My Thunder tiger Pro 46 keeps blowing or melting glow plugs. I use 10% nitro with a 11*4 prop. I started with the OS no.8 glowplug, but that lasted about three flights. Then I switched to the OS A3 which worked great for a while, but this past sunday the first one which lasted about 10 flights was dead and the next one only lasted one flight! Luckily I had a spare no. 8, and got two flights out of that. I KNOW my engine is not lean, its actually a bit on the rich side.(used a tachometer)other than that the engine is really running very smooth and reliable. Does anyone know what the problem might be? Any suggestions what other types of glowplugs I can use?

thanx!