The Avia BH-33 was a biplane fighter aircraft built in Czechoslovakia in 1927.
It was based on the BH-21J which demonstrated promising results by combining the original BH-21 airframe with a licence built Bristol Jupiter radial engine.
Other than the peculiar Avia hallmark of having an upper wing with a shorter span than the lower, it was utterly conventional, even featuring a tail fin for the first time in a Pavel Beneš and Miroslav Hajn design (previous aircraft had a rudder but no fin).
Initial tests of the first prototype were disappointing, displaying performance only marginally better than the BH-21, even when fitted with a more powerful version of the Jupiter.
Two further prototypes followed, both designated BH-33-1, each with an increasingly powerful Jupiter variant – one a Jupiter VI, the other a Jupiter VII.
The performance of the latter example was finally acceptable for the Czechoslovakian defence ministry to order a small production run of only five aircraft.
Three examples were sold to Belgium, where there were plans to build the type under licence, but this did not occur.
Licence production was undertaken, however, in Poland, where a single example was sold, along with a licence to build 50 aircraft.
These were designated PWS-A and put into service with the Polish Air Force in 1930.
Development continued with an almost total redesign of the fuselage, replacing the wooden, slab-sided structure with one of oval cross-section, built up from welded steel tubes.
Designated BH-33E, this was a world-class fighter for its time.
Nevertheless, the response from the Czechoslovakian military was not interested (although two were bought for the national aerobatics team), Avia again looked abroad for customers, this time selling 20 aircraft to the Kingdom of Yugoslavia, along with a licence to produce another 24.
Two or three examples were also bought by Soviet Union for evaluation.
In late 1929, a further development was flown as the BH-33L, featuring longer-span wings, and a Škoda L W-block engine.
This version finally brought the company the domestic sales that it had been hoping for, with 80 aircraft ordered by the Czechoslovak Air Force.
These became standard equipment with some air regiments up to the outbreak of World War II.
A single, final variant with a BMW built Pratt & Whitney Hornet engine was built as the BH-33H (later redesignation BH-133) in 1930, but this did not lead to production.
Two prototypes powered by Jupiter VI (second)
Jupiter VII (third) engines plus five serial built aircraft with Jupiter VII engine.
Yugoslav Version powered by IAM K9 engine, 22 built.
Version with longer-span wings, powered by a Škoda L engine, 80 built.
Version powered by Pratt & Whitney Hornet engine, one built.
Polish license built variant of the BH-33 with minor modifications,