THE GIPSY MAJOR ENGINE in its Series I form is used on numerous light aircraft. It is an inverted engine with four cylinders in line and develops 130 horse-power at 2,350 revolutions a minute. The recommended overhaul period for this air-cooled engine is as long as a thousand hours. A compression ratio of 5.25 to 1 makes this unit suitable for use with most high-grade motor-car petrols.
GIPSY is the description given all aero engines made by the De Havilland Company. Gipsy engines had a meritorious beginning in 1927, when the first one to be designed established a world speed record for light aircraft of 187 miles an hour. In the ten years that followed this achievement nearly 6,000 Gipsy engines were produced and the number is continually increasing. These engines have done duty in all parts of the world.
The original Gipsy engine was a 120 horse-power experimental engine. After it had been detuned to 100 horse-power this engine was produced in large numbers as the Gipsy I. One of these engines was fitted to a Moth aeroplane and sealed so that no repairs other than running adjustments could be made to it. After 600 hours’ flying, during which 51,000 miles were flown, the engine was dismantled and put into new order at a cost of a little over £7. Today 600 hours is the normal period of duty between overhauls of the Gipsy Six Series I engine. No intermediate top overhauls are necessary.
The Gipsy II and Gipsy III (see page 343) and the Gipsy Major engines were logical developments of the Gipsy I. The Gipsy III, like the modem Gipsy Major, was an inverted-type engine.
Because of their remarkable record of reliability, Gipsy engines have been widely used for racing, record breaking, long-distance flights and in air-liner work. Up to the end of 1936 no fewer than twelve Gipsy engines had flown the Atlantic Ocean. C. W. A. Scott, who won the England to Australia race in 1934, had up to the end of 1936 flown 4,000 hours with Gipsy engines without having had a single forced landing due to engine failure.
The Edgware (Middlesex) engine works of the De Havilland Company are at present concentrating on the production of Gipsy Major, Gipsy Six and Gipsy Twelve engines. The factory covers an area of twelve acres and produces a number of engines which approaches 1,000 a year. All Gipsy engines from the original record-breaking Gipsy I to the latest twelve-cylinder engines being used on the De Havilland Albatross aircraft have been designed by Major Frank B. Halford.
Major Halford designed a highly successful six-cylinder in-line aero engine as long ago as 1916. This engine was the first to have two exhaust valves and one inlet, and was used in a developed form in many aircraft used in the war of 1914-18. Since 1916, Major Halford has been actively engaged in designing engines, largely for aircraft.
As early as 1917 Major Halford was exploiting the advantages of the inverted-type engine. In 1929 he evolved the Gipsy Ghost engine, an eight-cylinder V type power unit of 200 horsepower. There is a staff of seventy engine draughtsmen and others associated with the work of De Havilland engine design, under the guidance of Major Halford.
The Gipsy Major engine was first produced in 1932 as an improved form of the Gipsy III. Many single-engined aircraft are fitted with the Gipsy Major engine, including the Tiger Moth and the Miles Magister, two elementary trainers used by the Royal Air Force (see the chapter “Trainers of the RAF”). It is used also in the Dragonfly two-engined five-seater, and was the power unit chosen for the De Havilland Dragon air liner which did much to make unsubsidized commercial air line work possible (see the chapter on “British Airways”).
The inverted-type Gipsy Major engine is a four-cylinder in-line engine with the valves operated by push rods. The valves are located in the cylinder heads. Two types of this engine are made, and they are known as Series I and Series II. The design of the two types is on similar lines, but the Series II is designed to operate a controllable-pitch airscrew, and has a higher compression ratio. The object of the higher compression ratio is to take advantage of the modern petrol fuels with high octane values (see the chapter “Modern Aero Engines”).
The Gipsy Major is a left-hand tractor engine; that is to say, it is designed for aeroplanes with tractor airscrews in which the airscrew revolves in a clockwise direction when viewed from in front of the aircraft. The capacity is just over six litres for both types. The maximum horse-power for the Series I engine is 130 at 2,350 revolutions a minute, and 140 for the Series II at 2,400 revolutions a minute.
Motor-Car Fuels are Suitable
The Gipsy Major is an air-cooled engine in which ease of installation and maintenance are features. No fundamental changes in design have been made to the engine since its introduction, but detailed improvements have been achieved. One notable effect of these has been the increases in the periods between overhauls. In July 1933 the period was increased to 750 hours; in August 1937 it was possible to extend the recommended overhaul period of the Series I to 1,000 hours.
The Series I engine has a compression ratio of 5.25 to 1, which makes suitable the use of any high-grade motor-car fuel, other than that containing tetra ethyl lead. The drive to the air screw is direct; the bore of the cylinders is 4.646 in. and the stroke 5.512 in. The weight of the engine complete with airscrew hub is 305 lb. An electric starter or hand-turning gear can be fitted as an extra.
The cruising revolutions are 2,100 and the petrol consumption during cruising is between 6 and 7 gallons an hour. This figure rises to about 9 gallons an hour when the aircraft is climbing. The Series II Gipsy Major differs from the Series I in such ways as the compression ratio of 6 to 1 and the use of special fuels. The cylinder heads are of aluminium alloy, with inserted valve seats of steel instead of heads of aluminium bronze with valve seatings machined in the material of the heads themselves. The pistons are forged in aluminium alloy instead of being cast in heat-treated aluminium alloy.
Provision is made for the engine oiling system to provide oil at the correct pressure to operate the pitch-changing mechanism of the propeller. The bore and stroke of the two types is the same, but the weight of the Series II is 5 lb. more. In spite of the extra power output of the Series II, the petrol consumption figures are approximately the same for both types.
Although the Series II engine is normally intended to take advantage of the improved aircraft performances made possible by controllable-pitch propellers, it is suitable for use with a fixed-pitch propeller should this be desired.
Like the Gipsy Major engines, the Gipsy Six engines are made in two types. The Series I is for normal fuels and a fixed-pitch propeller; the Series II is intended for operation with a controllable-pitch propeller and requires fuel of higher octane value.
The Gipsy Six engine is a six-cylinder engine with the cylinders arranged in line. The maximum output of the Series I is 200 horse-power at 2,350 revolutions a minute; that of the Series II is 205 horse-power at 2,400 revolutions a minute. Although the maximum output of the Series II is but little higher than that of the Series I, the Series II is rated for a usefully higher continuous output.is website.
DESIGNED FOR CONTROLLABLE-PITCH AIRSCREW, the Gipsy Major Series II engine develops 140 horse-power at 2,400 revolutions a minute. The capacity of the engine is just over six litres. Although the general design is similar to that of the Gipsy Major Series I engine, the Series II differs in the materials used, in the compression radio, and in small details.
The general design of the Gipsy Six Series I engine is similar to that of the Gipsy Major Series I. It may be considered as a Gipsy Major Series I engine to which two more cylinders have been added to produce smoother running and greater horse-power. This similarity is a great advantage to operators who may have Series I Gipsy Major and Gipsy Six engines in use because many components such as cylinders, cylinder heads, pistons, connecting rods, valves and valve gear are interchangeable.
The Gipsy Six Series I engine has been in production since 1934 and has figured in many record flights. It is largely used in commercial aviation, an i it is the power unit for the De Havillan Dragon Rapide and Express Air Liners.
Both the Gipsy Six engines have the same cylinder bore and stroke, and the dimensions are similar to those of the Gipsy Major engines. The compression ratios of the two Series I and of the two Series II engines are the same. As the Gipsy Six Series II engine is of more recent introduction than the Series I, it incorporates many improvements in general design.
The Gipsy Six engines are of the inverted type, are left-hand tractor engines and have a capacity of just over nine litres. The engines are supplied fitted with electric starters. The weight of the Series I is 468 lb. and of the Series II 469 lb.; the extra power of the Series II is thus obtained with virtually no increase of weight. The output of both engines at 2,100 revolutions a minute is 185 horse-power, but the normal cruising revolutions a minute of the Series II are higher than those of the Series I; thus greater power is available.
In both Gipsy Six engines separate cylinder barrels and heads are used for each cylinder. The pistons in both instances are of the slipper type with fully floating gudgeon pins. There are
three piston rings below each gudgeon pin; two are compression rings and the third is a scraper ring — a feature which enhances the good oil-consumption figures of the engines. The Series I consumes 1-4 pints of oil each hour at cruising revolutions and the Series II consumes 3-5 pints.
Inverted Twelve-Cylinder V Engine
The most interesting engine in the De Havilland range is the company’s largest engine, the Gipsy Twelve. This is based on well-tried principles that have been proved over many years. It is logically developed from the Gipsy Major Series II and Gipsy Six Series II engines. The Gipsy Twelve is an inverted-type engine with the cylinders arranged in V form. A compact engine is thus produced, with a small frontal area for its power output. Unlike the majority of V twelve-cylinder engines of today, the Gipsy Twelve is air-cooled.
So far as such items as cylinder barrels, cylinder heads and pistons are concerned, the Gipsy Twelve may be considered as two Gipsy Six Series II engines combined. Many of the spares for Gipsy Major Series I and Gipsy Six Series II engines may be used for Gipsy Twelve engines. Because of this, the Gipsy Twelve has a big advantage over other new types of engines, for a network of spares and service organizations is already to be found for it covering most parts of the world.
The bore, stroke and compression ratio of the Gipsy-Twelve cylinders are identical with those of the Gipsy Major Series II or Gipsy Six Series II engines. The total capacity of the engine is exactly twice that of the Gipsy Six, but the engine develops more than two and a half times the horse-power of a Gipsy Six Series II engine. The maximum output of the Gipsy Twelve, which is a supercharged engine, is 525 horse-power at 2,600 revolutions a minute, with a supercharging pressure of +3½ lb. per square inch.
AIR-COOLING is used for the Gipsy Twelve engine, which has the twelve cylinders arranged in two rows of six. The circular casting for the supercharger is seen at the end of the crankcase in this photograph, taken from the rear of the engine. With a capacity of a little over twelve litres, the Gipsy Twelve develops 525 horse-power at 2,600 revolutions a minute. In many ways the design of this engine is based on the Gipsy Major design. Constant-speed propellers are normally intended to be used with the Gipsy Twelve.
Although in normal operation this power is required only for the few minutes of a take-off, the engine has been successfully run at this output for five hours continuously. The normal maximum cruising revolutions are 2,200 and the drive to the airscrew is through a reduction gearing of 1 to 0.667. The engine is designed for use with constant-speed airscrews. The engine has been passed by the Air Ministry for military and commercial use. As a military power unit, the Gipsy Twelve is known as the Gipsyking I. The military version varies from the civil model only in the auxiliary units that may be added and in minor external features.
The small area of the circular front cowling of the Gipsy Twelve enables the propeller to work at high efficiency. The cowling is unbroken by any openings, and forms a clean line right to the point of the airscrew spinner — an important consideration with modern cruising speeds in excess of 200 miles an hour. This unbroken cowling is obtained by an entirely new method of aero-engine cooling. Cooling is achieved from the rear of the engine by ducts.
The cooling is controllable, and the air is supplied from openings in the leading edge of the wing. These openings are arranged three-quarters the radius of the propeller from the centre of the engine. By the use of this position, and by suitably designing the ducts, the lift of the wing is not materially affected, and the drag is so small as to be immaterial.
The positions of the cooling ducts ensure that sufficient cooling air is obtained when the aeroplane is moving slowly, because they are directly in a strong part of the propeller slipstream. The air is forced at pressure to the sides of the cylinders, past the fins and out by an exit at the back of the underside of the engine cowling. By altering the opening of the exit, the degree of cooling may be adjusted for maximum efficiency at all aircraft speeds.
Considerable attention has been given in the design of the Gipsy Twelve to accessibility. The magnetos, governor unit for the constant-speed propeller, and vacuum pump for operating instruments on the aircraft are on the front of the engine. The electric starter is on the top engine cover, and the electric generator, which has a flexible drive, is on the side. The carburettor is below the engine. Only items requiring little attention are placed at the rear of the engine. The hydraulic pump for undercarriage and flap operation is mounted vertically on the rear face of the engine, with all the connexions placed just below the top cowling.
Eight Main Bearings
Crankcase and other cover castings are in “Elektron”. The crankshaft is a nickel-chrome steel forging, machined all over and rotating in eight main bearings. The airscrew shaft, which is geared to the crankshaft, contains a tubular torque bearing shaft running right through to the back of the engine, where it drives the gearing which operates the supercharger. The supercharger is of centrifugal type, and the impeller rotates at 20,000 revolutions a minute. The supercharger is situated between the carburettor and the inlet manifolds. Automatic control of the supercharger and of the mixture is provided by the carburettor.
Hot oil circulates round the supercharger intake, and round vital parts of the carburettor. A hot and cold air intake control is also provided. These precautions eliminate all possibility of ice formation.
The engine is 82.6 in. long, 31.5 in. wide and 37.4 in. high; the dry weight is 1,058 lb. The petrol consumption when cruising between 7,500 and 10,000 feet varies from 20 to 30 gallons an hour, according to the cruising speed.
A new De Havilland engine which is to be in full production in 1939 is the Gipsy Minor. This 90 horse-power engine has been produced to power a new De Havilland low-wing monoplane — the Moth Minor. This engine is a development on smaller and simpler lines of the Gipsy Major. The simplifications have been made mainly from the maintenance point of view to keep down the running costs of the Moth Minor. In the Moth Minor the new engine gives a cruising speed between 105 miles an hour and 115 miles an hour when running at sixty-five per cent of its full power.
It is anticipated that large numbers of Moth Minors will be sold; for this reason the Gipsy Minor engine is designed to be suitable for economical production in large numbers. As with other Gipsy engines, the Gipsy Minor will no doubt be used eventually in many makes of aircraft.
THE GIPSY SIX ENGINE may be considered as a six-cylinder version of the Gipsy Major. The Gipsy Six Series II engine is shown in this photograph; the cylinder details are the same as those tor the Gipsy Major Series II. Similarly, the Gipsy Six Series I is based on the design of the Series I Gipsy Major. The horse-power of both Gipsy Six types is 185 at 2,100 revolutions a minute. In this photograph the hub of a controllable-pitch propeller is shown fitted to the engine.
