I could be wrong, but I don't think I've seen the following project before.
It's described as a 1979 project, the de Havilland Canada Dash X by TsAGI's Tekhnicheskaya Informatsiya (No.2, 1984), which I suppose indicates that it must have been the DHC-10 in the company's designations sequence. If it's already somewhere on the forum, sorry about it, but I wasn't able to find it...
If there isn't already a mention of this project elsewhere, however, I suggest that this topic be renamed as "Various de Havilland Canada projects" since there are already several different types tackled here. Thanks!