On Thu, 12 Jul 2007 10:20:48 +1000, Andrew Rowley wrote:

Ron Wanttaja wrote:

One reason: They don't like 100LL. They're approved (and certified) to operate
on it, but the lead forms an abrasive sludge that means the oil has to be
changed more frequently.

Not that big of a deal with a private owner, but an FBO won't like having to
take a rental off the line twice as often to change the oil.

The Rotax specified oil change interval if you run unleaded is 100
hours. If you use 100LL, it is 50 hours.

They're reasonably specific about what type of oil to use though - the
best seems to be semi-synthetic motorcycle oil. Full synthetic is also
a no-no if you're using 100LL.

What is the typical oil change interval for a Lycoming or Continental?

Typically 50 hours if the engine mounts a filter, 25 hours if it doesn't. It's
just that whole "abrasive sludge" thing, especially as it's getting into the
gearbox.

The fact is, Diamond initially sold the Katana with the Rotax (DA-20), then
apparently offered a upgraded 100 HP Rotax conversion (DA-20-A1), then finally
abandoned the Rotax for a Continental in the DA-20-C1. Certainly some FBOs
would be biased against the Rotax as something new, but I think if the promised
fuel and maintenance savings had come true, it would have overcome that.

Most of the homebuilders with 912s seem to like them; my own analysis of
homebuilt crashes shows the four-stroke Rotaxes are about as reliable as more
traditional engines. But there's a difference between fifty hours per year vs.
fifty hours per month.

Ron Wanttaja