I visited with Steve Eberhart and Larry Helming, two 7 builders in Evansville, over the weekend. I had a chance to visit a Harmon Rocker ll builder along with an 8 builder with some homebrew ideas incorporated on his fuselage. In the process, this was my intent, I picked Steve's brain (trained in electronics) and Larry's, well read on aero electrics.
First of all, I'm like the Holiday Inn Express guy, no I don't know anything about what I am going to say here, I just know the key words, well maybe a little more now. I would seriously recommend anyone thinking about aero electronics to visit Aeroelectric.com and join the list. Buy the book for $30 and you will be able to easily design and install your electrical runs more efficeintly along with essential redundancy. The basic premise here is to have three buses: a main bus, an essential bus and a battery bus. The battery bus is not switched and is alway hot. This is for things you never want turned off and to always receive current from the batter, ie, electronic ignition. The main bus is just that, the rest of your stuff. The key thing in the design, and it is very simple if I can understand it, is the essential bus. This bus normally sits next to the main bus and normally receives power from the main bus. In case of a short, or runaway alternator regulator that disables your electrical system you simply take the main bus out of the system and now are running off your essential bus. A diode is installed between the essential bus and main bus to keep current from flowing back into the main bus (I even know what they do now). The essential bus carries systems that you determine to be essential to a safe landing. Do you want a radio, do you want your TC to work or how about trim. I know in a KR, the system is not that intricate but the essential bus keeps you from having to shut things down by simply throwing a switch. Some will say, "I can just go to battery and do the same thing." Well, not exactly. He recommends you limit the amps on the essential bus to something like 6 amps. If you have a, say 20 amp battery look how much time you have to do something. It may not now be an emergency. One of neatest things I have seen in his book and illustrations is the use of a current limiter between the alternator and the system. Instead of having to run a big ol thick wire into the cockpit to a fuse or breaker, it is simply a hard contact between the two, on the firewall, that will break if an overvolt situation occurs. I have had first hand experience where a breaker did not break in an overcharge situation when the battery was mistakenly switched out before the generator was removed from the line. A very large spike hit the panel with a great deal of smoke and systems, not of the pilots choosing, were permanently removed from the system. If you have just a main bus installed and can still get too it, I would recommend you look at this and go the essential, battery route. Electric Bob has the part numbers you need and great illustrations. Once again, I'm just the Holiday Inn Express guy who can speak the language but it just learning to understand it. One thing I have learned though is this is elegantly simple, rediculously inexpensive and immeasurable in added safety. Dana Overall 1999 & 2000 National KR Gathering host Richmond, KY RV-7 slider/fuselage http://rvflying.tripod.com do not archive _________________________________________________________________ Help STOP SPAM with the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=features/junkmail
