The common fix for this is to use 100LL fuel. Any aviation engine that is 9:1 compression will also be tagged as 100LL minimum fuel octane rating. That changes the lean detonation back into a harmless misfire.
Jeff Scott On Mon, 28 Nov 2005 07:32:51 -0600 "Oscar Zuniga" <taildr...@hotmail.com> writes: > I'll toss out a snip from William Wynne's "broken crank" webpage > since it > deals with leaning the mixture and may be of interest not just to > KR/Vair > operators: > ========================== > When leaning, he would lean until he saw a decrease in airspeed, and > then > slightly enrichen it. The evidence at teardown showed that either > this > leaning technique or his Ellison EFS-3A installation was the cause > of lean > operation and evidence of detonation. In many installations, > especially > aircraft without mufflers or flown by pilots with headsets, > detonation in > the plane cannot be heard. It is important that pilots trained in > flying > Cessna 150s to lean the aircraft until the engine runs slightly > rough and > then enrichen it slightly, should not use this technique on a > Corvair > engine, especially below 8,000 feet. The difference is simple: a > Continental or Lycoming with a compression ratio in the 7:1 range, > when > excessively leaned from cruise power settings, will experience a > lean > misfire in the cylinder. A lean misfire is a harmless event > compared to > detonation. Here, the air/fuel mixture has reached a point where it > will > not ignite. Conversely, leaning an engine with a 9:1 compression > ratio like > a Corvair has the potential to detonate the engine long before it > lean > misfires. This is aggravated by high available density, as in low > altitudes > or throttle openings yielding MAPs more than 24". Corvair engines > can be > leaned, it just requires an EGT and common sense. The contribution > of > detonation to crank failure will be the hardest factor to replicate, > model > or evaluate. But, successful builders will avoid detonation for a > multitude > of reasons, not just its potential contribution to crank failures. > ============================== > > > Oscar Zuniga > San Antonio, TX > mailto: taildr...@hotmail.com > website at http://www.flysquirrel.net > > > > _______________________________________ > Search the KRnet Archives at > http://www.maddyhome.com/krsrch/index.jsp > to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > please see other KRnet info at http://www.krnet.org/info.html > >
