Boulton & Paul Р.29 Sidestrand

Опыт, полученный в ходе разработки двухмоторных бомбардировщиков Р.5, Р.15 и Р.25, фирма "Boulton & Paul" воплотила в самолете Р.29 Sidestrand, спроектированном согласно спецификации 9/24 к среднему дневному бомбардировщику с экипажем из трех - четырех человек. ДальшеMore>>> Первый из двух прототипов Sidestrand Mk I поднялся в воздух в 1926 году. Поскольку машина являлась развитием ранее построенных и испытанных самолетов, фирма сразу получила заказ на 18 серийных бомбардировщиков.
   Серийные машины начали поступать в 101-ю эскадрилью британских ВВС в 1928 году. Первую партию из шести самолетов собрали в варианте Sidestrand Mk II с моторами Bristol Jupiter VI мощностью по 425 л. с. с непосредственным приводом на винты, как на первых двух прототипах. За первой серией последовала вторая из девяти машин с моторами Bristol Jupiter VIIIF, оснащенными понижающими редукторами. Эти самолеты обозначались Sidestrand Mk III. Три последних выпущенных бомбардировщика изготовили в варианте Sidestrand Mk II.
   Sidestrand поступил на вооружение только в 101-ю эскадрилью. Три экземпляра Sidestrand Mk III доработали в вариант Sidestrand Mk V(Overstrand). В декабре 1934 года начался процесс замены самолетов Sidestrand более совершенными бомбардировщиками.


ТАКТИКО-ТЕХНИЧЕСКИЕ ХАРАКТЕРИСТИКИ

   Boulton & Paul Р.29 Sidestrand Mk III

   Тип: средний бомбардировщик с экипажем из трех - четырех человек
   Силовая установка: два звездообразных мотора Bristol Jupiter VIIIF мощностью no 460 л. с.
   Летные характеристики: макс, скорость на высоте 3050 м - 225 км/ч; время набора высоты 4570 м - 19 мин; практический потолок 7300 м; дальность 800 км
   Масса: пустого 2726 кг; максимальная взлетная 4627 кг
   Размеры: размах крыла 21,92 м; длина 12,40 м (увеличена до 14,02 м после установки сервокомпенсатора руля направления); высота 4,52 м; площадь крыльев 91,04 м2
   Вооружение: по одному 7,7-мм пулемету Lewis на носовой, над- и подфюзеляжной турелях, до 476 кг бомб на внутренней подвеске в фюзеляже и снаружи под центропланом нижнего крыла

Flight, September 1927

THE BOULTON & PAUL "SIDESTRAND”
Two Bristol "Jupiter" Engines

   AMONG the new types of machines which took part in the "Parade" at the last Royal Air Force Pageant at Hendon was the Boulton & Paul "Sidestrand," a day-bomber fitted with two Bristol "Jupiter" engines. This machine, like all Boulton & Paul productions of recent years, is of all-metal construction, and retains the typical features of the long list of Boulton & Paul twin-engined machines which commenced with the "Bourges." Needless to say, however, the "Sidestrand" incorporates a number of new features, chief among which is, perhaps, the good aerodynamic form of the fuselage and engine nacelles, or rather the good combined forms of the two, "interference effect" having very successfully been reduced in this machine. It is becoming increasingly clear that the combined drag of two bodies placed close together is likely to be different from, and usually larger than, the sum of the two drags obtained separately. By systematic research, in their wind tunnel and full scale, Boulton & Paul have succeeded in evolving a combination of fuselage and engine nacelles, the drag of which is very low, and the effect is noticeable in the performance of the machine, particularly on take-off, climb and ceiling.
   Unfortunately, although a number of "Sidestrands" are being built for the Air Ministry, it is not permissible to publish performance figures, nor a number of other details which would have been found of considerable interest. Permission has, however, been obtained to give the following characteristics of the machine:
   Engines, two Bristol "Jupiters" Series VI; wing span, 72 ft. (21-95 m.); wing chord, 7 ft. (2-135 m.); wing area, 965 sq. ft. (82 sq. m.); length overall, 41 ft. (12-5 m.); height, 14 ft. 10 in. (4-54 m.). Weight empty, 5,275 lb. (2.400 kg.); weight loaded, 8,850 lb. (4,020 kg.) wing loading, 9-17 lb/sq. ft. (45 kg./sq. m.). Power loading, on 1,000 h.p., 8-85 lb. per h.p. (4-02 kg./h.p.).

Flight, March 1928

THE BOULTON & PAUL "SIDESTRAND I"
2 Bristol "Jupiter VI" Engines

   IN attempting to convey to readers of FLIGHT an adequate idea of the new Boulton & Paul twin-engined bomber which has recently gone into production for the Royal Air Force squadrons, two ways are open: One might concentrate on the merits of the machine (and they are many) for the particular purpose for which it was designed, or one may approach the subject along more general lines, examining the machine as an aircraft pure and simple, with but minor regard to its particular function as a military weapon. In the former case one would merely be describing a machine which is a very excellent bomber, while by taking the alternative approach the merits of it as a piece of aeronautical engineering can be examined. On the whole, we believe that the majority of our readers are likely to be more interested in the general aerodynamic and structural features, and as there are certain restrictions which prevent a full discussion of the military equipment, the following notes will be devoted to the general design of the "Sidestrand," bearing in mind that the machine has been designed as a three-seater day bomber, and that therefore certain specified loads had to be carried, loads consisting partly of equipment, partly of machine gun armament, and partly of bombs. What percentage of each is involved we are not in a position to state.

Aerodynamic Design

   Those of our readers who have followed his interesting series of articles on "Aircraft Performance" in our monthly technical Supplement THE AIRCRAFT ENGINEER will have obtained a fairly good idea of the general design policy of Mr. J. D. North, Boulton & Paul's Chief Engineer and Designer, and in examining the "Sidestrand" one looks for such features as Mr. North has advocated in his articles. Among these perhaps none was more prominent than the reduction of induced drag by having a high value of the ratio of Span2/weight, and a glance at the general arrangement drawings and some of the photographs will show that the "Sidestrand" has a very large span for its area, or, as we used to say before modern aerofoil theory became the fashion, high "aspect ratio." While Mr. North drew attention to the importance of large span, he also pointed out that for large machines it is difficult to obtain a high value of the span2/wt. ratio because of the increased wing weight which quickly puts a limit to the span which it is economic to employ. In the "Sidestrand," therefore, one may take it that an endeavour has been made to get the best compromise between wing structure weight and aerodynamic efficiency, and it will be of interest to examine briefly how far the wing arrangement of the "Sidestrand" may be expected to have reduced that part of the wing drag which is due, as Mr. C. C. Walker puts it to "carrying a certain weight on a certain span at a certain speed."
   The total loaded weight of the "Sidestrand" is 8,850 lb., and the span is 72 ft. The value of Span2/W is therefore 0-518 and the monoplane value of the ratio of lift to induced drag is, at 70 m.p.h. for instance, 20-31. As the gap/span ratio of the "Sidestrand" is about 0-14, this value is increased to 25-9 for the biplane arrangement used. Thus at 70 m.p.h. the induced drag is only 342 lb., which is remarkably low and corresponds to a thrust horse-power of 64 b.h.p. only for overcoming induced drag at that speed. Since at this low speed (corresponding probably fairly well with the climbing speed of the machine) the induced drag is a large percentage of the total wing drag, it is seen that the "high aspect ratio" wing arrangement does appear to have proved extremely beneficent. The span2/weight value of 0-518 is quite high for a machine of this weight, and in a number of machines this ratio only reaches a value of 0-3 or so. We believe that actually in the "Sidestrand" the extra wing weight which was the "price paid" for the higher value of Span2/W amounted to some 200 lb., but at that it paid to carry the extra weight.
   While on the subject of wing design, a few words concerning the method used by Mr. North and his staff in the choice of wing section may be of interest. The method was outlined by Mr. North in his series of articles to which reference has already been made, and consists in starting off with a consideration of the operational conditions to be met, and then, taking as a basis a good streamline shape, curving its centre line to give the required aerodynamic characteristics, the original streamline section being chosen of such a thickness that it will accommodate spars of sufficient depth. Thus, in any Boulton & Paul machine one is not likely to find any stereotyped wing section, although some of those in use may, more or less accidentally, have a fairly close resemblance to certain "accepted" sections. Incidentally, the original streamline shape taken as the basis is generated by the generalised Schoukowsky theory.
   The wing cellule having been carefully designed to meet the particular operational conditions of the type in question, great care is again taken in the design of fuselage and engine nacelles. In the case of the "Sidestrand," for instance, a start was made with a body of very good streamline shape, generated as in the case of the wing sections, a model of which was tested in the wind tunnel. The cockpits were then added one by one, the drag being measured after each such addition. If a certain cockpit shape or arrangement was found to add unduly to the drag, modifications were made until the figure had been reduced to what appeared to be the lowest practicable value. Take for example the prone gun position under the fuselage. Obviously this might easily increase the body drag to a very high figure, but by persistent experimentation the drag caused by this gun emplacement was ultimately reduced to a very low value indeed.
   The engine nacelles were the subject of similar research and the form finally chosen, which is well shown in several of our photographs, has given about as low a drag as it is possible to attain with engines placed outboard. The research included wind tunnel tests with model airscrews running, and at large angles, it having been found that the "interference drag" is largely an induced drag and liable to be greater at large angles, thus affecting performance on climb, etc.
   Undercarriage design, although perhaps more of a structural than an aerodynamic problem, also shows this striving for aerodynamic "cleanness," the undercarriage of the "Sidestrand" being of remarkably low frontal area for a machine of this size.
   Altogether the Boulton and Paul "Sidestrand" is a machine which well repays a close study, the results of the very great care taken in its aerodynamic design being reflected in the performance figures which will be found at the end of this article.
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Specification

   The main dimensions of the "Sidestrand I" are shown on the general arrangement drawings. The weight of the machine light, is 5,275 lb. (2,400 kg.), and the load carried is 3,575 lb. (1,625 kg.), giving a total loaded weight of 8,850 lb. (4,025 kg.). The wing loading is 9-37 lb./sq. ft. (45-9 kg./m2). Power loading (on normal power of 450 b.h.p. per engine) 9-84 lbs./h.p. (4-47 kgs./h.p.). "Wing Power" = 0-95 h.p./sq. ft. (10-25 h.p./m2).

Performance

   Speed at ground level, 125 m.p.h. (201 kms,/hour).
   Speed at 5,000 ft. (1,525 m), 130 m.p.h. (209 kms./hour).
   Speed at 10,000 ft. (3,050 m.), 129 m.p.h. (207-7 kms./hour).
   Speed at 15,000 ft. (4,570 m.), 122 m.p.h. (196-5 kms./hour).
   Landing speed (engine off), 51 m.p.h. (82 kms./hour).
   Landing Speed (engine on), 47 m.p.h. (76 kms./hour).
   Climb to 10,000 ft. in 10-5 mins.
   Climb to 15,000 ft. in 19 mins.
   Service ceiling, 21,500 ft. (6,560 m.).
   Absolute ceiling, 23,000 ft. (7,000 m.).
   Full-throttle range at operational height, 750 miles (1,200 kms.). The actual range at economic speeds is, of course, considerably higher.

Evening Quantities

   High-speed figure 16
   Distance figure 3-5.
   Altitude figure 6-25.
   These values are unusually high for a twin-engined biplane, and appear to bear out the claims for high aerodynamic efficiency. For instance, if a propeller efficiency of 75 per cent, is assumed at top speed, the "absolute" drag coefficient of the whole machine at top speed works out at 0-023 a value well above the average for a machine of this type.

Flight, July 1928

THE BOULTON & PAUL "SIDESTRAND”
Two Bristol "Jupiter" Engines

   THE "Sidestrand" designed by Boulton and Paul, Ltd., of Norwich, is an all-metal three-seater, high-performance bomber, powered by two Bristol "Jupiter VI" radial air-cooled engines. In addition to the bomb load, the "Sidestrand" carries machine guns in the forward gun turret in the nose, and on the aft turret behind the wings. A prone gun position is also provided for the rear gunner.
   Fuselage. - Of tubular construction, the tubes being of the "locked-joint" type, manufactured from flat steel strip. The joints between longerons and struts are effected by bolting, magnesium alloy "pads" with flat faces on their outer sides being slipped over longerons and strut ends. The bracing is by tie rods. The fuselage is of good streamline shape and has very low air resistance.
   Wings. - Arranged in the form of an equal-span biplane, the wings are of all-metal construction, steel being the material chiefly used. The wing spars are built up from flat steel strip, rolled and drawn to the desired section, the strips of which the spar is composed being joined by riveting. The wing ribs have channel section flanges and girder webs formed of short lengths of tube. The wing covering is fabric. Ailerons with Frise balances are fitted to both top and bottom wings.
   Tail. - Like the wings, the tail is of all-metal construction as regards its structure, and the covering is fabric. Horn balances are provided for rudder as well as elevator.
   Engine Installation. - The two "Jupiter VI" engines are mounted outboard on the lower wing, on steel tube structures designed to avoid placing torque-reaction stresses on the wing spars. The mountings are of the hinged type, which permit of swinging the engine out for inspection and adjustments. There are three petrol tanks, placed in the fuselage, comprising a front main tank, an aft main tank, and a service tank.
   Undercarriage. - Of simple two-wheeled type, with oleo-pneumatic telescopic legs of long stroke, giving excellent shock-absorbing qualities. The wheel axles are of the bent type, hinged to the lower longerons of the fuselage. Thus there is no obstruction below in the way of dropping bombs, etc.

Flight, June 1929

BRITISH AIRCRAFT AT OLYMPIA

BOULTON & PAUL, LTD.

   IT is not entirely certain who first thought of exhibiting an aircraft with its fabric stripped off on one side, up to the centre line, the machine being covered from the centre line to the wing tips on the opposite side. During the war a number of captured German aircraft were on view at the Agricultural Hall, Islington, and Sergeant Turner, who was in charge of the work of erecting the German machines for exhibition purposes, had the idea of stripping one side, leaving the other covered. The effect was extraordinarily good, as one was able to examine every constructional detail on one side of the machine while, by walking over to the other side, one saw the machine as it appeared when completely covered. It may be that this form of showing had been done previously. Personally we do not remember, but it would be difficult to imagine a better way of exhibiting an aircraft, provided the exhibitor really wishes all the details to be seen.
   On the Boulton & Paul stand visitors to Olympia will have an opportunity to see the latest type of "Sidestrand" so exposed, and as this machine is extremely interesting in all three main respects : Structural design, aerodynamic design, and internal equipment, the Boulton & Paul stand will be well worth visiting.
   It has usually been taken for granted that an aircraft with engines on the wings must of necessity be less efficient, aerodynamically, than one in which the entire power plant is housed in the fuselage. In other words, that of two machines, one a single-engined and the other a multi-engined, having the same wing loading and the same power loading, the single-engined type will always have the better performance. The difference cannot be entirely accounted for in the usual performance estimates, in which one adds the drag of individual components, and the extra drag of the multi-engine type is usually put down to "interference" between adjacent components. As a result of numerous wind tunnel and full-scale experiments, Boulton & Paul have been able to produce a series of twin-engined machines in which this interference effect has gradually been lessened, until in the "Sidestrand III" which will be exhibited, the performance is about equal to that which would be expected from a single-engined machine with the same power loading and wing loading.
   The "Sidestrand" is a three-seater medium-range day bomber fitted with two Bristol "Jupiter" engines, which carries fuel for a range of 700 miles at 130 m.p.h., and a military load which includes 500 lbs. of bombs, three defensive gun positions - which between them leave no "blind spots" - ammunition, sending and receiving wireless, oxygen apparatus, parachutes, etc., etc. The machine is an equal-winged biplane, slightly staggered, and with a small sweepback to the sections of the wings outside the engines.
   The upper wing is built in three, the lower in four sections. The two lower centre sections are attached to the lower longerons of the fuselage, and carry at their outer ends the engine mounts. Below the engines are attached the undercarriage legs, and extending above the engine mounts are struts to support the upper centre section. Outside the engines the outer sections of the wings are connected by two pair of interplane struts on each side, together with the usual streamline wire bracing. "Frise" type ailerons are titled to both top and bottom wings.
   The fuselage is built on a rectangular framing and provided with domed top and bottom fairings. It is of a form developed by experiment to give a remarkably low resistance. The body is very narrow in comparison with its depth, a fact which allows an excellent view downward over both sides to all members of the crew, and at the same time gives ample room for the stowage of the very complete military equipment carried. It is specially to be noted that the main bomb load in this machine is carried within the lines of the lower fuselage fairing, an arrangement which markedly reduces the resistance of the loaded machine.
   In the extreme nose of the fuselage is a forward gun position with Scarff ring and Lewis gun. Below this is a prone bombing position. Just aft of this gun position is the pilot's seat, and immediately behind is a second open cockpit below, where the wireless gear is arranged. A walk way beneath the pilot's seat gives access from the nose gun and bombing position to this cockpit.
   The extreme nose of this fuselage is a separate monocoque structure, hinged to the fuselage frame, which can be opened. This gives access to the interior equipment, much of which is arranged on panels which can be withdrawn for overhaul and readjustment with remarkable ease.
   Aft of the wings is a tail gun position, comprising a Scarff ring mount and Lewis gun at the top of the fuselage, with a prone gunning position below it from which a clear field of fire below the tail is obtained. Forward of this rear position stowage and mountings for a camera are provided. The main fuel tanks are carried in the fuselage below the upper centre section.
   The two engines are carried, one on each side, in streamlined nacelles built on to the lower centre sections of the wings. Each engine mount proper is carried on a frame or "gate" hinged to the nacelle structure in such a way that the whole engine may be swung round to give access to the auxiliaries at the rear without the need for disconnecting any fuel, oil or control connections. The pins on which these gates swing are hardened and ground taper to fit accurately into the hinge blocks, and as a result opening and closing of these gates is never attended with any difficulties caused by drooping of the gate on its hinges. Oil tanks are arranged in the nacelles behind the engines, and the whole assemblage is faired by easily removable but substantial cowling.
   The undercarriage - of very wide track - consists of a pair of "Vees" below each engine nacelle, each supporting an axle hinged to the lower edge of the fuselage below the front spar attachment. The front leg of each pair of Vees is telescopic, and incorporates compressed air springing together with an oil damping system. This type of undercarriage leg is covered by Boulton and Paul patents, and has proved to be exceedingly satisfactory in service.
   The tail unit is of normal monoplane type, fitted with adjustment gear for the tail plane, elevators having the Boulton and Paul type of "shielded horn" balance, and a rudder which is both horn-balanced and fitted with a servo-control. This consists of a small auxiliary rudder carried behind the main rudder on outriggers. This auxiliary is operated from the pilot's rudder bar by crossed wires, so that it is moved in the opposite sense to that in which it is desired that the main rudder should move. The resulting air force on the auxiliary rudder then tends to force the main rudder in the desired direction, and thus relieves the pilot of a large proportion of the operating loads. As a result it is possible to turn the "Sidestrand" against one engine, the other being switched off, in steeply banked turns, without undue effort.
   Except for the fabric covering and for certain fairings which are of three-ply and spruce, the "Sidestrand" is of all-metal construction. Both steel and aluminium alloys are used, the choice of material being dictated by the loading conditions of the individual members concerned.
   The main dimensions of the "Sidestrand" are: Length, overall, 41 ft.; wing span, 72 ft.; wing chord, 7 ft. 9 in.; wing area, 980 sq. ft. The tare weight is 6,010 lbs., and the gross weight 10,200 lbs., the load being made up as follows: Petrol (230 gallons), 1,780 lbs.; oil (23 gallons), 230 lbs.; crew (3 with parachutes), 600 lbs.; military load. 1,580 lbs.
   Following are the official performance figures of the Mark II "Sidestrand" fitted with "Jupiter VI" engines. Full speed at 5,000 ft., 130 m.p.h.; at 10,000 ft., 129 m.p.h.; at 15,000 ft., 122 m.p.h.; at 20,000 ft., 106 m.p.h. Climb to 5,000 ft. in 5 minutes; to 10,000 ft. in 10-5 minutes; to 15,000 ft. in 19 minutes; and to 20,000 ft. in 35-5 minutes. The service ceiling is 21,500 ft., and the landing speed, 51 m.p.h.
   The actual machine to be exhibited at Olympia will be a Mark III "Sidestrand," fitted with geared "Jupiter VIII" engines housed in special nacelles, and fitted with Townend rings. These changes result either in the machine being able to carry a greater military load, or with the same load a marked increase in performance is to be expected. For instance, it is estimated that the full speed at 10,000 ft. will be about 140 m.p.h., and that the ceiling will be at least 23,000 ft.
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Flight, October 1930

AN IMPROVED "SIDESTRAND”
Latest Version Fitted with "Jupiter" XF Engines

   SINCE Boulton & Paul, Ltd.. of Norwich, first introduced their "Sidestrand" twin-engined bomber, several versions have been produced, each new version representing an increase in performance and general utility. It may be recollected that in a detailed description of the first "Sidestrand" (see FLIGHT of March 29, 1929) the conclusion was arrived at that that machine was an exceptionally efficient one, aerodynamically, for a twin-engined aircraft. With a gross weight of 8,850 lb. (4,025 kg.) the "Sidestrand I" had a top speed of 130 m.p.h. up to about 9,000 ft. The "Sidestrand I" was followed by the Mark II, and that in turn was followed by the Mark III, with "Jupiter" VIII engines. In the meantime the gross weight increased in accordance with increasing requirements, and in the "Sidestrand III" had reached 10,200 lb. as compared with the original figure of 8,850 lb.
   More recently the "Sidestrand III" has been equipped with "Jupiter" XF engines, the fitting of which has, for the same gross weight, brought about a very considerable increase in performance. Another gain in performance has resulted from the fitting of Townend rings over the engines. It may be recalled that recently Boulton & Paul, Ltd., acquired the sole rights for the manufacture of these rings, and in the "Sidestrand III" with "Jupiter X F" engines the Townend rings have, it is estimated, been responsible for a gain in speed of something like 10 m.p.h. at 20,000 ft.
   The extra speed now possessed by the latest "Sidestrand III" is believed to have made that machine one of the fastest, if not actually the fastest, heavy class of service type in existence.
   As the machine is the latest type, actual performance figures may not be given, but the makers believe that none of the standard fighting aircraft is capable of overhauling the new "Sidestrand III" at its normal operating altitude. Some of the very latest fighters are thought to be just a shade faster than the "Sidestrand III," but these are not yet in general use.
   Although the "Sidestrand III" is designed for service work, it would appear that a machine somewhat on the same lines might prove a very useful fast air-mail machine.

Flight, May 1931

THE LATEST "SIDESTRAND"
Supercharged Bristol "Jupiter" X.F. Engines have now been fitted with the result that, although the take-off and landing characteristics are not affected, the Speed at Altitude and Rate of Climb are greatly improved

   APART from the fitting of supercharged engines, and the provision of Boulton & Paul combined Townend Rings and exhaust collectors, the "Sidestrand" shown in the accompanying photograph is identical with previous "Sidestrand" day-bombers produced by Boulton & Paul, Ltd., of Norwich. It will be recollected that the "Sidestrand" was first equipped with two Bristol "Jupiter VI" engines, and afterwards with two "Jupiter VIII F" engines. With these power plants the machine has always been noted for its excellent all-round performance and great manoeuvrability. The fitting of the supercharged "Jupiters," combined with Townend drag-reducing rings incorporating the exhaust collectors, has naturally increased the performance at altitude, while at the same time maintaining the take-off and landing characteristics of the earlier types.
   The "Jupiter X.F" develops a maximum output of 560 b.h.p. at 11,000 ft., and the result of fitting two of these engines has been that the rate of climb increases gradually to that height, at which it has become no less than 1,400 ft./min. Similarly, the maximum speed increases from 150 m.p.h. near the ground to nearly 170 m.p.h. at 13,000 ft., and the speed remains above 160 m.p.h. up to 18,000 ft. This height, by the way, is reached in the remarkably short time of 15 minutes, with full load, of course.
   Good as these figures are, Boulton & Paul claim that they could be materially exceeded. It must be remembered that the "Sidestrand" was designed several years ago, for use with normally-aspirated engines, and it is claimed that by designing in the light of more modern knowledge, especially for the modern supercharged engines now available, a better ratio of gross weight to tare weight, as well as a better performance, could be achieved. For example, it is estimated to be within the range of practicability to design a supercharged twin-engined bomber with the offensive and defensive qualities of the "Sidestrand," a range of some 1,000 miles, and a top speed of more than 200 m.p.h. at operating height. These are bold claims, certainly, but we feel certain that a firm of the standing of Boulton & Paul would not make them without having studied the subject sufficiently to be justified in their claims.
   The discussion of the relative advantages of twin-engined and single-engined aircraft has by no means ceased, nor has, so far, any very decisive conclusions been reached. Both schools still have their strong advocates, and very convincing arguments are advanced by both sides.
   The twin-engined school points to experience with the standard "Sidestrand" (which is the only twin-engined day-bomber in use in this country), having shown that the machine is practically immune from successful attack by existing types of single-seater fighters, due partly to the good performance and manoeuvrability, and partly to the fact that it provides a steady gun platform, undisturbed by nose engine slipstream and vibration, and with an all-round view and field of fire. The "Sidestrand" with supercharged engines, it is claimed, would be able, owing to its nearly 30 m.p.h. greater speed at operating height and increased manoeuvrability due to greater power reserve, to avoid engagement by enemy machines under all normal circumstances, while it would have greater tactical advantages than the older type if it did accept combat.
   Another advantage claimed for the twin-engined machine as compared with the single-engined is that it is able to return to its base after one engine has been put out of action, thus greatly reducing the wastage of machines, and, probably, improving the moral of the crew. In this connection it should be pointed out that both the standard and the supercharged "Sidestrands" are able to climb with full load with one engine stopped.
   It has been the custom to regard the twin-engined biplane as necessarily inferior in aerodynamic efficiency to the single-engined type. When we described the "Sidestrand" in detail (FLIGHT, March 29, 1928), we pointed out that Mr. J. D. North and his technical staff appeared to have got the drag down to a figure comparable with that of a single-engined machine. In the latest type, modifications have been introduced, and Townend rings fitted, which further reduce the drag, and there is now no doubt that the latest "Sidestrand" is one of the most efficient twin-engined aircraft ever produced.

Main Data of Supercharged "Sidestrand"
   Length, overall, 41 ft. 0 in. (12.5 m.).
   Wing span, 72 ft. 0 in (21.95 m.).
   Wing chord, 7 ft. 0 in. (2.13 m.).
   Wing area, 1,000 sq. ft. (93 sq. m.).
   Power plant, 2 Bristol "Jupiter X.F" at 560 h.p.
   Fuel capacity, 260 gallons (1,180 litres).
   Weight, empty (including all fixed equipment), 6,877 lb. (3,125 kg.).
   Weight, fully loaded, 10,200 lb. (4,640 kg.).
   Ratio, gross weight/tare weight, 1.485.
   The following performance figures refer to full gross weight of 10,200 lb.
   Maximum speed at 11,000 ft. (3,350 m.), 167 m.p.h. (269 km. /h.).
   Maximum speed at 18,000 ft. (5,500 m.), 161 m.p.h. (259 km./h.).
   Rate of climb at 11,000 ft., 1,400 ft./min. (7.1 m./sec.).
   Time to 11,000 ft. (3,350 m.), 8? min.
   Time to 18,000 ft. (5,500 m.), 15 min.
   Service ceiling, 30,000 ft. (9,150 m.).
   Landing speed, 54 m.p.h. (87 km./h.).