By J. Mac McClellan, EAA Director of Publications
I know many owners of conventional airplanes who look with envy at the array of advanced flat glass avionics built for experimental airplanes. Without the burden of demonstrating their avionics meet FAA certification requirements, makers of glass panels for homebuilts can make new technology available much quicker, and for a fraction of the price. But the rules forbid owners of standard-category airplanes from permanently installing non-certified avionics in their airplanes.
Does it make sense that a pilot could be forced to fly with decades-old spinning-rotor gyros powered by a not-very-reliable vacuum pump when advanced non-moving electronic gyro systems are available and affordable for homebuilts?
Dynon Avionics, a leader in flat glass displays for the amateur-built experimental market, doesn't think so and has developed at least a partial solution with its new D1Pocket Panel portable primary flight display (PFD).
The D1 is a small electronic display that measures about 3.5 inches square. It weighs just 7.1 ounces. Yet it can show attitude based on its own internal non-moving electronic gyros. It uses GPS to show ground track, ground speed, and altitude, along with rate of climb. And it can operate for at least four hours on its own internal battery power or can be connected to aircraft power for indefinite operation.
Dynon configured the D1 like a conventional PFD with the blue-brown attitude display, a compass arc at the bottom with digital track presentation, and speed on the left and altitude on the right.
Dynon ships the D1 with a suction cup mounting arm that can be attached to any smooth, flat surface in the cockpit. Or, if you have an empty 3-inch instrument hole in the panel a clever mounting pad uses little "fingers" to grasp the edges of the instrument cutout and hold the unit firmly in place. Those "temporary" mounting systems are important only for standard airplanes because you can't "install" the D1. If you have an experimental, however, you can mount the D1 any way you wish.
I have to say that when I took the D1 Pocket Panel out of the box I was skeptical that it could be more than a curiosity during real-life flying. The display is plenty readable even in bright sunlight, and Dynon has an excellent reputation for the quality and performance of the electronic gyros in its panel-mounted systems, but the D1 is so lightweight and compact.
Could it really be a usable backup to conventional gyro instruments?
After charging the unit overnight I took it out to my Baron. The suction cup stuck firmly to the left side window and I could adjust the gimbaled mount so the D1 was level and near the corner of the cockpit where the windshield and glareshield meet.
The idea is to mount the D1 so that it is as parallel as possible to the wings and as square as possible to the longitudinal axis. You then use a little rocker switch on the side of the D1 to adjust the attitude display to match the attitude of the airplane. This all took only a minute, at most.
After takeoff and in smooth air I fine-tuned the attitude to match the level flight attitude of the airplane. And I was impressed that the D1 accurately matched the attitude displayed by the Garmin electronic gyro AHRS in the panel. The D1 stayed accurate in attitude through fairly steep turns of 45 degrees or so, and during shallow bank turns that can be an even bigger challenge for gyros when it comes to precision.
When I fired up for the next flight the D1 came up with the same settings so no adjustment of attitude was needed. After a few flights I became convinced that I really could stay right side up in the clouds with only the D1 as reference should that become necessary. And compared to the old emergency fallback of a turn coordinator only to establish attitude after a vacuum pump failure the D1 is something like, well, about 100 times easier to fly. I get to fly many million-dollar jets with 3-inch PFD backup instruments in case all else fails and the D1 comes close to matching the performance of those very costly units.
But there are differences between the Dynon D1 and certified backup PFDs, and that is heading, speed, and altitude.
The D1 shows speed, but it's GPS-derived ground speed, not airspeed. The "heading" display is GPS ground track, not magnetic heading because it has no compass sensor. And the altitude on the D1 is GPS altitude, not the pressure altitude of a normal altimeter or air data computer.
So, the speed you see on the D1 is true airspeed combined with the effects of wind. And, depending on atmospheric conditions, the GPS altitude can be several hundred feet different from the conventional altimeter.
I don't find the speed and altitude and track issues to be a big deal for pilots depending on the D1 as a backup. Nearly all airplanes-even those with glass panels-will have mechanical/pneumatic airspeed indicators and altimeters installed and those are unlikely to fail merely because the vacuum pump or spinning gyros failed. It's easy to compare the altitude and airspeed on the conventional indicators to those on the D1 and mentally compensate between glances at the instruments.
And if you care about magnetic heading, the whiskey compass is always there.
The Dynon D1 is priced at $1,425 complete with the various mounting systems, charger, a power adapter cord, and a little portable GPS antenna if you need it; I didn't. Compare that to the cost of a second vacuum pump, or electrically powered spinning gyros, or any of the certified AHRS backup displays; it is remarkably low-cost.
No, you can't permanently install the D1 in a standard airplane yet, but now you have affordable and reliable modern backup gyros just like the guys in the well-equipped experimentals.
Dynon's dealers are selling the D1 here at Oshkosh this week. Check with Aircraft Spruce, Wicks Aircraft Supply, and Gulf Coast, Pacific, and Sarasota avionics.