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Borovkov-Florov I-207/5 Object 10
Florov and Borovkov continued with the "Object 10" project airplane that had a clear influence of the I-207 fighter, which is why the literature has sometimes named it I-207/5.
The project for this aircraft was ready for 1940 and envisaged the use of a Shvietsov M-71 engine. The fundamental objective of this new project was to achieve a design capable of eliminating all the difficulties encountered during the I-207 tests.
The aim was to demonstrate the possibility of creating a highly maneuverable biplane fighter with minimal resistance to advance, capable of competing with the best monoplane fighters of the time. The selection of a biplane wing box, according to its creators, should guarantee a more compact aircraft with better visibility for the pilot.
On this occasion and in order to achieve a wing as thin as possible, the builders decided to use a gull-type wing configuration for the upper wing and inverted gull for the lower wing. As in the I-207, the use of any type of bracing or upright was not foreseen. According to calculations the “Object 10” should reach a speed of 650 km / h with a turn time of 14 - 16 seconds.
In an attempt to achieve the highest possible speed, the builders designed from the beginning of the design stage, the use of reactive engines.
As early as July 1939 the engine manufacturer Merkulov had proposed the use of auxiliary ramjets in piston-engined aircraft. These ramjets were characterized by using the same jet fuel as the main power plant. These motors were called DM, acronym for Dopolnitielni Motor or auxiliary motor.
DM motors were designed as short-term supports for those moments in combat when additional speed was required. The first tests of these auxiliary engines were developed on a Polikarpov I-15bis in late 1939. The results were promising and for this reason in 1940 the constructors Borovkov and Florov installed these engines on the I-207/3. The test pilot of Factory No.207, LM Maximov, carried out about twenty flights without difficulties on this plane.
In the “Object 10” project the DM was installed inside the rear fuselage, behind the cockpit. In this way, its installation did not affect performance during the flight under normal conditions. The DM could be switched on by the pilot. For this, some side doors were opened that allowed air access to the engine and it was turned on. An increase in speed was calculated to about 840 km / h.
Unlike the previous models, the tail section was designed as a monocoque duralumin structure with a structure similar to that used in the wing. This was due to the need to reinforce the tail for the installation of the DM engine and to the need to avoid possible fires caused by the hot exhaust gases from the ramjet.
The armament was designed in such a way that it could be added or removed depending on the mission. The initial version was armed with two ShKAS 7.62 mm machine guns and a BS 12.7 mm machine gun, which could be replaced in field conditions by two 23 mm guns in the ground attack version. The armament had to include the possibility of transporting 250 - 500 kg bombs and dropping them accurately during dive on the target.
In the design, 350 - 400 kg were estimated for the armor and the installation of the guns. The cockpit and vital organs of the plane had to be protected. In the fighter version, the pilot's back was protected by 8.5 mm thick concrete armor capable of defending the pilot from the firing of normal caliber weapons. The frontal armor was provided by the radial motor. This, together with the small dimensions of the plane, guaranteed an important level of safety to the pilot. The fuselage fuel tank was also protected.
A feature was the retractable type tricycle undercarriage. This configuration had been successfully tested by the TsAGI on an SB bomber. As early as 1940, several Soviet models included this type of landing gear in their design. In the case of "Object 10" this decision was forced by the fact that the tail was occupied by Merkulov's engine.
The "Object 10" project was handed over to the NKAP in the summer of 1940. This project envisaged the use of a Shvietsov M-71 engine and a maximum armament capacity of 1000 kilograms. The armament could be made up of 250 or 100 kilogram bombs, although the possibility of using eight RS-82 reactive rockets under the wings was envisaged. The armament was also composed of two 12.7 mm and two 7.62 mm machine guns.
The cockpit armor comprised a 4 - 4.5mm armored seat plus an 8.5mm cement plate at the rear of the seat.
The project data showed a speed of 658 km / h without the auxiliary engine in the fighter version. The ground attack model had to fly at a speed of 550 km / h.
The project was reviewed by a directed commission for academic BN Yuriev on 3 August 1940, which considered objective the construction of the aircraft in its hunting version high manoeuvrability and in its version with two FAB-250 or four FAB- 100. The commission noted that the actual speed to be reached without the auxiliary engine would be only 605 km / h.
With these results, this variant in general could become an excellent ground attack aircraft. The possibility of using the M-82 engine was also evaluated.
With the start of the war, neither this model nor its development known as "Object 11" were built.
Object 10
Engine: 1x Shvetsov M-71 (1700/2000 hp); 1x Merkulov DM ramjet
Wing span: 9.5 m
Wing area: 24.0 sq.m
Length: 8.35 m
Takeoff weight: 3500 kg
Wing loading: 146 kg/sq.m
Max speed w/out ramjet: 650 km/h
Max speed with ramjet: 750-800 km/h
Climb to 8000 m (with ramjet active): 8.0 min
Flight range: 800 km
Armament: 1x 12.7 mm Berezin BS, 2x 7.62 mm ShKAS or 2x 23 mm cannons. 
Crew: 1

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