True or not, Japanese site says that there were three prototypes for Pashinin I-21.
No.2 prototype : modify wing plan shape.
No.3 prototype : 1.5m shortened wing span.
No.3 prototype.
http://forum.valka.cz/topic/view/33611/Pasinin-I-21-3-prototyp
"The aircraft was designed as a low-wing monoplane of mixed construction, the front part of the hull was welded from steel tubes and the surface was of Duralumin panels. The rear portion was made up of a shell of variable thickness of plywood (1.5-3 mm). The wings were straight, the entire wing leading edge through two steel beams, ribs were aluminium alloy and to them was bolted on překližkový surface, plywood was once again a variable thickness. The landing gear was retractable, he turned 90 ° and is pulled to the rear flat into the wings. M. m. Pašinin so went an entirely different path than his former boss n. n. Polikarpov, which has long sought to improve the original I-16.
With the construction of the prototype was begun in the fall of 1939, and construction took approximately half a year. Delivery 11.07.1940 test pilot P. U. Fokin performed the first take-off and 18. August of this year, the prototype was brought to the air in long-legged version, at that time already took place, during which the State exam, the I-21 piloted test pilots Suprunem and Štěfanovskim. Both pilots have criticized the longitudinal instability of the prototype. This instability was removed from the second prototype by modifying the wings, it was straight from the center of the bent backward. The flight characteristics of the aircraft were significantly better, even with a weak engine VK-105P has reached a decent top speed – 573 km/h at an altitude of 5000 m.
In January 1941 was completed the third and final prototype, šípovitost wing, leaped at the end arches were removed, this will reduce the margin and reciprocally and wing area. Tests of this airplane started from 5. April 1941 and lasted until June of this year. By reducing the load-bearing surfaces of the aircraft's behavior worsened and especially during take-off and landing, and it was ultimately the reason why it was rejected, and it was not included in the State examinations. Race # 21 was at that time under the authority of s. a. Lavočkinovi, and it was also the end of the Pašininovu OKB and the entire project I-21 was canceled."
I'm not sure drawings title by me are correct or not. Some site says that top drawing shows No.3 prototype aircraft. https://military.wikireading.ru/8043
To increase longitudinal stability, air center was moved to rearward direction?