Jerry's Kitfox

Project Report

As some of you know, your editor has been helping Jerry Pilon with the building of his Kitfox.   My contribution, with Jerry’s supervision, has been to assemble the panel and install the wiring.  

  To begin with, Jerry purchased a volume written by Bob Knuckles, which is an education in it’s self in the design and installation of DC wiring in experimental aircraft.  In his book, he begins with very basic circuitry and progresses to more complicated design of dual ignition, dual battery, and dual alternator aircraft.  Some of the schematics are particular to Rotax engines and some are aimed at non magneto engines.

  The designs he suggests are very conservative when it comes to wire size and fuse/circuit breaker placement.   Especially for engines with electric ignition he puts the emphasis on battery health and what he calls an “essential buss” circuit that lets you, in the event of alternator failure, switch to a circuit that only powers the essential instruments for flight.  You don’t have to decide, during the emergency,  and loosing the alternator in an all electric airplane is an emergency, what to shut off and what is required to get on the ground, in order to save the battery.   You can do that with the flip of one switch.

  Knuckles also promotes using fuses instead of circuit breakers.   His experience working on heavy iron was that he replaced more bad circuit breakers than failed instruments.  He believes circuit breakers are a dinosaur that is too expensive to replace due to certification costs.   His point is,  if a breaker pops, are you going to keep pushing it back in until you see smoke or are you going to land and determine what caused the overload.   In the latter case,  a fuse performs the same function and is less expensive to the builder.  In fact, twenty automotive type fuses can be mounted in a fuse block approx.  4 X 8 inches in size and every electrical device in the aircraft can have it’s own fuse instead of ganging several instruments on one breaker like commonly done in certified aircraft.  The automotive folks have gone one step farther and make a fuse that lights up when it blows making it very easy to spot the problem.

  We have mounted Jerry’s fuse block under the panel on a drop down panel.   It is accessible in flight, but,  like my Cessna 150, I don’t want to be changing fuses in flight.  In the 10 years I have owned 75J I have only blown one fuse and that was when the Genave Transponder burned up,  (blew a power tube), while we were near Marshall County one day.

I actually had one Buss fuse fail when I was checking them and tried to remove it from the holder,  It had been in there so long, it corroded fast to the fuse holder and pulled apart when I removed it.  

  Fuses/breakers do fail from age and should be checked once in a while.  At least every ten years (that’s a joke son).

  Fused or breakers, the important thing is that they work and prevent the wires from turning red.   After all, that is the primary purpose of the devices.  Most of them are sized to protect the wire, not the device attached to the wire. 

  The Kitfox wiring is nearly finished and the first test of the circuits was very successful.