soviet experimental aircraft

Simple Flying

The kalinin k-7 - russia's experimental flying fortress.

Your changes have been saved

Email is sent

Email has already been sent

You’ve reached your account maximum for followed topics.

History: Why Did Continental & United Airlines Agree To Merge?

What happened to air new zealand's mcdonnell douglas dc-10s, alaska airlines flight 261: 5 shocking facts about the tragedy over the pacific ocean.

Twin-boom aircraft are something of an unknown quantity in contemporary aviation. However, this striking design was more common in the early to mid-twentieth century. In fact, one of the largest aircraft constructed before the 'jet age' featured this characteristic structure. This was a Soviet experimental aircraft constructed in the early 1930s, known as the Kalinin K-7.

Design and specifications

Sporting a twin-boom fuselage and conspicuous underwing pods, Konstantin Kalinin designed the K-7 experimental aircraft in the early 1930s. Construction on the first (and only) example began in Kharkiv in 1931. Today, this location represents Ukraine 's second-largest city. The construction process took two years, and the Kalinin K-7 eventually first flew in August 1933.

Alongside its twin-boom structure, War History Online also reports that the K-7 boasted a conspicuously large wingspan of 53 meters. This was almost twice the length of the aircraft (28 meters). These wings were 2.3 meters thick and had a surface area which outranks that of the Boeing B-52 Stratofortress (454 vs. 370 square meters).

The K-7's height measured 12.4 meters. Six wing-mounted Mikulin AM-34F V-12 propeller engines provided the majority of the aircraft's power. Each of these could deliver up to 750 horsepower. A seventh 'pusher' engine was located at the rear of the aircraft. The resultant performance figures for the K-7 were as follows:

• Speed -  225 km/h / 140 mph
• Service ceiling - 4,000 meters / 13,000 feet
• Empty weight -  24,400 kg
• Loaded weight -  38,000 kg

Stay informed:  Sign up for our  daily aviation news digest .

Operational versatility

Kalinin designed the K-7 to be a versatile aircraft that could suit a number of purposes. Primarily, it had a military function, with the underwing landing gear pods also housing machine gun turrets. According to migflug.com , it could also carry 9.6 tons of bombs in this configuration. For such missions, the aircraft required 11 crew members.

However, the K-7 could also be configured for use in civilian/troop transport missions. Using seats located in its aforementioned 2.3-meter thick wings, it could carry 120 civilians or 112 paratroopers alongside its 11 crew members. This also left space for seven tons of cargo, such as mail.

A short-lived design

Avgeeks today continue to be fascinated by the majesty of larger aircraft. Indeed, the heaviest aircraft ever built, the Antonov An-225 'Mriya,' is also a Ukrainian design. However, aesthetic appeal does not always translate to commercial success. For example, we have recently seen this with the demise of the Airbus A380 . Unfortunately, this was also the case for the Kalinin K-7.

Between August and November 1933, the K-7 made just seven test flights. The last of these, on November 21st, ended abruptly when a structural failure in one of its two booms caused the aircraft to crash. 14 crew members died in the accident, as well as one person on the ground.

There has since been extensive speculation regarding the potential of sabotage regarding the aircraft's crash. While two further prototypes were ordered, they were never finished. The Soviet Union ultimately canceled the project in 1935, before these new aircraft could reach completion.

The K-7's designer, Konstantin Kalinin, had been a First World War pilot before he became an aircraft designer. While only one example of the K-7 was produced, his smaller designs were more successful. 39 of his K-4 were built, as well as 260 of the larger K-5. However, according to Bill Yenne's  The Worst Aircraft Ever , Kalinin was executed aged just 51 in the Stalinist purges of 1938.

Nonetheless, to have constructed an aircraft capable of carrying 120 passengers just 30 years after the Wright brothers' first flight remains an impressive feat, perhaps regardless of the type's ultimate failure.

• Skip to primary navigation
• Skip to main content
• Skip to primary sidebar

Warrior Maven

Center for Military Modernization

Military History: Russia’s Innovative Su-47 Fighter Jet

The Su-47, was an experimental aircraft designed for the Soviet Union in the 1990s. Called the Berkut it is highly recognizable due to its wings, which are swept forward.

· June 26, 2023

by Maya Carlin, Warrior Contributor, Weapons

Meet the Su-47: The Su-47, previously designated the S-32 and S-37, was an experimental aircraft designed for the Soviet Union in the 1990s. Called the Berkut, or Golden Eagle, it is highly recognizable due to its wings, which are swept forward instead of aft and give the Berkut a very unique look.

In fact, experience from the Su-47 informed manufacturer Sukhoi’s development of the forward-swept-wing KB SAT SR-10 trainer.

Although the Su-47 does not fly the skies anymore, a number of its advanced technologies remain integral for Russia’s more modern fighters, including the Su-35 and  Su-57 fighter .

Su-47: Forward Sweep

As early as the 1920s and 1930s, aircraft designers became interested in forward swept wings.

Changing the geometry of wings can do many useful things aerodynamically and in the case of forward sweep, they allow for exceptional maneuverability and excellent control at slow speeds.

These advantages are not with counters, however.

Forward swept wings induce a great deal of aerodynamic instability in an aircraft.

Instead of wanting to return to straight and level flight, the Berkut and indeed any forward swept wing aircraft has a strong tendency to want to roll off one way or another requiring constant vigilance from the pilot.

In addition, sweeping the wings in this direction produces a great deal of stress on the wing, requiring very strong materials to prevent the wings from snapping.

These difficulties proved impossible to overcome early on. In the 1940s, Nazi scientists attempted to construct a bomber with forward swept wings; however, the materials of the time meant that the wings would be excessively heavy to make them strong enough not to fall off.

In the 1960s, a German manufacturer was able to develop a small forward-swept bizjet, the HFB-320, but it wasn’t until the ‘80s that a forward sweep was given to a military aircraft in the Grumman X-29.

The Su-47 first flew in the late ‘90s and immediately demonstrated the maneuverability of a forward-swept wing. Advances in computing technology allowed Sukhoi designers to include a sophisticated fly-by-wire system which helped eliminate the difficulties of an unstable aerodynamic design.

Two D-30F-11 turbojet engines powered the Su-47 , but was ultimately replaced by more sophisticated Al-41F thrust-vectoring turbofans.

As explained in an earlier 19FortyFive piece, “similarly to the F-16, the S-57 was so responsive it relied on a fly-by-wire system to automatically correct its aerodynamically unstable characteristics.”

What happened to the Su-47?

Ultimately, the breakup and fall of the Soviet Union doomed the Berkut . With a lack of financial support from the Russian Air Force, Sukhoi invested most of the design funds themselves.

While some of the technology from the Su-47 was incorporated in the 4.5 gen  Su-35 and fifth gen  Su-57 it was ultimately deemed unfit to be a standalone fighter and only one was ever built. While it was displayed at the MAKS airshow in 2019, it is now relegated to static roles as a demonstration of technical advancements.

Maya Carlin is a Senior Editor with 19FortyFive. She is also an analyst with the Center for Security Policy and a former Anna Sobol Levy Fellow at IDC Herzliya in Israel. She has by-lines in many publications, including The National Interest, Jerusalem Post, and Times of Israel.

More From Warrior Maven