Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.
Issue link: http://experimenter.epubxp.com/i/126719
A D - I -Y G l a s s Pa n e l in my day job. But my last 12 years were in engineering management, and my technical skills were rusty. What if I designed the entire panel? Could it be accomplished safely? Mitigating Fears With Design I began laying out the system design for a personal computer–based glass panel and identifying the make or buy components. After a lunchtime chat with friends, it was obvious that I was starting at the wrong place; backups need to be defined first. But you can't define backup instrumentation until you have a mission. If you think it through and internalize the mission as gospel, the backup equipment alone must fulfill the mission. A tight definition of our cross-country mission is "If there is a problem, then we will continue to our next waypoint, land safely under any conditions, and thereafter fix the aircraft." Of course, route planning must include strategic waypoint selection. Another major consideration was that the glass panel was going to be a multiyear development, interwoven with family trips, and may not be perfect. To meet these goals, I implemented TSO-certified round instruments and a Garmin SL-30 (radio, VOR, and ILS) powered by a separate standby bus and battery. The standby master switch is wired to deplete the standby battery, and if necessary, then deplete the main battery. Other than audio and a trickle charger circuit, no other connections exist between the backup and primary components so one cannot affect the other. On just one inexpensive 12AH standby battery, our RV-10 will fly in instrument conditions for 1.5 hours and shoot an ILS approach with the master switch off. From a design point of view, this was an excellent strategic decision because I didn't need to implement any backup considerations in the glass section and probably saved money overall. 20 Vol.2 No.5 / May 2013 A small but interesting puzzle was solved by the Garmin audio panel. If the headset is wired into the audio panel and the power to the audio panel is off because the master switch is off, then how can the headset work with the backup radio? In every audio panel that I have wired, there are normally closed relays that bypass the internal audio panel logic and directly tie the pilot headset to "Comm1" when the power is off. So my backup Garmin SL-30 radio is "Comm1" and the Garmin 430W is "Comm2." Since the backup instrumentation is "anded" into the primary panel, several unforeseen bonuses began to emerge. With the standby master on, additional radio frequencies could be queued into the SL-30 when entering complex airspace, and a glass panel GPS WAAS approach could be monitored with the backup ILS should an outage occur during a critical time. Recently, I was in actual weather on a GPS WAAS approach, and the LPV was suddenly downgraded to an LNAV approach. I simply refocused and flew the ILS approach, never touching a button. Core System Design The initial glass panel goals were quite simple, yet had farreaching results. No vacuum system would be installed, and we would maximize the display size, minimize the num-