Two sleek Chinese stealth fighters streaked across the skies over Zhuhai on Nov. 1, marking the official debut of Beijing's brand new J-20 Mighty Dragon jet. One of the only fifth-generation stealth fighters ever built, the aircraft's unveiling is a symbol of the impressive progress China's air force has made over the past two decades. The stealth fighter's design, however, also contains several important weaknesses, a reminder of the limitations in military aviation China is still struggling to overcome....