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***image1***In the 1960s and 1970s, as noted in previous articles, trying for additional performance by “swinging” the wings of military aircraft was all the rage.
What is less well known is that in the late 1930s there was another attempt to increase performance by moving the wings, albeit in a seemingly much more radical way.
At that time, dual wing biplane fighters were being replaced by single wing monoplanes, even though the greater area of the biplane wings offered some significant advantages − slower landing speeds and much greater maneuverability, to name two − but for most of the world’s air force leaders, the lower drag of the single wing monoplane provided a much higher top speed, and this trumped maneuverability.
***image2***Nevertheless, two innovative Soviet designers, Vladimir V. Shevchenko and Vasili V. Nikitin, took up the challenge of trying to develop a “folding fighter,” one that could change its wing configuration from a biplane to a monoplane. The idea was accepted in November 1938, and the pair began construction of a “concept” prototype, the IS-1.
On the ground the IS-1 seemed to be a biplane with retractable landing gear, but the lower wing was hinged to the fuselage at the root. After takeoff, the pilot raised the lower wing with a hydraulic system; the lower wing retracted flush with the upper wing as the landing gear retraced into the fuselage, as shown in the pictures above. The entire process took less than 10 seconds.
The IS-1’s first in-flight transition from biplane to monoplane was made in June 1940, and the wings were folded and unfolded in flight without difficulty and with no handling problem. With this demonstration of the concept’s validity, a true fighter version, the IS-2, was quickly built. But, while the IS-2’s wing performed flawlessly, the extra weight of the retraction mechanism made its performance below that of standard monoplane fighters.
Nikitin proposed a much more powerful version, the IS-4, with not only the folding wing but also with another radical feature, tricycle landing gear.
Unfortunately, a new radial engine intended for the IS-4 was abandoned after severe development problems, and while the IS-4 was being modified for a new engine in mid-1941 the Germans invaded the Soviet Union. With the invasion, Stalin directed that all production efforts be directed towards conventional “frontal” aircraft, and the IS-4 was abandoned. Nikitin continued to work on even more advanced “folding fighters,” but none progressed beyond wind tunnel tests, and the world’s first variable geometry fighter faded into oblivion.
E-mail questions and comments to marshall.michel@ramstein.af.mil.
