Revolutionary Design Philosophy
Ted Smith, a Douglas Aircraft project engineer, conceived the Commander 520 while working on the A-20 bomber during World War II. Smith recognized a market gap for a high-performance business aircraft that could match airline speeds while serving smaller airports. In December 1944, he founded Aero Design and Engineering Company in Culver City, California, with fellow Douglas engineers, dedicating over 10,000 hours to redesigning the aircraft for civilian certification requirements.
Engineering Innovation
The 520's twin Lycoming GO-435-C2 geared radial engines represented a significant technological advancement for light aircraft. Each engine produced 260 horsepower, with the combined 520 horsepower inspiring the model designation. The geared design allowed the engines to operate at optimal RPM while driving two-blade Hartzell propellers at efficient speeds. This configuration enabled the aircraft to achieve a maximum speed of 211 mph and a service ceiling of 24,400 feet—performance previously reserved for much larger aircraft.
The 520 featured several pioneering design elements, including retractable tricycle landing gear, baglike wing fuel cells holding 150 gallons, and an all-metal construction that replaced the wood-and-fabric materials common in contemporary light twins. The aircraft's gross weight of 5,400 pounds included an empty weight of 3,800 pounds, providing substantial payload capacity for business operations.
Production and Market Entry
Manufacturing began in August 1951 at a leased 26,000-square-foot facility in Bethany, near Oklahoma City. The first production aircraft was delivered on February 5, 1952, to Asahi Shimbun Press Company in Tokyo, which also served as an international demonstrator. During one notable demonstration flight over Washington, D.C., the pilot shut down one engine and feathered the propeller to showcase the aircraft's single-engine capabilities to potential customers.
Production continued until 1954, with exactly 150 units manufactured. The relatively short production run reflected both the specialized nature of the business aviation market and the company's transition to improved variants.
Military Evaluation
Although designed for civilian use, the 520 attracted military attention during the early Cold War period. The U.S. Army evaluated three aircraft designated YL-26 (later redesignated U-9A in 1962). The U.S. Air Force conducted more extensive testing with one Model 520 as the YL-26A, though this aircraft was lost in a 1955 crash.
The military services ultimately selected the improved Model 560A for limited procurement, with 14 aircraft designated L-26B (later U-4A). Two of these aircraft served notable roles as presidential transports, shuttling President Dwight Eisenhower between Washington and his Gettysburg, Pennsylvania farm. One additional aircraft was transferred to the Army as a U-9B.
The Manufacturer's Evolution
Aero Design and Engineering Company underwent significant corporate changes during the 1950s. Originally a subsidiary of Rockwell-Standard Corporation, the company was renamed Aero Commander in 1950. Rockwell-Standard became Rockwell International in 1965, continuing to develop the Commander series through various iterations including turboprop variants reaching the 695B model.
In later years, Gulfstream Aerospace acquired the Commander line, with production of the family finally ending in 1986 after more than three decades. Today, Twin Commander Aircraft LLC holds the type certificate and continues supporting the existing fleet with parts and service.
Performance Legacy
The Commander 520 established performance benchmarks that influenced business aviation for decades. Its 196-mph cruise speed at 10,000 feet and 60 percent power represented a 40-50 percent improvement over contemporary light twins. The aircraft's 850 to 1,000-mile range enabled non-stop flights between major business centers, while its ability to operate from shorter runways provided access to smaller airports closer to final destinations.
Pilots praised the 520's stability and handling characteristics, particularly its predictable behavior in single-engine operations. The tricycle landing gear simplified ground handling and reduced insurance costs compared to conventional-gear competitors.
Current Status
While exact numbers of airworthy examples remain unknown, the Commander 520 established the foundation for one of general aviation's most successful aircraft families. The March Field Air Museum in California displays a preserved U-9A, representing the type's military service. The aircraft's influence extends far beyond its 150-unit production run, having demonstrated the viability of the business aviation market and inspiring competitors to develop similar high-performance light twins that continue serving corporate operators worldwide.