Avia B-71

 

In May 1935 the First Czechoslovak Republic signed a non-aggression pact with the USSR, which included a mutual economic aid clause. That treaty also included that Czechoslovakia (one of the world's leading arms exporters at the time) granted license production rights for their 75mm Skoda C-5 mountain gun and 75mm Skoda R-3 anti-aircraft gun to the Soviets. In exchange, Czechoslovakia received a license to build the Tupolev SB.

In virtue of that agreement, a contract was signed between Technoexport (Soviet Union's external trade organization) and the Czechoslovak Ministry of National Defence on 15th April 1937. A total of 61 Tupolev SBs would be delivered straight from the USSR and Avia (subsidiary of Skoda) would build another 161 SBs at their Cakovice plant. The SB received the denomination of B-71 given by the Czechoslovenske Letectvo (CL - Czechoslovak Air Force) and was planned to serve both in the bomber and long-range reconnaissance roles.

The Soviet-supplied SBs were equipped with Czechoslovak-built engines, armament, radios and instruments. Those instruments were sent to Fili, Moscow, to be fitted to various airframes at GAZ 22 factory. It was estimated that the unit price for each of those SBs was set at $ 118.460 of the time, that's $ 2.519.362,55 adjusted for 2023 inflation. 

The Avia B-71 was powered by two Hispano-Suiza H.S.12 Ydrs engines, yielding 860 hp of power each and built under license by CKD-Praha. The original four 7,62mm ShKAS machine guns were replaced by three Czechoslovak 7,92mm ZB vz30 machine guns.

When compared to the SB 2M-100-A, it differed in various details. As we've just written, one vz30 machine gun was placed in the nose, instead of the origina two ShKAS. Two balance weights were added in the lower-right wing and the B-71s were equipped with radios, while the SB 2M-100As lacked any radio equipment. The B-71 had a retractable antenna fitted in the right rear fuselage. Those features were copied by the Soviets in the late-built SB 2M-100As. 

The first three Soviet-delivered machines were sent in March 1937. The first machine was assigned to the Vyzkummy a Skusební Letecky Ústav (VZLU - Research and Experimental Aviation Institute) at Prague-Letnany airport for trials on 17th April 1937. This first aircraft retained the cartridge case ejection tunnel present on every SB, but not in every subsequent B-71. The right nose step on these three initial aircraft, was mounted higher in production B-71s. The first three B-71 had front and back sights on the vz30 machine guns, however, those sights were not fitted in production aircraft.

The Soviet-built 61 B-71s were flown from Fili, Moscow to Kiev (Ukrainian SSR), where they were delivered to Czechoslovak pilots who flew the type from Kiev to Kocice (Czechoslovakia) via Romania. Once in Czechoslovak territory, the CL assigned the B-71 to their units. The first three were assigned to an operational squadron on 13th March 1938. Those B-71 intended for the bombardment role were assigned to the 5. Letecky Pluk (5.LP - Aviation Regiment) based at Brno-Turany airport and the 6.LP based at Prague. The B-71s intended for long-range reconnaissance were assigned to the 1.LP, at Prague and the 2.LP at Olomouc, Northern Moravia. 

The Germans invaded Czechoslovakia on 15th March 1939, so the B-71 was active with the CL for one year and two days, forming the Protectorate of Bohemia and Moravia. Avia had not begun license production of the B-71 yet, so every B-71 that fell into German hands was of Soviet production.

Sources:

1st Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

2nd https://en.wikipedia.org/wiki/Tupolev_SB

3rd https://massimotessitori.altervista.org/sovietwarplanes/pages/sb/tapani/b-71/czech%2Bslovak/czech%2Bslovak.htm

Avia B-71 in use with Germany

 

When occupied Czechoslovakia on 15th March 1939, they seized a total of 59 serviceable B-71, all of them from Soviet production, stationed on various Czech airfields. 

The Germans hastily applied their markings on the bombers, disarmed them and deleted a circular window on both sides of the rear fuselage. Most B-71s were flown to Merseburg (Saxony-Anhalt), to be put in storage. During these flights, some Czechoslovak pilots assisted German ones carrying out ferry flights. Bohuslav Sikmund and Josef Navesnik were part of one of those flights. They flew from Hradec Králové but, instead of following the course to Merseburg, they defected to the USSR on 26th April 1939. 

One B-71 was sent to Rechlin Test Centre in April, where it was employed for various engine flight tests until June. 

As we've already covered in this post thirty-two B-71s were sold to Bulgaria in September 1939, for which they received civilian German codes in order to ferry them to Sofia. The Slovak Air Arm also received three B-71, as we already saw here.

Avia had already many plans for the B-71 in March 1939, however, the Germans found the B-71 ideal for the target-tug role, so they ordered 76 Avia B-71A (a target-tug variant) to Avia and Aero. 

A total of 41 B-71As were completed at Avia's factory in Cakovice, close to Prague, with the first machine taking off on 21st July 1939. In September that first machine was assigned to Erprobungstelle (Test Centre) at Tamewitz. The last Avia-built B-71A rolled out from the factory on 27th August 1940. 

Aero manufactured a total of 35 B-71As, however, it wasn't until 22nd May 1940 when the first Aero-built B-71A left the assembly line at Prague-Vysocany. It was assigned to Luftdienst Kommando 1/7 (1/7 Air Service Command) at Lechfeld airfield, in Bavaria. 

The B-71A differed in many ways from the Soviet-built B-71. They lacked armament and the central section of the nose glazing was covered by a metal sheet. The V-shaped step below the emergency roof hatch on starboard was also removed. It was also equipped with a fixed radio antenna placed on top of the fuselage and aft of the cockpit, replacing this way the retractable one on the lower part of the fuselage. A rear-view mirror was also installed on top of the canopy frame. As we've said, most of the B-71s had their rear circular small windows deleted and the B-71A was not an exception. On the left, a crew entry step was placed, just aft of the rear wing.
Both lower gun position and bomb bay were replaced with the target-towing equipment, which consisted of a winch, a drum with the 2,5 mm diameter cable and a 3 m  (9ft 10 in) long canvas target sleeve. The winch varied in length, ranging from 6 m (19 ft 8 in) to 9 m (29 ft 6 in). This equipment shifted aircraft's centre of gravity, so, in order to compensate, 240 Kg (529 pounds) of ballast were added to the navigator's compartment in the nose. 

Both production runs received Luftwaffe's colours, markings and insignias and most of them were assigned to Luftdienst Kommando 6 (Air Service Commando 6). They were employed both for target towing and meteorological flights. Some were also flown by the Ausbildungsgruppe 104 (Training Group 104), Jagdfliegerschule 4 (Fighter Pilot Training Unit 4) and even by the secret bomber wing Kampfgeschwader 200. 

The B-71A was widely used by the Luftwaffe thanks to its well-built all-metal structure and good performance. By March 31st 1944 there were still 57 B-71A in service with the Luftwaffe. That number was, however, reduced to just nine by September 30 1944 due to shortage of spare parts.

The B-71B was an improved variant of the B-71A that came out in late 1940. The target-towing cable was lengthened to 1.000 m (3281 ft). The tow-cable operator's canopy was moved forward to allow the additional space needed for the improved target-towing device. This new device was 70 kg (154 pounds) heavier than that of the B-71A. The rear cockpit's canopy was also moved forward.

The B-71B differed in many ways from its predecessor. Two triangular-shaped windows aft of the nose-glazing were deleted and a t-shaped boom was added on top of the antenna mast. A step was installed on top the port wing's rear extension and a holding boom was also mounted behind the rear canopy. Bomb bay doors were welded and the nose compartment exit hatch was relocated aft. Some late production machines were fitted with a windshield in front of the rear-aft sliding canopy. Winch compartment was replaced forward and the two stabilization booms on the housing's rear were deleted. The oval rear fuselage windows were also removed. Three additional pylons were installed under each wing. 

A total of 35 B-71Bs were built by both Aero and Avia. Aero built ten at Prague-Vysocany, the first of which left the assembly line on 18th October 1940 and was assigned to Luftwaffe's main test and evaluation centre at Rechlin. The last Aero-built B-71B was accepted by the Luftwaffe on 26th November 1940. 
Avia's factory at Cakovice manufactured 25 B-71B to the Luftwaffe, with the last aircraft being completed on 30th April 1941. Between July 1939 and April 1941 a total of 111 Avia B-71A and B-71Bs were manufactured by Avia and Aero for the Luftwaffe.

Sources:

1st Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

2nd https://en.wikipedia.org/wiki/Tupolev_SB

3rd https://massimotessitori.altervista.org/sovietwarplanes/pages/sb/tapani/b-71/german/german.htm

Tupolev SB & Avia B-71 in service with Poland and Slovakia.

 

The Tupolev SB was a high-speed, twin-engined three-seat Soviet monoplane bomber which flew for the first time in 1934. It was also built under license in Czechoslovakia under the denomination of Avia B-71. It was mainly used by the USSR, but there were some foreign users as well, among them, the following ones:

• Poland: During World War 2 some Polish pilots in the USSR were trained with the Tupolev USB (the dual-control trainer variant). These pilots belonged to the 9th Group stationed at Buguruslan, in Chkalov oblast (nowadays Orenburg oblast). Just after the war, five USB trainers were delivered to the Aviation Officers School at Deblin, in the Lublin Voivodeship, to serve as trainers. In 1947 they were re-engined with M-105 engines. This change required a redesign of the exhaust collector system, while different propellers with more ogival spinners were also installed. Three of the five USB served with the Wojska Lotnicze (Polish Air Force)  at the Aviation Officers School until August 1949. This marked the longest use of the Tupolev USB outside the USSR, than any other country.
  
  
• Slovakia: When Germany invaded Czechoslovakia in March 1939, the state was split into the Protectorate of Bohemia and Moravia and the independent Slovak Republic. The Slovenské vzdusné zbrane ( SVZ - Slovak Air Force) had a total of 300 aircraft, among them three Avia B-71. 
  Just before the annexation, one B-71 had to perform a forced landing in the Slovakian part of Czechoslovakia, where it remained well after the split. Hungarian troops occupied the Carpatho-Ukraine region (Ruthenia) and looked to expand their borders in southern Slovakia. This soon led to various clashes which eventually escalated into the Slovak-Hungarian War of late March 1939 in the context of which, on 24th March ten Magyar Királyi Honvéd Legiero (MKHL - Royal Hungarian Air Force) Junkers Ju.86K-2 bombers attacked the airfield of Spisská Nová Ves, in the Kosicé region. This raid damaged one B-71 stationed there.
  The B-71 that force landed in Slovakia before the German occupation, was repaired during the spring of 1939 and received SVZ codes and the blue V3 registration. It was also fitted with German radio equipment, a direction finding loop antenna and an antenna mast mounted on the upper fuselage behind the cockpit. Two additional rack antennas were also fitted to the lower rear fuselage with the original retractable antenna being retained. Both balance weights were also removed from the lower right wing.
  On 18th April 1943 five Slovak airmen scaped to neutral Turkey in the blue V3 B-71. Sergeant Anton Vanko took off from Trencianske Biskupice airbase, close to the town of Trencin, in western Slovakia. Aboard the B-71 were Privates First Class J.Koman, J. Bzoch, L.Slezak and L.Pollak. The B-71 flew from Trencianske Biskupice to Kestanelik, in the Çanakkale province of Turkey, where they were interned for a brief period of time. The five Slovak airmen then travelled to England via North Africa, where they joined the various Czechoslovak Royal Air Force's (RAF) squadrons. Vanko became a Supermarine Spitfire pilot at the No. 312 (Czechoslovak) Squadron at RAF Bradwell Bay, in Essex. Unfortunately he was killed in a take off accident on 8th December 1944.

Sources:

1st Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

2nd https://en.wikipedia.org/wiki/Tupolev_SB
3rd https://massimotessitori.altervista.org/sovietwarplanes/pages/sb/tapani/b-71/czech%2Bslovak/czech%2Bslovak.htm

Avia B-71 in service with Bulgaria

 

The Avia B-71 was a license-built Czechoslovak variant of the Tupolev SB. This variant saw service with Bulgaria.

In September 1939 Bulgaria bought 32 B-71 from Germany. Those machines were originally built at the GAZ 22 factory, in Fili, Moscow oblast, and were delivered to the Ceskoslovenské letecvo (CL - Czechoslovak Air Force) in March 1939, just before the German Occupation.

The Germans handed the B-71s to the Vazdushni Voyski (VV - Royal Bulgarian Air Force) at Merseburg, Germany and were not operational until early 1940, when they were assigned to the 5. Bombardirovochen Polk (5.BP - 5th Bomber Regiment), based at Plovdiv. The B-71 received the nickname of "Zherav" (crane) from Bulgarian pilots.

The Bulgarian B-71s saw combat for the first time in late September and early October 1941 when Greeks in the Bulgarian-occupied region of Thrace revolted. Three B-71s took off from Plovdiv and bombed the Greek town of Drama, in north-western Macedonia. This turned to be the only combat mission of the 5.BP during the period that Bulgaria was allied with Germany.

On 5th September 1944 the USSR declared war on Bulgaria (which, until then, had remained neutral in the Axis war against the USSR) and the Soviet Army invaded three days later. During this period, the pro-Soviet Bulgarian faction called "Democratic Party of the Patriotic Front" led by Kimon Georgiev, seized power and declared war on Germany on 9th September. 

In November 1944, the 2. Yato (Squadron) of the 5.BP had a total of 21 B-71 on strength. On 14th November the 5.BP was redeployed from Plovdiv to Vrazhdebna, close to Sofia, from where they took part in various bombing missions against the retreating Wehrmacht. On these missions, the B-71s had not a precise targets, but where instructed to take upon targets of opportunity in certain pre-defined areas where the VV thought German troops were concentrated. 

The Bulgarian B-71s were heavily employed over Yugoslavia. On 18th November three B-71s attacked a German train at the Vuchitran train station, causing heavy damage to the train. The next day four B-71s bombed the Zhitarica railroad station. Although they were meet with heavy anti-air fire, they returned safely to Vrazhdebna. 

Two days later, on 20th November, several B-71s flew a 'free hunting' mission against targets of opportunity in the regions of Mitrovica and Rashka, attacking a train north of Mitrovica at 12:30 hours. In this bomb run Zherav 4's bomb bay doors malfunctioned and couldn't release its bombs and Zherav 11, flew by Sgt. Manol Dojchev became disoriented and had to force-land at Staro Zhelezare, close to Plovdiv. 

The fourth and final bombing mission of the Bulgarian B-71s took place the next day, on 21st November when four B-71s joined a formation of approximately 15 Lockheed P-38 of the US 15th Air Force. The B-71s bombed a motorized German column near Kamenica while the P-38s attacked a railroad station near Mitrovica. This constituted the only joint Bulgarian-American action against Germany during World War 2. During this action Zherav 4 lost its bearings and had to force-land at Shtarklevei.

After this attack the front moved beyond the range of the B-71s. During their service period with Bulgaria, they made a total of 14 sorties during those four missions in which they destroyed a total of two railroad stations, three trains and one German motorized column, at the cost of no Bulgarian airman killed or wounded.

Sources:

1st Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

2nd https://en.wikipedia.org/wiki/Tupolev_SB

3rd https://massimotessitori.altervista.org/sovietwarplanes/pages/sb/tapani/b-71/bulgarian/bulgarian.htm