Avia BH-21

Single-Seat, Single-Engine Biplane Fighter

Czechoslovakia | 1925

"The Avia BH-21, and interwar fighting biplane, originated out of Czechoslovakia and was produced to the tune of 184 examples."

Authored By: Staff Writer | Last Edited: 09/15/2021 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site; No A.I. was used in the generation of this content.

Despite a history of aircraft design dating back to 1920, the Avia concern of Czechoslovakia did not produce a fighter aircraft in notable quantity until the arrival of the "BH-21" biplane fighter. Preceding this design was a collection of monoplanes and biplanes covering both civilian and military market types, all beginning with the "BH-1" racer of 1920 (one being built). The well-regarded BH-21 was produced in 184 total units and ended up serving both the Czechoslovak Air Force and Began Air Force for its time.

Designed in 1922 to an official Czechoslovak Defense Department requirement calling for an all-modern fighter solution, the BH-21 was a further evolution of the earlier BH-17 design (indeed, the latter served as the former's prototype) - a single-seat, single-engine biplane fighter appearing in 1924 and manufactured in 24 examples. It owed much to the BH-6 and BH-8 before it and showcased excellent speed - doomed only by unreliability which served to end its operational life with the Czechoslovak Air Force.

The BH-17 was subsequently redesigned in 1924 to become the BH-21 and the new model retained the original's Hispano-Suiza HS 8Fb water-cooled engine of 300 horsepower, the powerplant built locally through the Skoda Works. Key alterations of the base design included a simplification of the interplane support structure (gone was the cumbersome pyramidal support ahead of the pilot) and relocation of the all-important radiator from its placement at the undercarriage to installation along the ventral fuselage line.

The resulting design sported the typical over-under biplane wing assembly though the upper member was set a short distance ahead of the lower. Both were straight in their general form with the complete unit seated ahead of the cockpit and midships. The engine took up its usual place at the nose and drove a two-bladed propeller assembly. The open cockpit was set at midships with a windscreen forward and headrest aft - offering relatively excellent vision out-of-the-cockpit. Slab sides were used across the fuselage and the tail unit was capped by a single, small-area rounded rudder fin with low-set horizontal planes. The undercarriage involved a fixed, wheeled main leg assembly under the forward center mass of the aircraft with the tail support by a simple tail skid.

Having beaten out designs from competitors Aero and Letov, the Avia BH-21 was ready for its first-flight in January of 1925 and trials were undertaken as soon as February of that year. Authorities liked what they saw and contracted for 139 of the fighters to serve the Czechoslovak Air Force. After this endorsement, the Belgian Air Force trialed the design in June and this resulted in 45 additional aircraft being ordered: 39 of this lot were produced locally in Belgium by SABCA (Societe Anonyme Belge de Constructions Aeronatiques) with a further 5 coming from SEGA (Societe d'Etudes General d'Aviation) and a single example being provided by Avia itself).

As military fighters, the biplanes were modestly armed through 2 x 7.7mm Vickers Machine Guns in fixed, forward-firing mountings over the nose, these synchronized to fire through the spinning propeller blades. The Czechoslovak Air Force retained their BH-21 stock of fighters into 1933, falling years shy of participation in World War 2 (1939-1945).

BH-21 designated the definitive operational form of the series while "BH-21J" was a "one-off" specimen powered by the British Bristol "Jupiter" air-cooled radial piston engine (this work then led to the "BH-33" fighter offshoot). The "BH-21R" was a modified racing form with clipped wingtips, proving itself a speedster in several national air races of 1925 (this variant included a "boosted" HS 8Fb engine rated at 400 horsepower).

As built, the Avia biplane had a length of 22.5 feet, a wingspan of 29.1 feet, and a height of 9 feet. Empty weight was 1,690lb with a Maximum Take-Off Weight (MTOW) of 2,370lb. The fighter reached maximum speeds of 160 miles-per-hour and ranged out to 385 miles, reaching an altitude of 23,000 feet in 35 minutes.

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Power & Performance
Those special qualities that separate one aircraft design from another. Performance specifications presented assume optimal operating conditions for the Avia BH-21 Single-Seat, Single-Engine Biplane Fighter.

1 x Hispano-Suiza 8Fb V-8 liquid-cooled inline piston engine developing 300 horsepower driving two-bladed propeller at the nose.
Propulsion

155 mph
250 kph | 135 kts
Max Speed

118 mph
190 kph | 103 kts
Cruise Speed

26,001 ft
7,925 m | 5 miles
Service Ceiling

388 miles
625 km | 337 nm
Operational Range

655 ft/min
200 m/min
Rate-of-Climb

City-to-City Ranges
Operational range when compared to distances between major cities (in KM).

NYC

LON

PAR

BER

MOS

TOK

SYD

LAX

NYC

Structure
The nose-to-tail, wingtip-to-wingtip physical qualities of the Avia BH-21 Single-Seat, Single-Engine Biplane Fighter.

1
(MANNED)
Crew

22.5 ft
6.87 m
O/A Length

29.2 ft
(8.90 m)
O/A Width

9.0 ft
(2.75 m)
O/A Height

1,687 lb
(765 kg)
Empty Weight

2,370 lb
(1,075 kg)
MTOW

Design Balance
The three qualities reflected below are altitude, speed, and range. The more full the box, the more balanced the design.

RANGE

ALT

SPEED

Armament
Available supported armament and special-mission equipment featured in the design of the Avia BH-21 Single-Seat, Single-Engine Biplane Fighter .

2 x 7.7mm Vickers Machine Guns (fixed, forward-firing) mounted over the nose and synchronized to fire through the spinning propeller blades.

Variants
Notable series variants as part of the Avia BH-21 family line.

BH-21 - Base Series Designation; definitive series production mark; 139 produced for Czechoslovak Air Force; 39 produced for Belgian Air Force.

BH-21J - Single example unit fitted with Bristol "Jupiter" air-cooled radial piston engine; forerunner to BH-33 biplane.

BH-21R - Modified racing aeroplane with clipped wing mainplanes.

Operators
Global customers who have evaluated and/or operated the Avia BH-21. Nations are displayed by flag, each linked to their respective national aircraft listing.

Total Production: 184 Units
Contractor(s): Avia Motors - Czechoslovakia

[ Czechoslovakia; Belgium ]

Relative Max Speed

Hi: 200mph

Lo: 100mph

Aircraft Max Listed Speed (155mph).

Graph Average of 150 MPH.

Era Crossover

Showcasing Aircraft Era Crossover (if any)

Max Alt Visualization

Production Comparison

184

36183

44000

Entry compared against Ilyushin IL-2 (military) and Cessna 172 (civilian) total production.

MACH Regime (Sonic)

Sub

Trans

Super

Hyper

HiHyper

ReEntry

♦

Aviation Timeline

EarlyYrs

WWI

Interwar

WWII

ColdWar

Postwar

Modern

Future

♦

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Image from the Public Domain.

Mission Roles
Some designs are single-minded in their approach while others offer a more versatile solution to airborne requirements.

AIR-TO-AIR COMBAT

Recognition
Some designs stand the test of time while others are doomed to never advance beyond the drawing board; let history be their judge.

Military lapel ribbon for the Golden Age of Flight

Going Further...
The Avia BH-21 Single-Seat, Single-Engine Biplane Fighter appears in the following collections:

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