DECEMBER 7, TQ39 @G07 461 $» BRITAIN'S AERO ENGINES Units jor Military and Civil Purposes : Sleeve-Vahe Developments : Liquid- Cooled Range Extended ALVIS A PROMISING nine-cylinder radial in a power class which has hitherto been neglected by British designers is the . This unit is well suited for advanced training duties. Particularly noteworthy are the small overall dimensions, the diameter being 41.5m. and the length 52m. There are two valves to each cylinder, each being operated by inde­ pendent, completely enclosed and pressure-lubricated rocker gear. The engine is supplied complete with flexible or fixed four-point mounting, and all accessory drives ire taken from a gear box. A much larger unit is the Alvis Pelides, a 14-cvlinder two-row radial of 52m. diameter. Take-off power is 1,060 h.p. Alvis, Ltd., Holyhead Road, .

ARMSTRONG SIDDELEY ALTHOUGH Armstrong Siddeley Motors, Ltd., have ^ supplied large numbers of Tiger VIII and IX 14- cylinder two-row radials to the Royal Air Force, interest now centres round the Cheetah series. The Cheetah IX and X are in service in such well- established and widely used types as the Anson and The Pixie, a neat 50 h.p. four-in-line made by Aero Engines, Ltd.

AERO ENGINES TNTENDED for use in light two-seaters weighing up to •*• about i,20olb. the 50 h.p. Pixie, as made by Aero Engines, Ltd., is an inverted air-cooled four-cylinder-in­ line unit. End-to-end cooling is used, an air chute being fitted on each side of the engine. The crankcase and cylinders are of unit construction, and are cast in heat- treated magnesium alloy. A top cover provides access to the crankshaft, which is carried by three main bearings. Aero Engines, Ltd., Kingswood, Bristol.

An Armstrong Siddeley Tiger VIII installed in an Armstrong- Whitworth Whitley bomber.

Airspeed Oxford. Both are nine-cylinder radials of 13.65 litres capacity, but the Mark X engine is the more reccat design. It was, in fact, the first medium-powered engine in regular production to be designed for use with a variable pitch airscrew. The engine is made up of the following principal com­ ponents: the front cover, to the lower part of which is secured the oil pump unit and which carries also the control valve for the v.p. airscrew; the crankcase, which houses the crankshaft and connecting rod assembly and to which the cylinders are secured ; the induction case, which carries the rotor; and, finally, the rear cover. The Alvis Leonides is an attractive 9-cylinder radial giving The cylinders are in two parts, the aluminium alloy 450 h.p. for take-off.

Large Views of Outstanding Engines Appear on Pages a-h; For Tabulated Data See Page 464. 462 !@KfiT DECEMBER 7, jg^g

Pegasus XXII is a medium-supercharged engine giving 1,010 h.p. for take-off. Mercury's VIII and IX are of smaller diameter than the Pegasus series and power such machines as the Blenheim and the Gladiator. The Mercury VIII is the standard power plant of the Mark I Blenheim, but the Blenheim IV has a later version of this engine which is known as the Mercury XV, having a redesigned cylinder head. The Mercury has for some time been in full production in the Shadow Industry, and is probably the most widely used of any aero engine now in service. The medium-super­ charged engines of the Mercury series are the XI and XII Three versions of the Perseus sleeve-valve radial are irj production, the series X, XI and XII. The last, in civil- rated form, is fitted in the D.H. Flamingo and the military versions power the and Roc and the . The small-diameter 14-cylinder Taurus, as fitted in the and Fairey Albacore, develops 1,065 h.p. at 5,000ft. and measures 47fin. in diameter. This unit would be admirable for installation in a twin-engined fighter. A larger unit, the Hercules II, gives 1,375 n-P- at 4,000ft, This engine is in full quantity production, and a further developed type is to be built in France. A Liore 45 bomber has already been fitted with Hercules engines. On 100-octane fuel the highly supercharged The Short " G " class flying boats are fitted with four gives 920 h.p. for take-off. Hercules IV engines which give 1,380 h.p. for take-off and weigh i,68olb. The Bristol Aeroplane Co., Ltd., Filton House, Bristol. head and the steel barrel ; each has two valves. Drives for the auxiliaries are enclosed in a box on top of the rear cover, the generator on the Cheetah X being mounted on COVENTRY CLIMAX top of the box. Armstrong Siddeley Motors, Ltd., Coventry. HTHE American Continental A-50, A-65 and A-75 hori- zontally opposed engines are built under licence in this country by Coventry Climax Engines, Ltd. A notable BLACKBURN feature is the fuel injection system, which replaces the carburetter and is claimed to have several advantages, the 'TTIE Cirrus Engine Department of Blackburn , most important being freedom from manifold icing with­ -*- Ltd., are concentrating on the 90 h.p. Cirrus Minor out application of heat to the air intake. and the 150 h.p. Cirrus Major. Both these engines are of the inverted four-cylinder air-cooled type. The following Coventry Climax Engines, Ltd., Friars' Road, Coventry. description will apply to the Major. Actually, the Major uses the same type of cylinders as the Minor. These are machined all over from a steel ingot COVENTRY VICTOR and are located in the crankcase by a large spigot and four '"PHE Victor flat-four light aero engine which develops studs. The cylinders are castings in "Y" alloy and are -1- 50 h.p. at 3,000 r.p.m. has a three-bearing crankshaft detachable, being spigoted on the cylinder and secured with massive centre bearing ; pressure lubrication to all by twelve studs equally distributed round the cylinder. bearings ; dry sump system, and a geared starting handle, The crankshaft is carried in five plain bearings with a ball if required, to enable the engine to be started from the thrust bearing at the front end. A Claudel-Hobson car­ cockpit. buretter is fitted. The Coventry Victor Motor Co., Ltd., Coventry. The crankcase is an alloy casting with all pressure oil- ways carried internally. A dual Amal fuel pump is fitted on the rear of the engine, being driven off the camshaft. A cylinder cooling chute and baffle plate are fitted as standard equipment, and detachable inspection panels are provided to facilitate removal of sparking plugs for clean­ ing. The B.T.H. inertia starter is driven by a small electric motor driving the engine through a reduction gear. Cirrus Engine Department, , Ltd., Brough, E. Yorks.

BRISTOL TN view of the diversity of Bristol poppet-valve and •*• sleeve-valve radial engines now being delivered, our space may be better employed with a brief general dis­ cussion of the characteristics of the various units rather than with a detailed structural examination such as has already frequently been made in Flight. The Pegasus XVIII is a two-speed supercharged poppet- valve unit used to power the Hampden and Wellington bombers. It is now in quantity production by the Shadow Industry. The two-speed gear of the high-speed centri­ fugal supercharger is hydraulically controlled, the impeller/ camshaft speed ratio being changed by three double-acting hydraulic clutches. The unmachined block of the 250 h.p. V-8 D.R.P. sleeve- The standard power plant of the Short Sunderland, the valve unit. DECEMBER 7, 1939 !@G07 ^^

D.R.P. ENGINES machined from solid steel forgings, and each is carried in eight plain lead-bronze bearings. There are four overhead URING the last eighteen months Mr. D. R. Pobjoy has camshafts, one for each bank of cylinders. Hydraulic D been working on an interesting series of sleeve-valve tappets are incorporated in the valve rockers, which are engines. Furthermore, it is an open secret that he has been mounted on hollow spindles over the camshafts. engaged on the design of a big two- A special S.U. carburettor is fitted below the super­ for air liners, but this, like the sleeve-valve units, must charger. This is of the twin-choke, fully automatic type, await the return of peace. and embodies a two-position mixture control and a four- The photograph reproduced on page 462 shows the un- stage boost control. Ignition is by two magnetos with machined block of a 250 h.p. eight-cylinder vee-type sleeve- separate twenty-four-point distributors all situated on the valve engine known as the Velox. The crankcase and front cover and driven through gears from an extension of cylinder barrels, it will be seen, are cast integral. the starboard crankshaft. D.R.P- Engines, Ltd., Little Tottington Court, near A double-entry supercharger of centrifugal type is fitted Aylesjord, Kent. at the rear of the engine, the impeller being driven by spur gears through layshafts from the long centre shaft. D. Napier and Son, Ltd., Acton, London, W.3.

HE Gipsy Twelve and the Gipsy Minor are compara­ , POBJOY tively recent editions at each end of the De Havilland T T^HE latest Pobjoy engine, the Niagara V, differs from range of engines. Intermediate types are the Gipsy Major x its predecessors, e.g., the Cataract III and Niagara III, Series I and Series II and the Gipsy Six Series I and in that it takes advantage of 87 octane fuel, having a suit­ Series II. All engines are of the inverted in-line, air-cooled ably high-. To withstand greater loads type, the Minor and Major having four cylinders, the Six (the maximum power is 137 h.p.) certain main parts have six cylinders, and the Twelve twelve cylinders, arranged been strengthened, but, despite the fact that the net weight in two banks of six. has been increased to 185 lb., the specific weight has been By far the most widely used type is the Gipsy Major, reduced to less than 1.5 lb. /h.p. which will be selected here for description. Pobjoy Airmotdrs, Ltd., Rochester, Kent. The cylinder barrels are machined all over from carbon- steel forgings. Wall thickness and depth of finning are adjusted to ensure even cooling and to prevent distortion. ROLLS-ROYCE The detachable heads are of aluminium bronze, and are held to the crankcase by long steel studs. A LTHOUGH Rolls-Royce engine production has for a The slipper-type pistons have fully floating gudgeon pins **• considerable time centred on the Merlin; the smaller located by external circlips and washers and one scraper types have not altogether disappeared from the picture. and two compression rings below the gudgeon pin. For example, the Kestrel XXX powers the I A nickel-chrome-alloy steel forging, the crankshaft is advanced trainer, and the Peregrine, a higher-powertd unit statically and dynamically balanced, and runs in five white- of similar_ capacity, has been produced for installation in metal main bearings, there being a ball bearing to take the military prototypes. It is felt, however, that our space thrust at the front end. The crankcase is an aluminium- should be devoted to the Merlin. alloy casting, the lower half of which carries the main This is a geared twelve-cylinder vee-type engine with a crankshaft bearings. Elektron is used for the top cover. total cylinder displacement of 27 litres. The most com­ The Gipsy Major II has a compression ratio of six to monly used versions are the Merlin II and III, which are one and detachable heads of aluminium alloy. Dome- installed in very large numbers of R.A.F. fighters and topped pistons, stellited exhaust valves and stronger valve bombers. A later development is the Merlin X, which, springs are other new features. fitted with a two-speed supercharger, combines the quali­ De Havilland Aircraft Co., Ltd., Hatfield Aerodrome, ties of both the full and moderate blower systems. Herts. The general design of the Merlin follows previous Rolls- Royce practice The crankcase is an aluminium casting in two halves, bolted together ; the top half includes a portion NAPIER of the reduction gear casing, whilst the lower half carries the oil pumps and filters, and drives for accessories such A LTHOUGH the Fairey Seafox light reconnaissance sea- as the undercarriage pump or low-pressure air compressor. •^ planes have 16-cylinder Napier Rapier engines, this in­ The auxiliary drive wheelcase is fitted to a vertical facing teresting power plant is now out of production, having formed at the rear end of the crankcase. Main bearings are made way, like the Dagger III, for the larger and much split mild-steel sheels lined with lead-bronze. more powerful Dagger VIII. The crankshaft is a one-piece steel forging, machined all The Dagger VIII has twenty-four cylinders arranged in over and nitrogen hardened. " H " section connecting rods eight formations, i.e., there are four blocks of six cylin­ ders each, two blocks vertical and two inverted. The crankcase is of alu­ minium alloy, and is in two halves joined along the hori­ zontal centre line. A detach­ able nose piece forms the cover for the main reduction gears, and houses the drives for the magnetos, distributors and air-screw control units. The two crankshafts are

The installation of the Rolls- Royce Merlin in the Super- marine Spitfire fighter. Current versions have a variable-pitch airscrew. 4b4 DECEMBER 7, jr,,t BRITAIN'S AERO ENGINES Leading Characteristics of the Modern Range

No. Maximum Altitude and Reduction Com­ Internatio Rating Take­ Maker's Name and Arrange­ Cool­ and Capa­ Sear pres­ off Engine Type ments of ing Stroke city Ratio sion Altitude Power Diy Cyls. Ratio (Super­ Engine Power Altitude Engine Power Weight charging) Speed Speed

AERO ENGINES mm. Litres ft. r.p.m. b.h.p. ft. r.p.m. b.h.p. b.h.p. lb Pixie ... 4 IX. A. 80.77 x 100 2.048 D. 5.58 S.L. 2,350 45 S.L. 2,624 50 — 129} ALVIS Leonides 9R. A. 122X112 11.78 0.5 :1 \ 6.3 8,250 3,000 435 9,000 3,100 410 450 708 0.63 :1 / Pelides 14 R. A. 146x165 38.67 — 6 5,000 2,150 1,065 7,500 2,150 675 1,060 1,475 ARMSTRONG SIDDELEY Genet Major IA 7R. A. 108 X 114.35 7.32 D. 5 S.L. 2,200 150 S.L. 2,425 165 — 327 Genet Major IV 7R. A. 108x114.5 7.32 0.663 :1 5.25 S.L. 2,400 160 S.L. 2,700 180 — 367 Lynx IVC 7R. A. 127x139.7 12.4 D. 5 S.L. 1,900 215 S.L. 2,090 240 — 515 Cheetah VA 7R. A. 133.3 X 139.7 13.65 D. 5.2 S.L. 2,100 285 S.L. 2,400 326 —. 596 Cheetah IX 7R. A. 133.3 x 1.39.7 13.65 D. 6.35 6,000 2,100 310 7.300 2,425 350 340 635 Cheetah X 7R. A. 133.3x139.7 13.65 D. 6.35 6,750 2,300 325/340 7,000 2,425 355 360/375 694 6,2001 „e 2,375 1 840 1 6,600 1 2,450 1 Tiger VIII 14 2-R. A. 139.7x152.4 32.7 0.594 : 1 6.2 8621 918 12,800 J-'*' 2,200 / 56 / 15,000/ 2,450/ 782/ 1290 Tiger IX 14 2-R. A. 139.7x152.4 32.7 0.594 :1 6.2 6,250 2,375 775/805 6,500 2,450 810 845/880 1,260 BRISTOL * Mercury VIII, IX ... OR. A. 146x165 24.8 0.572 :l\ 13,000 2,400 785/825 14,000 2,650 840 725 1,005 (+5) 0.50 :1 / — Mercury XI, XII ... DR. A. 146x165 24.8 0.50:1 — 3,500 2,400 780/820 6,000 2,750 890 830 1,005 (+5) Pegasus XC ... 9R. A. 146x190.5 28.7 0.50 :1 — 3,500 2,475 710 740 5250 2,600 830 920 1,030 Pegasus XXII, XXIII 9R. A. 146x190.5 28.7 0.50 :1 1 4,000 2,250 800/840 6,500 2,600 890 1,010 1,030 (+5) 0.572 :1 / — Pegasus XVII, XVIII 9R. A. 146x190.5 28.7 0.572 : 1 1 — 4,750 \:-S. 2,250 780/815 1 3.0001 2,600 1,000 1 965 1,130 (+5) 0.50 :1 / 14,750 / 720/750 / 15,500 / 885/ Pegasus XIX, XX ... 9R. A. 146x190.5 28.7 0.572 : 1 1 8,500 2,250 800/835 10,000 2,600 925 835 1,130 (+5) 0.50 i 1 / — Pegasus XXV, XXVII 9R. A. 146x190.5 28.7 0.50 :1 \ 11,000 795/830 9,500 915 830 1,035 (+5l 0.572 : 1 / — — — Hercules II 14 R. A. 146 x165 38.7 0.444:1 — 5,000 2,400 1,100/1,150 4,000 2,750 1,375 1,300 1,680 Hercules IV 14 R. A. 146x165 38.7 0.444 :1 4,500 1,010/1,050 5,500 1,220 1,380 1,680 Taurus II 14 R. A. 127x137 25.4 0.444 :1 — 5,000 — 860/000 5,000 -~ 1,065 1,010 1,300 Perseus X 9R. A. 146x165 24.9 0.50 : 1 — 14,500 2,40—0 700/730 15,500 2,75—0 880 750 1,110 Perseus XI, XII 9R. A. 146x165 24.9 0.572 :1 \ — 6,500 2,400 715/745 6,500 2,750 905 830 1,105 (+5) 0.50 : 1 J — Perseus XIIC, XIVC 9R. A. 146x165 24.9 0.50 : 1 1 4,000 2,250 680/710 6,000 2,600 815 890 1,100(+10) 0.666 :1 / — Aquila IV 9R. A. 127x137 15.6 0.50 :1 — 4,500 2,600 450/470 6,000 3,000 540 600 830 CIRRUS (Blackburn) Minor 4 I.L. A. 95X127 3.605 D. 5.8 S.L. 2,300 82 S.L. 2,600 90 82 227 Major 150 4I.L. A. 120x140 6.33 D. 5.8 S.L. 2,000 138 S.L. 2,450 150 132 325 DE HAVILLAND Gipsy Minor 4 I.L. A. 102x115 3.759 D. 6 S.L. 2,250 80 S.L. 2,600 90 80 210 (±5) Gipsy Major I 4 I.L. A. 118x140 6.124 D. 5.25 S.L. 2,100 120 S.L. 2,350 130 130 300 Gipsy Major II 4I.L. A. 118x140 6.124 D. 5.25 S.L. 2,400 140 S.L. 2,400 140 — 310 (±5) Gipsy Six I 6 I.L. A. 118x140 9.186 D. 5.25 S.L. 2,100 185 S.L. 2,350 200 200 450 (±7i) Gipsy Six II 6 I.L. A. 118x140 9.186 D. 6 S.L. 2,400 205 S.L. 2,400 205 205 469 (±71) Gipsy Twelve 12 I.V. A. 118x140 18.372 0.667 :1 6 7,500 2,400 405/420 7,750 2,450 410/425 525 1,058 NAPIER Rapier VI 16 H. A. 89x89 8.830 0.390 :1 7 4,750 3,650 355/370 6,000 4,000 380/395 365 713 Dagger III 24 H. A. 97x95 16.8 1 : 2.69 7.75 3,580 3,500 700/725 8,000 4,000 780/805 760 1,305 Dagger VIII 24 H. A. 97x95 16.8 0.308 : 1 7.5:1 9,000 4,000 925 8,750 4,200 1,000 955 1,399 POBJOY Niagara III 7 R. A. 77x87 2.835 0.468 :1 6 S.L. 3,300 88 S.L. 3,650 95 95 156 Niagara V 7R. A. 81x87 3.130 0.4375 :1 — S.L. 4,000 125 S.L. 4,600 137 119 • 185 ROLLS-ROYCE Kestrel XIV, XV, XVI 12 V. CW. 127X140 21.3 0.632 :1 6 11,000 2,600 690 14,500 3,000 745 670 955 Kestrel XIV, XV, XVI (v.p.) 12 V. C.W. 127x140 21.3 0.477 :1 6 12,250 2,750 715 14,500 3,000 745 745 985 Kestrel XXX 12 V. 127 X140 21.3 11,750 2,400 550 14,250 2,750 600 720 •967 Merlin II, III 12 V. E.Gw. . 137.2x152.4 27 0.47—7 : 1 6— 12,250 2,600 900 16,250 3,000 1,030 890 1,335 Merlin X 12 V. E.G. 137.2 x 152.4 27 0.477 : 1 2,500 12-S. 2,6001 1,040 5,250") 3,000 1 1,145 1 1,065 1,394 13,250 / 965 17,750/ 1,025/

A. — Air. W. = Water. C.W. = Composite water. E.G. = Ethylene Glycol. R. = Radial. 2-R. = Two-row Radial, H. = " H " formation. V. = " V formation. L. =. In Line. I. = Inverted. H.O. = Horizontally opposed. D. = Direct Drive. S.L. = Sea Level. 2-S. = Two-speed Supercharger. are fitted in pairs, each pair consisting of a plain rod and screw. A cast aluminium reduction gear casing houses the a forked end. The bearing blocks are lined with lead- forward roller bearings, and is secured by bolts to the bronze. Lubrication of big-end bearings is by pressure feed crankcaSe which houses the rear roller bearings. through the crankpin. The supercharger is of the high-speed centrifugal type, The cylinder banks are set at an angle of 60 deg., and driven through a train of multiplying gears, fitted with a are of the monobloc aluminium type, the heads and water- slipper mechanism. jackets being in one casting. In the Merlin X engine a special supercharger drive is Six "wet" cylinder liners are inserted in each block. provided with a change-speed gear operated by oil pressure. Cylinder banks are fitted to the crankcase by long studs. The supercharger pressure is controlled by an automatic The top joint is formed by a soft aluminium alloy ring, boost regulator of a new type, eliminating dead movement whilst the lower end of the liner is provided with a spring- loaded, coolant-tight joint. There are four valves per which is noticeable in the '' fixed datum '' type previously cylinder, the exhaust valves having sodium-cooled stems. employed. Carburettor is of the twin choke type, of Rolls- The coolant is circulated by a centrifugal pump of ample Royce S.U. design. Two air passages are coupled by single capacity. Rolls-Royce forward-facing air intake. A single-spur reduction gear transmits power to the air­ Rolls-Royce, Ltd., 14-15, Conduit Street, London, W. o w o w 3 03 M 33

en (a)

The Rolls-Royce Merhn X typifies the latest British practice in the construction of high-powered twelve- cylinder liquid-cooled yee engines. It has a two-speed supercharger and is rated at 1,040 h.p. at 2,soo ft LIQUID-COOLED MODERNITY in low gear and 965 h.p. at 13,250 ft. in high gear. Maximum outputs at 5,250 ft. and 17,750 ft are 1,145 nP- and 1,025 h.p. respectively. The dry weight is 1,349 lb- ffi0SR DECEMBER 7, 1 939

From the basic Rolls-Royce Kestrel design (21.3 litres cap­ acity) the two engines illus­ trated on this page have been developed. The Peregrine (above) emphasises perform­ ance, whereas the Kestrel XXX (below), being required for in­ stallation in trainer aircraft, is of com­ paratively low power. The Pere­ grine is rated at 860 h.p. at 13,500ft. whereas the normal output of the Kestrel is 550 h.f. although 720 h.p. is available for take-off.

KESTREL CAPACITY mmmmmmmmmmmmmmmmmmmm wmmmmmmmmm^mmmmm ^^^^^^^^mmmmmmmm

1,000 H.P.; 4,200 R.PM. a w o w a w w

00

The Napier-Halford Dagger VIII is a unique engine. It has twenty-four small air-cooled cylinders arranged in four banks in the form of a letter H. For a capacity of only 16.84 litres it gives a maximum output of 1,000 h.p. at a height of 8,750 ft. This is achieved by running the engine at very high speeds, the maximum being 4,200 r.p.m. The compression ratio is high at 7.5:1. Dagger engines form the standard power plant of the Hereford bomber as now being delivered to the R.A.F. FLIGHT, December 7, IQOQ FLIGHT, December j, 1939

Of the two upper views the one on the left shows the Taurus and that on the right the Hercules. The illustrations are more or less to scale. It will be seen that the Hercules is fitted with drive to the separate accessory gearbox. Note also the comparatively " clean " appearance of the engine, which is largely due to the sim­ plicity of the sleeve-valve cylinders.

Of the three bottom views that on the extreme left shows a section of the front of a Hercules. The engine shown in side view to the right of this is the 9-cylinder Perseus and the illustration below is of the Taurus.

Offered by the Bristol Com­ pany as " a definite advance upon their famous poppet- valve predecessors " the sleeve-valve engines illus­ D trated on these pages are among the most highly developed radials in the world. It is claimed that they enable substantial sav­ ings to be made in opera­ tional costs and out-of-ser- vice time due to their essential simplicity, ­ mum maintenance require­ ments and fuel economy. The largest type is the 14- cylinder Hercules, develop­ ing nearly 1,400 h.p. ; next in size is the 14-cylinder 1,065 h.p. Taurus intended for high-speed military air­ craft ; then the general purpose 9-cylinder Perseus (800/900 h.p.). The 600 h.p. Aquila is not inclu­ ded on these pages as its production has been tem­ porarily overshadowed by the types illustrated. / FLIGHT, December jt ig^g

On the left is the Arm- strong Siddeley Cheetah X as installed in the Air- speed Oxford advanced twin-engined military trainer. It is moderately super­ charged and gives a take­ off output of 375 h.p. with a variable pitch airscrew though when installed in the Oxford it drives air­ screws of the fixed-pitch wooden type. Much of the success of this engine can be attri­ buted to the automatic variable - datum boost control and the auto­ matic mixture control fitted to its Claudel Hob- son carburetter. Below is the Cheetah IX, an earlier type of similar characteristics but not equipped for the opera­ tion of a variable-pitch airscrew. The Cheetah IX is the standard power plant of the Avro Anson.

RADIALS FOR TRAINERS

Since the original Cheetah engine was put into production several years ago this widely employed Armstrong Siddeley type has established itself as one of the most reliable and efficient radials in the world for use in military trainers and light general-purpose types. The engines illustrated on this page (Mark IX and Mark X) are in service in their hundreds. An even later model, the Cheetah XI, has been developed to give no less than 460 h.p., which is extremely creditable considering the small dimensions of the engine. DECEMBER 7, 1939

AIR-COOLED INVERSION

The 90 h.p. Cirrus Minor (right) and the 150 h.p. Cirrus Major (below) are in production at the engine works of Blackburn Aircraft, Ltd. Both represent the latest practice in the construction of small inverted 4-cylinder-in-line air-cooled engines and both are installed in elementary training machines which are employed for the instruction of R.A.F. pilots. The Minor is fitted to over twenty different types of aircraft operating in fourteen countries.