Kitfox

Installing a Jabiru Engine in a Kitfox  by Dave Jalanti

This beautiful Kitfox IV plane has a 4-cylinder 2200 cc Jabiru aircraft engine which produces 85 hp and weighs only 132 lbs (60 kg). It is a horizontally opposed, direct-drive, air-cooled engine in the “tractor” configuration.

With the cowl removed, you can see the engine placement and mechanical connections. Jabiru Engines have dual redundant, solid state, self-energizing ignition systems and a single pressure compensation carburetor. The direct-drive, air-cooled features of Jabiru Engines simplify the design and the normal operating range is from 2500 to 3000 RPM.

Those of us that build our own aircraft, particularly one in the new LSA category, may find that using one of the trusty certificated engines isn’t an option.  We need smaller, lighter engines with reasonable power output and of course dependability.  Additionally, cost, ease of installation, maintainability, sales and technical support are essential considerations.  The plane I chose to build is a Kitfox IV.  With the proper engine this plane would satisfy the kind of flying I enjoy most – local adventures into grass strips and 1 to 2 hour cross country trips.  When I ordered my Kit from Skystar, to ease the monetary outlay, I did not order one of the Rotax engines they offered.  As time went on and my project progressed, I had to make an engine decision.  I researched various engines that would fit the Kitfox including the Stratus and NSI Subaru, Raven, Cam 100 and of course, the Rotax.  It wasn’t until Sun-N-Fun 1998 that I became aware of the Jabiru engine.  Immediately I was attracted to the clean simple design and outstanding quality. I wanted to know more about this engine and going beyond first impressions is prudent, so I started more seriously researching the Jabiru and talking to whomever I could that had any experience with these gems.

Advantages of the Jabiru Engine in a Kitfox

Let’s take a look at some of the Jabiru features, their advantages and some considerations. The 85 hp 2200 cc and the 120 hp 3300 cc engines are the same in concept and share many components.  Depending on the Light Sport Aircraft, either of these engines could be appropriate for use. The HP range I was interested in was 65 to 100 so the Jabiru 2200 satisfied my first requirement.  The price at the time was also very attractive and was considerably less than the major competition, the Rotax 912.  Since my purchase in 1998 the prices of these engines for various reasons, have increased.  These costs are now closer to that of other engines of similar power but still below the major competition.  Cost aside, there are plenty of additional reasons to consider using a Jabiru engine.

Direct Drive Engine

One of the biggest advantages is that the Jabiru engine has no reduction drive.  Direct drive eliminates complexity as there are no gears or belts.  There are no backlash issues, less to go wrong, less to maintain and less weight.  However, the Jabiru engines mentioned here develop maximum power at 3300 RPM which is a relatively high speed to turn a prop.  This means the prop must be shorter than usual for most engines in these power ranges.  It is known that turning a longer prop at lower RPM is more efficient and generally results in better performance.  On the other hand, if your plane has a prop to ground clearance issue, the shorter prop may turn out to be a great advantage.

Air-Cooled Engine

Many modern engines of similar power rely on liquid cooling.  While liquid cooling is effective at reducing rapid temperature changes and often permits close fitting cowls, it adds a great deal of complexity and weight.  A liquid cooled engine requires more maintenance and there are more opportunities for in flight engine related problems.  Jabiru engines are air / oil cooled, reducing weight, complexity and maintenance requirements.  However, as with any air / oil cooled engine, proper ducting and cowl design is essential for keeping the engine within normal operating temperatures. 

Constant Pressure Carburetor

With only one carburetor on the Jabiru 2200 or 3300 engine, there is no need to synchronize multiple carburetors and no need for throttle/choke cable splitters or fuel line “Ts”.  The carburetor used on either of these engines is a 40 mm Bing constant pressure type.  With a constant pressure carburetor, there is no mixture adjustment. The carburetor compensates for air density automatically.  On the Jabiru, the carburetor is mounted low and behind the engine. If a leak should occur, the fuel will be able to exit the bottom of the cowl so there is far less chance of fuel ending up on a hot engine or near an electrical circuit. 

Solid State Ignition System

The Jabiru utilizes a dual solid state magneto ignition system with dual spark plugs and wire harnesses.  The battery is only needed for starting.  Permanent magnets on the flywheel passing independent coils for each distributor trigger the ignition.  The distributor caps and rotors are common Bosch automotive components.  Since the magnetos are solid state, the rotor is the only moving part in the distributor.  This keeps it simple, safe and inexpensive to maintain.  In flight, the dual redundant ignition systems are in play for your safety.

There is an alternator built into the center of the flywheel.  The alternator output is rated at 20 amps continuous.  Twenty amps would seem to be a marginal output but thanks to modern avionics and equipment operating at much lower current values, a 20 amp alternator is likely to satisfy the requirements of most light sport aircraft.  

These engines are delivered complete, with no need to order a lot of special or Jabiru specific components.  The prop bushings and squash plate are included, as is a complete stainless steel exhaust system, engine mounting hardware, voltage regulator, and starter relay. There are a couple styles of air boxes and oil coolers available.  The muffler can accommodate carburetor heat as well as cabin heat muffs which are available.  Of course the engine mount and prop are selected based on the aircraft and engine being used.  There are a variety of two blade wood props that work well and are light weight and inexpensive compared to composite or metal props.  If the builder is installing a Jabiru in an aircraft for which there is no Jabiru history, some experimenting may be necessary to zero in on the best prop for that aircraft / engine combination.

Lower Overhaul Costs

Another nicety of the 2200 and 3300 Jabiru engines are the TBO requirements.  At 1000 hours, a minor top overhaul is recommended and at 2000 hours, a major overhaul is recommended.  The overhaul costs are far less then for certificated engines and the time before overhaul is better than most non-certificated engines and far better than two stroke engines.

This wraps up the major technical highlights and gives many of the reasons I choose to use a Jabiru engine in my Kitfox.   Anyone building an LSA will need to evaluate their situation and make a decision.  I’ll just say I’m very comfortable with the decision I made and when I build another aircraft, I’ll be sure it can be fitted with a Jabiru.     

Jabiru Engine Installation Process             

I’m only going to devote one paragraph to the installation of the Jabiru 2200 in my Kitfox. Reason being, the purpose of this article is to share my experience without being so specific to my particular installation that what I say won’t apply to Jabiru engine installations in other aircraft.   

With that said, the installation of the Jabiru 2200 in my plane took some interesting twists and turns.  The majority of the gyrations were self induced as I made the decision not to use the stock Kitfox cowl.  I choose to use a Skyfox cowl which I was able to acquire from Jabiru. This decision was made because the Skyfox is an Australian knock-off of the Kitfox that was fitted with the Jabiru engine. Wrongly, I assumed the cowl would fit my plane with little or no modification.  When it did not, I researched and discovered that the Skyfox was similar to the Kitfox model III.  My Kitfox model IV has more rake in the windshield and the frame members behind the windshield interfered with the cowl.  It was necessary to cut away a large portion of the upper cowl to clear the frame and a new flair had to be constructed to blend the cowl into the windshield.  In the process I also lengthened the windshield because the Skyfox cowl was lower and flatter then the Kitfox cowl.  This in turn meant lowering and flattening the instrument panel which meant fabricating a new glare shield.  Truly the ripple effect in action.  There have been enough other builders making similar changes to their Kitfox IVs that I decided to write a detailed document, a kind of “how to” including a number of photos.  This document is available thru Jabiru USA in the form of a CD.  In addition, I’ll gladly talk with anyone wanting or needing to know more specifics. 

Engine Mounts

Since the Jabiru 2200 and 3300 engines are so similar, the installation processes for both are virtually the same.  However, I will point out some things I learned during the 3300 installation in my friend, Bill DeVries’s Kitfox series 7.  

 Engine mounts for a wide variety of aircraft are available that we can supply.   We can let you know if a mount is currently available for your plane. There is also a list of supplied engine mounts on the Jabiru website.  If your plane is not on the list, I encourage you to contact them as they may be able to fabricate what you need. 

I found it easier to install the engine mount to the engine before attaching the mount to the firewall; however this may not always be the case.  Following the supplied instructions, the proper installation of the rubber vibration dampers, mounting bushings and associated hardware is simple.  In this process, it is necessary to compress the rubber vibration dampers.  What I found to work quite well is an automotive valve spring compression tool.  In most cases a large pair of channel lock pliers can also be made to work just fine.  Next would be to lift the engine and mount into position on the airframe.  A small engine hoist, possibly from a local tool rental business works great.  In working with Bill on his installation of the 3300 an engine crane made the job a breeze.  A block and tackle or a come-along could also be used.  In my case, with the 2200 engine weighing only about 130 lbs, a friend and I lifted the engine in place while another friend installed the bolts through the firewall and threaded the nuts on.

Engine Mount Modifications

Jabiru supplied the engine mount for installing the 3300 in Bill’s Kitfox series 7.  We found the mount to be rather short.  That is to say, there was very little room between the back of the engine and the firewall.  Installing the air induction system would be problematic and it may not function correctly if the airflow was to be restricted.  We determined that moving the engine forward 2 inches would solve that issue.  It would also make more room for the battery and in general make the engine easier to inspect and maintain.  What we didn’t know was how much moving the engine might affect the CG.  The Kitfox series 7 was originally set up for installing a Rotax 912S.   Already having the 912S mount and cowl, Bill was able to determine that the prop flange of the Rotax would be about 2-1/2 inches further forward.  The complete engine installation of a 912S would weigh about the same as the Jabiru 3300 but because of the reduction drive on the Rotax, the CG of the engine itself is slightly further forward. So our suspicion was that moving the engine ahead 2 inches shouldn’t put us out of the forward CG limit.  To be sure, we made up some 2 inch spacers that we mounted between the firewall and the engine mount.  Then Bill completely assembled all the major components to the airframe.  We temporarily placed the remaining components in their relative locations, leveled the plane and did a preliminary weight and balance.  The results were what we expected.  The CG was right at the forward limit.  This is excellent since adding the pilot / passenger, fuel and baggage all move the CG back so Bill will have the full CG envelope to work with when loading the plane.  Working thru Jabiru USA, Bill had a new mount built that was 2 inches longer. 

Fitting the Muffler on the Kitfox

The final fit of the muffler should be done along with the fitting of the cowl so clearances can be checked.  The muffler slips directly onto the exhaust pipes and is retained with four springs.  In general, the engine installation is quite straight forward and the biggest issue may be fitting the cowl.  Currently there are cowls available for the Sonex and Zenith CH601 and a number of others.      

Cylinder Head Cooling

The engineers at Jabiru wanted to be sure the cylinder heads received adequate cooling air.  Rather than supplying the engine with baffling that would need to be modified for a particular aircraft, or relying on the builder to have adequate knowledge and skill to fabricate baffling, Jabiru developed fiberglass air ducts that the builder fits to the engine.  The builder needs to fabricate and bond in place a couple of simple air deflectors and drill a few holes and attach rubber strips to the inlet of the ducts to seal against the inside of the cowl.  Jabiru supplies ducts for aircraft with either tractor or pusher configurations. 

Installing the Propeller

The engine is supplied with prop bushings and squash plate.  In most cases, Jabiru USA can supply or order the prop and mounting hardware.  Depending on the prop selection, it may be necessary to have the holes in the prop bushings enlarged.  This is best done on a lathe to keep the holes true.  If a fiberglass spinner is chosen, some holes will need to be drilled and some nut plates need to be fastened to the spinner bulkheads.  The spinner will need some minor trimming and sanding before painting.  The raw edges of the fiberglass spinner will beat up the finish on the prop so using a couple layers of duct tape to protect the prop during the fitting of the spinner is a good idea.  If the builder chooses a prop for which we have the aluminum spinner option, all the fitting is done and it is simply a matter of assembly.

Installing a Throttle Extension

The Bing carburetors used on these engines have a very short throttle lever.  If the plane you are building uses a throttle quadrant or some other lever system, this isn’t a problem.  If the plane is being built with a push/pull throttle knob, the travel from idle to full throttle is only about one inch.  This short travel makes it difficult to control the engine speed.  I developed a simple to install throttle extension that increases the travel of the knob to 2.4 inches.  This difference makes the engine much more controllable.  Jabiru USA has these extensions available along with installation instructions.  

Locating the Air Box

The remainder of the engine installation involves mostly components that mount on the firewall and cables or wires going through the firewall.  Once the locations where the throttle and choke cable go thru the firewall have been established, it is wise to decide first where to locate the air box as it is likely the largest item to be installed on the firewall and acceptable locations are limited.  If the battery is to be placed on the firewall, because it is also large, it should be positioned in conjunction with the air box and before all remaining items.  If the builder decides to use a gascolator, it should be placed next.  Basically, after that, the items with the least flexibility should be mounted before things like the voltage regulator or starter relay.  Whenever possible, it is good practice to run fuel lines well below electrical wiring.  

Flying Behind the Jabiru Engine

During the course of constructing my Kitfox, I had plenty of sources for advice.  Between Skystar’s (now Kitfox) technical assistance and instruction manuals, advice from the folks at Jabiru Australia and Pete Krotje of Jabiru USA, most any question I had could be dealt with.  Supplied with the Jabiru engine were manuals that covered installation, break-in procedures, general descriptions, maintenance and overhaul data.  In addition to all these resources, I had two EAA Technical Advisors and an IA look over the plane at various stages of completion.  The Albany, NY FISDO sent two gentlemen to review my logs and documents and to give my plane its final inspection.  All went well and the following morning was picture perfect for the maiden flight.

Blue skies forever and totally calm….. Well, at least the air was calm, couldn’t say that about my nerves! After a few more minutes of taxi testing and another check of the plane and myself, I decided to go flying.   At the runway’s edge with a hand held radio and digital camera, my buddy Dave Burgess witnessed the first departure of N53KD!  The Jabiru responded well as I steadily pushed the throttle home.   I didn’t have to coax the plane to leave the ground.  Within a few seconds and about 300 feet, the Kitfox lifted into the air on its own.  The engine was running strong and steady, and the plane was handling with a level predictability I didn’t expect.  What wasn’t predictable were the cylinder head temperatures reaching their limits before reaching pattern altitude.  The blinking red light of my Grand Rapids EIS got my attention, letting me know the situation.  Lowering the nose a bit and throttling back some was enough to reverse the trend and the temperatures started heading for a more normal operating range.  Even at this lower power setting the plane was climbing so I continued up to 3000 ft. MSL, made some gentle turns and did some slow flight over the airport to get the feel of the plane.  The rest of the first hour in the air was uneventful and the first landing went very well.   

Over time Jabiru has made a number of improvements to their engines.  Because my engine was serial number 22A478, it already had the upgraded steel connecting rods and solid push rods but arrived with the smaller 32 mm carburetor rather then the 40 mm carburetor of the newer engines.  The primary difference between the carburetors is power.  My engine was originally rated at 80 hp.  The newer engines with the 40 mm carburetor and upgraded induction system are rated at 85 hp.   As with many of the Jabiru engine upgrades, the 40 mm carburetor and induction system can be retrofitted to older engines, so I purchased the components and upgraded my engine.  I found the engine quite easy to work on and made the modifications during a couple of evenings after work.   The performance differences were quite noticeable.  Shorter take-off distances, better climb rates and higher top speed.  I actually had to be careful under certain situations to not allow the engine to rev beyond its 3300 rpm redline.  To help absorb this additional power I re-propped the engine with a longer prop with more pitch.  There was only a slight reduction in the rate of climb and the cruise speed as well as the top speed increased by 10 mph.

Kitfox Performance with a Jabiru Engine

Now that my Jabiru engine has the refinements and upgrades making it equal to 4-cylinder Jabiru engines being sold today, let’s talk about some of the performance numbers.  I’m not a professional test pilot with a lot of instrumentation so the performance numbers I’m sure aren’t as accurate as they could be.  I was careful though to be as thorough as my abilities permit and not to exaggerate the numbers.  In fact, if there was any doubt about the results of a particular test, I would lean toward the conservative side.  My plane as mentioned already is a Kitfox IV.  It has the shorter speedster wings, an empty weight of 655 lbs and a calculated ramp weight of 1030 lbs. at the start of the following tests.  

Let’s start with take off distance.  I flew to nearby Columbia county airport for this part of my evaluation.  There I was able to fill the tanks and use a well marked, level, paved runway that is only 187 ft MSL.  The temperature was 65 F and the winds were light and variable.  I used the edge of the runway number as my starting point and was able to determine the lift-off point with reasonable accuracy using the center line marking on the runway.  I did three take-offs using the technique of allowing the plane to lift off on its own accord as I had on the maiden flight.  The results of these take-offs seemed consistent so I measured my take off roll with a 100 ft tape and came up with 320 ft.  Remember, this is with a Kitfox built with the shorter wing.  A Kitfox with the standard longer wing may defy gravity sooner and climb at a higher rate.

After each take-off, I established the best rate of climb speed of 65 mph and observed a consistent ROC indication of 1100 FPM up to pattern altitude.   After the three take-offs I wanted to get a more accurate indication of the rate of climb so I left the pattern and went over the Hudson River where I could safely start at 500 ft MSL, bringing the Jabiru engine to full power and once again establishing a climb speed of 65 mph.  As the plane went through 1000 ft MSL I started the lapsed time on my digital wrist watch.   I continued this climb all the way to 5000 ft MSL.  The lapsed time for this 4000 feet of climb was 3 minutes 49 seconds or an average of 1050 fpm.  At the start of this climb the Jabiru was turning 2950 RPM and the highest CHT was 265 F.  As I approached 5000 ft. MSL the engine was turning 2880 RPM and the highest CHT was 315 F, still well below the maximum CHT of 394F.

Speed Checks

For speed checks I used my Garmin III GPS and established an average true ground speed over a triangular course.  Over the past two years I have done this exercise a number of times with consistent results so I’m quite confident the numbers are accurate.  Keep in mind that this is being done in a Kitfox, a plane that is rather draggy and designed more for short field and low and slow operations.   At 2500 ft MSL I flew a triangular course with headings of 360, 120 and 240 degrees.  At 75% power, 2930 RPM, (my usual cruise setting) the average GPS ground speed was 102 mph.  The fuel burn at this setting has been 3.5 GPH.    Using the same procedures but at full power, the Jabiru 2200 tops out in level flight at 3280 RPM resulting in an average speed of 112 mph.  Without a fuel flow gauge, it would be difficult to establish the fuel burn at full throttle so that is a number I cannot provide.  I’ve also tested other in-flight aspects of this aircraft not related to the engine.

In Summary

 Did the Jabiru engine meet my expectations?  You bet it did!  In some ways it exceeded my expectations as did the company and Jabiru USA.  It has proven to be an excellent match for the Kitfox IV, providing great performance, reliability, and economy.  The engine starts quickly, runs smoothly and is easy to maintain.

To date my experience flying behind the Jabiru 120 hp. 3300 engine has been limited.  I did have the pleasure of a demo ride in the Jabiru USA Esqual VM1, powered by a Jabiru 6 cylinder 3300.  The Esqual is a terrific performer, as you may expect, the 6-cylinder engine is even smoother than the 4-cylinder.  On the take-off roll, it pulled with authority and throttled back in a fuel-saving, comfy cruise we were seeing 120 kts.

For many Kitfox builders like my friend Bill, this 120 hp. 6-cylinder engine was a great match-up for the plane he built.    If you are currently building or plan on building, and if one of the Jabiru engines offered is in the horsepower range you need, you will be doing yourself a disservice if you don’t take a close look at these extremely well engineered power plants.  Great performance, safe, light weight, efficient and simplicity at its best!

Slow and Low Over the Hudson

On a beautiful evening when the air is calm is when I like to fly. From the cockpit of my Kitfox, I enjoy the rolling terrain of the Catskills and the reflections of the sky on the Hudson River as I fly over. It is truly a pleasure.

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