Jumbo Sized Landing Gears

The 12-Wheeled Supersized Landing Gear

Westly Davidson – Skynetics
V0.1 – Dec 2024

The 12-wheel landing gear configuration (quad-triple) is a fascinating engineering innovation of the mid-1960’s in the Soviet Union. It was designed to meet the unique challenges posed by specific aircraft and found on the first version of the Tu-144 Soviet supersonic passenger jet and the a rare version of the Tu-142 maritime patrol aircraft. The arrangement demonstrates how technical ingenuity is applied to overcome structural, operational, and environmental constraints.

The Tu-144: Supersonic Aviation 1968

The Tu-144, developed in the late 1960s, required a landing gear design capable of supporting its substantial weight while integrating into its thin delta-wing profile. This aircraft, often referred to as the “Soviet Concorde,” presented several challenges due to its early supersonic design and unconventional structural layout. Initially (the prototype 68001) had a quad-triple axle landing gear configuration featuring 12 tyres per assembly. This approach was essential for several reasons:

1. Weight Distribution: The Tu-144’s heavy airframe (~180’000kg) required the load to be evenly spread over a larger footprint, particularly to preserve the integrity of runways of the era. Runways often faced significant wear due to heavy aircraft loads, and the 12-wheel setup helped minimise damage.
2. Space Constraints: Unlike many modern aircraft, where wing mounted landing gear retract into the main fuselage, the Tu-144’s design left little room for this due to engine placement and its thin delta wings. In the prototype, engines were mounted closely together, leaving minimal space for gear retraction. On retraction the 12-wheeled bogie rotated front upwards into near alignment with the main structure. The complete assembly pivoted forward in the wing bays. In the final retracted position the 12-wheeled bogie was relatively parallel to the ground plane, but inverted in comparison to the ground (extended) position. Therefore, in the retracted position the complete assembly had a very ‘flat’ profile allowing it to fit within the thin section of the wings.
3. Runway Compatibility: The reduced wheel diameter allowed the gear to fit within the limited space while distributing the aircraft’s significant weight across more contact points. This arrangement also helped maintain runway integrity when operating on less prepared surfaces.

While effective, this design was not without its compromises. As the Tu-144 was updated to include a modified engine design which changed the shape of the landing gear bay. The quad-triple gear was replaced by an quad-tandem axle arrangement (8-wheel). This new design had larger wheels spaced further apart, allowing for more stowage into the new bay between the engines that was tall but narrow. However, despite the reduced wheel count and larger wheels, the inboard and outboard wheel pairs are mounted with a substantial distance between them. While this would mitigate concerns regarding flotation and the runway sub-base layers, their seemed to be inadequate space to package the brake assemble within the wheel. Meaning that their seemed to be a design compromise between flotation, structural weight and packaging adequately sized brakes (remembering the brake technology available of the time). An interesting aside is that the TU144 is one of the few commercial aircraft to use a braking parachute.

Engineering Trade-Offs in Landing Gear Design

The evolution of the Tu-144’s landing gear highlights the critical trade-offs involved in such designs. Initially, the 12-wheel configuration was essential to manage the challenges of flotation and stowage. However a redesign of the engines and engine installation prompted a redesign of the landing gear. The quad-tandem axle configuration, though using fewer wheels, struck a balance between practicality and performance.

It’s also noteworth that the American SST, the Boeing 2707-300 design also proposed a 12-wheel landing gear.

The Tu-142: A Versatile Maritime Aircraft

Another example of the 12-wheel landing gear configuration can be found on a special version of the Tu-142, a long-range maritime patrol and anti-submarine aircraft derived from the Tu-95 bomber. Unlike the Tu-144, the Tu-142’s 12-wheel setup was developed for specific operational needs, particularly in extreme environments.

The Tu-142 variant equipped with quad-triple landing gear was reportedly designed for use in tundra conditions. This likely involved operations on semi-prepared or frozen runways, where weight distribution and surface adaptation are more critical. By spreading the load across 12 tyres per landing gear assembly, the aircraft could safely operate on softer or uneven surfaces without becoming stuck or damaging the runway. While detailed technical information about this variant is scarce, it is clear that the gear was tailored to meet the unique demands of its operating environment.

Advantages of the Quad-Triple Axle Configuration

The quad-triple arrangement, though uncommon, offers several advantages in specific scenarios:

1. Enhanced Load Distribution: By dividing the aircraft’s weight across multiple tyres, the design reduces the stress placed on individual tyres and the underlying surface. This is particularly useful for large, heavy aircraft operating on less robust or uneven runways.
2. Runway Preservation: The configuration spreads the load over a larger area, reducing the likelihood of runway wear or damage, a crucial factor for aircraft operating in remote or underdeveloped regions.
3. Redundancy and Safety: In the event of tyre failure, the presence of additional wheels provides a level of redundancy, ensuring the aircraft can safely land even with minor issues.

Challenges and Limitations

Despite its benefits, the 12-wheel configuration is not without challenges. The increased number of tyres and axles adds to the overall weight of the landing gear assembly, reducing payload capacity. Additionally, the complexity of retracting and stowing such a system can lead to higher maintenance demands and increased costs. These are additional factors likely contributed to its limited use, as seen in the redesign of the Tu-144 and the specific operational context of the Tu-142.

Broader Implications for Aircraft Design

The examples of the Tu-144 and Tu-142 underscore the importance of landing gear design in overall aircraft performance. Landing gear configurations must balance multiple factors, including weight distribution, structural constraints, and environmental adaptability. The quad-triple axle arrangement, while rare, represents a creative solution to unique engineering challenges.

Conclusion

The 12-wheel landing gear configuration stands as a testament to the ingenuity and adaptability of aerospace engineers. While its use has been limited to specialised aircraft like the Tu-144 and Tu-142, the design offers valuable lessons in managing weight, space, and operational demands. As aviation technology continues to evolve, these innovative solutions remind us of the challenges and triumphs of aircraft design in the pursuit of progress.