The engineers of the concorde, one of the first supersonic airliners, pushed the
envelope in many ways. they designed innovative air intakes and engines that would
provide power and acceleration at both high and low speeds. supersonic flight generates
tremendous heat, so the engineers created special layered windshield glass and durable,
heat-dissipating white paint. to allow the pilots to see the runway without affecting the
concorde's needle shape, engineers gave the plane its characteristic "droop nose."
pilots lowered the hinged nose cone to improve visibility during takeoff and landings,
then raised it again to maximize aerodynamics during flight.
what does this author mean by the term pushed the envelope?