We Fly: Piper Archer DX

A diesel-powered training aircraft for the future

Turning to Bart Jones, who was sitting beside me in the cockpit as we flew over the Florida coast, I told him the battery wasn’t working in my headset. The whomp that active noise reduction creates when the power’s going made for quite a distraction. After a beat, and with a nonchalant shrug, he took off his headset. I did the same. It was actually quieter in the cockpit without my headset than with it, and we could hear each other just fine. We shared a laugh and looked out over the Atlantic Ocean spread before us. After a moment of companionable space, and listening to ATC on the speaker, he said, “Maybe we’d better replace the batteries and put them back on.”

Piper Archer DX at a Glance

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Jones—the chief pilot for Piper Aircraft—and I go back probably 20 years, and I’ve had the pleasure of following developments in the company’s training-aircraft series with his guidance. The Piper Archer DX, with its diesel engine and full authority digital engine control system, now tops the list in evolutions that the long-lived Cherokee has made to march forward with the times—but in ways beyond the obvious. I checked in with the company to see what those changes brought to the legendary trainer.

William T. Piper
William T. Piper (left) and racks of legacy parts (right) speak to the company’s heritage. Courtesy Piper Aircraft

The Engine

The Continental CD-155 engine starts with a block that has Mercedes heritage. Built by the Technify Motors GmbH division of Continental in Germany, the engine produces 114 kW or 155 hp at maximum power—the same as takeoff power—at 2,300 rpm, which it can maintain up to 8,000 feet msl.

The CD-155 can burn diesel or jet-A, at a compression ratio of 18-to-1. Because jet-A is more efficient than avgas, and the fuel tanks on the DX essentially replicate the volume of those found on a standard Archer, the DX can stay aloft for longer than its traditionally fueled siblings. Best economy power (65 percent) runs at 1,960 rpm and provides 105 hp in comparison—enough to keep the Archer DX aloft for nearly 7 hours at 4,000 feet msl, based on a fuel flow of 5.4 gph. The throttle quadrant holds a single power lever for the fadec system, making fuel and power

management simple for the pilot.

We saw the results during our demo flight: At 75 percent power, with a fuel flow of about 6.3 gph and a true airspeed of 120 knots, we could fly around far longer than most folks have the desire to. The advantage for a busy flight school operation lies in the number of flights able to “turn” before refueling becomes necessary. Half tanks (24 gallons) easily allow for a two-and-a-half-hour flight with ample reserves.

The walk-around reveals just a couple differences—most notably in the fuel-port placards for jet fuel and up front behind the spinner. The engine inlets are shaped to optimize airflow for the CD-155, and the three slender blades of the MT propeller gleam white in the sunlight.

Piper Archer DX flight deck
A. The standby EFIS, the EFD1000 from Aspen Avionics, provides a backup attitude indicator, airpseed and altitude, and heading ­indicator, along with a wide range of other functionality. B. The Garmin G1000 NXi avionics suite features FliteCharts and SafeTaxi for better situational awareness on the ground. C. What’s different? For one, the engine information is shown on the multifunction display, which is customized for the diesel-engine operations. D. The fadec’s single power lever in the throttle quadrant also ­signals that this is not your usual Piper Cherokee. Courtesy Piper Aircraft

Start It Up

The fadec system turns engine management into a straightforward exercise, and that begins with the change to the startup sequence. For those of you who recall the hot start of certain aged Warriors on a summer’s day, you can look forward to—fondly—a much simpler, responsive procedure, with a couple new tests to run before takeoff.

That said, the procedure will feel a little different for those without much experience operating a fadec-equipped aviation diesel engine. And it takes some planning ahead; starting the aircraft with external power is not allowed, per the pilot’s operating handbook. You’ll need to use extra master-switch discipline to avoid draining the battery accidentally—but you probably should anyway.

Jones walked me through the prep for my first engine start: setting the thrust lever to idle and turning on the alternator, battery and main electrical-bus switches. Because the fadec requires electrical power to operate, all three switches must be on for normal operation. In case of a loss of alternator or the main ship’s battery, a standby battery will power the fadec, but that standby shouldn’t be activated in normal ops—so it’s there when you need it.

Next, I turned on the electric fuel pump and the engine master—a guarded switch, one you definitely don’t want to bump against in flight. Jones pointed out the glow control light, which we checked on and then off. At that point, I engaged the starter, and it swung the prop through for a quick start. Once it was up and running, we went through the checks of the fadec backup battery, switching off the alternator and main battery in sequence to ensure the engine kept purring along. Red warning lights should illuminate at this point if anything’s amiss.

After the engine warmed up for a couple minutes, we also went through a check of the fadec and propeller adjustment. With the thrust lever at idle, I pressed the fadec test button to see if the indicators would come on and prop rpm would increase. Behind the scenes, the system is moving between its B component (or channel), with rpm decrease, and its A component, with another rise and fall in prop rpm to show the engagement of the prop control. It returns to idle on its own at the conclusion of a successful test. With one more run-up bringing the lever fully forward to check maximum rpm (at 94 percent power, it should be between 2,240 and 2,300 rpm), and then back to idle, we were assured of the engine’s readiness for flight.

With one more reassuring look to see that the alternator, battery and main bus switches were on, the rest of the checklist proceeded on course in a familiar way. The fuel-selector valve still allows for a left-right-off position, but the valve lever itself felt a little different in my hand; you have to lift out on a knob to slide it into the off position—a good safety feature when switching tanks is the norm. Frankly, we won’t have to use the selector quite as often, given the lower fuel burn as compared to traditionally powered Archers. Still, we could set a time-based reminder in the G1000 NXi in the panel to keep us on track.

Continental CD-155
The Continental CD-155 is a four-cylinder, inline ­diesel-cycle engine, with dual overhead cams and four valves per cylinder with direct fuel injection. It’s turbocharged and liquid-cooled, with a reduction gear (­­­1-to-1.69 ratio) bringing the engine’s higher rpm down to an ­appropriate, subsonic speed for the prop. Courtesy Piper Aircraft

Operational Elements

Taxiing out on a busy day at Vero Beach, Florida, generally takes patience closely followed by decisive action. Jones manned the mic while I lined us up amidst the trainers from various schools taking advantage of the gorgeous spring day, still a couple weeks ahead of what would become a massive slowdown in flight training. None of us knew that was imminent, but I would love to be back in that conga line, regardless of how many gallons I burned waiting my turn for takeoff—which were not many in the DX.

We had a breezy day in Vero, but the DX handles the crosswind takeoff without much fuss. Jones had me keep full power in until we reached about 1,000 feet, and then I brought the single-lever fadec smoothly back to 75 percent power. Our climb rate met expectations on the just-warmer-than-average day; we were at ISA 4 degrees Celsius at our maneuvering altitude of 4,500 feet msl. After leveling off, we made a few runs in a racetrack to check the airplane’s speed and fuel flow.

Cruising at more than 75 percent power (about 2,030 rpm) is not recommended—and that’s good advice for long engine life whether it’s running on 100LL or jet-A. You’d get a few more knots of speed from cruising at what the POH calls the “percent load” of 90 or 100, but the fuel burn shoots up to just under 9 gph, and you lose the key advantage of the engine-airframe combination—its endurance—without much payoff and increased stress on the engine itself.

With our main goal being to try out the engine’s performance and operational differences, we didn’t spend a lot of time on airwork; the wing is the same as on the Lycoming-powered Archer TX, as is the aircraft’s max gross weight. I checked on those handling characteristics by pulling back the power lever for slow flight and engaging the manual flaps using the familiar lever between the seats. We gently mushed around the sky a bit as I turned and then went into a power-off stall, at roughly the book speed of 45 knots. Anyone transitioning from another PA-28-181 of pretty much any vintage since the mid-’80s will feel right at home. The airplane really has good low-speed habits, with no surprises.

The odor of the jet fuel is one difference, though, to become accustomed to, but I figure that’s because we’re used to avgas, which is another acquired taste. The whiff—like a passerby’s transient drift of cologne—came to me at points throughout the flight, but my registration of it faded away as we flew.

Piper Aircraft factory
The ­Piper Aircraft factory in Vero Beach combines ­historic ­hangars with modern production. Courtesy Piper Aircraft

With a VFR descent back through the lifting condensation level—the happy little layer of fair-weather cumulus marking the coast—we made our way back into the fray at Vero. Other than the usual monitoring of engine gauges on the G1000 NXi, the descent, approach and landing speeds and the configuration targets were roughly the same as in the TX.

All of the functionality within the integrated flight deck is available to the pilot, whether the Archer DX is used for primary or instrument training—or privately owned as an efficient, friendly personal airplane. The standard avionics package includes Garmin’s SafeTaxi and FliteCharts, for situational awareness on the ground and in flight. The DX also comes with an Aspen EFD1000 standby flight instrument, which has integrated within the single unit a 3.5-inch diagonal primary flight display showing attitude, altitude and airspeed and a 3.5-inch heading indicator with navigation-display functionality.

You can add a slew of options, with some skewed toward training or international ops, such as the BendixKing ADF and DME. Most add either connectivity (GDL 59 Wi-Fi Datalink or Flight Stream 510 with Connext) or situational awareness tools such as weather, traffic and flight recording (GDL 69A with SiriusXM radio and weather, GTS 800 traffic advisory system, or the Appareo Vision 1000 flight-monitoring system).

If I were fitting out the DX for myself—a fun exercise, to be sure—I would opt for the GFC 700 autopilot and exchange the standard ADS-B Out-only GTX 335R transponder for the GTX 345R that includes ADS-B In. I’d also spring for the satellite radio. Flying cross-country with tunes is a luxury that’s hard to walk back from—though I could always plug in my iPhone to the standard twin USB ports, I suppose.

Piper ­Archer DX
The ­primary differences between the Piper ­Archer DX and its brethren pertain to the fuel and engine differences, such as the fuel ports for jet-A, streamlined intakes, and a sleek 3-blade prop behind the spinner. Stephen Yeates

Factory Evolutions

An original part of the Vero Beach factory built in the 1960s remains, and the plant has witnessed a lot of change over the course of those decades. You can see that building when you’re standing on Piper’s ramp near where they make customer deliveries. A couple were in process during our visit, for schools such as Middle Georgia State University in Macon, Georgia, and CTI Professional Flight Training in Memphis, Tennessee.

Inside the factory, only a handful of tooling from the first run of Cherokees remains; their brethren have been replaced incrementally with modern machines as Piper makes continuing investment in its production lines. Still, an inventory of parts, forms and tooling lies ready, stacked up in a library of towering shelves in case a piece needs to be called out of storage to craft a legacy Piper part.

I walked through the plant with Jackie Carlon, senior director of marketing, who gave me a detailed tour and history. Carlon has been on board with the company since 2007, watching it navigate through the Great Recession of 2008, as well as the ramp-up of university flight departments and training organizations around the world in response to the determined rise of airline travel and subsequent pilot shortage. Though that expansion—predicted by Boeing’s Commercial Market Outlook of 2019 to continue through the next 20 years—is on hold for the moment because of the novel coronavirus outbreak this past spring, Piper’s manufacturing unit can scale up or down to readily support the existing fleet while continuing to build up new models through the pressurized, turboprop-driven M600.

Piper put together the DX in response to customer feedback, including that from international operators who needed a diesel solution as avgas gets more expensive—and sometimes impossible to obtain—in various countries. There’s also an application for the model among high-volume training customers stateside, who could gain real economies from the use of a more efficient engine-airframe combination. As finances tighten across the globe in response to market contraction heading into the second half of 2020, the DX may indeed find a ready home. The model may also resonate with prospective students who want to fly an airplane that’s just a bit “greener,” fitting more readily into the sustainable aviation future, all the while supporting them faithfully through every maneuver.

This story appeared in the June/July 2020 issue of Flying Magazine

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