This effort has included attempts to modify for unmanned flight the MiG-21 (ph) and with greater success an aircraft called the L-29 (ph).
这些无人飞行器中包括改进的无人飞行器米格-21和称之为L-29的飞机。
2
Pomerranz, Kenneth L. "The Making of a Hinterland: State, Society and Economy in Inland North China, 1900-1937", Ph. D. Dissertation, Yale University, 1988.