In 1936 Bolkhovitinov considered the problem of high-speed military aircraft. He choose a layout with two M-103 engines, installed one after the other (tandem) with the transmission on coaxial propellers.
He constructs a paired set of engines, followed by bench testd. Bench tests were promising, so in 1937 under the leadership of Bolkhovitinov a high-speed short-range bomber was conceived, indexed "C" (there were several options for decoding the index: "Stalin," "Spark," "Spartacus").
In parallel with the construction of short-range bomber DB, Bolkhovitinov began the design of another aircraft, equipped with a similar twin powerplant. This a project of high-speed long-range fighter-1 twin engine M-107. This was designated "I". The development was carried out until the spring of 1941 however, an unexpected obstacle has stopped development of the machine. April 25, 1941 Bolkhovitinov was summoned to a meeting of Deputy People's Commissar Balandin aviation industry. Present at the meeting, Director Motor Works Lavrent'ev and chief designer of engines Klimov reported the impossibility of creating a two-seat trainer M-107P engines.
The main cause of failure was it was thought that in this engine the elongated shaft at working speeds could have resonance problems. Bolkhovitinov were asked to choose any other type of engine available in the country and to convert it for the project. The designer chose the diesel M-40, and while it was heavy, but consumed half as much fuel.
Change the engine caused change for the whole project. Preliminary survey was conducted during May - June 1941, returneing ro the designation "C".
I-1 was then included in the plan of an experimental aircraft in 1941, due to the large similarity of the scheme and design of aircraft with "C", 2M-103 and "C-2", equipped with one engine M-103 (front-engine was left in place, but its transmission has been disabled from the second propeller.
In general, the draft I-1 was tested by repeating the "C", but with a much more powerful Klimov M-107 engines. Different from the prototype were vertical stabilizer and skid. The stabilizer was 4.5 m without end plate.
This fighter was never completed due to the refocusing of the bureau.
The draft I-1 had been identified, many new technological approaches for assembly, riveting and bonding aircraft components, in-flight pilot's ejection, corresponding to speed range 600-750 km / h.
- Efficiency coaxial propellers at high relative received (large pitch speed, ie, a big step corresponds to a high flight speed) for 2 - 4% higher than the efficiency of a single-screw combinations.
- At take-off mode at angles the blade is less than 35 ° coaxial propellers efficiency is somewhat lower than the efficiency of single screw. For large values of the power factor of coaxial rod bolts pas-off mode, more than a single screw rod coated (equivalent of the working surface) equal to the total coverage of coaxial.
- In order to power the front and rear screws were the same when you reach maximum efficiency, the angle of the blade rear propeller must be 1 -1,5 ° less than the angle of the front propeller.
- Change the distance between the screws combinations to the extent permitted by design considerations (within the width of the blades), a noticeable effect on the value of efficiency does not have,
During the war, however, put into practice the results of the research was not possible.
With the intention of creating a high speed light bomber, Viktor Bolkhovitinov designed what is commonly referred to as the Bolkhovitinov S or Sparka. During flight trials the Soviet Air Force (VVS) referred to the aircraft as S-2M-103, for skorostnoy (high speed) with two M-103 engines; however, a number of other designations have been applied over the years. The common “Sparka” designation means twin—because the aircraft had two engines mounted in tandem. Other designations are BBS-1 for blizhniy bombardirovshchik skorostnoy (short range bomber, high-speed), BB for blizhniy bombardovshchik (short range bomber), and LB-S for lyohkiy bombardirovshchik-sparka (light bomber-paired).
The Sparka was a low-wing aircraft of all-aluminum construction with stressed skin. The aircraft had a twin fin tail to increase the rear gunner’s field of fire. The undercarriage was fully retractable; the main gear retracted toward the rear, and the wheels rotated 90 degrees to lie flat within the wings. The pilot and navigator/bombardier/gunner sat in tandem under a long canopy. Between the pilot and second crew member was a small bomb bay for 882 lb (400 kg) of bombs. A plexiglass section on the bottom of the aircraft just aft of the bomb bay provided the bombardier a view of the ground. The aircraft was 43 ft 4 in (13.2 m) long and had a relatively short wingspan of 37 ft 4 in (11.38 m). The Sparka weighed 12,460 lb (5,652 kg).
The Sparka was powered by two Klimov M-103 engines positioned in tandem in the aircraft’s nose. Each engine drove half of the aircraft’s six-blade, coaxial contra-rotating propeller unit. This engine and propeller arrangement was similar to the FIAT AS.6 installed in the Italian MC.72 and the Hispano-Suiza 12Y installed in the French Arsenal VB 10. With this engine arrangement, the front engine drove the rear propeller, and the rear engine drove the front propeller via a drive shaft that ran through the Vee of the front engine.
The Klimov M-103 engine was derived from the M-100, which was a licensed copy of the Hispano-Suiza 12Ybrs. The M-103 had a 5.91 in (150 mm) bore and 6.70 in (170 mm stroke). Total displacement was 2,200 cu in (36.05 L). The engine produced 960 hp (716 kW). A radiator was installed in a large duct just below the rear engine, and it cooled both of the Sparka’s engines.
Bolkhovitinov started design work on the Sparka in 1937, and prototype construction began in July 1938. The aircraft made its first flight in January 1940 (some say late 1939) with B. N. Kudrin at the controls. VVS testing took place from March through July 1940. The Sparka showed good speed, reaching 354 mph (570 km/h). However, the take-off run was excessive, landing speeds were high, and visibility over the nose was impaired. In addition, some trouble was encountered with the rear engine’s propeller drive shaft breaking due to excessive vibrations. Even so, the aircraft received a positive assessment, noting that the installation of the tandem engines eliminated a considerable amount of drag over two separate nacelles.
A new wing was designed with a NACA-230 airfoil section to improve take-off and landing performance. The aircraft was tested with this new wing from September to December 1940, and it did improve the aircraft’s take-off and landing characteristics.
Some say the single engine version was really a separate aircraft (known as S-1) that flew in January 1940 to test the airframe configuration. This seems unlikely because of the time frame involved. The twin-engine Sparka (S-2) would have been nearly complete by the time the single engine airframe test ship first took to the air, making major changes impossible and minor changes difficult. Official trials took place in March 1940.
The Sparka was reconfigured for a single 960 hp (716 kW) Klimov M-105P (some say 103P) engine, which was installed in the forward engine bay. The M-105P was a development of the M-103P; both had a smaller bore of 5.83 in (148 mm), but the stroke was unchanged, and could be fitted with a cannon to fire through the engine’s Vee. The aircraft was tested on skis in early 1942 but was underpowered with the single M-105P, attaining a top speed of 249 mph (400 km/h).
Development on the Sparka was abandoned in mid-1941, partially a result of the German invasion. In addition, the factory where the Sparka was built was needed to produce the Petlyakov Pe-2 attack bomber.