There are many factors involved in today's varied flying styles that can induce or reduce the proclivity toward preignition/detonation. Even just a change in the person tweaking the needles makes a big difference.

When we all flew either scale, sport, pattern or pylon, it was easy to issue generalized edicts and for them to hold up as being absolutely true for many years. Not so today. Unfortunately, once in the habit of issueing edicts, it is a very difficult habit to break. It is always done with the best of intentions, however, so give we older fellows a break.

In the early Seventies, which was like yesterday to many of us, the Super Tigre G60 Bluehead would sizzle and fry on a warm humid day if ran on fuel with much more than 5% nitro. This happened. It's no one's imagination or hallucination. It used to cause me physical pain to see fellows install a brand new, never ran, G60 Bluehead into a scale model with a tightly enclosed/poorly ventilated cowl, fuel it with 15% nitro, install an over sized prop to clear thescale cowl and then start it up, only to peak it out for the first flight. Invariably, if the engine did not overheat and quit before they decided to land, it surely would sit there in the pits smoking and making krinking/tinking noises as it cooled down. Another brand new engine had been doomed to a life time of less performance than it was capable of performing had it been broken-in properly with the compression adjusted for the amount of nitro being used and the size of the propeller being employed.

Then the fellows that abused these engines in such a way bad-mouthed the brand and model of the engine as being junk. Thankfully, most folks hearing these stories already knew the teller's disposition, so no one actually believed what they said anyway.

Once you have heard the sizzle (while running) and the krinkling sound (after running), it will never leave your memory.

Things DO change over time, however, so not every old edict remains in effect for a given engine brand forever. With our old friend, "a ganging of tolerances", it is quite possible that some engines come from the factory with the perfect compression for running 30% nitro fuel. It is also possible that the next engine off the production line might have a problem with fuel containing only 10% nitro. It is the luck of the draw. The important thing is to recognize the symptoms and to then know what to do about them.


Ed Cregger