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Design For Today   1   1933  Page: 224
 
 The Evolution of the Moth
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THE EVOLUTION OF THE MOTH

By Alec Davis

Three photographs which show how the design of an aeroplane is influenced by its function. The Handley-Page Air Liner {left) needs a large body for the accommodation of passengers and luggage necessitating a large wing space and powerful engines. The Hawker Super-Fury single-seater fighter {centre), though no larger than a Moth, has an engine of several times the power, giving it high speed and great manoeuvrability. The Gloster troop-carrier {right) is designed to take thirty soldiers in full kit, and to lift this great load needs four Rolls-Royce engines developing 2,000 h.p., which are arranged in tandem pairs to lessen wind resistance. By courtesy of Flight


Some 500 private aeroplanes are owned in this country to-day. In 1926 there were two dozen. The growth of private flying that these figures indicate is far more noteworthy than the achievement of the latest “stunt” flier, for it is of direct interest to the citizen of moderate means. He may well ask, How much more will this movement spread? and Shall I ever sell my car and buy a ’plane?

I do not think that the aeroplane will ever replace the motor-car. It demands too much skill in handling and too much space on the ground. Most Britons are town or city dwellers, and few large centres of population have really accessible aerodromes. But several have done or are doing their best to improve this state of affairs. Country houses and seaside resorts and hotels are also making landing-grounds in many parts of the country, thereby increasing the usefulness of private aeroplanes.

THE FlRST MOTH

The last eight years have seen the birth and evolution of suitable machines. All aeroplanes should be fast and reliable; an aeroplane intended for the tourist private owner must combine economy and simplicity with these basic qualities. Soon after the war, economical light aeroplanes were built and flown, but they never became popular, for nearly all used such low-powered engines that they were unreliable. The de Havilland Moth, introduced in 1925, was the first light aeroplane to combine economy and reliability. Its excellence is shown by the fact that to-day, eight years later, it is still the most popular type in Britain—perhaps in the world. Detail improvements have been made from time to time, and the development of the Moth epitomises the development of all touring aeroplanes.

By comparison with some of its predecessors, the 1925 Moth was not a light aeroplane at all. But it had enough structural strength and engine power to be reliable—and it flew about seventeen miles on a gallon of petrol. It was a biplane, so that its wings could be easily folded for storage. It had a wooden frame with plywood-covered fuselage, making for ease of repair. It carried a pilot and one passenger in tandem open cockpits with duplicate controls, so that it could be used for training. The A.D.C. Cirrus engine made the Moth possible. Rated at 27/60 h.p., it had four cylinders arranged in line and cooled by air. They had to project some distance above the top of the fuselage to ensure that the cooling air-flow was adequate; and this naturally interfered with both streamlining and visibility.

MORE POWER

One of the first improvements made in the Moth was the introduction of the Cirrus Mk. II engine, which was well cooled though it did not project so far. The new model gave an improved performance, as it developed 30/80 h.p.; but it was, in turn, soon replaced by the 98 h.p. Gipsy, built by de Havillands themselves for the Moth machine (though later fitted to many other types). Similar in general design to the Cirrus, it made possible a further improvement in streamline, as it was almost totally enclosed at one side and the top.

Meanwhile, the undercarriage of the Moth had been re-designed. One would imagine that an aeroplane was of all things most free from past
Design For Today   1   1933  Page: 225
 
 The Evolution of the Moth
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1. An early type of Moth. Its Cirrus engine projects considerably to ensure adequate cooling.
2. A later Moth with Cirrus Mk. II engine. The undercarriage shows a complete breakaway from earlier practice which was influenced by the road vehicle.
3. Moth aeroplane with Gipsy engine—both made by the de Havilland Aircraft Company. The re-designed nose gives a better streamline.
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traditions in design, but actually the landing gear until recent years was based on road-vehicle practice. The two wheels on a typical machine were joined by a straight axle. Despite the springiness of the shock-absorbing legs of the undercarriage, a hump in the ground was likely to tip the machine sideways, with possible damage to a wing-tip. Or long grass might wrap itself round the axle of a taxi-ing ’plane and tip it forward on to its nose, probably snapping a propeller blade. These considerations are perhaps unimportant for aircraft using first-class aerodromes, but not so for the private owner, who may often land on ordinary grass fields or aerodromes that are not much better.

America was, I believe, the home of the new type of “split” undercarriage for single engine light planes, but the Moth was the first machine to make it popular in Britain. In this type, each wheel is practically independent of the other, and the dangerous straight axle is absent.

ENTER THE COUPÉ

As the Moth made flying popular, the demand for comfort grew, and a coupe was introduced, consisting of a structurally normal Gipsy Moth biplane with a light, transparent lid over the two cockpits. The section immediately above each was hinged at one side, folding over to allow pilot and passenger to reach their seats. But this coupe was merely an adaptation of the “next best thing,” and in 1930 the de Havilland company decided to produce two distinct types of aeroplane for the private owner—the open Moth biplane and a new monoplane, the Puss Moth, with cabin for pilot and two passengers. For the Puss Moth a new engine developing 120 h.p. was designed. It was again an air-cooled four-cylinder type, but inverted by comparison with its forerunners—the cylinders hung down from the crankcase. It could be cowled- in completely at top and sides; a hole in the nose of the ’plane sufficed to keep it cool. Known as the Gipsy III, it further improved streamlining and visibility and was fitted in Moth as well as Puss Moth machines.

Soon after this, the Royal Aircraft Establishment —the D.O.R.A. of aeroplane design—at last gave its approval to the use of wheel brakes, which not only enable an aeroplane to use a smaller landingground but also make it easier to handle on the ground, as it can be turned by braking one wheel. The pilot needs no outside help when taxi-ing.

HAPPY LANDINGS

The brake and the “doughnut” wheel were adopted in the Moth at about the same time. Previously, aeroplane tyres, on which the greatest shock is probably the landing bump, were similar in shape to motor tyres, which remain (almost) always on the ground. The doughnut consists of an extremely fat low-pressure tyre on a wheel so small
Design For Today   1   1933  Page: 226
 
 The Evolution of the Moth
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4. A similar machine fitted with a coupe head—the first type of enclosed Moth.
5. A later Gipsy Moth with doughnut wheels and brakes. (This and numbers 2 and 3 have a fuselage of metal construction with fabric covering—an alternative to the standard wooden construction with plywood covering.)
6. The Fox Moth, with open pilot's cockpit and cabin for three passengers. The Gipsy III inverted engine is cooled by air entering the opening just visible in the nose of the fuselage
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that it is really a hub. It is another improvement of great benefit to the owner-pilot using rough and perhaps boggy aerodromes.

From the Moth with inverted engine the Tiger Moth was adapted for use in the Royal Air Force; this necessitated the rearrangement of wings and cockpits so that either pilot or passenger could leave by parachute. Being particularly suitable for aerobatics, the Tiger Moth is used by civil as well as military pilots, but it is mainly of interest in the present context because of its place in the evolution of the Fox Moth. This is the newest type of Moth biplane in quantity production to-day. Tail, nose and wings are interchangeable between the two types, but the Fox Moth has a wider and deeper fuselage; for between its wings is a cabin for three passengers, with a pilot’s cockpit—either open or roofed—behind. The Fox Moth carries four people —five on short flights—and develops twice the power of the first Moth, yet its petrol consumption is no higher.

PLANES FOR TO-DAY

In 1925 the would-be buyer of a touring aeroplane found no practical alternative to the Moth; to-day the choice of suitable machines is wide. The de Havilland company recently produced another remarkable type in the Leopard Moth, developed from the Puss Moth monoplane. A machine of this type, hastily completed in time for the King’s Cup Race, won it; while two others were among the finishers. The Leopard Moth, which costs £1,275, should prove popular among travellers of the wealthier class, for it carries three people in comfort at 120 miles an hour—and 20 miles to the gallon of petrol. The pilot sits in the same cabin with, but in front of, the passengers, who are seated side by side. A Leopard Moth could be stored in a shed adjoining a house of medium size, for its overall dimensions are only 26 ft. 6 in. by 12 ft. 6 in. with wings folded.

Another new aeroplane has brought the price of private ownership down with a jerk; the Miles Hawk open two-seater costs £395 and cruises at 100 miles an hour, with a range of 400 miles. In other words, a standard Hawk can fly non-stop from London to Glasgow in just over three and a half hours and still have some fuel in reserve. This type is a monoplane of simple construction, fitted with a Cirrus engine. Like most British touring aeroplanes, it has folding wings and uses ordinary No. 1 petrol.

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Readers who are interested in the historical development of the aeroplane should visit the Science Museum, where they can see some of the very early machines such as Lilienthal's glider (1896), another curious but unsuccessful model with feathered wings, and the original Wright aeroplane (1903), as well as several modern types.