A.Weyl Fokker: The Creative Years (Putnam)

The Fokker V.27

   The parallel development with a water-cooled engine was the Fokker V.27 (Factory No. 2734). It was generally similar to the V.26/28 but somewhat larger and heavier. As the V.27 was also intended for the second fighter trials, Fokker chose the new 195-h.p. Benz Bz.IIIb V-eight engine, both geared and ungeared. This engine was, at that time, the most advanced of the various high-speed eight-cylinder developments that were more or less based on the Hispano-Suiza.
   This Benz engine was shorter than the Mercedes and permitted a more compact installation. In the V.27 advantage was taken of this fact, and the Benz was neatly installed and cowled, with a circular frontal radiator that was fitted with shutters. Fokker was very pleased with it.
   It seems that both versions of the Bz.IIIb engine were fitted to the V.27. In its original form the aircraft had the direct-drive engine; in its ultimate form, as an armoured trench fighter, it had the geared version.
   The V.27 wing was wholly covered with plywood; the ailerons were plain surfaces, inset from the tips as on the V.27’s contemporaries. The cabane struts were widely splayed to reduce the cantilever span as much as possible.
   Schuetzenmeister made two officially observed climbs on the V.27 on June 5, 1918. The time recorded for the first was poor because the engine was not running properly, but the second was a fully competitive effort; better, in fact, than the performance of other fighters with the same engine.
   The report on the V.27’s handling characteristics stated that landing was easy and the stalling speed low, but the aircraft had an unpleasant tendency to spin abruptly when stalled. Possibly the centre of gravity was rather far aft.
   After the fighter trials, Fokker learned that the Army wanted an armoured single-seat fighter for the protection of infantry support aircraft and for ground-attack duties. A design requirement was that the aircraft structure must be able to withstand hits without collapsing. A new Service type category DJ had been created, and the A.E.G. were building all-metal prototypes.
   Fokker thought the V.27 might meet this requirement if it were armoured. The radiator seemed to be conspicuously vulnerable, but Platz produced an idea for protecting it. This consisted of a disc of armour plate that was fitted to the airscrew hub and faired by a large-diameter spinner. The armour disc completely covered the radiator, consequently six radial blades were attached to its rear surface to drive, cooling air through the radiator. This cooling fan seems to have worked so well that Fokker wanted to use it on a new interceptor fighter that needed no armour.
   Later, Fokker obtained a patent (D.R..P. 335,745 of October 2, 1918) for a simplification of this arrangement. The patent drawings show a flat piece of armour plate bolted to the airscrew. The armour could be of different shapes and had various slots in it; apparently there were to be neither spinner nor fan blades. Platz recalls that a scheme of this kind was tried but remained experimental.
   The armour on the V.27 fuselage consisted of 2-5-mm. steel plate on the sides and bottom of the fuselage and behind the cockpit. The pilot’s seat had been moved forward to reduce the area that required armour plate, consequently the wing cut-out had to be enlarged. The armoured version of the V.27 was given the new designation V.37.
   The V.37 was either too late for consideration or not promising enough to warrant adoption as a Service type. It does not seem to have undergone a type test, nor was a structural examination made.

The third fighter trials

   From October 15 to October 31, 1918, the third and last comparative trials for the selection of fighter aircraft were held at Adlershof. The object was the selection of types for quantity production during the winter in readiness for the offensives planned for the spring of 1919.
   This time it was indicated that it would be preferable for prototypes to have the 185-h.p. B.M.W.IIIa engine. It was intended that in production aircraft this would be supplanted by the more powerful 240-h.p. B.M.W. IV, which was expected to start coming off the production line in December. It was hoped that fighters with engines of 240-350 h.p. would anticipate developments on the Allied side. This was an optimistic view, because the 300-h.p. Hispano-Suiza and the new, light 350-h.p. and 400-h.p. air-cooled radial engines developed in Britain would have made their appearance in Allied fighters. The aerodynamic and technological advances in German airframe design might not have compensated for the lack of engine power and engine development.
   Prototypes with 145-220-h.p. rotaries were also admitted to the competition as secondary choices. No official decision on the production of further rotary-powered fighters had been taken, because there was insufficient evidence of the serviceability of these engines under operational conditions with the ersatz castor-oil lubricant. Moreover, the supply of this oil was still uncertain.
   The IdFlieg therefore made it plain that there was little purpose in selecting a rotary-powered type at this time, except perhaps for the equipment of the home-defence fighter squadrons. These units had come to be increasingly important, owing to the increase of deep-thrusting bombing raids by the Allies.
   For the initial selection, nine prototypes with the B.M.W.IIIa engine were presented. The V.36 was one of Fokker’s entries, the V.29 the other.
   The Fokker V.29 was a parasol monoplane, generally similar to the Fok. D.VIII except in power-plant and size. Although larger than the D.VIII it was smaller and lighter than the V.27.
   The Pfalz Works entered two high-performance biplanes, the Pfalz D.XVf and a “special Df” fighter experiment. Both were developments of the Pfalz D.XII, but they were cleaned up and had a minimum of external bracing. Like all Pfalz products, their workmanship and materials were impeccable.
   From the L.F.G. came a parasol monoplane, the Roland D.XVII. This could not compare with the Pfalz or Fokker types. Albatros contributed the Alb. D.XII, a braced biplane of low structural weight and a promising come-back by this firm. It was the lightest of all the B.M.W.- powered types but did not look robust enough for front-line service.
   Also very light and promising was the Rumpler D.I, now modified and improved and displaying excellent detail design. The Zeppelin D.I re-appeared, its defective wing joints reinforced after the tragedy of the second trials. This all-metal cantilever biplane had passed a stiff structural examination at Adlershof. It now carried a jettisonable fuel tank externally under the fuselage.
   Finally, there was the latest version of the Junkers D.I (by this time, Fokker and Junkers had separated). One or two of these Ju. D.Is had been sent to fighter squadrons for evaluation. They had been quickly returned as entirely unsuitable, with acrid comments on their peculiar flying qualities. Now the Dessau firm was trying again.
   Six rotary-powered prototypes participated in the trials. Fokker’s two entries were the Fok. D.VIIIe and the Fok. D.VIIIg. The Siemens-powered Fok. D.VIIIs did not appear, owing to either a lack of a suitable airscrew or engine trouble.
   The Kondor Works submitted two versions of a cantilever parasol monoplane: the Kondor E.III with UR.III, and the Kondor E.IIIa with 200-h.p. Goebel Goe.IIIa. A strut-braced parasol, the Roland D.XVI, was entered by the L.F.G.; it had an Sh.3 engine. Also powered by the Sh.3 was the steep-climbing Albatros D.XI, a biplane. A special new Siemens type could not be completed in time, and the firm was represented by a standard Siemens-Schuckert D.IV biplane. This type was already in operational use on the Western Front and was proving successful.
   The trials followed the pattern of the previous competition: the climbing tests were flown by the pilots of the firms, under the supervision of the Adlershof technicians. These were followed by the usual speed-comparison flights. Several “heats” were flown until a reliable assessment of speeds was obtained.
   For the B.M.W.-powered types the first speed comparison was flown at 1-0 km. altitude and without use of the engine’s mixture control. After this, the aircraft were raced between 3-0 and 5-0 km. altitude with full use of the mixture control. A Fok. D.VIIF was flown in this test, presumably for purposes of comparison.
   At a height of about 4-0 km. (13,000 ft) the Fokker V.29 and Junkers D.I were the fastest aircraft. The Junkers was slightly the faster below that height; above it, the V.29 was faster. The Fokker V.36 was next; it was rather slow at low altitudes but still better than the Fok. D.VIIF; at higher altitudes the V.36 was considerably faster than the Fok. D.VIIF. Following the Fokker V.36 in level-speed performance came the Rumpler D.I and Albatros D.XII with little to choose between them. Bringing up the rear, in descending order, were the Pfalz Df No. D.8364/17, Fokker D.VIIF, Zeppelin D.I, Pfalz D.XVf, and the Roland D.XVII.
   Of the Siemens-powered fighters, the Roland D.XVI proved faster than the Siemens-Schuckert D.IV and, up to 4-0 km. altitude, faster than the B.M.W.-powered Fok. D.VIIF. At 4 0 km., the Roland D.XVI was as fast as the Fok. D.VIIF; above that altitude it was slower.
   The Fok. D.VIIIe proved considerably faster than the Kondor E.III with the same UR.III engine.
   In the climbing tests, the Rumpler D.I was unquestionably the best: it climbed to 7-0 km. (23,000 ft.) in 24-7 minutes. The next-best performance was put up by the Roland D.XVI, which needed 26-1 minutes to reach the same height. The Fokker V.36 took 31-1 minutes; for some reason the V.29 was unplaced (the barograph often froze, and this rendered climbs invalid). Both the Rumpler D.I and Albatros D.XII managed to reach nearly 8-0 km. (26,300 ft.) with their regulation military load.
   In flying qualities the Fokker V.29 was rated to be about the best of the aircraft. Its manoeuvrability and behaviour when gliding and diving were judged to be superior to the corresponding characteristics of the Fok. D.VIIF. The take-off was regarded as good but rather long: this was attributable to the higher wing loading. For the same reason the landing speed was rather high, and the V.29’s tendency to float was adversely criticized.
   The Fokker V.36 was not so well liked, because its aileron control was rather heavy, but in general it was regarded as an improvement over the standard Fok. D.VIIF.
   The Junkers D.I was cordially disliked. It was obvious that the Junkers works had failed to profit from Fokker’s skill as a test pilot. This Junkers failing persisted: even ten or more years after the war, Junkers aircraft usually had flying characteristics inferior to those of contemporary Fokker types, despite extensive experimental work at Dessau.
   In general handling qualities the Albatros D.XII was judged to be superior to the standard Fok. D.VII. However, the structure of the Albatros flexed too much in flight, giving an impression of insufficient strength.
   The Rumpler D.I was thought to be good, on the whole, apart from a tendency to slip inwards and spin on steep turns. To save weight, its fuselage had been kept too short.
   In the final assessment, the Fokker V.29 and Rumpler D.I shared top place; there was a tie for second place between the Fokker V.36 and the special Pfalz Df. The Roland D.XVI would have been placed third if its handling qualities had been better.
   The Armistice was signed before the final choice was made; but both Fokker and Rumpler could have counted on receiving substantial contracts for the V.29 and Ru. D.I respectively.
   And yet the supervention of the Armistice may have been a blessing for Fokker. Platz had won his fight for plain, unbalanced ailerons, but his latest products were on the verge of attaining critical speeds for wing flutter. If the V.29 had gone into operational use, wing flutter and failures would have followed inevitably. Equally inevitably, Fokker would have been under grave suspicion, yet this time he would have been innocent.