7.5 DUCTED FAN EATING GLOW PLUGS

[GRUBB595]

:cry: Help! Any idea why this 7.5 ducted fan would start destroying glow plugs? Many times after only several minutes into flight with new plug, engine will die and plug shows coil fried to a crisp. I have tried several different brand plugs for ducted fan but results always the same. I have also tried several brands of ducted fan fuel too. I am original owner of this engine from Jet Hangar Hobbies and it has no changes to head, gasket, etc. The capper is that it then started to run totally erratic where I could not get tuning to settle down including idle, transition and high speed no matter what I did with either remote needle valve or idle mixture. I am at the stage now where I have disassembled and cleaned carb but have not run it yet. I hope dirt was the initial problem but this has been spread out very infrequently over about 4 years (due to reluctance to fly this bad boy) however the way I recall it the engine was initially tuning normally even though it was frying the plugs. The erratic running came next. Tuned pipe is set up properly as it initially ran troublefree. The only other consideration is this all arose a bit after I got the engine back from K&B repair dept. (few years ago) due to bent rod from hydraulic lock so I wonder if they could have messed up the head gasket, etc. but thats not likely - I hope. Think there's any hope for this engine? Thanks!

[MECOA]

The problem you are porbably having is the nitro content and compression ratio. please read these links...

http://www.mecoa.com/faq/compression/compression.htm

http://www.mecoa.com/faq/glowplug/glowplug.htm

How much nitro, what plug exactly are you using?

[GRUBB595]

Thanks for reply.......I just ran it recently with different glow plug and fuel - COOL POWER 15% and A8 plug. It was excellent in several areas - start, transition and high speed response to needle adjustment plus the plug seemed fine afterwards. Only one big problem though was that at full power it would surge up and down I reckon several hundred RPM i.e it would pretty much still stay "on the pipe" but just cycle off and on the peak power at a very regular, quick pace like a dirt biker blipping the throttle at the start line. Of course its possible there was some radio problem moving throttle servo but there's no history of this (I was not able to see carb or servo as installed). I am thinking it's overheating and cooling down rapidly? But no associated problems with overheating noted. Too much nitro? Before this run with freshly cleaned carb I had been using Wildcat fuel for ducted fans when it had serious problems but I can no longer read the nitro or oil of it. I had also tried several types and brands of plugs all with same burnout problem. Jet Hangar Hobbies guy recently told me I should use Cool Power 5% with a bit of Exxon 2380 Turbine oil mixed in but I have not had a chance to try it yet. Thanks again for checking this out.

[GRUBB595]

DOH! Looks like it was radio problem making it surge. Tested it today. Added Exxon 2380 Turbine Oil to Cool Power 15%, used McCoy 9 Plug. Seemed perfect on ground in every phase of running. Got in air for about 45 secs. and had nice dead stick landing after sudden engine failure with 1 tiny, momentary glitch that I convinced myself was a wind gust making gyro do a little dance. Just for fun stuck pin in nipple on tuned pipe and it "seemed" like it broke some resistance, changed to Hangar 9 Ducted Fan Plug (their name), took even more time to set idle and hi-speed (again seemed flawless) and launched her. She gave a little glitch on climbout then in the turn radio failure and fatal crash into ground. Said out loud, "it was probably dumb to try to fly it." Of course radio checked fine when remains were tested. Pretty certain at max RPM some wire or metal (plane is loaded with glow driver, gyro, etc) was thrumming with a sour note! Looks like engine problems taken care of somewhere among cleaning carb, plugged exhaust nipple, different plug or Cool Power w/ real turbine oil.