Spicer Sonex/Jabiru

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I was reading in the latest edition of Sport Aviation about Tony
Spicer's Sonex. He uses a Jabiru 3300 engine in it and reportedly gets
great performance from the plane with that engine. An interesting
tidbit of information in the article was a comment that an improvement
to the 3300 engine has the engine putting out its rated h.p. at a much
lower r.p.m. The original figures put the 120 h.p. output at 3300
r.p.m. which most people figure is a little high as it limits the
diameter of prop that can be used, this plus most Continental/ Lycoming
drivers are used to seeing their r.p.m. numbers run several hundred
r.p.m less. I consider this engine improvement to be substantial, but
I can't figure out why none of the Jabiru dealerships ( and I think I
checked them all ) have no mention of this engine improvement. You
would think an improvement such as this would be front page news on
their websites. If the engine has been improved to this extent, you
would think their sales would increase. Their marketing gurus must be
asleep. They DID however, waste no time in getting their latest price
increase published. To their credit, though, they also list the new
h.p. increase of the 2200 engine from 80 h.p. to 85 h.p.

Neal

[Peter Dohm]

This bothered me as well.

But, first, let me get a disclaimed out of the way: The Sonex is small
enough, and fast enough, that the 3300 r.p.m. prop is probably large for the
aircraft and any longer prop will probably be less efficient in cruise;
unless a prop isspecifically made with the correct washout for the specific
application. That seems to eliminate most of the popular inexpensive props
for aircraft like the Sonex, KR2, etc. Therefore, on the Sonex and KR2, in
my ever so humble and very personal opinion, the quest for lower r.p.m. is
PURE CRAP; unless you need to trade away your cruising speed for s.t.o.l.
performance.

With that out of the way, I have similar questions to the ones that Neal
discussed.

"Full Power" is a nebulous term, unless defined. For example, since the
Sonex can be build and flown with both the 3300 and 2200 engines, and since
it performs reasonably with the 2200 engine; I could choose the "flat rate"
(to borrow a perfectly applicable term from the turbine conversion
providers) the 3300 to the power rating of the 2200. So long as I climbed
streeply enough, that should give me "full power" to around 5000 feet--which
is a popular number for turbine conversions which might otherwise exceed the
torque rating of the engine mount...

Which brings me back to the issue at hand. Assuming that all of the
measurements were made, we are really talking about a torque increase of
less that 8%. The "bad neighbor policy," consisting of tuned straight pipes
instead of a muffler, plus the change to a throttle body should be worth a
lot more than 8%! However, the prop was changed as well; in what appeared
to be an uncontrolled test.

Therefore, with a change of only 8%, the prop might be the only change. Or
the torque improvement might have been 15% and the prop change lost 7%.

How can we tell? Did anyone really learn anything?

All of which brings me to an ongoing gripe about "technical" articles in
Sport Aviation and Experimenter/Sport Pilot. They "fly" without a
checklist!

When a standard data panel is used, as it is in AOPA Pilot, it also serves
as a checklist for a minimum amount of standardized data. Conversly, when
the numbers are embedded in the text and there is no obvious and consistent
checklist, it is not practical to know what was omitted; nor even whether
the featured project included sufficient information to be worthy of an
article.

As a further illustration (flame); my copy of Sport Pilot, which arrived in
yesterday's mail, included an interview article titled "A Subaru for a
Karatoo." The builder's goal was to change from his two stroke engine to a
four stroke engine with a better power to weight ratio ... of ... something
.... ??? ... engine ... aircraft ... aircraft and fuel ... I still don't
know...

If a series of data panels had been filled in and included, showing what he
had, what he obtained, and possibly what he rejected (the Corvair and VW
were not well explained); it could have been an informative article.

As it was, I was able to glean from the pictures that he started with a tail
wheel aircraft with a two stroke engine and a spur gear reduction drive and
that he now has a tail wheel aircraft with a four stroke engine and a spur
gear reduction drive. Other than that, I have only whatever questions I may
have started with plus one more: How hard is he running that soob?

> wrote in message
oups.com...
> I was reading in the latest edition of Sport Aviation about Tony
> Spicer's Sonex. He uses a Jabiru 3300 engine in it and reportedly gets
> great performance from the plane with that engine. An interesting
> tidbit of information in the article was a comment that an improvement
> to the 3300 engine has the engine putting out its rated h.p. at a much
> lower r.p.m. The original figures put the 120 h.p. output at 3300
> r.p.m. which most people figure is a little high as it limits the
> diameter of prop that can be used, this plus most Continental/ Lycoming
> drivers are used to seeing their r.p.m. numbers run several hundred
> r.p.m less. I consider this engine improvement to be substantial, but
> I can't figure out why none of the Jabiru dealerships ( and I think I
> checked them all ) have no mention of this engine improvement. You
> would think an improvement such as this would be front page news on
> their websites. If the engine has been improved to this extent, you
> would think their sales would increase. Their marketing gurus must be
> asleep. They DID however, waste no time in getting their latest price
> increase published. To their credit, though, they also list the new
> h.p. increase of the 2200 engine from 80 h.p. to 85 h.p.
>
> Neal
>