Space technology behind Party flag in Tian'anmen Square flypast

BEIJING, July 2 (Xinhua) -- An aerial display echelon passed over Tian'anmen Square on Thursday, flying the flag of the Communist Party of China (CPC), as part of a grand ceremony to celebrate CPC's centenary.

The Party flag hanging beneath a military helicopter was made with space technologies by the China Academy of Space Technology (CAST), which is the main development institution of the Shenzhou spacecraft and the core module of the country's space station, Science and Technology Daily reported Friday.

To ensure that the flag flew smoothly, the CAST researchers made use of spacecraft aerodynamic deceleration technology and their experience in developing spacecraft parachutes.

The flag, measuring 9 meters long and 6 meters wide, was transported over the square at a flight speed of between 160 km and 180 km per hour. At such speeds, the aerodynamic impact would cause the tail of an ordinary flag to shake violently, resulting in partial damage along its edge, and eventually the whole flag would be torn apart.

To tackle this issue, the researchers chose a special material used for spacecraft parachutes. The material's fibers are only one third of the thickness of ordinary human hair, but it is 17 percent stronger than that used for the Shenzhou spaceship parachute, while being 15 percent lighter.

They also employed special coating technologies in the material to make the flag rainproof while ensuring the pattern was clearly visible. Any rain drops falling on the flag would slip off quickly.

However, it was not sufficient to rely entirely on the strength of this special material. The airflow might still damage the fabric at high speeds, and the tail of the flag might become deformed rather than lying flat.

After conducting several simulations and analyzing test data, the researchers added a pair of stabilizing "wind pockets" at the top and bottom edges of the flag's tail area. In flight, the wind filled these pockets, thereby increasing the aerodynamic stability of the flag and allowing it to unfurl perfectly over Tian'anmen Square without sustaining any damage.