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

Airspeed AS.6 Envoy, part one

The Airspeed AS.6 Envoy was a British light twin-engined transport aircraft designed and built by Airspeed at Portsmouth Aerodrome, in Hampshire.
As the type was quite popular, it was exported to many countries:

• Australia: As the aircraft became famous thanks to air races, it became very popular within commonwealth's airlines, so the Australian airline Ansett Airlines bought two exemplars. A private-owned Envoy which was registered as VH-UXY and modified with a long-range fuel tank filling the middle of the cabin, was piloted by Charles Ulm when it disappeared in December 1934 when attempting to flight the Pacific route between Oakland, in New Zealand to Honolulu in Hawaii. 
• China-Guangxi: The warlord of this Southern province had at least one Envoy serving with his Air Force. Further details are unknown but it was most probably destroyed during the Second Sino-Japanese War.
• Independent State of Croatia: Two Airspeed AS.6E were given to the ZNDH (Independent State of Croatia's Air Force) by the German Luftwaffe. They were used in the light transport role and were destroyed during the course of the War.
• Czechoslovakia: The Czechoslovak's National Airways, CSA, ordered four AS.6 Envoy JC in 1937 to equip their air routes. When Czechoslovakia was annexed, all of them were passed over to the Luftwaffe.
  Additionally one machine was bought by Vítkovické horní a hutní tezirstvo (Vitkovice Mine & Steel Co.) in 1936 based in the Czech city of Ostrava and was used by his president.

Sources:

1. https://en.wikipedia.org/wiki/Airspeed_Envoy

2. https://en.wikipedia.org/wiki/Croatian_Air_Force_(Independent_State_of_Croatia)

3. http://britishaviation-ptp.com/airspeed_as6.html

4. https://www.valka.cz/topic/view/114447/Airspeed-AS-6E-Envoy

Aero A.300

The Aero A.300 was a Czechoslovak medium bomber aircraft that flew for the first time on 20th April 1938 and, in spite of what its numbering could suggest, it was an improved and refined version of the previous Aero A.304.
It was designed by Aero to replace the locally-built Bloch MB.200 that were already obsolete by 1937. The Aero A.304 transport/bomber was taken as the basis for this new bomber project.
It was a monoplane of conventional design with retractable wheeled undercarriage that was powered by two Bristol Mercury IX engines which delivered a power of 820hp each and drove a three bladed two-pitch de Havilland-Hamilton propeller.
It was armed with three defensive 7,92mm VZ.30 machine guns. One in the nose, other one under the fuselage and a third spinal one in a retractable turret. It had a payload of 1000kg (2200lb) of bombs that were carried internally and a crew of four, pilot co-pilot, navigator and radioman .
Only one prototype was built at Aero's installations in Prague and, after being tested, it proved to be the second fastest Czechoslovakian ever built, only surpassed by the Avia B.35 fighter. Despite being so promising, the Munich agreements and the subsequent Czechoslovak national crisis, paralized the development and manufacturation of the project.

Sources:
1. https://en.wikipedia.org/wiki/Aero_A.300
2. https://forum.valka.cz/topic/view/3758

Avia B-35

The Avia B-35 was a prototype single-seat monoplane fighter designed and built in Czechoslovakia in the years prior to the World War II.
It was a low-wing monoplane with an elliptical wing. Fuselage was made out of steel tube and the wings were made entirely out of wood. It had also a fixed landing gear, hoping that it would improve the speed, but in reality it was just an improvised solution because the mechanism for retracting the undercarriage wasn't yet available.

The first prototype, labelled B-35/1 showed good flying characteristics and was powered by an Hispano-Suiza 12Ydrs piston engine. The engine was changed shortly after to a 12Ycrs in order to refit the nose to instal a cannon there to fire through the propeller hub. The testing of the first prototype ended on 22nd November 1938 when the prototype crashed killing it's test pilot, Arnost Kavalec.
A second prototype, B-35/2 was already almost completed and featured redesigned ailerons and flaps. It flew for the first time on 30th December 1938 and it was tested on February 1939. It's known that a pre-production series order was placed, but the German occupation of Czechoslovakia in March 1939 stopped it.

Sources:
1. https://en.wikipedia.org/wiki/Avia_B.35
2. Salamander Books - The Complete Book of Fighters

Avia Bk-534, Czechoslovak Users

Now it's the time for the last post about the Avia B-534, this time covering the native and some foreign and exotic users of the Bk-534.

The Bk-534 was designed to have a 20mm Oerlikon FFS-20 cannon firing through the nose and just two 7.92mm machine guns firing through the sides of the nose.
Apparently there were some problems to adapt the new gun that weren't solved until the summer of 1938. In order to make more airplanes, Avia decided to replace the cannon with a third machine gun in the nose with an extra amount of ammunition.
As the time was running out due to the German occupation of the Sudetenland, two series of the Bk-534 were produced, with only three of the second batch serving in the Czechoslovak Air Force and the remaining 63 ones serving either with the Luftwaffe or the Slovak Air Force after March 1939 when the rest of the Czechoslovak state was occupied by Germany.

Sources:
1. https://en.wikipedia.org/wiki/Avia_B-534
2. Salamander Books - The Complete Book of FIghters

Avia B-534-IV, Czechoslovak users, part two.

The Avia B-534-IV demonstrated an excellent performance at a flying exhibition in Switzerland in 1937. The German Bf.109 won the categories of best climbing and diving and the German competitor pilot, handling a Henschel Hs.123 pushed his biplane to claim the second post, so the Avia B-534-IV got the next three places. It did even manage to outflight other fighters taking part, including the Bf.109 even if it was 11 Km/h slower than this one.

As Czechoslovakia was occupied in March 1939, this airplane couldn't be used in combat by it's native nation. By that date, high performance monoplane fighters such like the German Bf.109, the British Hawker Hurricane or Supermarine Spitfire or the American Curtiss P-36 were raising the bar for fighter/interceptor standards and biplanes were started to be obsolete.

Sources:
1. https://en.wikipedia.org/wiki/Avia_B-534
2. Salamander Books - The Complete Book of Fighters

Avia B-534-IV, Czechoslovak users, part one.

The last Avias B-534 to be done carried the serials 534.174 to 534.193 and they all belonged to the IV series.

This variant was characterized by their enclosed canopy and, even if it's not that visible, they had a metal light alloy propeller manufactured by Letov. Those and various other refinements made the IV series to reach top speeds of over 200mph, placing it on par with the best biplane fighters of those years.
Another small changement was the replacement of the tail skid with a tail wheel and, after having made some field testing, the main wheel spats were often removed after discovering that they clogged very easily with mud.

Sources:
1. https://en.wikipedia.org/wiki/Avia_B-534
2. Salamander Books - The Complete Book Fighters

Avia B-534-IV - Czechoslovak Policial units

The Avia B-534-IV was also used by the Czechoslovak gendarmerie's aerial branch in order to perform aerial patrols in their territory.

We apologize for this post being this short but we only could find graphical info about the Czechoslovak Gendarmerie usage of the Avia B-534.

Avia B-534-III

Following the sales success from the II series, the Czechoslovak Air Force ordered another batch of B-534 to be made.

In 1936 a second order was placed to Avia to manufacture more B-534. The first 25 of them belonged to the B-534-III denomination and were started in the second half of 1936. The III series featured some minor changes like aerodynamic refinements which saw the frontal carburator's air intake streamlined. Mudguard spats were also added, however as they tended to clog, they were usually removed.

This was the least produced variant before switching to the famous B-534-IV version, which was a success in sales. However, it was used by many countries like Bulgaria, which used it in very limited numbers, Germany or Slovakia.

Sources:
1. https://en.wikipedia.org/wiki/Avia_B-534
2. Salamander Books - The Complete Book of Fighters

Avia B-534-II - Native Users

The Avia B-534-II was a Czechoslovak biplane single-seat fighter airplane from the 1930s.
The II series were a modification of the first series ordered by the Czechoslovak air force and comprised 45 airplanes.
Like the I series, they were armed with four guns, however, as the wing mounted gun in the original version was troublesome, these guns, upgraded to the vz.30, were placed in the fuselage together with the other two, firing through the propeller.

Some small number of them were tested with a bubble cannopy, certainly a very modern innovation for the era, but it was an experimental feature rather than an standard fit.
It was also powered by the Hispano-Suiza 12Ydrs V12 engine.

Sources:
1. https://en.wikipedia.org/wiki/Avia_B-534
2. Salamander Books - The Complete Book of Fighters

Avia B-534-I - Native users

The Avia B-534-I was a direct variant of the Avia B-34/2 which flew for the first time on 25th May 1933 and was designated retroactively as B-534.1 on September of that same year.
After further testing, an order of 34 airplanes followed which was soon increased to 147 on 17th July 1934.

It was a single-engine biplane fighter powered by a license built Hispano-Suiza inline engine and a fixed landing gear. The first airplane of the I type were delivered for the first time in October 1935 and 100 of them were supplied to the Czechoslovak Air Force.
The I series was based on the second prototype and was armed with four 7.92mm vz.28 guns, two of them placed in the sides of the engine, just like the B-34 and two of them mounted on the lower wings, however, those proved to be troublesome and only the first 47 airplanes were armed with them.
It was powered with an Avia built licenced version of the Hispano-Suiza 12Ydrs engine delivering 850hp of power. It had capacity for 347 litres of fuel which were located in two fuselage tanks of 90 and 257 litres.

Sources:
1. https://en.wikipedia.org/wiki/Avia_B-534
2. Salamander Books - The Complete Book of Fighters

Avia B-34

Here we are again, this time with another Czechoslovak fighter airplane.

It was the first design of Frantisek Novotny for the Avia Company who later would design the famous Avia B-534.
It was an all-metal single bay biplane of conventional configuration with tailwheel undercarriage and the main wheels were fitted with large spats.
The first prototype made it's maiden flight on 2nd February 1932 and that leaded to some modifications specially on the tail and engine cowling. The revised version was ordered by the Czechoslovak Air Force. An experimental version of this airplane, fitted with an Hispano-Suiza 12Ybrs piston engine was the official prototype of the Avia B-534-I.
It was powered by an Avia Vr.36 which was a licensed version of the Hispano-Suiza HS-12Nbr engine, which could deliver 740hp of power. It was armed with two fixed forward-firing 7.92mm vz.28 machine guns fitted in nacelles in the front-lateral part of the airplane.

Twelve B-34 entered service in September 1934 with the Czechoslovak Air Force and they served in the 37. Stíhací Letká (37. Fighter Squadron) where they served until 1937 when they were relegated to training duties. Even if it had bad reputation it was a robust airplane with only one crash during it's active career.
Eight were seized by Germany when the Czechoslovak State ceased to exist in March 1939 and at least three were lost in crashes and most probably others were retired from use. The remaining ones were handed over to the new Slovak Air Force which used at least one of them for training purposes at the Tri Duby airfield until at least August 1944 when they became part of the combined squadron of the Slovak Insurgent Air Force in September 1944. However there are no evidences that they were used in combat and they were destroyed by the Slovaks when the uprising failed.

Sources:
1. https://en.wikipedia.org/wiki/Avia_B-34
2. Salamander Books - The Complete Book of Fighters

Avia BH-33L & BH-33H

This is the last post before our holidays, so there won't be new post until early August.

The BH-33L was the third development of the BH-33 which was intended to be used as the standard Czechoslovak fighter and was to be known as the Ba.33.
The prototype flew for the first time in late 1929 and was introduced in 1930. It had basically the same fuselage as the BH-33E but it featured longer-span wings of greater area and was powered by one 580hp Skoda L engine. It was armed by two modified Vickers 0.303in machine guns called Mk.28 which were mounted between the cylinder banks.
It did indeed serve as the standard Czechoslovak fighter during the early 1930s.
After the end of the Czechoslovak republic in 1939, some airplanes were used by the Slovak Republic, which used then for a short period of time in training duties.

The BH-33H was a single prototype powered by a Pratt & Whitney Hornet engine, just like the Vought O2U. Most probably it was Avia's trial on introducing it to the American market.

1. Salamander Books - The Complete Book of Fighters
2. https://en.wikipedia.org/wiki/Avia_BH-33

Aero A.102

We start this Saturday with one of the most elegant Czechoslovak fighters ever made.

The A.102 was a Czechoslovak fighter aircraft of the early 1930s that showed a big difference in design patterns from other previous Czechoslovak fighters. it was ordered by the MNO (Czechoslovak Defence Ministry) and was intended to be the state of the art of the national aeronautical industry.

It was powered by an 800hp Gnome-Rhône Mistral radial engine, it was made of all-metal and was to be armed with four 7,7mm machine-guns.

Initially it was going to be a biplane, however it was decided to turn it into a gull-winged monoplane just because it was the most fashionable trend in central Europe during the early-to-mid 1930s.

The first of two prototypes flew for the first time in July 1934 with four Czech Model 30 guns installed in the wings in order to fire outboard of the propeller arc. Both climb rate and maneouvrability were good and there were plans to install a more powerful 930hp Mistral-Major Krsd engine in one of the prototypes but given the poor landing characteristics, it was discarded.
Even if those previously mentioned rates were good, the lack of flaps, the excessive wing loading rate and the touch-down speed of 110km/h were rated as excessive by the MNO. It suffered a forced landing and an accident in 1936 but the prototype was restored in 1937 in order to exhibit it at the national aircraft exhibition, but by that year the MNO the Avia B.35 monoplane to be better and further development of the A.102 wasn't continued.

There are unconfirmed rumours that one of the two prototypes ended up fighting in the Spanish Civil war, in the Republican side.

Sources:
1. The complete book of fighters
2.https://en.wikipedia.org/wiki/Aero_A.102