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JAI JAI-4 Iskra
In January 1932 the JAI began, on its own initiative, the development of tailless flying wing airplanes. IG Nieman considered the aerodynamics a good basis for in-depth studies.
Pavel Georgievich Bening, one of the engineers of the KA Kalinin construction bureau, was invited as the main constructor of the group. The group was reinforced with the addition of AA Krol, Alexandr Alexeyevich Lazariev and Sergei Ivanovich Kuzmin.
In January 1933 work began on the design of an experimental flying wing airplane. The calculations showed that due to the absence of the empennage the aerodynamic resistance should decrease by 5%. When designing the model, the manufacturers decided to abandon the use of a long fuselage, forcing the implementation of a swept wing with a permanent center of pressure profile. The wingtips were provided with vertical surfaces with the rudders.
Originally it was decided to build non-motorized versions for testing. In parallel with construction of the experimental gliders, Osoaviajimoviets JAI and PP Postyshev, work began on the three-seater experimental JAI-4 Iskra or "Osoaviajimoviets Ukraini" (in Russian: ХАИ-4 Искра, "Осоавиахимовец Украины") to highlight the participation of this society in financing the development of the project.
With accumulated experience, In the summer of 1934 engineers AA Lazariev, NG Bening and AA Krol completed work on the new original design experimental aircraft.
The "Iskra" was conceived as a three-seater, low-wing, tailless, monoplane aircraft with a 100-hp Shvietsov M-11 engine in thruster configuration, located behind the crew cabin and wing configuration.
The construction was of wood with fabric covering. The fuselage presented a semi-monocoque structure with straight sides and a curved upper surface and was developed on the centerplane spars. Inside the fuselage the cockpits and crew cabins were located.
The wing, integrated with the fuselage, had a trapezoidal shape with a 22º sweep on the leading edge and 11º on the trailing edge, also characterized by a slight positive dihedral. The M-11 was selected.
The wing construction was made of wood and had two trunk-type stringers, which crossed the entire fuselage. The coating was plywood with fabric and lacquered to finish it.
The trailing edge was fully mobile and divided into four sections. The ailerons, of normal type, were located in 65% of the wingspan and between them the elevons were located. The wingtips ended in empennages to which the rudders were attached. These were constructed of wood integrally with the wing and covered with plywood. In the lower part of the empennage the supports fixed to the stringers were installed. The rudders were covered in fabric. As a noteworthy feature, it should be noted that the empennages were located at a certain angle with respect to the vertical and were slightly inward. This configuration generated a thrust effect and made it possible to reduce the inductive resistance of the wing. The wing quality with this innovation was increased by 8% in relation to a conventional wing. In parallel, the bearing capacity grew by 7%.
The JAI-4 was, along with the SAM-13 of Moscaliov, the first model with tricycle gear designed and built in the USSR. The front wheels had a rubber ball and the rear wheels were made of wood. The rear wheel was steerable and the main wheels were linked by a hydraulic link, so that, in the event that one was out of balance, the other would react by trying to resolve the situation. This innovation allowed the JAI-4 to start takeoff with a 0º angle of attack and gradually increase it, which shortened the takeoff run. This hydraulic system also allowed the retraction of the main gear.
The powerplant selected was the 100-hp Shvietsov M-11 five-cylinder engine driving a 2.4-meter-diameter, two-bladed wooden propeller. The pitch of the propeller could be modified on the ground. The removable powerplate was constructed of welded steel tubes in a pyramidal shape with an annular structure at the end, to which the motor was attached. The fuel system incorporated tanks with a capacity for 4 hours of flight.
The crew cabin was located at the front of the fuselage and closed by a transparent cover. The rear two-man cabin featured windows on both sides.
The control system of the moving surfaces was by means of cable. The rudders were operated by the pedals, the elevator and ailerons were operated with the joystick.
In order to obtain the aerodynamic characteristics of the future airplane, in May 1933, a series of reduced-scale models were tested in the aerodynamic laboratory of the JAI. After validating the solution, construction began.
The JAI-4 was built at the GVF Aviation Repair Workshops in Kharkov (JARM), located in Sokolniki and the financing of the project was assumed by the Central Committee of the Osoaviajim of Ukraine. Construction and flight tests were entrusted to Alexandr Alexeyevich Lazariev. The plane was finally ready by the summer of 1934.
At the beginning of June, 1934, the plane was taken to the airfield in Sokolniki and on June 20 the test pilot BN Kudrin took flight for the first time. Initially it was difficult to get the plane off the ground. During the roll and due to the moment of the propeller the front gear was compressed and the angle of attack decreased, being insufficient. The effectiveness of the elevator was lost and the aircraft could not lift off the ground. Only when it reached 180 km / h was it able to take flight.
In the air the "Iskra" showed problems with longitudinal flight control and delays in the response to the control lever due to a large moment of inertia caused mainly by the large forward cabin and the location of the engine. The flight path was undulating. There was also a lack of longitudinal stability due to the vertical surfaces being outside the action of the propeller.
During the flight a height of about 600 meters was reached. The low ceiling was motivated by the low dive moment of the propeller and the low effectiveness of the elevons. The pilot was forced to raise the aircraft while keeping the stick in a neutral position.
After 15 minutes of flight and making two circles over the airfield, the pilot decided to land. The landing was also difficult and could only be achieved at high speed with a small angle of attack. The plane touched down abruptly by cutting the engine at a height of close to one meter. The landing gear managed to withstand the impact with the ground.
The takeoff problems were mainly motivated by the incorrect location of the engine in the elongated fuselage, which generated an important moment of inertia in relation to the transverse axis. The unstable behaviour of the aircraft on takeoff and landing was also motivated by the negative action of the elevons. During take-off, these surfaces incline upwards, achieving an S-shaped profile in this area that led to a decrease in lift. During landing, when tilting downwards, the opposite happened, lift increased and the plane tended to rise.
During August 1934 the pilot BN Kudrin made two more flights and then the tests were continued by LS Ryzhkov. The tests carried out between 1934 and 1935 made it possible to define the main principles and bases for the flight of airplanes in a tailless flying wing configuration.
JAI-4 Iskra
Engine: Shvietsov M-11, 100 hp
Wingspan: 2 m
Wing area: 21.24 m²
Length: 4.7 m
Empty weight: approx. 600 kg
Maximum takeoff weight: 850 kg
Maximum speed: 180 km / h
Landing speed: 100 km / h
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