On Wed, 27 Aug 2008 16:11:51 -0500, Jim Logajan wrote:

Ron Wanttaja wrote:
On Tue, 26 Aug 2008 21:07:46 -0700 (PDT), "
wrote:

everyone says "ooh -- auto...dangerous" but no
one can explain exactly why.

1. Ignition systems with insufficient redundancy.
2. PSRU failures.
3. Difficulty in implementing efficient liquid cooling systems.

But doesn't the Rotax 912 have reduction gearing and liquid cooling? It is
getting put into an awful lot of aircraft models - particularly LSAs.

Certainly, and my data shows that the Rotax 912, in homebuilts at least, has a
safety record pretty much equal to that of traditional certified engines.

My posting was an attempt to answer the OP's question on why some people believe
auto engine conversions are dangerous. The three items I mentioned are in the
top four causes of auto-engine failures. Looking at my 1998-2006 homebuilt
accident database and comparing fixed-wing applications, the rate of occurrence
of ignition system problems is four times higher for auto conversions than
traditional engines. And the traditional engines had no cases of PSRU or
cooling failure.

I believe it's possible to convert an auto engine and achieve reliabilities
equal to that of a traditional certified engine. It's just that the accident
reports show that many people can't achieve that goal. It's basically the same
people installing the Continentals as the Subarus, or the Rotax 912s and the
Fords. But the average builder seems to have less problems getting the Lyconts
and Rotaxen to be reliable.

Ron Wanttaja