I've been researching the history of pre-jet aircraft and I've come across several famous, and not so famous, blended-wing aircraft. The idea seemed to show promise but never really caught on, even for a limited span of time or confluence of technological factors e.g. weight vs engine power etc.
Just to be clear, I'm not interest in flying wing and/or tailless aircraft whose early problems are well known, but rather those designs that have tails but have a fuselage shaped to produced a significant component of lift.
Just a few of the designs I've stumbled across:
Cunliffe-Owen OA-1 (Burnelli license)
There are quite a few more I don't have handy web links for. Junkers did a couple that would probably qualify.
The large number of designs from all over the world show that the basic idea offered promise but all the designs eventually went no where despite being tried in many countries, economies and even political systems. That in turn seems strange because in the 1920s-early-1940s, lift seemed more important than speed for larger multiengine aircraft i.e. just getting a load airborne at all was worth quite a few other tradeoffs. As engines grew more powerful that tradeoff lessened but for at least 15-20 years a high lift design should have been more desirable than a high speed one for larger aircraft.
The failure of many different designers over the course of three decades to make the blended wing work suggest to me that the basic idea has some inherent disadvantage/s that outweighed any gains. Unfortunately, none of the resources I have consulted offer any clues to why the designs did not "take off."
I suspect the designs showed some rapid onset of stall of instabilty but that's just an uninformed hunch on my part.