A.Weyl Fokker: The Creative Years (Putnam)

The Fokker V.36

   Fokker’s own development of the basic D.VII produced new types in the V series. Of these, the V.22 and V.24 have already been mentioned.
   In the summer of 1918, the Fokker V.34 and V.36 (Factory No. 2656) appeared. It seems probable that their development proceeded more or less simultaneously. It is believed that the V.36 at least was originally powered by the high-compression 220/240-h.p. Benz Bz.IVu engine, but was soon converted to have the 185-h.p. B.M.W.IIIa. In this latter form of the V.36, its fuselage was apparently identical with that of the V.34, which also had the B.M.W.IIIa.
   In these two aircraft, the B.M.W. installation had an oval radiator of a new type, and the engine was more cleanly cowled. The wings had the same span as those of the Fok. D.VII, but were of smaller area; the new aircraft were also shorter, the V.36 being roughly the same length as the D.VI.
   The V.34 had a rudder of the same shape as that of the V.33, whereas the vertical surfaces of the V.36 resembled those of the Fok. D.VII. The undercarriage of the V.34 appeared to be virtually identical with that of the D.VII.
   The V.36 aircraft had a better climbing performance than the D.VII, and was Platz’s final development of the basic V.11 before the end of the war.
   One major innovation distinguished the V.36 from its predecessors. In this aircraft, the radical step of transferring the main fuel tank from the fuselage to the undercarriage axle fairing had been taken. This would have been warmly welcomed by every pilot. By 1918, owing to the widespread use of tracer and incendiary ammunition, the number of aircraft shot down in flames had increased alarmingly.
   In face of this obvious threat to morale, the IdFlieg was pressed to do something to reduce the fire risk. Inventors were encouraged to produce ideas, and the IdFlieg stipulated that all future fighter aircraft should embody adequate safeguards against fire, both from enemy action and from crash damage.
   Platz suggested the transformation of the undercarriage wing into the fuel tank. Fokker thought it a good idea. If such a tank were struck by incendiary bullets, no burning petrol would reach the pilot or damage vital parts of the aircraft, such as the tail unit. This offered a good chance of escape from such a situation; and in the event of a crash landing the tank was too far from the engine for there to be a risk of fire. It seemed an excellent solution.
   Fokker conducted ground tests at Schwerin, using coloured water and fuel for the purpose. These showed that no escaping petrol was likely to reach the cockpit or tail surfaces. The V. 1 fuselage was resurrected for the tests. Fokker also seems to have made some demonstrations in flight, using coloured water.
   He took out several patents on undercarriage tanks. His German D.R.P. 332,048 of April 6, 1918, related to the location of fuel tanks within the axle fairing; there were two tanks, one in front of and one behind the axle. D.R.P. 356,749 of December 24, 1918, covered the final version in which the tank was a one-piece component of streamline cross-section, and the axle passed through it in a box-type housing. All undercarriage tanks had a streamline section; the lifting-aerofoil section of the early axle fairing was abandoned.
   There was, of course, one obvious disadvantage in this arrangement of the petrol tank: considerable pressure was required to force fuel up into the small gravity tank. Submerged fuel pumps were unknown at that time; had they been available, they would have provided an ideal solution. Another fault that emerged after service experience had been gained by the Dutch Army was a proneness to leak after rough landings.
   However, when Fokker demonstrated the V.36, its undercarriage tank was welcomed as the solution to a difficult problem. It was sufficient to make the aircraft and subsequent types popular. Influential pilots made great efforts to secure undercarriage tanks for their own aircraft, but as far as is known, no Fokker aircraft was ever flown operationally with such a tank.
   The V.36 participated in the third fighter trials held at Adlershof during October 1918, and proved to be distinctly better than the Fok. D.VIIF. It was faster at altitude, and its flying qualities were better, although the aileron control was still considered heavy. In climb it was inferior only to the Rumpler Ru.D.I. This was a biplane of exceptionally low weight and elaborate structural features; it had been designed by J. Spiegel in collaboration with F. Budig and E. Rumpler (but was claimed to be Rumpler’s personal brainchild). The final version of the Ru. D.I was scheduled for quantity production at the time of the Armistice.
   Good though the V.36 was, it was not ordered in quantity before the war ended. In any case, its production was unlikely, because much faster fighters would have been needed in 1919.

After the war

   For all the victors’ insistence on the handing over of all Fok. D.VIIs, they made little enough use of the examples they acquired. Britain apparently took no notice of this product of a defeated enemy, but stuck to wire-braced wing structures with thin aerofoils for nearly twenty years. Many British aerodynamicists regarded thick aerofoils as bad; structural experts regarded cantilever wings as dangerous; and the A.I.D. cordially disliked welding, for had not a welded rudder failed on a B.E.2 in 1914?
   In France, welding was accepted, but the advantages of the welded steel-tube fuselage were not appreciated. French designers in the post-war years were more interested in developing metal structures for wings, consequently they took no real interest in the Fok. D.VII.
   The D.VII’s influence on American design thinking was considerable, however. In 1918-19, a total of 142 Fok. D.VIIs were shipped to the U.S.A., where they were thoroughly tested in a variety of forms and with a variety of engines. Some had the 230-h.p. Liberty 6, one the Packard 1A-1116. A report on the Liberty-powered D.VII dated February 13, 1920, by the Service test pilot L. P. Moriarty, stated that the flying qualities of the aircraft were exceptionally good. Manoeuvrability and control response were very good; the high stalling angle permitted near-vertical firing; and the field of view was better than that provided by most biplanes. The performance at altitude was somewhat inferior to that of the original Mercedes-powered Fok. D.VII.
   The German radiator was not big enough for the Liberty engine, however, and it lacked shutters. Lubrication suffered from surging because the oil pump was at a higher level than the tank.
   Two Mercedes-powered D.VIIs took part in the U.S. Army Air Service’s First Transcontinental Reliability and Endurance Test, held between October 8 and 31, 1919. The final report recommended aircraft designers to study the features of these aircraft; and the Mercedes engines were reported to have given “a wonderful performance”.
   In 1922 the Dutch Fokker works were asked to build for the U.S.A, a Fok. D.VII development with the 300-h.p. Hispano-Suiza engine, which was then being manufactured in the U.S.A, under licence by the Wright-Martin Co. The resulting aircraft was designated Fokker D.IX by its makers. It was slightly larger than the D.VII, had a flat frontal radiator and the undercarriage petrol tank, and its angular rudder was somewhat like that of the V.33 and V.34; it had no fin. To the U.S. Army Air Service it was known as the PW-6.
   The influence of the Fok. D.VII structure on American design thinking was far-reaching. Many of the biplanes built in the U.S.A, until the mid-1930s followed the box-spar-and-N-strut formula of the Fokker.
<...>

J.Herris, J.Leckscheid Fokker Aircraft of WWI. Vol.5: 1918 Designs Part 1: Prototypes & D.VI (A Centennial Perspective on Great War Airplanes 55)

Fokker V34
  
  The Fokker V34, Works Number 3254, was a refined, slightly smaller development of the Fokker D.VII to improve its performance. Its oval radiator and two distinct designs of rudder are its most easily noticed differences, but perhaps the most important was reduced wingspan and reduced chord upper wing that eliminated the need for a center-section cutout. It was built in September 1918 and on October 10 was sent to participate in the Third Fighter Competition, but it was not selected as the winner, indicating it was not a significant improvement over the standard D.VII, which remained in production until the end of the war. Power was provided by the BMW IIIa, the best inline engine available at this time.

Fokker V34 Specifications
Engine: 185 hp BMW IIIa
Wing: Span 8.45 m
Area 17.6 m2
General: Length 6.76 m
Height 3:01 m
Empty Weight 628 kg
Loaded Weight 864 kg
Maximum Speed: 200 km/h




Fokker V36

  Analysis of the information available on the V36, Works Number 3256, indicates that it was as closely related to the V34 as the V18 was to the Vll, and the V27 was to the V28 and V29. Following the adoption of the cantilever wing, Fokker had obviously become inclined to develop pairs or even trios of prototypes that were closely related to one another.
  Visually, the V36 was closely related to the D.VII. The rear fuselage, including the horizontal tail surfaces, fin and rudder were almost identical, but the fuselage was about half a meter shorter compared to the D.VII. The forward fuselage, with its oval engine cowling and radiator, closely resembled that of the V34. The lower wings appeared to retain the layout seen on the D.VII, while the upper wing had a reduced chord, resulting in a smaller wing area.
  The fuel tank was relocated into the undercarriage axle wing fairing, which was intended to reduce the fire hazard to the pilot. Like the V34, it was built in September 1918, and together they were shipped on 10 October 1918 to participate in the Third Fighter Competition. Again, detailed information concerning the assessment of the type by the participating pilots is not available, but it was not selected as one of the winning designs.

Fokker V36 Specifications
Engine: 185 hp BMW IIIa
Wing: Span 8.935 m
Area 17.6 m2
General: Length 6.46 m
Height 3.045 m
Empty Weight 637 kg
Loaded Weight 871 kg
Maximum Speed: 200 km/h
Climb: 1000m 1.75 min
2000m 4 min
3000m 6.75 min
4000m 10 min
5000m 13.5 min
6000m 18.25 min
Endurance 1.5 hr.

O.Thetford, P.Gray German Aircraft of the First World War (Putnam)

Fokker V 34
   Virtually a revised B.M.W.-engined D VII, the V 34 featured the same type empennage as the V 33; the engine was also housed in a neater cowling with a more ovoid radiator. Engine, 185 h.p. B.M.W. IIIa.


Fokker V 36
   With no record of V 35, the next prototype to appear was the V 36 - yet another D VII derivative. Stemming from the V 34, a return to the original D VII style fin and rudder may be noted. A second V 36 prototype was constructed, and this machine had no centre-section cut-out, and a fuel tank was installed in the axle fairing. Engine, 185 h.p. B.M.W. IIIa. Span, 8.935 m. (28 ft. 3 7/8 in.). Length, 6.46 m. (21 ft. 2 3/8 in.). Height, 3.045 m. (9 ft. 11 7/8 in.). Area, 17.6 sq.m. (190.08 sq.ft.). Weights: Empty, 637 kg. (1,401 lb.). Loaded, 871 kg. (1,916 lb.). Climb, 1,000 m. (3,280 ft.) in 1.75 min., 6,000 m. (19,680 ft.) in 18.25 min. Armament, twin fixed Spandau machine-guns.

W.Green, G.Swanborough The Complete Book of Fighters

FOKKER V 34 & V 36 Germany

   The V 34 and V 36 single-seat fighters were the final developments of the basic D VII undertaken during World War I, and differed essentially in their vertical tail surfaces. Both were powered by the 185 hp BMW IIIa six-cylinder water-cooled engine, both featured an oval frontal radiator and both were sent to Adlershof on 10 October 1918 to participate in the third D-type competition. Apart from the vertical tail (which was essentially similar to that of the D VII), the V 36 differed from the V 34 in having one major innovation: the main fuel tank was transferred from the fuselage to the undercarriage axle fairing. Further development of these D VII derivatives terminated with the end of World War I. The following data are specifically applicable to the V 36 armed with two synchronised LMG 08/15 machine guns.

Time to 3,280 ft (1 000 m), 1.75 min.
Empty weight, 1,404 lb (637 kg).
Loaded weight, 1,920 lb (871 kg).
Span, 29 ft 3 3/5 in (8,93 m).
Length, 21 ft 2 3/4 in (6,46 m).
Height, 9 ft 11 9/10 in (3,04 m).
Wing area, 189.45 sq ft (17,60 m2).