The earliest steps in England, or indeed anywhere, to unify such standards were taken by the Royal Aircraft Factory at Farnborough in 1913. They were extended and improved as experience developed under the Aircraft Inspection Department (A.I.D.) in England (towards the end of 1915), and later under the British Engineering Standards Association, which in 1921 was instrumental in founding in Paris the "Comité International pour l'Unification Aeronautique" to internationalize the same work. To goitia porg ogul vev k Components. Fuselages, wings, undercarriages, tail planes and controlling surfaces, prior to 1914 were not, save in one or two cases, designed as self-contained units, i.e. their manufacture was usually completed during erection into the aeroplane. This involved handfitting, trial and error adjustment, constant inspection and slow production, while spares were not interchangeable. By 1915 each component became a unit in itself, made to limits, corresponding with the connexion points, and interchangeability was safeguarded by the use of jigs and fixtures. By 1919 even components were subdivided into standardized parts, and the assembly of components into a complete aeroplane could be effected after delivery to the field. The jigs and fixtures were usually confined to the location of junction fittings on which the structure was erected. These replaced the fixtures of 1915, which held all members of the component in position during construction, but proved not to be satisfactory, owing to the distortion of the finished piece on removal from the fixture. Girder types of construction, such as fuselages, wings, etc., were latterly constructed to jigs rather than on fixtures, in order that their truth of erection might be more permanent. Monocoque constructions, however, were always built on cradles or moulds, which definitely determined their final shape; the individual members, being free from initial load, were free from distortion on removal from the mould. The development of portable gauges (gauge points mounted on tensioned wires) occurred in 1916. In 1917 component junctions were designed so that all positioning was determined by one joint, clearance in one direction being allowed on the remaining joints; the gauging of components was simplified thereby, and many of the more costly gauges could thus be superseded by simpler ones used in conjunction with a measuring operation. Woodwork. Wood is eminently suitable for light construction and for obtaining a rapid output by machining. The mechanical properties and suitability of various timbers were little known in 1913. Bamboo, the lightest timber, was found unsuitable in about 1911; it lacks uniformity in size, and is difficult to connect at the end of members. Ash (Fraxinus excelsior) and hickory (Carya alba, Hichora ovata) were early used, but hickory is scarce, and variable in its mechanical properties, and ash is heavy as well. Ash is restricted to use where high flexibility and shock-resisting are essential. Silver spruce Sitchenis, Carr.) was introduced in 1913 for spars, struts, and other members, being uniform, light and suitable for machining for weight reduction. Between 1913 and 1915 accurate information of the strength and elasticity of this timber was acquired. Methods of converting the timber for the various uses were determined in order to eliminate defects peculiar to coniferous timbers, such as spiral grain, cross and diagonal grain, dote or rot, gum pockets, alternating hard and soft grains, low density, wide-ringed timber and brittle or lifeless timber (brash). The great demand in 1916 in England led to the importation of unseasoned timber, needing to be conditioned for use, The French and Americans had already experience of this. Kilns were erected in England (on the Sturtevent system of drying). Humidities, temperatures and time periods of drying were determined. Control of the moisture-content of timber was found to be essential. obje timbers were tried in 1918, the peculiarities of each being allowed for: Quebec Spruce (Picea alba and Picea nigra, Link.).els 280 sbilg White Sea White Deal (Picea excelsa, Link.). mom bolism & White Sea Red Sea Yellow Deal (Pinus sylvestris, Link.).boqmeb West Virginia Spruce (Picea rubeus, Sargent). North Carolina Spruce (when this is the same as West Virginia Spruce, but grown in North Carolina), now abrow at boxpol Louisiana Red Cypress (Bald.). (4) Jumboqadi Port Orford Cedar (Chamaecyparis Lawsoniana, Murr.)now enois New Zealand Kauri (Agathis (Dammara] australis).colendo enw Canadian White Pine (Pinus Strobus, Link.). to shines gilt to b gaismoal bre Oregon Pine (Pseudotsuga Douglasii, Carr.). Cypress, which is very variable, liable to brittleness and unsuitable for glueing, was barred in 1918. Oregon pine, which is liable to fracture under shock, and may split when cut into small dimensions, must be restricted to struts and used in the solid. Small knots in the deals can be allowed in laminations if the knots be distributed to obtain uniformity of the member. Laminated struts were used in 1919, with fabric binding to safeguard against the opening out of joints. Early in 1918 box sections, which have all the advantages of laminating, were used, and their use continues. About 1915-6 the glues used in the above processes were classified into three grades: (1) the best for airscrews; (2) for less highly stressed joints; (3) for unimportant details. Glue shops were maintained at a constant 70° Fahrenheit. Micro-investigation of glued joints proved the value of carefully preparing the timber and glue; timber was aged to prevent warping, by storing in the 70°-F. rooms for long periods before glueing. Roughing of the surfaces to be glued was adopted to secure keying. In 1915-6 it was found that if an entire series of laminations were glued in one operation before clamping the first joint would become chilled before the clamping occurred. Later, by using trained crews and special appliances for quick glueing and clamping, the en bloc process of glueing with the more rapid output became possible and satisfactory. Where heated-glue rooms could not be used, "liquid " glue or jelly glues (containing an ingredient which delays the setting point of the glue, thus allowing of ordinary temperatures-55° F. to 60° F.-with 1910 fittings for the structures, attachment of bracings, etc., were made of mild steel, a metal selected, no doubt, because it could be worked cold. This was often used in double thickness to ensure against flaws. Oxy-acetylene welding was often used in joints, even in some that were subject to stress. Tubes and plates were welded together to make sockets, and bent to shape without being subsequently normalized. Failures at welds led to the substitution in 1915 of mild-steel drop forgings. These were machined all over to save weight and to get the size accurate to tolerances too small for the stamping industry at that time. Metal Fittings. time for assembly of parts) were adopted. The correct temperature for forging and subsequent heat treatment of the forging in high tensile steel was not currently known. The facilities were lacking, and the control of the temperatures needed was left too much to the estimate of the skilled operative. Stampings brittle and unreliable for use, as well as difficult to machine, were made. In 1915-6 the impact test, long known but little used, was supported by the War Engineering Committee of the Royal Society, and was found valuable for ensuring that the material so tested would bear prolonged shock stress. ve buxa By 1917 the call for speedy output led to a reversion from forgings to sheet-metal sockets and fittings, using a low carbon sheet-steel of 26 tons' ultimate tensile strength. The pressings were shaped in jigs which ensured an adequate radius at the bend, and they were normalized to remove strains due to bending or punching. Where complicated fittings were built up of simpler pressings these were riveted and soldered together to avoid welding. Dip-brazing of such constructions came in in 1918, with the advantage that the temperatures could be better controlled than when brazed with a blow-pipe. Such pressings are interchangeable and need less gauging and inspection. Turnbuckles, universal joints, shackles, etc., hitherto machined from the bar, were re-designed for quicker manufacture from sheet metal. Bracings. In 1910-1 80-ton steel "piano wire" was much used for bracing the structure, but the fastenings for this had only some 60% of the strength of the wire; the loops stretched, and the structure was soon distorted. Flexible cables spliced on to wiring plates and adjusted by turnbuckles were then used with greater safety, but these also stretched and increased the air resistance, to reduce which wooden fairings were applied to the cables. Solid wires swaged to streamline form, and left thick at the ends for screwing, were made as early as 1911, but they were difficult to manufacture. In 1913 this fair section was abandoned for the elliptical, to allow of rolling instead of swaging the rods, while a special steel and heat treatment evolved by the Royal Aircraft Factory overcame the difficulties. These wires were not generally adopted till, in 1915, standardized aeroplanes led to a demand which warranted bulk production. c. Wires of streamline section were swaged, not rolled, because these unsymmetrical sections tend to curve over sideways as they pass out from the rolls. The elliptical-section wires were called " Rafwires,' to distinguish them when they were standardized. The screwing of the end of these wires was carried on after heat treatment (at 550° C.). Subsequently the wires were tempered at a lower temperature gazobni Hid (450° C.), and later the tempering was abandoned. Round swaged a boli 2 node or booties pato labor gui tie-rods were made from the same steel as the streamline wires drawn to an ultimate strength of 80 tons per sq. in. without any sub-la-sol aller-insto lo su sequent heat treatment. The adoption of tie-rods and streamline bevolqms dynol 1970 and 9oub wires for bracing extended the period for which the aeroplane retained mot boubong erow alle-inco its truth, while it was improved both in speed and climb by the babivog p fair wires. bolare ni homoges grobed mosi Ievos adT dgid os Flexible cables used for controls consisted generally of seven blijo in strands, each of 19 wires of 90-ton tensile. To increase the war out on noin put a single lay cable of larger strands was used. This cable could not nader oc be spliced, and joints were made by turning the ends, wrapping with llanila wire, and soldering a process that requires much care. od 199ja bolining no In a few cases in 1919 the structures were built on the strut-tie woll ning principle without wire bracing; this gave quick erection and main gomb yd ALPE tained very well the truth of structure.olod angyali la abhilys agoon le Dope. The fabric stretched over the wings becomes slack after Gnome, 20 exposure to alternations of humidity. Prior to 1909 rubber cotton-bnu od fabric was tried, and alternatively the plain cotton was tautened by od 30 painting with flour paste. In 1909 thin sheets of cellulose acetate were applied over the cotton, and later the substance was dissolved in acetone and applied with a brush, camphor being used to keep the coat pliable; however, the camphor evaporated, and thereupon the dope cracked on exposure. The search for a suitable softener that did not evaporate from the dope was prosecuted. Tetrachlorethane was tried with success, but it proved dangerous to the operatives applying it in enclosed places. Moreover, sunlight decomposed tetrachlorethane; to yield hydrochloric acid, which eventually attacked the fabric. na 9 of Vovi 19gqoo10 no boblow ban FIG. 19a. or the power absorbed by the engine itself, had first to be determined Standardization of the actual flow measurement of carburetter om-idw jets in place of orifice-diameter calibration made it possible to tune yllup engines for bench tests on a few minutes' running only. Also standard jets suitable for flight purposes were substituted for benchtest jets before delivery, so that the time of tuning-up on installation of the engine into the aircraft was diminished. In 1916 a petrolflow meter, whereby the actual flow into each carburetter is indicated, facilitated the determination of petrol consumptions. on now and Early in 1915 the British Aeronautical Inspection directorate suge gested the following nickel chromium steel for crank-shafts, connect 12.5% to 14.5% zinc, 2.5% to 30% copper, alloy with virgin aluminium, The pouring temperature is 660°C. The percentage of scrap is high, say, 10% to 15% in the simplest forms of block, and up to 30% or 40% for more complicated designs. To overcome the porosity of castings, stove enamelling of the interior of the blocks or the application of water-glass under pressure is used. olid,ut eti The Royal Aircraft Factory experiments in 1915 led the way in aircooled stationary cylinder engines in the use of aluminium heads gilled for cooling, using a steel liner and inserted valve seatings. For rotary-engine cylinders in one instance a thin steel liner was shrunk into a finned aluminium shell which formed a jacket, the head of steel being secured to the liner with a plain metal-to-metal joint by bolts from the head to the crank-case, thus securing the cylinder as a whole.bas noilor si es aus and i suoi p Cylinders of all types before erection on engines are tested internally to 450-500 lb. hydraulic pressure, and for the jackets to 30-40 pounds.uddur oor of 101 viibinud lo enoitenisals of Connecting Rods Connecting rods, as regards material, followed crank-shaft practice in the standardization of plain nickel chrome steel, heat-treated to give 50-60 tons tensile strength. boilqge 99 The 6-cylinder and early 8- and 12-cylinder types conformed to motor-car practice in the use of solid H" section shanks and white-metal big-ends, without a bronze bush, the cap being held usually by four bolts or studs. To reduce the crank-shaft length of certain type engines the connecting rods on one side of the engine were provided with lugs to carry a wrist-pin, this wrist-pin, on one side of, and parallel to, the big-end bearing, carrying the auxiliary connecting-rod. Alternatively to the same end a pair of rods superposed. In one case, a hollow circular sectioned shank carried an integral big-end, white-metalled internally and externally, the second rod, being fork-ended, oscillating on the sleeve formed by the first rod. The comparatively thin and flexible section of the inner rod sleeve, however, enhanced the difficulty of white-metalling and led to cracking in running.ni os doidw alsoiben biop-oiteos art Au further development therefore (of square hollow sectioned shank) provided a bronze shell rigidly gripped by the forked ends of the outer rod, while the inner rod oscillates on the middle portion of the shell, which is white-metalled internally to provide the main bigend bearing, as shown in fig. 21.00 9vil of oss i bod y boilgget Howd of boboon doidwand od neds 1930 etsoo oft not bount nie 976 vtibimud wol bus tuisoqmot tastenonde en gave of sub 191w lo dieoqsb sds biova otob ovloe -ixelt oonil oqig ni booubortni adut roddu Later, mild-steel cylinders turned from forged blanks were used in lieu of cast iron. Valve pockets, sparking-plug bosses, and thin sheet jackets were then welded on as first tried by Vickers in 1909. Aero-engine cylinders are also cast together in one block for the sake of the rigidity of the cylinders one to another. At first, following motor-car practice, cast iron was used for this. Towards the end of 1916, however, aluminium, with its low weight and high heat conof constare digt.nl lio bna lortog yd bothai dilide otom-aniviib bns not-gniooo simeque eu im i vlived og gniau yd booea lort in visto lo 11 luau od gainimistobal Tot lottog gatadiw aiT bosincoluv-on 191360 enigns oftyd bodhoads Towoq od to hode sy ei saati tud nuod gs not no bas u The cherectol 19ts lowonen belinsuper ti bas pool and gitas sign 915w obuo bas n od bas omamyb nigose ignitest tol boes. base of olqining igni ai tie oft doir of pe Connecting-rods of rotary and radial engines consist usually of one master rod, ball or roller-bearinged, with the big-end enlarged to form circular lugs to secure wrist-pins carrying the plain or auxiliary type of rod of the remaining cylinders. One exception provided a bigend consisting of a separate lead bronze shell (in two halves bolted together) mounted on ball bearings and provided on the inside with white-metalled concentric grooves in which oscillate the concen 08 of nomizoa bus lovo onigno designe to and gied 75119d760 to 30sme olt Isutos 10 obibade onus of sidizao ji abem nol FIG. 20, 19tomsib-solina laatst oal vino ninnu atunim wol & no test dood oong qutrically formed heels of the connecting rods. ductivity, took its place. The first prominent "Mono block" (see fig. 20) comprised a mild-steel cylinder liner complete with head and valve seats, screwed into an aluminium block which took four cylinders, and constituted a complete enclosed water-jacket. The liners were not in contact with the cooling water, and with bigger cylinders overheating and loss of contact between the liner and the surrounding aluminium jacket occurred particularly in the flat head. A natural development, therefore, was to remove the top of the liner, leave it open, and let the aluminium itself form the combustion head of each cylinder. Two difficulties then had to be overcome (1) The provision of a gas-tight joint between the top of the liner and the jacket and head; (2) the insertion of rings in the head to form valve seatings. The first was overcome by screwing the liner hard up against the shoulder in the head, and the second (which was achieved without distortion or burning of the seatings) by casting-in or expanding-in steel or hard bronze rings. To improve further the cooling of the cylinders, the lower portion of the aluminium jacket in contact with the liners was omitted, the liner being held only by a screw thread of some 1-in. depth at the top and a rubber joint and ordinary lock nut ring at the bottom. olano Lavau and sonia 21 The form of aluminium cylinder head and jacket casting is complicated, and experiments, both as regards method of casting and choice of aluminium alloy, led to the selection of a mixture of Jess 101 15ste muimondo lodin garollo di batagg Initially, the ordinary small-end bronze bush system with gudgeon pins fixed in the piston was used. Later, variations with loose bushes and loose gudgeon pins were developed, the pins in the latter being secured endwise in the piston by wire circlips let into grooves on the outside edges of the piston bosses. Rough machining before heat treatment is necessary on the rotary type master-rod stamping which has a large big-end mass and a comparatively small stem section, to secure uniform structure and freedom from quenching cracks. The elimination of all sharp corners and abrupt changes of section is essential. Main Bearings.-Ball, roller and white-metal bearings are to be found in various types. The two former permit of high loading and reduce the length of the engine (bearing loads approximating to 100% over normal practice being found to give a total life commensurate with the rest of the engine under service conditions). White-metal main bearings, usually bronze shelled, are secured either by separate loose caps bolted on or studded to the top half crank-case; or, as in usual German practice, by the bottom half crank-case itself, which carries the lower halves of the whole of the crank-shaft bearings; this adds to the rigidity and general strength of the engine, but increases the difficulty of production and fitting. Valves Valve breakage, originally a trouble, was almost eliminated by the standardization of valve steels and by stamping the valves emperature so that the grain flow in the valve head swept continuously and uniformly from the rim into the throat and stem, thus providing strength to resist sheer at all points of the head. The original practice, before bulk production warranted the use of stampings, had been to turn valves from the solid bar, a procedure which gave in the head a grain flow parallel to the stem, For exhaust valves a steel having 14% tungsten and 3.5% chromium is necessary in certain of the hotter stationary-type engines. For the cooler-running engines a high-chromium stainless steel gives satisfaction. Either of such steels would be satisfactory for inlet valves, but, for economy of such high-grade materials, a plain nickel steel is used with great success. (R. K. B.-W).. V. AERO ENGINES. Historical Résumé. For many years mechanical flight was delayed for want of a light engine, and indeed from the first flight to the present day (1921) the aeroplane was ahead of its prime mover. Flight should have been possible in 190r when Manley, in the United States, built for S. P. Langley a fivecylinder radial petrol engine developing 52 H.P. and weighing only 2.9 lb. per H.P. By bad fortune this engine was, however, never used in flight until 1914, when it was mounted in the Langley aeroplane for which it was intended. For their first flights in 1903, the brothers Wright built a four-cylinder car-type engine of 12 H.P. weighing 12.7 lb. per H.P. By 1905 it was improved to 19 H.P., with a weight of 9-5 lb. per H.P. and, as redesigned in 1908, gave 35 H.P. and weighed 5.5 lb. per H.P. The aero engine proper dates from about 1909, and the progress made is traceable reliably by the results of competitive tests held from time to time. Such tests were carried out in France, 1909-11-13, in coöperation with La Ligue Nationale Aerienne and the Auto Club de France; in England in 1909-1214; in Italy in 1913, and in Germany in 1912-4. A certain section in England centred its hopes erroneously on the use of very small engines, A. V. Roe made the wonderful achievement of flying an aeroplane with only 9-10 H.P. in 1909. The Alexander prize of 1911 at first stipulated for engines of only 25 H.P. This was increased by the Advisory Committee at the request of the supt. of the Army Aircraft Factory to admit 40 to 75 H.P." and was won by 24 hours' continuous running by a 50-60 H.P. Green sent in on Sept. 11 1911. This engine weighed 296 lb. complete, and developed an average of 53 5 H.P. The British Government competition of 1914, although won by a 110 H.P. Green engine, was chiefly useful in showing the merits of the 100 H.P. Gnome and the 90 H.P. RAF. Both of these did yeoman service in the war, but soon proved to be too small. In Germany, the development of the airship led to the earlier study of larger aero engines, although the German competition of 1914 was won by a 100 H.P. Benz, weighing 4 2 lb. per H.P. "The importance of the aeroplane in war service gave an immense impetus to engine development along two main lines; (a) An extensive development of high tensile steels and aluminium alloys, and a more scientific use of the materials, led to a diminution of the weight; (b) attention to detailed design, guided by scientific investigation, greatly increased the mean effective pressure developed in the cylinders and the thermal efficiency. The speed of rotation was also increased so that output was augmented, while at the same time fuel consumption was reduced. Modern aero engines may be divided into two classes: (a) Engines which are developments of the motor-car type, i.e. all the water-cooled vertical, Vee, and broad-arrow engines; (b) types designed specially for aerial flight, i.e. the radial rotary engines and the air-cooled Vee engines. The rotary air-cooled type, which was one of the earliest of these, was almost entirely due to the French, e.g. the Gnome, Le Rhone and Clerget engines. In this type minimum weight was the objective. The arrangement of the engine, with its cylinders radiating star fashion in one plane and operating on a single crank, afforded a crank-shaft and crank-case of minimum dimensions and accordingly gave a motor of extremely light weight. To increase the cooling by air draught, and save the weight of a fly-wheel, the cylinders were made to rotate round making the cylinders of steel, with very thin walls, and the the crank-shaft, which was fixed. Weight was economized by difficulties due to distortion of such thin cylinders with heat were ingeniously met by using a brass obturator ring, as subengines. stitute for the cast-iron piston rings which are universal in other In 1909 a number of rotary engines of powers ranging from,. 30 to 100 H.P. were available. Of these the 100 H.P Gnome was the most powerful. In 1913 a 14-cylinder Gnome of 160 H.P was launched, and on a British army aeroplane achieved the fastest flight up to that time, namely 130 m. per hour. At the outbreak of war in 1914, the 100 H.P. Monosoupape Gnome, and at a slightly later stage the 110 H.P. Clerget and the 100 H.P. Le Rhone came into current use, and the 160 H.P. Gnome was, unfortunately from the war fighter's point of view, discarded on the score of complication. In France in," 1917 a higher-powered Monosoupape developing 150 H.P. was put into commission, while in Great Britain the BRI and the BR2 rotaries, developing respectively 150 and 220 H.P., were produced. Including the propeller boss the later Mono-Gnome weighed 2.03 lb. per H.P. and the BR2 2-21 lb. per H.P. In 1914, and indeed at a later stage, none of the rotary engines were quite satisfactory; the type suffers from certain, inherent disadvantages. It is liable to the distortion and overheating of its cylinders; the earlier examples required special precautions against catching fire, its petrol and oil consumptions" are high; and it requires frequent dismantling and overhauling. In spite of this the best of these rotaries formed the basis on which European air experience was founded, and as recently as 1912 the best aero engines (from the point of view, be it understood, of the aeroplane's performance, which is dominantly a' matter of weight) were probably the Gnome rotaries weighing from 30 to 35 lb. per H.P. At this time long-distance flights were exceptional and therefore their large fuel and oil consumption was not so serious, Throughout the war, and especially in its earlier stages, they gave their best service in machines of the single-seater high-speed class, in competition with the heavier water-cooled vertical engines on which the German i air service relied almost entirely. When the distance of flight was extended, the water-cooled car-type engine came to the front partly because the smaller weight of fuel to be carried compensated for the greater weight of the engine itself, and partly because it was at that time more reliable. The following table shows the total weights of engine, fuel and oil, for flights of different duration, in the case of a typical air-cooled rotary engine weighing 2.25 lb. per H.P. and consuming 1.10 lb. of fuel and oil per H.P. hour, and of a watercooled engine weighing 40 lb. per H.P. and having a total consumption of 0.55 lb. per H.P. hour. For longer flights than 3 hours the water-cooled engine is here. shown to involve a smaller gross weight. It was largely emulation of the rotary which forced the pace of the progress on the car-type engine. This led to the replace- } ment of cast iron by sheet metal for water-jackets; to the use of thin steel instead of cast iron for cylinder barrels and of aluminium for cylinder head castings, and to the use of two, and in some cases three, rows of cylinders operating on a single crankshaft and mounted on a common crank-case. The use of steel or aluminium alloy instead of cast iron for the pistons had been initiated in experiments for motor-cars. In some few cases air-cooling was adopted, c.g. in France the 70 H.P. eight cylinder Vee Renault of 1912, and notably in England, the 90 HP eight cylinder. Vee RAF of 1913-4, and the 140, H.P twelve-cylinder Vee RAF4a, all of which had cast-iron L-headed cylinders. The last-named engine weighed 4.0 lb. per H.P. and gave excellent service during the war. No air-cooled engine with these large cylinders reached the stage of production in quantity during the war. A number of British radial engines were, however, developed in 1918, and of these the "A.B.C. Dragonfly," having nine steel cylinders, giving 300 H.P. and weighing 2.22 lb. per. H.P., and the 450 H.P. Cosmos Jupiter," having nine steel cylinders with an aluminium patch containing the inlet and exhaust ports bolted to each head, and weighing 1-42 lb. per H.P., are worthy of mention. Still the car engine of given cylinder capacity remained | up to 6 in. and up to 50 B.H.P. per cylinder, give an output and appreciably heavier than the contemporary rotary, until care fuel-consumption of similar order to those from the best waterful studies in 1916-17-18 were made to increase the output cooled cylinders. per unit of cylinder volume, and the thermal efficiency. The volumetric efficiency was increased by improving the design of the inlet pipes, valves, and valve gearing, and the combustion space of the cylinder. The thermal efficiency and the mean effective pressure were increased by augmenting the compression. Since high compression is only practicable with a compact and symmetrical combustion chamber the L-headed cylinder was replaced by the overhead valve-cylinder. Moreover, since high compression necessitates good cooling of the cylinder, the water-cooled engine gained a distinct relative advantage over the earlier air-cooled engines which were, in general, inadequately cooled. As a result of these steps in the detail design, the brake mean effective pressure was raised from the 75 to 95 lb. usual on cars, to as high as 130 lb. per sq. in. in the best modern aero engines, while at the same time the petrol consumption was reduced to approximately 0.45 lb. per B.H.P. hour, a value some 40% better than that of the average car engine. As compared with these it will be recalled that the 150 MonoGnome of the same date weighed 2.03 lb. per H.P. A 12-cylinder Vee experimental engine with aluminium cylinders was built at the Royal Aircraft Factory in 1916-7 and gave excellent results in flight and on the test bed. This developed 210 H.P. and weighed 3.0 lb. per H.P. Prior to 1914 the American aero engine was mostly of the car type, and was outdistanced during the first two years of the war by the more intensive development in those countries active In many cases the output was also improved by increasingly engaged. At that time the 160 H.P. Curtiss was probably the speed of the engine. The speed of the rotary engine was limited to about 1,200 revolutions per minute, by the stresses due to centrifugal force. In the fixed cylinder engine, however, much higher rotational speeds could be adopted by attention to the balance of the moving parts, and to the design of the bearings. These speeds now range from 1,400 to 2,100 revolutions per minute, reduction gears being used for the airscrew drive in the case of the larger and less rapidly flying aeroplanes. The resultant weight economy was considerable. Thus the 300 H.P. Hispano-Suiza water-cooled Vee, rotating at 2,000 r.p.m., weighed only 1.80 lb. per H.P. and the 450 H.P. Napier "Lion" of 1921 only 1-89 lb. per H.P. In each case these weights include that of the propeller boss, but not that of the radiator and its water, which would add approximately 0.55 lb. per H.P. These advances in the car type of aero engine were accompanied by improvements in the specialized type. In 1912 the radial engine with fixed cylinders was represented by a few examples of which the 9-cylinder, water-cooled "Salmson " developing 110 H.P., the 6-cylinder, water-cooled "Laviator the most outstanding engine in America, and when the United States declared war in 1917 her need for high-powered acro engines became acute. In May 1917 it was decided, in conference with the Allied Mission in the United States, to design and build the Liberty engine, of which an 8-cylinder model was completed for test on July 3 1917. This was not put into production, as advices from France indicated that demands for increased power would render it obsolete before it could be produced in quantity. Efforts were then concentrated on a 12cylinder model, the first of which passed its 50-hour test on Aug. 25 1917. This engine is a water-cooled Vee, originally developing 400 H.P. and weighing 2.0 lb. per H.P. More recent improvements have increased the output to 510 H.P. and reduced the dry weight per H.P. to 1.75 lb. or about 2-3 lb. with cooling water and radiator. The progress in the average aero engine in service between 1910 and 1918, in power, weight, and efficiency, is shown in the following table. The main details are abstracted from the report of the American National Advisory Committee for Aeronautics in 1918: developing 80 H.P., and the 6 and 10 cylinder, air-cooled "Anzani" developing 60 and 100 H.P. are among the most noteworthy. The Salmson was developed at a later stage as a 14-cylinder, two-row engine of 200 H.P. and the Anzani as a 20cylinder, four-row engine of 200 H.P. These engines were French, but since 1914 British designers have greatly advanced the science of the air-cooled engine. The fixed radial engine has a number of features of superiority over the rotary. It enables a normal type of carburetter and of piston to be used; it eliminates the large windage losses; while since the cylinders are not exposed to centrifugal stresses aluminium alloys can be used. This light and highly conducting metal has greatly helped air-cooling. Owing to the greater ease of installation of the air-cooled engine in an acroplane, the absence of a fragile radiator liable to freeze on descent from great heights, as well as to its adaptability to work in the tropics, much attention was paid during the war to the design of aircooled cylinders. A composite construction using aluminium alloy for cylinder heads was evolved at the Royal Aircraft Factory, Farnborough, between 1915 and 1921, with the result that air-cooled cylinders became available which, for diameters 2.8" 55 Since the water-cooled engines cannot function without radiator and water, an addition of 0.55 lb. per H.P. has been made in their case to render Table A comparative. The weights after deduction of 0.55 lb. are actual measurements, and include those of the propeller boss and of the gear, if any. In cases where the respective makers produce a series of engines of different powers, only representative examples have been quoted. During the latter part of the war, the demand for engines of large H.P. for bombing acroplanes and dirigibles led to the production of many experimental engines, which were available by 1921, e.g. the 800-900 H.P Sunbeam Coatalen, the 850 H.P Fiat, the 1,000 H.P. Lorraine Dietrich, and the 1,000 H.P. Napier "Cub." Types of Engines.-Of the total heat from the fuel, 25% to 35% cooling or direct air-cooling if the normal operation of the engine is to passes through the walls and piston and must be dissipated by waterbe maintained. Water-or air-cooling have their respective advantages and disadvantages. For the water-cooled engine is claimed: (1) A lower cylinder-wall temperature; a reduced tendency to the burning of exhaust valves and pistons; and more effective lubrication. |