Why did the Royal Aircraft Establishment ask Airspeed to fit flaps and air brakes to its Courier?

The Courier combined a low cantilever wing, a retractable undercarriage and a fuselage of very carefully drawn lines for its day. That cleanness, which gave it speed, had a drawback noted by the Enciclopedia ilustrada de la aviación: once in the air, it was very difficult to get back onto the ground. Because of that same advanced aerodynamics, two Couriers ended up as research aircraft: one for the Royal Aircraft Establishment (RAE), the British aeronautical test centre, and another for Napier, which used it to develop its Rapier engine.

Airspeed modified the RAE aircraft with high-lift devices, drag-producing elements and modified controls, for test purposes. According to the same encyclopedia, the work was done in 1935 and consisted of Handley Page slotted flaps on the trailing edge of the outer wing sections, air brakes in the centre section next to the fuselage, and drooping ailerons. Used judiciously, they served to increase the aircraft's lift or its drag, precisely what an aeroplane that was hard to slow down was lacking.

The Spanish-language encyclopedia attributes the order to the Royal Air Force, which had acquired a five- or six-seat AS.5A in February 1934 as a communications aircraft and returned it to Airspeed in 1935 for the modification. English-language works place the modified Courier with the RAE. The two acronyms designate different institutions: the RAF is the air force and the RAE the research establishment. The RAE's link with the type went back further: George Stainforth, an RAE pilot, had made the prototype's first flight in April 1933.