Andrew, Andy and all,
The French kit builder Dyn Aero is currently installing Jabiru engines in
his two seater and four seater models. As is often the case in new setups,
there are still a few details to work out in order to have the installation
perform and cool correctly.
What is interesting in the process is that we can make direct comparisons
between the proven Rotax installation and the new Jabiru firewall forward
packages.
The main issues to date are cooling and design or choice of a propeller.
They've just built a Jabiru powered demonstrator two seater at just 225 kg
empty weight for 450 MTOW. I've not flown the machine yet, but it is
impressive indeed.
Now it is fair to admit there are a few difference between the performance
of Rotax and Jabiru :
- The propeller is EXTREMELY noisy at takeoff, whereas the noise level in
flight is acceptable. On the contrary the Rotax installation are remarkably
quiet. We talked about the prop, and indeed there is a catch with the Jab :
if you want the power, you need prop diameter and do make noise. If you
reduce the diameter to reduce tip speed you loose efficiency and available
power.
- The performance is slightly less with the Jab, but when you're looking for
the ultimate weight saving this might not be an issue.
Now Andy, just a few remarks:
>
> 1. Simplicity. The Jabiru is designed as an aircraft engine, uses all
> 'aircraft' (AN/SAE) fastenings,
- This is a non-issue since we've been using metric system since the French
Revolution ;-) Nevertheless I understand our US friends may be reluctant to
change from their old units from Colonial times ;-D
is direct-drive and air cooled. No gearbox,
> radiator, header tank, fluid pipework, etc.
- The Jabiru does have an oil cooler, so there IS some pipe work to do after
all. OTH the Rotax does LOOK complicated, but the installation is a breeze.
Bolt it on, connect the oil and water hoses, and voila.
To date I've not heard of any gearbox trouble.
> 5. Sound. The Jabiru's maximum RPM is 3300, not over 6000.
>
- The sound has nothing to do with the engine RPM : at low RPM, the Jabiru
3300 has an nice and moderate growling note, whereas as stated above the
2200 makes a lot of noise at takeoff RPM.
The Rotax engines are extremely quiet, mainly due - I suppose- to the slow
turning prop. By the way, the max RPM on the Rotax is 5800 RPM, not "over
6000" ;-)
To sum it up, the Jabiru 2200 considered as a very light and simple engine
for a two seater. In a four seater (325 kg empty with a 912S) the 3300 poses
problems due to it's length and forward CG location. The weight are rather
close between the 3300 and the Rotax engines.
Regards,
Gilles Thesee
Grenoble, France
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