August 5, 2008
By Ian J. Twombly
Designing an instrument panel, the actual work of deciding which instrument goes where and which radio goes in what slot, should be an easy task. It should be all about the needs of the pilot. But there are always complications. There are always snags that make it harder than it should be.
When designing the instrument panel for AOPA’s Get Your Glass Sweepstakes Piper Archer, we experienced our fair share of snags. That’s not to say it was a horribly difficult project. On the contrary, Peter Fiorot, the panel designer at Penn Avionics in West Chester, Penn., made it relatively painless thanks to lots of knowledge and some good tools.
We visited Penn Avionics while the Archer was undergoing paint, interior, and maintenance at Oxford Aviation in Oxford, Maine. Because laying out the panel and cutting the metal for the one-piece panel is a lengthy process, we wanted to get started early. Fiorot, who serves as both the shop’s panel designer and an avionics technician, sat us down and we got to work. The choices began immediately, not the least of which was how many of the primary instruments to keep after installing the Aspen Avionics EFD1000 primary flight display.
We decided to start at the beginning with the most important part—the primary instruments. The Aspen serves as the primary attitude indicator, directional display (HSI), vertical speed indicator, airspeed indicator, altimeter, and turn coordinator. In other words, it’s all we needed. Well, OK, that’s not entirely true. FAA rules require that we also have a back-up airspeed indicator, altimeter, and attitude indicator. Incidentally, buyers of both the Aspen PFD and the up-coming multifunction display will be able to get rid of all back-up instruments, thanks to the dual air data computer and attitude and heading reference systems.
Given that the Aspen does all six of the primary instrument functions in only two of the holes, we had space left over for some of the other instruments. We decided that the VSI would be the first to go. It’s generally the least useful, and with two independently powered attitude sources, there’s no reason to fly climbs and descents with the VSI. The turn coordinator was also on the chopping block. It was just about to serve out its existence with a yellow tag on a mechanic’s shelf somewhere, but it was given a second life thanks to the S-Tec Fifty Five X autopilot. A turn coordinator is required for this unit, and although it can go behind the panel, we had the space to keep it up front. Will it be used? I doubt it. But then again, it’s always nice to have.
The final layout ended up looking surprisingly normal, even with a new glass centerpiece. The back-up airspeed indicator and altimeter retain their long-held positions, while the back-up attitude indicator moves to the spot traditionally held by the TC, which then gets kicked to the left. A number two nav head will go where the VSI was. Finally, because we were left with two open holes to the right of the six pack (usually occupied by two nav heads in this vintage Archer), we had plenty of room for the JP Instruments EDM 800 engine analyzer, and the SA-200 altitude preselect and remote annunciator for the S-Tec Fifty Five X.
When deciding on the radios for the Archer, the Aspen obviously weighed heavily. As we said last week, the original plan called for the Aspen MFD, but since that won’t be certified in time, we went with Avidyne’s EX500. Garmin was the clear choice for GPS to drive the Aspen, primarily because it allows for the most integration possible. We decided on two GNS430W units, thereby giving the airplane dual GPS, nav, and comm. Add in the PS Engineering audio panel, Garmin transponder, and S-Tec autopilot, and we had to fit six units in less than 10 inches of vertical space. Thankfully, the Archer also has room for a second radio stack to the right, thereby giving us more room for the radios.
In an ideal situation, the audio panel would be at the top of the primary stack, followed by the MFD and the two 430W. Then the right stack would be the transponder and autopilot. No go in the Archer. With less than 10 inches between the glareshield and a horizontal support directly above the yokes, this was never going to happen, especially when the MFD is half of that space. To make matters worse, the shop told us that room behind the Archer panel is at a further premium because the glareshield slopes down rapidly, reducing the amount of vertical space to much less than what’s seen on the panel itself. It became a chess game at that point. Which piece of equipment is used the most? What never gets touched? Clearly the transponder should be to the far right. That was a given. And since the Archer has a pretty hefty subpanel, and we had a remote annunciator on the main panel, we decided to move the autopilot to the bottom left, below the yoke. One GPS and the MFD had to be in the main center stack, we reasoned. The audio panel should also be at the top of that stack, as is traditional.
Unfortunately, things weren’t going to go our way. With the EX500 being roughly a foot long, we only had room to put in one GPS and the MFD in the center stack. The Archer’s sloping glareshield meant the MFD had to go on the bottom, something we had hoped to avoid because it puts the GPS slightly farther away. What we were left with is the best possible scenario given the variables. The second GPS, the audio panel, and the transponder are now on the right stack, still within easy reach for most pilots.
Next week: The panel work begins
E-mail the author at [email protected]
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