Chizhevskiy BOK-5 flying wing prototype (TsKB-13)

Less known than the Kalinin prototypes of the same period, the BOK-5 was a single-engined flying wing aircraft with a semi-monocoque fuselage, originated at the Byuro Osovykh Konstruktsiy (Bureau of Experimental Aircraft). The project was led by Vladimir Antonovich Chizhevskiy and aimed at developing trailing edge controls for tailless aircraft. With a wingspan of 9.86 meters (32 ft 4 in) and a length of 4.365 meters (14 ft 4 in) the BOK-5 was quite a small machine. It was powered by a Mikulin M-11 engine, which drove a two-blade propeller and developed 100 hp during cruise. Although the aircraft's structure was metallic (aluminum or dural, depending on the source), the flying surfaces were fabric-covered for the most part. The landing gear was fixed, with a tailskid.

Funding for the BOK-5 was granted in 1935 and the aircraft was completed in early 1937, but flight-testing was delayed because of last minute adjustments. Pilot I.F. Petrov finally flew the prototype during the fall but had a landing incident which partly damaged it. After repairs and more improvements, the plane revealed itself as an easy-to-fly and very good machine, and suggestions were made to develop a long-range tailless heavy bomber from it, the BOK-6 (also known as the TB), but nothing came of it, and despite its virtues, the BOK-5 never led to a production version. The BOK was eventually absorbed into OKB Sukhoi in 1940.

General characteristics

• Crew: 1
• Length: 4.365 m (14 ft 4 in)
• Wingspan: 9.86 m (32 ft 4-1/4 in)
• Wing area: 23.15 m2 (249 ft2)
• Empty weight: 596 kg (1,314 lb)
• Gross weight: 764 kg (1,684 lb)
• Powerplant: 1 × M-11 5-cyl radial, 74.6 kW (100 hp)

Performance

• Maximum speed: 174 km/h (108 mph)
• Range: 600 km (373 miles)
• Service ceiling: 4,850 m (15,900 ft)

Main sources

• The Osprey Encyclopaedia of Russian Aircraft 1875–1995, by Bill Gunston, Osprey
• History of the Smolensk aircraft plant: http://www.smaz.ru/eng/root/history.php
• http://www.airwar.ru/enc/law1/bok5.html
• Secret Projects - Flying Wings and Tailless Aircraft by Bill Rose, Midland
• A beautiful scale model online: http://vvs.hobbyvista.com/Modeling/BuroOsobikhKonstruktsij/BOK-5/Scratchbuild/Stern/index.php
• An R/C model online: http://forum.rcdesign.ru/f82/thread211189-2.html#post2219853

Decades later Chizhevsky suggested using BOK-5 as aerobatic aircraft for DOSAV / DOSAAF (Voluntary Society for Assistance to the Army, Air Force and Navy). Supposed to use a more powerful AI-14.(260 hp)

Thanks for the info, borovik! Was it actually flown aerobatically at all?

Wonder what became of the prototype in the end...

From Samolety mira (Aircraft of the world) magazine, July-December 2001:

Many info on the BOK-5 is here: http://propjet.ucoz.ru/forum/9-17-3,
and here: http://scalemodels.ru/modules/forum/viewtopic_t_31978.html

Some more photos...

Smashing, folks! Thank you so much.

And here is a color profile showing the most unusual scheme that appears in some photos. Any explanations for it?

In the summer of 1937 one of two BOK-5, took part in a parade in Tushino and for this purpose (and then only at a certain stage of his career) was painted by a-la Firebird. The correctness of color reproduction, we can only guess ...)) http://vvs.hobbyvista.com/Research/BOK/BOK-5/index.php

borovik said:

In the summer of 1937 one of two BOK-5, took part in a parade in Tushino and for this purpose (and then only at a certain stage of his career) was painted by a-la Firebird. The correctness of color reproduction, we can only guess ...)) http://vvs.hobbyvista.com/Research/BOK/BOK-5/index.php

Click to expand...

Interesting, thanks. Is it for the same reason that the Kalinin K-12 was painted like a bird, too?

borovik said:

In the summer of 1937 one of two BOK-5, took part in a parade in Tushino and for this purpose (and then only at a certain stage of his career) was painted by a-la Firebird.

Click to expand...

A little correction: it was in 1938. The aircraft was flown by NII VVS test pilot, captain Vladimir Datsko. This was a part of official (state) flight trials of 2nd BOK-5 prototype which took part at NII VVS Experimental aircraft division since August 15 to September 19, 1938.

The first prototype passed through joint flight trials (Zavod No.35 and NII VVS) since August 31 to September 27, 1937; its leading test pilot was renowned Mikhail Nyukhtikov.

Stargazer2006 said:

Interesting, thanks. Is it for the same reason that the Kalinin K-12 was painted like a bird, too?

Click to expand...

Yes, sort of. Both aircraft were painted in such way for Tushino Air Parade, but K-12 actually in 1937 while BOK-5 a year later.

borovik said:

The correctness of color reproduction, we can only guess ...))

Click to expand...

Here is another color interpretation of this weird painting scheme...

I had seen some b/w pictures before of BOK-5, I never realized it was this colourful. Very nice. Alexander, Stéphane: thanks!

I am pretty confused about the wing control surfaces. From google's translation of the russian from airwar.ru it sounds like the junkers type surfaces are the elevons whilst the controls attached to the wings seem to be the flaps.


Can anyone confirm if this is the case?

hole in the ground said:

I am pretty confused about the wing control surfaces. From google's translation of the russian from airwar.ru it sounds like the junkers type surfaces are the elevons whilst the controls attached to the wings seem to be the flaps.

Can anyone confirm if this is the case?

Click to expand...

The red parts are ailerons. The blue parts are elevators.

The yellow parts are deflectable part of the wing, which could be swiveled by the pilot on angle from +3 to -5 deg. for longitudinal trim of the aircraft. These parts served the function of horizontal stabilizer, and were called “suspended stabilizer”.

Ah! Thank you very much!

Found another beautiful plan of the BOK-5 in Sovietskiye Samolyete, by I. K. Kostenko (1973):

And another one from an old Soviet book: