Editing Polikarpov I-16 (section)

==Design and development==
While working on the [[Polikarpov I-15]] biplane, [[Nikolai Nikolaevich Polikarpov]] began designing an advanced monoplane fighter. It featured cutting-edge innovations such as retractable landing gear and a fully enclosed cockpit, and was optimized for speed with a short stubby fuselage, and a [[Wright R-1820]] radial engine in a [[NACA cowling]]. The aircraft is small, light and simple to build.{{Citation needed |date=December 2015}}

Full-scale work on the '''TsKB-12''' prototype began in June 1933, and the aircraft was accepted into production on 22 November 1933, a month before it took to the air. The TsKB-12 was of mixed construction, using a wooden monocoque fuselage and wings employing a KhMA chrome-molybdenum steel alloy wing spar, dural ribs and D1 aluminum alloy skinning on the center and leading edges, with the remaining portions of the wings fabric-covered. Another modern feature were the [[aileron]]s which ran along almost the entire trailing edge of the wing and also operated as flaps (in the manner of more modern [[flaperon]]s) by drooping 15°. The cockpit was covered by a 40-centimetre-wide (16&nbsp;in) canopy which featured an Aldis-type tubular gun sight which could slide back and forth on runners fitted with rubber bungee cords.  A 225&nbsp;L (59.4&nbsp;US gal) fuel tank was fitted directly in front of the cockpit. The main [[landing gear]] is fully retractable by a hand crank. The armament consisted of a pair of [[7.62×54mmR]] (0.30&nbsp;in) [[ShKAS machine gun]]s in the wings, mounted on the outboard side of the main gear and 900 rounds of ammunition.<ref>Gordon & Dexter 2002, pp. 16–17</ref> 

These features were proposed at first by [[Andrei Tupolev]]; however, the NII VVS (Air Force Scientific Test Institute) was more concerned about the stresses a typical combat aircraft was subjected to in combat, and initially considered the risk too great. However, [[TsAGI]], with the help of the 3rd Design Brigade under the leadership of [[Pavel Sukhoi]] and [[Aleksandr Putylov]], eventually convinced NII VVS that what was being proposed was not only feasible, but would enhance the aircraft's performance.{{Citation needed |date=December 2015}}

The TsKB-12 was designed for the [[Wright R-1820 Cyclone|Wright Cyclone SR-1820-F-3]] 9-cylinder radial engine (rated at 529&nbsp;kW/710&nbsp;hp); a license to build [[Shvetsov M-25|this engine]] under the supervision of the [[OKB#OKBs in aerospace industry|OKB-19]] [[Shvetsov]] design bureau in the [[Soviet Union]] was being negotiated. As the license was not yet approved, Polikarpov was asked to settle for the less powerful M-22 (Soviet-built version of the Gnome-Rhone Jupiter 9ASB, which itself was a licensed version of the [[Bristol Jupiter]] VI) with 358&nbsp;kW (480&nbsp;hp). This was deemed acceptable because the projected top speed still exceeded 300&nbsp;km/h (185&nbsp;mph).<ref>Gordon & Dexter 2002, pp. 14, 16</ref> 

The M-22-powered TsKB-12 first took to the air on 30 December 1933 with the famous Soviet test pilot [[Valery Chkalov]] at the controls. The second TsKB-12, with a Cyclone engine and three-bladed propeller, flew in January of the following year. Initial government trials in February 1934 revealed very good maneuverability, but the aircraft did not tolerate abrupt control inputs.  Thus the TsKB-12 was deemed dangerous to fly and all [[aerobatic]]s were forbidden. The M-22 version was preferred due to the vibration of the Cyclone-powered aircraft. Pilots commented early on about the difficulty of climbing into the cockpit, a trait that persisted through the I-16's service life. Before continuing test flights the designers had to answer the question of spin behavior. [[Wind tunnel]] testing suggested that the TsKB-12, with its short tail, would enter an unrecoverable [[spin (flight)|spin]], but real-life trials were necessary to confirm this. Since Cyclone engines were rare, it was decided to risk the M-22 prototype for this purpose. On 1 and 2 March 1934, Chkalov performed 75 spins and discovered that the aircraft had very benign stall behavior (dipping a wing and recovering without input from the pilot when airspeed increased) and intentional spins could be easily terminated by placing the controls in the neutral position.<ref>Gordon & Dexter 2002, pp. 17–18</ref>  The stories of vicious spin behavior of the I-16 perpetuated in modern literature is unfounded (perhaps extrapolated from [[Granville Gee Bee Model R Super Sportster|Gee Bee]] experience). {{Citation needed|date=October 2012}} In fact, the I-16's stablemate, the [[biplane]] [[Polikarpov I-153]], exhibited much worse spin characteristics. {{Citation needed|date=October 2012}}

Service trials of the new fighter, designated '''I-16''', began on 22 March 1934. The M-22 prototype reached 359&nbsp;km/h (223&nbsp;mph). The pioneering presence of a complex, triple-strut manually retracted main landing gear design was prone to jamming and required considerable strength from the pilot, who directly operated the rearmost strut's upper end, moved with a manually turned jackscrew running spanwise within the wing structure, to "slide" outwards and inwards on each side to respectively get the main gear retracted and extended, with the main strut (the forward-most of the trio) needing to shorten its length during its retraction to fit the mainwheel into the lower fuselage, performed by the middle-location strut's geometric arrangement and pivot locations.<ref>[http://www5a.biglobe.ne.jp/~t_miyama/po16leg.html Animation of the I-16's maingear retraction cycle]</ref> Most of the test flights were performed with the gear extended. On 14 April 1934, the Cyclone prototype was damaged when one of the landing gear legs collapsed while it was taxiing.<ref>Gordon & Dexter 2002, p. 18</ref> On 1 May 1934, the M-22 prototype participated in the flyover of [[Red Square]].<ref>Gordon & Dexter 2002, p. 18</ref> Approximately thirty I-16 Type 1 aircraft were delivered, but were not assigned to any [[Soviet Air Forces|VVS]] fighter squadron. Most pilots who flew the I-16 Type 1 for evaluation purposes did not find the aircraft to have many redeeming characteristics. Regardless of pilot opinion, much attention was focused on the Cyclone-powered aircraft and the M-25 (the license-built Cyclone). 

The third prototype with a Cyclone engine incorporated a series of aerodynamic improvements and was delivered for government trials on 7 September 1934. The top speed of 437&nbsp;km/h (270&nbsp;mph) no longer satisfied the Air Force, who now wanted the experimental [[Nazarov M-58]] engine and 470&nbsp;km/h (290&nbsp;mph). Subsequently, the M-22-powered version entered production at Factory 21 in [[Nizhny Novgorod]] and Factory 39 in [[Moscow]]. Because it was the fourth aircraft produced by these factories, it received the designation '''I-16 Type 4'''.<ref>Gordon & Dexter 2002, p. 21</ref>  Aircraft fitted with these new engines required a slightly changed airframe, including armor plating for the pilot and changes to the landing gear doors (particularly, the hinged lower mainwheel door)<ref>[http://www5a.biglobe.ne.jp/~t_miyama/po16cov.html Animation of the I-16's lower mainwheel door mechanics during retraction]</ref> to allow for complete closure.

The M-25 fitted I-16, the I-16 Type 5, featured a new engine cowling which was slightly smaller in diameter and featured nine forward-facing, radially-set shuttered openings to control cooling airflow, a redesigned exhaust with eight individual outlet stubs, and other changes. The M-25 was rated at 474&nbsp;kW (635&nbsp;hp) at sea level and 522&nbsp;kW (700&nbsp;hp) at 2,300&nbsp;m (7,546&nbsp;ft). Due to the poor quality of the canopy glazing, the I-16 Type 5 pilots typically left the canopy open or removed the rear portion completely. By the time the Type 5 arrived, it was the world's lightest production fighter (1,460&nbsp;kg/3,219&nbsp;lb), as well as the world's fastest, able to reach speeds of 454&nbsp;km/h (282&nbsp;mph) at altitude and 395&nbsp;km/h (245&nbsp;mph) at sea level. While the Type 5 could not perform the high-G maneuvers of other fighters, it possessed superior speed and climb rates, and had extremely responsive aileron control, which gave it a very good roll rate, which led to precision maneuvers in loops and [[split-S]]s.

A total of 10,292 single-seat aircraft were produced between 1935 and 1942; the number of two-seat trainer variants produced varies between 843 and 3,189.<ref>Gordon & Dexter 2002, p. 55</ref>