Biggles and friends encounter large Russian bombers on several occasions during their sojourn in Finland in Biggles Sees It Through. Johns was not specific about the aircraft type but there is enough description in the text to narrow done the chocies.
Russia used three bomber types during the Finnish WInter War: the Ilyushin DB-3, the Tupolev SB series, and the Tupolev TB-3. Of these, the most likely candidate is the TB-3 four engine heavy bomber.
For one thing, Biggles in Chapter 6 says of the bomber that it is too big for four of them to handle. The SB and the DB-3 were of the same weight and class as their own Bristol Blenheim and would therefore have been easily managed. On the other hand, he says he saw the ground crew using tractors to haul the Russian bombers--a procedure which would certainly be needed for the massive 11 ton four engine TB-3.
Then again, in Chapter 3, a flight of 5 of these bombers discharge some 50 Russian paratroopers. This is historically accurate. The TB-3 was actually used for the transport of Russian paratroops and given its size, each of the five could easily carry a stick of 10 jumpers. In Chapter 8, Ginger has to climb out on the wing and onto the fuslage to signal to Eddie Hardwell that he was surrendering. This was plausible--the routine procedure for a paratrooper on a TB-3 was to climb out onto the wing and drop off the inboard trailing edge.
Eddie Hardwell calls the bomber a "pantechnicon"--a term which would certainly suit the ungainly, antiquated appearance of the TB-3 with its open cockpit and large (sometimes double) fixed main undercarriage wheels.
Ginger shoots a TB-3 down towards the end of the story.