This feature was first displayed in model form at the Zhuhai Airshows several years ago. Since then, these initial concepts have progressed to the point that actual flying prototypes are now available.
Traditionally, aircraft with very long endurance, including HALE UAVs, had to rely on very long and straight wings. This can be clearly seen in U-2 aircraft during the sixties and more recently in the Global Hawk UAV.
Such as wing configuration gives them the ability to loiter for an extended period thanks to the lift provided by the large wing area without expending a lot of fuel. This is somewhat similar to glider aircraft.
One drawback is that a long wingspan makes the wings very rigid and drag and reduces the maneuverability of the aircraft. High G forces would cause too much stress and the wings would simply break apart.
One alternative approach to solve this problem is known as the box wing or diamond wing concept, which can reduce wingspan and drag, but without sacrificing the advantages offered by longer wings, including extended endurance.
The box / diamond wing configuration basically consist of two wings, a swept and forward-swept wing, combined into a single joined-wing. The forward wing has a longer span than the rear wing and situated lower with a structural cross-link.
The result is a aircraft with reduced weight and a higher aspect ratio that doesn't need such a long wingspan. At the same, the aircraft is more maneuverable due to the shorter wings.
The box / diamond wing also allows better handling abilities, both in the air and on the ground because very long wings makes aircraft difficult to handle on the airfield and to store in most hangars.
The Soar / Soaring Dragon was one of the earliest models displayed by China featuring the box/ diamond wing. Specifications included:
- Length 14.3 m
- Wingspan 25 m
- Height 5.4 m
- Normal takeoff weight 7500 kg
- Mission Payload 650 kg
- Cruising altitude 18000 m
- Cruising speed 750 km/hr
- Range 7000 km
The original Xianglong concept has evolved into a family of box / diamond wing UAVs, with smaller and larger prototypes in the testing stage utilizing different configurations such as the vertical stabilizer.
Credit original poster, via Chinese Internet