Hi Tex,
Well, in the back of my mind was the dim possibility of creating a Spanish Civil War add-on at some stage. I simply wanted to experiment with a few SCW-era planes done as add-ons for SFP1 to see how they appeared visually in terms of the game. (I presume because WWI planes were so small TK has re-sized the default views compared with the jet era.) And also if and how they'd fly. And if they did, whether they'd seem so fast (200-300mph vs 100mph) as to look silly.
Of course I also compared the data .ini files to see what had changed since SFP1. As you say, quite a lot - although the basic format is the same.
I tried the Curtis Hawk III biplane without luck. Game ran as usual, but I couldn't make it appear in the menus - even after fiddling the INI file to changes the dates of appearance, nationality etc. I also shortened the range to WWI dimensions, in case that was an issue, too. But fiddling with the control surfaces and the actual flight dynamics is far, far beyond me right now.
Other SFP1 add-ons that looked worth trying for the same purpose were the SM79, JU87B and JU52.
I should stress (*flashing lights here*) that I wasn't about to mod anything done by anybody else - except for private home use - without their explicit permission. I know that's been a problem with this series of games.
Any advice gratefully received!