Complex sentence: Neither Concorde nor the Tu-144 are limited in their maximum speed by the airframe drag, nor by the engines thrust, they are limited by the airframe heating and structural integrity of their similar aluminium alloys.
Split into simpler sentences: Neither Concorde nor the Tu-144 are limited in their maximum speed by the airframe drag, nor by the engines' thrust. They are limited by the airframe heating and structural integrity of their similar aluminium alloys.