В.Кондратьев Самолеты первой мировой войны

Вскоре после запуска в серию истребителя-триплана Dr.I фирма "Фоккер" вернулась к "традиционной" бипланной схеме. В декабре 1917 г. Рейнольд Платц, разработал самолет под заводским обозначением V.13. Его фюзеляж был практически идентичен фюзеляжу "драйдеккера", но, вместо трех несущих плоскостей, самолет имел два крыла увеличенного размера и площади, соединенных N-образными стойками из стальных труб. От своего предшественника машина унаследовала толстый профиль деревянных крыльев с полотняной обшивкой и безрасчалочную схему бипланной коробки.
   В январе-феврале 1918 г. V.13 принимал участие в конкурсе перспективных моделей истребителей в Адлерсхофе. Самолет показал хорошие скоростные данные, но по другим параметрам - уступил более энерговооруженному и аэродинамичному истребителю той же фирмы "Фоккер" D.VII, который приняли на вооружение по результатам конкурса.
   Тем не менее, с апреля по август 1918-го была построена небольшая серия в 59 машин, получивших обозначение "Фоккер" D.VI. Во многих из них них использовался задел двигателей, деталей и узлов, собранный для только что снятого с производства Dr. I. Большинство самолетов оснащалась немецкими ротативными двигателями "Оберурсель" Ur.II, остальные - шведскими моторами "Тулин". Вооружение - два синхропулемета LMG 08/15. Первый серийный экземпляр построен 26 апреля 1918 года.
   Лишь незначительное число D.VI в течение лета поступило на вооружение немецких истребительных эскадрилий западного фронта, большинство же отправили в учебные подразделения.
   Семь самолетов в августе 1918 г. приобрела Австро-Венгрия. Эти машины были куплены без вооружения и оснащены австрийскими авиапулеметами "Шварцлозе".
  
  
ДВИГАТЕЛЬ: "Рон" шведской постройки (110 л.с.) или аналогичный "Гебель Гоэ" германского производства.
  
ВООРУЖЕНИЕ: идентично "Фоккеру" Dr.I.
  
  
ЛЕТНО-ТЕХНИЧЕСКИЕ ХАРАКТЕРИСТИКИ
  
   Размах, м 7,66
   Длина, м 6,19
   Площадь крыла, кв.м 17,7
   Сухой вес, кг 392
   Взлетный вес, кг 582
   Скорость максимальная, км/ч 190
   Время подъема на высоту
   2000 м, мин.сек 5,30
   Потолок, м 5940

A.Weyl Fokker: The Creative Years (Putnam)

IN ERSTER LINIE ALLE APPARATE D.VII ...

   Fokker’s personal design inspirations cooled off after the spectacular failure of the V.8 monstrosity, and Platz was able to get on with sensible designs. He wanted to develop a monoplane with a cantilever wing. Fokker was not keen on the idea: monoplanes were out of fashion. A biplane on the lines of the V.4 would probably have a better chance of winning production orders, provided it was as simple as the triplane and its wings were not obvious cantilevers.
   A competition for the selection of new fighter types was shortly to be held at Adlershof. Fokker insisted on entering as many types as possible: in his opinion, the broad approach offered the best prospects of success. The IdFlieg had indicated their intention of ordering rotary-powered fighters as well as aircraft with stationary engines. The Army had invited attention to the promising new 160-h.p. Siemens engine, and stated that they wished to consider prototypes with this engine.
   With all these considerations before him, Fokker again decided on the parallel development of two prototypes, one a light, rotary-powered aircraft, the other a larger machine with a 160-h.p. Mercedes.
   It was decided that the new type should be a sesquiplane. Platz’s first attempt was the V.9, a small biplane that originally had an 80-h.p. Oberursel engine. After the first flight tests this was replaced by a 110-h.p. Le Rhone. The V.9’s direct descent from the V.4 was apparent: its fuselage, tail unit, undercarriage and engine mounting were all virtually identical with those of the triplane. The V.9’s lower wing had the same compounded spar arrangement and was located in a recess in the underside of the fuselage. The upper wing was of greater span and chord, and its two box spars were at a conventional distance with drag bracing between them. The cabane structure consisted of two tripods of steel tubes and was somewhat similar to that of the V.1. Both wing spars were bolted to the four apices of the tripods.
   Both wings were integral structures covered with fabric, and were dimensioned as cantilevers. Merely to reduce their flexing under load, and to satisfy Fokker, a V-strut was fitted between them. The lower end of the strut was made broad enough to provide an attachment that was connected to both the basic spars of the lower wing. Without knowing it, Platz had thereby avoided the structural weakness of the Albatros fighters - the possibility of oscillatory torsion of increasing amplitude in the lower wing under certain conditions of flight. The V.9 cabane structure needed no diagonal bracing, consequently the aircraft was truly verspannungslos.
   The aerofoil section of the V.4 was employed in both wings. There was no stagger, and the wings were made without dihedral. Ailerons were fitted to the upper wing only; to Platz’s displeasure, they had horn balances.
   The pilot’s forward field of view was unobstructed. The upper wing was somewhat above his eye-level, and a large cut-out was made in the trailing edge in order to improve his outlook. Despite the greater wing chord, the field of vision was better than that of the Fok. Dr.I.
   The V.9 was rather a small aeroplane, with a span of about 7-5 m. (24-6 ft.) and a length of less than 5-9 m. (19-5 ft.). It was also very light, and its wing loading was about the same as that of the Fok. Dr.I. In its final form the V.9 was demonstrated at Adlershof, but it was never subjected to an official structural test, nor was it fitted with guns. It remained purely experimental.
<...>
   Yet another experimental biplane fighter was built and tested at Schwerin before the end of 1917. This was the rotary-powered Fokker V.13, which appeared in two versions, each with a different engine.
   The V.13 design was intended to have a better climb performance at altitude and a higher ceiling than the V.9. To this end the wing area was increased. The lower wing no longer had the compound spar box of the V.4: it was of greater chord and had separate spars like that of the V.11, consequently N-type interplane struts were employed. The upper wing was also larger than that of the V.9. The V. 13 cabane was generally similar to that of the V.11, differing only in having the front strut of the tripod attached to the forward end of the lower longeron. The tail group resembled that of the V.9; there was no fin.
   Power for the first version of the design, V.13/I, was provided by a 110-h.p. Oberursel (Le Rhone) UR.II.
   The V.13/II had the 160-h.p. Siemens-Halske Sh.3 eleven-cylinder birotary engine, which necessitated a taller undercarriage; otherwise it was a replica of V.13/I. It had an excellent rate of climb and a high service ceiling. Fokker, of course, considered that the ingenious Sh.3 engine was an imposition laid upon him by the IdFlieg, and hoped to replace it by the new 145/160-h.p. Oberursel UR.III as soon as the first pre-production engines became available. As far as is known, the V.13/II remained experimental.

The first Adlershof fighter trials

   The first of the three comparative trials for the selection of new singleseat fighters began late in January 1918. The idea was admirable in theory, but it must be admitted that the results, on the whole, were no more than moderately satisfactory. This was because some of the notable fighting pilots who flew the competing aircraft were in the pay of individual firms, and consequently gave biased opinions in favour of the products of those firms. Three years of war and the insidious growth of bribery in Germany had not passed unnoticed by the young fighting pilots, and it is perhaps not surprising that their conceptions of honour had become somewhat tarnished. Ultimately it became an open secret that certain officers in command of fighting formations received favours from certain firms for “plugging” their products and denigrating those of their competitors.
   Among the laudable exceptions was Manfred von Richthofen, who set an example as a conscientious Prussian officer of absolute integrity. At the other end of the scale was Hermann Goering, later a notorious member of the Hitler gang. Officers serving with or under him knew that he could be bought.
   The aircraft manufacturers made the most strenuous efforts to capture the bulk orders and went to almost any length to win the approval of the pilots for their products. All firms, Fokker included, had entertainment managers whose job it was to arrange lavish dinners and parties for the pilots. These young men were consequently seldom in any physical condition to assess any aircraft dispassionately. Valuable presents such as gold cigarette cases were distributed; the more “progressive” pilots were paid in cash.
   When the competitive flying began, the Adlershof aerodrome - normally strictly out of bounds to all civilians - swarmed with commercial representatives of the aircraft industry. After this impromptu trade fair had gone on for a week or two, greatly impeding the flight trials, the officers in charge of the competition decided to clear the aerodrome of those civilians who had no immediate connexion with the trials. The party-worn pilots could then get on with the real business of sampling the prototypes that had passed the structural examinations or were otherwise assessed as safe enough for familiarization flights.
   The ban on civilians applied to Fokker. Not to be outdone, he flew over the forbidden area in one of his old experimental aircraft to have a look at what was going on. He could do this easily enough, for he had retained one of his old sheds on the Johannisthal side. Why this had not been requisitioned in August 1914 is a mystery. In it he had strategically planted his aeroplane and his personal mechanic Schmidt.
   One cannot but admire the thorough and extensive preparations that Fokker had made for these trials. He entered no fewer than eight aircraft: four biplanes, three triplanes and a mid-wing monoplane. While the trials were in progress, a further monoplane followed. This was the V.20 which, as described in Chapter X, was designed and constructed by Platz within the space of a week while Fokker was at Adlershof.
   The best mechanics of the Fokker works were at Adlershof too. Indeed, the Fokker team was the best organized of ah the competitors.
   Although Albatros, L.F.G.-Roland, Pfalz, Rumpler, Siemens, Schutte-Lanz and other companies had made efforts to comply with the suggestions of the IdFlieg, they had not prepared so comprehensively nor so wisely as Fokker. It soon became clear that he had presented prototypes that were good in all respects that mattered, and had not been developed in one specific direction at the expense of all other considerations. Most of the other types excelled in one aspect of performance but failed to be satisfactory in a general way. It was one of Fokker’s great gifts as a pilot to sense how the qualities of an aeroplane should be blended to produce a really practical and useful aircraft. He never sought to have emphasis on any specific quality - say, speed, or climb, or ease of handling - but preferred to achieve a balance that would meet with the approval of operational units.
   Of Fokker’s four biplane entries, two (the V.11 and V.18) had the latest high-compression version of the 160-h.p. Mercedes, the type D.IIIau. The IdFlieg wanted to compare prototypes with this engine because it had been ordered in quantity from Daimler.
   As noted earlier in this chapter, the V.13/II had the 160-h.p. Sh.3 engine for the same reason. However, the Sh.3 had not then passed its type test and was not in quantity production, only small batches being built.
   Fokker also succeeded in his desire to oppose the Siemens-Halske engine: he managed to get one of the first of the new Oberursel UR.III rotaries and had it installed in the V.13/I for demonstration against the V.13/II with its Sh.3. He seemed oblivious to the fact that the new Oberursel was inferior in altitude performance and propulsive efficiency. As it was a modification of the well-tried Le Rhone, he was convinced it was better suited to operational needs.
   The IdFlieg had indicated that two fighter types would be chosen for quantity production, one with the Mercedes engine and another with a rotary engine not yet specified. Fokker hoped it would be the Oberursel: the Siemens people hoped equally that it would be their own engine, which was then being evaluated at the front.
   Soon after the trials began, Fokker asked Manfred von Richthofen to try the V.11 He flew it on January 23, 1918. When he landed he told Fokker that it had a good performance and was manoeuvrable, but its flying qualities were unsatisfactory. This was so: it was tricky to handle and directionally unstable; when dived, it had a strong tendency to swing. This was unacceptable in a combat aircraft. Its stalling characteristics were unpleasant and might lead to accidents. If these vices could be remedied, the V.11 stood a good chance of success. Von Richthofen was delighted to note that Fokker had incorporated the control grip and gun triggers that he favoured, in place of the usual press-buttons.
   Fokker heeded von Richthofen’s criticism: he knew it was justified. He had had little opportunity to fly the V.11 himself, but his brief acquaintance with it had sufficed to tell him that its flying characteristics were unpleasant, and that it needed careful handling.
   And so it was that the extensive modifications that have already been described came to be hastily undertaken in the Fokker shed at Johannisthal. Expert welders and other workmen, with tools and materials, were summoned from Schwerin to work all hours over the week-end under Fokker’s direction. Fokker took great care to conceal the extent of these modifications from the technical officers and other competitors. This was a wise precaution, for the structural reliability of the aircraft might have been questioned after such extensive rebuilding. Fokker let it be known that the V.11 had had a slight landing mishap and needed some repairs. It was normal practice for minor repairs or engine overhauls to be undertaken during the trials, and any suspicion that might have attached to the V.11’s temporary disappearance was further reduced because the job was done at a week-end, when the aerodrome was deserted.
   With Fokker’s usual luck, everything went smoothly. A trial flight showed him that the V.11’s handling characteristics were greatly improved, although at the expense of some manoeuvrability. But it was now really safe to fly, and could be dived without any swing developing. At the first opportunity, Fokker suggested to von Richthofen that he should try the aircraft again: the control gearing had been adjusted, Fokker explained, and the Herr Rittmeister would now find it more pleasant to fly. Von Richthofen was surprised that these “small adjustments” had made the V.11 so delightful to handle; it was now vice-free. He urged other pilots, notably Loerzer, to try it. It seemed to be a really promising aeroplane.

The Trials

   The Adlershof trials began on January 21, 1918, a mild day with only a thin layer of cloud at about 13,000 ft. All works pilots were busily engaged on the climbing tests under the control of the Adlershof technicians. These officials weighed every aeroplane before and after flight, noted the type of airscrew used on each (to ensure that the same one would be used in the speed tests), and installed two sealed and calibrated barographs. Refuelling was supervised to guard against the use of any special mixtures. All of these precautions were necessary to avoid cheating by enterprising manufacturers.
   The best climbing performance was put up by a Siemens-Schuckert D.III fitted with a special Siemens Sh.3 engine: this gave about 220 b.h.p. on the ground and drove its airscrew at 2,000 r.p.m. instead of the usual 1,800 r.p.m. maximum. This S.S.W. D.III reached an altitude of 6-0 km. (20,000 ft.) in twenty-two minutes. Service pilots, however, found this aircraft rather tricky to land and less manoeuvrable than the Fokker biplanes.
   Fokker demonstrated the not-yet-modified V.11 and, later, the V.13/I with its new 145-h.p. UR.III engine at low altitudes. His superb handling of these aircraft made a great impression. Another UR.III engine was tested in a Fokker triplane.
   The second day was again mild. The V.9 fitted with a 110-h.p. UR.II, had to make a forced landing outside the aerodrome owing to engine trouble after a climbing trial, and was damaged. The new Junkers D.I low-wing monoplane was flown against an Albatros D.Va, an obsolescent type. The Albatros was flown by Hauptmann Schwarzenberger, the head of the fighter experimental section of the Flz. and its chief test pilot. The Junkers was flown by Fokker, as a director of the Junkers-Fokker Works. To everyone’s amazement the Junkers proved the slower of the two. Fokker explained afterwards that the Junkers had an airscrew whose pitch was too fine; his engine threatened to overspeed and consequently he had to throttle down. There was undoubtedly something wrong with the airscrew, for it disintegrated in flight. Fokker managed to land the monoplane undamaged.
   Later in the day he tried the V.13/I with the UR.III, but the engine was still running unsatisfactorily.
   On the third day the fighter pilots were allowed to try those prototypes that had been structurally cleared. Oberleutnant Bruno Loerzer tried one of the new Siemens-Schuckert D.IIIs but, despite his skill and experience, crashed it when landing. Oberleutnant Ritter von Tutschek turned turtle in an Albatros D.Va fitted with the high-compression Mercedes. As already mentioned, Manfred von Richthofen tried the unmodified V.11; he found it faster than the Albatros D.Va, against which it was flown for comparison of speeds. The representatives of other firms grew uneasy when von Richthofen flew the Fokker V.11 as his first aircraft: a rumour that he “was sold on Fokker” went around. This was quite unjustified. Manfred von Richthofen, then as always, was completely impartial and unbiased.
   Fokker’s pilot Schuetzenmeister climbed to 4-0 km. (13,200 ft.) in the V. 13/I, but the engine failed to give the expected power. Fokker demonstrated the V.17 mid-wing monoplane for the first time. When it was matched against the V.11, the Pfalz D.IIIa and the Albatros D.Va, the monoplane was the slowest of all. It was during the afternoon of this day that Fokker made the telephone call to Platz that resulted in the V.20, which Fokker flew at Adlershof eight days later.
   On January 25, misfortune befell the Fokker team. While thick fog covered the aerodrome, a mechanic of the Oberursel works taxied the V.13/I into the V.18. This aircraft and an Albatros standing nearby were extensively damaged.
   When the fog lifted during the afternoon, the Fokker works pilot Grosse climbed in the V.11 to 5-0 km. (16,500 ft.) in 30-7 minutes, despite unfavourable weather. In a later climb he put up the impressive time of 25-2 minutes to the same altitude.
   In their first discussions with the Adlershof technicians, the fighter pilots expressed disappointment with all the aircraft they had sampled. Climbing times of 25 to 30 minutes to reach 6-0 km. (20,000 ft.) were regarded as acceptable, but all the new types were slow. This opinion reduced the chances of those firms who had aimed primarily at producing fast-climbing fighters; it had a particularly adverse effect on the types with the Siemens Sh.3 engine. The conclusion was that fighters with water- cooled engines were preferable for operational purposes; they were faster but did not have such good climbing performances.
   Another of the Siemens-Schuckert D.III biplanes made a crash landing and turned over. An identical aircraft, however, made the climb to 6-0 km. (20,000 ft.) in 20 minutes. The Fokker V.13/I, flown by Schuetzenmeister, took 22 minutes to climb to 5-0 km. (16,500 ft.).
   Few flights were made during the seventh day because most of the pilots were too fatigued, from one cause or another. Fokker, as a lifelong abstainer, had no hangover, and flew the V.17, climbing to 5-0 km. (16,500 ft.) in 24 minutes. This was a good performance on the low power of the V.17’s UR.II engine. The V.18 had been repaired and made a trial climb, piloted by Heide; its time was disappointing, however.
   The next day was distinguished by a dense fog and the removal of all unnecessary commercial representatives from the aerodrome.
   In the quieter atmosphere that followed, the trials continued with more serious flight testing and sober discussion of the results. Climbing trials, speed comparisons and mock combats were held, interspersed with familiarization flights by the fighter pilots. There were sundry crashes, all in landing accidents. The second Schutte-Lanz D.III, a promising design by W. Bleistein, was written off after a particularly ill-judged landing.
   During the first few days of February, the Fokker triplane variants with the 200-h.p. Goebel Goe.III and 145-h.p. Oberursel UR.III engines made spectacular climbs, piloted by Matthias and Grosse. They failed to give the Fok. Dr.I a new lease of life, however, for the type was regarded as much too slow. The climbs served only to demonstrate the capabilities of the new rotary engines.

The Choice

   The fighter pilots were now asked to indicate which two of the various prototypes they thought best, one with the Mercedes engine, the other with a rotary.
   Two different types had to be selected because the German Army Flying Corps did not believe in complete standardization of its aircraft or engines. There was the pre-war example of Austria to point the dangers of standardization in a field that was developing rapidly; and there was the further operational proof of the British Royal Aircraft Factory types. The German engineering experts welcomed the official policy which, by spreading responsibility over a number of firms, provided a form of insurance against set-backs.
<...>
   There was much less unanimity about the choice of the rotary-powered fighter type. The pilots said that all the prototypes with rotaries were more difficult to handle than the V.11, and their engines gave the impression of being less reliable. This was perfectly true.
   Pfalz, the L.F.G. and Siemens had made efforts to produce fighters with a fast rate of climb and high ceiling. These were useful characteristics where interception was the prime consideration, but the engines were all still in the experimental stage. Until these new engines had been developed to an acceptable standard, the well-tried Le Rhone would have to be retained for operational purposes. The Flz experts concurred.
   Some pilots expressed preferences that puzzled the Service test-pilots: recommendations were made in respect of aircraft that were obviously inferior and had been included in the trials merely because they were interesting and not unsafe.
   There was agreement over the Siemens entries: although they had an excellent rate of climb and were reasonably fast at altitude they were much too tricky and obviously required further development. The Siemens-Halske engine was not yet sufficiently reliable.
   The Pfalz D.VII, which unfortunately had the same engine, had given a better account of itself and was considerably faster. It was well built and fairly easy to handle. The Pfalz D.VI won a measure of support by virtue of its 110-h.p. Le Rhone engine, but its performance was inadequate. A majority regarded the L.F.G.-Roland effort as a wash-out.
   Finally, Manfred von Richthofen’s advice prevailed. He recommended the Fokker V.13 as the best all-round type. It was easy to fly, very manoeuvrable, and otherwise similar to the V.11. As the V.11 had already been recommended, the similarity of the two types would be an advantage when pilots had to switch from one to another.
   The V.13/II with its Siemens engine had a measure of support from the IdFlieg officials. Little had been seen of it during the trials, partly because it had been damaged, partly because the owner of the Oberursel firm had little interest in promoting the Siemens engine. In a climbing test, Mathias had flown the V.13/II to an altitude of 4-5 km. (15,000 ft.) in 19-5 minutes. Although this fell appreciably short of Leutnant Mueller’s record climb of 5-0 km. (16,500 ft.) in 13 minutes on the Service version of the Siemens-Schuckert D.III with the same engine, it was considerably better than the performance of the Fokker V.13/I with the 145-h.p. Oberursel UR.III.
   But the fighter pilots wanted neither the Siemens-Halske Sh.3 nor the Oberursel UR.III: they preferred the 110-h.p. Bente Le Rhone which had proved so satisfactory in the Fok. Dr.I. Their final choice of a rotary-powered aircraft was the Fokker V.13, but with the 110-h.p. Le Rhone.
   This recommendation was accepted by the authorities, but the type was ordered in small numbers only, pending the availability of a more powerful rotary for operational service.
   Hauptmann von Falkenhayn of the Kogenluft’s staff told Fokker of the decisions and congratulated him on his double success. Fokker was asked how soon he could arrange for type tests to be made, and how quickly he could supply production aircraft. He retorted that he could promise nothing, for his factory was cluttered up with those A.E.G. C.IV trainers that the IdFlieg had inflicted on him.
   At that moment Fokker did not know that this very problem had been discussed when the question of giving him direct orders was considered, and the IdFlieg had agreed to cancel the A.E.G. contract in favour of the new fighter types. The alternative would have been to order only prototypes from Fokker and place the production contracts with better-equipped firms. This idea was rejected, however; the A.E.G. trainers were not too badly needed, and there was no wish to stifle Fokker’s eagerness to get production going.
Fokker was promised, on the spot, a provisional order for 400 V.11-type aircraft, subsequently designated Fok. D.VII, at £1,250 per airframe (1914 value), a very generous price. He was told to initiate production with all possible speed: to expedite matters, the existing prototypes should be modified to production standard for test purposes. This was the biggest order Fokker had received up to this time.
   His amazement grew when he learned that his main rivals, the Albatros concern, were to build the V.11 under licence; so were the Ostdeutsche Albatros Werke and the A.E.G. This was a triumph for the little Dutchman who, at a time when his paternal subsidy looked like being cut off, had thought of offering his services as a flying instructor to the Albatros Werke before the war. For every licence-built V.11 he was to get a standard fee of 5% of the airframe price.
   Viewed against the other prototypes submitted for the Adlershof trials, and bearing in mind the supply position in blockaded Germany, no better choice than the V.11 could have been made. Its selection was amply vindicated by its subsequent operational success. The choice of the V.13 was also sensible in the circumstances.
   Fokker had succeeded by rights and had arrived at the top of the German aircraft industry. He had beaten his competitors fair and square in the most exacting competition ever held, for the largest German contracts ever awarded. All he now had to do was to keep Reinhold Platz at work and not let him feel too important!
  
The Fokker D. VI

   The V.11 still needed detail improvements and minor modifications. Fokker hoped to improve its climb, reduce the weight a little, and improve the flying qualities even further. A second specimen of the V.11 was built for Adlershof.
   The V.13 was therefore the first of the two successful designs to undergo an official type test. The aircraft that was tested was re-converted to have the 110-h.p. UR.II engine. Early in February 1918, a few days before the fighter trials ended, a V.13 airframe was tested to destruction at Adlershof. A report dated February 18, 1918, cleared the airframe without restriction. Even the (formerly rare) Case C loading had been sustained without any structural failure. Platz had accomplished the near miracle of complying with all BLV requirements without even knowing of their existence.
   The type test of the 110-h.p. version, the Fok. D.VI, took place on March 15, 1918. In the climbing test an altitude of 5-0 km. (16,500 ft.) was reached in 29-9 minutes: the service ceiling was 5-6 km. (18,500 ft.). This was not good enough for service on the Western Front, and only limited production was recommended until a development with the 200- h.p. Goebel Goe.III engine could be evaluated. Single aircraft with the first pre-production Geo.Ill engines were ordered. Take-off and landing of the UR.II-powered Fok. D.VI were surprisingly good, the runs being 35 m. (37-5 yd.) and 40 m. (44 yd.) respectively. The empty weight was now 427 kg. (940 lb.), whereas originally the unarmed V.13 had weighed 393 kg. (865 lb.) empty. The standard armament consisted of two LMG 08/15 machine-guns synchronized by the Zentral-Steuerung.
   The V.13/II with 160-h.p. Siemens Sh.3 was type-tested on May 15, 1918. It was not accepted for production, however, because operational trials of the Siemens-Schuckert D.I1I had shown the engine to be troublesome. Moreover, the Goe.III-powered version of the Fok. D.VI was then in production and was to be operationally tested by home-defence fighter units. The first Goebel-powered Fok. D.VI (D.1643/18, Factory No. 2625, engine No. 66) underwent its acceptance flight-test at Schwerin-Goerries, flown by Grosse, on May 21, 1918.
   Some three weeks earlier, a production Fok. D.VI (D. 1631/18, Factory No. 2613) had been delivered for engine trials with the 145-h.p. DR.III (engine No. 2884). Few examples of this variant were supplied, however.
   The Fok. D.VI saw little operational use on any major front. Its performance in speed and climb was not good enough; and it was slow to accelerate in a dive. On July 1, 1918, only twenty-one Fok. D.VIs were in operational use; on September 1 the total was twenty-seven. After this date all aircraft of this type were relegated to home-defence and training units.
   Seven Fok. D.VIs with UR.II engines were sold to the Austrian Army on August 19, 1918. They were shipped without acceptance flight tests. These aircraft had the Factory Nos. 2614-2617, 2623, 2624 and 2628; they were part of a block originally ordered by the IdFlieg, consequently their allotted Order Nos. (D.1632-1635/18, D.1641/18, D.1642/18 and D.1644/18) were cancelled. The Austrian D.VIs differed from standard in their armament: they had a fixed, synchronized Schwarzlose machinegun on the fuselage, and a free Mannlicher on the upper wing.
   All the airframe details of the Fok. D.VI so closely resembled those of the D.VII that no separate detailed description is needed. Its engine installation was similar to that of the Fok. Dr.I. The D.VI undercarriage was almost identical with that of the early production D.VII, and it was identical with that of the Fok. E.V or D.VIII.
   In all, about sixty Fok. D.VIs were supplied to the Army under contracts covering the Order Nos. D.1621/18 to D.1700/18; none were acquired by the Navy. Production ceased early in June 1918.
  
The Fokker V.33

   Development of the basic V.9 design did not cease with the termination of D.VI production. Late in the summer of 1918 a further development was built as the V.33. It was smaller and lighter than the production Fok. D.VI but was intended ultimately to take more powerful rotary engines. The V.33 was first flown with a 100-h.p. Oberursel; subsequently a 110-h.p. Le Rhone was installed.
   In its original form the V.33 had a V-type interplane strut, although it had two separate spars in the lower wing. This was soon replaced by an N-strut, however. The wing-tips were more rounded than those of the Fok. D.VI; they resembled those of the V.26. Like most rotary-powered Fokker types, the V.33 had no fin, but its rudder was larger and of a more angular shape. The ailerons were not horn-balanced.
   The V.33’s performance seems not to have warranted further development or a type test. Fokker liked the little biplane, however, and he took it with him to Amsterdam when he cleared out of Germany after the war. He tried to sell it as a sporting single-seater but, failing to do so, he seems to have flown it for pleasure at Schiphol until about 1922.

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

Fokker V 9
   Built in the autumn of 1917, the V 9 again used many of the triplane subassemblies. The lower wing featured the single compound spar as in the Dr 1; the upper wing had two spars. No less than two pyramids of three struts supported the centre-section on either side, making a round dozen struts altogether. Engine was at first 80 h.p. Oberursel U O, but later the 110 h.p. U II was fitted. Span, 7.7 m. (25 ft. 3 1/8 in.). Length, 5.9 m. (19 ft. 4 3/8 in.). Area, 17.1 sq.m. (184.68 sq.ft.). Loaded weight, 580 kg. (1,276 lb.).


Fokker V 13
   Two versions of the V 13 were built, one powered with 145 h.p. Oberursel U III and the other (above) with 160 h.p. Siemens-Halske Sh III geared rotary. The type was developed from the earlier V 9, but had a lower wing with two spars and "N" interplane struts. The centre-section struts were also simplified. As may be seen, the Siemens-engined version required a very stalky undercarriage to give the necessary clearance for the large-diameter, slow-revolving (900 r.p.m.) airscrew. The Oberursel-engined model eventually went into small-scale production as the D VI with the lower-powered U II of 110 h.p. installed. At the D types Competition the V 13, at a loaded weight of 668 kg. (1,470 lb.), climbed to 4.900 m. (13,448 ft.) in 19.5 min. on 3rd February 1918 in the hands of test pilot Matthias.


Fokker D VI

   During the winter of 1917-18 two rotary-engined prototypes designated V 13/1 and 13/2 were being built in the Fokker works at Schwerin. These aircraft were powered with the new 145 h.p. Oberursel U III and 160 h.p. Siemens-Halske Sh III engines respectively and made their first public appearance when sent to Adlershof for the first of the D type competitions in January 1918. Although both engines were far from trouble-free, the airframe itself was considered promising enough to place a small production order. Production aircraft were, however, to be fitted with the eminently reliable 110 h.p. Oberursel U II, which engine was virtually a straight copy of the French 110 h.p. Le Rhone.
   From April 1918 production continued alongside the D VII, but was comparatively slow due to the priority accorded the latter, and when D VI production was terminated in August in order to accelerate D VII supplies, only fifty-nine examples had been built. Of these some seven aircraft were handed over to the Austro-Hungarians, and it has been reported that on these aircraft armament consisted of twin Madschlinger automatic rifles mounted on top of the upper wing, but it seems more likely that they were in fact fitted with Schwarzlose machine-guns. A few D Vis found their way variously to front-line units, one of which was Jasta 84; the remaining machines were used by the fighter-pilot training units.
   An intelligence report extract recorded that about 5th August 1918 Jasta 80 received six D VIs, but they could not be used much due to poor quality oil and consequent unreliability of the Oberursel engine.
   In design and construction the Fokker D VI was something of a hybrid, be fuselage and tail surfaces stemming from the Dr I and the wings being a scaled-down D VII derivation. The 110 h.p. Oberursel rotary engine was enclosed in a cowling which extended to the lower longerons and which was fitted with a faceplate fretted with two large circular vent holes. The fuselage structure was of welded steel tube which reduced in diameter as it tapered to a vertical knife-edge aft. All bays were braced by a loop of cable joined with a single turnbuckle for tensioning. Triangular sheets of ply, to form a faired profile, were clipped to either side of the nose and extended as far back as the cockpit. The rounded top decking forward of the cockpit was also ply-covered, and another triangular ply panel was clipped aft if the cockpit, and all was then completely covered with fabric. Of steel tube framing, the balanced rudder was of the distinctive comma profile and hinged directly to the sternpost. The triangular tailplane and split, balanced elevators continued the triangular outline and were likewise of steel tube and fabric covered. Two steel struts braced the tailplane to the underside of the fuselage.
   In construction, the cantilever wings were greatly similar to those of the D VII. They were based on two hollow box-spars of deep section that tapered towards the tips (the taper being on the lower side only, the top was perfectly flat), on which were threaded the plywood ribs, which were extensively fretted with lightening holes. The leading edge was covered with thin three-ply sheet as far back as the front spar, to which the edge of the ply was tacked. Both wings were in one piece, the spars of the lower wing passing right through the fuselage, as in both the D VII and the earlier Dr I. Overhung, balanced ailerons were fitted to the t op wing only. They were framed from welded steel tube and operated by cables running through the top wing and attaching to control horns: all surfaces were fabric covered. The forward pyramid and single rear centre-section struts were exactly as in the D VII, and likewise of streamlined steel tube. The "N" type interplane struts were also of streamlined steel tube and served largely as ties simply to stop the wings vibrating rather than in any great structural capacity. No cables were used to brace the wings.
   With its lifting surface axle fairing, the undercarriage chassis was almost identical to that of the Dr I, although the track was increased considerably to improve ground stability and lessen the tendency to pirouette. The vee struts were of streamlined steel tube, and elastic-cord shock absorbers bound the axle to the cast housing at the apex. An ash tailskid, internally sprung, was fitted just forward of the sternpost.
   Although the pilot sat rather below the top wing in the D VI, the wide centre-section cut-out gave a good view from the cockpit. The machine was comparatively fast - faster at low altitude than the D VII - and of good manoeuvrability. If it had not been for the eventual success of the D VIII, it would doubtless have been built in greater numbers.

TECHNICAL DATA
   Description: Single-seat fighter.
   Manufacturer: Fokker Flugzeug-Werke G.m.b.H. Schwerin am Mecklenburg (Fok.).
   Power Plant: One 110 h.p. Oberursel U II 9 cylinder rotary engine.
   Dimensions: Span, 765 m. (25 ft. 1 1/4 in.). Length, 6.23 m. (20 ft. 5 3/8 in.). Height, 2.55 m. (8 ft. 4 3/8 in.). Area, 17.7 sq.m. (191 sq.ft.).
   Weights: Empty, 393 kg. (865 lb.). Loaded, 583 kg. (1,283 lb.).
   Performance: Maximum speed, 196 km.hr (122.5 m.p.h.). Climb, 1,000 m. (3,280 ft.) in 2.5 min., 3,000 m. (9,840 ft.) in 9 min.. 5,000 m. (16.400 ft.) in 19 min. Duration, ca . 1 1/2 hr.
   Armament: Two Spandau machine-guns firing forward.


Fokker V 31
   V 31 was simply a modified Mercedes-engined two-seater Fokker D VI with towing gear to act as a tug for the V 30. No photograph available.


Fokker V 33
   In the summer of 1918 Platz made a partial redesign of the V 9, with a twin-spar lower wing fitted and with unbalanced, high-aspect-ratio ailerons fitted to the upper wing. The rudder at last made a departure from the previous rounded-comma pattern which, either with or without fin, had characterised all Fokker aircraft. The V 33 was a handy little machine which Anthony Fokker himself used as a personal aircraft. He took it back to Holland with him after the war, where it was flown from Schipo as late as 1922. Engine was 110 h.p. Oberursel U II.

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

FOKKER D VI Germany

   One of the single-seat fighter types evolved by Fokker for participation in the first D-type competition (the so-called D-Flugzeug-Wettbewerbe) that was to be held at Adlershof in January 1918 was the V 9 ordered on 24 August 1917 with a 110 hp Oberursel Ur II rotary. An unequal-span, single-bay, staggered biplane with fuselage, engine installation, undercarriage and tail assembly virtually identical with those of the Dr I, the V 9 was followed by five further prototypes, these being the similarly-powered V 12 and V 16, the 160 hp Steyr-built Le Rhone-engined V14, and two 160 hp Siemens-Halske Sh III-engined V 13s. The V 13s participated in the D-type competition, and, despite the fact that the Sh III engine was unavailable, this type was ordered into production by the Idflieg as the D VI. It was necessary to install the 100 hp Ur II engine in the series model, which, although manoeuvrable and offering a relatively good performance for the power available, was eclipsed in every respect by the parallel D VII. Orders were, in fact, placed for 270 D VIs, but these were cut back to 60 of which seven, plus the V12, were delivered to the Austro-Hungarian Luftfahrttruppe. The armament of the D VI consisted of paired synchronised 7,92-mm LMG 08/15 guns and the type was confined by the Fliegertruppen to home defence tasks.

Max speed, 122 mph (196 km/h).
Time to 3,280 ft (1000 m), 2.5 min.
Range 186 mis (300 km).
Empty weight, 866 lb (393 kg).
Loaded weight, 1,290 lb (585 kg).
Span, 25 ft 1 in (7,65 m).
Length, 20 ft 5 1/4in (6,23 m).
Height, 8 ft 4 1/3 in (2,55 m).
Wing area, 190.53 sq ft (17,70 m2).


FOKKER V 33 Germany

   The V 33 was the ultimate development of the line of rotary-engined fighter biplanes stemming from the V 9. Smaller and lighter than preceding fighters in the series, the V 33 was apparently intended as a contender in the final D-type competition, although, in the event, it did not compete. It was initially flown with a 110 hp Oberursel Ur II nine-cylinder rotary, this eventually being replaced by a 145 hp Ur III 11-cylinder rotary. The single example of the V 33 was taken to the Netherlands after the Armistice and used by Anthony Fokker as his personal aircraft until 1922. The following data are applicable to the V 33 after application of the Ur III engine.

Time to 9,840 ft (3 000 m), 7.4 min.
Empty weight, 875 lb (397 kg).
Loaded weight, 1,358 lb (616 kg).
Span, 23 ft 9 in (7,24 m).
Length, 17 ft 10 4/5 in (5,46m).
Height, 7 ft 7 in (2,31m).
Wing area, 147.47 sq ft (13,70 m2).

E.Hauke, W.Schroeder, B.Totschinger Die Flugzeuge der k.u.k. Luftfahrtruppe und Seeflieger 1914-1918

01. — 010. Flugzeuge ausländischer Produktion (Самолеты иностранного производства)
04.100— 04.108 Fokker D.VI St 160