During the interwar years, many countries invested in the development of tailless and flying wing
aircraft designs, and the Soviet Union was no exception to this. Several radical designs were
built and tested during the 1920s and 1930s, and today we are looking at the Kalinin K-12.
Konstantin Kalinin was no stranger to unconventional aircraft designs,
at the beginning of the 1930s he had designed and built the colossal K-7,
which we covered in an earlier video, and it should come as no surprise that he, too,
was toying with the idea of a flying wing or tailless aircraft design.
In 1933, he drew up plans for a new bomber aircraft and submitted three different
proposals to the VVS Scientific Test Institute. Two of these designs looked suspiciously normal,
one was a conventional monoplane, and the other was a twin-boom design with twin engines,
but the third was a more adventurous tailless design. Appreciating that multipurpose
aircraft had a higher chance of receiving approval in during a time of tight budgets,
Kalinin also included plans for the aircraft to be converted to a transport for civilian use.
After some deliberation, the tailless design was chosen as it boasted a lower overall weight,
as well as reduced drag characteristics compared to the other two models,
and Kalinin received approval to develop a prototype that would be designated as the K-12.
Initially, development work began with the construction of scale models that were to be used
in wind tunnel tests. Though tailless designs had been tried before in the Soviet Union, less than a
handful had actually been built, and Kalinin had to make doubly sure that his design would fly,
and fly well. The last thing he wanted was to attract the ire of his superiors, and with Stalin
being especially trigger-happy with his recent purges, the risks for Kalinin were pretty high.
During the early stages of development work, Kalinin had to try his best
to both resist official pressure to develop the plane as fast as possible,
whilst also at the same time keeping ahead of the competition,
as Rival designer Cheranovsky was also working on a tailless design of his own.
Once the wind tunnel tests had concluded that Kalinin’s design should fly, and fly safely,
work then began on a half-scale manned glider. This had a wingspan of 9 meters and a length of
5.2 meters. It was constructed mainly from wood and fabric, and it was equipped with a fixed
undercarriage comprising of two main wheels and a tail skid. The wings had a relatively
high chord-thickness ratio and were completed in two sections, the inner section was flat,
and the main spars connected with the mounting points for the fixed landing gear,
the lower section of the outer wing tapered down in thickness towards the wingtip,
upon which was mounted the horizontal stabiliser and rudder. Running along almost the entire
trailing edge of the wing were a series of slats -for added stability- and the ailerons, of which
the inner pair could apparently act as flaps, but treat that with a pinch of salt as I could only
find one particular source that claimed that. The k-12 Glider was complete by early 1934,
and during the following 12-18 months over 100 successful test flights were completed
with test pilot Borisov at the controls. It seems that there was space for both a pilot
and an observer on this aircraft, but whether an observer ever flew on it is unknown. Almost
no information survives about the Glider or its test flights, but it can be safely assumed that
they must have mostly gone well as construction on a full-scale prototype began in early 1935.
Unlike the glider, this aircraft was completed with a frame that was built from Chromansil
steel, however the majority of the wing and fuselage surface was still fabric covered. Some
drawings seem to hint at an all-metal design as well, but for reasons we
will shortly cover this never eventuated. There was provision for a three-person crew:
a pilot in an closed cockpit that sat above the wing leading edge, a bomb aimer in the nose who
could also operate a forward facing gun, and a rear gunner. The intended defensive armament
was two single 7.62mm ShKAS machine guns, however these were never installed on the prototype.
It had been intended to power the K-12, which was also now known as the BC-12, with a pair of
9-cylinder M25 radial engines, which was a licence-built version of the Wright R-1820-F3
Cyclone. But these were not available when the K-12 was nearing completion,
and so it was fitted with a pair of M-22s instead,
which themselves were a licence-built version of the Bristol Jupiter.
Though they developed 435hp, they were deemed underpowered for the task of getting the K-12
into the air, but with no alternative available the design team had to significantly lighten the
prototype before its first flight. This meant that the planned machine guns were never fitted,
and the undercarriage – which had been planned to be retractable – was installed as a fixed
unit instead. Along with some other changes that involved removing unnecessary equipment from the
cockpit and bomb aimers station, the aircraft’s take-off weight was lowered to the point where it
was hoped that the engines would bear it, and the first flight took place in July of 1936.
Thankfully the engines did bear it, and after a few more flights to confirm that it was
reasonably safe, the aircraft was flown to Moscow in October to undertake trials with the VVS.
During these trials, the test pilots gave it a mixed review, with the main complaints being that
the central fuselage was too large, and its poor aerodynamics negated the benefits of the tailless
design. They concluded by asserting that even with the installation of more powerful engines
and a retractable landing gear, the k-12 would not be able to outperform conventional aircraft.
This, along with the outbreak of the Spanish Civil War and the general heating-up of
tensions throughout Europe, prompted the VVS to cancel development of the K-12 in
favour of more conventional designs, such as the DB-3. This was also helped by several political
opponents of Kalinin, who had the ears of several well-placed members within the soviet air force.
Kalinin’s prospects briefly revived in 1937 when the K-12 was allowed to fly in the Tushino
Air Day Demonstration. For this it had been repainted in a strikingly bright colour scheme,
representing that of a fire bird, and supposedly this impressed several senior
officials who demanded a resumption of testing and pre-production work.
What follows on from this differs depending on what source you’re reading,
and honestly the clarity on these events feels about as thick as mud. That being said, I shall
attempt to provide a balanced explanation. One version of the story goes as follows:
When the program was originally cancelled in, the factory in which the K-12 had been built,
factory number 18, had its resources re-assigned to the production of the DB3 long range bomber.
However, Kalinin took advantage of his position as chief designer, and he diverted some of the
factory’s resources back to the development of a small production series of 10 K-12 bombers.
Because of this, the production of the DB-3 at the factory was affected and Kalinin was
investigated for manipulation of state resources. He was subsequently arrested by order of Stalin,
sentenced, and shot on the same day: October 22nd 1938.
The other version of the story states that the production of 10 K-12s had indeed been authorised
by senior officials, who had been impressed by the aircraft’s demonstration. This had
angered Kalinin’s rivals, who had hoped that the project’s cancellation would put him out business,
and they conspired to get him arrested on trumped up charges of spying – for which he
was arrested by order of Stalin, sentenced, and shot on the same day…however this source puts
the date of his execution in 1940, which seems to conflict with most other sources,
which by dint of accuracy makes the previous story the more likely scenario.
The true story behind Kalinin’s death may never be fully known, but it is clear that the 10
incomplete models of the K-12 were scrapped, and the Kalinin design bureau was disbanded.
Before his death, Kalinin had hoped his tailless aircraft would lead on to more advanced designs,
such as his envisioned K-14 medium bomber, and the even larger four-engine K-17,
but this would never come to pass, and so ends the story of the Kalinin K-12.