Rotec Liquid Cooled Heads for Jabiru Engines
By Marino Boric, EAA 1069644, for Light Plane World
Numerous owners of Jabiru-powered airplanes worldwide have the same problem in certain meteorological conditions. As the air outside warms up — let's say over 85° F — the most consulted gauge is the CHT (cylinder head temperature). Those flying in really hot regions like Texas and Australia have an even bigger problem. For the pilot, relief is a sip of cool water from the bottle, but for the "fever" in the engine compartment there wasn't a solution until Paul Chernikeeff from Rotec Engineering in Australia got an idea.
So, what's the problem? The fact is that lots of Jabiru engine owners have an overheating problem on hot days on the ground and in the air. Taxiing, high-power static operation, and running the engine on idle on the ground during hot days mean pushing the needle of the head temperature indicator in red arch after two to three minutes. Paul described the problem with these words: "Rotec LCH [liquid-cooled heads] were designed and developed to combat a myriad of Jabiru head problems. These are mainly overheating, chronic distortion, detonation, and upper cylinder distortion."
Cylinder heads showing evidence of warping with carbon buildup from the engine running rich to avoid overheating
The Idea and the Implementation
Paul is Rotec Aerosport technical director and was asked by a customer who flew into a major Australian national aviation event, if he as an engine manufacturer, can solve that problem. Well, that meeting happened almost two years ago, and it was crucial for the birth of the decision to build the water-cooled cylinder heads. After the first unsatisfactory attempt to lower head temperature with custom-made cylinder head valve cover — made of billet aluminum — featuring huge cooling fins, the only solution for Rotec was to use the only "real" cool water as coolant. On this point I have to go just a little bit more scientific. Water has more than 20 times greater thermal conductivity or the ability to conduct heat than air and has over four times the specific heat of air (the amount of heat per unit mass required to raise the temperature by 1° C). The specific heat of water is higher than any other common substance. As a result, water plays a very important role in temperature regulation. The specific heat per ounce for water is much higher than that for metal. All this said, it's obvious why water or liquid coolant makes such a huge difference compared to air. Additionally the water is just perfect for heat removal in constricted cowl areas, having the ability and the possibility to remove heat directly from the hottest part of the engine — from the cylinder head and the exhaust valve.
CAD model drawing of water-cooled Jabiru head
Patterns and core molds were designed on CAD and machined at Rotec, then sent to a local foundry for sample castings by end of 2010. The raw castings are made from 601T6 (356A) casting alloy and are heat treated and shot preened prior to final machining. Rotec was able to manufacture the first set of LCHs by the beginning of 2011 and tested them on the customer's Jabiru 3300, six-cylinder engine, delivered just days before with compression problems. "The prototype engine fitted with Rotec LCH ran for four hours continuously at WOT [wide open throttle], and the water temperature never exceeded 185° F [85° C]," Paul said. The CHT was measured under the spark plug of the rearmost cylinder peaked at 230° F (110° C) during that test.
Installation diagram shows the path of the coolant
"These tests were repeated over a period of two weeks and the results were the same every time. The ambient temperature during some of these tests reached 88° F (31° C). Needless to say the results not only met but exceeded our expectations said the Rotec owner. After 30 hours of ground testing, the engine was installed back into the SP-6 Jabiru airframe and was taken for a flight.
What's Needed for the Conversion?
Liquid-cooled cylinder heads and appropriate kits are now available for all Jabiru engines including the 2200, 3300, and 5100-cc models. To convert air-cooled Jabirus to LCHs, the following Rotec parts are needed: Four, six, or eight heads—they come with all water inlet and outlet fittings, head bolts, etc. The heads are fully machined with new valve seats and guides and require the transfer of original components like valves and rocker arms. All heads are crack and pressure tested for leaks and/or impurities in the casting. Price $650 each, Davies Craig EWP 80 L/min electric water pump kit, $210, and a hose and clamp coolant kit, $245/$270 for four/six cylinders.
Non-Rotec parts needed for installation include: coolant radiator, Rotax-size 8 x 12 inches (200 x 300 millimeters), cowling scoops, and a plenum for the radiator.
Rotec is now delivering complete kits for each Jabiru engine type; the total price includes an addition of listed components. One Rotec head fits all Jabiru models; for those not willing or not able to perform the swap of components from the Jabiru to Rotec head, Rotec is offering to do it free of charge. All heads are crack and pressure tested for leaks and/or impurities in the casting. For queries and assistance, there is a Rotec engines network, but the best course according to Paul is to contact him directly by phone, Skype, or mail.
Paul Chernikeeff in his shop
Pros According to the Manufacturer
- Head temperatures run between 175° F to 230° F (80° C to 110° C)
- Retorque of heads/bolts no longer required
- Better compression creating more power
- No cylinder head and valve recession
- No detonation
- No engine shock cooling
- Equal CHT spread across all cylinders
- Offers the possibility of cabin water heating
- Make the advertised TBO achievable
- Engine cooling even after engine switch-off
Cons (by the Author)
- Increased complexity
- Modification of cowling needed, radiator and plenum installation
- Weight penalty: 5 pounds for Jabiru 3300 engine
- Aircraft downtime
- 1.8 amp/hour current draw for electric pump
- Probable loss of manufacturer warranty
- Additional expense
On my question about the durability of the Rotec heads, I got the following answer from Paul: "We just got in the first delivered prototype engine for quality check, and we discovered that after 100 hours of field use the engine heads and compression is like it was on delivery—like new. Retorque of heads/bolts was not needed."
Prototype Rotec water-cooled heads after 120 hours of use
All in all this seems to be an interesting and sound solution for Jabiru engines — especially in hot climates — that is likely to extend the engine life significantly, slashing the CHT by 50 percent. It brings the simple Jabiru engine to Rotax complexity level, adding some weight. Even though there's weight increase, it's stunningly low because six Rotec heads are 3.3 pounds lighter (1.5 kilograms) than the original, and the electric water pump is lightweight. But it draws 1.8 amp from the electrical system. I would say it is a worthwhile solution especially for hot regions; it gives the airplane owner peace of mind and longer engine life but with added complexity and cost. Rotec has sold 350 cylinder heads in the last 11 months. That many customers could not be mistaken. For more information, go to www.RotecAerosport.com or e-mail RotecEngineering@bigpond.com.
Marino Boric graduated as an aeronautic engineer, acquired a PPL and CPL/IFR, and also flew as a military pilot. As a graduated professional journalist and editor, he specializes in aviation and propulsion and travels worldwide writing for special interest magazines and scientific publications in four languages. Marino is a contributing editor to EAA Sport Aviation and e-Hotline.