Tupolev Tu-155 / Tu-156
The Soviet Union flight tested a modified Tu-154, designated Tu-155, incorporating engines fueled by liquid hydrogen and natural gas. The Tu-155 first flew 1988. The Tu-155’s NK-88 engines were developed by Nikolai Kuznetsov’s design engineering team. The engines and other new systems and components have been tested on specially designed rigs, with particular attention being given to fire and explosion protection.
The airframe iyself is the work of the Andrei Tupolev experimental design office in conjunction with the aeronautical industry’s Institute of Science. The cryogenic fuel tanks, which necessitated development of over 30 new systems, are installed at the rear of the passenger cabin.
Photos show two external ducts, located immediately above and below the cabin windows.