The hopes of peace
Wart1me advances were not really very great because thoughts were too muddled and most of those concerned were too close to their problems to see them in perspective. In general, the aeroplane emerged from the conflict with three or four times the engine power with which it entered it, but otherwise very much the same as the better types of 1913. True, it had become rather more robust, but in the main there had been few new ideas, it was more a case of increasing the size of parts to make them stronger than of refining their design. There were a few brilliant exceptions to the rather dull average and it was upon these that I concentrated in the latter part of the previous chapter.
Of the aeroplanes that really were the foundations of future development, the Fokker and Junkers types stood out in both the structural and aerodynamic fields without reference to their duties, while the Handley Page and Vickers bombers were to set the pattern in their class for over a decade. Otherwise, the big Felixstowe flying-boats were probably the best general contribution on the Allied side. The single-seater fighters, both of Britain and France, had served their turn well, but they were outmoded and though they remained in service long under the axe of peacetime economy, they had contributed little to the design of the fighters that followed them.
In 1919, everyone believed that aviation was the coming thing and there were a myriad designs for sports planes, transports , mail planes, etc. from all the established companies and from many an optimistic sub-contractor—only to have the depression of 1920-21 bring both civil and service aviation almost to a standstill.
One of the great efforts of 1919 was to be first across the Atlantic and the Daily Mail offered a prize of £10,000 as an encouragement. Several aeroplanes were designed for the purpose, among which the Sopwith biplane in which the late Harry Hawker made his unsuccessful attempt was an interesting example of contemporary ideas on long-range flying. This aeroplane was a simple, single-engined biplane with a crew of two, pilot and navigator. The fuselage was deep and long, since its main duty was to carry a large petrol tank. The cowling
behind the cockpit was cunningly contrived as a dinghy— which failed to work when the aeroplane was actually ditched in a rough sea—but no attempt was made to reduce drag by enclosing the cockpit. The wing span was large, fifty feet, to lift the fuel load.
The first direct Atlantic crossing was actually made by John Alcock and Arthur Whitten-Brown (both of whom were knighted for their achievement) on June 14-15, 1919, from Newfoundland to Ireland, in a modified Vickers Vimy bomber with two Rolls-Royce Eagle engines. The Vimy had a good disposable load, so that by adding more tanks in its capacious fuselage the necessary range could be obtained without unduly overloading it. That first direct Atlantic flight took 16 hrs. 12 mins. for a distance of 1,890 miles, a remarkable feat of deadreckoning navigation.
Commercial services were soon opened between London and Paris, later to Brussels and other large cities. The first aeroplanes used were conversions of single-engined day bombers, the D.H.4 and D.H.9. These were very crude, just a bulbous cabin for two or three built on to the rear fuselage where the gunner was originally stationed. Rough as were these aeroplanes they served the pioneers of air travel for a year or two and laid a foundation of experience upon which the first commercial aeroplanes could be designed.
There were other, more ambitious conversions too. The Handley Page O/400 and V/1500 were fitted out as air liners with basket seats and windows let into their capacious fuselages. The four engines of the V/1500 proved too expensive to feed with petrol and there was scarcely the demand in traffic to make up its payload of three tons or so. The O/400 adaptation, however , was reasonably successful and from it was developed the W.8 air liner, which in turn was evolved into the Hyderabad bomber in the later twenties—a full turn of the wheel!
A serious attempt to design a true commercial aeroplane was the Vimy Commercial, which might be considered as the true father of all air liners. Rex Pierson, the Vickers Aviation designer, went a step further than others of his day by evolving a practical fuselage. Using the wings and tail of the Vimy bomber, a plump oval wooden monocoque fuselage, without the clumsy cross-bracing that impeded the movement of passengers in the converted bombers, provided something like present-day air liner comfort for ten passengers. Large oval windows gave these early travellers some taste of the magnificent view to be had from the air.
It is interesting to compare this early "main liner" with the de Havilland Dove, about the smallest "feeder liner" in use today. The engine power is almost the same, two 375 h.p. water-cooled Eagles in the Vimy, two 305/345 h.p. air-cooled Gipsy Queens in the Dove, each aeroplane was built for ten passengers and a crew of two seated in fuselages of approximately the same size. The Vimy had a span of 68 ft., a length of 43 ft. 9 in., the Dove's span is 57 ft., for a single wing, length 39 ft. 4 in. Cruising speed of the Vimy was about 80 m.p.h. at a height of 6,000 ft., while the Dove does 180 m.p.h. at 8,000 ft—maximum speeds, 101 and 210 m.p.h. respectively. This advance in a period of almost thirty years reflects not only the improvements due to scientific knowledge of streamlining and structures, better aerofoils, retractable undercarriages , and variable-pitch propellers; but also the growth in the demands of the air lines by which today's small route equals the traffic of the early main routes.
There was in the immediate post-war period an enthusiastic belief within the aeronautical fraternity that the thousands of qualified pilots would take to the air as their chief recreation and sport, that there would be a renaissance on a glorious scale of the old flying days. What a rude awakening there was; within a year there was an almost complete eclipse of private flying because of the world economic crisis which followed an initial post-War boom. Many aeroplane manufacturers made small sports plane prototypes, few of which showed much original thought, being no more than small versions of the single-seater scouts. People did realize the impossibility of the average pilot's pocket supporting the fuel consumption of engines much over 100 h.p., but there were few smaller motors to choose from.
One of these early sporting aeroplanes deserves mention, not so much for its originality as for its history—this was the Avro Baby, a small biplane with a 60 h.p. water-cooled engine. Completely conventional, and in fact rather ugly, this little biplane made several notable flights in the hands of the Australian Bert Hinkler. London to Turin in a day, about eight hundred miles non-stop at an average speed of 84 m.p.h., was the best and set a standard for small aeroplanes which was not equalled for over a decade. The London-Turin flight was, in fact, the first stage of a pioneer trip to Australia, which was only stopped because Hinkler was refused permission to cross the then uncharted Iraq desert. That same little Avro was still flying fifteen years later, when it had been fitted with an 80 h.p. air-cooled engine and an extra cockpit, so making it a lively, if rather cramped, two-seater.
Economy after the war was so rigid that even the United States, very much the rich relation even in those days, operated its air mail services across the American continent with converted D.H.4 day bombers, of which they had a vast surplus. A type of civil aeroplane did emerge from this period of economy, and that was the single-engined six or eight-seater biplane. These aeroplanes took a very similar form: a span of about 45 ft., an engine of 300-400 h.p. and a deep fuselage almost filling the gap between the planes. More often than not the pilot sat behind the cabin where his forward view was far from good but where, as Frederick Koolhoven a rather cynical
Dutch designer is reputed to have said, "The pilot will probably survive the crash and I shall get an intelligent report of what went wrong." In some designs the fuselage filled the whole gap between the wings and the pilot sat just ahead of the top plane. In those days it never occurred to anyone to improve the pilot's comfort and efficiency by putting him in an enclosed cockpit. Since the journey from, for example, London to Paris took about two and a half hours there was considerable fatigue when flying in winter weather.
The reason why, on these single-engined types, the pilot was placed aft or ahead of the wings was once again a question of balance. The crew is a fixed quantity in the weight of an aeroplane, since it can scarcely fly on its own, and can therefore be placed well away from the centre of gravity. The centre of gravity (c.g.), the point at which the whole weight of the aeroplane is pivoted, must lie within relatively small limits— usually not much more than a foot. To achieve this balance any movable load, fuel, passengers and freight, must be distributed about the c.g., not all lumped behind or in front of it. Since the c.g. of a conventional aeroplane is located near the leading edge of the wing, the cabin always straddles the wing chord. Fuel, a weight that varies in flight, is also put in or near the wing so as to reduce the amount of trim change that will occur as it is used.
These early air liners had their cabin-load of passengers between the wings, their fuel usually in tanks mounted under the top planes and the engine and pilot balancing each other in front and behind the wings. Where the designer managed to get the pilot ahead of the wings, to improve his view, the nose was usually very short because of the weight concentration, so that the cockpit was noisy and cramped.
In the early twenties, as air travel became less of a novelty there was more need for larger aeroplanes. This need was met mainly by twin-engined biplanes that were usually built in parallel with their bomber counterparts. As examples, the Handley Page W.8 air liner and the Hyderabad bomber were almost identical as aeroplanes save for the cabin for 14 in the one and the bombs and gun positions in the other. Similarly in France, the bulky Farman Goliath served the air force and the air lines.
All these aeroplanes clung closely to the conventional, both in layout and in structure. Here and there a designer tried to "clean up" the outline by reducing the number of wires and struts and by improving the fuselage shape, but little real originality was apparent at that time. An exception was, once again, Antony Fokker. Toward the end of the war he had evolved yet another fighter, this time a cantilever parasol monoplane, the DVIII. When the War ended Fokker and his astute works manager loaded everything they could, including many completed aeroplanes and much factory equipment, on to railway trucks and, by persuasion, threats and bribery got the lot across the frontier into neutral Holland, the designer's fatherland. With this nucleus Fokker started his modest postwar business. From the DVIII layout he evolved his first civil aeroplane, the FI. This was a single-engined passenger plane with a wooden cantilever wing set on top of the steel tube and fabric fuselage—one of the first high-wing monoplanes other than the parasols.
The reason why the high-wing arrangement, which has several obvious advantages, had been neglected was the difficulty of bracing the wing. As in the case of the early Morane Parasols, designers were thinking in terms of kingposts and wires. Fokker, having discovered how to make his wing selfsupporting , saw that he could take advantage of the low-set, easily-entered fuselage, the excellent downward view for pilot and passengers and the natural pendulum stability which the layout offered. The usual way of making an aeroplane laterally stable is to give the wings dihedral, but if the weight hangs below the wing dihedral is seldom necessary.
From the first Fokker came a long line of high-wing passenger monoplanes with one, two, three and four engines (each with the characteristic Fokker structure and the Fokker commashaped rudder) that were to give K.L.M., the Dutch airline, a superlative fleet for nearly twenty years. So practical were these air liners that an American company was set up to build them in the U.S.A. and some were made under licence in this country. It was really from the Fokker aeroplanes that the idea of the strut-braced high-wing monoplane was evolved. One of the Fokker designs, the Universal, proved very successful in the backwoods of Canada and the U.S.A., where the high wing proved a great advantage over a biplane because it rose clear above obstructions whether on land or as a floatplane. American designers wanted to improve on the biplane, but they were not sure about the cantilever wing, so one or two tried a compromise . They made the structure of the wing partially selfsupporting and then held the spars at mid-span to the bottom of the fuselage by a pair of struts. One such aeroplane, normally a six-seater, was made by Ryan and with one of them, the Spirit of St. Louis, Charles Lindbergh made his non-stop solo flight from New York to Paris on 21-22 May, 1927, 3,726 miles in 37 hours, the second direct crossing of the Atlantic. That flight was the first nail in the coffin of the biplane. Although they would be the last to admit it, aeroplane designers are as fashion-conscious as the dress designers of Paris. The success of the Ryan monoplane led to a spate of high-wing monoplane designs, first in the United States, then in France, until finally the fashion reached England—but only in the next decade for the British are in all things more traditional than fashionable.
Germany was forbidden by the Treaty of Versailles from having an air force or from building military aeroplanes. This left her free to devote the money other nations were spending on defence to a state airline and this in turn germinated the Fokker seed that had been sown in the Junkers company of Dessau. The Junkers low-wing monoplane designs, originally single and two-seater military aeroplanes, were developed into civil types. First there were single-engined cabin monoplanes , such as the W34, and later came the G31 three-engined air liner which was developed into the famous Ju 52 air liner, freighter, bomber and paratroop carrier.
All Junkers designs were characterized by their light metal construction. The corrugated metal skin was very stiff and took
most of the flight loads, aided by a lattice-like internal structure with several light tubular spars instead of the two main loadbearing spars of those days. The corrugated skin also made possible lightweight, rigid fuselage "boxes" of remarkable volume. The Junkers company also discovered some of the problems connected with the low-wing layout. Lateral stability they found, had to be achieved by a considerable dihedral
angle and they also learned, through some bad accidents, about a phenomenon called buffeting. With a thick low wing a very disturbed wake is left behind as the air flow stalls and this can vibrate the tail plane to the point where it breaks off— even today this still occurs.
With the speeds of those days, say 100 to 150 m.p.h., the extra drag of the corrugations in the skin was negligible because they all lay along the line of the air flow.
The Junkers Ju 52-3m was a sufficiently successful aeroplane to last until the end of the Second World War, in which it was the principal German transport aeroplane—in fact some are still in use in France and Scandinavia in 1953. The Junkers was another nail for the biplane, or two nails if you like, since it was the forerunner of both the all-metal stressed skin and the low-wing monoplane air liners.
In 1923 a British competition was held to try to evolve a good light aeroplane for private flying. Unfortunately, the conditions were unrealistic, since the designers were asked to make two-seaters with only 25 h.p. The results were remarkable as aerodynamic-cum-structural feats of ingenuity. By great efforts weight was kept down to the absolute minimum and streamlining was of the best, so that speeds of 90 m.p.h. were attained with the tiny engines. However, only by resorting to fabric for almost everything could these results be achieved and the aeroplanes were far too delicate for everyday use in the hands of average pilots. The mistake at the Lympne trials was to place too much emphasis on fuel economy, which resulted in much too low powers.
It was in 1926 that one of the decisive events in the evolution of the aeroplane took place—and how insignificant was the occurrence at the time! Geoffrey de Havilland designed the D.H.60, Moth, two-seater. Abandoning the idea of using either an old war surplus engine, cheap to buy but extravagant on fuel, or a motor-cycle engine of inadequate power he arranged with his friend Frank Halford to make an engine specially for his new aeroplane. D. H. decided that he needed 60 h.p. to take two people around the sky at a reasonable speed in a vehicle that would stand up to everyday handling by amateur pilots. Halford used his ingenuity to make a simple air-cooled fourcylinder , in-line engine, christened the Cirrus, using as many parts and tools from the eight-cylinder wartime Renault as could be done without impairing the efficiency of the new design, because large stocks were held by the Aircraft Disposal Co. Ltd. of Croydon.
The Moth was an absolutely simple aeroplane, bearing all the old D.H. features. It had a plywood box fuselage with two open cockpits, wooden fabric-covered wings with a single pair of interplane struts on each side, the tail was also wood and fabric and of the typical graceful D.H. shape. Fuel was carried in a streamlined tank in the centre section. The undercarriage was a simple pair of steel tube vees with a cross axle and using rubber blocks for shock absorbers. One of the features that made the Moth was the fact that its wings could be folded in a few minutes, so making it possible to house the machine in a small and inexpensive shed.
The Moth proved to be the perfect compromise for the needs of the day and had a unique success all over the World. From it sprang the light aeroplane movement in Great Britain, the Flying Doctor Service in Australia, the expansion of bush flying in Canada, and many other pioneering projects in many lands. The reason for the Moth's success was a reasonable performance for a reasonable fuel consumption (about 20 m.p.g.) and simple construction without frills, so that maintenance and repair were easy and quick.
The many great Moth flights, such as Amy Johnson's to Australia, are outside the scope of this book, and a list of them would make too lengthy a digression. It is, however, interesting to recall that as the Moths sold by the hundred, so they were improved by fitting more powerful engines, until the final version, the Moth Major, had more than twice the horsepower of the original and could fly nearly half as fast again. The effects of the Moth's success were far-reaching in many ways. From it was directly developed the Tiger Moth upon which the R.A.F. pilots of the Second World War learned to fly. The Moth laid the financial foundation of The de Havilland Aircraft Co. Ltd. and focused the company's main interest, almost alone among European aircraft firms, on the civil market, while it established Halford's reputation as an outstanding engine designer and started his long and close association with de Havilland that culminated in the Ghost jet engine. So it is true to say that if there had been no Moth there might well have been no Comet.
The twenties were the years in which wood began to give place to metal in real earnest. Apart from Junkers, however, most of the metal aeroplanes were tentative efforts to replace wood by metal—not to design for the new material. In 1919 Short Brothers, Britain's first commercial aircraft manufacturers , had built the Silver Streak biplane, an all-metal aeroplane with a metal monocoque fuselage. Except for the fuselage this was a conventional aeroplane in which metal replaced wood for the framework. It was, nevertheless, a bold effort and one that was too daring to receive the attention it deserved. The British Air Ministry did, however, gradually take a lead in encouraging metal construction, but more on the lines of replacing wood by metal in the structure, so that R.A.F. aeroplanes could stand the heat and humidity of the tropics better—the Ministry showed little appreciation of the unconventional or of designing to suit the characteristics of metal. In 1923 Short Brothers built a tiny single-seater flyingboat with two 700 cc. motor-cycle engines, the Cockle, which had the first all-metal hull in the World and in the following year they built a metal hull for the F5 military flying-boat. This work was quickly followed by a series of magnificent biplane flying-boats, including the Singapore and Calcutta, for the R.A.F. and Imperial Airways. These designs established
basically the best shapes for metal construction, as well as for water performance and minimum aerodynamic drag. The hull of a flying-boat must ride well on the water, either at anchor or when taxi-ing and it must also, like a speedboat, rise up on the surface at speed so that it helps the wings to lift the craft into the air. These are quite difficult requirements to reconcile, as anyone who has seen a speedboat wallowing in a
heavy sea when at rest can guess. To make the hull hydroplane, that is ride up on top of the water at speed, there must be a step across the bottom to break the suction of the water. To reduce concussion when alighting a sharp vee bottom is required to cut into the water, this is naturally not so effective for hydroplaning as a flat surface and it throws up spray—which can blind the pilot and damage engines and propellers. The vee bottom was accepted as a necessary evil and the spray was suppressed by flaring out the chines; but this in turn led to increased air drag, so the chine flare was generally kept as small as possible until it gradually disappeared. Just as ships are tested as models, so flying-boat hulls are evolved by patient experiments with models dragged through long water-tanks.
In the late twenties, British ideas on hulls could be epitomized by the Short Calcutta fifteen-passenger flying-boats used by Imperial Airways on the Mediterranean leg, from Genoa to Alexandria, of their Empire air route to India. The Calcutta had a comfortable cabin in the hull, which was roomier than that in most contemporary landplanes, but the two pilots still sat in an open cockpit. The three engines were 525 h.p. Bristol Jupiter air-cooled radials, mounted between the wings. The empty weight was 12,804 lb.; loaded weight 20,500 lb.; the span of the larger top plane was 93 ft. and the cruising speed was 110/120 m.p.h., which was about average for 1928.
Other countries were also interested in flying-boats and in the latter part of the decade the need for metal hulls was generally recognized—plywood, however well protected, absorbed many hundreds of pounds of water in use. The Canadian Vickers company had built several biplanes for fishery and forestry patrol, while the Consolidated and Sikorsky companies had evolved parasol monoplane boats for the U.S. Navy. The Germans, however, once again showed an interest in the unusual. Rohrbach built a number of all-metal boats with cantilever monoplane wings that were a step toward the flying-boat as we know it today. These aircraft were characterized by narrow-beam hulls that were very deep and which were seaworthy in rough water. They did not take off well and for that reason this form of hull was abandoned, yet today we are returning to it and the latest ideas point to a length/ beam ratio of 12 to 1 as the most efficient.
Dr. Claude Dornier, who had designed large aeroplanes and seaplanes for Count Zeppelin, evolved his own peculiar and very effective type of flying-boat. He went straight away to all-metal construction and perhaps it was this that made him design for flat panels. The Dornier hull was a flat-decked, straight-sided affair with an almost flat bottom—not unlike a very large speedboat. Possibly this arose because most of the testing was done from Lake Constance and the comparatively sheltered waters at Friedrichshafen, where a good take-off was more important than rough-sea performance. To stabilize his boats, Dornier dispensed with the fragile wingtip floats and used stub wings or sponsons—actually called Domier-Stiimmel.
Arguments for and against these sponsons rage even to this day: one side says they are robust, have low drag, help take-off and give some lift; the other affirms that they do not stabilize in rough water, that if a sea breaks over one the boat will capsize, that their drag is deceptive and their lift negligible! Coupled to hull and sponsons Dornier had a large metal wing of parallel chord, partly strut-braced from the sponsons, and carried on struts above the hull. Engine nacelles were close on top of the wing, instead of being raised on struts.
The flying-boat designer's main problem, after he has got a satisfactory hull, is to keep his engines clear of spray, which can swamp the air intakes and break the propellers. In the biplane the wing cell is above the hull and the engines fit naturally between the planes; in the monoplane of those days the engines were usually mounted above the wing or both the wing and engines were carried above the hull on struts. In all cases this made a top-heavy aeroplane. On the water the weight of engines and wing above the hull is no help to stability and in the air there is an unusual grouping of forces. The centre of
drag is low, because of the hull, while the centre of thrust is high. This means that when the engines are opened up there is a tendency for the nose to go down and, conversely, when throttling back, the nose will rise unless counteracted by the controls. This is the reverse of normal practice and is one reason why flying-boats are generally considered to be more tricky to fly than landplanes.
The Dornier boats, the twin-engined Wal, four-engined Super-Wal and the huge Do X were all true to type, differing only in scale. They were very successful for their day, they crossed the Atlantic, were used by many countries, and a substantially similar design to the Wal, the Do 18K, was in service during the last War, yet they were a dead end in flyingboat evolution.
However, even if the Do X was no progenitor in layout, its conception was remarkable for the twenties. With a span of 157 ft. and a length of 133 ft., it weighed 61,800 lb. empty, 108,100 lb. fully loaded, of which about 11 tons was payload. It could reach 150 m.p.h. with the help of its twelve engines. This, in fact, was its trouble, there were no engines suitable
in its day and instead of four or six large units, recourse had to be made to such a large number that the complication in control runs and in tuning and maintenance were dreadful. The monstrous hull, large even today, was arranged in three decks; on top the pilots, engineers, navigators and radio men; on the main deck the passengers and freight; in the hold the fuel tanks. On one notable occasion the Do X lifted 170 passengers , a record that remained unbroken for many years, but it was normally intended to carry about eighty. The curious name was a joke of Dr. Dornier's, he said he called it "X" because it was an unknown quantity.
Perhaps the best way to wind up this chapter is to review the aeroplanes at the close of the decade, which was by coincidence a time of change in the outlook of aeroplane designers. Looking through "Jane's" for 1929 it is surprising to see so many shapes of aeroplanes that have just come to nothing; some that looked promising faded rapidly into oblivion, others that appeared quite undistinguished led long and useful lives, and a few were the clear-cut forbears of the present breed.1 In this country in 1929, we flew the world's first 200 m.p.h. fighters, the Hawker Hornet and the Fairey Firefly. These were of a new class, called interceptors, that were intended to take off and climb rapidly to meet the enemy. Until that date, fighters were expected to patrol and in all countries a speed of about 150 m.p.h. was considered adequate, since bombers could only do about 120 m.p.h. In those days there was no enemy in view, for Germany was unarmed by the Treaty of Versailles and Russia, rebuilding after a revolution, was too busy to menace her neighbours, so that air war was a very theoretical affair—almost a game. Nevertheless, the R.A.F. adopted one of these aeroplanes, renaming it the Hawker Fury and it was the forerunner of the Hurricane.
This Fury had a metal structure with fabric covering and it was in layout a biplane little removed from the Camel tradition. Two synchronized Vickers guns were still the armament and the pilot was still in an open cockpit, being given a good view by a rising fuselage line and heavily staggered wings. The engine was a Rolls-Royce Kestrel supercharged, water-cooled veetwelve of 500 h.p. in a closely fitting streamlined cowling. It was this engine, very new in 1929 (and known as the "F" type) which made possible the Fury's fifty-miles-an-fiour superiority in speed over other fighters, it could do 214 m.p.h. 1 Jane's All the World's Aircraft (Sampson Low, Marston) is the recognized annual reference book of the aviation world. ,
when most others were still at the 160 m.p.h. mark. A feature of the Fury was its low drag ventral radiator.
To keep the interceptor fighter company the Air Ministry issued a day bomber specification that lifted the speed of these machines out of the 120 m.p.h. rut, though it did not improve their striking power. The Hawker Hart had the same engine and similar construction to the Fury, but it carried two, pilot and gunner-bomb-aimer. Unloaded it could do 187 m.p.h. at 10,000 feet and reach that height in y\ minutes. But the authorities decided that the simplest way to carry bombs was to hang them under the lower wing, just as in 1918, so that the loaded (i.e. operational) performance was away below that when it was light. The Hart was basically a fine aeroplane, in fact it was too good! Its trials were so successful that an economically minded government decided to adopt it for all sorts of duties and in the next ten years it was variously accoutred for use as a ship-plane, general-purpose type, two-seater fighter, army co-operation aircraft and as an advanced trainer. Around its outside were hung long exhaust pipes, message hooks and many gadgets, until finally its failing performance was boosted by a more powerful engine and it was renamed the Hind. At a period when fourteen passengers was about the average load for an air liner Imperial Airways and Handley Page seemed very rash with their forty-seater H.P.42. True, the first of these aeroplanes did not fly until late in 1930, but they were a conception of the twenties. Experience proved that the H.P.42s were in fact well conceived and for ten years they paid their way, the eight examples having the unique distinction of flying more than ten million miles (over 100,000 hours) without a fatality. This wonderful record had a sad ending, because one aeroplane was lost without trace in the Iraq desert during the War.
To achieve a layout that would accommodate forty passengers in the comfort required, and it was true luxury equal to Pullman rail travel, the designer adopted something like a flying-boat layout. The cabin portion of the fuselage was a plump light-alloy shell with a corrugated outer skin and a plywood lining. The passenger accommodation was divided so that there were two cabins, each seating 20, in front and behind the wings, with the freight compartment in line with the engines —a precaution against noise and broken propellers. In point of fact a propeller did break once and the pieces flew off damaging the fuselage and breaking two of the other propellers. The pilot landed the loaded aeroplane in a field with no further
damage than a broken tail, which caught in a hedge. This forced landing was unexpected with a four-engined aeroplane, but the 50 m.p.h. stalling speed of the H.P.42 made it possible, whereas it would have meant almost certain disaster with today's landing speeds.
But to return to the H.P.42. The pilots had an enclosed cabin in the nose and, also almost unique, controllable pneumatic wheel brakes were fitted. The biplane wing cell was mounted above the fuselage with the lower centre-section cranked downward at the roots. This gave all the passengers an unimpeded view from their large windows, permitted entry without steps and allowed the engines to be grouped closely round the centre-line of the aeroplane. The wings had a metal framework with fabric covering and the interplane struts were arranged to avoid wire bracing, with its consequent maintenance adjustment. The rear fuselage was made from metal tubes and covered with fabric. The tail was a biplane affair in order to give enough surface for stability and control, although a monoplane shape was originally planned. The H.P.42, known incidentally as the Heracles class when fitted as a forty-seater for the European routes and as the Hannibal class when equipped as a long-range eighteen-seater with extra freight space for the Middle East routes, was an outstanding example of designing for a purpose.
A comparison of the H.P.42 with the forty-seater Vickers Viscount of today makes an interesting commentary on design progress over twenty years—the Viscount figures are in brackets.1 Span 130 ft. (94 ft.), length 89 ft. 9 in. (81 ft. 2 in.), height 27 ft. (26 ft. 9 in.), loaded weight 30,000 lb. (56,000 lb.), payload 9,000 lb. (7,260-13,300 lb.), cruising speed 95-105 m.p.h. (340 m.p.h.). The engines of the H.P.42 were four air-cooled Bristol Jupiters of about 500 h.p. making 2,000 h.p. in all, compared with the four Rolls-Royce Dart propeller turbines of 1,400 h.p., that is 5,600 h.p. total. A feature of the H.P.42 was the fitting of automatic slots to the outer ends of the top plane. These slots were a Handley Page patent that had recently been made standard on all R.A.F. types.
Slots, or more precisely the "slats", were simply small aerofoils mounted on hinges at less incidence than the wing itself, which, remaining unstalled when the wing stalled, lifted off the wing and smoothed out the airflow over the ailerons, so that the pilot could maintain control and prevent his wing 1 The Viscount, though designed to carry 40, can be fitted for 53 passengers.
dropping with the consequent incipient spin. Developed to the full, slots can be used with flaps to make a lightly-loaded aeroplane fly at 30 m.p.h. In 1929 Handley Page built such a biplane, the "Gugnunc", for the American Daniel Guggenheim Safe Aircraft Competition and this aeroplane was the true progenitor of such types as the Fieseler Storch or the Prestwick Pioneer.
Continuing to browse through "Jane's", there are some weird and wonderful shapes in the French section, angular bombers and fantastic fighters for the most part. At the end are some graceful parasol monoplanes of metal construction under the name of Wibault. There is also the Wibault 210-C1, a low-wing monoplane fighter which, despite its fixed undercarriage and unduly thick wing section, was probably the first of the modern fighters. Fitted with a rather bulky 500 h.p. Hispano-Suiza engine (instead of the compact Kestrel) it is
scarcely surprising that the maximum speed was only 186 m.p.h.
The German section of "Jane's" reveals numerous slabsided biplane "mail carriers" and "trainers", as well as larger monoplanes that we were to realize later were disguised military prototypes for the Luftwaffe, at that time still banned by the Treaty of Versailles. The B.F.W. company had made a very attractive light two-seater low-wing monoplane, the M-23. The designer was Dipl. Ing. Willy Messerschmitt. With a plywood box fuselage and a cantilever wing, part plywood, part fabric covered, the M-23 represents the birth of the modern light aeroplane, an honour it shared with the Klemm L.26.
The American industry of the period produced a particularly undistinguished collection of aeroplanes, the biplane still predominating, remarkable for the variety of shapes there were to do the same jobs. Henry Ford was at the peak of his brief venture into the aeroplane market. In 1925 he bought the Stout Metal Airplane Co. and organized the production of the Ford Tri-Motor at the astonishing rate for 1929 of four a week. This aeroplane might well have been a Junker-Fokker design, for it was a high-wing monoplane very like the Fokker air liners and with the corrugated duralumin skin beloved by Junkers. The Tri-Motor owed its appeal to being a robust, easily maintained aeroplane with no frills. The deep, flat-sided fuselage gave a roomy cabin (with direct access from the ground) for thirteen, having six feet of headroom and four feet six inches of width. The underslung side engines, the slipstream from the nose engine and the flat "tin" sides made it a noisy aeroplane, but that mattered little in a land of noise! The thickness of the cantilever wing and the fat fuselage prevented the Tri-Motor from being very fast, but with three 425 h.p. engines it could cruise at 115 m.p.h.
On the West Coast of America, at Los Angeles, a small aeroplane company had built an unusual six-seater monoplane. The company was Lockheed, now one of the largest in the States, and the aeroplane was called the Vega. The cantilever wing and oval fuselage were so nearly the perfect combination of true streamlines that they look as "right" today as they did then, only the fixed undercarriage appears out of place in such company. Behind the sleek fuselage of the Vega lay an unconventional method of manufacture. An oval wooden monocoque with a curved taper would have been very expensive, but in this case the shell was made from spruce veneers glued together in a concrete mould under 150 tons pressure. The moulding was done in two halves and the shells were then attached to light frame members. This was obviously a quick and cheap way of making fuselages as long as enough aeroplanes of one type were bought to cover the mould costs. The Vega had a cabin for six and the pilot sat alone in a small cockpit let into the leading edge of the wing, which did little to break the general streamlining. The whole success of the Vega lay in the concentration on essentials. At first the heads of the radial engine cylinders protruded for cooling, but as soon as the N.A.C.A. cowling proved itself this was universally fitted.
The N.A.C.A. cowling is the circular hood that is now always used to improve the air flow over air-cooled radial engines. It was, in fact, the introduction of these cowlings that "made" the radial engine, since it completely overcame the drag disadvantage from which this type suffered in comparison with the water-cooled engine. Curiously, the N.A.C.A. cowling, far from being an innovation, was really a return to that used on the old rotaries.
Figures for the Vega show how good must have been the aerodynamic design. Either a 220 h.p. Wright Whirlwind or a 425 h.p. Pratt and Whitney Wasp could be fitted, data for the latter version are given in brackets. Span 41 ft., length 27 ft. 6 in., empty weight 1,650 lb. (2,050 lb.), loaded weight 2,918 lb. (3.675 lb.), max. speed 135 m.p.h. (170 m.p.h.), cruising speed 110 m.p.h. (135 m.p.h.), landing speed 50 m.p.h. (55 m.p.h.), sea level climb 925 ft./min. (1,500 ft./min), service ceiling 15,900 ft. (17,250 ft.), range 550 miles (900 miles), price £2,950 (£4,000).
Possibly the greatest influence on streamlining and aerodynamic refinement over this period was the Schneider Trophy Contest. Immediately after the War the entrants had been flying-boats, then the Americans had used some sleek Navy biplane racers on floats to win and take the Trophy to the States. In 1926 the Italians won with their even neater Macchi low-wing monoplanes. In 1927 the R.A.F. competed for the first time—previously the British entries had been private ones, not national efforts like those of the other countries— and won with a Supermarine S.5.
This S.5 monoplane was just about the cleanest thing that could be conceived in its day, and the designer was the late R. J. Mitchell, whose genius later produced the immortal Spitfire. The story of this success goes back to 1925 when Mitchell designed a racing seaplane, the S.4, for the Schneider Trophy Contest. This aeroplane met with an accident before the race, but it set up a British Seaplane Speed Record of 226.6 m.p.h. The S.4 looked very clean, with a slender fuselage and its small cantilever wings sprouting from the fairings of the side blocks of its W-type Napier Lion engine. The S.5 of 1927 had the same engine, by now giving 800 h.p., and the design was revised: the wing was dropped to the bottom of the fuselage and a system of wire bracing was carried right round the aeroplane, as it were, from fuselage top to wing, to floats, across the floats and back to the fuselage via the other wing. By reverting to wires, and they were specially thin streamlined ones, the designer was able to make his wing and float struts much thinner and so in the balance, reduce frontal area. The fuselage cross-section was made the smallest possible that would allow a pilot into it, his head sticking up in the fairing running back from the centre cylinder block. The S.6 of 1929 (there was no contest in 1928 because nobody was ready) had a Rolls-Royce "R", twelve-cylinder vee engine and this change in engine shape was the main cause of difference in appearance. Once again the fuselage, wing and float crosssection was kept to a minimum. Float lines were improved aerodynamically, and an all-metal wing replaced the wooden one of the S.5.
In high-speed flight heat is a great problem and in the ( Schneider seaplanes the difficulty of shedding waste engine heat was very great. Ordinary honeycomb radiators are efficient dissipators of heat, but they present large frontal area and drag, particularly when they have to deal with 800 h.p. as in the S.5. The solution for this aeroplane was to cover the wooden wing with a thin double skin of metal through which the cooling water was circulated. This worked well enough for a racer, although as a cooling system it was inefficient and would have been too heavy and too easily damaged for service use. In the S.6 the double-skin radiator formed the actual surface of the wing structure and helped to carry the flight loads, so saving weight and making the wing thinner. The 1,900 h.p. of the "R" engine demanded every available square inch of wing area and when the S.6B was built for the 1931 Contest even the top surfaces of the floats had also to be used to deal with the additional waste heat from the 2,300 h.p. engine fitted in this model. Oil too had to be kept cool and in all three aeroplanes the oil tank was in the fin and the coolers were the corrugated panels that can be seen running along the sides of the fuselages.
Fuel supply was another problem for these racers, a problem that increased in proportion to the power of the engine fitted. The wing was very thin, the fuselage barely large enough to hold engine and pilot, so the floats had to be used as fuel tanks. Although far from being practical vehicles, these Schneider racers provided invaluable experience in the problems of highspeed flight to the pilots and to the airframe and engine designers , so that they can truly be said to have been the founda- t tion on which the Spitfire was built. The S.5 won at 281.65 m.p.h. in 1927 and did 319.5 m.p.h. over a 3 km. course in 1928; the S.6 won at 328.63 m.p.h. in 1929, later raising the World's Speed Record to 357.7 m.p.h.; the S.6B won at 340.08 m.p.h. in 1931 (this completed the hat trick and the Royal Aero Club now holds the Trophy for all time), raised the record to 379.05 m.p.h., and then, with a special 2,600 h.p. sprint engine, ^ reached 407.5 m.p.h.—a speed that was not to become operational for fighters for another dozen years.
It is important to realize that these seaplane speeds were far above those reached by any contemporary landplanes. This may sound curious when one remembers that, however clean
were their lines, the floats had a frontal area as large as the fuselage. The reason behind this anomaly was simply that speed had been achieved by cutting down wing area, which had raised wing loadings and stalling speeds so that only the . virtually unlimited space available in the sea allowed safe take-off and landing. The two devices that were to make possible high speeds and reasonable take-offs, landing flaps and variable-pitch airscrews, were then only in the laboratory stage —they had been invented, but their uses had not been fully appreciated.
Before leaving the twenties and the ideas of speed in those days, there is one little aeroplane that must be mentioned. This is the original, diminutive de Havilland Tiger Moth, a racing aeroplane of 1927. Built partly for racing and partly for research this tiny machine showed just what could be done when a designer concentrated on one aspect of performance. With an air-cooled four-cylinder engine of only 130 h.p. and using the same approach to streamlining as in the contemporary S.5 a top speed of around 200 m.p.h. was achieved—and that without the help of a retractable undercarriage. In the hands of Hubert Broad the Tiger Moth set up a light aeroplane speed record over a 100 km. (62 mile) circuit of 186.4 m.p.h. in August 1927. There was one particularly novel feature in the Tiger Moth, the wire wing bracing resembled that of the S.5, with wires running to fuselage top and undercarriage. This was only possible because the vees were rigid, the wheels being made with internal springing—a feature later to be used successfully on R.A.F. fighters.
Finally, there is another example of the application of streamlining to a special purpose, which was to have farreaching effects in the future, the Fairey Long-Range Monoplane . This aeroplane was built for research into long-distance flying and also to attempt to gain for Britain the World's Distance Record—in which it was unsuccessful. In this design streamlining was used to reduce drag, not to raise speed, but to lower air resistance so that the aeroplane would require the minimum engine power to pull it through the air, so increasing the distance it could cover on its fuel supply. The 82 ft.-span, fabric-covered, wooden wing was, in effect a flying fuel tank' and the 500 h.p. Napier Lion water-cooled engine gave a cruising speed of 100-110 m.p.h. Because an engine sheds less heat when it is cruising well throttled, and most economically, a retractable radiator was used so that no more than was absolutely necessary need be pushed out into the slipstream
to cause drag. The Long-Range Monoplane was dogged by bad luck and head winds from the Balkans onward prevented it from breaking the World's Distance Record on April 24-25, 1929, when S/Ldr. A. G. Jones-Williams and F/Lt. N. H. Jenkins flew from Cranwell, Lincs, to Karachi, the first nonstop flight from England to India, 4,130 miles in 50 hours 48 minutes. This first Fairey Long-Range Monoplane was lost in a crash in 1931 and a second was built which, on February 6-8, 1933 set up a World's Distance Record of 5,309 miles by flying from Cranwell to Walvis Bay in British South-West Africa in 57J hours, piloted by S/Ldr. O. R. Gayford and F/Lt. G. E. Nicholetts.