Overview
The Fokker D.XXI fighter was designed in 1935 by Dutch aircraft manufacturer Fokker in response to requirements laid out by the Royal Netherlands East Indies Army Air Force (Militaire Luchtvaart van het Koninklijk Nederlands-Indisch Leger, ML-KNIL). The D.XXI was designed as an inexpensive, rugged, and compact fighter aircraft that would possess respectable performance for its era. Entering operational use in the early years of the Second World War, it provided yeoman service for both the Luchtvaartafdeling (Dutch Army Aviation Group) and the Finnish Air Force. Additionally, a few examples were constructed by the El Carmolí factory before it fell into rebel hands during the Spanish Civil War. Following the invasion and occupation of the Netherlands in May 1940, several captured Dutch D.XXIs were subsequently placed into service with the Luftwaffe.
Origins
On 14 November 1934, design proposals for a new fighter aircraft were submitted by Fokker to the Luchtvaartafdeling (Dutch Army Aviation Group). Fokker's design team, led by Erich Schatzki, and based at the firm's newly completed plant in the southern district of Amsterdam, had sought to incorporate and combine various new concepts and recent features from successful fighter aircraft, including the previous C.X and D.XVII aircraft. The proposed aircraft was a low-wing monoplane which adopted an entirely enclosed cockpit; initial design work had been conducted in cooperation with British engine manufacturer Rolls-Royce, and it had been originally envisaged that the type would be powered by a Rolls-Royce Kestrel IV. According to aviation author G.H.
Kamphuis, the prospects for series production of the new fighter looked doubtful shortly after the first flight was performed due to a high level change in Dutch defence policy; Minister for Foreign Affairs Hendrik Colijn informed the Ministry of War that, in response to the changing international situation, a higher priority would be placed on building up a substantial bomber capability over new fighter aircraft. The change in policy emphasising bombers over fighters was somewhat controversial, in part due to order for new fighters and reconnaissance aircraft being both under consideration at this time, while a requirement for a new training aircraft had also been identified.
In addition to the Luchtvaartafdeling's interest in a trainer aircraft, the service had also attached great importance to the concept of a heavily armed 'cruiser' aircraft capable of performing multiple mission types. Further doubts and confusion were added by the emergence of a competing aircraft proposal in the form of the Koolhoven F.K.58, which had also been designed by Ir. Schatzki. The F.K.58 was somewhat more advanced than the D.XXI, possessing a retractable undercarriage and a higher top speed of 520 km/h. It was decided that the D.XXI and F.K.58 should participate in a series of comparative tests against one another, leading to the D.XXI prototype being dispatched to Soesterberg Air Base, Utrecht, in November 1936. However, head-to-head testing between the two types was delayed by the F.K.58, which did not perform its first flight until September 1938.
Into production
During 1937, the Dutch government gave funding and its approval for a limited expansion of the Army Aviation Group, which resulted in an order being placed for 36 Fokker D.XXI fighters, to be powered by the 830 h.p. Bristol Mercury VII or VIII engines. In 1937, the Finnish government decided to place an order for an initial batch of seven aircraft, further negotiations were also conducted towards the acquisition of a manufacturing license, under which Finland proceeded to domestically produce further aircraft as well. Between 1939 and 1944, the State Aircraft Factory (Valtion Lentokonetehdas) at Tampere manufactured a total of 93 aircraft.
Throughout 1940 and 1941, the Finnish State Aircraft Factory set about reconditioning the aircraft that had been used in the Winter War for continued service; an additional 50 D.XXIs were ordered in 1941, which were powered by the Pratt & Whitney R-1535 Twin Wasp Junior engine, acquired via Sweden. These can be identified by their longer cockpit glazing, smooth cowl, and large ventral air intake under the cowl. The two fuselage-mounted machine guns on these D.XXIs were relocated in the wings and the vertical tail surface was increased in size to offset the new engine. Owing to the increased loaded weight, the R-1535-powered D.XXI had a slightly reduced performance and was not as maneuverable as the Mercury-powered versions. The Danish government ordered a pair of D.XXI fighters along with arrangements for its own manufacturing license. The Danish D.XXI fighters were powered by a 645 h.p.
Bristol Mercury VI-S radial and carried a Madsen 20 mm cannon under each wing. Ten aircraft were completed by the Royal Army Aircraft Factory in Copenhagen prior to the German invasion of Denmark in April 1940. The Second Spanish Republic also acquired a manufacturing license for the D.XXI. Reportedly, a total of 50 fuselages were manufactured on the Spanish production line; however, the Spanish plant in which the fighter was being produced was overrun by Nationalist forces before any of the Spanish-built aircraft were completed. Some sources say that a single Spanish D.XXI managed to escape capture after the production facility was captured.
Design
The Fokker D.XXI was a low-wing monoplane fighter aircraft. Following standard Fokker design practice of the period, it featured a welded steel tube fuselage that was largely covered by fabric, including the flight control surfaces; element forward of the trailing edges of the wings were covered by detachable aluminum panels instead. The wings were of a wooden construction, being composed of two box spars attached to ribs made of plywood. The aircraft was outfitted with a fixed spatted undercarriage with cantilever legs; braking was provided by independently-operated pedals using compressed air. The cockpit of the D.XXI was fully enclosed by a plexiglas hood featuring large sliding sections, and was entirely jettisonable in an emergency situation to enable pilots to bail out.
Pilots were protected against turnover injuries by means of a pylon built into the structure of the aircraft set behind the seat. Fuel was housed in a tank located aft of the engine, wing-mounted auxiliary fuel tanks could also be installed. The main armament consisted of two pairs of 7.92mm M36 FN-Browning machine guns, housed within the wings, carrying 300 rounds of ammunition each. Upon its entry to service in 1938, the D.XXI represented a significant leap forward for the Dutch Army Aviation Group, whose fighter force had until that time consisted of aging biplanes with open cockpits. The new Fokker quickly proved to be an extremely sturdy aircraft, being capable of attaining a speed of 700 km/h in a dive. During the early production of the D.XXI, Fokker's design office considered a number of developments to the basic design, including a wing re-design.
A number of alternative engines were considered, including such power plants as the Rolls-Royce Kestrel V and the Pratt and Whitney Twin Wasp Junior. During 1938, work on three extensively modified versions known as the 150, 151 and 152 were initiated. These aircraft were to be powered by the Bristol Hercules, the Rolls-Royce Merlin and the Daimler-Benz DB 600H. Retractable landing gear was incorporated into these redesigns.
Operational history
The Fokker D.XXI was first used in combat by the Finnish Air Force during the 1939–1940 Winter War between the Soviet Union and Finland. Upon the war's outbreak, a total of 41 aircraft were in Finnish service, all powered by the Mercury VIII engine. On 1 December 1939, the D.XXI achieved its first victory with the shooting down of a Soviet Tupolev SB. The conflict between Finland and the Soviet Union was resumed in the Continuation War (1941–1944), the D.XXI was again a key element of the Finnish Air Force. The D.XXI, although much slower and more lightly armed than the Bf 109, performed surprisingly well in combat due to its manoeuvrability. It was also one of the few aircraft that could follow a Stuka bomber into its dive. Nonetheless, the numerical superiority of the Luftwaffe led to the destruction of most Luchtvaartafdeling D.XXI fighters during the campaign.
Some were captured during and after 15 May, but their later fates are unknown. The LVA (Netherlands Air Force) scored a total of 38 victories against the Luftwaffe during their struggle against the German juggernaut. Sixteen of those went to Fokker D.XXI pilots.
Variants
;D.XXI: Prototype serial no FD-322 ;D.XXI-1: Pattern aircraft supplied to Denmark, three built, powered by Bristol Mercury VIS engines. Armed with 2x machine guns and 2x Madsen cannon ;D.XXI-1:Production aircraft built at the Royal Army Aircraft Factory, ten built powered by Bristol Mercury VIII engines. ;D.XXI-2: 53 Built, of which 36 were delivered to the RNLAF. ;D.XXI-3: Finnish license-built D.XXI-2s, fitted with additional cannons in 1940. Number built: 35 ;D.XXI-4: Upgraded D.XXI-3, powered by Pratt & Whitney R-1535-SB4C-G Twin Wasp Junior engines. Number built: 55 ;Project 150: Proposed version powered by a Bristol Hercules radial piston engine. Not built. ;Project 151: Proposed version powered by a Rolls-Royce Merlin piston engine. Not built. ;Project 152: Proposed version powered by a Daimler-Benz DB 600H engine. Not built.
Operators
; * Hærens Flyvertropper (Danish Army Aviation Troops) – Received three aircraft and built ten on license. Locally designated as "IIIJ" ("third fighter aircraft"). **Jydske Flyverafdeling – two. Eskadrille ; * Finnish Air Force – Received seven aircraft and built 90 on license. ** No. 10 Squadron, Finnish Air Force ** No. 12 Squadron, Finnish Air Force ** No. 14 Squadron, Finnish Air Force ** No. 24 Squadron, Finnish Air Force ** No. 26 Squadron, Finnish Air Force ** No. 30 Squadron, Finnish Air Force ** No. 32 Squadron, Finnish Air Force ; * Luftwaffe – Operated an unknown number of captured Dutch aircraft. ; * Dutch Army Aviation Group – Received 36 aircraft. ; Spanish Republic * Spanish Republican Air Force – May have completed one aircraft.
Aircraft on display
A Mercury-engine Finnish-built Fokker D.XXI, FR-110, is on display at the Finnish Air Force Museum, Jyväskylä, Finland. This is the highest scoring (10 victories) D.XXI airframe. It was the mount of Lt. Viktor Pyötsiä during the Winter War. In 2022, a flyable replica was completed at Hoogeveen Airport by veteran aircraft restorer Jack van Egmond. A number of original parts was used and the plane was built according to original Fokker build specifications as Jack van Egmond is in possession of 397 out of 416 Fokker blueprints. It made its first flight on 23 May 2022. The Crash 40-45 museum in Aalsmeer, The Netherlands, displays the remains of the original no.229, consisting of the engine, fuselage tubing remains and partial cockpit. A full-scale static replica was built by Fokker in 1988 and is on display at the Nationaal Militair Museum in Soesterberg, The Netherlands.
This replica has an incorrect set of undercarriage pants, as these differed between Dutch and Finnish D.XXI models and the wrong drawings were used.
Bibliography
* De Jong, Peter. Le Fokker D.21 (Collection Profils Avions 9) (in French). Outreau, France: Éditions Lela Presse, 2005. . * Eberspacher, Warren. Fokker D-XXI, Volume 1: Dutch and Danish Aircraft (International Squadron Monograph No.1). St. Paul, MN: Phalanx Publishing Co. Ltd., 1994. . * Gerdessen, Frits. Nederlandse Militaire Luchtvaartt VI: Fokker D-XXI (deel 2) (in Dutch). Spijkenisse, the Netherlands: Stichting Vrienden van het Militaire Luchtvaart Museum/Afdeling Luchtvaartkennis KNVvL, 1991. No ISBN. * Gerdessen, Frits and Luuk Boerman. Fokker D.XXI: History, Camouflage and Markings – Operations of the LVA/ML Fokker D.XXI (Dutch Profile 5) (bilingual Dutch/English). Zwammerdam, the Netherlands: Dutch Decal, 2007. No ISBN. * Green, William. "D-XXI: Ancestor of Alliance". RAF Flying Review Vol. XVII, No. 12. * Green, William. "Four Guns and a Canopy". RAF Flying Review, Vol. 19, No.
2. * Green, William. "The 'Halfway-House' Fokker". Air Enthusiast, August 1971. * Green, William. "The Last of the Fighting Fokkers". RAF Flying Review. * Heinonen, Timo. Thulinista Hornetiin – 75 vuotta Suomen ilmavoimien lentokoneita (in Finnish). Tikkakoski, Keski-Suomi, Finland : Keski-Suomen ilmailumuseo, 1992, . * Hooftman, Hugo. Fokker D-XXI (Nederlandse Vliegtuig Encyclopedie 5) (in Dutch). Bennekom, the Netherlands: Cockpit-Uitgeverij, 1978. * Kamphuis, G.H. The Fokker D.XXI (Aircraft in Profile number 63). Leatherhead, Surrey, UK: Profile Publications Ltd., 1966. * Keskinen, Kalevi, Kari Stenman and Klaus Niska. Fokker D.XXI (Suomen Ilmavoimien Historia 3) (in Finnish, with English summary) . Espoo, Finland: Tietoteos, 1974 (2nd edition 1977). . **4th improved edition republished in two parts as: ***Keskinen, Kalevi and Kari Stenman.
Fokker D.XXI Mercury (Suomen Ilmavoimien Historia 3a) (in Finnish). Helsinki, Finland: Hobby Kustannus Oy, 2000. . ***Keskinen, Kalevi and Kari Stenman. Fokker D.XXI Wasp (Suomen Ilmavoimien Historia 3b) (in Finnish). Helsinki, Finland: Hobby Kustannus Oy, 2000. . * Ledwoch, Janusz. Fokker D.XXI (Wydawnictwo Militaria 5) (in Polish). Warsawa, Poland: Wydawnictwo Militaria, 1995. . * Raunio, Jukka. Lentäjän näkökulma 2 (in Finnish). Forssa, Finland, 1993. . * Skulski, Przemysław. Fokker D.21 (Seria "Pod Lupą" 10) (in Polish, with English summary). Wrocław, Poland: Ace Publication, 1999. . * Taylor, John W.R. "Fokker D.XXI" Combat Aircraft of the World from 1909 to the present. New York: G.P. Putnam's Sons, 1969. . * Toll, Karl. "The Last of the Fighting Fokkers". Airpower, January 1982.
External links
* Fokker D.XXIs to Finland * Fokker D.XXI Walk-around (photographs) * Rebuild Fokker Holland