Working in A. N. Tupolev's design bureau (AGOS), which was then part of the TsAGI structure, and at plant No. 156, first as a design engineer, then as a brigade chief, Pavel Osipovich Sukhoi became deputy chief designer. And the first project he is working on in his new position is the ANT-25 aircraft. This aircraft was developed with the prospect of a military version of the DB-1, which is a long-range single-engine bomber. I must say a very unusual scheme for a long-range bomber. In 1939, becoming the chief designer of his own design bureau, P. O. Sukhoi receives the Resolution of the Defense Committee, entitled "On the creation of new prototype fighter aircraft in 1939-40." This decree required the design and construction of a single-seat cannon fighter. Thus, the aircraft, later named Su-1, becomes the first project of the new design bureau and P. O. Sukhoi as chief designer. The main difference between the Su-1 and the fighters created at that time in other design bureaus was the power plant as part of the engine and turbocharger. The turbocharger made it possible to increase engine power and altitude, thereby improving flight performance.
It is natural for a person to remember the events that happen to him for the first time in his life. First love, first project, first steps in a new position, etc. Often, the memory of these events leaves a deep imprint on the mind and affects the further train of thought and views. It looks like something happened to P. O. Sukhoi, since it was he who initiated the development in 1942 of a long-range bomber project with one engine, equipped with a turbocharger.
In the middle of 1942, the team of the design bureau of plant No. 289 began the preliminary design of a long-range night bomber with an AM-37 engine. The work was completed in September. When designing the DB-AM-37, the designers set themselves the task of creating an economical, easy-to-manufacture long-range bomber with flight characteristics close to those of the TB-7 (Pe-8) aircraft. According to the designers, when comparing these two aircraft, the DB-AM-37 aircraft had a clear advantage, since “for transferring the same cargo at equal speeds over equal distances, the DB aircraft will require 4 times less engines and fuel and 2-2, 5 times fewer crew members. In addition, for the manufacture of a DB aircraft at the plant, 15-20 times less duralumin and 4-5 times less labor intensity will be required …"
According to the preliminary design, the DB-AM-37 aircraft was a single-engine three-seater cantilever midwing with a single-fin tail unit and a retractable landing gear.
The fuselage was technologically divided into two parts: the cockpit and navigator and the main part of the fuselage:
- the cockpit of the pilot and navigator was made entirely of armor steel with a thickness of 1.5 mm and was attached to the main part of the fuselage using butt joints;
- the main part of the fuselage was a monocoque wooden structure. In front, at the top, there was a UTK-1 turret. In the lower part, under the wing, there is a bomb bay. Above the bomb bay was a welded steel gasoline tank. The rear of the fuselage housed the shooter who controlled the hatch installation, and also housed various equipment.
The wing - two-spar, trapezoidal, - in the plan consisted of two detachable consoles, docked with the nodes on the fuselage. Box-type front spar with birch veneer shelves and plywood walls. Rear spar with pine shelves and plywood walls. Ribs - wooden construction, with the exception of the side rib and the second rib (in the chassis attachment area). Plywood sheathing. In the toe of the wing and between the spars there were gas tanks (two in each console) of a welded structure of armor steel, 1.5 mm thick. The toe tank and the bottom panel of the inter-spar tank were included in the wing power scheme. The wing mechanization included ailerons and Shrenk-type landing flaps. The frame of the ailerons and the landing flaps are made of duralumin. Ailerons are covered with linen. There was a trim tab on the right aileron.
The tail unit consisted of a keel and a stabilizer of a wooden structure with plywood sheathing. The rudder frames are made of duralumin with linen sheathing. The steering wheels had weight and aerodynamic compensation and were equipped with trim tabs. The maximum use of wood and canvas suggests that the aircraft was not designed for the distant future, but for mass production during the war.
The chassis is three-wheeled with a tail wheel. The main supports were retracted downstream into special fairings on the wing, and the wheels rotated by 90 ° into the wing niches. The tail support with the wheel was retracted into the fuselage. The cleaning and release of the landing gear and landing flaps was carried out using the hydraulic system. The pressure source is an electrically driven hydraulic pump.
The aircraft control system is of a rigid type.
The AM-37 liquid-cooled piston engine (1400 hp) with a variable-pitch propeller was mounted on a welded steel motor frame, attached to the cab assemblies. The engine was closed by a hood, the lower flaps of which served as armor plates with a thickness of 1.5 mm.
Small arms - the upper turret UTK-1 with a machine gun of 12, 7 mm and 200 rounds of ammunition was served by the navigator. The hatch mount with a 12.7 mm machine gun and 200 rounds of ammunition was serviced by a shooter.
Bomb weapons were placed in the bomb bay. Normal bomb load - 1000 kg, in the reloading version - 2000 kg.
The crew consisted of three people: pilot, navigator-gunner-radio operator, gunner.
The armor of the crew, engine, oil and water radiators and gas tanks provided protection against fragments of anti-aircraft shells. In addition, to protect the rear from large-caliber weapons, the pilot and navigator had armor plates 15 mm thick, and the gunner of the hatch mount had armor plates 15 mm thick.
The draft design of the long-range night bomber DB with the AM-37 was reviewed at the Research Institute of the Air Force KA. In the Conclusion, approved by the chief engineer of the Air Force on October 21, 1942, it was noted that the presented draft design: “… cannot be approved for the following reasons:
1. A single-engine scheme of a long-range aircraft is inexpedient in terms of reliability and safety of flight.
2. The author of the project intends to install the AM-37 engine on the plane. The motor has been discontinued, has not been tested in widespread use and has a number of significant defects.
3. The takeoff properties of the aircraft (especially the night one) are unsatisfactory. (The takeoff run is 1030 m in the normal version).
4. The location and number of the crew will not ensure the normal performance of the combat mission:
a) it is physically difficult for one pilot to fly at night for 10 hours at an altitude of 6000-8000 m;
b) the navigator will not be able to fulfill the duties of a navigator, bombardier and radio operator, especially since his workplaces are located in different cabins."
In addition, in the conclusion on the preliminary design of the DB-AM-37, the remarks of the consultant of the Air Force Research Institute of the Spacecraft, Major General IAS V. S. Pyshnova:
“The desire to build a bomber with high performance, ie. good balance between bomb weight and fuel consumption is commendable. However, you should not get very carried away in this matter. Improving performance comes at the cost of a lot of design work and good design.
The promise to quadruple productivity is beyond doubt.
First, it is hardly advisable to make a single-engine bomber long-range. Here it is not only about reliability, but also about the possibility of placing special equipment. The aircraft has an unusual crew accommodation. The navigator's shelling is severely constrained by the wing.
The main question is about flight weight. Night start is difficult and should not be carried out with extremely heavy weight. The normal flight weight of this aircraft can hardly be more than 8000 - 8500 kg. The required size of the aerodrome should be approximately 2 times longer than the take-off run, i.e. over 2 km. The designer should be invited to work more on the project."
At the end of October P. O. Sukhoi sent to the Air Force Research Institute of the spacecraft "Supplement to the draft design of a long-range night bomber with AM-37."
It noted: “The preliminary design presented earlier for consideration was revised from the point of view of replacing the AM-37 with the M-82FNV. The replacement had little effect on the general layout of the aircraft, simplifies the VMG and the wing design due to the absence of a water radiator, which was previously located in the wing, with the M-82. When switching to M-82, it is planned to install two TK-3 …
Dimensional data, payload, construction and materials used (wood) remain the same as in the version with the AM-37 engine. Weight characteristics change insignificantly …"
Apparently, having received an opinion on the draft design of the DB with AM-37, the chief designer, based on the comments and suggestions noted in it, decided to rework the draft design, and in several versions. By mid-December 1942, work was completed on draft designs: a single-engine four-seat long-range night bomber DB-M82F with a 2TK-3 and a twin-engine four-seat long-range bomber DB-2M82F with a TC. The factory report for 1942 noted that these projects were not submitted to the Air Force Research Institute of the spacecraft for consideration.
In general, the project does not look as absurd as it might seem. Sukhoi himself chose the Pe-8 for comparison and reference point. But as an analogue, it would be necessary to choose DB-3F both in terms of characteristics and experience of use. Most of the tasks performed by the DB-3F during the war did not require flights to the maximum range. Having one pilot, the bomber was successfully used for strikes against enemy rear lines at a depth of 500-1000 km. It was for the "work" on the operational rear areas that the Sukhoi bomber could fully realize itself. Proof of this is the successful use of the American Grumman TBF (TBM) Avenger and Douglas A-1 Skyraider, whose characteristics were even lower. By reducing the flight range, it was possible to increase the combat load and improve the booking of the engine. The result would be a good single-engine torpedo bomber for working at operational-tactical depth. Although in any case, launching a series of new aircraft during the war years was impossible.
