Specific impulse I_sp = 1,000–1,800 s at Mach 3 (3–5× higher than solid rockets)
originator
René Lorin (1913 patent), Albert Fonó (1915/1928), I. A. Merkulov (1939/1940), René Leduc (1949 Leduc 0.10)
Core Principles & Analysis
Proposed by French inventor René Lorin in 1913 and Hungarian engineer Albert Fonó in 1915–1928, a ramjet eliminates all spinning compressor and turbine shafts, relying on the vehicle's forward supersonic motion and an inlet diffuser cone to ram-compress incoming air.
Because a ramjet produces zero static thrust at rest, it must be accelerated past ~Mach 0.5–1.0 by a rocket booster or carrier aircraft (or operate as a combined-cycle turboramjet, as in the Pratt & Whitney J58 engines of the Mach 3.2 Lockheed SR-71 Blackbird).
Above Mach 5–6, slowing airflow to subsonic speeds in a conventional ramjet diffuser generates excessive shock-heating and molecular dissociation losses, requiring a Supersonic-Combustion Ramjet (scramjet) in which fuel mixes and burns within a supersonic airstream in milliseconds.