Lavočkin La-7UTI

Lavochkin La-7UTI
(Lavochkin La-7UTI)

The first example of the trainer version of the famous Lavochkin La-7 fighter aircraft was created by remaking the serial La-7 machine serial number № 45211521 in March 1945 at the Gorkom plant. The aim was to construct a "spar" for pilot schools, which would introduce the piloting of the La-7 to pupils more thoroughly than the La-5UTI (Uchebnoy Trenirovshchik Istrebitel - classroom training fighter) used until then. Five months later, the plant sent the machine to the Scientific Research Institute of Aviation (НИИ ВВС) for testing. During the ongoing state tests, which were completed on 16.8.1945, a number of deficiencies were found, consisting in the deterioration of flight characteristics (displacement of the centre of gravity), excessive temperature increase in the cockpit and also in insufficient instrumentation. For these reasons the machine was returned to the factory for rework.

The solution to the centre of gravity problem was, in the words of a classic, solved "primitively but effectively". Two 25 kg cast-iron segments were fitted into the engine compartment of La-7UTI serial number № 46210117, which shifted the centre of gravity and improved flight characteristics. The tailwheel, unlike the La-7, was non-retractable, but was equipped with a semi-automatic braking mechanism. The installation of additional thermal insulation of the engine and improved cabin ventilation was achieved by reducing the temperature in the cockpit. The aircraft was retrofitted with an RSI-4 (РСИ-4) radio and a landing reflector. A curtain was added to the pupil's cabin, used to obscure the view from the cabin for practicing flying without visibility. The installation of the RPKO-10M radio compass (РПКО-10М), the AFA-IM aerial camera (АФА-ИМ), and the PAU-22 photogun (ПАУ-22) was mandatory.

After all these modifications, new tests were conducted from the sixth to the nineteenth of October 1945, led by engineer V.I. Alexejenko (V.I.Alexeyenko). The first test pilot was A.G. Prošakov (A.G. Prošakov), the second D.G. Pikulenko (D.G.Pikulenko). Although the piloting technique from the cockpit of both instructor and student was identical to that of the La-7, and there was even a simplification of the landing manoeuvre, the La-7UTI did not pass the state tests. This was due to the still too high temperature in both cockpits (instructor 28°C and student 35°C at an outside temperature of 10°C), the absence of the possibility of emergency landing gear extension by the instructor as well as other shortcomings.

Therefore, in January 1946, the third "batch" of La-7 arrived for trials, namely the machine with serial number № 46210325. However, paradoxically, the elimination of the reproached deficiencies again shifted the center of gravity of the machine, and the additional weights on the reducer housing not only reduced its performance, but were evaluated as dangerous for the operation of the machine.

Lavochkin's design bureau did not give up, however, and in April of the same year sent another machine for state trials. It was a machine already known to us with serial number № 46210117, from which the weights were removed and a balancing plate was added to the elevator, which reduced the forces acting on the control lever. Nevertheless, the machine suffered from the old problem of centre of gravity shift, for which reason the stability margin was judged to be insufficient.

The next prototype La-7UTI in the sequence is machine serial number № 46210514. This time, however, it was diametrically different from its predecessors. The problem with the center of gravity shift was solved by moving the oil cooler under the second row of engine cylinders, thanks to which it was possible to dismantle the balancing weights. The aircraft thus lost 111 kg of weight. The company tests of the modified machine took place from 16.7.-16.8.1946, and because they were successful the machine was handed over to the Scientific Research Institute of Aviation for further tests. During these tests it was shown that the piloting technique of the La-7UTI in both cockpits was the same as that of the combat La-7. The machine also succeeded in endurance tests and all indications were that the road to series production was open for this type. However, the opposite was true.

During one of the test flights conducted by test pilot Viktor Masič (Viktor Масич) two elevator hinges broke off and only thanks to the test pilot's piloting skills the machine was saved and the defect was corrected. Because at the same time the machine was also blamed for the lack of communication between instructor and student, a large number of reception failures and the short range of the radio station, the machine was returned to correct these deficiencies.

Once these had been eliminated, there was finally nothing to prevent the La-7UTI from being introduced into series production to supplement the large number of La-5UTIs in use in flight training schools until then.

https://www.airwar.ru
war.ippk.ru/projects/19/2.htm

foto+výkres

Maličká poznámka k onomu "nadměrnému zvýšení teploty" v pilotním prostoru. Ruské prameny uvádějí, že původní podoba způsobovala teploty cca 50 stupňů. Po úpravě se pohybovaly v rozmezí 15 - 30 stupňů.