Hmm... As I can see, such a version of the Stal-5 is mentioned only by foreign sources (especially B. Gunston's encyclopedia which I myself have never seen, but Wikipedia etc. refer on it). In
all Russian sources, the Stal-5 project is mentioned only as a 18-seat flying wing airliner. And that is not only in Shavrov's book first published in 1969 (see
http://www.eroplan.boom.ru/shavrov/chr10/civil/putilov.htm), but also in "100-year-long Flying Wing History" by Dmitry Sobolev, published in 1998.
The Stal-5 was projected by Alexander Putilov since 1933; in early 1934 (according to Shavrov) the mockup was approved and the wing spar for static stress tests was made. This spar featured with excellent quality and was even exhibited in Moscow Polytechnical Museum. Then it was decided, before construction of actual Stal-5 prototype, to test its unusual layout in flight. For this, the 1/4 scale piloted model was built and tested in 1935. But the results were not very exciting: the experimental aircraft appeared very stringent in control. The decision was that the airliner could not be safe enough, and the project was cancelled. Instead of it, Putilov created a single-engine, 5-seat Stal-11 with classic layout:
http://www.dmitray.narod.ru/stal11.htm.
The Stal-5 resembled something like Burnelli without tail booms. Its wingspan was 23 m, wing area 120 m2. The aircraft was powered by two Mikulin AM-34F engines, 860/900 hp each. Empty weight was about 5500 kg, takeoff weight about 8000 kg. You can see a
very rough 3-view at
http://www.eroplan.boom.ru/shavrov/chr10/civil/putilov.htm.
Unfortunatley I haven't seen any photos or pictures of experimental Stal-5 piloted model, although it was really flown. But it's known that it wasn't a direct copy of its big brother: the wing trailing edge was almost straight, and the tail fins were mounted on the wingtips. The wingspan was 6 m, wing area 15 m2; engines were two 45-hp Salmsons.
Maybe Gunston confused the Stal-5 with Chizhevsky BOK-6 project? It was also a flying wing with two M-34 engines - but BOK-6 was a bomber. It also was never built, and I have no more info on this project. Maybe
borovik knows anything more? ???