It was on this day in aviation history that a heavily modified de Havilland Canada DHC-5 Buffalo took off on its first flight as de Havilland C-8A Buffalo, the Augmentor Wing Jet STOL Research Aircraft, NASA -716.
In 1965 the research program had started and it culminated in the need for proof of concept aircraft. After an extensive period of wind-tunnel tests with models, it was time to put the theory to practice! The aircraft was the worlds first jet transport demonstrator for STOL capability.
de Havilland C-8A Buffalo, the Augmentor Wing Jet STOL Research Aircraft, NASA -716 (from public domain)
The de Havilland Canada DHC-5 Buffalo was extensively modified to investigate the realm of Short Take-Off and Landing in a research program from NASA in collaboration with the Canadian government.
The modifications were carried out by Boeing, de Havilland Canada and Rolls-Royce Canada. The main (and most visible modifications were;
Reduced wingspan to simulate wing loading similar to possible future aircraft.
Leading-edge slats were fitted over the full wingspan
Double surface flaps with a venturi shape
Rolls Royce 801 SF (Split Flow) bypass engines replaced the standard turboprops.
The Split Flow engine was a bypass engine with a special bypass duct in which separated the hot (core engine) airflow and the cold (bypass air).
The hot (core engine) flow was channelled through Pegasus-engine swivelling nozzles (like on the BAe Sea Harrier). This assured an engine exhaust flown directed in the same direction as the flap downwash.
The cold (bypass air) was channelled into a flap venturi which resulted in extra airflow over the flaps. Augmented flaps (source public domain)
In this design, ejecting fan air between the upper and lower segments of the augmentor flaps enhanced lift. The fan flow was cross-ducted from each engine to the augmentor flaps so that the system would provide a balanced lift with one engine inoperative. The engines' jet exhaust could be vectored from 6 degrees to 104 degrees below the horizontal. The tests with this aircraft started on this day in 1972 and the flight were a joint operation of the NASA Ames Research Center and the Canadian Department of Industry, Trade and Commerce.
NASA-716 during one of the test flights, note the downward flow of the smoke plume from the engines (source public domain)
The test results were impressive;
nominal approach speeds 60 knots
lowest demonstrated approach speed 50 knots
Take off and landing distance of fewer than 1000 feet over a 50-foot high obstacle were achieved
Ground rolls as short as 350 feet were achieved
The test programme came to an end in the fall of 1981. Editorial note; Different dates are mentioned in different sources for this first flight.