В.Кондратьев Самолеты первой мировой войны

"ФОККЕР" D.I/D.IV / FOKKER D.I/D.IV
  
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   Вскоре был разработан усовершенствованный вариант - "Фоккер" D.IV, оснащенный 160-сильным мотором "Мерседес" D.III (или 150-сильным "Бенцем" Bz-III) и вооруженный двумя пулеметами. Размах крыльев был увеличен, а на верхней плоскости появились элероны с роговой аэродинамической компенсацией.
   D.IV был создан практически одновременно с "Альбатросом" D.I, однако машина Фоккера во многом проигрывала своему конкуренту за счет худшей аэродинамики. В результате "Альбатрос" стал в Германии основным фронтовым истребителем, a D.IV построили в количестве всего 33 экземпляров. Несколько из них отправили в Австро-Венгрию, еще семь или восемь штук купила Швеция.
  
  
ЛЕТНО-ТЕХНИЧЕСКИЕ ХАРАКТЕРИСТИКИ
   D.I D.IV
Размах, м 9,05 9,70
Длина, м 6,3 6,3
Площадь крыльев, м2 20,0 21,0
Сухой вес, кг 463 606
Взлетный вес, кг 671 840
Скорость макс, км/ч 145 160
Время набора высоты
   1000 м, мин. 3,5 3,0
Потолок, м 4300 5000

A.Weyl Fokker: The Creative Years (Putnam)

Fokker’s next product, the M.20, was an attempt to better the Albatros types by using the same engine, the 160-h.p. Mercedes. Fokker had already tried to instal one such engine in the M.18, but the structural tests were so discouraging that the development was not pursued. Now it was essential to revive the idea, especially as the 160-h.p. Oberursel gave neither speed nor altitude performance and was not liked by pilots.
   The M.20 was little more than a rehashed Fok. D.I, modified to accommodate the larger and heavier engine and two machine-guns with their double supply of ammunition. To compensate for the increased side area forward of the centre of gravity a triangular fin with an area of 0-35 sq. m. was fitted. The prototype was provided with ailerons when it was presented for its type test early in October 1916. However, Fokker had not bothered to increase the structural strength of the airframe: wing spars, etc., were all identical with those of the Fok. D.I. This was asking for trouble.
   The new type was subjected to structural tests at Adlershof from October 2 to October 7, 1916. This was an uncommonly long time for any new type, particularly for an aircraft that was little more than a modification of three tested and approved designs.
   Fokker was again asked to attend the tests - he had complained about prejudice against his products - and he was there, morose and bitter. The tests did nothing to cheer him up: the wings collapsed in the Case A test (see Appendix III) when the sand loading reached 4-32 times the scheduled load. The acceptable minimum factor was 5. Failure occurred when a bolt that held the turnbuckle of a main bracing cable tore out. Closer examination revealed that both the cable and turnbuckle had been under strength. On top of this, Fokker was unable to deny that the turnbuckle did not even fit the cable; this, he explained, as if it were a valid excuse, was attributable to a “mistake” in the assembling of the aircraft.
   New components were obtained from Schwerin and the loading was repeated. This time another turnbuckle broke, in a cable attached to the fuselage.
   The engineers conducting the tests now urged that all major cables in the wing bracing be replaced by cables of 65 % higher strength. Even this could not produce a load factor better than 4-77, and further strengthening of the wing bracing was needed.
   Detail tests in the Adlershof laboratories proved beyond any doubt that the material of the bracing cables was so inferior that it should never have been used in any aircraft. Fokker had bought it, probably very cheaply, apparently from scrap.
   Until this shocking discovery was made, all cables, turnbuckles and bolts had been supplied by Schwerin. This was the accepted procedure during official strength tests. Now, however, the testing engineers replaced such Fokker-supplied components with material from government store. This was an unprecedented action. Braced with this good-quality cable and components, the M.20 wing cables could be loaded to a factor of 5-03 without undue deformation. The loading was then discontinued in order to preserve the aircraft for the other loading cases as required by the BLV. To achieve this minimum result, the Adlershof technicians had had to perform five major sand loadings and two subsidiary loadings, apart from many laboratory investigations.
   The report on this first stage of the M.20 testing contained a stern warning to Fokker that he ought to arrange for more efficient supervision of his production, and that the utmost care ought to be taken to ensure that no defective materials were embodied in any vital structure. Valuable lives might have been saved if Fokker had heeded this admonition. As it was, he departed fuming that those slide-rule wielders had again got the better of him.
   Structural tests for Cases B and D were resumed after the damaged wing had been replaced by a new one from Schwerin. This was actually a concession, because the minor damage to the wing ought to have been repaired and the subsequent tests conducted on the same set of wings.
   The required load factor of 3-5 in Case B was not attained: the rear spar buckled in one of the inboard bays of the new wing when the sand load corresponded to a load factor of 3-31. Again, Fokker was present.
   The IdFlieg now insisted on a stronger rear spar. When the wings were accordingly modified, a load of 3-58 was achieved in Case B and 3-00 in Case D without undue deformation or failure of any vital member.
   Structural tests of the tail unit revealed the need for further modifications. The elevator collapsed under only 72 % of the specified minimum loading, while the rudder stood up to 98% of its load. All the tests had to be repeated after the components had been strengthened.
   By this time a number of production aircraft had already been completed. Fokker had again hoped that they would be rushed to the front without waiting for structural testing. In all of these prematurely constructed aircraft, the centre-section bracing had to be reinforced by the addition of a diagonal strut on each side. The resultant N-struts became a characteristic of succeeding biplane types.
   Towards the end of 1916 the fuselage of the Fok. M.20 was tested, complete with a new fin. The structure collapsed at only 68% of the specified minimum tail load; what was worse, it collapsed through buckling of the lower longerons. This was not a local failure in an easily replaced member: it pointed to serious underdimensioning or shoddy material or negligent workmanship - not, as Fokker liked to explain apologetically, “merely a slip during assembly”. The IdFlieg demanded the use of stronger steel tubing in the fuselage structure and the immediate modification of all the aircraft of the type already built at Schwerin. A considerable part of Fokker’s big profits was going down the drain, but he had only himself to blame.
   The structural investigation established beyond doubt that the Fokker works relied on guesswork when designing new aeroplanes, that they did no experimental stressing, and that their products could not be trusted. All this was brought home to Fokker by the responsible officers of the IdFlieg who studied the reports.
   Fokker went back to Schwerin. He felt defeated, thanks to his weak spot - engineering. However, he had already entrusted Platz with the organization and running of a laboratory for the conduct of strength-testing materials, components and entire aircraft structures - at minimum cost, of course. Fortunately, Platz was good at this sort of thing: he was not only exceptionally skilled and interested, but could be relied upon to spend not a penny more than was absolutely necessary.
   What was equally essential was a new and better design. After Kreutzer’s death, Fokker tried two new designers, one after the other. Where these “aeronautical experts” had come from and where they went to, nobody knew. They were newcomers to aircraft design and lacked experience. Neither was able to satisfy Fokker; neither completed a single experimental aircraft before being sacked.
   Fokker was given an initial order for twenty Fok. D.IV aircraft; this was later increased to thirty. This was disappointing to him, of course, but he later admitted that the flying qualities of the Fok. D.IV had not been so good as those of the Fok. D.III. Nevertheless luck had not completely deserted him: the Albatros D.III fell into disrepute just when the first Fok. D.IV reached the Western Front. This allowed the D.IV to have some initial success in January and February 1917, notably with Jasta 2 (now named the Boelcke Squadron). But by April 1917 the Fok. D.IV had become useless for the Western Front. Very few went to the front, anyway, and of those only four were left by October 1917 to serve somewhere in Russia or Mesopotamia. Altogether thirty-three D.IVs were supplied, the additional three being special versions with wings of longer span and greater area.
   The D.IV was the last Fokker type to have side radiators. These were forbidden on new types after November 10, 1916. Wing-mounted radiators were to replace them.

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

Fokker D I and IV

   With the eclipse of the E type monoplanes, the Fokker establishment brought forth its D I biplane in the summer of 1916. Evolved from a series of prototypes designed by Martin Kreutzer, it was an uninspired and singularly mediocre aeroplane and only passed into comparatively limited production, because little else was available to replace the outdated E III on the Western Front.
   Developed from the M 18 prototypes, the D I was the production version of the M 18z, the "z" indicating zweistielig (i.e. two-strutter, or two-bay). Being a two-bay biplane spanning some 30 ft., with only a 120 h.p. Mercedes D II engine, it was decidedly under-powered as a single-seat fighting machine. However, due largely to lack of any stiff opposition, it managed to give a reasonable account of itself, sufficient at least to impress the authorities (reinforced no doubt by Fokker's persuasive volubility) to place production orders for the type.
   On the Western Front the D I soon began to encounter doughtier opponents, and could not compete in manoeuvrability and climb with the lighter and more nimble rotary-engined Nieuports the Allies were bringing into use. Hence it soon fell into disrepute with the pilots who had to fly it, and it was relegated to the Eastern Front and to non-operational duties. Some machines were sold to the Austro-Hungarian authorities. In a final endeavour to extract the utmost use from the type, Fokker slightly modified and enlarged it and re-engined it with the 160 h.p. Mercedes D III, in which guise it was designated D IV (M 21). Performance increase, however, was only marginal, and the engines could be - and were - put to much better use by the Albatros firm in their D I type.
   There was nothing unconventional about the D I; it was an orthodox two-bay biplane. The fuselage followed the same style of welded steel-tube construction as in the E type monoplanes, braced in all planes with stranded cables to form a rigid-braced box-girder structure. The nose section had to be completely re-worked to accommodate the six-cylinder in-line motor, which was quite neatly enclosed within somewhat bulbous metal panels, with just the fore part of the cylinder block remaining exposed, which facilitated servicing. The cooling system consisted of two long, narrow, "honey-combed" radiator boxes on either side of the nose, adjacent to the leading edge of the wings. Aft of this point the fuselage was fabric covered and tapered to a horizontal knife-edge. Although slightly different in size and area, the complete empennage was identical to that of the E types in both profile and proportion: again there were no fixed fin surfaces.
   The wings were of straightforward parallel-chord layout, of equal span and with a slight angular rake to the tips. The upper wing was sited quite close to the fuselage on short steel-tube centre-section struts which were welded direct to the longerons. A peculiar feature on the centre-section was the raising of the line of the leading edge. A large angular cut-out in the trailing edge, together with the wing at approximately eye level, gave the pilot an excellent field of forward and upward vision. Interplane struts were of circular steel tube faired off with wooden fairings: the middle of the inboard rear struts was "notched out" to allow passage of the warp control wires, which passed over pulleys on the rear centre-section struts and so down to the control stick.
   The undercarriage was a conventional vee-type chassis of steel tube with wooden fairings, and sprung with elastic shock cord. The wooden tailskid was hinged to an inverted tubular pylon which also served as a pivot anchorage for the lower extremity of the rudder.
   With the installation of the 160 h.p. Mercedes D III power plant and a slight increase in overall dimensions, the D IV had an improved performance and the level speed increased slightly, but it still lacked the manoeuvrability expected of a fighter. As the Albatros D types became available in increasing numbers, the Fokker D Is and IVs lapsed into the obscurity of non-operational duties with the Fliegerschulen (Flying Schools). Total production of D I was twenty-live and of D IV thirty-three.
   With the formation of the Jagdstaffeln in the summer of 1916 the majority were inevitably equipped with a heterogeneous collection of single-seaters transferred from the escort duties with the various Fl. Abt. units. One such to have some Fokker biplanes on its establishment was Jasta 2 and Leut. Grafe from this unit was surprised in a D I by Capt. Albert Ball, V.C., on 21st September 1916, when he closed with it among clouds some 5,000 ft. over the Bapaume Cambrai road. He was able to approach, apparently completely unobserved, and put in an attack from below at exceedingly close range. He plainly saw his tracers entering the Fokker in the region underneath the engine and pilot's seat, and the machine disappeared into the clouds in a side-slipping dive. The subsequent crash was not observed, and Capt. Ball was not credited with this victory. However, it was eventually established that the Fokker did crash about a kilometre east of Bapaume and that the pilot was killed.

TECHNICAL DATA
   Description: Single-seat fighting scout.
   Manufacturer: Fokker Flugzeug-Werke G.m.b.H. (Fok.).
   Power Plant:
   One 120 h.p. Mercedes D II 6 cylinder in-line water-cooled engine (D I).
   One 160 h.p. Mercedes D III 6 cylinder in-line water-cooled engine (D IV).
   Dimensions:
   Span, 9.05 m. (29 ft. 8 3/8 in.). Length, 5.7 m. (18 ft. 8 1/2 in.). Height, 2.25 m. (7 ft. 4 5/8 in.). Area, 22 sq.m. (238 sq.ft.). ( D.I.)
   Span, 9.7 m. (31 ft. 10 in.). Length, 6.3 m. (20 ft. 8 in.). Height. 2.45 m. (8 ft. 0 1/2 in.). Area, 21 sq.m. (227 sq.ft.). (D IV.)
   Weights:
   Empty, 463 kg. (1,019 lb.). Loaded, 671 kg. (1,476 lb.). D I.
   Empty, 606 kg. (1,333 lb.). Loaded, 841 kg. (1,850 lb.), D IV.
   Performance: Maximum speed, 150 km.hr. (93-75 m.p.h.), D I; 160 km.hr. (100 m.p.h.), D IV. Initial climb, 1,000 m. (3,280 ft.) in 5 min., D I; 1,000 m. (3,280 ft.) in 3 min., D IV. Duration, 1 1/2 hr.
   Armament:
   D I one fixed Spandau machine-gun forward.
   D IV two fixed Spandau machine-guns forward. (Usually not more than one gun was fitted to obtain improved performance.)

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

FOKKER D IV (M 21) Germany

   A contemporary of the M 19 and the last of the Fokker fighters to be ascribed solely to Martin Kreutzer, the M 21 was, to all intents and purposes, the D I (M18) with twin-gun armament and the 160 hp Mercedes D III six-cylinder water-cooled engine. The M 21 was assigned the service designation D IV and two were at the Front on 31 August 1916, but saw no combat service. The performance of the D IV proved disappointing by comparison with contemporary types and the Idflieg considered that supplies of the 160 hp Mercedes should be assigned to other types. Production was, in consequence, restricted to 40 aircraft for the Fliegertruppen, one being experimentally fitted with a refined engine cowling and large propeller spinner. In addition, four D IVs were built for Sweden where they arrived in March 1918.

Max speed, 99 mph (160 km/h).
Time to 3,280 ft (1 000 m), 3.0 min.
Range, 137 mis (220 km).
Empty weight, 1,336 lb (606 kg).
Loaded weight, 1,852 lb (840 kg).
Span, 31 ft 9 1/10 in (9,70 m).
Length, 20 ft 7 8/10 in (6,30 m).
Height, 9 ft 0 1/4 in (2,75 m).
Wing area, 226.05 sqft (21,00 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)
04.51 - 04.92 Fokker D.II (Type M 20) Dm 185