I got my classic Jet Central Rabbit back from its annual 25-hour inspection, and upgraded it for one of Jet Central’s newest features: the Power Box. This upgrade cleans up and simplifies turbine engine setup and installation, reducing the connections between the turbine and the engine-control unit (ECU).
The Power Box only requires two fuel hoses and one S-Bus cable between it and the turbine. The fuel pump and fuel solenoid valves are inside the Power Box. The rpm and temperature sensor cables that ran from the turbine to the ECU were eliminated because this part of the ECU is located within the turbine.
The kerosene hose from the hopper, the turbine battery, and the throttle input from the receiver are connected to the Power Box. The Power Box has mounting tabs to allow bolting into a secure place in the airframe where access would be easily available to connect the ground support unit (GSU), a small unit introduced last year.
It is smaller than a standard servo and I’ve seen the GSU mounted in a visible place in the model with a switch between it and the ECU. It is the ultimate in convenience. There’s no excuse not to monitor your start-up sequence.
Because the ECU is located within the turbine’s front housing, the Power Box primarily handles fuel management and serves as a connection point. Experience has shown that the most troublesome part of a turbine installation is the kerosene solenoid and fuel pump installation. Reduced hose connections and their associated fuel leaks, damaged wires on solenoids, and the space they take up are issues addressed with this compact, simple Power Box box.
ECU electronics are robust systems and are seldom replaced. The S-Bus Power Supply cable allows communication with the Power Box to control the fuel pump, fuel solenoids, throttle commands, and communication with the GSU.
The ECU is configurable for either a 7.4-volt two-cell LiPo, or a 9.9-volt three-cell LiFe battery. I have one turbine running on a 9.9-volt LiFe battery and I love the strong start performance. I suspect it’s because the lower current draw of the higher voltage has favored this setup.
My Vampire has flown on the same 3,800 mAh, two-cell 8C LiPo battery with no issues, however, last winter the cold weather starts were getting weaker. It is time to step up to the higher voltage of the three-cell LiFe.
I plan to convert my DerJet Vampire’s Rabbit installation to the Jet Central Power Box, then I’m off to some winter weather jet flying. I’m looking forward to this new system. The installation will take less space with the Power Box replacing the fuel system. Come to think of it, even the ECU mount is no longer necessary. This will be easier to convert than reinstall all that it replaces. I love the new advances in Jet Central’s turbine packaging.
Years ago (and more than 200 flights ago), I mounted landing lights on the Vampire’s main gear struts with a simple aluminum bracket that is held to the aluminum strut with J-B Weld—that epoxy we all know and love from the hardware store. I’m happy to report that the bond has held through all of the abuse, including grass-field flying, with no issues.
A neat thing about J-B Weld epoxy is that it is thick enough to build up details on landing gear that can then be machined with a lathe, Dremel tool, or whatever you have to add detail to any aluminum landing gear strut for improved scale detailing.
This success with J-B Weld led to my last build. How would I attach the main gear door to a set of Tam Jets struts? Since this was a simple sport jet, a Jet-Teng Models 1.7-meter Viper, I didn’t feel the need to get too fancy. It was the middle of the flying season, so I didn’t have enough patience to make any brackets.
I made up a 1/4-inch plywood spacer from the strut to the gear door to obtain proper spacing, routed a half-round edge to inset the brake line, then used J-B Weld to attach the plywood spacer to the strut.
After installing the landing gear in the wing, I raised the main gear up into the wheel wells and set the strut gear doors in place, sanding away the 1/4-inch plywood spacer until I attained a flush fit. I actually sanded approximately 1/32-inch greater than necessary, then continued with the simple installation
I used a mix of epoxy and Cabosil (a thickening filler for the epoxy) to epoxy the strut gear door in place while the door was taped in place on the wing. After the epoxy set, I used thick Zap CA to attach the brake line to the back edge of the 1/4-inch plywood spacer where I had previously routed the edge to accept the tubing. The gear door fits nicely to the wing surface when it is in the closed position and includes a clean brake line install—simple, quick, and clean.
This has proven to be a rugged install, holding up well for the season, however, it is very difficult to remove should gear-strut maintenance be required.
The Tam Jets strut is a simple spring-type suspension, so I hope it won’t require frequent disassembly. On landing-gear struts with built-in shock assemblies such as my Vampire, this would not have worked out so well. The shock oil level must occasionally be serviced, and this is done by disassembling the landing gear strut to add oil as required.
World Jet Masters
For those interested in competing or visiting the International Jet Model Committee (IJMC) World Jet Masters, it’s time to start planning. The 2015 IJMC World Jet Masters will be in Leutkirch im Allgäu, Germany.
The US team selection will take place this year, and Roger Shipley has again stepped forward to organize the team selection process. The plans for a qualifier (if required) will be similar to previous years, with many of our qualified, IJMC-trained judges at the ready to support our team selection process.