Panel Ideas

One of our guiding principles in this project is to have a modern, all-electric avionics system. We have found Bob Nuckols' Aeroelectric Connection to be a pretty good source of information for home-builders on this topic: www.aeroelectric.com. We've also found some interesting discussions on the Matronics's site: http://www.matronics.com/digest/.





Early on, we decided that since a lot of our flying would be done with two of us sharing the duties, we wanted the right and left seats to be "created equal" as much as possible. This led us to the idea of using an LCD screen on each side that could be swapped between engine info and primary flight instruments, depending on who is currently flying. Radios, moving maps, and backup flight instruments will then fill out the middle of the panel. Given the limited relatively small size of the RV-7 panel, we quickly decided that we needed to go with 2-1/4" backup flight instruments, rather than 3-1/8". This would turn out to be a somewhat limiting choice, but we can live with it.

Although it will be some time before we buy the avionics, we plan to install the autopilot servos while we still have easy access. After a fair bit of trolling around the web and talking to lots of fellow home-builders, we decided that TruTrak, www.trutrakflightsystems.com, was the clear choice for us. Besides hearing lots of good things about the design, performance, and reliability of TruTrak's servos and controllers, we really liked the option of getting a single instrument that served as both a backup attitude reference and the autopilot controller. Unfortunately, our decision to stick with the 2-1/4" instruments means we will be limited to the single-axis Pictorial Pilot, rather than than the two-axis ADI Pilot product. I talked to the designer of this device at Oshkosh, and he told me that he really tried to fit the ADI Pilot into a 2-1/4" form factor, and it just didn't work. This doesn't mean that we won't have a pitch autopilot however. We plan to use the Altrak VS product, which provides a simple altitude and vertical speed select functionality. One other limitation of combining the autopilot with the backup instrument is that both the Pictorial Pilot and the ADI Pilot use the analog Digitrak controller, rather than the digital Digiflite controller. The advantage of going digital would be that it can accept digitial steering over an ARINC 429 bus. However, it also costs a fair bit more, and we are already over budget on this panel!





More web trolling, email traffic with vendors, and visits with the vendors at Oshkosh has led us to conclude that, as of today, Grand Rapids, www.grtavionics.com, has the system closest to what we would have designed ourselves. Although the screen resolution is not as good as the competition, and their use of Windows CE for the display unit operating system disappoints us, they seem to have the best AHRS (attitude heading and reference system) design, and this is the guts of the EFIS. Also, they have a tight integration with the TruTrak autopilot that we like, and can drive it to follow a heading reference from the nav radios, and their bus concept gives us enough flexibility to achieve our goals, although we are afraid we will be close to maxing it out. An important consideration for us is also their claim that they will be offering a WAAS, IFR-certified GPS option. They already have a VFR version. If this comes to pass, it may put us over the top on the decision to go with GRT, since it will save us a ton of money vs. buying something like the Garmin GNS 430.

Finally, we are leaning toward the Garmin GTX327 transponder and Garmin SL30 nav/comm, since they are priced competitively and seem to offer better technology than the competition. Still TBD are (1) do we really need an audio panel, or could we live with just an intercom and marker beacon receiver and (2) do we need a backup nav/comm radio? There are a couple topics in play on the backup nav/comm that need to be resolved. One is whether or not GRT comes out with the IFR GPS option. If they don't, and we get a separate IFR GPS anyway, we will likely make it a GPS/nav/comm unit like the GNS 430. Since this unit effectively has the SL30 built in, we could drop the separate SL30 in this case, if we were OK using handheld nav/comm and handheld GPS as a backup. Besides cost, the other issue with backup nav/comm is antenna placement. We are hoping to use the Bob Archer antennas (http://home.hiwaay.net/~sbuc/journal/bob_archer.htm) that mount inside the wingtips, to try and keep the drag down as much as possible. Unfortunately, Archer's vertically-polarized tip antenna won't fit in the new RV-7 vertical-stabilizer tip, so we are going to see how using one of his horizontally-polarized antennas in the wingtip works for comm. If the gain is adequate, we will see about taking the 3 dB hit for a splitter so that a backup comm radio could share the antenna. We'll try this out with the handheld first, then look into adding a comm-only backup comm radio to the panel. Note that we don't have this issue for nav, since we only plan to have one VHF nav radio, the other nav being provided by a precision-approach-certified WAAS IFR GPS.

The last two images here, which I made using epanelbuilder, www.epanelbuilder.com, show some variants on these options. You have to use screen capture to get the images off the webpage, unless you pay them!