Koolhoven F.K. Designations

[Apophenia]

The biography of Sytze Frederik Willem 'Frits' Koolhoven has been well-covered online. The Dutch aviation pioneer is probably best-known today for his designs for Armstrong-Whitworth in Britain during WW1. An imaginative designer (albeit with a few idée fixe), once back in the Netherlands, Koolhoven had no manner of luck in choosing employers. Finally he struck out on his own. His firm survived [1] but, as it's usually phrased, he remained forever in the shadow of Anthony Fokker.

Frits Koolhoven developed a reputation for strongly-held opinions on aircraft design and construction techniques. One example is the firm bias he would develop against low-set monoplane wings. That led to some odd configurations - like the low-set gull wings of both the 1936 F.K.53 cabin monoplane and the 1938 F.K.56 combat trainer prototype. [2]

While Fokker was unable - financially and technologically - to make the leap to stressed-skinned aluminum construction, Frits Koolhoven remained thoroughly wed to traditional 'mixed' construction - even falling out in later years with ML officials by insisting that wooden-framed tailplanes were stronger than the officially-preferred steel-tube structures. Koolhoven once jokingly referred to aluminum as "geëlektrificeerde modder" or 'electrified mud'.

Nevertheless, Koolhoven's odd approaches could result in brilliance. The unorthodox, mid-engined F.K.55 fighter probably owed a great deal to the advanced concepts of its French engine-maker, Lorraine. But it was Frits Koolhoven who arranged to send a highly-detailed mockup to the Salon de l'Aéronautique in Paris in 1936. For years, many were convinced that this convincing mockup was the prototype F.K.55. Great theatre ... even if the real F.K.55 prototype may have disappointed.

Koolhoven's sometimes quirky attitudes made it difficult for him to get along with officialdom. The relatively small size of NV Vliegtuigenfabriek Koolhoven's Waalhaven facility also made it difficult for the firm to meet those military orders it did receive. Still, the Ministrie van Defensie responded to Koolhoven's offer of lower prices than his competitors. Make what you will out of Koolhoven's failure to deliver a single F.K.58B fighter or to even begin work on the F.K.59 recce-fighters (despite Bristol having delivered their engines).

In some Koolhoven histories, the company is described as surviving its founder ... including efforts in aviation. These are said to include the building of two gliders. Actually, the T.10 and/or T.20 gliders in question [3] were built by NV Machinefabriek v/h Van Driel en Van Ommeren which happened to be on the site of the former Koolhoven factory. There is also online mentions of Koolhoven having negotiated a license for the production of SIPA S.200 Minijets. [4] That deal is also properly attributed to Van Driel en Van Ommeren not to Koolhoven.

Below is a summary of Frits Koolhoven's work life and aviation associations:

1910 - Koolhoven attends Hanriot flying school near Rheims, France
- Koolhoven obtained pilot's licence, number 290, on 08 November 1910
-- NB: Koolhoven bought (rather than built) a Hanriot monoplane

1910 - Koolhoven ties to convince his employer* to build aircraft
- * This was car- and engine-maker, Minerva Motors SA of Antwerp
-- Failure, Koolhoven leaves for Maatschappij voor Luchtvaart

1910 - Director of Operations, Maatschappij voor Luchtvaart
- Maatschappij voor Luchtvaart = Society for Aviation
-- Management firm for flight schools at Ede and Soesterberg
-- Maatschappij voor Luchtvaart became bankrupt in 1911

1911 - Koolhoven constructed improved Farman-type, 'Heidevogel'
- aka 'Holland', improved Farman biplane, built at Soesterberg

1912, early - Designer, Société de Production des Aéroplanes Deperdussin
- With Louis Béchéreau, devised Deperdussin Monocoque racer

1912 - Designs 2-seat Deperdussin TT monoplane with Béchéreau

1912, Summer - Works Manager, British Deperdussin Company Ltd.
- Devised TT derivatives for flying school and military use

1912-1913 - Designed 'Seagull' hydro-monoplane seaplane
- 'Seagull' recce floatplane designed for Admiralty contest
-- There is some debate over extent of Koolhoven's involvement*
-- Some accounts suggest Koolhoven assisted Lt. JC Porte, RN

1913 - Works Manager/chief designer, Armstrong Whitworth Aircraft
- Properly, the Sir W. G. Armstrong Whitworth Aircraft Company

1917 - Chief designer, British Aerial Transport Company Ltd (BAT)

1919 - Koolhoven and Dutch lt-vl L. Coblijn form airline, COBOR*
- * NV Handel Maatschappij COBOR with an F.K.26 leased from BAT
-- Flew 18 Sept.-late Oct. 1919, resumed op'ns March-April 1920

1920, April - BAT failing, Koolhoven returned to the Netherlands

1920 - Automotive designer,* Trompenburg aka Spijker (or Spyker)
- * Koolhoven was involved in the design of the Spijker C-4
- * Or did Spyker also hope to remain in the aviation business?

1922-1926 - Chief Designer, NV Nationale Vliegtuig Industrie (NVI)
- Nationale Vliegtuig Industrie = National Aircraft Industry

1926, Early* - Quit NVI and began Koolhoven Vliegtuigen Rijswijk
- Technical office situated in an attic in suburban Rijswijk
- Koolhoven Vliegtuigen Rijswijk = Koolhoven Airplanes, Rijswijk
-- * Some sources say January 1926, others February 1926
-- * Some sources also day Koolhoven didn't quit, was dismissed

1926 - NVI failing, Koolhoven leased NVI hangar at Waalhaven
- Hangar-based business is called Luchttuigenfabriek Koolhoven
- Luchttuigenfabriek Koolhoven = Koolhoven Aircraft Factory

1926 - Koolhoven's design office and constr. facility joined
- Conjoined firm established as NV Vliegtuigenfabriek Koolhoven
- NV Vliegtuigenfabriek Koolhoven = Koolhoven Airplanes Factory Co.

1927 - NVI finally declares bankruptcy (some sources say ca. 1930)

1933-1934 - New investors via Rotterdam banker Jacob Mees, P.Rzn
- Aug. 1934, NV Koolhoven Vliegtuigen Capital f 500,000
-- Banker/sport flyer Mees later became president-commissaris*
-- * Chairman of Supervisory Board of Vliegtuigenfabriek Koolhoven

1938, March - Fokker designer Erich Schatzki hired by Koolhoven

1940, 10 May - Koolhoven factory detroyed by Luftwaffe bombing

1946, 01 July - Koolhoven dies of a stroke/cerebral haemorrhage

__________________________________

A few Koolhoven aircraft references:

Frits Koolhoven en zijn vliegtuigproduktie, Dik Top (in coöperation with Jan den Das), Repro-Holland, Alphen aan den Rijn, 1996 (Trans. 'Frits Koolhoven and his aircraft production')

Koolhoven - Nederlandse vliegtuigbouwer in de schaduw van Fokker, Theo Wesselink and Thijs Postma, Unieboek, 1981 (Trans. 'Koolhoven - Dutch Aircraft Builder in the Shadow of Fokker')

De jonge jaren van de luchtmacht: Het luchtwapen in het Nederlandse leger 1913-1939, [Lt Gen] Dirk Starink, Uitgeverij Boom, 2013 (Trans. 'The Early Years of the Air Force: Air Weapon of the Dutch army 1913-1939')

De vliegtuigen van Frits Koolhoven - Luchtvaartarchief Herman Dekker - http://www.hdekker.info/DIVERSEN/Koolhoven.htm

The aircraft designer Frederik (Frits) Koolhoven: A gifted and prolific designer - http://www.alexdenouden.nl/artikelen/koolhoven.htm

__________________________________________

[1] Indeed, the firm survived Koolhoven himself. NV Koolhoven Vliegtuigen eventually folded in 1953 or 1956 (depending upon source).

[2] Newly-arrived engineer Erich Schatzki got around Koolhoven's eccentric bias. In redesigning the F.K.56 and designing his F.K.58 fighter, Schatzki positioned the low-set wings just above the bottom of the fuselages.

[3] The first Akerboom-Schmidt T.10 (PH-202) was built in Amsterdam. The second (PH-205) was built by Nijs & van Driel. There is ongoing confusion over the total numbers built. (See: http://www.hdekker.info/DIVERSEN/t10.htm Twee, of Drie, of Vier? De Akerboom-Schmidt T-10 en T-20 and Sailplane & Glider, Oct 1953, Vol XXI, No 10, pg. 6.)

Sailplane pilot Jan K Hoekstra is often mentioned in connection with the T.10 but what if any involvement he had in the construction of these gliders is unknown. What is known is that the NV Machinefabriek Van Driel & Van Ommeren built the forward fuselage of the 2-seat T.20. It was intended that this be mated with existing wings, rear fuselage, and tailplane from a T.10. Whether this was ever done is unclear (but unlikely).

[4] See: https://www.flightglobal.com/FlightPDFArchive/1953/1953 - 1042.PDF
__________________________________________

 

[Apophenia]

Koolhoven Aircraft Designations

Prior to his arrival in Britain in late 1913, Frederik Koolhoven designed several aircraft. The first was a Farman-type biplane named Heidevogel (Heatherbird) which Koolhoven usually referred to as 'Holland'. On arrival in France, he worked with Louis Béchéreau on the radical Deperdussin Monocoque. Later in 1912, he designed the British Deperdussin Seagull. Those aircraft all received names but were any of them ever assign 'F.K.' numerical designations?

It is widely agreed that the 'F.K.' designations began with Koolhoven's arrival at Armstrong-Whitworth. However, there is an argument to be made that the 'F.K.' designations may have begun earlier ... and then numbers were reassigned during Koolhoven's Armstrong-Whitworth period. Several sources, including Dirk Top's Frits Koolhoven en zijn vliegtuigproduktie, list the 1911 Heidevogel as the first F.K.1. (Those following this line usually assign A.W.1 to the 1914 Sissit).

Amongst others, Archieven.nl [1] lists the 'FK2' as a British Deperdussin 2-seat trainer. [2] There are also references to the F.K.3 being a British Deperdussin "70 hp Gnome", the F.K.4 being a "100 hp Gnome Déperdussin 1911", and F.K.5 being a "100 hp Gnome Déperdussin 1912". I have including all of these in my list rather than attempting to determine which is the real designation - I lean towards the possibility that earlier 'F.K.' designations were 'recycled'.

There are other problems with that retrospective list compiled by Frits Koolhoven in 1926 ... upon which most attempts at Koolhoven designation listings are based. For example, Koolhoven designated the British Deperdussin Seagull as the F.K.6 while the Armstrong-Whitworth F.K.6 escort fighter, he called the 'F.K.12'. Since that confusion, nobody has been quite sure what the real F.K.12 project actual was.

Being arbitrary, I have listed the F.K.12-F.K.19 as 'Armstrong-Whitworth' projects. But should they have been listed as 'Koolhoven' projects instead? Perhaps. Does anyone have compelling evidence either way?

From F.K.20 onwards, attributions become a little simpler. F.K.20 to F.K.28 all fall under the British Aerial Transport marque. The F.K.29 to F.K.34 belong under NV Nationale Vliegtuig Industrie (NVI) ... with the exception of the F.K.30 (which was not built under after NVI had failed). I have listed the F.K.30 as a 'Koolhoven'. Beginning with the F.K.35, I have listed designs as 'Koolhoven' products. The unbroken Koolhoven 'F.K. list runs unquestioningly to the F.K.59 (under which there were three distinct projects). There are cryptic mentions of an F.K.60 project dating from 1940 ... but, frustratingly, with no details whatever.

At the end of the 'F.K.' listings, I have added some of the known Koolhoven Ontwerpen and their numbers where known (many thanks to lark for his generous aid here!). The gaps in this second list hint at the volume of missing Ontwerp numbers. Records for many of these unbuilt projects will have been lost with the Koolhoven records when the Luftwaffe bombed Wallhaven on 10 May 1940. But mention of some of these 'missing' Koolhoven Ontwerpen must have survived. Anyone have anything more?
_____________________________________

[1] It is notable that this Archieven.nl list omits both the Sissit and Armstrong-Whitworth F.K.2 (as an F.K.3 precursor). That would be enough to discount the British Deperdussin 2-seater claim had not Koohoven himself applied the F.K.2 designation to both his "3-cylinder Déperdussin" and the "Queen Anne" (or Sissit)!

[2] This would be the 'Anglicised' Deperdussin TT fitted with 60 hp or 100 hp Anzani radials as well as 70 hp and 100 hp Gnome rotary engines. These 2-seaters were used by the British Deperdussin Flying Schools at Hendon and Brooklands as well as being submitted for the British Military Trials of August 1912 (the prize being won by the 100 hp Gnome-powered British Deperdussin 2-seater).

 

[Apophenia]

Koolhoven F.K. Aircraft Designations

Koolhoven F.K.1 -- 1911 Heidevogel (Heatherbird)
- F.K.1: Improved Farman-type biplane; aka 'Holland'
-- Controversial designation, possibly not assigned

Armstrong-Whitworth F.K.1 -- 1914 Sissit biplane* scout
- F.K.1: Small single-seat, single-bay scout; 1 x built
- F.K.1: 1 x 50 hp Gnome rotary tractor,** span (??) m
-- Controversial designation; possibly desig. as A.W.1
-- * F.K.1 originally conceived of as monoplane scout
-- ** F.K.1 originally designed to have 80 hp engine
-- F.K.1 mod. w/ fixed tailplane and enlarged ailerons
-- https://78.media.tumblr.com/b57627470911ca175bf9e7a82f4d9c11/tumblr_inline_nicqbltcPK1t90ue7.jpg
-- F.K.1 named Sissit but aka 'Queen Anne'***
-- *** Suggesting that the design was overweight?

British Deperdussin F.K.2 -- 1912 2-seat trainer
- F.K.2: 'Anglicised' Deperdussin TT monoplanes
- F.K.2: 1 x 60 hp or 100 hp engine,* span 10.50 m
-- * Both Anzani radials and Gnome rotaries fitted
-- Controversial designation; possibly not assigned

British Deperdussin F.K.2 -- 1912 single-seat trainer
- F.K.2: 'Anglicised' Deperdussin Type A monoplane
- F.K.2: 1 x 35 hp Anzani Y-3 engine, span 8.50 m*
-- Ground trainer** aka 'School Type' or 'Taxi-Type'
-- * Span for standard Deperdussin A was 8.76 m
-- ** Albeit capable of short hops/delivery flights
-- https://www.awm.gov.au/collection/C159106
-- Controversial desig., from 1926 Koolhoven list

Armstrong-Whitworth F.K.2 -- 1915 2-seat recce biplane
- F.K.2: Tandem-seat, 2-bay biplane; x 2 (7 ordered)*
- F.K.2: (Orig.) 1 x 70 hp Renault engine; span 12.22 m
- F.K.2: (Mod.) 1 x 90 hp Renault air-cooled V-8 engine
-- * Contract No.94/A/103 (5328-5334) became F.K.3s
-- Controversial desig. but no record of an 'A.W.2'

British Deperdussin F.K.3 -- 1912 2-seat scout/trainer
- F.K.3: 'Anglicised' Deperdussin Monocoque monoplane
- F.K.3: 1 x 70 hp Gnome rotary engine, span 10.50 m
-- aka "70 hp Gnome" by Frits Koolhoven himself

Armstrong-Whitworth F.K.3 -- 1915 2-seat recce biplane
- F.K.3: Tandem-seat, 2-bay biplane, improved F.K.2*
- F.K.3: 1 x 90 hp RAF 1a V-8 engine; span 12.22 m
-- B.E.2c replacement but inferior; most used as trainers
-- * Modernized structure; aka 'Little Ack'; 343 x built
-- aka "100 hp RAF two-seater scout" by Koolhoven
-- 3v: http://flyingmachines.ru/Images7/Putnam/AW/56-1.jpg

British Deperdussin F.K.4 -- (Project) 1911 scout/trainer
- F.K.4: 'Anglicised' Deperdussin Monocoque monoplane
- F.K.4: 1 x 100 hp Gnome rotary engine, span 10.50 m
-- Controv. desig., aka "100 hp Gnome Déperdussin 1911"

Armstrong-Whitworth F.K.4 - 1915 2-seat airship gondola
- F.K.4: 1 x 100 hp Green inline 4-cyl.; span (??) m; x ~20
-- F.K.3 fuselage re-used as SS.40-49 airship gondola*
-- http://members.ziggo.nl/henrikaper/koolhoven/armstrong-whitworth/images/armstrong-whitworth-fk4.jpg
-- * SS.27 airship also used an F.K.3-based gondola**
-- ** Unclear whether those also were designated F.K.4

British Deperdussin F.K.5 -- 1912 2-seat scout/trainer
- F.K.5: 'Anglicised' Deperdussin Monocoque monoplane
- F.K.5: 1 x 100 hp Gnome rotary engine; span 10.50 m
-- Controv. desig., aka "100 hp Gnome Déperdussin 1912"

Armstrong-Whitworth F.K.5 -- 1915 3-seat escort fighter
- F.K.5: Single-engine unequal span triplane heavy fighter
- F.K.5: 1 x 250 hp R-R Eagle V-12, span (??) m; 1 x built
-- Twin gun nacelles mounted on wider-span middle wing
-- https://www.secretprojects.co.uk/forum/index.php/topic,7951.msg232709.html#msg232709

British Deperdussin F.K.6 -- 1912 2-seat floatplane
- F.K.6: Tractor monoplane floatplane for Admiralty
- F.K.6: 1 x 100 hp Anzani 10-cyl. radial; span 14.00 m
-- 'Seagull', originally simply the 'Hydro Monoplane'
-- NB: Attributed to Lt. JC Porte, RN with Koolhoven
-- Controversial desig. from Koolhoven's 1926 list

Armstrong-Whitworth F.K.6 -- 1915 3-seat escort fighter
- F.K.6: Single-engine unequal span triplane heavy fighter
- F.K.6: 1 x 250 hp R-R Eagle V-12; span 18.89 m; x 1*
-- Gun nacelles mounted further outboard on middle wing
-- * No.7838; 7841 and 3684-3685 (for RNAS) cancelled
-- 3v: http://flyingmachines.ru/Images7/Fighters/25-2.jpg
-- 3v: http://flyingmachines.ru/Images7/Putnam/AW/72-1.jpg

Armstrong-Whitworth F.K.7 -- 1916 2-seat recce biplane
- F.K.7: 1 x 160 hp Beardmore inline; span 13.26 m; x 1
- F.K.7: Intended replacement for the F.K.3 and B.E.2c
-- F.K.7 production plans transferred to improved F.K.8*
-- * A411 built; order for A729 to A777 was cancelled

Armstrong-Whitworth F.K.8 - 1916 2-seat recce biplane
- F.K.8: Production version of F.K.7 scout/light bomber*
- F.K.8: 1 x 160 hp Beardmore inline; span 13.26 m
-- * Rebranded to match Royal Aircraft Factory R.E.8?
-- aka 'Big Ack' (vs F.K.3 'Little Ack), 1,650 x F.K.8 built

Armstrong-Whitworth F.K.9: (Project) 1916 2-seater
- F.K.9: aka "180 hp Lorraine two-seater, 1916"*
-- * According to retroactive 1926 Koolhoven list
-- Unclear whether related to Clerget F.K.9 design

Armstrong-Whitworth F.K.9 - 1916 quadruplane fighter
- F.K.9: 2-seat fighter; private venture to Spec. No.2c
- F.K.9: 1 x 110 hp Clerget rotary; span 8.46 m; x 1
- F.K.9: (Project) "180 hp Lorraine two-seater, 1916"
-- Central Flying School trials dictated modifications*
-- * New wings, cowling, an increased u/c track, etc.
-- Further revised F.K.9 ordered into prod. as F.K.10

Armstrong-Whitworth F.K.10 - 1916 quadruplane fighter
- F.K.10: Improved development of the F.K.9 airframe
- F.K.10: 1 x 130 hp Clerget rotary engine; span 8.61 m
-- 8 built;* production order issued but later cancelled
-- * Including 2 by Phoenix Dynamo Manufacturing Co.
-- * In-production Sopwith 1 1/2 Strutter found superior
-- https://www.secretprojects.co.uk/forum/index.php/topic,25577.msg277796.html#msg277796

Armstrong-Whitworth F.K.11 - (Project) 1916 multiplane
- F.K.11: Fifteen-wing design; planned engine unknown*
-- F.K.11 was to employ the fuselage from the F.K.10
-- * Probably the 130 hp Clerget 9B as per F.K.10
-- https://www.secretprojects.co.uk/forum/index.php/topic,25577.msg277795.html#msg277795
-- http://members.ziggo.nl/henrikaper/...tworth/images/armstrong-whitworth-15wings.jpg

Armstrong-Whitworth F.K.12 - 1917; no firm details
- F.K.12: Poss. FK.8 with modified cooling, u/c, exhausts
-- Koolhoven confused F.K.12 with F.K.6 in his 1926 list

Armstrong-Whitworth F.K.13 - 1917 biplane recce-fighter
- F.K.13: Higher-powered F.K.8 derivative; x 1 (N513)*
- F.K.13: 1 x 200 hp Sunbeam Maori V12, span (??) m
-- aka Fleet Fighter Reconnaissance Biplane; not accepted
-- * Note: This serial falls between the final 3 x F.K.10s
-- http://members.ziggo.nl/henrikaper/koolhoven/armstrong-whitworth/images/armstrong-whitworth-fk13.jpg

Armstrong-Whitworth F.K.14 - (Project) fighter concept
- F.K.14: Identified by Koolhoven as an A.W. project
- F.K.14: no other details
-- https://www.flightglobal.com/FlightPDFArchive/1953/1953 - 0618.PDF

Armstrong-Whitworth F.K.15 - (Project) airship gondola
- F.K.15: Gondola design/concept for 1912 Beta II airship

Armstrong-Whitworth F.K.16 - (Project) airship gondola
- F.K.16: Gondola design for 1912 North Sea airship*
-- * F.K.16 gondola based on the fuselage of F.K.3

Armstrong-Whitworth F.K.17 - (Project) airship gondola
- F.K.16: Gondola design for 1912 North Sea airship*
-- * F.K.16 gondola based on the fuselage of F.K.3**
-- ** Koolhoven himself may have had no involvement

Armstrong-Whitworth F.K.18 - (Project) flying boat
- F.K.18: "2-engine flying boat" according to F.K.*
-- * But also called F.K.22 precursor by Koolhoven
-- J.M. Bruce repeated fighter claim in Flight letter
-- https://www.flightglobal.com/FlightPDFArchive/1953/1953 - 0618.PDF

Armstrong-Whitworth F.K.19 - (Project) Aircraft
- F.K.19: Identified by Koolhoven;* no other details
-- * Armstrong-Whitworth light air-cooled engine?**
-- ** If so, unlikely to have Koolhoven involvement

BAT F.K.20 - (Project) 1917 shipboard biplane fighter
- F.K.20: Single-seat, single-engined naval biplane
-- Claimed derived from A.W. F.K.18 fighter concept
-- Archeiven.nl lists "FK20, BAT-jager ... shipplane"
-- F.K.20 seems to lead to both F.K.21 and F.K.22
-- http://www.britishaviation-ptp.com/b/bat.html
-- https://www.flightglobal.com/FlightPDFArchive/1953/1953 - 0618.PDF
-- http://members.ziggo.nl/henrikaper/...port/images/british-aerial-transport-fk20.jpg

BAT F.K.21 - 1917 2-bay biplane fighter trainer
- F.K.21: Single-seat* trainer; no other details
-- * Archeiven.nl lists "FK21, BAT éénpersoonsjager"
-- * 'BAT single-seat fighter', fuselage as F.K.20
-- http://www.britishaviation-ptp.com/b/bat.html
-- https://www.flightglobal.com/FlightPDFArchive/1953/1953 - 0618.PDF
-- http://members.ziggo.nl/henrikaper/...port/images/british-aerial-transport-fk21.jpg

BAT F.K.22 - 1918 single-seat biplane fighter, x 3
- F.K.22: Unstaggered, 2-bay wings; monocoque fuselage
- F.K.22: (As planned) 120 hp ABC Mosquito 6-cyl. radial
- F.K.22: 1st/3rd prototype, 170 hp ABC Wasp I radial
- F.K.22: 2nd prototype, Gnome Monosoupape rotary*
-- * 2nd airframe later fitted with 110 hp Le Rhone 9J
-- aka BAT Bantam II (see related F.K.23 Bantam I)**
-- ** J.M. Bruce lists as the F.K.22 Bat or Gnôme-Bat
-- https://www.flightglobal.com/pdfarchive/view/1952/1952 - 3424.html
-- http://www.airwar.ru/image/idop/fww1/fk23/fk23-5.jpg

BAT F.K.23 - 1918 single-seat biplane fighter; 3 x built
- F.K.23: 1 x 170 hp ABC Wasp I radial; span 7.62 m
-- F.K.23 was a refined development of the F.K.22
-- http://www.airwar.ru/image/idop/fww1/fk23/fk23-6.jpg
-- aka BAT Bantam I (BAT Bantam II was F.K.22, above)
- F.K.23A: Dutch NVI version;* 1 x 200 hp ABC Wasp II
-- * Based on a surplus F.K.23 airframe bought from BAT
- F.K.23(??): F.K.23 refitted w/ AS Lynx IV in Netherlands**
-- ** Another of the 12 F.K.23 airframe bought from BAT
-- http://www.airwar.ru/image/idop/fww1/fk23/fk23-4.jpg
-- 3v: https://www.flightglobal.com/pdfarchive/view/1919/1919 - 0663.html
-- https://www.secretprojects.co.uk/forum/index.php/topic,13780.msg135102.html#msg135102

BAT F.K.24 - 1919 tandem 2-seat biplane trainer; x 1*
- F.K.24: 2-bay biplane; wide-track u/c; simple construction
- F.K.24: 1 x 170 hp ABC Wasp I radial; span 8.10 m
-- * 6 planned; only one built; orders cancelled Nov 1918
-- aka BAT Baboon; interchangable wing panels, elevators

BAT F.K.25 - 1918 single-seat biplane fighter, 3 x built
- F.K.25: 1 x 320 hp ABC Dragonfly radial; span 7.72 m
-- Prototype crashed killed test pilot Lt. Peter Legh*
-- * Legh followed Koolhoven from Armstrong-Whitworth
-- Devel. terminated due to unreliability of Dragonfly
-- aka BAT Basilisk
-- 3v: www.airwar.ru/image/idop/fww1/fk25/fk25-1.gif

BAT F.K.26 - 1919 single-engine biplane 4-pax airliner; x 4
- F.K.26: 1 x 350 hp R-R Eagle VIII engine; span 14.03 m
- F.K.26: 4 pax in forward cabin + 1 x pilot in rear cockpit
-- aka Commercial Mk.I; 4 x completed before BAT closed
-- http://members.ziggo.nl/henrikaper/koolhoven/worlds-first-airliner/
-- 3v: https://www.flightglobal.com/pdfarchive/view/1919/1919 - 0495.html

BAT F.K.27 - 1918 2-seat* biplane sporting a/c; 1 x built
- F.K.27: 1 x 200 hp ABC Wasp II radial; span 7.90 m
-- * Staggered side-by-side seating, aerobatic/racer
-- https://upload.wikimedia.org/wikipe...10120_p19.jpg/450px-BAT_F.K.27_010120_p19.jpg

BAT F.K.28 - 1920 high-winged single-seat ultralight a/c
- F.K.28: 1 x 40 hp ABC Gnat HO2 engine; span 4.57 m
-- aka BAT Crow; twin-boomed with an underslung pod
-- https://i.ebayimg.com/images/g/TYgAAOSw9NdXsoNO/s-l300.jpg

NVI F.K.29 - 1923 light passenger-carrying* biplane; x 1
- F.K.29: 1 x 100 hp Bristol Lucifer 3-cyl.; span 10.00 m
-- * 1 + 2 pax; F.K.29 was a refined BAT F.K.26 design
-- http://all-aero.com/images/stories/koolfk29.jpg

Koolhoven* F.K.30 - 1927 high-winged 2-seat light a/c
- F.K.30: Tandem-seat pod-and-boom pusher (pedestal)
- F.K.30: 1 x 50 hp Siemens radial engine; span 10.50 m
-- aka Toerist, sometimes also referred to as Week-end
-- * Design for NVI, built by Luchttuigenfabriek Koolhoven
-- http://www.airwar.ru/image/i/law1/fk30-i.jpg
-- 3v: http://aviadejavu.ru/Images6/FT/FT1927/02/68-1.jpg
- F.K.30F: (Project) Light flying boat derivative of F.K.30**
-- ** The significane of that 'F' suffix remains unclear

NVI F.K.31 - 1923 2-seat parasol recce-fighter; x 17
- F.K.31: 1 x 420 hp Bristol Jupiter IV; span 13.70 m
- F.K.31: LVA,* 1 x 400 hp Bristol Jupiter 9-cyl. radial
-- * Performance too low; 4 passed to NEI's LA/KNIL
-- LA/KNIL F.K.31s had modified horizontal tailplane
- De Monge M.101 C2 : French license-built; x 1**
-- ** 20 x M.101 A2 ordered for Poland;cancelled
-- M.101: 1 x 420 hp Gnome-Rhône 9Ac Jupiter
- F.K.31: 8 x Finland; 1 x 450 hp Bristol Jupiter IV
-- http://members.ziggo.nl/henrikaper/koolhoven/story/images/fk31.jpg
-- 3v: https://www.modelbrouwers.nl/albums/coppermine/albums/userpics/14089/FK_31_3.jpg

NVI F.K.32 - 1925 tandem 2-seat biplane trainer
- F.K.32: 1 x 130 hp Clerget 9B;* span 7.10 m, x 1
-- * Offered with Bristol Lucifer in place of rotary
-- aka Koolhoven F.K.32; no F.K.32 orders placed
-- http://resolver.kb.nl/resolve?urn=urn:gvn:SFA03:SFA022811881&size=large

NVI F.K.33 - 1925 3-engined high-wing 10-pax airliner
- F.K.33: 3 x 230 hp AS Puma 6.cyl.* span 17.80 m; x 1
-- * 2 x tractor engines + pusher mounted above wing
- F.K.33: 1 x prototype; operated by KLM in 1925-26
-- 3v: http://airwar.ru/image/idop/cw1/fk33/fk33-1.gif

NVI F.K.34 - 1925 parasol 3-seat recce-fighter seaplane
- F.K.34: Private venture twin-float naval recce aircraft
- F.K.34: 1 x 520 hp Hispano-Suiza 12G; span 13.00 m
-- Series of accidents involving floats; no MLD order
-- https://images.memorix.nl/nda/thumb/620x620/9a071cf1-8f51-27c5-5338-d2e71de68fd3.jpg
-- 3v: http://www.airwar.ru/image/idop/other1/fk34/fk34-1.gif

Koolhoven F.K.35 - 1926 2-seat variable config. aircraft
- F.K.35: Assembled as monoplane/biplane/floatplane*
-- * Sole unflown F.K.35 built as low-wing monoplane
- F.K.35: 1 x 600 hp Bristol Pegasus VI; span 10.50 m
-- aka (erroneously) as the NVI F.K.35; never flown
-- Archeiven.nl lists tweepersoons jager/verkenner
-- https://www.flightglobal.com/pdfarchive/view/1926/1926 - 0881.html
-- http://members.ziggo.nl/henrikaper/koolhoven/koolhoven-vliegtuigen/images/koolhoven-fk35.jpg

Koolhoven F.K.36 - (Project) 1926 enlarged F.K.35
- F.K.36: Assembled as monoplane/biplane/floatplane*
-- * As per F.K.35 but with slightly larger airframe
-- * Twin-float seaplane F.K.36 display model built
-- Other sources say F.K.36 as float vers. of F.K.35**
-- ** According to Wesselink/Postma, 1981, pg.59

Koolhoven F.K.37 - (Project) 1927 multiple desig. applied
- F.K.37: Desig. for various layout studies in 1927 period
- F.K.37 (1): Ontwerp 1016; 3-engined high-wing airliner
-- F.K.37 (1) monoplane similar layout to earlier F.K.33
- F.K.37 (2): Ontwerp 1017; 3-engined high-wing airliner
- F.K.37 (2): For KLM; akin to F.K.33 but tractor radials
-- F.K.37 (2) also had deeper fuselage and longer wings
- F.K.37 (3): Ontwerp 1018; 3-engine monoplane bomber
- F.K.37 (4): Ontwerp (??); ?-engine monoplane bomber
-- Some sources list as single-engine monoplane bomber
- F.K.37 (5): 3 x early concept studies; led to F.K.38 (qv)
-- F.K.37 (5-1): Ontwerp 1038 single-engined airliner*
-- * Possibly parasol configuration (as per later F.K.38)
- F.K.37 (5-2 & 5-3): no other details

Koolhoven F.K.38 - (Project) 1927 fighter study
- F.K.38: Single-engined, related to F.K.39 (below)
- F.K.38: no other details

Koolhoven F.K.39 - 1927 2-seat fighter studies
- F.K.39: (Project) Various fighter design studies*
-- Built display model shows parasol with radial**
-- * Probably a Pegasus but may be a Jaguar
-- ** See Wesselink/Postma, 1981, page 52
-- http://members.ziggo.nl/henrikaper/koolhoven/koolhoven-vliegtuigen/images/koolhoven-fk39.jpg

Koolhoven F.K.40 - 1928 high-wing light transport; x 1
- F.K.40: 1 x 230 hp G-R 5K Titan radial;* span 14.50 m
-- PH-AES; sole F.K.40; served in Republican Spain
-- * Offered with alternative 300 hp P&W Wasp Junior
-- https://www.flightglobal.com/FlightPDFArchive/1930/UNTITLED0 - 0211.PDF
-- 3v: http://aviadejavu.ru/Images6/FT/FT1930/02/211-2.jpg
- F.K.40-2m: (Project) Twin; 2 x wing-mounted engines**
-- ** Inline inverted 4-cyl., probably DH [/i]Gipsy Major[/i]s
-- aka Ontwerp 1094

Koolhoven F.K.41 - 1928 3/4-seat cabin monoplane, x 6
- F.K.41: High-wing strut-braced; fixed main u/c gear
- F.K.41: 1 x radial or air-cooled 4-cyl.; span 10.50 m
- F.K.41: Prototype; 1 x 75 hp Siemens Sh.13A radial
-- c/n 4101; reg. H-NAER/PH-AER; aka Sportcoupé
-- http://www.maritiemdigitaal.nl/index.cfm?event=popup.viewimage&img=imh/Afbeeldingen\030003.jpg
-- http://aviadejavu.ru/Images6/FT/FT1929/07/35-7.jpg
- F.K.41a : hypothetical designation
- F.K.41b: 1 x 120 hp DH Gipsy III, eg c/n 4105 PH-AGQ
-- http://www.maritiemdigitaal.nl/index.cfm?event=popup.viewimage&img=imh/Afbeeldingen\030002.jpg
- F.K.41c : (??) 1 x online mention;* 105 hp engine
-- * 1932 League of Nations Air Commission document, pg.220
-- http://digital.library.northwestern.edu/league/le00069f.pdf
- F.K.41d : hypothetical designation
- F.K.41e : Original designation for the F.K.42, c/n 4201
- F.K.41/I : Koolhoven designation for Dessoutter Mk.I
-- aka F.K.41 Mk.I; 1 x 105 hp Cirrus Hermes 4-cylinder
- F.K.41/II: Koolhoven designation for Dessoutter Mk.II
-- Same as F.K.41 Mk.II; 1 x 130 hp DH Gipsy 4-cylinder

Koolhoven F.K.42 - 1929 2-seat training monoplane
- F.K.41e: Orig. designation of F.K.42 serial c/n 4104
-- F.K.41e/F.K.42 was new fuselage with F.K.41 wings
- F.K.42 : Tandem seat parasol trainer; x 1 PH-AGO
- F.K.42: 1 x 110 hp Cirrus-Hermes;* span 10.50 m
-- * Some sources list 230 hp Gnome-Rhône Titan**
-- ** Presumably in a confusion with the F.K.40

Koolhoven F.K.43 - 1931 high-wing cabin monoplane
- BFK.43: 1st prototype; SAFA-built for Baxter; PH-AFW*
-- * Société Anonyme Française Aéronautique; see #20
- F.K.43: 1 + 3 passenger light cabin air taxi;** x 12
- F.K.43: 1 x 130 hp DH Gipsy Major, span 11.00 m
-- ** 9 x in KLM fleet (but usually listed as x 6) [1]
- 'Fokhoven': Post-war production by Fokker; x 8
- 'Fokhoven': 1 x 165 hp AS Genet Major IA*** 7-cyl.
-- Ordered by Frits Diepen Vliegtuigen NV
-- *** As per Fokker S.IX trainer, aka AS Civet I
- 3v: https://modelbrouwers.nl/media/cache/f3/cf/f3cf4eb1ca83f835e30ca361e03442a0.jpg

Koolhoven F.K.44 - 1931 sports monoplane, x 2*
- F.K.44: 115 hp Cirrus-Hermes IIB; span 11.00 m
- F.K.44: High-winged lightplane; reg. PH-AJM
-- Special order a/c,* aka 'Koolmees' (Tomtit)
-- * c/n 4401 never completed, order cancelled
-- * c/n 4402 for Jacob Mees (hence 'Koolmees') [2]
-- http://1000aircraftphotos.com/Contributions/Shumaker/11772L.jpg

Koolhoven F.K.45 - 1932 single-seat sports biplane*
- F.K.45: Single-bay biplane; c/n 4501, F-AMXT**
- F.K.45: 1 x 115 hp Cirrus-Hermes IIB; span 7.00 m
-- * Commissioned by French test-pilot, René Paulhan
-- ** Temporary registration Z-1(PH), then PH-AIF

Koolhoven F.K.46 - 1933 2-seat tandem biplane trainer
- F.K.46: 1 x 130 hp DH Gipsy Major; span 8.00 m; x 12
- F.K.46 Cabriolet: Fitted with a removable canopy
- F.K.46L: Lightweight version; 1 x prototype only*
- F.K.46L: 1 x 95 hp Walter Minor 4-cyl.; span 8.00 m
-- * PH-ALA c/n 4609; destroyed Schiphol 10 May 1940
- F.K.46S: 'School' variant; aka 'De Koe' (The Cow)
-- http://www.airwar.ru/image/idop/other1/fk46/fk46-4.jpg

Koolhoven F.K.47 - 1933 2-seat tandem sports biplane
- F.K.47: 1 x 130 hp DH Gipsy Major 4-cyl.; span 8.00 m
-- Improved F.K.46 type; 1 x prototype only (PH-EJR)*
-- * Crashed at Bonn, July 1933; airframe later repaired

Koolhoven F.K.48 - 1934 high-wing 6-pax feederliner; x 1
- F.K.48: Mixed constr. (wood wings, steel-tube fuselage)
- F.K.48: 2 x 130 hp DH Gipsy Majors; span 15.20 m, x 1
-- KLM Rotterdam-Eindhoven route; air taxi; crew trainer
-- PH-AJX 'Ajax' KLM Rotterdam-Eindhoven route 'til 1936
-- Thereafter, flew on short routes & as an air taxi/trainer
-- 3v: http://aviadejavu.ru/Images6/FT/FT1935/01/146-2.jpg

Koolhoven F.K.49 - 1935 high-wing twin-engine recce a/c*
- F.K.49: 2 x 130 hp DH Gipsy Majors; span 16.00 m; x 1
-- * 'Foto verkenner' (photo-recce) intended for LVA**
-- ** '950' only, other 2 x LVA a/c, never completed
-- Onboard darkroom; or 2-litter medevac; or 4 pax
-- 3v: http://aviadejavu.ru/Images6/FT/FT1935/11/611-2.jpg
- F.K.49A: 3 x variants with wider/longer nose, 5 pax
-- Turkish Air Force; 2 x 305 hp Ranger V-770B-4
-- Finland (Merivartiolaitos);* 2 x 285 hp Hirth 508C
-- * Finnish Coast Guard ordered x 2 float/wheel gear
-- Finnish F.K.49A flown as LVA 1001 before delivery
- F.K.49R: Romania vers.; 2 x 240 hp Argus As 10 C3
-- 2 incomplete F.K.49R destr'd Waalhaven, 10 May 1940

Koolhoven F.K.50 - 1935 high-wing 8-passenger feederliner
- F.K.50: 2 x 400 hp P&W Wasp Junior T1Bs; span 18.00 m
- F.K.50: Mixed constr. (wood wings, steel-tube fuselage)
- F.K.50 : 1st & 2nd aircraft; 2 + 8; single fins & rudders
-- c/n 5001/HB-AMI; c/n 5002/HB-AMO; 355 hp Wasp Junior
-- 3v: http://aviadejavu.ru/Images6/FT/FT1935/10/400-1.jpg
- F.K.50A: 3rd aircraft; twin fins/rudders; smaller cowlings
- F.K.50B: (Project) Turreted military variant; not built
- F.K.50B: Larger radials, retr. main u/c' nose/dorsal turrets
-- F.K.50B meant for Republican Spain; too late for civil war
-- https://www.secretprojects.co.uk/forum/index.php/topic,2742.msg21938.html#msg21938
-- 3v: http://aviadejavu.ru/Images6/FT/FT1936/08/2329-1.jpg

Koolhoven F.K.51 - (Project) 1934 recce-bomber for Sweden
- F.K.51: Twin Pegasus land/floaplane; 1st use of designation
- F.K.51: Referred to as Bombplan; see Ontwerp 1093 below

Koolhoven F.K.51 - 1935 2-seat advanced training biplane
- F.K.51: 1 x 350 hp-to-450 hp radial engine; span 9.00 m
- F.K.51: LVA trainer, 1 x 350 hp AS Cheetah IX radial
-- 25 x LVA 2-seat advanced trainer version (E-1 to E-25)*
-- 29 x LVA verkennerversie (recce variant; 400 to 428)
-- 15 x MLD; E-1 to E-15; 1936-1937 (+ 2 x repl. a/c 1938)
-- 45 x LA/KNIL (of 60 ordered) K-1 to K-45/K-101 to K-145
-- * Some sources list 44 x total MvD deliveries as of 10 May
-- Pg 251 https://pure.uva.nl/ws/files/1764152/128309_12.pdf
- F.K.51 (Spanish version): 1 x 400 hp AS Jaguar 14-cylinder
- F.K.51bis: 1 x 450 hp Wright Whirlwind R-975-E-3 radial
-- Total F.K.51/F.K.51bis exports to Republican Spain x 28

Koolhoven F.K.52 - 1937 2-seat recce-fighter* biplane
- F.K.52: Canopy, fixed u/c, Fokker C.V replacement*
-- * Offered as tweepersoons-eenmotorig gevechtsvliegtuig
-- * Or a generic '2-seat, single-engined combat aircraft'
- F.K.52: 1 x 830 hp Bristol Mercury VIII; span 9.80m
- F.K.52 prototype: 1 x 645 hp Bristol Mercury VIS 9-cyl.
-- PH-AMZ) crashed during 1937 LVA Soesterber demo.**
-- ** Lower wing snapped off; design strengthened
- F.K.52: PH-ASW, 'ASX, 'ASY, 'ASZ, ' PH-ATA unsold
-- 1939: Spanish Republic offered to buy all 5 aircraft
-- End of 1939: LVA places orders for 36 x F.K.52s***
-- ***To replace C.X (which would then replace C.Vs)
-- Post May 1940: German occupiers scrap 2 x F.K.52s
-- 1940: Count von Rosen donates 2 x F.K.52 to Finns
-- PH-ASW & PH ASX to Ilmavaimot as KO-129 & '130
-- In Finnish service, the FK.52 dubbed 'Kolhoveneiksi'
-- 3v: https://modelbrouwers.nl/media/albums/642/8402/fk52_wesko1_6.jpg

Koolhoven F.K.53 - 1936 2-seat light cabin monoplane
- F.K.53: Low-placed gull wings; side-by-side-seating
- F.K.53: 1 x 62 hp* Walter Mikron 4-cyl., span 10.50 m
-- * Contemporary sources list Mikron power at 50 hp
-- aka Koolhoven Junior, designed by ir. J. van Hattum
-- F.K.53: 1936 c/n 5301; reg PH-ALH/PH-ALN/PH-FKJ
-- F.K.53: 1938 c/n 5302; registration PH-ATG
-- http://www.maritiemdigitaal.nl/index.cfm?event=popup.viewimage&img=imh/Afbeeldingen\030067.jpg

Koolhoven F.K.54 - 1938 3-seat cabin monoplane, x 1
- F.K.54: High-winged; rearward-retracting main gear
- F.K.54: 1 x 130 hp DH Gipsy Major II; span 11.00 m
- PH-APR commissioned by C.E. van 't Groenewoud
-- http://members.ziggo.nl/henrikaper/koolhoven/koolhoven-vliegtuigen/images/koolhoven-fk54.jpg

Koolhoven F.K.55 - 1938 single-seat fighter a/c; x 1
- F.K.55: 1 x 720 hp Lorraine Pétrel V-12; span 9.60 m
- F.K.55: Shoulder-wing, mid-engined, mixed constr.*
- F.K.55: Extension shaft from engine to contra-props
-- * Steel-tube fwd fuselage; wood aft; wooden wings
- F.K.55: 1936 mockup; Paris Salon de l'Aéronautique
- F.K.55: 1938 prototype w/ temporary fixed main u/c
- F.K.55: (Project) Prod. version; Lorraine Sterna V-12
- F.K.55: (Project) Low-winged derivative of F.K.55**
-- ** Such a variant is reported, can anyone confirm?
-- https://www.secretprojects.co.uk/forum/index.php/topic,7244.msg63477.html#msg63477
-- https://oldmachinepress.com/2016/07/20/koolhoven-fk-55-fighter/

Koolhoven F.K.56 - 1938 advanced combat trainer;* x 11
- F.K.56: 1 x 350-to-400 hp radial engine; span 11.50 m
-- * Or overgangsvliegtuigen (transitional trainer)
- F.K.56: 1st prototype; 1 x 400 hp Wright R-975E-3
- F.K.56: 1st prototype; c/n 5601; civil reg. PH-ASB
-- Gull wing; mod. F.K.51 fuselage; J. Weyer design
- F.K.56: 1939 2nd prototype; 1 x 350 hp AS Cheetah
- F.K.56: 2nd prototype; c/n 5602; civil reg. PH-ATE
-- Straight wing; retr. u/c; redesign by ir E. Schatzki
-- PH-ATE destroyed by German bombing 10 May 1940
- F.K.56: 1939 pre-prod'n version for LVA; c/n 5603
-- 5603 w/o in crash; leading to stiffening of wings
- F.K.56: Prod'n; 420 hp Wright Whirlwind R-975E-3
- F.K.56: Export version for Yugoslavia and Belgium
-- c/n 5613 for Yugo. + 2 near completion; May 1940
-- Belgian order for x 20 received 12 February 1940
-- http://www.belgian-wings.be/images/Milpics/Interbellum/interbellum_a_m/Koolhovenfk5803.jpg
- F.K.56A: Same as F.K.5601 (??); no other details
-- Rapport S.175: Contrôle van de sterkte van het vliegtuigtype FK.56A
-- http://www.nederlandseluchtvaart.nl/forums/showthread.php?40287-FK-56
- F.K.56B: Same as F.K.5602 (??); no other details
-- Rapport S.212 and Rapport S.214 (same source)
-- https://db.wingstovictory.nl/documentatie/17-FK56 opmerkingen Harry van der Meer.pdf

Koolhoven F.K.57 - 1938 twin-engined feederliner; x 1
- F.K.57: Twin-tailled; low-winged; spatted main gear
- F.K.57: 2 x 205 hp DH Gipsy Six II 6-cyl.; span 13.20 m
-- c/n 4301 PH-KOK commis. by JEF de Kok (hence reg.)
-- Sole F.K.57 was destroyed at Ypenburg; 10 May 1940
- F.K.57: (Project) Military variant with retractable u/c*
-- * Offered to the LVA as a multi-engine pilot trainer
-- http://1000aircraftphotos.com/Contributions/KleinBernhard/6033L-1.jpg

Koolhoven F.K.58 - 1938 single-engined fighter*
- F.K.58: Low-winged single-seater; retr. main u/c
-- F.K.58 aka Koolhoven Ontwerp 1166
- F.K.58: 1 x 1,080 hp radial (various); span 10.97 m
- F.K.58 : 1 x Hispano-Suiza 14Aa-10 14-cyl.; x 7
- F.K.58 : 1st prototype c/n 5801 PH-ATO
-- W/O after 12 Jan 1939 accident at Ghent, BE
- F.K.58A: 1 x Gnome-Rhône 14N-16 14-cyl.,** x 14
-- * Ordered by French Ministère des Colonies
-- ** 10 x sub-contracted to SABCA in Belgium
- F.K.58B: (Project) LVA order with Bristol Taurus III
- F.K.58B: 36 ordered 22 July 1939, none delivered [3]
-- Taurus export ban, alternative Mercury proposed [4]
- Ontwerp (??): F.K.58 w/ German DB 600 inverted V-12
- Ontwerp (??): More powerful radial [5]

Koolhoven F.K.59 - Designation re-used at least 7 times
(NB: Projects below may not be listed chronologically)
- F.K.59 (1) (Project) Open 2-seat sports plane*
-- * "Sportsplane" mentioned by Wesselink, 2012
- F.K.59 (2): (Project) Twin-engine floatplane
-- Mid-winged, twin-float MLD torpedo-bomber
-- 1937 design, full-scale mock-up completed
-- https://www.secretprojects.co.uk/forum/index.php/topic,2742.msg140146.html#msg140146
-- https://www.secretprojects.co.uk/forum/index.php/topic,2742.msg21897.html#msg21897
- F.K.59 (3): (Project) Modernized version of F.K.52
- F.K.59 (3): 2-seat recce-fighter biplane for the LVA
- F.K.59 (3): 1 x 840 hp Mercury XV 9-cyl.; span 9.80m
- F.K.59 (IV) : (Project) Reconnnaissance biplane
- F.K.59 (V) : (Project) Twin-engined float monoplane torpedo-bomber
- F.K.59 (VI ): (Project) Twin-engined float monoplane torpedo-bomber
- F.K.59 (VII ): (Project) Reconnnaissance triplane; based upon the FK.52
-- 36 x F.K.59 ordered for LVA on 21 November 1939**
-- ** Mercury XVs delivered but constr'n never begun

Koolhoven F.K.60 - (Project) (??) no details
- F.K.60: (??) Reported as a Koolhoven project
- F.K.60: "mentioned shortly before May 1940"
-- http://www.nederlandseluchtvaart.nl/forums/showthread.php?40337-Koolhoven-FK-702
-- NB: What-If Koolhoven-Desoutter FK-60 (dizzyfugu)
-- NB: What-If Hercules-powered F.K.58, (Hood, WesWorld)

___________________________________________

[1] Full KLM F.K.43 fleet names were: Bromvlieg, Citroenvlinder, Dar, Juffertje, Krekel, Libel, Luis, Nonvlinder, and Olietor. During WW2, 4 x KLM F.K.43s were impressed for the LVA as 960, 963, 965 and 966.

[2] A well-known sports flyer of the day, Rotterdam banker Jacob Mees directed a number of new investors to NV Koolhoven Vliegtuigen.

[3] Many sources claim a Dutch order for 40 x F.K.58Bs. If true, the 'extra' 4 x fighters were not covered by the MvD's 22 July 1939 order.

[4] Proposed alternative Mercury VIII engines would have come from ML stocks. Option presented to Minister of Defence AHQ Dijxhoorn who rejected the Mercury-powered F.K.58B in favour of more powerful US-built fighters. In April 1940, Dijxhoorn ordered 24 x Curtiss-Wright CW-21Bs.

[5] The DB 600 and "more powerful radial" engines for F.K.58 developments is mentioned in Blue Skies, Orange Wings by Noppen, pg 200. So too is the suggestion of alternative Mercury VIII engines for F.K.58Bs but this is confirmed in https://pure.uva.nl/ws/files/1764152/128309_12.pdf
________________________

Known Frits Koolhoven Ontwerpen Numbers (and gaps)

BAT (Design No.?) - (Project) Flying boat
-- BAT flying boat design concept (no details)*
-- * But see Armstrong-Whitworth F.K.18 discussion

Koolhoven Ontwerp 1016 - (Project) 3-engined airliner
- Ontwerp 1016: One of 5 x design concepts for F.K.37
- Ontwerp 1016: Monoplane; layout akin to earlier F.K.33

Koolhoven Ontwerp 1017 - (Project) 3-engined airliner
- Ontwerp 1017: One of 5 x design concepts for F.K.37
- Ontwerp 1017: For KLM, as F.K.33 but tractor engines
- Ontwerp 1017: With deeper fuselage & longer wings

Koolhoven Ontwerp 1018 - (Project) 3-engined bomber
- Ontwerp 1018: One of 5 x design concepts for F.K.37
- Ontwerp 1018: Presum. related to Ontwerp 1016/1917

Koolhoven Ontwerp 1029 - (Project) ~192? pusher fighter
-- Mid-wing, twin-boomed pusher fighter designed for export*
- Ontwerp 1029: 1 x (??) hp radial,** span (??) m
-- * Ontwerp 1029 was offered to Sweden and Norway
-- ** Single-row engine, presumably a Bristol Jupiter

Koolhoven Ontwerp 1030 - Ontwerp 1037 (??)

Koolhoven Ontwerp 1038 - (Project) 1-engined airliner
- Ontwerp 1038: One of 5 x design concepts for F.K.37
- Ontwerp 1038: Possibly parasol-winged configuration

Koolhoven Ontwerp 1039 - Ontwerp 1088 (??)

Koolhoven Ontwerp 1087 - (Project) 193? 2-seat biplane
- Ontwerp 1087: Biplane trainer; concept leads to F.K.46
-- https://www.secretprojects.co.uk/forum/index.php/topic,2742.30.html

Koolhoven Ontwerp 1088 - Ontwerp 1092 (??)

Koolhoven Ontwerp 1093 - (Project) 1934 medium bomber
- Ontwerp 1093: Monoplane bomber for Swedish Flygvapnet
- Ontwerp 1093: 2 x Bristol Pegasus radials;* span 25.00 m
-- * 650-to-700 hp; Bristol Pegasus II L3 mentioned specifically
- Ontwerp 1093: Aka F.K.51 Bombplan (1st desig. application)
- Ontwerp 1093: Alt wheels or twin floats; SE chose Junkers Ju 86K

Koolhoven Ontwerp 1094 - (Project) 193? light cabin transport
- Ontwerp 1094: aka F.K.40-2m; twin-engined* F.K.40 deriv.
-- * Wing-mounted engines; appear to be DH Gispy-Majors

Koolhoven Ontwerp 1095 - Ontwerp 1098 (??)

Koolhoven Ontwerp 1099 - (Project) 193? twin-engined bomber
- Ontwerp 1099: 2 x inline engines; low-winged; & twin-tailled*
-- Nose turret; dorsal gun position; + ventral 'dustbin' position
-- * Small, near-circular and larger, ellipical fins also proposed

Koolhoven Ontwerp (??) - (Project) 1935 flying boat for MLD
- Ontwerp (??): Pylon-mounted wing; 3-engined, 'stummeln'*
-- * Dornier Wal-style stummeln sponsons specified by MLD
-- Artist concept marked '189'; nose & dorsal turret armament

Koolhoven Ontwerp 1101 - (Project) 193? single-seat biplane
- Ontwerp 1101: Biplane fighter with retractable main gear
-- 1 x (??) hp Lorraine 12H Pétrel; radiator as per Ontwerp 1117

Koolhoven Ontwerp 1102 - Ontwerp 1104 (??)

Koolhoven Ontwerp 1105 - (Project) 1936 3-seat recce-fighter
- Ontwerp 1105: 1 x radial or inline engine;* span (??) m
-- * 720 hp Wright Cyclone F-52 or (??) hp V-12 (poss. Kestrel?)
-- Low-wing scout/light bomber (verkenner/licht bommenwerper)
-- Ontwerp 1105 poss. rival to 1936 Fokker 'Gesloten verkenner'
-- http://www.maritiemdigitaal.nl/index.cfm?event=popup.viewimage&img=imh/Afbeeldingen\067818.jpg
-- https://www.secretprojects.co.uk/forum/index.php/topic,2742.msg172430.html#msg172430

Koolhoven Ontwerp 1106 - Ontwerp 1112 (??)

Koolhoven Ontwerp 1113 - (Project) 193? light cabin a/c
- Ontwerp 1113: Leads to 1936 F.K.53 2-seat monoplane

Koolhoven Ontwerp 1114 - Ontwerp 1116 (??)

Koolhoven Ontwerp 1117 - (Project) c.1936 fighter/recce
- Ontwerp 1117: 2-seater with enclosed cockpit canopies
- Ontwerp 1117: 1 x (??) hp R-R Kestrel V-12,* span (??) m
-- Strut-braced parasol wings; cantilevered main u/c legs
-- * Air intake for coolant radiator situated above engine
-- * Engine type may be Lorraine 12H Pétrel V-12

Koolhoven Ontwerp 1118 - Ontwerp 1123 (??)

Koolhoven Ontwerp 1124 - (Project) 193? airliner
- Ontwerp 1124: Twin-engined sesquiplane layout

Koolhoven Ontwerp 1125 - (Project) 193? light feederliner
- Ontwerp 1125: 2 x (??) hp air-cooled inlines; span (??) m
-- Semi-cantilever high-wing; fixed main u/c; single tailplane
-- Perhaps an early take on the F.K.49 retaining F.K.48 features

Koolhoven Ontwerp 1125 - Ontwerp 1141 (??)

Koolhoven Ontwerp 1142 - (Project) 193? twin-engine bomber
- Ontwerp 1142A: Mid-wing fixed main u/c;* medium bomber
- Ontwerp 1142A: 2 x (??) hp radial engines; span (??) m
- Ontwerp 1142B: Twin-float medium bomber/torpedo bomber
-- Ontwerp 1142B was offered to Norway (as M.F.11 repl.?)
-- * Arrangement suggests connection with F.K.50 series
-- https://www.secretprojects.co.uk/forum/index.php/topic,2742.msg172412.html#msg172412

Koolhoven Ontwerp 1143 - Ontwerp 1150 (??)

Koolhoven Ontwerp 1151 - (Project) c.1937 civil flying boat
- Ontwerp 1151: 2 x 290 hp Menasco C6S-4s;* span 16.00m
- Ontwerp 1151: Small amphibian flying boat; 2 crew + 4 pax
-- * C6S-4 Super Buccaneer; 290 hp (for T/O); sust. 260 hp
-- Mixed const. (wood wings;** alum. fuselage); 'Stummeln'
-- ** Folding wings seem to have been an option

Koolhoven Ontwerp 1152 - Ontwerp 1153 (??)

Koolhoven Ontwerp 1154 - (Project) 1937 fighter-bomber
- Ontwerp 1154: Monoplane (gevechtsvliegtuig?)

Koolhoven Ontwerp 1155 - Ontwerp 1163 (??)

Koolhoven Ontwerp (??) - (Project) 1938 Oceaanvliegboot
- Ontwerp (??): 100 ton; 180 pax; metal constr.; flying boat
- Ontwerp (??): twin props; grouped engines;* span 70.00 m
-- Research 1936; design 1938; rejected by KLM's A. Plesman
-- * From 2 x pairs tandem inlines up to 10 x 'raw oil' engines

Koolhoven Ontwerp (??) - (Project) 1938 civilian flying boat
- Ontwerp (??) - 2 x (??) hp radial engines; span (??) m
-- Engines on pylon-mounted wings; 'stummeln' sponsons

Koolhoven Ontwerp (??) - (Project) 1938 2-seat recce-fighter
-Ontwerp (??): Mid-wing monoplane; cruciform tail; bomb bay
-- Designed by ir. Van der Eyk; list as "modernised F.K.52"*
-- * Monoplane concept actually more of an F.K.52 replac't
-- * "modernised F.K.52" may be conf'n with F.K.59 biplane

Koolhoven Ontwerp 1164 - (Project) 1938-1939 jachtkruiser
- Ontwerp 1164: 2 x (??) hp (??) engines; span (??) m
- Ontwerp 1164: 4-seat jachtkruiser based upon F.K.50B

Koolhoven Ontwerp 1165 - (Project) (??) hypothetical designation

Koolhoven Ontwerp 1166 - (Project) single-engined fighter
- Ontwerp 1166: 1 x 1,000 hp (??) radial engine; span ?? m
- Ontwerp 1166: Single-seat French colonial fighter aircraft
-- Ontwerp 1166 built as the F.K.58; first flew 17 July 1938

Koolhoven Ontwerp 1167 - (Project) 1938-1939 jachtkruiser
- Ontwerp 1164: 2 x (??) hp (??) engines; span (??) m
- Ontwerp 1164: 4-seat jachtkruiser based upon F.K.50B

Koolhoven Ontwerp 1168 - Ontwerp 1170 (??)

Koolhoven Ontwerp 1171 - 1938 3-seat twin-float recce seaplane*
- Ontwerp 1171: 1 x (??) hp (??) radial engine;** span (??) m
-- Low-wing monoplane; broad semi-cantilevered float struts
-- * To same 1938 MLD contest as the also-unbuilt Fokker T.10W
-- * Based on its exhaust outlet, engine is prob. Wright Cyclone

Koolhoven Ontwerp 1172 - 1939 twin-engine transport monoplane
-- https://www.secretprojects.co.uk/forum/index.php/topic,2742.msg301245.html#msg301245

Koolhoven Ontwerp 11(??) ...

 

[hesham]

Amazing work as usual my dear Apophenia,

and you can add;

Ontwerp 1087;
https://www.secretprojects.co.uk/forum/index.php/topic,2742.30.html

Ontwerp 1113 A & B was FK.53

Ontwerp 1124;
https://www.secretprojects.co.uk/forum/index.php/topic,2742.msg299279.html#msg299279

Ontwerp 1154;
https://www.secretprojects.co.uk/forum/index.php/topic,2742.msg300880.html#msg300880

Ontwerp 1172;
https://www.secretprojects.co.uk/forum/index.php/topic,2742.msg301245.html#msg301245

 

[Apophenia]

Thanks Hesham, those Ontwerpen have been added

 

[hesham]

Thanks Hesham, those Ontwerpen have been added

Thank you my dear Apophenia,

and also you can add;

- Trainer aircraft Project before F.K.51
- Sporting aircraft Project of 1930s
- Large flying boat Project of 1932
- Torpedo bomber Project,powered by two engines,1937
- Twin engined transport flying boat Project of 1932
- Transport flying boat Project of 1932 also
- Recce flying boat Project of 1930s,powered by three engines
- Twin engined sporting and light transport aircraft Project of 1934

 

[Apophenia]

Thanks Hesham. Hopefully Ontwerp numbers will emerge for those projects one day.

 

[hesham]

Thank you my dear Apophenia.

 

[Apophenia]

A minor update: I've added the F.K.56A and F.K.56B to the above list but have no details on either.

Both variants are mentioned on Nederlandse Luchtvaart in their FK 56 thread:
http://www.nederlandseluchtvaart.nl/forums/showthread.php?40287-FK-56 (see Reply #10)

Forum member Classic (Ronald) quotes reports held by the nationaal archief including:

Rapport S.175
Contrôle van de sterkte van het vliegtuigtype FK.56A

Rapport S.212
Rapport over de contrôle der sterkteberekening van den vleugel van het Koolhovenvliegtuig type FK 56B

Rapport S.214
Rapport over de contrôle der sterkteberekening van het onderstel van het Koolhoven vliegtuig type FK56B

Reports S.219 and S.221 discuss the third aircraft, 'FK 5603', so 'FK.56A' and 'FK 56B'/'FK56B' may refer to prototypes. Does anyone know for sure?

In those reports, I also see mention of an 'FK56-LVB':

Rapport V.1213
Berekening van de kritische snelheid voor onstabiele vleugeltrillingen van het vliegtuig Koolhoven FK56-LVB in drie uitvoeringen - inhoudsopgave - in opdracht van het Luchtvaartbedrijf (LVB) te Soesterberg (LVA).

Having come across a number of manual drawing titled "F.K.56 L.V.B.", I've come to think of this as a generic term for the February 1939 production version. Accordingly, I'm dropped mention of the 'F.K.56 LVB' as separate variant. As for the online 'F.K.56 LVB' three-view drawing of February 1940, I'm leaning towards the conclusion that the distinctions shown have more to do with somewhat sloppy technical art than with planned design revisions.

 

[Stargazer]

Perfect job, Apophenia, as was to be expected of you!! ;D

I'm even surprised it took you so long to come up with this one, I had a feeling the subject had already been tackled on the forum (but I guess we only skimmed the surface at the time we discussed the early Armstrong-Whitworth designs).

For what it's worth, I'm attaching an article from the Aero magazine, specialized, in WW1 and vintage aviation, about Koolhoven's early designs. Can't remember exactly where I got it from, but I have a feeling it was from one of our forum's members, possibly lark or Schneiderman (if not, sorry to whomever shared this with me!) I'm also adding the TXT version of a page I saved from the web a long time ago (where from, I couldn't say).

 

[Apophenia]

Thanks Stéphane! I too was surprised to find that a Koolhoven list hadn't already been done. Your early Armstrong-Whitworth designations were my prompt for a complete F.K. listing. Of course, that list - especially the Ontwerp numbers - would have been impossible without lark's assistance. Even then, hesham had to remind me of a host of others ;p

Many thanks for the attachments. Good to see WW1 Aero giving some credit to Bod Noorduyn

That great text document I recognize. De vliegtuigen van Frits Koolhoven was originally done by the inimitable Herman Dekker:
http://www.hdekker.info/DIVERSEN/Koolhoven.htm

 

[hesham]

Thank you my dears Skyblazer and Apophenia.

 

[hesham]

In my files,

the F.K.59 was allocated to a 7 designs;

three mentioned by dear Apophenia,also;

F.K.59/IV was a biplane recce Project
F.K.59/V was anther monoplane float torpedo bomber Project,powered by two engines
F.K.59/VI was a third concept for monoplane torpedo bomber Project,powered by two engines
F.K.59/VII was a recce triplane Project,based on FK.52

 

[hesham]

Info from the book,Frits Koolhoven en zijn Vliegtuigproduktie,but I don't have it;

the F.K.37 was allocated to a three different concepts,one mentioned by dear Apophenia,

F.K.37/II was a transport biplane Project,powered by three engines
F.K.37/III was a monoplane bomber Project,maybe light or medium bomber,powered by one engine

 

[hesham]

In my files,

the FK.39 was powered by Bristol Jupiter engine,and FK.51 had a version for single seat fighter or fighter trainer.

 

[PF-18]

Hello, I am new to this site and I am interested in little-known project planes, the FK-45 was used in France by an aerobatic pilot René Paulhan, I hope to make a model of this plane, here is a photo, but I especially need a good plan in 3 views
Greetings

 

[Arjen]

@PF-18 Searched for images with 'koolhoven 45' - sometimes the dumbest cues are the best.
Images found here:
http://www.airwar.ru/enc/law1/fk45.html

 

[Arjen]

Images from Koolhoven - Nederlands vliegtuigbouwer in de schaduw van Fokker by Theo Wesselink and Thijs Postma, Unieboek 1981.

Data from the book:
- engine: 115 hp Cirrus Hermes
- max speed: 210 km/h at sea level
- start weight: 580 kg for aerobatics
- span: 7.04 m
- length: 5.57 m
Dutch registration PH-AIF

Third image: the man with the hat is Frits Koolhoven, the pilot might be René Paulhan.

 

[PF-18]

Fantastic ! exactly what I needed, the plan is simple but with the photos I think I can make a model of it.
A big thank-you

 

[Stargazer]

Koolhoven F.K.43 - 1931 high-wing cabin monoplane
- BFK.43: Baxter-built 1st prototype, PH-AF
- F.K.43: 1 + 3 pax light cabin air taxi,* x 12
- F.K.43: 1 x 130 hp DH Gipsy Major, span 11.00 m
-- * 9 x KLM use, usually listed as x 6 [1]
- 'Fokhoven': Post-war prod'n by Fokker, x 8
- 'Fokhoven': 1 x 165 hp AS Genet Major IA** 7-cyl
-- Ordered by Frits Diepen Vliegtuigen NV
-- ** As per Fokker S.IX trainer, aka AS Civet I
- 3v: https://modelbrouwers.nl/media/cache/f3/cf/f3cf4eb1ca83f835e30ca361e03442a0.jpg

Regarding the "Baxter-built" F.K.43... This was actually built in France under license.
The commercial name of the company was "Baxter-Aviation", but in fact the aircraft was built by S.A.F.A. (Société Anonyme Française Aéronautique). The following two pages are from the 1931 French aviation directory.

 

[Stargazer]

1912, early - Designer, Société Provisoire des Aéroplanes Deperdussin

Nope. This was a derisive interpretation of the acronym S.P.A.D. by the defenders of Deperdussin, out of bitterness after his short-lived company folded (he had been involved in dubious financial transactions). The real meaning was Société de Production des Aéroplanes Deperdussin. Blériot took over the company's assets, retaining the name for the productions of this subsidiary.

Source: Aviation Magazine International, 1 March 1985.

 

[hesham]

Koolhoven F.K.51 - 1935 2-seat advanced training biplane
- F.K.51: 1 x 350-450 hp radial engine, span 9.00 m
- F.K.51: LVA trainer, 1 x 350 hp AS Cheetah IX radial
-- 25 x LVA 2-seat advanced trainer version (E-1 to E-25)*
-- 29 x LVA verkennerversie (recce vers., 400 to 428)
-- 15 x MLD, E-1 to E-15, 1936-1937 (+ 2 x repl. a/c 1938
-- 45 x LA/KNIL (of 60 ordered) K-1 to K-45/K-101 to K-145
-- * Some sources give 44 x total MvD delivers as of 10 May
-- Pg 251 https://pure.uva.nl/ws/files/1764152/128309_12.pdf
- F.K.51: Spanish vers., 1 x 400 hp AS Jaguar 14-cyl
- F.K.51bis: 1 x 450 hp Wright Whirlwind R-975-E-3
-- Total F.K.51/F.K.51bis exports to Rep. Spain x 28

F.K.51W was a reconnaissance floatplane project

source,

https://www.marktplaats.nl/v/verzam...vliegtuig-encyclopedie-4-delen-ex-bibliotheek

 

[Apophenia]

F.K.51W was a reconnaissance floatplane project ...

Yes, but this monoplane recce-bomber with (optional) float gear was unrelated to the built F.K.51 biplanes.

In Luchtvaartkeneis 2024 Nummer 1 (pp 30-31), Frits Gerdessen wrote an article entitled De eeste Koolhoven F.K. 51: de bombplan. This article explains the vast differences between the built 1935-36 F.K. 51 trainer and a 1934 bomber concept for Sweden referred to by the same designation ... but also identified as the Ontwerp 1093.

Designed by ir. Jacques Leijh this earlier F.K. 51 Bombplan, this was to be a low-winged monoplane with twin tails. The Flygvapnet specified twin 650-to-700 hp Bristol Pegasus radials (with the Pegasus II L3 mentioned specifically by Gerdessen). In the case of the F.K. 51 Bombplan, these would be pylon-mounted above the wings (think Sud-Est S.E.400 but without the reversed gull wings). Span would have been 25.00 m, overall length 18.75 m.

To meet the Swedish specification, the F.K. 51 Bombplan could have its retractable main undercarriage replaced with twin Short Brothers floats (as illustrated in Gerdessen's 3-view drawing for his article). Alas, there is no sign whatever in that article of any Dutch-style 'F.K.51W' designation.

As we know, in Nov 1934, the Flygvapnet would select the rival Junkers Ju 86K design to fill its specification.

 

[hesham]

Koolhoven F.K.37 - (Project) 1927 trimotor airliner
- F.K.37: High-wing monoplane similar to NVI F.K.33
- F.K.37: 3-engined* pax aircraft intended for KLM
-- * Arranged as per F.K.33 but all tractor radials
- F.K.37 (II ): (Project) Tri-motor transport biplane
- F.K.37 (III): (Project) Single-engined monoplane bomber

As I know,there are a five designs, called F.K.37,and not only three.

 

[Apophenia]

As I know,there are a five designs, called F.K.37,and not only three.

Okay. We've got monoplane and biplane trimotor airliners and a single-engined monoplane bomber listed. What were the other two F.K.37 variants meant to be?

 

[hesham]

It's as following for F.K.37,

1) High-wing monoplane similar to NVI F.K.33, Ontwerp 1016
2) As above (monoplane) but with higher fuselage and longer wing, Ontwerp 1017
3) Three-engined (not single) monoplane bomber, Ontwerp 1018
4) Another bomber,but with unknown numbered of engine
5) Early design,which led to develop F.K.38,in three concepts,one was
single-engined airliner, Ontwerp 1038

 

[hesham]

Also from my files,

F.K.29/II was a monoplane passenger transport project
F.K.30/II was a two seat trainer project,with one 45 Anzani engine
F.K.37/VI was biplane for advertisement and publiction duty project,powered
by three 300 hp engines
F.K.37M II was another transport project (not crew trainer)
F.K.38/III was a cargo aircraft project,maybe a version of F.K.38/I, Ontwerp 1042

One of the sources