Blackburn L.1 Bluebird

Запущенный в серийное производство в 1927 году, деревянный биплан L.1 Bluebird имел уникальное для английских легких двухместных самолетов размещение экипажа - бок о бок. Прототип L.1 был построен для участия в проводившихся Министерством авиации в 1924 году ДальшеMore>>> испытаниях легких самолетов в Лиме. Он был оснащен мотором воздушного охлаждения Blackburne Thrush с объемом цилиндров 1100 см3. Машину не успели закончить в срок, но в дальнейшем она получила новый двигатель Armstrong Siddeley Genet мощностью 60 л.с (45 кВт) и должна была участвовать в конкурсе, проводившемся в сентябре 1926 года. К сожалению, и на этот раз Bluebird остался в стороне из-за проблем с шасси. Полоса неудач закончилась несколько дней спустя, когда самолет выиграл гонки на кубок Гросвенор, показав скорость 137 км/ч. Машина успела выиграть еще одну гонку, прежде чем в июне 1927 года была потеряна в катастрофе - столкновении в воздухе.
   Первые 13 серийных самолетов, получивших обозначение L.1A Bluebird II, были оснащены моторами Genet II мощностью 80 л.с. (60 кВт) и поставлялись аэроклубам в Восточной Англии и Йоркшире. Один экземпляр, построенный по спецзаказу, был оснащен поплавковым шасси и получил широкую известность благодаря полетам вдоль побережья Англии. Два Bluebird II были проданы в Бразилию.
   Самолет L.1B Bluebird III появился в 1927 году. Первую машину этого типа переделали из 14-го серийного Bluebird II - полотно обшивки хвостовой части заменили на фанеру, а в центроплане верхнего крыла установили топливный бак. После демонстрационного турне по различным городам на самолет установили двигатель ADC Cirrus III мощностью 90 л. с. (67 кВт). Была заложена серия из шести Bluebird III с моторами Genet мощностью 60 л. с. (45 кВт), но последний самолет так и не был достроен.
   Последняя модификация, L.1С Bluebird IV, появившаяся в 1929 году, имела полностью переработанную конструкцию и лишь внешним видом напоминала предшественников. Из-за возросших требований к мощности силовой установки самолеты этого семейства оснащались различными типами двигателей. Загруженная военными заказами компания "Blackburn" первоначально смогла построить лишь три Bluebird IV. Выпуск 55 самолетов был поручен фирме "Saunders-Roe" с острова Уайт, но, фактически, последние 20 машин были достроены "Blackburn".
   У самолетов Bluebird IV была интересная судьба - многие из них участвовали в дальних перелетах, наиболее заметным из которых сал преподносившийся как первый в мире кругосветный перелет на легком самолете. Его совершила миссис Милдред Брюс в период с 25 сентября 1930 по 20 февраля 1931 года. Однако следует отметить, что участки маршрута Токио - Сиэтл и Нью-Йорк - Гавр путешественница преодолела на борту корабля. Последний сохранившийся Bluebird, 11-я серийная машина, пошел на слом в 1947 году.


ТАКТИКО-ТЕХНИЧЕСКИЕ ХАРАКТЕРИСТИКИ

   Blackburn L.1C Bluebird IV

   Тип: двухместный туристический самолет
   Силовая установка: один двигатель жидкостного охлаждения de Havilland Gipsy I мощностью 100 л. с. (75 кВт)
   Летные характеристики: максимальная скорость 166 км/ч у земли; крейсерская скорость 138 км/ч на оптимальной высоте; скороподъемность у земли 219 м/мин; дальность полета 756 км
   Масса: пустого 472 кг; максимальная взлетная 794 кг
   Размеры: размах крыла 9,14 м; длина 7,06 м; высота 2,74 м; площадь крыльев 25,08 м1

Flight, September 1924

THE BLACKBURN "BLUEBIRD" LIGHT BIPLANE (No. 12)
1,100 c.c. Blackburne Radial Engine

   In producing light 'plane two-seaters at the present time two courses are open to designers. One is to design for the Lympne competitions, i.e. solely with the object of gaining marks according to the formula used as a basis for judging, and the other is to attempt to anticipate the form which the cheap school machine of the future will take. Although there is no reason to believe that it will not do quite well in the competitions, the "Bluebird" biplane of the Blackburn Aeroplane and Motor Co., Ltd., of Leeds, belongs rather to the second class, inasmuch as its designers have not gone out of their way to produce a "mark collector," but have rather aimed at developing a type in which such features as are deemed desirable in a school machine are incorporated.
   One result of this is that the "Bluebird" is a side-by-side tractor biplane, it being presumably assumed that this type is more convenient for school work, while certainly as a private "run-about" the side-by-side arrangement would tend to be more sociable and conversation somewhat easier than in the tandem type. The side-by-side position necessarily means a relatively wide fuselage, with consequent increase in cross-sectional area and possibly slightly higher resistance. We say possibly because it has not by any means been definitely proved that a "fat" fuselage of good streamline shape is worse, from the resistance point of view, than one of small cross-sectional area, but having various excrescences that spoil its lines.
   In the case of the Blackburn "Bluebird," the fuselage is built in two separate sections, the front portion being ply-wood covered and having its corners rounded off, while the rear portion is the usual longerons and struts type with wire bracing.
   The cockpit, as already stated, has accommodation for two occupants sitting side by side, and a door on each side gives ready access to the "office." As prescribed for the competitions, dual controls are fitted, the rudder-operating foot-bar having a parallel movement, while the elevator and ailerons are worked by a single control column centrally placed. This column can be readily adapted to either "branch" control or to plain knob. The deck fairing runs through between the two halves of the cockpit, and there is a small separate windscreen ahead of each coaming.
   The main planes of the "Bluebird" are of orthodox construction, with spruce spars and ribs, the latter being of the Warren girder type and very light (5 ozs. each). The drag struts inside the wings are in the form of Duralumin tubes, and the drag bracing is 4 B.A. tie rods. The inter-plane struts are also in the form of Duralumin tubes, fitting into Duralumin sockets and taper pins.
   As will be seen, from the general arrangement drawings, the wings axe set at a fairly pronounced dihedral angle, and, what is more unusual, they are slightly swept back so as to give the correct trim for the particular placing of the pilots. Incidentally, it may be pointed out that with the side-by-side seating arrangement no change in trim takes place when the machine is being flown solo, and thus it is never necessary to carry any ballast. The wings are made to fold back, hinged ribs being fitted in the trailing edge adjacent to the hinges.
   The undercarriage is of simple V-type, and the fact that the fuselage is of considerable width has allowed of keeping the chassis V's vertical, as seen from in front. The shock-absorbing gear is in the form of telescopic tubes, with rubber blocks working in compression, and recoil dampers are incorporated.
   All control surfaces are of large area, and it is expected that the machine will be very manoeuvrable, even when close to the stalling angle, a very necessary precaution in view of the low-speed tests which have to be flown close to the ground.
   The three-cylinder Blackburne radial engine is mounted on triangulating tub.es meeting on dead centres, and there is a fireproof bulkhead between the engine and the cockpit. The petrol tank is mounted in the top plane centre section, and for the purpose of the competitions is fairly small and takes the contour of the wing section. For use later on, should a larger petrol capacity be required, a larger tank can easily be fitted. It might be mentioned that the machine has been "stressed" for a more powerful engine, and should, as seems likely, a 1,500 c.c. engine be required later, the only change necessary is the substitution of larger cylinders and pistons, the Blackburne crank-case and crankshaft having been designed for the larger capacity.

Flight, September 1926

British Light ‘Plane Development & Lympne Meeting

THE 1926 MACHINES

No. 1. The Blackburn "Bluebird" (Armstrong-Siddeley "Genet")

   The Blackburn "Bluebird" is the original side-by-side biplane designed for the 1924 Lympne meeting, for which it was finished too late to take part, modified and strengthened up to take the Armstrong-Siddeley "Genet" engine. The mounting of the engine is, of course, new, but is of the same type as that used for the original Blackburne engine in the 1924 machine. Of other alterations mention may be made of a slight modification of the cockpits. Originally these were side by side, but they are now slightly staggered in order to give the seat width called for in the competition.
   The wide fuselage is of mixed construction, that is to say the forward portion, from aft of the cockpits to the nose, is of partly tubular construction, while the rear portion is a normal box girder with four wood longerons and wire bracing. The covering of this portion is of fabric, while in front the covering is in the form of three-ply wood. The two portions of the fuselage can be readily detached from one another.
   The biplane wings are of normal construction as regards their main spars and ribs, which are of wood, but the drag struts inside the wings are duralumin tubes, with steel wire drag bracing, while the inter-plane struts are also of duralumin. The wing section used is that known as T.64.
   The undercarriage is of the simple V-type, with the front "legs" telescopic and containing rubber rings working in compression.
   The Armstrong-Siddeley "Genet" engine is bolted to the fireproof bulkhead which closes the fuselage proper in front, and the petrol tank is mounted in the top centre-section so as to obtain direct gravity feed. The tank itself is of aluminium throughout, with welded joints, a form of construction giving very light weight. The oil tank is placed just ahead of the fireproof bulkhead. The Blackburn "Bluebird" has an estimated top speed of 85 m.p.h., a cruising speed of 70 m.p.h., and a landing speed of 32 m.p.h.

Flight, December 1927

BLACKBURN "BLUEBIRD" Mk. II
New Model

   THIS two-seater light aeroplane has been modified and is now produced as an improved model. The position of the engine has been lowered, and this has given the top and bottom curves of the nose a more symmetrical shape. There is now an increased gap between the wings, and part of the top centre 'plane has been cut away at the trailing edge, which greatly improves the view. The chassis track is wider and it gives the machine a better ground stability when taxying.
   In the cockpit, a central bridge member which used to interfere between the heads of the pilot and passenger is removed, and the side structure is considerably lowered, thereby allowing deeper side doors. The general result in this respect is a much more roomy cockpit. Certain detail modifications have been made in the wing structure, which now has heavier spars. Two control columns are fitted, the rudder bars simplified, whilst the engine controls, which were formerly operated by levers on a shaft across the top of the cockpit, are set on a central quadrant low down between the pilot and passenger.
   This means flying with the left hand from the port cockpit if a pilot wishes to keep one hand on the engine controls. There are additions to the equipment, including a fire-extinguisher and a number of tools. The "Genet" 65 h.p. engine is mounted on a sheet-duralumin box frame and is very accessible. A priming pump has been installed in the cockpit and, in co-operation with an efficient magneto impulse starter, it makes starting up an easy task. A handle starter is also fitted to the engine for the seaplane type of "Bluebird."
   Land chassis and seaplane chassis are interchangeable, the attachments being made at the same joints on the fuselage. The floats are of the pontoon type and constructed of duralumin, supported by a rigid structure of steel tubes.
   The following are some performance figures relating to the sea and land types :-
   Land 'Plane :- 88 m.p.h. top speed at ground level; 75 m.p.h. cruising speed; 35 m.p.h. landing speed; endurance at cruising speed, 4 hours; service ceiling, 9,000 ft.; absolute ceiling, 11,300 ft.; take-off time against 5 m.p.h. wind, 10 secs.; rate of climb from ground level, 400 ft. per minute.
   Seaplane :- 84 m.p.h. top speed at sea level; 82 m.p.h. top speed at 5,000 ft.; 330 ft. per minute climb from sea level; 38 m.p.h. landing speed; take-off time against a 5 m.p.h. wind, 25 secs.; range in calm at cruising speed (70 m.p.h.), 280 miles; service ceiling, 7,500 ft.; absolute ceiling, 9,300 ft.
   The Mark II model was flown in the King's Cup Race and Grosvenor Cup Race this year, and certain improvements then followed to the oil system, controls, tail-setting, and propeller. After this it emerged on to the market again, and the first customer was the Suffolk Aeroplane Club, followed by the Yorkshire Aeroplane Club, who ordered three machines.
   Mr. Charles Blackburn, commercial manager of the Blackburn Aeroplane Co., left Brough Aerodrome, Yorkshire, on November 23, in a Mark II "Bluebird" (Genet engine) to make an aerial tour. The following places are being visited by him in the order given: Hadleigh Aerodrome, Suffolk; Martlesham; Lympne; Tunbridge Wells; Hamble; Stag Lane; Croydon; Sherburn; Middlesbrough; Renfrew; Newcastle; Manchester; Liverpool; Bristol; Castle Bromwich; Coventry; Norwich; C.F.S. Wittering; Nottingham, and Brough. Any communications from people interested in this tour should be sent to Mr. Charles Blackburn's Monomark BM/BRBF, W.C.I.

Flight, October 1928

British Exhibits At The Berlin Aero Show 1928

THE MACHINES

THE BLACKBURN AEROPLANE CO., LTD.

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   The Blackburn "Bluebird III" is a modified version of the Mark II. It has the petrol tank in the top centre plane, whereas the tank in Mark II was installed inside the fuselage behind the dashboard. A larger oil tank having a capacity of 5 gallons (4 gallons of oil and 1 gallon air space) is also fitted. Further, the ailerons have been shortened to give lighter control. The wings are of normal spruce spar and built up rib construction with internal bracing of spruce drag struts and steel tie rods. External bracing consists of streamline wires. The design of the folding joints ensures that no undue stress is put upon the wings or joints when folding. Steel tubes only and streamline wires are used in stressed portions of the centre structure. The fuselage is composed of two units, which are complete in themselves and detachable from each other for repair or replacement. The engine mounting, consisting of duralumin plate box structure, is secured by four bolts to the cockpit structure and separated from the cockpit by a fireproof bulkhead. There is a normal tail plane with elevators of large area hinged at the rear spar. A special feature of the control surfaces is that the same hinge fitting is used for ailerons, elevators, and rudder. The wings can be folded in 4 mins. by one person.
   The aileron and elevator controls are operated by two side-by-side control levers, either of which may be detached when dual control is not required. Two side-by-side rudder bars control the rudder, and a central control lever and quadrant, easily operated from either seat, controls the engine throttle. The run of the control cables to the control surfaces is arranged as simply and accessibly as possible. Aileron cables run from a central lever behind and below the cockpit seat to the bottom planes, the cables passing over the hinge centres in order to ensure satisfactory folding. The two ailerons on each side are interconnected by rigid struts and the compensating cables return through the bottom planes along the same run as the operating cables. Rudder cables run externally direct from lugs on the outer extremities of the rudder bars to the rudder, and the elevator cables also run externally from levers at the ends of the control stick shaft to the elevator king levers.
   Petrol feed is by gravity. There are side doors to the cockpit where pilot and passenger are seated side-by-side. The machine is fully equipped for service with the following: air speed indicator; altimeter; cross level; revolution indicator; oil pressure gauge; switches (dull ignition); petrol priming system; petrol contents gauge; fire extinguisher; tyre pump; pliers; screwdriver; movable spanner and engine tools (supplied by engine makers).
   The all up weight of the land 'plane type is 1,455 lb.; wing loading 6-1 lb./sq. ft.; h.p. loading 21-3 lb./h.p.; top speed at ground level 88 m.p.h.; cruising speed 75 m.p.h.; landing speed 35 m.p.h.; endurance at cruising speed 4 hrs.; service ceiling 11,300 ft.; take-off (5 m.p.h. wind) 10 secs.; rate of climb from ground level 400 ft./min. The engine is the Armstrong-Siddeley "Genet" 65 h.p. air-cooled radial.
   Wing span is 28 ft., gap 5 ft. 3 ins., chord 4 ft 9 in. Folded width 9 ft. 10 in. Overall length 26 ft. 7in.
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Flight, January 1929

THE BLACKBURN "BLUEBIRD" MARK IV
D.H. "Gipsy," A.D.C "Cirrus III," or Armstrong-Siddeley "Genet"

   OF all-metal construction, with side-by-side, or "sociable," seating arrangement, and with a choice of three power plants, the new "Bluebird," Mark IV, which is now nearing completion at the Brough works of the Blackburn Aeroplane and Motor Company, Ltd., should have a very wide appeal, the more so as the machine has retained the feature of the earlier models - interchangeable land and float undercarriages. At one time it was rather thought that the side-by-side arrangement of the two occupants would result in a loss of performance. Model tests in a wind tunnel have, however, indicated that this is not necessarily the case, and although the production type of "Bluebird," the Mark IV, has not yet been flight tested, there is every reason to expect that the top speed will be well over 100 m.p.h. More than that we need not say here. The actual performance figures will become available before long, and will then speak for themselves.
   In designing the all-metal "Bluebird," the general lines of earlier models have been retained, but a number of changes and improvements have been made, and the "lines" of the somewhat wide fuselage are extremely pleasing, and much better than one would have imagined possible with a side-by-side seating arrangement. The cockpit is by no means cramped, so that the good form has not been obtained by any sacrifice in this direction. For elementary school work it should be a considerable advantage to have the pupil placed next to the instructor, where conversation can be carried out comfortably, and where, moreover, the pupil can watch as well as feel the movements which the instructor makes with the various controls. For touring there can be little doubt that the "sociable" seating arrangement has many advantages, and as a sort of "conservatory roof" is to be an optional fitting on the production machine, those who prefer the shelter of a coupe will be able to fly in comfort in almost any kind of weather.
   Of the aerodynamic design little need be said, as this follows in the main the earlier wooden machines. Attention has already been drawn to the fact that by making use of the wind tunnel, and experimenting with different "noses," it has been possible to reduce the drag of the machine to quite a low figure. The biplane wings are of normal design, but in the tail an innovation has been made in that there is no vertical fin surface. The rudder has a large balance, and is of large area, giving powerful directional control, even at large angles of incidence. If desired, the "Bluebird" can be fitted with Handley Page automatic wing-tip slots on the upper wing. Ailerons (of the Bristol-Frise type) are fitted to the lower wing only.
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Brief Specification

   The main dimensions of the "Bluebird" Mark IV, are given on the general arrangement drawings on page 41. These drawings show the machine with de Havilland "Gipsy" or A.D.C. "Cirrus III" engine. When the Armstrong-Siddeley "Genet" is fitted, the wings are given a slight sweepback. Actual performance figures are not yet available, but the calculated top speed is well over 100 m.p.h.
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   In the case of the "Genet" engine, this load is increased by 5 lb., representing that amount of extra oil. The maximum permissible flying weight is 1,550 lb (703 kg.)

Flight, June 1929

BRITISH AIRCRAFT AT OLYMPIA

BLACKBURN AEROPLANE & MOTOR CO., LTD.

   IN addition to the machines exhibited on their own stand, the Blackburn Aeroplane and Motor Co. will have on view two "Bluebirds." These, however, will be exhibited on the stand of Auto Auctions, Ltd., who have been appointed sole world concessionnaires for this type of light 'plane. The descriptions of the "Bluebirds" will, however, be found at the end of the notes dealing with the aircraft shown on the Blackburn stand, and readers are reminded that prospective purchasers should apply to Auto Auctions, Ltd., for more detailed information than can be given in the limited space we have available.
   On the Blackburn stand itself four complete machines will be exhibited, or rather three complete machines and one large flying-boat hull, for the wings of which there is not sufficient room at Olympia. The four machines are: The hull of the "Nile" commercial flying-boat, a "Ripon II" torpedo, bomber or reconnaissance biplane, the "Lincock" light single-seater fighter, and the "Nautilus" reconnaissance deck-landing fighter.
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   As mentioned above, two Blackburn "Bluebirds" Mark IV, will be exhibited on the stand of Auto-Auctions, Ltd. One of these will be a new machine fitted with "Cirrus III" engine, while the other will be the first all-metal "Bluebird" ever built, the actual machine on which Squadron-Leader Slatter flew from England to South Africa on a holiday during March and April of this year. Thus visitors to Olympia will have an excellent opportunity to inspect a machine that has already covered many thousands of miles, and to see for themselves how it has stood up to the work. Squadron-Leader Slatter's machine is fitted with a De Havilland "Gipsy" engine. The "Bluebird" can also be supplied as a seaplane, and on the stand of Auto-Auctions, Ltd., there will be on view an undercarriage of the two-float type, the floats being of duralumin. This float undercarriage will be the actual one used by Col. the Master of Sempill on a large number of flights in the period from August last year until quite recently, when the undercarriage was returned to the Blackburn works for reconditioning.
   Except for the difference in power plants, the two "Bluebird IV" machines exhibited will be almost identical, and the following notes may, therefore, except where otherwise stated, be assumed to apply to both machines.
   The "Bluebird IV" is designed for use by flying clubs, private owners and flying schools. A unique feature of its design is that the two occupants are seated side by side, and not in tandem as is the case in other light 'planes. As already mentioned, it can be supplied either as a land machine or as a seaplane, the two undercarriages being interchangeable. Handley Page automatic wing tip slots and a coupe head can be supplied at extra cost. One of the "Bluebirds" exhibited will have the "Cirrus III" engine and the other the De Havilland "Gipsy," but power plants such as the "Hermes" and the Armstrong-Siddeley "Genet" are also suitable.
   The fuselage is of all-metal construction, steel being the material most extensively used. It consists of four detachable units: engine mounting, centre and cockpit section, rear fuselage, and stern unit. For the "in-line" types of engine, the engine mounting is of steel tubular construction, but for the "Genet" a duralumin plate is used. The centre and cockpit structure has steel tube longerons and duralumin transverse frames. The rear fuselage portion has struts and longerons of steel tube, while the sternpost unit is of similar construction, with a steel tubular sternpost. Joints between struts and longerons are made by steel plate fittings, and tubular rivets through longerons and struts. The whole structure is about the nearest approach to "Meccano” construction which has yet been evolved, and should be remarkably serviceable in spite of its simplicity and cheapness.
   The cockpit has, as already stated, side-by-side seating arrangement, and dual controls are fitted, one set of which is easily detachable if the machine is wanted for passenger-carrying. The seats may be tipped up, or easily removed altogether, to give access to the controls, and the floor of the cockpit has detachable floor boards which can also be easily removed. The instruments are neatly arranged on a small dashboard, with a pigeon hole on each side for small personal articles such as gloves, goggles, etc. A luggage compartment capable of holding two average size suitcases is provided behind the cockpit, with access through a side door. Another compartment for long articles such as golf clubs, guns, fishing rods, etc., is let into the top of the fuselage behind the cockpit. Side doors give easy access to the cockpit itself.
   The biplane wings are also of all-metal construction, with very simple drawn section spars of high-tensile steel strip. Ailerons are fitted to the bottom planes only. The top centre-section is formed by a tank of aerofoil section, and this tank is easily removed when the wings are folded. The standard tank has a capacity of 22 gallons, but a 30-gallon tank can be fitted if desired.
   An undercarriage of the divided type is fitted, each half being composed of a bent axle, a radius rod and the telescopic leg. The latter incorporates a metal springing device and an oil dashpot.
   Main dimensions of the "Bluebird IV" are: Length, o.a., 23 ft. 2 in.; wing span, 30 ft.; width, folded, 9 ft. 10 in.; chord, 4 ft. 6 in.; wing area, 270 sq. ft. The normal gross weight is 1,496 lbs., and the total load carried 536 lbs.
   As a land machine with "Cirrus III" engine the "Bluebird IV" has the following performance :- Full speed, 107 m.p.h.; cruising speed, 82 m.p.h.; landing speed, 45 m.p.h.; climb from ground level, 780 ft./mins.; service ceiling, 15,000 ft.; normal range, 330 miles.

Flight, April 1930

AIRCRAFT FOR THE PRIVATE OWNER

BLUEBIRD

   THOUGH designed by the Blackburn Aeroplane Co., of Brough, the Bluebird is built by Sanders-Roe, Ltd., of Cowes, and is marketed by Auto-Auctions, Ltd., of Burlington Gardens, London, W.I.
   This position is unlike any other at present in the industry, and it came about because the Blackburn Co. realised that with their extensive contracts for machines for the Air Ministry they could not hope to organise their factory economically to produce commercial machines in large quantities, therefore, instead of attempting to make any compromise they delegated all the orders for Bluebirds which they might receive to Saunders-Roe to deal with at their newly-arranged factory at Cowes. As for the selling side Auto-Auctions, who have a very strong position in the motorcar world, saw that the sales side of aircraft was bound to develop on the same lines as that of motor-cars, where the large agent controls large areas as regards the sales, and thus leave the manufacturer free to devote himself entirely to manufacturing and, moreover, enabling him to stabilise prices by receiving larger contracts from the agents. They therefore, secured the sole selling agency for the Bluebird, and Sqd.-Ldr. Ridley, a director of the firm, handles this side of their business. Sqd.-Ldr. Ridley has a very distinguished war record in the R.A.F., and therefore knows what he is about when it comes to aeroplanes.
   The Bluebird has, as is now well known, one cockpit with the seats arranged side by side. This arrangement is one that is becoming very popular, and certainly for the private owner there can be little doubt that the majority would prefer having their passenger alongside them, so that they can talk in a normal voice instead of having to have earphones and be completely cut off from the other cockpit.
   Constructionally the Bluebird is very modern and is made of metal throughout. The covering is fabric, but the structure is chiefly composed of steel. This is one of the few machines in which the wings are also built of steel, the spars being drawn sections of high tensile steel strip.