The tandem landing gear configuration is a distinctive design, involving a single support structure with wheel assemblies arranged in tandem. Rarely used, this layout has appeared in select early 20th-century aircraft and modern military designs, showcasing its unique engineering challenges and advantages in stowed packaging size and whilst accommodating improved ground load distribution.
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Exploring the Rare Single-Tandem Landing Gear Configuration: A Historical and Modern Perspective
The tandem landing gear configuration is a rare and fascinating design used in aviation, characterized by its unique layout. In this configuration a single structural supporting a bogie beam with two mounted wheel assemblies arranged one in front of the other, with each on its own axle. More completely, this would be named a single-tandem – a single wheel assembly for two axles arranged in a tandem configuration. This configuration is easily confused with the with dual-tandem Landing Gear (with a total of 4 wheels), or multiple independent landing gears in tandem as on the C-130. This single-tandem arrangement has been implemented sparingly, with notable examples emerging during the early 20th century and resurfacing in some modern aircraft.
Early Examples of Tandem Landing Gear
The first known application of single-tandem landing gear was on the Short Bomber, produced between 1915 and 1917, with a total of 83 units constructed. In this aircraft, the left and right wheel pairs were connected to a common frame fixed to the airframe, and bearing some similarity to a four-wheeled cart under the airframe. This early arrangement set the stage for further innovations.
A much more advanced example came with the Junkers G.38 passenger transport, also built under license in Japan as the Ki-20 bomber. At the time, it was the largest production aircraft globally, boasting a maximum takeoff weight (MTOW) of 21,250 kilograms. The tandem gear, which remained extended in flight, had reduced frontal area benefiting the aircraft’s aerodynamic efficiency. Some variants even incorporated aerodynamic fairings. Vertical loads were supported by a spring/damper mechanism connected to the wing, while lateral and longitudinal stability was managed by a lateral strut to the fuselage.
The Gap in Usage During the War Years
Interestingly, there were no recorded examples of tandem landing gear from the wartime era. However, the design re-emerged during the jet age with notable examples like the pre-production Canadian Avro Arrow (CF-105), which first flew in 1958, the British TSR-2, which debuted in 1964, and the highly successful Saab 37 Viggen. Each design had MTOWs of 31,500, 46,900, and 19,274 kilograms.
Both the Arrow and Viggen incorporated wing-mounted landing gear systems with thin tires (7.7inchs and 6.6inchs respectively). These retractable systems were carefully engineered to integrate seamlessly within the thin delta wings of the aircraft.
The TSR-2, a much heavier aircraft, faced unique challenges with its tandem gear. The design utilized fuselage-mounted landing gear that retracted forward into the fuselage bay alongside the engines. This configuration required a considerable more complex mechanism to function effectively and it’s development was problematic.
Modern Applications and Notable Designs
The tandem landing gear configuration continued to find niche applications in modern military aircraft. The fourth-generation MiG-31, which first flew in 1975, implemented this design with an MTOW of 46,200 kilograms. Like the TSR-2, its landing gear was fuselage-mounted and retracted forward. However, its design differed by placing the wheels out of plane with each other, enabling improved rough-field operations. The MiG-31 remains in active service today, particularly in the Russia-Ukraine conflict.
The Sukhoi Su-34 fighter/bomber, with a MTOW of 45’000kg, also employ a single-tandem landing gear. This aircraft was developed from the earlier Su-27 which (MTOW of 33’000kg) employs a single wheeled landing gear. It’s notable that the Su-34’s tires are exceptionally wide, measuring 400 millimetres (~16in), to accommodate rough-field performance.
The Chinese J-36 Fighter
One of the latest aircraft to use this configuration is the Chinese Chengdu J-36, a presumed three-engine 6th generation fighter designed for advanced military operations. At the time of writing this article little information is available about this aircraft, its landing gear arrangement likely reflects the need to maximize the weapon bay space by minimising the landing gear stowage bay.
Historical Curiosities
Three notable examples of tandem landing gear include the Kalinin K-7 from 1933, the Vickers Valiant bomber from 1951, and the C-130 Hercules (1954). The Kalinin, however, is more accurately described as having a fixed quadricycle gear arrangement. The Valiant and the still in-service C-130 Hercules both feature two single-wheeled landing gear structures in a tandem configuration, highlighting the diversity of landing gear innovations throughout aviation history.
Conclusion
The single-tandem landing gear configuration, though rare, has left a unique mark on aviation history. From early experimental designs to modern military applications, it remains a testament to the ingenuity of aircraft engineers. As aircraft continue to evolve, it will be interesting to see when this configuration will next be adopted.
