Mid-1930s Czechoslovakia saw a push to modernise its air force, prompting Avia to develop a next-generation monoplane fighter to replace the biplane B-534.
The result was the Avia B.35, a transitional design combining modern and conservative elements
Steel tube fuselage with metal skin forward and fabric aft.
Wooden elliptical wings and a fixed, spatted undercarriage.
Powered by a Hispano-Suiza 12Ycrs V-12 engine (860 hp), due to the unavailability of a 1000 hp unit.
Evolution Towards the B.135
Despite its outdated features, the B.35 proved highly manoeuvrable in testing.
Avia refined the design into the B.35/3 prototype, introducing
Retractable landing gear.
All-metal wings, replacing the wooden structure.
Improved aerodynamics and pilot visibility.
Birth of the B.135
The B.35/3 became the basis for the Avia B.135, finalised in 1938.
Key design features
Cantilever low-wing monoplane.
Enclosed cockpit with raised fuselage spine.
Armament
1× 20 mm MG FF cannon (hub-mounted) and 2× 7.92 mm vz. 30 machine guns (wing-mounted).
Retained the Hispano-Suiza engine and fixed-pitch wooden propeller.
Bulgarian Interest and Production
Bulgarian Air Force officers visiting Avia were impressed by the B.135/1 prototype.
A contract was signed for
12 aircraft were built in Czechoslovakia.
62 engines and a licence for 50 additional airframes to be built by DAR
(as the DAR 11 “Lyastovitsa”).
However, DAR lacked the capability to produce the aircraft, and only the original 12 were completed.
The RLM (German Aviation Ministry) halted further production and engine deliveries after 35 units, steering Bulgaria towards the Messerschmitt Bf 109.
Operational Use and Legacy
The B.135s suffered engine reliability issues, relegating them mostly to training roles.
On 30 March 1944, four B.135s intercepted USAAF bombers over Bulgaria.
One B-24 Liberator may have been downed in this rare combat engagement.
Ultimately, the B.135 remained a footnote in aviation history, a capable design overshadowed by geopolitical constraints and technical limitations.
