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JAI JAI-29 Korshun
The first JHA-29M “Korshun-M”
In 1976, after the development of the JAI-28, based on the Okshinis BRO-11 glider, the collective of the Student Bureau of Construction of the JAI decided to move towards a version motorized.
The need to power the glider was motivated by the desire of the Aviation Construction Club (KAK) students to fly higher and farther. The operating peculiarities of the BRO-11 had already been mastered, but the short flights from the hills were no longer interesting. The simplest variant was to put a motor in the BRO, but given the simplicity of the structure it did not seem like an easy task. The development team of this device was made up of about 20 students, among whom were V. Silokov, S. Alexandrov and N. Lavrov, under the direction of Anatoli Barannikov.
In the original design stage, the JAI-29 Korshun (in Russian: ХАИ-29 Коршун) differed slightly from the BRO-11, both in its external appearance and in the materials used in its construction. The main difference was seen in the front area: instead of the wooden ski, a structure of three radial bars was installed in this area that served as landing gear and base for the pilot's position, the engine mounting and the wing mounting.
The Korshun was capable of flying from any level field without the need for a runway, tug or any other special condition.
Originally the PD-10 "Kolibri" engine was selected as the power plant. To avoid complications, the engine was located above the center of gravity. This decision also allowed, in case of failure, to withdraw the engine and continue using the device as a glider. Thus, in this way, the engine was located under the wing, which constituted the fundamental cause of the successes and mistakes of the model.
The JAI-29 "Korshun" was approved by the technical commission and took flight for the first time in 1977.
Powered flights showed a lot of design flaws. During takeoffs, the powered BRO constantly drifted off course and tended to pit the wing, damaging the ends and caps. Soon there was not a single "pilot" who had not suffered these mishaps. It was clear that the engine power was insufficient and changes were necessary in the design of the aircraft.
Despite these problems, the JAI-29 would be used for the preparation of 13 pilots with a total accumulated of 47 hours.
The next development of the JAI-19 was known as Korshun-M and was projected and built in 1980.
Another BRO-11 glider was taken and the nose was lengthened, modifying the landing ski. The skeletal structure of the tail bar was moved downwards, the surface of the horizontal plane was increased and a fixed skid was added in the tail area, soon replaced by a steerable wheel. Instead of a bracket with cable tensioners in the nose of the cabin they installed two brackets from the ski to the wing spar.
In the absence of a more powerful engine, it was decided to increase the wing area by increasing the wingspan. The initial value of the wingspan was 9 meters, later reduced to 8.4 meters. The increase in mass made it necessary to recalculate the structural resistance of the apparatus and reinforce several points of the beams and the structure. In this way the classic form of the "Korshun-M" appeared.
The wing of the JAI-29 was similar in construction to that of the BRO-11 and had a single variable section spar. The stringer was built with duralumin angles and walls with supports. In the middle section of the stringer there was a duralumin plate to which the wing supports made of 30 XGSA chrome-moly steel were fixed. At the end of the spar were the fixings for the wing tips.
Due to the lack of pine, the ribs were made of fir and the reinforcement points with 1 mm plywood. The three force ribs were constructed of 8mm plywood with circular holes to lighten them. At the rear of these ribs the fixings for the ailerons were installed. Fir ribbons were glued to the partitions of the stringers to complete the profile up to the theoretical contour between the ribs.
The trailing edge of the wing was constructed of spruce and secured to the ribs with 1mm pieces of plywood. The leading edge was protected with 1.5 mm plywood sheets up to 2/3 of the span. The spaces between the force ribs and their neighbors were protected above and below with 1 mm sheets.
Wing structure of the Korshun.
The ailerons were made of wood with plywood ribs fixed to the side member using screws. The leading edge was protected with an acrylic layer. The spaces between ribs were covered with 1 mm plywood.
The stabilizer was constructed of wood and was generally similar in shape to the BRO-11, but with increased surface area and some structural reinforcement. The glider's wooden supports were replaced by others made of duralumin with a circular section. The elevator and steering rudders also featured a glider-like construction and were covered with glued calico.
All Korshun surfaces were coated with glued calico and then AK-113F aluminum powder paint.
The landing gear varied from model to model. Originally it was composed of a central wheel under the seat and a small one in the tail, with runners fixed to the side member on the wing intrados. Variants with two front wheels in pyramidal structure and skid or tail wheel were built and in at least one example a tricycle train with wide span main wheels was tested.
The cabin was designed for a standard size person and lacked regulations. The weight of the pilot could vary between 45 and 70 kg, but flights were made with pilots up to 100 kg. As the weight increased, the center of gravity moved forward, so it was necessary to compensate by placing a weight in the tail area.
The cockpit instrumentation included a US-250 speedometer, VD-10 altimeter, VR-10 barometer, KI-13 compass, two TTsT-13 thermocouples for measuring engine temperature, a tachometer, and a mechanical fuel level gauge.
The powerplant was also variable. The JAI-29M Korshum was powered by a gearless RMZ-640 piston engine capable of developing 5500 revolutions per minute driving a 1 meter diameter two-bladed propeller. The fuel system incorporated a tank with a capacity for 22 liters of gasoline, located in the wing center plane, feeding the engine by gravity.
Detail of the connection to the fuel tank.
The test flights showed that the modifications were effective.
Generally the flights on the JAI-29 reached up to 100 km in distance. Repairs, and there was a need for several, were carried out directly in the field. The simplicity of the construction allowed to carry out these interventions with ease.
The JAI-29M in flight.
The flights were carried out without authorization from the institute, since the prohibition was maintained, but the almost 25 students managed to accumulate in each flight season from 4 to 6 hours. The total accumulated flight time was 90 hours.
The JAI-29M "Korshun-M" exhibited at SLA-84.
The JAI-29M Korshun-M was shown in the III light aviation competition in Kiev together with the JAI-37 “Mikhail Yefimov” models and the JAI-36 seaplane.
The Korshun-5 was a refined version of the model.
The JAI-29S version introduced minor modifications. This model participated in several meetings of the Soviet SLA (Light Aviation Consortium).
In an experimental way the JAI-29S was used in aerial photography tasks, using an AFA camera. The experiences obtained allowed to develop the technical task for a light aerial photography aircraft. Projection work for this type of device began at the JAI.
The actual number of aircraft produced is unknown. At the JAI the students assembled various devices. A series production was planned and documentation for this process was prepared, but finally the model could not be introduced.
JAI-29M Korshun
Engine: RMZ-640
Propeller: 2-blade
Propeller diameter: 1m
Wingspan: 7.89-8.4 m
Wing area with ailerons: 11.83 m²
Wing profile: Р-2-14%
Wing chord: 1.1 m
Wing dihedral: + 3º-5º
Length: 5.24 m
Height: 1.86 m
Empty weight: 167.5 kg
Fuel Weight: 20kg
Pilot weight: 40 - 110 kg
Take-off speed: 55 km / h
Descent speed: 45 km / h
Cruising speed: 65 km / h
Maximum speed in horizontal flight: 75 km / h
Maximum speed: 120 km / h
Maximum ROC at 62 km / h: 1.5 m / s
Minimum descent speed without motor at 65 km / h: 1.8 m / s
Run and take off: 100 m
Maximum range: 150 km
Maximum ceiling reached: 3000 m
Maximum load: +3 and -2g
Aileron chord: 0.35 m.
Spoiler area: 2.7 m²
Stabilizer span: 2.35 m.
Horizontal plane surface: 1.9 m²
Angle of implantation of the horizontal plane: -1.5º
Elevator area: 0.82 m²
Elevator working angle: +29º to -32º
Empennage surface: 1.32 m²
Rudder surface area: 0.77 m²
Span between wheels: 3.44 m.
Front wheel dimensions: 300х125 mm.
Rear wheel dimensions: 90х30 mm
Seats: 1
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