It's piston driven. Forgot to mention. @ChiChiWerx

The ultimate example of this design philosophy is the flying wing, which we haven't even discussed yet, but of which the K7's design reminds me. The B-2's ratio is 2.49:1(!) and it's 1950s predecessor, the YB-49 was even higher (note the wingspans were exactly equal--I can discuss that more in length later, if you're curious) at 3.24:1. Flying wings are considered the most efficient design yet, with a near total elimination of parasite drag and optimization of the lifting surface. In other words: aerodynamic efficiency. And not unique to any Russian designs, but driven purely by aerodynamic and physical realities, of which Russian designers were well aware.

The K7 has a ratio of 1.89:1, the DB2, can't find the dimensions, but I doubt it was more than 2:1...in any event, still a product of aerodynamic efficiency driven by low engine power and airfields that were smaller than modern airfields, often lacking even paved runways. The high ratio is not purely Russian design feature, as illustrated below, Voyager, U-2, C-47, and the B-18 all had this basic design...here's another contemporary design that had all the Russian drawbacks, low engine power, high weight, requirement to operate from the constrained airfields of the time, the Boeing XB-15. The XB-15's wingspan to length ratio is 1.7 to 1, close to even the K7's ratio. But that's the answer: low powered engines coupled with a requirement to lift higher weights from short airfields drive a long wing.

The kalinin k7

@ChiChiWerx the db 2

Besides, even if you did show me a DB with a higher than 1.5:1 ratio...even up to a 2:1 ratio, you asked the question, that's the answer: aerodynamic efficiency. It's the most efficient subsonic configuration possible, given that era's engine power. And it's not uncommon or specific to these series aircraft. Even today, some very high ratios exist, such as the Voyager around the world aircraft (3.8:1) or even the U-2 (1.67:1)...all in the name of aerodynamic efficiency.

@Nickr show me.

@AircraftoftheRedStar, while good fuel storage capacity is a byproduct of a long, slender wing, that's not what drives that design. If that were true, early jet transports (707, Comet, etc.) would have had even more enormous wingspans due to enormous fuel consumption of early jets. Piston engines, on the other hand, consume much, much less fuel than jets...but provide much less power, thus driving an aerodynamically efficient wing, also known as a high aspect ratio wing in order to facilitate ops out of constrained airfields and at lower airspeeds. What record do you refer to...is it piston specific? I can guarantee you that record, if it's an all female distance record, has been surpassed many times by modern jet aircraft. 3,600+ miles isn't far...that's only a 7-8 hr leg in a modern airliner and we occasionally operate with all female crews, whether that's in the AF or the airlines. In the AF, that's a hop skip and a jump for a KC-135 or KC-10A and in the airlines, any aircraft larger than a 737 goes further than that hundreds of times a day.

@ChiChiWerx some did

They don't...that wingspan to length ratio is a product of 1930s technology and bomber/transport aircraft of that era generally had the same ratios. The Ilyushin DB 3's wingspan to length ratio is 1.5...the He 111's wingspan to length ratio is 1.38, fairly similar. The C-47's wingspan to length ratio is 1.5 as well. This configuration, a long slender wing, is aerodynamically efficient. Aircraft designed during the 1930s had fairly low (by today's standards) engine power, resulting in aircraft that cruised somewhere around 100 and 200 knots, a fairly low airspeed, but even at that low airspeed, those airplanes needed enough lift to stay airborne. Added to this, the need to takeoff in a reasonable distance with fairly sluggish acceleration drove that wing type. Even today with subsonic jet transport aircraft, it's not uncommon to have a wingspan longer than the fuselage, because a long, slender wing is still an efficient design at subsonic speeds...the 737 has a wingspan to length ratio right around 1:1, depending on type, while an Airbus 380 has a ratio of 1.1:1, where the wing is longer than the fuse. So, no, the DB series did not have ludicrously long wings, by any means.

If you look at the Ilyushin DB-3 and Ilyushin DB-4, they each have your average medium bomber wingspan because they were for medium-long range missions. On the other hand, the Tupolev DB-2 (ANT-37) has a ginormous wingspan. This was because it was designed as a very long range medium bomber. So, you need a very long wing to hold all the extra fuel to carry you that far. In fact, the DB-2 was flown nonstop for 3,671 miles with an all-female crew before making a crash-landing. This record still stands to this day.