The Henderson-Glenny H.S.F.II Gadfly was a British single-seat low-wing monoplane designed by K.N. Pearson and built by Glenny and Henderson Limited at Byfleet, Surrey, England in 1929.
The Gadfly was a low-wing monoplane with a fixed conventional landing gear and an open single seat cockpit. The first aircraft, powered by a 350NaN0 ABC Scorpion II engine, first flew at Brooklands in April 1929. It was designated the Gadfly I and was registered G-AAEY. It was fitted with Pearson rotary ailerons and re-designated Gadfly II when it achieved a world altitude record of 30210NaN0 in the 200 kg class on 16 May 1929 piloted by G.L.P. Henderson.
The second aircraft was a Gadfly II G-AARJ which first flew in August 1929 and was exported to Canada, where it was damaged beyond repair at Kitchener, Ontario, on 25 August 1931. The final aircraft was Gadfly III G-AARK which was the same as the Gadfly II but fitted with a 400NaN0 Salmson A.D.9 radial engine. It was withdrawn from use in 1930. The first aircraft G-AAEY was last based at Wolverhampton when it was scrapped in June 1934.