The Iconic Arrival of the Twin Navion Aircraft

The Twin Navion aircraft makes an impression long before it ever leaves the ground. Walking across the ramp of Arizona’s Chandler Municipal Airport (KCHD), just outside of Phoenix, under the warm spring sun, the presence of the brightly painted twin loomed large in the distance. Even before the owner, Troy Welch, and I completed our pre-flight inspection, we were interrupted not once but twice by a friendly inquiry of, “What is that?”

The first time, the question came from a couple loading their airplane in the adjacent parking spot. They were taken aback by the significant stature of the twin engine aircraft — after all, the tip tanks of its low wings were nearly the same height as the bottom of their Cessna’s high wing. The second curious onlooker had seen the unusual twin from across the apron but couldn’t identify it. He explained that he had to drive across the airport just to get a closer look.

Upon learning the airplane was a TEMCO-Riley D-16A Twin Navion, his expression quickly transformed into a broad smile of recognition. “I sure thought it looked like a Navion, but I never knew they made a twin-engine version,” he replied with excitement. A few minutes later, engines running and taxiing to the active runway, the same question came again — this time over the radio, as the ground controller’s curiosity joined the growing list of admirers.

North American’s Civilian Sedan
North American Aviation (NAA) scored a major PR victory when their B-25 Mitchell medium bombers, under the command of Jimmy Doolittle, became the first American aircraft to strike the Japanese home islands in 1942. Their equally famous and fantastically photogenic P-51 Mustang fighter had the range to accompany bombers deep into enemy territory and became the steed of many an ace.

With lucrative military contracts ending, NAA intended to use their name recognition to sell a civilian family hauler that could help to keep their post-war balance sheet in the black. Even the name of the aircraft would be a word invented for the purpose. The company’s stock exchange code was “NAV.” NAA added the “ion” and the first two letters were capitalized to further highlight the machine’s North American pedigree.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The NAvion’s robust design and construction drew directly upon NAA’s military experience. In fact, even the military was impressed enough with them to place multiple orders, which were used in various liaison roles and designated the L-17.

While no manufacturers achieved the civilian sales numbers they predicted after the war, NAA was successful enough selling NAvions to keep their core staff of engineers and laborers busy during the gap years between the winding down of P-51 production and the spooling up of their military jet aircraft production. By 1948, however, NAA was again receiving big military contracts to build fighters and bombers.

The decision was made to sell the NAvion to the Ryan Aeronautical Company. In 1949, Ryan re-started Navion production (with the “A” now in lowercase) at their San Diego facility. By the time production ended in 1952, over 2,600 had been built between both companies.

The type and production certificates have since changed hands at least a half-dozen times. The “Rangemaster” version was put into limited production in the 1960’s. It replaced the sliding canopy with a solid roof/door arrangement and added enough fuel capacity to boast a bladder-busting, 1,800-mile range. Less than 200 were built.

Multiple upgrade and modification programs have been popular, creating many subsequent model designations. Myriad engine types, aerodynamic clean-ups, and modernization mods have been approved, as well. Navions continue to be revered by owners and supported by both an active type club and the current Type Certificate owners in Minnesota.

Acme’s X-Plane
The most common complaint of early Navion owners was the relatively low power, given its bulk. Even Ryan’s final production model, the “Super 260,” was not considered to be a powerhouse. They were big, roomy, rugged, stable and reliable. Yet, they were not speedsters nor stellar climbers. Nonetheless, many owners loved their flying qualities and contemplated solutions to improve performance.

 

 

 

 

 

 

 

 

 

The Creation of the First Twin Navion Aircraft

One of the most fascinating chapters in the history of the Twin Navion aircraft began with businessman Chuck Daubenberger, who had built an impressive post-war aircraft collection. His single-engine Navion was among his favorites, but he was dissatisfied with its lack of redundancy — especially since he often flew over mountainous regions. Seeking greater safety and performance, Daubenberger approached Acme Aircraft Co. in California, where engineer Roger Keeney half-jokingly suggested adding a second engine. What started as a casual remark quickly turned into a serious engineering challenge that would give birth to one of the most distinctive twin engine aircraft designs of its era.

Daubenberger soon handed his Navion over to Acme, which brought together several North American Aviation aerodynamicists and engineers who had worked on the original NAvion design, along with former Douglas Aircraft experts. Their local contact at the Civil Aviation Authority (CAA — the predecessor to today’s FAA) assured them in writing that if they completed the engineering and testing work, the conversion could be legally approved under Major Repair/Modification Forms (337s).

The Acme team installed two used 125-horsepower Lycoming O-290 engines and matching cowlings. A hand-shaped nose bowl completed the prototype’s unique look. To compensate for the added power and to improve directional stability, the engineers mounted a spare horizontal stabilizer and elevator vertically in place of the original tail. Interestingly, this modification was done more for marketing appeal than for aerodynamic necessity, as calculations showed that the original surface area was already sufficient for engine-out control.

The prototype, initially known as the X-16, went through numerous small refinements during its testing phase. After about a year of hard work, the team achieved certification in November 1952, and the aircraft was officially renamed the D-16 — marking the creation of Daubenberger’s sixteenth airplane and the first certified Twin Navion aircraft.

In short order, higher-ups in the CAA got wind of the project and the fact that it had been certified via only Form 337s. They informed Acme that the certification was not valid, in spite of the 2,000+ engineering drawings that Acme had submitted detailing their modifications.

Acme and Daubengerger quickly prevailed, as their program and paperwork complied with the rules that existed at the time. However, the CAA learned a lesson, which soon led to the creation of the Supplemental Type Certificate (STC) process for approving major modifications to certified aircraft.

A second Navion was converted to a D-16 by Acme for Jack Riley, an entrepreneur and highly successful aircraft salesman, who purchased the rights to the design. Riley’s aircraft had 135hp O-290 engines. He soon purchased the original D-16, as well, and had it fitted with 150hp, O-320 engines. Slow production began at Riley’s facility in Florida in early 1953.

Production Twin Navions
Within months, demand was higher than Riley could meet, and the Texas Engineering & Manufacturing Co. (TEMCO) was sold exclusive rights to manufacture the D-16, marketed as the “Riley Twin.” Sixty D-16s were produced by late 1954. At that point, TEMCO introduced the D-16A, which they called the “Riley ‘55.” The A-model incorporated a welcomed horsepower boost to 340 via two 170hp Lycoming O-340s and full-feathering, constant-speed props. Other improvements included a 250-pound gross weight increase (to 3,600 lbs.) and optional tip tanks. Fuselage tanks were exchanged for nacelle tanks. The Riley ‘55 carried an impressive 144.5 gallons in wing center-section, nacelle, and tip tanks. The CAA convinced Riley to re-certify the D-16A under a new type certificate due to the sweeping changes.

Production ceased in late 1957 after 45 D-16As had been produced. Several prior conversions were later upgraded to D-16A configuration. Including prototypes, 107 Navion airframes eventually became Acme/Riley/TEMCO Twin Navions.
Another twin-engine Navion conversion program was certified, as well, though its details surpass the scope of this article. Known as the Camair 480 and 480C, the timeline follows very closely behind that of the Acme/Riley story.

But, the Camair was a very different animal, with 240hp Continental O-470 engines, many fiberglass components, a newly designed tail, and a much higher gross weight. It was, of course, faster but was even further behind the market trends than TEMCO/Riley was. Costing 50% more than a TEMCO/Riley conversion, Camairs struggled for sales. Only 33 were built (between 3 different manufacturers and spread out over a decade-plus timeframe).

In the end, the Twin Navion numbers stayed low, not because they weren’t wonderful airplanes but because they simply cost too much. Competition was fierce, with Piper selling its PA-23 Apache for the same price as a TEMCO/Riley ‘55 conversion (which, of course, required the buyer to also supply a Navion airframe to start the process). Cessna’s 310 and Beechcraft’s BE-95 Travel Air filled any remaining voids in the light-twin market, also selling well below the all-in price of a TEMCO/Riley or Camair converted Twin Navion.

Unique Among the Rare
A flying Twin Navion of any variety has become exceeding rare today. After all, these machines were built as Navions in the 1940s or early 1950s. With the exception of a few Camairs, conversions were all completed in the 1950s. So, only about 140 Navions were ever converted to twins, and these machines have all celebrated at least their 70th birthday now. Of the half-dozen or so examples believed to still be airworthy, Serial #TTN-39 is surely one of the most notable.

Originally manufactured by NAA in 1946 as Serial #NAV-4-418, sporting a Continental E-185 engine (205hp for takeoff, 185hp continuous), it was purchased by TEMCO in early 1954. After re-registration as N108N, TEMCO soon received approval to begin certification testing it as a twin with one Lycoming O-320 (150hp) and one O-340 (170hp). During testing, the second O-340 was eventually installed, making this airframe the prototype D-16A. It was flown by TEMCO throughout the rest of the D-16A’s production life, for testing and promotional purposes. Featured in many advertisements and magazine articles during that time, it acted as the poster child for the Riley ‘55.

In 1958, Jack Riley was the registered owner of N108N. Thereafter, it went through a steady sequence of a dozen owners but appears to have stayed relatively active, even winning a Best in Class award at Oshkosh AirVenture 2003. In Jan. 2017, it was acquired by its current owner, Troy Welch. A professional corporate pilot, flight instructor, and retired attorney, Welch still flies a Citation X+ in his day job while enjoying a variety of general aviation aircraft for more leisurely pursuits. His pride in being the caretaker of TTN-39 is obvious.

Getting Acquainted with the Twin Navion Aircraft

It’s probably worth noting that prior to my introduction to N108N, I’d never flown any version of a Navion. However, in my experience, most airplanes fly the way they look. Their overall appearance and features give hints as to how they’ll handle — and the Twin Navion aircraft was no exception.

First Impressions of the Twin Navion Aircraft

The T-Nav’s steep wing dihedral and towering tail practically scream stability. Its tall gear and big tires have an uncommonly sturdy look for a light twin. They tell you turf runways are no problem for this airplane. The broad fuselage and nose imply that cabin comfort and storage space were prioritized over speed. However, when one considers the 1,200-mile range of the D-16A, a comfortable cabin becomes a significant plus.

This first impression immediately sets the Twin Navion aircraft apart from many other post-war designs. It’s a machine built not just for pilots but for travelers — combining the practicality of a touring airplane with the performance of a classic twin engine aircraft.

Cabin and Cockpit Entry in the Twin Engine Aircraft

An exterior baggage door eases loading of the cavernous aft cabin, rated for 180 lbs. A smaller nose baggage area, rated for 134 lbs., is easily accessed through the flip-up nose cone. Well-placed steps and handles make climbing onto the not-so-low wing simple. Entering the cockpit, however, takes a bit more finesse. With the huge canopy slid full aft, you step over the fuselage side onto the cabin floor between seat rows. Rear-seat passengers enter easily, but moving forward requires some contorting to squeeze between the pilot seats while maneuvering around the sizable power quadrant.

The alternate method — stepping directly onto the pilot seat and sliding down — is only marginally easier, as the windshield frame extends too far aft to allow a simple vertical entry. Yet this slightly awkward process is no worse than with many cabin-class twin engine aircraft. Once seated, the cockpit feels surprisingly ergonomic. The Twin Navion aircraft’s design offers excellent sightlines and an open, spacious feeling uncommon in aircraft of its era.

Visibility and Panel Layout of the Twin Navion Aircraft

Visibility for all occupants is excellent. The seat pans sit high above the wing, placing the pilot’s eyes well above both the ground and the airframe — a perfect balance between comfort and awareness. Unlike many low-wing piston twins, neither the engine nacelles nor the long nose restrict the view. This is one of the subtle advantages that makes the Twin Navion aircraft so pilot-friendly and confidence-inspiring.

The panel layout of Welch’s aircraft retains a vintage charm. The radio stack sits far left and is partly obscured by the left yoke (especially for the right-seater). Yet the flight instruments have been refreshed into a standard six-pack configuration with a modern Garmin G5 attitude indicator. Magneto switches and the hydraulic pump control are tucked slightly to the right of the power quadrant. Despite its busy look, the quadrant itself is well organized.

As with many classic twin engine aircraft, the throttles are centered while the prop controls sit to the left. The quadrant also houses starter, primer, and fuel pump switches, plus flap, gear, trim, and carb heat controls. This thoughtful arrangement gives pilots intuitive access to all key systems — proof that even decades ago, the engineers behind the Twin Navion aircraft understood human-centered design.

The Personality of N108N
Toggling the 3-position electric switch left and right to prime the carbureted engines makes hot or cold starts predictable. Taxiing presents no unusual challenges, with responsive braking and steering and the availability of differential thrust if extra tight turns are necessary. Run-up and pre-takeoff checks are standard, as well. Check mags, carb heats, vacuum and hydraulic pumps, and cycle the props.

Like in all U.S. aircraft of this era, speeds are all in MPH. Initially, we were relatively light with only about 50 gallons of fuel, two adult males, and about 100 pounds of bags in the aft compartment. But, the afternoon temps in southern Arizona were in the high 80’s. Vmc (minimum control speed, single-engine) is marked as the lower redline of 86. Vyse is 102, but no blue line denotes it on the ASI.

However, the Navion’s big wing and thick airfoil are ready to fly before reaching Vmc. So, one can be patient and allow speed to build in a longer ground roll, or level in ground effect briefly to allow speed to accelerate past Vmc and towards Vyse before climbing. I did a little of both, and in short order, Troy and I were headed southwest for maneuvers enroute to Gila Bend Municipal Airport (E63).

Basic air work in the ‘55 was sedate. Stability abounds, making steep turns, slow flight, and stalls absolutely predictable. The big light twin (an oxymoron that feels totally appropriate) is surprisingly light on the controls but very well harmonized. However, trimming can be cumbersome. Both rudder and elevator trims are operated via small left/right cranks on the lower power quadrant. Rudder trim is intuitive in this arrangement. Elevator trim is not. Clockwise for nose down, counter-clockwise for up. In practice, it’s an exercise in gauging reaction to your input versus consciously cranking in the correct direction. I’m reminded of old Pipers with the trim crank on the ceiling. Each time a new input is needed, everyone seems to turn it the wrong way at first.

Trimming nit-picks aside, we were soon exploring single-engine operations. The T-Nav’s critical engine is on the left, as in most non-counter-rotating light twins. But, because the engines are only rated at 170hp each, this “criticality” is less noticeable than in more powerful twins. With the left engine at zero-thrust, we could easily maintain 200-300 FPM climbs well below full power on the operating engine. This was also easy to manage without adding rudder trim. With full power on the right engine only and trimmed out, 500+ FPM was sustainable right to our cloud-limited altitude of 4,500’ or so.

The literature says the Riley ‘55’s single-engine service ceiling at MGW is 6,000 feet. Of course, that’s likely a standard temperature calculation. Because we were somewhat altitude-limited by cloud coverage, we didn’t explore Vmc down to directional control loss. However, the single-engine flying we worked on made it obvious that the rudder was huge and very effective.

Landing and Flight Performance of the Twin Navion Aircraft

For pattern work, Welch’s preferred method in the Twin Navion aircraft is to slow below the common gear and flap extension speed of 116 mph and complete most actions abeam the numbers: set power, apply carb heat, extend flaps, and lower the landing gear. Straightforward enough — except for one caveat. The hydraulic flaps deploy slowly. Very slowly. By starting them down abeam the numbers, Welch’s preferred 20–25° landing configuration isn’t reached until late on the base leg. If full flaps (35°) are desired for a short-field landing, they won’t be fully extended until final approach.

Of course, this means lift and drag change almost constantly throughout the entire pattern, requiring close attention to both power and airspeed. While initially a bit distracting, it quickly becomes manageable. Welch believes a future rebuild of the hydraulic pump will resolve the slow-deployment issue. Once the selected flap setting is in place, trim can be adjusted for final approach speed, and everything falls neatly into place. Troy warned that pulling power too early combined with a high flare could cause an abrupt sink, but in truth, the Twin Navion aircraft proved to be remarkably gentle to land. It provided honest feedback and a comfortable sight picture almost immediately.

Cruise Efficiency and Handling in the Twin Engine Aircraft

At Gila Bend, Troy pumped just under 100 gallons of fuel into N108N as the temperature peaked at 93°F. Departing nearly 400 pounds heavier than from CHD, the twin engine aircraft didn’t seem to notice the difference. It handled with the same poise and balance as before. Of course, in a low-altitude engine-out scenario, performance differences would be more pronounced — but in normal flight, the aircraft remained impressively stable and forgiving.

Picking up our IFR clearance into Phoenix Sky Harbor International (KPHX), we climbed to 7,000 feet. Level at cruise, we set 75% power, leaned via EGT, and settled into a 160-knot true airspeed while burning just 20 gallons per hour — outstanding economy for a vintage twin navion aircraft. ATC requested 150 IAS during vectors for the ILS to Runway 25L, a few miles below the yellow-line speed. Descending into afternoon turbulence posed no challenge; the aircraft remained solid and responsive.

Established on the localizer and glideslope, we held 150 knots to a 3-mile final before letting the big props, stiff headwind, and extended gear and flaps slow us smoothly to Troy’s preferred stabilized final speed of 100–105 knots, crossing the threshold at 90.

Before I’d even cleared the runway centerline, Troy was already answering the tower’s inevitable question about his Twin Navion aircraft. Taxiing to Cutter Aviation, a lineman guided us to parking — and before both propellers had even stopped, three more curious onlookers appeared, all asking the same question once again:

“What is that?”

If you’re interested in aircraft design and stability, read also this article on sizing the empennage of multi-engine propeller aircraft: A Multidisciplinary Possibilistic Approach to Size the Empennage.