Power and weight. Just like any other airplane builder, I want lots of the former and as little as possible of the latter. When it came time to pick an engine for my Texas Sport Cub, power was not too much of a concern, but weight was really important. Thats what led me to the Jabiru 3300 engine. Darin Hart of Texas Sport Aircraft told me I could save a lot of weight by going with the Jabiru versus the Continental O-200 and, as an added bonus, I would pick up 20 horsepower. What a deal!
But what the heck is a Jabiru? Isnt it made in Australia or something like that? Is it any good? I didn’t know, but with a burning desire to save 30 pounds, and after a little more research, I decided to buck tradition and go with the Aussie engine. As I began doing my homework on the web (where else?) I ran into Jabiru USA in Shelbyville, Tennessee. The company runs six seminars a year on how to install and maintain Jabiru engines. I signed up for the next available course and bought a plane ticket to Nashville.
In at the Deep End
Over the course of three days 13 of us got a full dose of how to install, tune, maintain and even rebuild the Jabiru 3300 engine. That hardly seems possible, but we covered just about everything, including some hands-on experience installing the various parts, from motor mounts and cooling baffles to pistons and pushrods. Obviously, we were not going to go back home and open up Jabiru engine overhaul shops based on what we learned in three days, but I would feel confident replacing a cylinder on my own after this course. At the very least, I am now comfortable setting up my engine properly and having it ready to perform well on its first flight.
A cross-section of people signed up for the course. Three have shops and are planning to work on Jabiru engines for customers. They have experience with Rotax and other airplane engines and were looking to add to their businesses. The rest of us are amateur builders who are using or planning to use Jabiru engines in our airplanes. Six are building Zenith projects, either 601s or 701s. A Jabiru (airplane), a Titan, a Lightning and my Texas Sport Cub round out the rest of the field. This made for a diverse group, with some knowing a great deal about airplane engines and others knowing very little, but we got along quite nicely and learned a great deal.
The instructors spoke well to this diverse group, neither boring nor confusing anyone. (Well maybe some of the carburetor stuff caused a few eyes to glaze over, but what the heck.) The atmosphere was Southern casual, but our three able instructors were organized and covered the ground well. Nick Otterback carried most of the load, with able assistance in the hands-on portions from Mark Stauffer. Jabiru USA owner Pete Krotje provided us with background on Jabiru and development of the engines and airplanes that they make. He also had the unenviable task of explaining the arcane workings of the Bing carburetor to us-important stuff, but maybe not as exciting as some of the other parts. Otterbacks wife, Dana, pitched in with parts information and general support. Clearly she is an active and well-informed member of the team.
History Lessons
Once we dispensed with introductory formalities, we began with the history and design goals of Jabiru. Those goals are to make products that are simple to operate and maintain, reliable, inexpensive and compatible with available technology. Lets take these one by one and see how close they came to achieving those goals.
Are the engines easy to maintain? They certainly appear to be. No special tools are required to overhaul the engine. What other engine manufacturer can say that? Cylinder heads are bolted to the cylinders, so servicing valves, pistons, rings and barrels is easy. If you have the tools to do these jobs on a motorcycle or small car engine, you can do them on a Jabiru. Regular maintenance consists of changing oil and replacing the oil filter every 50 hours, and the filter is available at most auto parts stores. New NGK spark plugs should go 100 hours between cleanings and easily last 200 hours or more. The distributor caps and rotors can be replaced after 500 hours if they need it, and these too are automotive parts. Ignition timing is fixed, so there is no need for adjusting it. The carburetor may take some tweaking at first, but once set up it should require no further maintenance. If you wonder how we could feel comfortable taking this engine apart and putting it back together again ourselves after three days, we could do it because it is lawn-mower-engine simple.
Reliability is born of simplicity and constant improvement. With the first engines in service since the early 1990s, there is now an ample track record of their reliability. Many of the earlier engines have thousands of hours in service, validating the claimed TBO of 2000 hours. During the ensuing 27 years there have been more than 1000 improvements to these engines. This is only possible because every engine is CNC-machined from billet steel and aluminum. A change is just a matter of rewriting a few lines of computer code. A new, improved part can be produced the next day.
Set Up for Long Life
Problems seem to be mostly related to carburetor setup and cooling, two areas that admittedly require some extra attention in the initial installation of the engine. The carburetor issue is a trade-off for permanently dispensing with the mixture control. The cooling concerns are not unique to the Jabiru, but these engines are a bit more sensitive to poor installation than what is normally encountered with a Continental O-200. However, the payoff comes in consistent cylinder-head and exhaust-gas temperatures that definitely extend the life of the engine. Thus, the reliability is there if you do the setup work required.
To keep costs down, Jabiru uses off-the-shelf automotive parts where it can. Pistons come from the GM/Toyota world, and the hydraulic lifters found in all newer Jabiru engines are right out of a small-block Chevy. The alternator is a Honda motorcycle part, and the solid-state voltage regulator comes from a Kubota tractor. Valves and seats are modified Toyota parts. The common threads here are low cost and proven reliability. All 12 spark plugs can be replaced for less than $40. That will buy you two plugs for your O-200 at best. A top overhaul, which is recommended after 1000 hours, runs about $3500, with a complete overhaul about $6500. In the airplane world that is as inexpensive as it gets for an engine of this power.
With Jabiru engines now found in more than 60 countries, compatibility with available technology means simple and straightforward, as some of those 60 countries are not exactly on the leading edge of technological development. For instance, electronic fuel injection is out, and carburetors are in. Fancy electronic ignitions and FADEC systems are out, but reliable solid-state ignition is in. Special tools and fixtures to take things apart and put them back together are out, but working with the kinds of tools you can buy at Sears is in. Sophisticated technology in the service of a simple, reliable design-that is the Jabiru engine in a nutshell.
Circling Back to the Carb
The Bing carburetor helps to make operation of the Jabiru straightforward and reliable. Its signature ingenious vacuum-controlled throttle slide automatically compensates for engine load and altitude, making that red mixture-control knob obsolete. Those of you familiar with older motorcycles will quickly recognize the throttle slide and needle, but they work differently in the Bing carburetor than they do in more familiar Mikuni units. You old BMW riders are way ahead of us here, but for the rest of you, heres how it all works.
The throttle control in the cockpit is linked to a butterfly valve in the carburetor that provides gross control over air and fuel flow, but there is a second throttle, if you will, that regulates fuel and air flow based on ambient air pressure, throttle position and engine load. Open the throttle quickly, and the throat of the carburetor is not fully open until the engine is ready to use all that air and fuel. The diaphragm that controls the throttle slide must sense the need for all that extra charge first. In practice this all happens pretty seamlessly. It works by having a diaphragm that has ambient air on the bottom and carburetor air (vacuum) on the top. As the throttle plate exposes the carburetor to more vacuum from the engine, the slide is pulled up to open the intake passage. As the throttle plate closes, the decreased vacuum allows the slide to close off the carburetor fuel/air supply.
Fuel is controlled by a needle valve that is incorporated into the throttle slide. The needle is tapered to carefully meter the flow of fuel based on the position of the slide. Thus, the farther the slide opens, the more fuel is allowed into the airstream. By carefully designing the taper of the needle, exact control of the fuel metering is possible. All told, the carburetor has four fuel/air metering systems. The idle jet and idle mixture adjusting screw control engine operation up to about 1200 rpm. The main jet controls wide-open throttle mixture and has significant effect on mid-throttle operations. The needle (attached to the slide) and the needle jet control fuel between 1200 rpm and wide-open throttle. Lastly, the throttle plate, the only part that the pilot actually controls, determines how much vacuum the carburetor sees and smooths the transition from the idle circuit to the main fuel circuit.
What makes this all rather complicated is that a change to any one of these circuits causes changes to the other three. Tuning one of these carburetors can be a bit trying for the novice, so Jabiru USA takes the guesswork out of it for you by making recommendations based on the installation and initial running data that you provide.
Good Timing
Another interesting feature of the Jabiru engine is that you never adjust the timing. The dual distributors are gear driven off the cam in conventional fashion, but with the solid-state ignition there are no points to adjust and no way to change the timing even if you wanted to. Everything simply bolts into place to give a fixed timing of 25 BTDC. This saves a lot of maintenance time and effort, and that business of overhauling magnetos every 500 hours-gone. That little buzz box timing gizmo-out the window. Simple, reliable, easy to maintain-thats how all airplane engines ought to be.
If the carburetor is a little quirky by conventional airplane standards, so too is the cooling system. You cant just stick the cylinders out in the open air, hang a couple of sheet-metal eyebrows over the jugs and expect a Jabiru engine to be happy. The cooling system, somewhat like the Bing carburetor, must be tuned for optimum results. The engine comes with fiberglass shrouds that go over each bank of cylinders to channel air from the front of the cowl to the cooling fins of the cylinders and heads where it is needed. The tuning comes into play with small air deflectors that must be installed and adjusted by the builder to control airflow in a way that produces even cylinder-head temperatures. It sounds worse than it is, and Jabiru USA will be there to help you through the process. But it does seem strange to people who are used to working with Continental or Lycoming engine installations.
Weight for It
In the beginning I mentioned weight. This is a big selling feature of the Jabiru engine. The four-cylinder, 85-hp version weighs 134 pounds installed with carburetor, exhaust, starter, shrouds and oil cooler. This compares to an 80-hp Rotax 912UL with an installed weight of about 165 pounds, or 3 more pounds for the 100-hp 912ULS. The six-cylinder Jabiru with 120 hp weighs 180 pounds installed, a dozen pounds more than the less powerful Rotax. A better comparison is probably between the 120-hp Jabiru and the 115-hp Rotax 914UL. Here the weight is just about the same, but the normally aspirated Jabiru costs roughly half of what the turbocharged 914UL engine does. The more conventional Continental O-200 engine will come in at close to 210 pounds and makes 100 hp. All weights were provided by Jabiru USA and may vary depending on the particulars of the installation.
As for Jabiru USAs engine training course, I highly recommend it for anyone who is planning to use a Jabiru powerplant. Being able to see actual engine installations in various phases of completion and then ask questions based on what is right in front of you has great value. You could do the same thing over the phone, I suppose, but the engine installation would be much harder and less likely to turn out right the first time. All of this for $300-plus travel costs, of course-makes the Jabiru course well worth it.
For more information, call 800/522-4781, or visit http://www.usjabiru.com/.
