Hi Jschmus,
Your posts are welcome
XP-52 is an intriguing design. You're right that references can be found where it's described as an R-40C submission. But many others point in the other direction. In the list I published on post#2 from the present topic, which in my opinion comes from an authoritative source, the Model 16/XP-52 doesn't appear. According to it, Bell tendered its Model 13 to R-40C. Model 13 looked more like an enlarged P-39. In Bell Aircraft (Ed Putnam) I think there is a mistake on the description because the aircraft is associated to 1941 as "date of design". 1941 is too late for R-40C, however I think the real figure should be 1939 cited on Wings (August,1996 issue). BTW, there is an interesting windtunnel model with a different tail layout. I strongly recommend that magazine, which is still available, to all US pre-1945 fighter enthusiasts.
My personal opinion is Model 16 was designed a few months after Model 13, after Hap Arnold pushed for advanced lineal engine fighter (what latter was formaly requested as R-40C). While Model 13 was Bell's entry to R-40C, Model 16 could have been a parallel and more radical study based on Douglas DS-312A. May be Model 13 was to be R-40C "Phase One" entry and Model 16 would have been their entry for R-40C "Phase Two". As you probably know "Phase One" admitted designs based on existing technology while "Phase Two" demanded performance to the limits on totally new designs. The powerplant selected for Model 16 was the 1350 hp Continental IV-1430 which development was plagued with cooling problems that ended with its cancellation. Bell re-engined and thus re-designed its Model 16 into what the USAAC assigned the XP-59 designation. I don't know its Bell design number. XP-59 engine was the powerful and already in production Pratt&Whitney R-2800 Double Wasp radial (the same engine that powered F6F, Corsair or P-47 fighters). However, the USAAC cancelled the XP-59 in 1941 probably because it was found that it was not to be a revolutionary performer. By that time, late 1941, the USAAC selected Bell to concentrate all efforts into the production of US first operational jet fighter. Work on XP-59 was to judged a distraction of resources and thus terminated. However USAAC assigned the XP-59A designation to the jet to cover that program with the unrelated XP-59 work.
Regards,
Antonio