The Blackburn B-9, also known as the HST10 (HST for High Speed Transport) followed on from the Blackburn Seagrave (described separately), with its Duncanson Monospar wing. It was a twin-engines commercial monoplane built by the Blackburn Aircraft Company on the banks of the Humber at Brough, East Yorkshire.
In many ways, the concept of the B-9 (B9 was its test designation) anticipated the post-war De Havilland DH104 Dove executive and communications aircraft built in the mid 1940s.
The B-9 was an all-metal, twin engine, twelve seat aircraft with a retractable undercarriage whilst power was provided by two 365 hp Napier Rapier engines.
A military version was drawn up, following a request from the Air Ministry, but this was not built.
Construction of a civil prototype was commenced as a private venture in late 1934 and the type was intended from the outset to be a high cruising speed. To modern eyes it might have been seen as a somewhat high-risk project.
This view is justified when the design failed to gain Government support despite the Duncanson wing design, high-lift flaps, two entirely new engines and being the first Blackburn to include a hydraulically-operated retractable undercarriage.
The completed HST10 B-9 ready for tacy trials in July 1936.
The wing was of all-metal construction with fabric covering whilst the fuselage was of semi-monocoque construction with an Alclad skin.
Cabin accommodation was provided for twelve passengers and provision made for heating and ventilation even a toilet at the rear of the cabin. Two pilots were seated side-by-side in the nose.
The one-piece wing was mounted below the fuselage and featured a large wing root fillet to minimise drag.
Military orders for the Baffin and Shark delayed work on the HST10 and the project suffered even further following the tragic death of Mr Duncanson in a car accident. Nevertheless was completed structurally and inspected and signed off ready for taxying trials, by 7th July 1936.
The Blackburn HST10 B-9 was completed in 1936, but not flown due to the pressure of other work.
In the event, the HST10 remained unflown due to Blackburn directing their resources to meet the ever increasing demands of Shark and Skua production.
The HST10 remained in the flight hangar until it was donated in early 1939 to Loughborough College of Technology (Aeronautical Department) for use as an instructional airframe. It was finally dismantled in 1946.