I'm writing a book on the WW II Fokker D.21 fighter, and since I'm not a pilot, I'm coming here to ask your help regarding the aircraft's flying characteristics.
Photo © Peter de Jong
The D.21 had a fairly nasty tendency to stall into a spin, both at high speeds, whenever the stick was pulled too hard, and at slow speeds, for example when landing a little slow.
Dutch pilots say the unintended spins were always towards the left. I'm fairly certain this is related to engine torque. The Bristol Mercury engine was right-hand drive (turning clockwise when seen from the pilot, I suppose). Does this make sense?
The Finns produced a Pratt & Whitney Twin Wasp Junior-engined version, which was left-hand drive. So can I safely assume this version had a habit of spinning towards the right, the aircraft being very much unchanged apart from the engine installation?
The famous aerobatics pilot Michel Détroyat flew the D.21 prototype, and insisted that lateral stability was unaccepable and that wing dihedral should be increased from 1.5 deg to 7-10 deg. A redesigned wing was built and tested, but the great Finnish fighter leader Eka Magnusson rejected it and evidently thought the flying characteristics with the original wing were quite acceptable, and that the D.21 was reasonable bang for Finland's buck (having good climb rates and pretty good diving characteristics).
So my conclusion is that the high anhedral version was excessively stable, preventing the fighter from snapping into a roll quickly. And that Magnusson's view was the warrior's view, while Détroyat's view was the aerobatic pilot's view, demanding perfect flying characteristics for things like sustained turns and loopings. When Détroyat recommended the P-36 to France, this was apparently largely based on that aicraft's perfect flying characteristics.
Again, does this make sense?
Thanks a lot in advance,