The window shade fighter

The airplane wing is one of the most necessary and vexing parts of an aircraft. And for most of the century after the Wright brothers’ first flight, aircraft designers tried to solve the problem of how to design a wing that would be efficient at both low and high speeds. It was a quest that one designer dubbed “how to fool Mother Nature and the laws of physics.”

The modern solutions have been discussed in previous articles – variable geometry wing (F-111B) and the variable incidence wing (XF-91, F8U-3) – but other solutions go back much further, including flapping wings in the early part of the 20th century.

To solve the problem of making a wing large enough to generate a great deal of lift for takeoff and landing but having same wing low drag – small and thin – for cruise and high speed was taken on in the early 1930s in the Soviet Union’s Leningrad Scientific Research Aero Institute. Designer Grigorii I. Bakshayev had a novel idea about how to develop such a wing.

He designed a wing that had a high aspect (thin) center section and a larger wing in a shell around it that was literally cranked out for takeoff and landing and then cranked into the fuselage for normal flight. This outer wing shell, in essence, worked like a folding telescope.

The wing, called “Razdvizhnoe Krylo,” or extending wing, or more informally, “Matroshka,” after the Russian nesting dolls, was built into a simple two seat wooden conventional monoplane with fixed landing gear. This prototype technology demonstrator was flown successfully a number of times in 1937 with the observer cranking the six sections of the wing in and out. This process took about 37 seconds and increased the wing area by 50 percent.

The demonstrator performed well and was eventually shown to Soviet dictator Joseph Stalin, who became very enthusiastic about the concept and ordered it put into a fighter designated the RK-I (“Istrebitl,” fighter) with the “most powerful engine available,” the new VK-106 of 1,600 horsepower.

A prototype was built with the fuselage very much like a conventional fighter, but instead of the single wing of the technology demonstrator, the RK-I had two thin wings mounted in tandem and a hydraulically operated telescoping wing section that would move out and back to fill in the gaps between the two wings. This “window shade” arrangement allowed the ailerons on the trailing edge of the wing to remain clear.

This was a very dubious concept since, with the “shade” retracted, the downwash from the forward wing would probably have cut off the lift to the rear wing in some stages of maneuvering flight.

In the event, there were major delays with the VK-106 engine and was eventually cancelled. Since no one dared put any engine in the RK-I except the one Stalin demanded, the prototype languished in the fabrication shop. Stalin seems to have forgotten about the project, and it was eventually abandoned.

Readers may note that the old Soviet Union produced some of the most exotic (OK, weird) aircraft in aviation history. But it is unfair to mock these designs because many of them were aircraft that were on Western drawing boards – or in the heads of Western aircraft designers – but never made it to the prototype stage.

This was because in the West, these prototypes had to be paid for – either by the national government (usually) or by the aircraft company itself, so the project had to show real potential.

The Soviet Union, on the other hand, had a system of design bureaus whose responsibility was to design aircraft, either to meet government specifications or to follow ideas they thought were interesting.

Most importantly, given the convoluted state-controlled economy in the Soviet Union, the prototypes were, in essence, free. This meant the Soviet designers could build technology demonstrators that would never have seen the light of day in the West.

Interestingly, the Soviet’s large number of “unusual” prototypes produced few innovative production aircraft. Indeed, one is struck by how conventional Soviet production aircraft, military and civilian, were during its entire existence. The only innovations that reached full scale production were, for the most part, copies of Western designs, with a few notable exceptions like the Tu-95 Bear.

For questions or comments, e-mail Dr. Michel at marshall.michel@ramstein.af.mil.