U.S. developing SR-72 hypersonic aircraft

Lockheed Martin is working on a successor to the U.S. Air ForceÕs long-retired SR-71 spy plane. Dubbed Òson of BlackbirdÓ, the SR-72 would be capable of reaching Mach 6, or six times the speed of sound

Lockheed Martin SR-72 Construction of scaled demonstrator vehicle with single engine could begin as early as 2018

COMBINED CYCLE PROPULSION: Merges turbojet and ramjet engines

Turbojet: Provides thrust up to and beyond Mach 3, when ramjet takes over

Common inlet feeds air to both engines, reducing drag

Common exhaust nozzle

Dual-mode ramjet: Air and fuel are fed into combustion chamber and ignited, accelerating vehicle to Mach 6

Splitter rotates to direct airflow to required engine

AIRFLOW

Lockheed SR-71 Blackbird

Role Strategic reconnaissance

Crew Two (pilot and systems operator)

Propulsion Turbojet (x2)

Maximum speed Mach 3.3 (4,075km/h)

History First flight 1964 Retired 1999

LOCKHEED MARTIN SR-72

Strike and reconnaissance

Optionally manned

Combined cycle (x2)

Mach 6 (7,400km/h)

Test flight 2023 Operational 2030 (projected)

Sources: Aviation Week, Lockheed Martin