guille1434 wrote:Razz1: Did not know there were two versions of Fokker D.XXI that were used by the Dutch. I uploaded the "improved" D.XXI, and also an icon with this plane in Finnish Air Force (ahistorical, see my original post) markings. As I made the mask for this icon to use un the DCS program I cam make some other color schemes for it, so ask me if you want a differen version of the Dutch unit to use as the D.XXI-1. By the way, do you know (or someone here) what were the differences between both sub-models?
Thanks!!
Well, guess who's back

... Nice icons, by the way, but you asked about the Fokker D.XXI (or D.21 for short), so prepare for incoming!
I do not recall the Dutch using more than one version, and I took a look at the English wikipedia page and it does not make a lot of sense... Razz1, I think you've been fooled by wikipedia, but luckily the Finnish (Suomi) wiki page seems quite good, so you can translate that for the best wiki-info. It seems the English wiki uses a lot of obsolete info (Kamphuis from 1966, Green from the 70s), and some of the specs are incorrect, I'll get to that later.
Another thing, the 'variants' with sub-nrs (D.XXI-5) do not exist for the Dutch models: there was only a prototype, a trial machine and after some improvements a bunch were made for the Dutch airforce. These Dutch service machines had the best performance of all D.21's (still not very good, though), the Finnish made a licensed version which did not incorporate all the improvements Fokker made for the Dutch. The Finnish added some features of their own (capacity to mount snow landing gear, and later better gunsights and a better view from the cockpit). These first Finnish airplanes were comparable to the Dutch model but had a slightly lower top speed. These were the ones used with good results in the famous 'Winter War' against the Sovjet Union.
The Finns used the variant numbers, they were called 'series', and they were not necessarily different in equipment or performance, in fact there were only two major Finnish versions with regards to performance. I don't have all my books handy, but I made a google translation from the Finnish wiki, and together with my memory this should suffice for now.
The first Finnish series (Series I) were simply seven aircraft built by Fokker in the Netherlands and delivered to the Finns (in crates) without weapons; in the meanwhile the Finns were busy setting up their production line to build their licensed machines. They had bought a license for a couple of dozen more, I believe.
Series II were the first batch of machines the Finns built themselves; they were 14 machines (Finnish wiki).
Series III were the second batch of licensed machines. I don't know if there were any differences, but I know they had to make changes to the licensed machines' construction, they used a different kind of wood, could mount snow ski's, etc. It could well be that both series II and III had some or all of these changes. Also, they managed to make it cheaper to produce. The Finnish also acquired a new license to produce as many as they liked. The problem however, was that the Finns also built the engines (Bristol Mercury) locally, but that production was slow and they also needed the engines for other aircraft. And the Fokker was not that good, but it would be a shame to waste the production potential, because the Fokker was cheap, easy to build and relatively easy to fix. Which brings us to the next series:
Series IV ('D.XXI-4') wiki entry had me laugh when I read it for the first time, which was painful because I have a minor throat infection at the moment

. The series IV was a
downgrade by the Finns, since they couldn't produce enough Bristol Mercury engines to mount on the Fokkers. So they mounted some P&W Wasp engines instead, but this made the performance at medium and higher altitudes worse; at low altitude performance was slightly better. These 'Wasp'-machines were not really used as fighters much, but more for training and reconnaissance, apparently. They had better protection (a bit of armor, better fuel system protection) and better visibility from the cockpit.
Series V: Then, a while after the Winter War, Germany invaded the Sovjet Union, the Finns baited the Soviet Union in attacking them and thus started the 'Continuation War'. The Finnish government ordered more aircraft from their factory to replace losses, first a small series of 5 machines (quickly built from spare parts according to the wiki) which was delivered in the summer of 1944, and after that they started work on another order, but that was cancelled because the war was already over. Series V were the same as Series IV it seems.
Where the English wiki-information for the Bristol Pegasus engine for Series V came from I have no idea, but I haven't seen any evidence that it was ever mounted and it is likely the result of a mix-up by Kamphuis (1966). You see, around that time of the Series V the Finns also ordered their factory to make 5 Fokker C.X planes, and these biplanes had the Pegasus engine. So I guess this could be the origin of the mistake.
The specs: the top speed of 460 km/h is too high; this was the speed of the Dutch trial model without any combat gear, combat-ready models could do 446 km/h, the Finnish versions were a bit slower, the Finnish wiki has more accurate numbers for their versions.
Armament notes: Frequently mentioned are models fitted with cannons, but there were only two test machines with these, one was Finnish, it had two 20mm Oerlikon FF, and they didn't like it.
The other was Danish, they trialled a machine with two 20mm Madsen cannon, and later removed this armament. I don't know if the Spanish version had any noticable differences (The Spanish Republican faction had just started production before the end of the Civil War).