A.Weyl Fokker: The Creative Years (Putnam)

Before 1917 ended, Platz found enough time to realize his ambition of building a cantilever monoplane fighter. This, the V.17, was virtually a V.4 fuselage and tail unit fitted with a shoulder-high cantilever wing. The wing had two spars, conventionally spaced, and was covered entirely with plywood. This skin took care of the torsion, and was an early example of modern stressed-skin design. The engine was a 110-h.p. Le Rhone.
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   A remarkable example of this unprecedented capability was the hurried design and construction of an experimental single-seat fighter early in 1918. In this instance Platz established, unintentionally, a world record for speed in aircraft design and prototype construction. This record still stands and is unlikely to be bettered.
   During the first Adlershof fighter trials in January 1918, Fokker demonstrated the V.17 cantilever mid-wing monoplane with a 110-h.p. Le Rhone rotary engine. This aircraft impressed influential officers. Alive to this interest, Fokker telephoned Platz at Schwerin on a Saturday night in the following terms: “The V.17 is very good. I would like to show something similar but with the 160-h.p. Mercedes. I shall be here for two more weeks. Can you do it?” Platz thought he could, and set to work.
   Fokker can have had little idea of the work involved in the design and construction of a new prototype. The much heavier and longer engine needed a bigger and stronger airframe; it was not merely (as he may have imagined) a matter of putting a different engine into a V.17 airframe.
   The design drawings were completed during the Sunday following Fokker’s telephone call. On Monday morning the ribs for the tapered wing were drawn and the rib jigs laid out. The laminated spar flanges were glued up, the fuselage welding jigs were laid out and the structure welded up. The engine, airscrew, radiator, and some undercarriage parts such as the wheels, axle and shock absorbers, were borrowed from the Fokker V.ll. Workers were brought from the production shops to speed the rib making and to help with the assembly. Casein glue was, of course, used throughout, and the greatest delay was occasioned by the need to wait for glued parts to set and dry.
   On Saturday morning the new fuselage was ready, complete with engine cowling, undercarriage, and all installations such as controls, etc.; it was covered too. The plywood-covered wing was french polished by thirty carpenters. Platz had decided on french polishing in order to save the time that the drying of the more conventional dope and lacquer would have demanded. This was the fourth ply-skinned wing to be made in the Fokker Works.
   At 2 p.m. on that same Saturday the new type, V.20, was ready for its first flight. Fokker was still at Adlershof, so it was flown by Weidner, one of Fokker’s best works pilots. On the following Monday morning, the new V.20 stood on the tarmac at Adlershof, gleaming, immaculate, and ready to participate in the trials.
   The whole work of design and prototype construction had taken 6 1/2 days.
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THE FLYING RAZOR

   Platz clung to his ideal of simplicity: the cantilever monoplane. He had had to comply with Fokker’s demands for biplanes, triplanes, and even a quintuplane; in these designs his aspirations towards cantilever wings had to be suppressed as he watched the fitting of interplane struts. He remained convinced that one wing, unencumbered with struts or bracing, was all that was necessary.
   Fokker turned down all Platz’s monoplane ideas; he even went so far as to say that neither the fighter pilots nor the Adlershof theorists would accept such aircraft. But Platz went on expounding his conviction, and finally had his way when Fokker wanted him to design new types for the first fighter trials.
   The first Platz monoplane was the V.17, powered by a 110-h.p. UR.II engine. Despite his long opposition to Platz’s cantilever-monoplane ideas, Fokker liked the V.17. He flew it and liked it even more.
   There was no time to design and build a parallel type with a water-cooled engine before the Adlershof trials. But the V.17 went to Adlershof with the other Fokker prototypes to participate in the competition.
   The V.17 possessed all the significant features of the V.4 triplane without its top and bottom wings. The monoplane was a completely new design, however; the only Fok. Dr.I component it contained was the engine mounting. The one-piece wing had two box spars at a normal spacing. The fuselage was designed to accommodate the spars.
   There were fourteen main ribs on each side, and the entire wing skin was of plywood; thus the wing was inherently stiff in torsion. Its span was about 9-5 metres (31-4 ft.) and it had rounded tips.
   A novel structural feature, often repeated by Platz in later types, was the making of the ailerons as integral parts of the wings; they were simply cut out of the wing structure before the skinning was completed. This simplified manufacture and obviated the need for separate aileron jigs. Such ailerons, of course, could only be plain, unbalanced surfaces: the horn-balanced ailerons fitted to so many Fokker types were welded steeltube structures. In the V.17 the aileron-hinge axis was skewed.
   The weight of this experimental monoplane was reasonably low; but its low-powered engine kept performance down. The V.17 took 35 minutes to climb to an altitude of 5-5 km. (18,000 ft.). Even for early 1918 this was not good enough.
   At Adlershof, Fokker personally put the V.17 through the climbing test in order to obtain the best possible time. This climb was made on January 27, 1918, the Kaiser’s birthday. Fokker rounded off the festive day with a perfect demonstration of the new monoplane in daring manoeuvres at low altitude. This created such an impression that he felt the type might be adopted if its rate of climb could be improved.
   The parallel development of the V.20 with the 160-h.p. Mercedes and its completion within the space of a week, have been related in Chapter X.
   The V.20 wing had a different shape, possibly because lack of time precluded refinement. The tips were nearly square, and the hinge-lines of the horn-balanced ailerons were parallel to the trailing edges. The wing covering aft of the rear spar was of fabric, possibly to save weight. Plywood covered the remainder of the wing as far outboard as the last rib; the tip itself was fabric covered. The weight saving may have been aimed at improving the climb.
   With a monoplane wing to accommodate, the fuselage naturally differed from that of the V.ll, but the same radiator was used. The V.20 undercarriage was a slightly modified V.11 component.
   The V.20 was not the success that Fokker and Platz had hoped for. It was, of course, larger and heavier than the V. 17. Fokker considered it a promising type, yet he did not submit it for a type test. Both the V.17 and the V.20 would have passed the searching official strength tests with ease.
   Next in the monoplane line of development was the V.23 (Factory No. 2443), again a mid-wing monoplane. Platz says that it came nearest to his ideal, and he could not understand why neither Fokker nor the IdFlieg fell for it.
   In its general appearance, the V.23 looked less angular than any type since the V.3. The wing had rounded tips; and the ailerons were unbalanced, apparently having been made as integral parts of the wing and subsequently cut out. The same low-compression 160-h.p. Mercedes D.IIIa engine and wedge-shaped frontal radiator were used, but the engine cowling was neater and the drag-producing exhaust manifold of the V.20 was discarded in favour of a single downward outlet. There was no fin.
   The V.23 took part in the second fighter trials at Adlershof, during which it was mostly flown by the works pilot Kulisch, one of the pre-war Johannisthal aviators.
   In flying trim the V.23 weighed 839 kg. (1,850 lb.). It climbed to 5-1 km. (16,800 ft.) altitude in 31-5 minutes. It was turned down without a type test, mainly because the pilot’s field of vision, severely limited by the expanse of the wings, was regarded as insufficient for combat. Perhaps, too, it was thought that the climbing performance was not promising enough.
   As usual, Platz was unable to extract from Fokker any technical information as to why the V.23 was completely rejected. He suspected that the risk of injury to the pilot if the aircraft overturned might have been a reason. In fact, this is unlikely, as the official interest in the Junkers low-wing monoplane indicated. Had the authorities been seriously interested in the V.23, they would merely have insisted upon the addition of a crash pylon.
   It seems that the V.23 was preserved by Fokker, later taken to Amsterdam, and finally handed to the German Air museum in Berlin. If this is so, the aircraft must have been destroyed during the bombing of Berlin during the 1939 45 war.

A low-wing monoplane

   Platz’s suspicions that the V.23 was rejected because of the lack of crash protection must have been dispelled when Fokker asked for another experimental monoplane, this time of low-wing configuration.
   As a director of the Junkers-Fokker works, Fokker had repeatedly flown the Ju. D.I low-wing monoplane. He had noticed that the field of vision was much better than that provided by the mid-wing and shoulder-wing monoplanes that Platz had designed. Fokker also found that a low-wing monoplane was by no means unstable, even when it had much less dihedral than his own pre-war low-wing types.
   That Professor Junkers had secured a patent (DRP. No. 310,619 dated March 12, 1918) on low-wing arrangements embodying one-piece wings, did not worry Fokker. This time right was on his side and he was justified in ignoring this unreasonable German patent, for it had no substance and should never have been granted. Bleriot, Levavasseur and Fokker himself had in fact anticipated this “invention” by the sage of Dessau.
   Platz was not happy about Fokker’s latest request. This was not because any serious design problems were involved: he felt that a low- wing monoplane could not be sufficiently stable and safe in the air. Indeed, he is still unconvinced of the advantages of the low-wing arrangement, although he has designed several such monoplanes since 1918. He still regards the low-wing monoplane as deficient in stability and dangerous in the event of overturning on landing. If Platz had been a pilot his views might have changed. And the high-wing monoplane is not without its dangers in the event of a crash.
   In spite of his misgivings, Platz designed the V.25 low-wing monoplane (Factory No. 2732), powered by a 110-h.p. DR.II rotary. In appearance it was ahead of its time; twenty years later, with a contemporary engine, it would still have looked up to date. Yet Platz’s inhibitions were to lead him to abandon this promising line of development.
   The V.25 had a strong crash pylon behind the cockpit; it was faired over, and provided a streamlined head-rest for the pilot.
   The wing was tapered and had square tips with rounded corners. It was covered entirely with plywood. No attempt was made to give it greater dihedral than its predecessors had had; the upper surface of the front spar was quite straight. Possibly Fokker told Platz that a larger dihedral angle was unnecessary, for Platz himself seems to have feared that the low-wing arrangement might cause the aircraft to be stable in the inverted attitude.
   As usual, the mainplane was an integral structure. It was mounted in a recess in the bottom of the fuselage, like the bottom wing of the V.13. The wing attachment was so designed that the incidence could be varied on the ground for experimental purposes; three positions were possible.
   A somewhat novel feature, for the time, was the inset position of the ailerons; that is to say, they did not extend to the wing tips. In accordance with Platz’s practice, they were cut out of the wing when it was partly skinned. They too had plywood skin. The ailerons had no form of balancing; this may have prejudiced some pilots against the aircraft.
   The V.25 differed from its monoplane predecessors in having a triangular fin. Its rudder was generally similar in shape to that of the Fok. D.VII.
   There was no cable cross-bracing of the undercarriage. In its place an inverted-V strut was welded in.
   The V.25 took part in the second comparative fighter trials, but it had little chance of success, owing to its low-powered engine. It is a matter for great regret that Fokker did not see fit to try the aircraft with a more powerful engine. As it was, the V.25’s climb and speed were not impressive, although it was slightly lighter than the V.17.
   Fokker abandoned this advanced design without pressing for any further development. This was a case of his intuition letting him down: although he was on the right track and perfectly able to beat Junkers in the fighter contest, he failed to see the possibilities. Apart from the obvious move of fitting a more powerful engine, he could have beaten all his competitors by mounting the machine-guns in or underneath the wing, where they would have needed no synchronizing mechanism. He would then have had the simplest aeroplane of all, highly manoeuvrable and with superior fire power.
   This was probably the last time that Fokker imposed upon Platz a design formula to which the latter was opposed. And yet, this time, Fokker had been right!