Visitors look at helicopter models at the Second China Helicopter Exposition in Tianjin, north China, Sept 7, 2013. More than 300 exhibitors from over 30 countries and regions attended the four-day exposition, opened on Sept 5. (Xinhua/Wang Zhen)

Visitors look at helicopter models at the Second China Helicopter Exposition in Tianjin, north China, Sept 7, 2013. More than 300 exhibitors from over 30 countries and regions attended the four-day exposition, opened on Sept 5. (Xinhua/Wang Zhen)