Jabiru V Rotax reliability?

These are the considerations on Rotax & Jabiru of a member of this NG posted
some months ago from Jez:

Hi

Mirco
****

I've used/flown behind both, and they are very different. I have no firm
preference for one over the other, but have formed the following views based
on observations and experience.

The Jabiru is simple, light, easy to install and performs OK in a tractor
configuration. There have been reported overheating and reliability
problems when used as a pusher on some aircraft. It turns the prop at 3,300
rpm to produce it's 80hp, which is fine for a relatively high cruise speed
aircraft. Fitted to a slow (60kt cruise) aircraft the Jabiru did not
perform well, as the small prop that the relatively high rpm demanded gave
relatively poor efficiency. The most notable deficiency was in take-off and
climb performance, which could not be easily corrected by reducing pitch
without the danger of overspeeding the engine in level flight at full
throttle. On a higher cruise speed aircraft, like the Jabiru kit, the
engine peroms well, and gives adequate climb and take off performance.

The 912 has a gearbox so will turn a bigger prop at lower rpm. This gives
much more static and low speed thrust, so improves take off and climb
performance. The downside is that the engine is more complex (gearbox,
water cooled heads, air cooled barrels, plus oil cooler) and heavier (it's
also more expensive!). It has a proven reliability record though, and is
relatively insensitive to mounting configuration due to the water/oil
primary cooling.

We found that fitting the Jabiru with a bigger prop and pitching it to limit
rpm to 2,900 gave better performance than the standard small prop when
fitted to an Easy Raider high wing, low speed, UK spec microlight. This
limited the engine power output to around 70hp I guess, but the gain in prop
efficiency more than made up for the power loss in practice.

On Fri, 05 Sep 2003 02:52:57 -0500, Barnyard BOb -- wrote:


The trick is in separating the wheat from the chaff.


Barnyard BOb -- Lycoming powered RV-3

While the two-stroke Rotax engines certainly haven't won any reliability
awards, I had believed that the four-stroke Rotax 912s were quite
reliable.

Bob, you obviously have knowledge of a few 912 problems that I wasn't
aware of. Please tell us what you know about Rotax 912 problems.

I've got a few hours flying behind 912s, and they haven't scared me yet,
although I just about died of boredom during the climbs to 10,000 to do
spins in the Diamond Katana.

Thanks,
+++++++++++++++++++++++++++++++++++++++++++

Once man's junk is another mans treasure?

You may have gotten bored, but fleet users in the aviation industry are
anything but bored with the 912. Such was the case with CMSU, Central
Missouri State University. They HAD a Rotax powered Katana fleet for
students. Not anymore. I suspect the same motives drove the University
of Nebraska away from 912 powered Katanas, as well.

The newest Katana sports a Continental instead of a 912. Obviously,
lessons had to be learned learned at this level, too.

When it comes to performance, dependable power, resale and the need to
keep a fleet of aircraft in the air.... NOTHING in the class beats
Continental or Lycoming. Time and again, this proves to be true when the
smoke clears and the bull**** must end.

Just because a 912 won't kill you, doesn't mean it's a winner. It's
neither cheap nor popular, especially in the 912S version.

YMMV.
If it does, you haven't been at this flying business long enough.


Barnyard BOb -- 50 years of flight

I worked with Diamond quite a bit in the period when they were changing
over from the 912 powered Katanas to the Continental ones. Many customers
were very happy with the 912. This tended to be the customers that
understood that the engine was different from a Lycoming or
Continental,and needed to be operated and maintained a bit differently.
These customers tended to make TBO without difficulty. Customers that
treated the engine as if it was a Lycosaur had problems making TBO. In
particular, the local operator found that it was advantageous to change
the oil more frequently than Rotax recommended.

But most operators complained about poor climb performance, and many
potential customers did not want to buy anything that didn't have a good
ole North American made engine in it. So Diamond, like any successful
business, gave the customer what they wanted.

There is a fleet of 912 powered Katanas here in Ottawa, and the operator
is still very happy with them, except for the climb performance.

I don't disagree with your comments about performance (the 125 hp IO-240
poered Katana runs circles around the 80 hp 912 one) and resale. But I'm
still not aware of any reliablity issues with the Rotax 912, and it seems
that you don't have any knowledge of specific issues either.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/