The Bloch MB 130-136 family illustrates the doctrinal, technical and industrial hesitations that rippled through the French military aviation establishment before the Second World War.
The Bloch MB 130-136 family illustrates the doctrinal, technical and industrial hesitations that rippled through the French military aviation establishment before the Second World War. Only one type reached series production, the MB 131, for an operational concept that could not be achieved with the technology of the time.
In August 1933, the STAé Aeronautical Department of the French Air Ministry drew up a specification for a multi-seat combat aircraft, the M4 program. In October of the same year, the Air Staff issued a program for a fast multi-seat BCR (bomber, combat, reconnaissance) aircraft, designated Plan I. The aim was to provide reconnaissance groups with multi-role twin-engine aircraft able to perform long-range bombing and escort missions, in addition to specific reconnaissance missions. Carrying a 500-1,000kg bomb load, the aircraft had to be able to reach at least 350km/h at 4,000m altitude, with 1,300km range and three machine gun turrets for self-defense.
Eight manufacturers responded to the program, and six prototypes were built: the Amiot 144, the Aérienne Bordelaise SAB 80, the Bloch MB 130, the Breguet Br 460, the Farman 420 and the Potez 540.
The Bloch design bureau, directed by Maurice Roussel, created the MB 130 A, whose angular lines and “all-round” turret gave it the appearance of a smaller MB 210, an earlier design by the same team. Powered by two 760hp Gnome-Rhône 14 Kdrs engines, it was baptized “Guynemer” and fitted with a fixed, trousered undercarriage. It made its maiden flight at Villacoublay on 8 June 1934, flown by André Curvale and René Vaudequin.
After an initial series of flights, a retractable undercarriage was fitted, along with new 870hp Gnome-Rhône 14 Kirs/Kjrs engines and a ventral turret extended to the rear. The modified aircraft, redesignated MB 130 B, flew on 3 April 1935. Finalizing the design proved delicate, since no less than 17 different tail fins were tested. The aircraft, with the registration F-AKHS, was finally destroyed in 1937, injuring the pilot, Zacharie Heu. A float-equipped torpedo aircraft version, designated MB 130 M and equipped with two 760hp Gnome-Rhône 14 Kdrs engines, was unsuccessfully proposed in 1934.
In October 1935, there were plans to sign a contract for around 40 aircraft, but the contract never materialized, at least not in that form. The prototype underwent a lengthy evolution resulting in a new bomber and reconnaissance aircraft with a very different, more modern design: the Bloch 131 RB 4.
Beginning in late 1935, the concept of a BCR (Bombardement-Combat-Renseignement) combat aircraft began to lose ground in the French Air Force in favor of more specialized aircraft. So Marcel Bloch simultaneously developed an airplane that, while based on the initial Bloch 130 airframe, was given completely redesigned aerodynamics. This was the Bloch 131, a much more modern aircraft equipped with Gnome-Rhône 14 Kirs/Kjrs 870 hp engines. The new Bloch 131 was a four-seater reconnaissance-bomber aircraft (known as the RB4) that was no longer anything like its predecessor. The Bloch 131.01 was built at the Courbevoie plant and assembled at Villacoublay where, under registration number E-221, it first flew on August 12, 1936 with André Curvale and Armand Raimbeau at the controls.
A second prototype, the Bloch 131.02 RB5, registration number E-222, was presented at the 1936 Paris Air Show. It was able to carry a fifth crew member, the dorsal turret was moved, and a ventral turret was installed. This prototype first flew on May 7, 1937. During the summer of 1937, at which time the Société Avions Marcel Bloch became part of the Société Nationale de Constructions Aéronautiques du Sud-Ouest (SNCASO), the initial engines were replaced by Gnome-Rhône 14N 10/11 engines.
Series of the aircraft were ordered even before the 01 was tested. Between 1936 and 1937, five contracts for a total of 142 MB 131s and MB 132s were signed and replaced the initial contract for 40 type 130s. In 1938, under the ‘Plan V’ program for building advanced aircraft, all of these orders were changed to orders for the MB 131 model.
The first plane in the series produced in the SNCASO factory in Châteauroux-Déols (the factory was built in 1936 to provide good production conditions) flew on June 1, 1938. Tests on this plane with a semi-retractable ventral turret began at the same time as tests on the 02. The tests highlighted the unwieldy and complex nature of this apparatus and the fact that it would be better to install a stationary, aerodynamic gondola despite the loss of effectiveness at the firing post and the uncomfortable position the gunner would have to adopt. The 02 prototype was then turned into the 131 Ins and the 01 was abandoned.
The first series of 13 aircraft (nos. 3 to 15) were Bloch 131 R4 models (four-seater reconnaissance planes). This series was followed by five other (nos. 16 to 20) Bloch 131 Ins (dual-control trainer aircraft). The second prototype became the Bloch 131 Ins and was allocated to the French Air Force. The nineteenth serial aircraft (no. 21) was the first Bloch 131 RB4 (four-seater reconnaissance-bomber aircraft). More than one hundred of these were built.
Due to manufacturing delays, the first aircraft were not delivered until the autumn of 1938. In the end, the French Air Force took 141 machines, the 131, 132, and 133 prototypes having been reworked to the MB 131 series standards.
The MB 131 in service:
The units using the aircraft were as follows: GR I/14, GR II/14, GR I/21, GR II/22, GR I/35, GR I/36, GR II/36, GR I/55, GR II/55, and GR I/61.
On the eve of the declaration of war, 109 aircraft were in service in these units. They were unfortunately used for faraway daytime reconnaissance missions without an escort and hardly measured up to the Messerschmitt Me 109 employed by the Luftwaffe. As a result, starting in October 1939, aside from a few aircraft in the GR I/36 and II/36 units, they were withdrawn from the front line and relegated to training missions, towing targets, and fire missions in schools. As of May 10, 1940, 35 MB 131s were still in auxiliary service in reconnaissance groups and 64 were in training units. Between September 3, 1939 and June 24, 1940, eight aircraft were lost, four were shot down, and four were accident-damaged, for a total of ten killed. At the Armistice, 53 were inventoried in unoccupied France and in 1942, the Germans captured 21 that were then scrapped.
At the time the first series production contract was signed on 1 April 1936, Marcel Bloch was already proposing the MB 132, powered by 940hp Hispano-Suiza 14 Aa engines, alongside the Gnome-Rhône-powered MB 131. This version never materialized, due to the problems with the 14 Aa engine, and orders for the MB 132 were transferred to the MB 131.
This same contract called for the Bloch company to provide an MB 133 prototype. Like the MB 132, the MB 133 version was due to be equipped with Hispano-Suiza 14 Aa radial engines. However, it differed in having a twin tail in place of the single tail of its predecessors. The non-availability of the Hispano engine delayed the first flight. The aircraft sat in a hangar at Villacoublay for one year before flying, compared with a normal preparation time that rarely exceeded one or two months at the Bloch company. The delay was also due to the total reorganization – i.e. temporary disorganization – of the French aviation industry at that time: Société des Avions Marcel Bloch was nationalized and folded into the new Société Nationale de Constructions Aéronautiques du Sud-Ouest (SNCASO). It made its maiden flight at Villacoublay on 1 October 1937, flown by André Curvale.
Presented as an RB 4, it offered a top speed of 435km/h. Because of its late arrival, it was not competitive with more recent, faster models. Like the MB 132, it was converted to the MB 131 standard and handed over to the Air Force.
In 1936, the STAé Department issued program A21/1, calling for a medium B4-type bomber. This program can actually be viewed as a modified version of the 1934 B4 program. In particular, the failure of the large Hispano-Suiza and Gnome-Rhône engines led officials to accept a four-engine solution. The lower gun turret was also abandoned in favor of machine-guns firing through a hatch. Only two missions were specified: 800kg bomb load with 2,200km range, and 1,500kg bomb load with 500kg less fuel, the largest bombs being 200kg.
In response to this program, in view of the clear failure of the MB 133, the Bloch design bureau, working for SNCASO, came up with two models, one with two engines, the other with four. The first appeared to be an extrapolation of the Bloch 170 concept, though with no points in common apart from the engine cowlings and the construction principles, while the second was a derivative of the MB 130 family. The twin-engine aircraft received the designation MB 134, while the four-engine design was designated MB 135.
An initial project, featuring a new wing, twin tails and two 1,250hp Gnome-Rhône 14 P engines, showed little in common with the MB 131. This project came to an and with the abandonment of the 14 P engine, and the design bureau turned its attention to the second MB 134, which bore no resemblance to the MB 131 family.
Built in Courbevoie and assembled in Villacoublay, the MB-134-01 made its maiden flight on 22 July 1939, flown by René Le Bail and Jean Lapeyre. After some modifications, including an increase in the vertical tail surfaces, it finally entered the Orléans-Bricy test center in January 1940. On 21 April 1940 it was seriously damaged when a landing gear strut collapsed on landing following the in-flight failure of a hydraulic fluid reservoir.
During testing of the MB 134 a dispute broke out between Marcel Bloch and ministry officials. Opponents of Marcel Bloch accused him of trying to compete with bombers already in series production, thereby running the risk of causing complications in the production process, with no guarantee of achieving significantly better performance. Some suggested that the model be simply abandoned. The manufacturer was even criticized for the choice of the 14 Aa engine, even though this engine was initially specified by the Ministry for all the aircraft in the program. In the end it turned out that, with the same Gnome-Rhône 14 N-48/49 engines as its slightly older competitors, it was faster, reaching around 520km/h. This was due to its much lighter construction and reduced drag thanks to superior aerodynamics. Nonetheless, the dispute intensified, leading Marcel Bloch to step down from his management position at SNCASO on 13 February 1940.
In 1937, simultaneously with the first MB 134, and in response to the same revised program of 1936, the Bloch design bureau proposed a four-engine variant of the medium bomber, the MB 135. This aircraft featured the same wide fuselage, with a dorsal hump for the machine-gunner and his weapon. The wing was similar, though with a trapezoidal, instead of rectangular, center section. The engines were 710hp Gnome-Rhône 14 M 4/5s (subsequently 6/7s) with opposing rotation and Gnome-Rhône propellers. The bomb bay could accommodate a maximum load of 1,350kg.
The construction principles were those adopted for the other Bloch aircraft of the time: shell fuselage with boxes to increase stiffness, and oblique and longitudinal ribs to close the wing boxes. The manufacturer also tried to use only standard sheet and sections, made from duralumin.
The MB 135-01 was assembled at Villacoublay by SNCASO. It made its maiden flight at Villacoublay on 12 January 1939, flown by René Le Bail and René Lapeyre.
Despite its promising performance and excellent flight handling, it did not go into production. Even without the disaster of 1940, the Bloch MB 134 and 135, despite their undeniable qualities, would probably never have received a series production order. There were already two “fast bombers” in production (LeO 45 and Amiot 350) and the two new aircraft did not seem to represent a sufficient degree of progress to justify dispersing the industrial effort. In any case, over the coming months, SNCASO production resources were to be entirely dedicated to production of the Bloch MB 175 and MB 176.
A float aircraft variant of the first MB 134, the MB 136, was also proposed without success. Proposed with 14 N or 14 P engines (950 or 1,250hp), this torpedo-bomber would have been relatively fast for an amphibious aircraft (385 or 410 km/h depending on propulsion). However, it would have only barely satisfied the program requirements for combat scout capability in terms of payload and range. In addition it was being offered at a time when the Naval Staff were becoming less and less convinced of the need to use amphibious aircraft for certain missions. Accordingly, it did not progress beyond the project stage.