Aviation of World War II
In 1939, a former employee of the NKAP Mikhail Mikhailovich Pashinin, shortly after being appointed chief designer of the Design Bureau of Plant No. 21, proposed to develop a fighter with an M-105 engine. A small team of the design bureau in the fall of 1939 presented the customer with a preliminary design of the IP-21 (Pashinin fighter of plant No. 21 or I-21).
If the I-180 was a deep modernization of the I-16 by installing a new two-row air-cooled engine M-88, then the I-21 fighter was a deep modernization of the same I-16 by installing an M-105 liquid cooling motor. Thanks to this approach to design, 60-70% of the parts and assemblies of the new fighter were similar or directly identical with the I-16 parts, which, in turn, promised the possibility of rapid deployment of the I-21 serial production.
M.M. Pashinin was the first to propose a wing with a symmetrical torque-free airfoil NACA-0012-0009 (at the ends) for a fighter. The use of such a wing made it possible to develop a speed in a dive - up to 950 km / h according to the conditions of the strength of the wing, (in reality, flight at such speeds, already close to the speed of sound, would be impossible under the conditions of ensuring longitudinal stability). The very idea of achieving a high dive speed was completely relevant and corresponded to the general trend of transition from combat maneuvering in turns to dynamic vertical maneuver. *
According to the calculations of the OKB designers, the takeoff weight did not exceed 2400 kg. It was expected that the maximum speed at the ground would reach 523 km / h, and at an altitude of 5000 m - 613 km / h (the specialists of the Air Force Research Institute believed that it would not exceed 605 km / h). The use of jet pipes, which created additional thrust, was considered a reserve for improving the speed characteristics. The practical ceiling was estimated at 10,400 meters, and the climb time of 5,000 meters was 4.75 minutes.
In the future, to improve flight data, it was planned to install turbochargers and more powerful engines M-107 or M-120 on the I-21.
Construction I-21 is a single-seat fighter of a standard low-wing design. The design is mixed. Monocoque fuselage, glued from 0.5 mm veneer on a solid blank; pine frame, frames of the I-16 type from bent slats; wall thickness 3.0 mm with a decrease in the tail to 1.5 mm. The front part of the fuselage is a transitional truss made of steel pipes. The wing spars are the same as in the I-16, the ribs are duralumin, the wing sheathing is plywood from 3.0 mm in toe to 1.5 mm on aluminum rivets in a blind. Removable wooden keel, one-piece stabilizer, rudders and ailerons of the I-16 type. Management is tough. The cockpit without bulletproof glass.
Armament: one ShVAK cannon, firing through the propeller hub, and two ShKAS machine guns with 190 and 500 rounds of ammunition per barrel, respectively.
The design was very light and rational. A rare for 1940 advantage of the I-21 was the drop-shaped cockpit canopy, which provided all-round visibility.
* Dynamic modes based on the transformation of altitude into speed and speed - into a maneuver (dive followed by a combat turn or hill), require low aerodynamic drag (so that kinetic energy is not wasted on heating the air) and low evolutionary speed (the efficiency of the dynamic maneuver is determined by the difference between the squares of the maximum and evolutionary speeds).
July 11, 1940 pilot P.U. Fokin tested the I-21 in flight. In August, the car was shown at an air festival in Tushino and then transferred to state tests. The aircraft proved to be longitudinally unstable and was returned to the factory for revision. At the same time, a tendency to stall on the wing at high angles of attack was revealed, which was the reason for the development of a new wing, at the ends of which automatic slats were located.
According to preliminary data obtained in the fall of 1940, the maximum speed of the prototype at the ground reached 628 km / h, and the flight range was 780 km.
Unlike the military, Pavel Ulyanovich Fokin believed that during the takeoff run, the plane had no tendency to turn, the rudders obeyed well, and its takeoff and landing were much easier than that of the I-16.
It seems that the NKAP considered the car promising, and at the end of September the People's Commissar A.I. Shakhurin ordered to build a couple of more experienced fighters. On them it was ordered to eliminate all the shortcomings identified earlier, and on the fourth - to also place reinforced weapons.
Repeated state tests of the fighter ended on the eve of 1941, but their results were depressing. In addition to the previously identified defects, it turned out that the speed of the I-21 did not exceed 573 km / h, and other characteristics also worsened.
The second copy of the I-21 was also built with the M-105P engine instead of the planned M-107. Its factory tests were completed in October 1940.
The third copy of the I-21 was built in January 1941 and made its first flight on April 5. It had a modified wing and more powerful armament (instead of a 20 mm ShVAK cannon, a 23 mm BT-23 cannon was installed).
By order of the NKAP of November 10, 1940, the OKB S.A. was transferred to the plant number 21. Lavochkin. The same document instructed the enterprise to complete the refinement and testing of the third I-21, in May - June of the next 1941 the aircraft was tested at the LII. The conclusion on the test results was sent by the leadership of the Flight Research Institute to the Deputy People's Commissar for Experimental Aircraft Building A.S. Yakovlev. It noted:
“The I-21 was tested twice at the Air Force Research Institute, where defects were found, due to which, without completing the tests, it was returned to the designer for fine-tuning. For the third time, the I-21 with improvements was presented for control tests at the Flight Research Institute, as a result of which the main conclusions of the Air Force Research Institute were confirmed. "
As a result, the specialists of the Flight Research Institute decided that the I-21 should not be transferred for state tests. So the last point in the history of this fighter was put.