Fokker D.XXI Retractable Under Carriage

Discussion in 'Aircraft Requests' started by Marcel, May 11, 2008.

  1. Marcel

    Marcel Well-Known Member

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    I've read a lot of complains from Dutch fighter pilots about the fixed gear on this plane. They said a retractable version should have been much better. I know the Finns tried this on their version of the D.XXI. Does anyone know how it performed compared to the standard version?
     
  2. Mangrove

    Mangrove Member

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    It wasn't much better. The maximum speed only increased about 30 km/h but total weight was c. 200-300 kg larger than the fixed version. The explation may lie at the fact the Fokker was designed quite well at the beginning and the aerodynamics couldn't be improved as much as they would like to.

    Mechanic Erkki Eve tells how he added 200 rpms to the Mercury engine by allowing the throttle to be used freely. It seems the Valtion Lentokonetehdas had inhibit using the full manifold pressure as it would damage the engine at long run. The extra 200 rpms gave the Fokker 30 km/h more speed but could only be used at short time. However this is only a story which I can't verifye from the sources right now.

    For more info learn to read Finnish and buy Jukka Raunio's book "Lentäjän Näkökulma II". 8)

    Martti
     
  3. Marcel

    Marcel Well-Known Member

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    Thanks, Martti, so it seems the retractable gear wouldn't have made a difference. Are there any Finnish test reports available?
     
  4. Snautzer

    Snautzer Member

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    the retractable d21

    ace publication -->> fokker d21

    Fins adapted 2 planes

    one was the FR 117 Test began jan 1941. when the gear collapsed in july 41 they build it back to fixed
     

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  5. Snautzer

    Snautzer Member

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    Denmark tried 20 mm cannons They bended the wing to much when fired

    ace publication -->> fokker d21
     

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  6. Snautzer

    Snautzer Member

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    another reason is that the cost of installing the retractable gear was quite high.
     
  7. Marcel

    Marcel Well-Known Member

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    Hoi Snautzer,

    Yes that was why the D.XXI wasn't build like that in the first place. I read Jan Linzel's book and he was very angry about this decision. I was therefore wondering what difference it would have made, in sense of performance.
     
  8. Snautzer

    Snautzer Member

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    i havent seen test with it but i guess if the fins didnt bother...

    on the other hand if mangrove is right about 30 km/u increase with same power source... that would be a quite considerable improvement.

    maybe the winterwar threw a spanner in the works.
     
  9. Marcel

    Marcel Well-Known Member

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    Yes that would give the aircraft a level speed of, what, 490-500 km/h? Still slower than the 109, but the gap would definitely have been smaller.I think the Finns had prospects to get better, more modern planes by 1941.
     
  10. Snautzer

    Snautzer Member

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    me 109 wasnt the opponent for the fins,

    speed ~460 (fixed gear mercury engine)

    better put it up to IL16 type 18
     
  11. Graeme

    Graeme Well-Known Member

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    Hi Martti.
    Found an old article on the D.XXI which spoke of one example being fitted with "a completely redesigned wing, known as the E-I wing, which was tapered and had a considerable wash-out towards the tip".

    Mention is also made of a Finnish reconnaissance version that had "transparent panels extending almost to the tail plane."

    Any photos or drawings of these two versions?

    Fokker was also considering various alternative engines...

    [​IMG]
     
  12. Graeme

    Graeme Well-Known Member

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    Hi Marcel.

    What does your avatar say in English?

    [​IMG]
     
  13. Marcel

    Marcel Well-Known Member

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    It says:
    Royal airlines

    And below:
    The flying Dutchman, once a legend, now reality.

    It's a KLM comercial from the '20-'30ies.
     
  14. Mangrove

    Mangrove Member

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    30 km/h more is not a good trade when you get 300 kg more weight on the wheels and the wing. The Air Force HQ knew 30 km/h wasn't enough, the change would take too much time, was too expensive and the 415-420 km/h was good enough for the Recco Squadrons (LeR 1) in 1941-1942.

    Hello Graeme!

    Indeed there was a Fokker with elliptical wing design, the original design was for the Finnish VL Pyry if my memory serves me correctly. As the Finnish Aviation Literature isn't very high quality (no sources marked down) I can't be sure but what I remember from the visits at the Finnish National Archive the elliptical wing wasn't very good for D.XXI as the main strength of the Fokker in 1940- was agility, not speed. The modified Fokker couldn't dogfight as well as the original.

    On the other hand all Finnish Fokkers were modified to have wing slots as in 109. The speed loss was like 0-5 km/h but the new wing was more agile and had better landing characteristics.

    Never heard of it. Fokker "FR-92" was fitted with American Fairchild F-24 camera in 1942 and "FR-110" a Soviet one but that was it.

    Martti
     
  15. Cosmic Sea

    Cosmic Sea New Member

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    I haven't heard of 109's having slots in their wings. You might have mixed them with wings slats, which they did have. These were in the leading edge of the wing and popped up to increase lift in while manouvering or flying slower.
    The idea of the slots was the same however, but simpler. Holes going through the wing.

    Could that refer to the twin wasp-engined fokkers with the extended canopy?
    The second picture posted earlier is of a wasp-fokker, but the canopy doesn't show very well. Here's a photo from the side: Wasp-fokker


    Oh btw, it's my first post here, hello everyone!
    I registered a while ago but didn't participate until now.
    And sorry if this is considered necroposting.
     
  16. Snautzer

    Snautzer Member

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    well plse see increase in weight and speed for lets say the 109.

    30 k in speed better is very good. Pilots sold their mother to be faster. The reasons the fins didnt are other then mere lack of better results
     
  17. Marcel

    Marcel Well-Known Member

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    Don't worry about necroposting, the thread hasn't been that old :)
    Thanks for the pictures. Never saw thes extended glass cockpits on the D.XXI :thumbright:
     
  18. Cosmic Sea

    Cosmic Sea New Member

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    The extended canopy was a feature of the Finnish-manufactured twin wasp-engined Fokkers. As Bristol Mercuries were reserved for the Blenheim bombers so another engine had to be chosen to power the license-built Fokkers.
    These series (so called IV and V) had some changes when compared to the Mercury-engined ones, the most prominent being the extended canopy offering better visibility. Also, as a result of the installation of a two-row engine, the two fuselage-mounted machine guns were moved to the wings.

    Here's some more photos of Wasp-Fokkers: Photos of Finland's Continuation War, P.2

    In case you're interested, there's two books about Finnish Fokkers, one for each type.
    Suomen Ilmavoimien historia, osa 3a - Finnish Air Force History, part 2
    Suomen Ilmavoimien historia, osa 3b - Finnish Air Force History, part 2b
    They're bilingual, with photo captions in both in Finnish and English and there's an English summary at the end of the book.
     
  19. Snautzer

    Snautzer Member

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    another view
     

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