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Страна Конструктор Название Год Фото Текст

Fokker Dr.I (Fokker Dreidecker)

Страна: Германия

Год: 1917

Истребитель

Fokker - V1 / V2 / V3 - 1916 - Германия<– –>Fokker - V17/V20/V23/V25 - 1917 - Германия


В.Кондратьев Самолеты первой мировой войны


"ФОККЕР" Dr.I / FOKKER Dr.I

  В июле 1917 года немцам достался трофейный английский истребитель "Сопвич триплан", совершивший вынужденную посадку на вражеской территории. Многие германские авиафирмы сразу начали работы по копированию этой удачной машины.
  Наибольшего успеха добился авиаконструктор фирмы "Фоккер" Рейнольд Платц. Спроектированный им аэроплан во многом отличался от английского прототипа. Он имел типично "фоккеровский" фюзеляж и оперение с каркасом, сваренным из тонкостенных стальных труб и полотняной обшивкой. Важным нововведением были крылья относительно толстого профиля без наружных расчалок.
  Прототипы V.3 и V.4 были быстро построены, успешно облетаны и рекомендованы к серийному производству под обозначением "Фоккер" Dr.I (Dr - сокращение от немецкого Dreidecker - "драйдеккер" - триплан).
  Поначалу самолеты комплектовались 100-сильными ротативными моторами "Оберурсель" Ur.I, затем - 110-сильными Ur.II или импортными шведскими моторами "Тулин" той же мощности (копия французского двигателя "Рон" 9J). Иногда ставили трофейные 130-сильные "Клерже", с которыми самолет демонстрировал выдающиеся летные характеристики.
  Вооружение - два синхронных пулемета LMG 08/15.
  Первые два экземпляра машины в августе-сентябре 1917 г. успешно прошли войсковые испытания на западном фронте. В октябре новыми истребителями вооружили Первую истребительную эскадру Рихтхофена, а затем самолет начал поступать на вооружение других частей и подразделений.
  Всего было построено 318 "фоккеров" Dr.I. Пик их боевого применения приходится на май 1918 года. К началу этого месяца в немецких фронтовых эскадрильях числилось 170 машин данного типа. Но в том же месяце самолет был снят с производства.
  К концу войны в строю оставалось еще около 70 "драйдеккеров". К тому времени они уже считались морально устаревшими и большинство из них входило в состав тыловых эскадрилий ПВО.
  Надо отметить, что Dr.I, ставший сейчас на Западе своего рода символом авиации Первой мировой войны и образцом для постройки многочисленных летающих реплик, далеко не однозначно воспринимался немецкими боевыми летчиками. Обладая хорошей скороподъемностью и отличной горизонтальной маневренностью, он в то же время был весьма сложен в пилотировании и просто опасен для пилотов невысокой квалификации.
  По скоростным данным он уступал современным ему истребителям стран Антанты (особенно - ранние машины со 100-сильным мотором). Кроме того, на фронте выявилась недостаточная прочность крыльев, из-за чего произошло несколько катастроф. В ноябре 1917-го полеты на "драйдеккерах" даже пришлось временно запретить до устранения этого недостатка. Лишь через месяц самолеты с усиленными крыльями вернулись на фронт.
  Но при всех своих недостатках Dr.I был излюбленной машиной ведущих германских асов, так как он давал первоклассным пилотам наибольшие возможности в маневренном воздушном бою на близких дистанциях.


ДВИГАТЕЛЬ: "Оберурсель"Ur I, мощностью 100 л.с. (на первых серийных машинах), или "Оберурсель" Ur II, 110 л.с.

ВООРУЖЕНИЕ: 2 синхр. LMG 08/15 "Шпандау".


ЛЕТНО-ТЕХНИЧЕСКИЕ ХАРАКТЕРИСТИКИ

  Размах, м 7,20
  Длина, м, 5,76
  Площадь крыла, кв.м 18,66
  Сухой вес, кг 406
  Взлетный вес, кг 586
  Скорость максимальная, км/ч 165
  Время подъема на высоту
   2000 м, мин.сек 6,48
  Потолок, м 6000


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


Fokker V 3
  This neat little cantilever triplane was built at the request of the German authorities during February 1917. In construction it was identical to the Dr I, which was its eventual production form. It differed from the Dr I in having unbalanced ailerons and elevators, and the centre and lower wing were both of the same span. In flight the wings were found to vibrate considerably, and lateral and fore-and-aft controls were found to be insufliciently sensitive. Engine was 110 h.p. Oberursel U II.

Fokker V 4
  This machine was a development of the V 3 with light, hollow interplane struts fitted to damp out the wing vibration. Balanced ailerons were fitted, likewise balanced elevators, and these were squared off at the ends, this beting practically the only visible feature that distinguished the V 4 prototype from the production Dr I. Engine, 110 h.p. Oberursel U II. Span, 7.19 m. (23 ft. 7 1/8 in.). Length, 5.77 m. (18 ft. 11 1/4 in.). Height, 2.95 m. (9 ft. 8 1/8 in.). Weights: Empty, 406 kg. (893 lb.). Loaded, 586 kg. (1,289 lb.). Speed, 165 km.hr. (103.12 m.p.h.). Climb, 1,000 m. (3,280 ft.) in 2.9 min. Duration, 1.5 hr. Armament, two fixed Spandau machine-guns firing forward.


Fokker Dr I

  Following the success of the Sopwith Triplane used by the R.N.A.S. squadrons on the Western Front from the spring of 1917, adoption of the triplane layout was immediately given serious consideration by the major manufacturing concerns of the Central Powers, and in a comparatively short time the majority produced prototypes. Some, as in the Albatros Dr I, were simply an adaptation of an existing fighting scout, while others devoted much original thought to the project. One such designer was Reinhold Platz, who, since the death of Martin Kreutzer, had initiated most new projects in the Fokker drawing office.
  His original triplane prototype showed a completely revolutionary line of thought in an endeavour to extract the utmost advantage in manoeuvrability, offered by the reduction in wingspan without loss of wing area. This was the V 3 (there is still doubt as to whether the V prefix, now adopted, was intended to indicate "Versuchsmaschine" - experimental plane, or "Verspannungsloser" - wing without bracing), a diminutive triplane with cantilever wings based on deep-section hollow box-spars of great strength and considerable lightness. Although these wings were strong enough to dispense with orthodox interplane struts, a disconcerting vibration occurred in flight. The next machine to appear, the V 4, was fitted with light, hollow struts to obviate this vibration and at the same time modifications to improve manoeuvrability and control were put in hand, mainly in the addition of overhung balance portions on the ailerons, balancing of the elevators and the simplification of the tailplane shape from near semicircular to a triangular profile. In this guise the aircraft went into production in the summer of 1917; the first examples were designated F I, but after three machines had been completed the newly instituted military designation Dr I was applied.
  The fuselage and complete empennage followed the earlier successful Fokker formula, utilising welded steel-tube construction with transverse cable bracing to make a rigid box-girder structure. Power unit was mainly the 110 h.p. Le Rhone rotary. This may at first seem strange, but these engines had been built under licence in Sweden by the Thulin firm, and at one time some 700 were stored at Adlershof. Some 110 h.p. Oberursel engines (a straight copy of the Le Rhone) were fitted but preference was for the Thulin-built motor, the materials used therein being reputedly superior to the home product. A near-circular cowling housed the engine, the flat front plate being fretted with round cooling holes, although some machines had open front cowls similar to those fitted to French Nieuport scouts. The circular-section cowl was faired into the basic slab-sided fuselage by the clipping to the sides of triangular plywood panels which tapered aft as far as the cockpit. A similar plywood panel was attached to the curved decking aft of the cockpit, the whole then being fabric covered.
  Of deep section, the cantilever wings were identical in chord and construction and only differed slightly in span. These were built on a single spar which was actually two box-spars, joined together top and bottom with ply, to form a single compound unit of constant cross-section throughout its length. Circular lightening holes were extensively fretted in the plywood ribs and the leading edge was covered with thin plywood sheet extending as far aft as the spar, to which the sheet was tacked. The trailing edge was simply a wire which formed a scalloped profile when the fabric covering was doped. Ailerons were of welded steel tube with overhung balance portions; wingtips were fashioned from rejected ribs and ash tip skids were fitted to the under sides of the lower wings. Quadrant-shaped cut-outs were made at the inboard ends of the middle wing to improve downward vision from the cockpit.
  Centre-section and undercarriage struts were of streamlined steel tube, and an additional aerofoil lifting surface was built over the axles and spreader bars, the wheels being sprung with elastic shock cord. A stout steel-shod ash tailskid was fixed to the rear post, and light steel struts braced the tailplane to the underside of the fuselage.
  The Fokker Dr I entered service in August 1917 and was flown with success by many well-known pilots. Without doubt the most celebrated was the legendary "Red Baron", Manfred von Richthofen, whose "red triplane" has probably been the subject of more models than any other. However, doubt now seems to exist as to whether von Richthofen ever did fly a completely scarlet Dr T. Richthofen first flew a Dr I in September 1917 (102/17) and he subsequently used 114/17 (crashed 30th October 1917), 127/17, 141/17, 152/17, 477/17 and 425/17. Although not as fast as contemporary scouts, it was the agility of the Fokker that appealed to the leader of Geschwader 1 (as indeed it did to many other pilots), and once having flown the type, he used it almost exclusively until he was killed in Dr I 425/17 on 21st April 1918.
  A possibly more spectacular exponent of the Fokker Triplane was Werner Voss, a young pilot of Jasta 10, whose skill and dash resulted in a final score of forty-eight Allied aircraft. Voss received Dr I (103/17) on 28th August 1917. He was a born instinctive fighter, in contrast with Richthofen's calculated approach. The saga of his death is an epic in First World War literature. On 23rd September 1917, flying alone, he ran across a patrol of S.E. 5s from No. 56 Squadron led by the famous Capt. J. B. (Jimmy) McCudden, V.C., and managed to shoot holes into all of them before eventually being shot down by Lieut. A. Rhys-Davids, a young Welshman still in his teens. Another famous pilot, Heinrich Gontermann, renowned for his balloon-busting activities, was flying Dr I 115/17 on 30th October 1917 when a fault developed in the wing structure; but for the serious facial injuries received from contact with the gun butts when he crash-landed, he would probably have got away with it.
  As several other Dr Is had crashed in similar circumstances about this period, the type was temporarily grounded for the wing structure to be strengthened, and it did not resume operations again until the last weeks of 1917. It remained in service until the summer of 1918, but was not widely used outside the Richthofen Geschwader after the beginning of the year. Total production of the type amounted to 320, the last example being completed in May 1918.

TECHNICAL DATA
  Description: Single-seat fighting scout.
  Manufacturer: Fokker Flugzeug-Werke G.m.b.H. (Fok.).
  Power Plant: One 110 h.p. Oberursel UR II or Thulin-built Le Rhone 9 cylinder rotary.
  Dimensions: Span, 7.19m. (23 ft. 7 3/8 in.). Length, 5.77 m. (18 ft. 11 1/8 in.). Height 2.95 m. (9 ft. 8 1/8 in.). Wing area, 18.66 sq.m. (201.5 sq.ft.) including axle.
  Weights: Empty, 406 kg. (893.2 lb,). Loaded. 586 kg. (1,289.2 lb.).
  Performance: Maximum speed, 165 km.hr. (103.12 m.p.h.) at 4,000 m (13 120 ft ) Initial climb, 1,000 m. (3,280 ft.) in 2.9 min. Ceiling 20,000 ft. Duration ca. 1 1/2 hr.
  Armament: Twin fixed Spandau guns synchronised to fire forward through the airscrew. (Guns could be fired independently.)


Fokker V 5
  The V 5 was little more than a standard Dr I airframe fitted with the 160 h.p. Goebel III engine, solely for participation in the first D types Competition. It was slightly longer than the Dr 1 - 6.4 m. (21 ft. 0 in.) and somewhat heavier - empty 440 kg. (968 lb.), loaded 635 kg. (1,397 lb.). During competition, on 2nd February 1918, it climbed to 6,000 m. (19,680 ft.) in 20 min. No photograph available.

Fokker V 6
  Yet another variation of the triplane theme in the summer of 1917; with extended span and the lengthened fuselage slung above the lower wing. Power plant was 120 h.p. Mercedes D II.

Fokker V 7
  A standard Dr I airframe fitted with 160 h.p. Siemens-Halske Sh III geared rotary carrying four-blade airscrew. Weight showed increase: empty, 491 kg. (1,080 lb.); loaded, 686 kg. (1,509 lb.). It may be noted this machine did not have the lifting surface fairing over the axle.

Fokker V 10
  Purely a 145 h.p. Oberursel U III engined Dr I. The machine weighed 430 kg. (946 lb.) empty and 625 kg. (1,375 lb.) loaded. It climbed to 6,000 m. (19,680 ft.) in 23-5 min. and attained a ceiling of 9,500 m. (31,160 ft.). No photograph available.


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


FOKKER V 4 Germany

  The V 4, also referred to contemporaneously as the D VI - although possessing no relationship other than a common design origin to the fighter subsequently to be officially assigned that designation - was originally designed as a single-seat fighter biplane ordered on 13 May 1917 for the Austro-Hungarian Luftfahrttruppe. As a result of the service debut of the Sopwith Triplane, however, this aircraft was completed by Reinhold Platz - at the behest of Anthony Fokker - as a triplane. The V 4 (a prototype frequently to be erroneously referred to as the V 3) was an extremely compact aircraft powered by a 120 hp Le Rhone nine-cylinder rotary engine, having a slab-sided, rectangular-section, fabric-covered fuselage and three staggered cantilever wings. All three wings were of the same chord and section, but the top wing was of greater span than the equi-span middle and bottom wings. The V 4 was flown at Schwerin for the first time in May 1917, and, unlike preceding Platz fighter designs, had orthodox unbalanced ailerons on the top wing and unbalanced elevators. Aerodynamically balanced ailerons and elevators were introduced after initial flight testing, together with I-type interplane struts to reduce wing flexing. Two synchronised LMG 08/15 machine guns were fitted, and, in late August 1917, the V 4 was shipped to Austria-Hungary. Prior to this, on 5 July, a second and similar V 4 (alias D VI) had been ordered, and, six days later, a contract had been placed for two more as V 5s to be powered by the 110 hp Le Rhone, a copy of which, the Oberursel Ur II, was to power the series Dr I fighter. Performance, weights and dimensions of the V 5s were generally similar to those of the Dr I (which see).


FOKKER V 6 Germany

  Developed in parallel with the V 5 (the true prototype of the series Dr I) the V 6, ordered on 7 July 1917, represented an attempt by Platz to mate the 160 hp Mercedes D III six-cylinder water-cooled engine with a triplane airframe. In order to achieve a wing loading similar to that of the rotary-engined V 5 despite the substantially heavier D III engine, the wing span and area were increased, overall span being extended by 35.4 in (90 cm) and mainplane chord being increased, this last change dictating increased interplane gap. The lower position of the bottom wing led to deepening of the forward fuselage and cg considerations necessitated positioning of the cockpit well aft. The V 6, also referred to as the D VII, lacked the manoeuvrability demonstrated by the parallel V 5 (see Dr I) and development was discontinued. No data are available for this prototype.


FOKKER DR I (V 5) Germany

  The series version of the V 5, which, with a 110 hp Le Rhone, differed from the V 4 (which see) primarily in having an intermediate-span centre wing, the Dr I single-seat fighter triplane began to reach the Front in October 1917. In fact the second and third series aircraft had been evaluated from the latter part of August from Courtrai by Manfred von Richthofen's Jasta. Armed with two synchronised 7,92-mm LMG 08/15 machine guns, the Dr I was powered by the 110 hp Oberursel Ur II copy of the nine-cylinder Le Rhone rotary. The Dr I enjoyed some success in combat, being extraordinarily manoeuvrable, but deliveries to the Fliegertruppen were inhibited by engine shortages and the need to replace the wings of all early production aircraft, manufacturing standards of which were considered unacceptable by the Idflieg. The original V 5 was brought up to production standards and delivered as a Dr I, and 320 series Dr Is were delivered to the Fliegertruppen. One was supplied to the Austro-Hungarian MAG concern. Four prototypes with more powerful engines were completed as V 7s. One of these, with an 11-cylinder Oberursel Ur III rotary of 145 hp, participated in the first D-type contest at Adlershof, attaining an altitude of 16,405 ft (5 000 m) in 15.5 min. Two V 7s were delivered to Austria-Hungary, one with a 160 hp Siemens-Halske Sh III rotary and the other with a 145 hp Steyr-built Le Rhone, and the fourth was fitted with a 170 hp Goebel Goe III rotary.

Max speed, 115 mph (185 km/h) at sea level, 102 mph (165 km/h) at 13,125 ft (4 000 m).
Time to 3,280 ft (1000 m), 2.9 min.
Range, 186 mis (300 km).
Empty weight, 895 lb (406 kg).
Loaded weight, 1,292 lb (586 kg).
Span, 23 ft 7 in (7,19 m).
Length, 18 ft 11 in (5,77 m).
Height, 9 ft 8 in (2,95 m).
Wing area, 200.9 sq ft (18,66 m2).


Журнал Flight


Flight, March 14, 1918.

THE FOKKER TRIPLANE.

[The collection of captured enemy aeroplanes at the Enemy Aircraft View Rooms is constantly increasing, and every week brings something interesting of which we should like to inform our readers. It is not, however, possible to do justice to each new arrival before the next one follows, so rapidly do the numbers increase. As we have only available in our columns a limited amount of space which can be devoted to this particular subject, we are faced with the problem of either curtailing the matter of the articles or else perforce defer much that is of interest until space permits publication. A case in point is the Fokker triplane which has just arrived at the View Rooms. We are naturally anxious to place particulars of this interesting machine before our readers as quickly as possible, but at the same time, having far from finished our detailed description of the Albatros Fighter, we should like to complete this before turning our attention to other machines, however interesting. We, therefore, decided this week to somewhat, curtail the description of the Albatros, in order to be able to give just a brief outline of the features of the Fokker triplane. In so doing we regret having had to reduce the instalment dealing with the Albatros to less than it would otherwise have been, but trust that we have made up for this by being the first journal in the world, we believe, to publish illustrations of the Fokker triplane. To the authorities who have courteously given us every facility for dealing with this interesting machine, our readers no less than we ourselves are indebted for the following information.-ED.]

  IT has been one of the features of the development of German aeroplanes during the war that, up till comparatively recently their performance has been obtained by a constant increase in engine power rather than by highly efficient aerodynamical design. Such refinements as stream-lined cables, and "spinners" over the propeller boss were not in the past a characteristic feature of German aeroplanes. As, however, the demands for better and still better performance grew, the Germans were obliged to pay more attention to such details, and such machines as the Albatros chaser, with its stream-line semi-monocoque body, was one of the manifestations of this attempt at increased efficiency. The Fokker triplane marks a further step in the battle against that enemy of efficiency, Kx, once expressed by Mr. A. E. Berriman, we believe, as the price paid for the lift. In the Fokker triplane this price has been reduced to what would appear to be an irreducible minimum. So far has the designer gone in his reduction of head resistance as to eliminate all trace of external lift bracing. The Fokker triplane can, therefore, be said to be of the "wireless" type; more truly so than is the case with, for instance, the Curtiss "wireless" in which, although no wires are employed, the struts sloping out from the landing wheels to the lower plane perform the function of lift wires.
  No such struts are fitted on the Fokker triplane, the internal construction of the wings being designed to provide all the strength without any external aid of any kind. The interplane struts, which are really ties rather than struts, might conceivably have been omitted altogether, and so far as one is able to judge, their only function is to help to distribute the load more evenly between the three wings. It is well known that in a biplane the upper wing carries about four-sevenths of the total load (when the wings are of equal section, span, and chord) and the lower wing about three-sevenths. In a triplane much the same distribution is found, with the exception that the middle and lower wing each take a share (not equal) of the three-sevenths of the total load.
  In the Fokker triplane the upper wing is of larger span than the middle wing, which in turn is of slightly greater span than the lower wing. In consequence, as the three wings appear to be all of the same section, the upper wing must carry more than four-sevenths of the total load. In order to provide a better load distribution, the middle and lower wings are made to carry their share of the load on the top plane by connecting them to this via thin high fineness ratio struts, which are in reality ties as they are working in tension. This explains why the struts are so extremely thin (about 1/2 in.) and the moment of inertia of the strut section would be so small that the struts would buckle under a very small load if subject to compression.
  The fact that no lift bracing is employed naturally necessitates wing spars of considerable depth if the spar weight is to be kept reasonable low, and in the Fokker triplane this has been attained by making the wing section very thick in proportion to the chord. As a matter of fact the section is a far greater percentage of the chord than any we have ever seen on a modern aeroplane. For the time being we cannot go into details, this must be postponed until we do a full description of the Fokker, but roughly we should say that the maximum camber is in the neighbourhood of one-eighth of the chord.
  The two wing spars are placed very close together, and are enclosed in a box of three-ply wood. The function of this box is two-fold, it increases the strength of the spars for taking bending and at the same time acts as internal drift bracing. At the moment of writing we are not able to say whether or not any other drift bracing is employed, but we are inclined to think that this function is performed solely by the ply-wood box.
  The upper wing, which is in one piece, runs right across, and is supported on struts sloping outwards as in the Sopwiths. The other two wings each have a centre section rigidly attached to the body, the middle one resting on the top longerons and the bottom one running underneath the lower longerons, an aluminium shield streamlining the normal surface presented by the deep flat sides of this spar.
  From the illustrations it will be seen that the gap is unusually small, being very considerably less than the chord. The inefficiency thus caused is partly made up for by staggering the wings but even so one would imagine the machine to be somewhat inefficient. The interference owing to too close spacing of the wings chiefly affects the lift co-efficient, and as the machine is probably very lightly loaded compared with the majority of German machines - it is possible that the landing speed is not excessive.
  Strictly speaking the Fokker is not a triplane. It would be more correct to term it a three-and-a-half plane, as the wheel axle is enclosed in a casing of ply-wood which has a section somewhat similar to that of the wings. Experiments have shown that floats of such a section as to have a deeply cambered top surface may be made to support their own weight during flight. In the case of the Fokker triplane it appears probable that this ply-wood casing around the wheel axle carries a not inconsiderable load during flight. Its section appears capable of supporting a fair load per sq. ft. of area, and its inefficiency due to low aspect ratio is probably less than one would expect in a plane of an aspect ratio of about two, on account of the proximity of the covered-in wheels to the tips, the effect of which must be to stop end losses to a considerable extent.
  As regards the body of the Fokker triplane this is constructionally very similar to that of the Fokker monoplanes. Longerons as well as struts and cross members are in the form of steel tubes, and are joined together by welding. The internal bracing of the body is peculiar in that the bracing wires are in appearance in duplicate, although they are not so in effect.
  The arrangement, to which we shall revert again when dealing with the Fokker in detail, does not appear to possess any other advantage than that in each bay only half the number of loops have to be made in the wires.
  The tail plane, as well as the elevators and rudder, is made of steel, and is of a symmetrical section, much thinner than that of the Albatros, but otherwise similar to it in that no external bracing is employed. While this is quite satisfactory in the Albatros on account of the thick tail plane spars employed, it appears wholly inadequate in the Fokker, as the plane is very thin, and since, moreover, the trailing edge of the tail plane is a steel tube, which section, as is well known, is not a good one for a laterally loaded beam, owing to the fact that much of the material is massed around close to the neutral axis where it is not taking very much of the load.
  As exhibited at the Enemy Aircraft View Rooms the Fokker is not complete inasmuch as the engine has been removed. The cowling shows without a doubt that the engine must have been a rotary, and the mounting is of the type usually employed for rotary engines, i.e., a main engine plate bolted to the nose of the body, and a pyramid of steel tubes, supporting at its apex the rear end of the crank-shaft. A sheet of aluminium is placed immediately in front of the engine plate. The manner of cowling in the engine will be apparent from our illustrations, and does not present anything of particular interest, following as it does conventional practice.
  Although they are not in place in the machine as exhibited, it is evident from the aluminium casings for the cartridge belts that two synchronised machine guns have been fitted, one on each side above the fuselage. The usual triggers, operating the guns through Bowden cables, are mounted on the control lever, which latter is of the usual type.
  Painted on the side of the fuselage are the following data relating to the weight of the machine: Weight empty, 376 kg., useful load, 195 kg., total weight, 571 kg. (about 1,250 lb.)
  With these brief particulars we must leave the Fokker triplane for the time being, but later on we hope to return to it again, and to be able to give illustrations of some of its more important constructional details.


Flight, May 2, 1918.

THE FOKKER TRIPLANE.

[Just as we have completed the preparation of our data for an illustrated description of the Fokker triplane which is now exhibited at the Enemy Aircraft View Rooms, we receive from the Technical Department of the Aircraft Production Department of the Ministry of Munitions an official report on this machine. The report is somewhat brief, possibly owing to the fact that the design is now said to have been discontinued. That the German "Ace" Freiherr von Richthofen should have chosen for his favourite mount a Fokker triplane after this machine had been turned down by the authorities need not cause any surprise, and only goes to prove that this is not the only country in which opinions may differ as to what is or is not a safe and suitable design. We do not mean to infer that the machine on which the famous German pilot met his death was necessarily identical with the one here under review, which was built during the latter part of last year, and of which we have already published a brief description in our issue of March 14th. As a matter of fact the probabilities are that there were considerable differences. But thereby hangs a tale, which is recorded elsewhere in this issue.
  To return to the official report on the Fokker triplane. It is apparent, from a paragraph on the cover, that the authorities feel called upon to apologise for the brevity of the report, and it is stated that the report is issued for information, "though it is felt that the machine exhibits few instructive features." This is a policy with which we cannot in any way agree. It may happen - and, we think, very frequently does happen - that a thing which has proved a failure is very often far more instructive than one which was a success. After all there is always a tendency for anything successful to engender imitation, whereas failure tends to stimulate original thought which may in time lead to the production of something really good. Moreover, to come down to a specific case, although this particular design may have proved itself bad, who will venture to say that it may not contain the germ of an idea which someone may be clever enough to grasp and to turn to good account? We therefore propose to deal with this machine in our own particular manner and as fully as seems necessary, hoping that it will prove as interesting and instructive as our numerous correspondents have been good enough to tell us our previous articles of this nature have been. - ED.]

  THE Fokker triplane is chiefly remarkable on account of its total absence of external lift bracing, but offers, on closer examination, a number of constructional details, some good, some indifferent, and some frankly bad, but always interesting, which are well worth a careful study. It appears that, generally speaking, German designers either try to do without metal altogether, or else go to the other extreme and use it exclusively. In the latter ease it will often be found that welding is very extensively employed, even on jobs for which it is least suitable, as, for instance, fittings working in tension. This gives one the impression that German designers are divided into two schools. One, which does not trust welded joints and therefore attempts to do without metal as far as possible; and the other, being "all out for metal," which appears to have a childlike faith in the skill of their welders and uses welded joints in and out of place.
  The Fokker triplane indicates that its designer does not belong exclusively to either school, but is influenced by both. That is to say, he seems to have incorporated in his design the extremes of both schools. Where he uses metal he uses it exclusively and throws in a profundity of welded joints, and where wood takes his fancy he goes to considerable trouble to circumvent the difficulties attending wood construction, simply to be able to use wood where in many cases metal would have offered a much simpler solution. The explanation may be that den Heer Fokker commenced his aeronautical career as a disciple of the all-metal school - his old monoplane was, it may be remembered, built almost exclusively of steel - but is beginning to lean towards the all-wood school, whether by inclination or because of the conditions prevailing at present one cannot say. It is in the wing structure that the wood construction predominates, while the body is built entirely of steel.
  In conformity with his past preferences, Fokker has employed steel tubing throughout in the construction of the fuselage of his triplane. The longerons, struts and cross members are all made of this material, the diameter of the tubing employed varying somewhat locally according to the different stresses. Probably the gauge of the tubes varies also, but this we have not been able to verify, as none of the tubular members are cut through on the machine exhibited.
  The general arrangement of the body of the Fokker triplane is shown in Fig. 1 in plan and side elevation. It will be noticed that the lower longerons <...> a rather abrupt upward bend just behind <...>where the spar of the lower wing is attac<...> that secondary longerons are employed for <...> the continuity of the curve from this po<...> engine plate. At the rear the top lon<...> dropped a matter of a couple of inches to acci<...> the tail plane, much after the manner of the <...> Deperdussin monoplanes.
  In section the main body is rectangular, while the front portion carries in addition superstructures on top and sides, which carry the circular section near the engine gradually into the flat sides and top of the rear part. As regards the detail construction, struts and cross members are butt-welded to the tubular longerons. This does not impress one as a particularly good arrangement, since the effect of vibration on the welded joints may easily become serious.
  If the method of joining the members of the fuselage structure is open to criticism, the arrange<...> the bracing system is even more so. As briefly <...> out in our previous notes on the Fokker <...> the bracing wires of the body have the <...> of being in duplicate, but are in effect <...> they are merely looped around the tubular <...> forming the standard terminal at the <...> of struts and longerons. The details of this arrangement will be more easily understood from reference to Fig. 2. It will be seen that the only advantage gained by having the bracing wires so arranged is a saving of two loops and two ferrules in each wire. From the point of view of rapid production the gain thus effected cannot be considerable, while the saving in weight could only amount to a very few pounds in the whole body. Against this we have the weakness due to the fact that if one part of the wire breaks - whether the part with the wire strainer or the plain part matters little - the whole strength is gone, since the wire would, as soon as subjected to a tension of a few pounds, pull around the tubular anchorage. Another point suggests itself when examining the body bracing. When tuned up the tension in the wire is probably uneven, the plain part of each wire being tensioned to a less extent than the length incorporating the strainer, owing to friction between the loop of the wire and the terminal tubular quadrant. In certain instances this wire attachment has been varied to suit local requirements, but everywhere where other considerations do not have to be taken into account the anchorage and wiring is as shown in Fig. 2.

(To be continued.)


Flight, May 9, 1918.

THE FOKKER TRIPLANE.
(Continued from page 476.)

  FROM Fig. 1 (see page 474 in last week's issue) it will be seen that in the front portion of the body the strutting is so arranged that the usual diagonal wire bracing becomes superfluous, the tubular struts being arranged in a series of triangles which by themselves render the structure rigid. As a consequence the anchorage tubes differ somewhat from those employed in the rear part of the body. Generally speaking they take the form of straight tubes welded over the angle formed by adjacent struts, and instead of lying in a transverse plane, as do the rear ones, they are in the same plane as the sides of the body. As for the attachment of the struts themselves to the longerons, this is practically the same as that employed in the rear part of the body, i.e., by butt-welded joints. Here and there one finds additional fittings for receiving chassis struts or wing attachment, but these are supplementary rather than departures from the universally adopted scheme.
  As we have already mentioned, the rectangular section of the main body of the Fokker triplane is partly streamlined in front by superstructures secured to the sides and top of the body. These fairings take the form of triangular sheets of thin three-ply wood, attached to the upright struts of the body by means of short distance pieces of spruce and by aluminium clips, as shown in Fig. 3. The middle spruce rail of these fairings, it will be seen, runs back slightly farther than the top and bottom ones, and its rear end is not attached to the body except in so far as it rests against one of the body struts. Apparently the tension of the fabric body covering is relied upon to keep it in place. Reference will be made to the armament of the Fokker triplane later, but while dealing with Fig. 3, we would call attention to the mountings for the two machine guns, which this sketch shows. Each gun, it will be seen, is supported on two fork end brackets, the front ones of which are rigidly attached to one of the top cross struts of the body, while the rear ones are so designed as to allow of aligning the guns. Each of these supports is in the form of a fork end mounted on the end of a tubular pillar, which is in turn held in position at its lower end by a split collar on the transverse body strut. This collar may be shifted laterally along the horizontal strut and locked in position at any desired point, thus providing for the lateral alignment of the rear gun support. The vertical adjustment is effected by the vertical displacement of the pillar carrying the fork end, which is locked in position by the vertical part of the split collar or clip.
  Having dealt with the general construction of the body, we next come to consider its internal fitting up. The pilot's cockpit, which appears to be of somewhat less generous proportions than those usually found on German machines, gives a somewhat ascetic impression contrasted with the somehow cosy and comfortable cockpits of other machines of German origin. This may be partly accounted for by the fact that the body structure is steel tubing, but no doubt the chief reason is to be found in the inadequate upholstering of the seat, which is of the aluminium "bucket" type. The covering is some sort of pegamoid stuff, and looks on the whole "cheap and nasty." This appearance, by the way, is not confined to the seat only, but is noticeable throughout the machine. To finish, as we understand it, there is no pretence, and the workmanship, which is not, of course, by any means the same thing, although the two are frequently confused, even by those who ought to know better, is not by any means beyond reproach. On the whole we are inclined to think that the unfavourable impression left by an inspection of the Fokker triplane is due to bad finish and workmanship quite as much as if not more than to poor design. The pilot's seat is so mounted as to be capable of being easily adjusted in height. It is supported on a framework of steel tubes, as shown in Fig. 4. This framework is attached to the upright body struts by tour sliding collars, the upper two of which are split and fitted with a locking bolt, as shown in the inset, Fig. 4. This locking bolt is rather long, so as to make more accessible the wing nut which tightens up the split collar. The necessary adjustment is easily made from inside the body, both wing nuts being easily reached from the seat.
  The controls, which are shown in the central sketch of Fig. 5, consist of a vertical tubular control lever mounted on a longitudinal rocking shaft, and of a tubular foot bar for the rudder. The details of the control gear will be readily followed in the sketch. A large collar, to the top and bottom of which are welded the anchorages of the elevator cables, is pivoted to the rocking shaft by a horizontal bolt and is free to be moved through a considerable angle in a longitudinal plane owing to being so much larger in diameter than the shaft. The latter, which is carried in bearings formed by clips gripping the lower cross struts, is free to oscillate laterally, and carries near its forward end two cranks placed at an angle and staggered in relation to one another. From these cranks cables pass over pulleys on the top spar to the ailerons.
  At its upper end the control column carries a double-handled grip and the triggers for the machine guns, as well as the cut-out switch for the engine. The handle on the left is not, however, fixed in the usual manner, but serves, by being pivotted, for operating the engine throttle, via Bowden cables. Two triggers are provided by means of which either of the two machine guns can be brought into gear. On the front of the lever will be seen a bent steel rod which, on being pulled back, puts both machine guns into gear, thus firing them simultaneously. The connection is as usual by Bowden cables, and the interrupter gear is driven by a pinion engaging with the gear wheel that meshes with the magneto and oil pump drives. The gun triggers and other details of the control handle are shown in the inset in the bottom right-hand corner of Fig. 5.
  The foot bar for the rudder is in the form of a steel tube pivotted around a vertical tube resting at its lower end on a bracket under the floor boards and secured at its upper, after being bent back slightly, to the deck of the body. The pilot's feet rest in loops of thin tubing welded to the main foot bar, while the rudder cables are attached to the bar by two stirrups, the bolts for which have their bearing in a short length of tubing welded to the front of the foot bar.
  Throughout the body of the Fokker triplane extensive use is made of split collars similar to that shown in the upper right-hand corner of Fig. 5. Extra stiffness of the flange is provided by stamping this out to the shape of a shallow cup in which are the holes for the bolt locking the collar in position. Where, as frequently happens owing to the tubular construction, two of these collars have to be placed at right angles to one another, they are joined together by welding. This is the case, for instance, with the guides for the control cables running to the tail. These guides are shown in the bottom left-hand corner of Fig. 5, while yet another form of the clip, slightly different in detail but similar in principle, is shown on the left. This sketch represents the clip and guide tube for the aileron cable on its way from the cranks in the body to the pulleys on the spar of the top plane.
  As shown at the Enemy Aircraft View Rooms, the Fokker triplane did not show any signs of having been fitted with an instrument board, and of such instruments as revs, counter, altimeter, air speed indicators and fuel indicators there was no trace. On the right-hand side of the pilot the cardan support for the compass was still in place, and the bracket supporting it is of the form shown in the sketch, Fig. 5. On the left was a quadrant and shaft, evidently for controlling the fuel and oil. One large tank just behind the engine support is divided by a longitudinal bulkhead, the right-hand compartment containing the oil and that on the left the petrol. According to the official report on the Fokker triplane, the capacities of the two tanks are 4 gallons and 16 gallons respectively, or sufficient for a flight of 2 1/2 hours' duration.

(To be continued.)


Flight, May 16, 1918.

THE FOKKER TRIPLANE.
(Continued from page 512.)

  THE engine mounting on the Fokker triplane has already been briefly indicated in our side elevation and plan of the fuselage (see page 474 of our May 2nd issue). Fig. 6 is a perspective sketch further illustrating the general arrangement of the engine support. The main engine plate, which is in the form of a ring, is supported on a structure of steel tubes arranged in the shape of a four-pointed star. The rear engine support, on the other hand, is mounted on a pyramid of steel tubes, running to the same four points, i.e. the corners of the fuselage, as the four points of the star. The attachment to the body is shown in detail in Fig. 7. The apex of the three-legged pyramid formed by the two front bearer tubes and single rear bearer tube is welded to a longitudinal horizontal lug. This lug is in turn supported by a long bolt passing through a hole in a triangular corner plate welded to the vertical and transverse body struts. Thus by undoing the four bolts the whole engine mounting may be removed bodily. This is, of course, an advantage, but structurally the arrangement can only be considered very weak. Ultimately, it will be seen, a welded joint - that of the triangular corner plate to body struts - or, more correctly speaking, four of them, is relied upon to support the engine. This can scarcely be considered anything except very bad practice. In conformity with usual practice there is an aluminium capping plate covering the front engine bearer. This plate is held in place by the four bolts carrying the engine mounting, the bolts passing through and being locked on the front face of the aluminium plate, where they are easily accessible.
  The under-carriage of the Fokker triplane is of the now usually employed Vee type, but it differs in several respects from standard practice. Thus the fairing round the axle is of much larger dimensions than those usually obtaining, so much so that it constitutes in reality a supporting surface of an area that can by no means be considered negligible. In the official report on the Fokker triplane, this fairing is represented as being of symmetrical cross section. We confess that we are not quite decided as to whether or not this is correct. In the specimen shown at the Enemy Aircraft View Rooms, the fairing is very much damaged, and it is almost impossible to ascertain definitely what was the exact cross section, but from the fragments left intact we are inclined to think that the three-ply casing was not a symmetrical stream-line section, but rather a section approaching somewhat to that of the main planes, with the exception, possibly, that, it had a flat under-surface and a cambered top. However, this is somewhat in the nature of a conjecture, and we merely express it as our personal opinion. That the extra lift obtainable by making this member a lifting surface would be worth considering appears probable, since the inefficiency due to low aspect ratio would be to some extent compensated for by the proximity of the flat inner sides of the wheels to the tips of the surface, which would thus act as baffle plates and tend to reduce end losses.
  Constructionally, the casing around the axle consists of a covering of three-ply wood, supported on a rectangular section aluminium casing around the axle, and on two circular section aluminium tubes acting as auxiliary spars. The end of the axle casing is a steel box to which are welded the lower ends of the under-carriage struts. From this steel box also project the two tubular stubs to which are anchored the shock absorbers. This arrangement is shown on the right in Fig. 9, while the sketch on the left gives an idea of the general construction of the whole axle casing. The under-carriage is braced laterally by stranded cables in the front bay only.
  The struts of the under-carriage are secured to the body by a form of ball and socket joint, the socket being slotted for some distance from its open end. A short pin is passed through an opening in the ball-shaped end of the strut, and is locked by a small split pin. The joint looks extremely weak, and cannot, one imagines, have nearly as high a factor of safety as the strut which it is meant to secure.
  While on the subject of the under-carriage reference may be made to the tail skid. This is of wood and pivoted, the attachment being as shown in Fig. 8. The vertical tube supporting the tail skid is welded to the four longerons which at this point converge to within a very short distance of one another. At its upper end the tube secures the rear spar of the tail plane.
  Fig. 10 shows the tail plane and rudder. The former, as already pointed out, is brought down to the level of the top longerons, by dropping these for the last few feet slightly below those in the front part of the body. The main framework of the tail plane is in the shape of a trapezoid, three sides of which are formed by steel tubes of large diameter, while the fourth side is a wood beam. Over this framework the ribs are built, the flanges being in the form of small diameter steel tubes. These tubes are welded to thin collars surrounding the converging tubes, thus avoiding the possibility of weakening the larger tubes by heat. The construction of the elevator ribs is similar to that of the tail plane, while the rudder ribs are slightly different, being reinforced by short lengths of tube running zig-zag fashion from one flange to the other. The hinges for the elevator tube are of a very simple form, being in appearance short lengths of channel section metal bent around the tube and fastened by a single bolt to the tail plane spar. These hinges are extensively employed on the Fokker triplane, being used also for the rudder and aileron hinges. The elevator and rudder crank levers are welded direct to their tubes without the intermediary of a collar. Their general shape will be clear from Fig. 10.

(To be continued.)


Flight, May 23, 1918.

THE FOKKER TRIPLANE.
(Continued from page 536.)

WE now come to deal with the most interesting part of the Fokker triplane, the wing structure. It has already been pointed out that the machine is of the "wireless" type, inasmuch as there are no lift wires or landing wires, the only wires employed in the wing structure being the diagonal cross bracing between the centre struts sloping upwards and outwards from the body to the top wing. Aerodynamically this is advantageous from the point of view of low resistance, but structurally it is open to criticism on the score that it is difficult to provide adequate strength in such a structure, and that the only possibility of doing so is to employ a very deep wing section which will allow of using spars of such a section and depth that its moment of inertia is large without its area being excessive. This is precisely what the designer of the Fokker triplane has done. The wing section is one of far greater depth than one is accustomed to find on a modern fast machine, and inside this deep section he has built up a composite spar of somewhat unusual construction. Hitherto the vast majority of aeroplanes of any nationality have had wing spars which were either of the I or of the box section. In the Fokker spar we have neither strictly speaking, since it is certainly not an I section and only a box spar after making certain allowances. Briefly speaking, the principle of the Fokker triplane spar is the following: There are two spars as in the majority of other wings, but placed absurdly close together. Each spar is of the box type inasmuch as it consists of spruce flanges top and bottom, with a web of three-ply on each side. The top and bottom faces of these two spars are then united by a sheet of three-ply covering, them up so as to form in effect two boxes within a box. In this manner there is no need # or at any rate the designer appears to be of that opinion # for any internal wing bracing, this being provided by the top and bottom three-ply covering.
In Fig. 11 are shown some of the constructional details of the Fokker wings. The sketch at the top of the illustration shows the upper starboard wing in general arrangement. The construction is similar in all wings as regards fundamental principles, and only differs in minor details where this is necessitated by local requirements. The outward appearance of the wing spar is shown in the top sketch, and also the manner of attaching the ribs, which are prevented from sliding along the spar by little triangular section blocks of wood tacked to the spars. The sketch in the centre shows the construction of the spar, and one of the longitudinal partition, which occur at certain intervals along the spar. These partitions are made up of four strips of spruce, halved together and glued. The ribs have spruce flanges and very thin webs of three-ply wood, approximately 1 mm. thick.
The leading edge is formed by a long strip of three-ply, wrapped around the nose of the ribs, and cut out in triangular shapes, the apices of which are secured to the top of the spar.
As shown in the scale drawings of the Fokker triplane (published in our issue of May 2nd), the upper wing is supported from the body on two inverted Vees of steel tubing, sloping outward at a considerable angle. Details of the attachment of the apex of the Vee to the top spar are shown in the two sketches at the bottom of Fig. 11. Two channel section plates are secured to front and rear faces respectively of the spar, by two horizontal bolts passing through the spar. To the bottom end of each plate is welded a small lug, internally threaded, into which is screwed a vertical bolt, the other end of which passes through a lug on the strut structure and is secured in position by locknuts. It will be seen that by suitably adjusting the bolts securing the spar, the angle of incidence may be slightly varied. To the left of the strut attachment will be seen the pulleys for the wing flap cables, which run from this point to the cranks of the rocking-shaft in the body.
Mention has already been made of the fact that the interplane struts are extremely thin, and are in effect ties rather than struts. They are made of wood, and the attachment to the spars is shown in the remaining sketches of Fig. 11. That on the left shows the attachment to the lower spar, and the sketch on the right indicates how the same method, with slight modifications, is employed for securing the inter-plane struts to the middle spar. A shoe of thin sheet steel is wrapped around the end of the strut, and through it a long tubular bolt is passed, which also runs through the holes in the channel section plates on the sides of the spar. The principle is really the same as that for attaching the body struts to the spar. In the latter, however, the channel plate has its upper end bent over the edge of the spar, presumably to assist in relieving the bolts passing through the spar of the shearing stress.
In Fig. 12 are shown some of the details of the lower wing near the tip. On the right will be seen a sketch illustrating the peculiar construction of the extreme wing tip. This is formed by placing an ordinary rib horizontally, attaching it to the last main rib by triangular brackets of wood. The remaining sketches of Fig. 12 show the details of the wing tip skid. From the sketch on the left it will be seen that the skid is so close up against the lower surface of the wing that the machine would have to cant over at an alarming angle before the skid would come into play, and it is difficult to see how the skid could be of any great practical use. Its attachments are shown in the detail sketches, that on the left indicating how the skid is pivoted, while that on the right shows how the free end of the skid is secured. Small bolts pass through these fittings and are locked on the inside of the spar in the manner indicated in the small sketch.
The attachment to the body of the lower and middle wing is shown in the sketches of Fig. 13. That on the left, illustrates the bottom plane attachment. It may be remembered that the main lower body rails were passed over the bottom spar, auxiliary rails being provided for maintaining the continuity of the curve underneath the spar. This is indicated in the sketch on the left. The attachment itself is exactly similar in principle to that of the top spar to the body struts. Again provision has been made for adjusting the angle of incidence. The middle spar attachment, shown on the right, is to all intents and purposes the same reversed. In this connection it should be remembered that the spars run right across from side to side in one piece. This has an important bearing on the wing spar stresses, with which we hope to deal next week.

(To be continued.)


Flight, May 30, 1918.

THE FOKKER TRIPLANE.
(Continued from page 569.)

  Among the interesting features of the Fokker mention must be made of the wing section, which alone has made the "wireless" arrangement possible. Although wing sections are nowadays probably thicker, on an average, than they were some years ago, due to the more insistent demands for strength and light weight, there are few machines if any, that can compare in this respect with the Fokker triplane. The maximum depth, which occurs in the neighbourhood of the front part of the composite spar, is no less than 4.95 ins, or practically 5 ins, and this for a chord of only 1 metre (about 3 ft. 3 1/4 ins.). A scale drawing of the wing section is given in Fig. 14, from which the depth at various points along the chord can be found. The web of the rib, which is made of thin three-ply, is unusual in that it is not cut where it abuts against the spar faces, as is general practice, but is continuous from leading to trailing edge. This has been made possible by the fact that the composite spar is of a rectangular section of a maximum depth determined by the rib depth at the rear edge of the spar, which leaves a small space between the top and bottom faces of the spar and the rib flanges. Whether or not this provides any very great increase in the strength of the rib is perhaps doubtful, but keeping the spar of rectangular section would certainly appear to have advantages from the point of view of construction, as all the four strips of the spar may thus be kept of rectangular section instead of, as they would otherwise have to be, being shaped to fit the slopes of upper and lower faces of the spar. As regards the spar itself, reference has already been made in a previous instalment to its general construction. Fig. 14 gives the dimensions of the various component parts of the spar. These dimensions apply to the inner portion of the spar, near the root, and to this point only, as the dimensions vary throughout the length of the spar, an attempt having apparently been made to proportion, to a certain extent, the strength of the spar to the load at any point. As regards the four spruce strips of the spar, these are tapered in plan view, their width from front to back changing from about 2 ins. at the root to about 3/8 in. at the tip. The depth of the flanges, on the other hand, remains constant. The ply-wood covering or box spar has also been varied, the outer half being covered with one layer of three-ply, while the inner portion has an extra thickness of three-ply, making in reality a flange of six-ply wood.
  As the wings are to be regarded as cantilevers, the object of this construction is evidently to reduce weight to a minimum by reducing the size of the spar where the loading permits of doing so, that is to say more or less gradually from the root towards the tip.
  The opinion has been advanced that the Fokker triplane construction is extremely weak. So, on the face of it, would it appear to be, but as the machines have repeatedly been mentioned as doing good work, (although this may possibly refer to a later type) and since the arrangement is very unusual, we have thought it might be of interest to examine whether or not the Fokker system is as weak as one is apt to imagine at first sight. A reference to the front elevation of the machine (published in our issue of May 2nd) shows that the span of the upper wing is greater than that of the middle wing, which is in turn of greater span than the bottom one. From tests carried out by Mr. J. C. Hunsaker at the Massachusetts Institute of Technology (the results of which were published in "FLIGHT" for November 23rd, 1916), on triplane combinations of wing sections of the R.A.F. 6 type, it appears that for a triplane combination in which the three wings are of equal span and chord and not staggered, the triplane ky is .0004, while the value of upper, middle and lower wing ky is respectively .0006, .0002, and .0004. In other words, the ky of the lower wing is practically the same as that of the triplane combination, while that of the upper wing is very much greater and that of the middle wing considerably smaller. In the case of the Fokker allowance should be made for stagger and for the fact that the three wings are of unequal span, but as we have no data to go on, and since, moreover, any difference in interference caused by the unequal spans will probably not be sufficiently great to seriously affect our purpose of making an approximate estimate of the spar stresses, we shall disregard the difference due to unequal spans and take the figures as they stand. The weight of the Fokker triplane is given as about 1,260 lbs. The area of the top wing is about 83 sq. ft., that of the middle wing 54.5 sq. ft., and that of the bottom wing 51.9 sq. ft. Assuming the lift distribution to be the same as that found by Hunsaker, we obtain a lift of 9.21 lbs./sq. ft. of the upper wing, 3.09 lbs./sq. ft. of the middle wing, and 6.14 lbs./sq. ft. of the lower wing - the average loading being that of the bottom wing, or 6.14 lbs. per sq. ft.
  Fundamentally the Fokker wing bracing is such that each wing may be considered a cantilever beam, and they would be truly so except for the struts, or rather ties, connecting them. These ties, however, only serve to force the middle and lower wings, which are more lightly loaded on account of the load distribution and also by reason of their shorter span, and which have the same spar section as the upper wing, to share some of the load on the top wing. If, therefore, we disregard the assistance given the top wing by the other two, and if we further assume a uniform distribution along the span of the wing instead of taking into account that the portion of a wing near the tip is always more lightly loaded than the inner part, we can hardly be accused of being unduly optimistic with regard to the Fokker wing system.
  The load carried by the upper wing in the Fokker triplane is 9.21 x 83 = 764.43 lbs., say 770 lbs. The central span in about 5 ft. 2 ins., leaving on each side a cantilever of about 8 ft. 4 ins. or 100 ins. Assuming a uniform loading along the span, and remembering that the bending moment on the centre section wl^2/8 while that on the cantilever portions is wl^2/2, it will be seen that compared with the bending moment on the cantilever, the bending moment on the centre span is negligible. As a matter of fact it is only about 1,400 lb. in. The loading per inch run is 2.9 lbs., and the bending moment on the cantilever is wl^2/2 = 2.9 x 100^2 / 2 = 14,500 lb. in.
  From Fig. 14 it will be seen that the dimensions of the four spruce flanges of the spar are 2 1/8 ins. by 5/8 in., so that the area of the four spruce sections is 5.36 sq. ins. The depth of the spar is 4 ins., and the section modulus Z may be taken with sufficient accuracy as being equal to area of flanges multiplied by half the depth of the spar, or 5.36 x 2 = 10.72. Assuming the strength of spruce as being 8,500 lbs. sq. in. the moment of resistance of the spar flanges will be: 8,500 x 10.72 = 91,120 lb. in.
  Treating the box spar formed by the ply-wood separately, the section modulus Z = (1 / (6 x 4) ) x (7.88 x 64 - 7.38 x 52) =5.02, and the moment of resistance of the ply-wood box, assuming the strength of the ply-wood to be the same as that of spruce, will be: 8,500 x 5.02 = 42,670 lb. in.
  The total moment of resistance of the spar will then be 91,120 + 42,670 = 133,790 lb. in. Without knowing the travel of the centre of pressure on the Fokker wing section it may reasonably be assumed to be such that it may coincide with one flange of the composite spar, and to be on the safe side we shall take it that when the c.p. is in this position the strength of the composite spar is reduced to half. The moment of resistance is then 66,895 lb. in., and as the maximum bending moment was found to be 14,500 lb. in., the factor of safety is apparently about 4.5. This is without regard to the fact that this load is greatly reduced by the interplane struts, by how much is rather outside the scope of a descriptive article like the present to determine, but to which we may refer on a future occasion. One can, therefore, only arrive at the conclusion that the Fokker wing bracing system need not be inherently weak, although detailed calculations based upon more exhaustive data than we have available would possibly indicate that the spar weight compares somewhat unfavourably with, that of spars of more usual type and arrangement.
  As regards the aerodynamical qualities of the Fokker wing section, it is difficult to express an opinion. Generally speaking machines of the Fokker class have been found most efficient for their purpose when fitted with wings of a section giving a rather low ky, but a good L/D ratio, whereas the deeply cambered section, having a very high value of the lift coefficient, has generally a smaller L/D value. The opinion has been expressed that the Fokker wing section resembled that tested by Dr. Schukowsky. In order to ascertain if this were the case we have plotted the two sections shown in Fig. 15. Some difficulty was experienced owing to the fact that the dimensions of the Schukowsky aerofoil given in A. W. Judge's book "Properties of Aerofoils," did not, when plotted out, give a fair curve. However, by comparison with the small illustration in above book, we were able to plot out an approximately correct section of the Schukowsky aerofoil. In Fig. 15 the Schukowsky section is shown in dotted lines. It will be seen that except for the trailing portion of the upper surface there is little or no resemblance between the two sections. It would therefore be futile to attempt to predict, from a knowledge of the Schukowsky coefficients, the performance of the Fokker wing section. One can only point out that it appears probable that the section has been chosen primarily with a view to accommodate the very deep spars, and that it has been found in practice to give reasonably good results - probably especially at a considerable altitude. It would appear that the section is suited for good climb rather than for great speed, and according to German claims, the climb of the Fokker is what they like to boast of rather than the speed. Whether or not the latter is made up for by an ability on the part of the Fokker triplane to climb rapidly and to a great altitude, hence to dive on to its victim from above, we cannot say. It is possible that it may be. Taking it all around, it is doubtful if the gain in reduction of head resistance due to absence of external lift wiring is sufficient to make up for the necessarily heavier wing construction. Of strength, it would appear from the foregoing that one can only conclude that this can be provided to an adequate degree.
  The following dimensions and data are taken from the official report on the Fokker triplane :-
  Identification marks. - R.F.C. No. G. 125; Maker No. 1856; Military No. FOK. D.R.I. 144/17; date of construction, 20.10.17.
  Weights (as stencilled on machine). - Weight, empty, 376 kg. (829 lbs.); permissible load (including fuel), 195 kg. (430 lbs.); total weight, 571 kg. (1,259 lbs.).
  Weight of engine. - 334 lbs., including hub, magneto, oil pump and carburettor. (NOTE.-Weight of 110 h.p. Le Rhone is 330 lbs.)
  Tank capacity. - Petrol, 16 gallons (approximate) ; oil, 4 gallons (approximate) ; approximate duration, 2 1/2 hours at 10,000 ft.
  From the above it is possible to construct the following approximate weight analysis : Fuel, oil and tank, 170 lbs. (allowing tank, 18 lbs.); crew, 180 lbs.; military load, 98 lbs.; engine and propeller, 358 lbs. (allowing propeller, 24 lbs.); structure, 453 lbs. (including engine bearers and instruments); structure percentage, 36; surface of main planes, 205 sq. ft. (approximately); estimated B.H.P. (by analogy with 110 h.p. Le Rhone), 113; lbs. per square foot, 6.14; lbs. per B.H.P., 11.15.

В.Кондратьев - Самолеты первой мировой войны
"Фоккер" Dr.I, пилот Вернер Фосс, сентябрь 1917г.
W.Green, G.Swanborough - The Complete Book of Fighters
(A Dr I flown by Ltn Fritz Kempf of Jasta Boelcke
В.Кондратьев - Самолеты первой мировой войны
Фоккер Dr.I, пилот - лейтенант Г.Вейсс, апрель 1918г.
W.Green, G.Swanborough - The Complete Book of Fighters
A Dr I originally operated by Jasta 18 and subsequently acquired by the French.
W.Green, G.Swanborough - The Complete Book of Fighters
A US-built Gnome-engined Dr I replica.
W.Green, G.Swanborough - The Complete Book of Fighters
The V 4 was the original progenitor of the Dr I and entered flight test early summer 1917.
O.Thetford, P.Gray - German Aircraft of the First World War /Putnam/
Fokker V 4
Журнал - Flight за 1918 г.
Журнал - Flight за 1918 г.
121 h.p., the 120 being provided by the motor. - Wheeling a Fokker triplane out n the aerodrome.
Журнал - Flight за 1918 г.
GettingReady to Start. - A pair of Fokker triplanes in their native land.
Журнал - Flight за 1918 г.
The Fokker triplane in flight.
В.Кондратьев - Самолеты первой мировой войны
Реплика "Фоккера" Dr.I на ретроавиашоу в Новой Зеландии.
K.Delve - World War One in the Air /Crowood/
Albatros DVs and Fokker Triplanes of Jasta 12 line up at Toulis in March 1918.
H.Cowin - Aviation Pioneers /Osprey/
Each war has its glories and its myths and surely one of the greatest myths of the World War I airwar must be that centred around Anthony Fokker's triplane fighter, the Dr I. Feared by its pilots as being structurally flawed, the Fokker triplane was only built in relatively small numbers, after which it was rapidly replaced by the much superior Fokker D VII. Just how was it then that to this day, the Fokker Dr I is thought of as one of the Allies' greatest aerial adversaries? In part, the story involves the 'Red Baron', the publicity machine that surrounded him, as discussed in the frontispiece to this book and Anthony Fokker, who did his utmost to cultivate von Richthofen's favour. The other major part of the story lies with the panic that befell the German Air Ministry in the wake of the Sopwith Triplane's advent in February 1917, a panic, it should besaid, that was greater than that which had followed the debut of the Nieuport fighters a year previously. With a climb rate better than that of any current German fighter, coupled to superb agility, the Triplane literally cut a swath through the enemy machines over the Somme. Top priority, urgent requests for proposals went out by telegram from Berlin to industry, Germany must have a counter, it must, therefore, have its own triplane. In fact, no less than twenty different types of German triplane fighter prototypes were to appear over the next twelve months, of which more later. What happened quite early on shows not only how Fokker stole the lead on his competitors, but also casts light on the Richthofen/Fokker relationship. Richthofen first encountered a Sopwith Triplane on 20 April 1917 and was impressed. He soon passed his impressions of the machine and its capabilities to Fokker during one of his frequent visits to the front-line airfields. Armed with this first-hand briefing, Fokker, whose fighters had lost much of their credibility, put his design and engineering team onto the triplane project right away, thus gaining two months lead on the nearest of his competitors. By July 1917, Fokker had flown and tested his V3 prototype with fully cantilevered wings, that is with no interplane struts, that were added to V4, in the shape of simply T struts, to cure wing vibration. V4 became the first of three pre-production examples, carrying the military designation F I. Granted service clearance in mid August 1917, Fokker, himself, accompanied the second and third of these machines to Courtrai, where he personally gave Manfred von Richthofen and Werner Voss their type checks on F Is, serial 102/17 and 103/17, respectively. Deliveries of the 318 production examples, by this time redesignated Dr I, started in mid-October 1917. Unfortunately, for at least two early recipients of the Dr I, Lt Heinz Gontermann of Jasta 15, an Orden Pour Le Merite holder with 39 'kills' and Lt Pastor of JG I, their machines broke up in mid-air on 30 and 31 October 1917, the pilot being killed in each case. The problem was a flawed wing requiring the withdrawal of the Dr I pending rectification. Strengthened and returned to service by December 1917, the Dr I was always subsequently viewed with some suspicion by its pilots, the type being relegated to second-line duties as soon as possible as Fokker D VIIs weredelivered. Shown is von Richthofen sitting in his F I, 102/17 and chatting with fellow pilots of his fighter wing, JG I.
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H.Cowin - Aviation Pioneers /Osprey/
Lt Werner Voss stands in front of his Fokker F I, 103/17, which as leader of Jasta 10 he had received on 29 August 1917 and the machine in which he was to die less than a month later, on 23 September 1917.
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W.Green, G.Swanborough - The Complete Book of Fighters
Ltn Werner Voss' Dr I
K.Delve - World War One in the Air /Crowood/
The Fokker Triplane, Fl 103/17 of Werner Voss, one of the leading fighter pilots during 1917. His career started in November 1916 with Jasta 2 and by the following summer he had 30 victories and was commanding Jasta 10.
With a mechanic ready to swing the propeller and two more in attendance, this Fokker Dr I pilot prepares for take-off. Alongside the Dr I is a Pfalz D III of the same Jasta helping illustrate the mixture of types that remained characteristic of German front-line Jastas all the way through to the Armistice. In contrast, the British and French had long since realised the logistical, maintenance and operational benefits of standardising aircraft and engines at squadron level.
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Один из первых экземпляров "Фоккера" Dr.I с заводским номером 115/17, западный фронт, сентябрь 1917 г.
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K.Delve - World War One in the Air /Crowood/
Dr.I 144/17 of Ltn. Eberhard Stapenhorst, Jasta 11; this triplane was downed by anti-aircraft fire on 13 January 1918 and Stapenhorst was taken prisoner.
Журнал - Flight за 1918 г.
The Fokker triplane from behind.
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Журнал - Flight за 1918 г.
Front view of the Fokker triplane.
Журнал - Flight за 1918 г.
Side view of the Fokker triplane.
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The Fokker Dr1 was, despite its obvious failings, well liked by many of the pilots, a number of whom were reluctant to trade in their mounts even when technically superior fighters became available. It was one of those aircraft that acquired a mystique, a mystique that still survives today!
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K.Delve - World War One in the Air /Crowood/
Fokker Dr1 403/17 of JG1 with Lt. Janzen.
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O.Thetford, P.Gray - German Aircraft of the First World War /Putnam/
Fokker Dr I.
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O.Thetford, P.Gray - German Aircraft of the First World War /Putnam/
Fokker Dr I flown by Lt. Janzen of Jasta 6.
O.Thetford, P.Gray - German Aircraft of the First World War /Putnam/
Fokker Triplanes of Jasta 11. The pilot holding the stick is von Richthofen.
O.Thetford, P.Gray - German Aircraft of the First World War /Putnam/
July 1918. Goring, who was by then commanding the Richthofen Circus, stands by a Fokker Triplane. At this period ihe Fokker D VII (seen in background) was entering service in increasing numbers.
O.Thetford, P.Gray - German Aircraft of the First World War /Putnam/
Fokker Triplanes o f Jasta 26.
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W.Green, G.Swanborough - The Complete Book of Fighters
Developed in parallel with the V 5, the V 6 had a larger wing span and area, and a water-cooled Mercedes D III engine.
O.Thetford, P.Gray - German Aircraft of the First World War /Putnam/
Fokker V 6
O.Thetford, P.Gray - German Aircraft of the First World War /Putnam/
Fokker V 7
В.Обухович, А.Никифоров - Самолеты Первой Мировой войны
Журнал - Flight за 1918 г.
THREE-QUARTER REAR VIEW OF THE FOKKER TRIPLANE. - This illustration gives a good idea of the general arrangement of this interesting machine. Note the small ply-wood plane enclosing the wheel axle.
Журнал - Flight за 1918 г.
THREE-QUARTER FRONT VIEW OF THE FOKKER TRIPLANE. - The thickness of the wings can be imagined from an inspection of this drawing. The pin-jointed struts are really ties rather than struts as they are working in tension.
Журнал - Flight за 1919 г.
A SOPWITH TRIPLANE ON THE WAY FOR A DOUBLE EVENT.
W.Green, G.Swanborough - The Complete Book of Fighters
Fokker Dr I
Журнал - Flight за 1918 г.
Fig. 1. - Plan and elevation of the body of the Fokker triplane to scale. Note the slot for accomodating the lower wing spar, and the drop in the top longerons for the fixed tail plane.
Журнал - Flight за 1918 г.
Fig. 2. - Sketch showing the bracing system employed in the body of the Fokker triplane. The wires only appear to be in duplicate. Inset shows tubular quadrant serving as an anchorage for all the bracing wires.
Журнал - Flight за 1918 г.
Fig. 3. - Sketch showing the three-ply fairings and their attachment on the Fokker triplane. The fork end brackets for the two machine guns should be noted.
Журнал - Flight за 1918 г.
Fig. 4. -The pilot's seat of the Fokker triplane. By means of the split collar and bolt arrangement shown in the inset, the seat may be quickly raised or lowered to suit the pilot.
Журнал - Flight за 1918 г.
Fig. 5. - The controls and some of their detail on the Fokker triplane. The insets show a typical clip and some of the purposes for which it is employed.
Журнал - Flight за 1918 г.
Fig. 6. - General arrangement of the engine mounting on the Fokker triplane.
Журнал - Flight за 1918 г.
Fig. 7. - Details of the engine mounting on the Fokker triplane.
Журнал - Flight за 1918 г.
Fig. 8. - The tail skid and its attachment on the Fokker triplane. On the right, details of the shock absorbing arrangement.
Журнал - Flight за 1918 г.
Fig. 9. - Sketch showing construction of casing around axle of Fokker triplane. On the right, details of the shock absorbers.
Журнал - Flight за 1918 г.
Fig. 10. - The tail planes of the Fokker triplane.
Журнал - Flight за 1918 г.
Fig. 11. - Some of the wing details of the Fokker triplane.
Журнал - Flight за 1918 г.
Fig. 12. - Details of the wing tip and its skid on the Fokker triplane.
Журнал - Flight за 1918 г.
Fig. 13. - Attachments of wing spars to body on the Fokker triplane. On the left is shown the attachment of the bottom plane, while the sketch on the right shows how the middle plane is secured to the top body rails.
Журнал - Flight за 1918 г.
Fig. 14 - The wing section, to scale, of the Fokker triplane. The web of the rib is made of very thin three-ply wood, and the flanges of spruce. The composite spar consists of four strips of spruce and of a box made of plywood.
Журнал - Flight за 1918 г.
Fig. 15. - A comparative sketch showing differences between the Fokker wing section and Dr. Schukowsky's aerofoil, described in "Properties of Aerofoils," by A. W. Judge. The Fokker section is shown in full lines. It will be noticed that only the trailing portion of the upper surfaces of the two sections coincide.
Jane's All The World Aircraft 1919 /Jane's/
General Sketches of the Fokker Triplane by M.Lagorgette.
O.Thetford, P.Gray - German Aircraft of the First World War /Putnam/
R.Kosin - The German Fighter since 1915 /Putnam/
W.Green, G.Swanborough - The Complete Book of Fighters
The Dr I, illustrated by the general arrangement drawing, enjoyed notoriety out of all proportion to its success in combat.
W.Green, G.Swanborough - The Complete Book of Fighters
Developed in parallel with the V 5, the V 6 had a larger wing span and area, and a water-cooled Mercedes D III engine.
Журнал - Flight за 1918 г.
В.Кондратьев - Самолеты первой мировой войны
Fokker Dr.I