttle for 1 minute, just short of peak rpm about 200-300. Shut it down. Check the plug. If its blown or distorted - shim the head up. If the plug is fine, the problem is most definately the engine going lean late in the flight - fuel system)
We wasted plugs for years in pylon. That last 1/3 of a tank, with a conventional tank, will guarantee you a blown plug - the clunk has no option but to suck some air as it bounce around. And at those rpms, it is bouning around a great deal. It only takes a few seconds of air bubbles to cause the engine to go over the edge. Our only option was to take off rich, and wait for it to go lean. With a bubble-jett or tetra tank, the engine simple never sees air bubbles, and holds the needle setting all the way to the last drop in the tank.
Let me know about you tank setup.
Bob