The Mosquito Family Tree

by J Paul Andrews

Measured in years alone, the three-decade span immediately preceding American entry into World War II was relatively short. Thus, the events of 1911 can hardly be considered as ancient history — even in aviation. But the intervening years have brought so much aeronautical progress, have seen so many aircraft companies flourish then fail, that a present-day aircraft business operating under its 1911 leader is a distinct rarity. De Havilland Aircraft, Ltd, whose parent organization opened for business in the brightest year of aviation's adolescence, thus has a historical claim to fame almost matching the exploits of its current product, the Mosquito bomber.

Looking back, it seems that no year before or since has produced more aeronautical achievements than did 1911. In that year, M P Prier of France made the first nonstop flight between London and Paris, Earle Ovington went aloft with the world's first air mail, and C P Rodgers made the first air crossing of the North American continent. By the end of that year, military aviation was 118 years old, the powered plane had been a reality for 8 years, and 548 men in various parts of the world had been licensed as airplane pilots. Completely obscured by these more dramatic incidents, a small plant had been organized at Hendon, England, to build Farman biplanes under license. Unimportant then, that small enterprise stands today as an undertaking of greater aeronautical import than all other feats of 1911. Descendants of the first Farman built by Airco and of the first de Havilland design flown from a racetrack at Newbury, are now making the London-Paris flight a nightly routine, are carrying military mails at speeds incomprehensible to Ovington, could, if necessary, cross the United States a hundred times in the forty-eight days embraced by Rodgers' hop.

While the first Geoffrey de Havilland worked independently on his airplanes with F T Hearle, Holt Thomas, already known in aviation as a founder of the Gnome and Rhone businesses, was establishing his Farman plant in July, 1911. Within nine months, the plant had produced, sold enough planes to show a profit and convince stockholders that aviation was profitable, could be even more remunerative with expansion. When the first year's profits of several thousand dollars were eclipsed in 1912, Thomas brought de Havilland and Hearle into the company as engineers — and from that day forward, Airco's products of de Havilland genius were headed for every corner of the world. From 1914 to 1918, Capt de Havilland worked almost constantly on military aircraft designs, spent two months in France with Britain's air forces, returned to produce the DH-2, DH-4, and DH-9 before the end of the war. The latter, and the famous DH-9A, were all single-engined biplanes but shortly before the Armistice, the twin-engined DH-10, designed specifically for bombardment of Berlin, appeared on the scene. More than 250 9s and 10s were produced each month during the closing days of the war, Airco prospered until early in 1919 — then Airco gave up the financial ghost.

In 1920, the Birmingham Small Arms Company, which had taken over financially-troubled Airco the previous year, closed its aircraft department, gave de Havilland and his companions the incentive to start their own business. Quartered in rented sheds at Stag Lane Aerodrome, in North London, the new firm started operations on September 25th with a capital of approximately $250,000. During the early years, which saw profits grow from $10,000 in 1920-1921 to $20,000 in the second year, business of the de Havilland enterprise was largely drawn from conversion of military planes marketed by government disposals agencies, by production of DH-9c ships for the air-taxi service operated by Alan Cobham, and by sale of DH-34s to Daimler Airways and Instone Air Line, the former flying 100,000 miles with de Havilland equipment between April and December, 1922.

Then the firm started to move on original designs. Three DH-42s were ordered by the Air Ministry, the Australian government bought several DH-53 light monoplanes. The DH-50 found a ready market after gaining 999 points of a possible 1,000 in judging at the Gothenburg aviation meeting. By 1925, the de Havilland Moth was in use with aviation clubs in England and Australia, Imperial Airways had established air service between Cairo-Karachi with five DH-66s, DH-9As were being produced in Australia. But it was the little Moth which was to ultimately win popular favor, bring fame transcending the reputations of all preceding de Havilland types.

A small machine, with a 60-hp Cirrus fronting its pair of open cockpits, the Moth biplane first came into prominence late in 1925 when two light-plane addicts put their money on the line. One year later, the de Havilland Gypsy replaced the low-powered Cirrus, and the line was launched on a series of improvements leading ultimately to the present-day Tiger Moth with 130-hp Gypsy Major engine, the standard primary trainer for the RAF, RCAF. When popularity of the Moth pointed to greater power as the one answer for the touring market who wanted speed and comfort, the Puss Moss was introduced in 1930 only to give way in 1932 to the high-wing Leopard Moth and the small cabin-type Fox Moth. The Hornet Moth, a two-place touring biplane, appeared in 1937 and the low-wing Moth Minor completed the pre-war cycle in 1938 and 1939.

Shortly after the first Moth flew, de Havilland made an important contribution to Great Britain's entree into world aviation by introducing a series of three-engine Hercules airliners, previously mentioned as the DH-66, which served well in Australia and Africa, continuing a de Havilland reputation in civil air transport which had begun with operation of the DH-16, an adaptation of the DH-9A, on the London-Paris run in 1919. Others in this series included the Napier-powered DH-18 of 1920, the DH-34 of 1922, and the Siddeley-powered DH-50 of 1924. The biggest of the line was the 14-passenger DH-54 Highclere which used a 650-hp Rolls-Royce Condor engine in 1925.

It was, however, another de Havilland product — the inverted Gipsy Three engine — which made possible a new approach to the entire air transport field and led to development on the Fox Moth mentioned previously. With the government discouraging any forms of financial subsidy in the swaddling days of civil aviation, this four-place ship with 120-hp engine fostered the DH Dragon of 1932, gave new hope to financially-harried operators. The Dragon series carried eight passengers and baggage more than eight miles on an Imperial gallon of fuel, became the standard plane for small operators demanding economy, maximum pay load. After the Dragon came the Dragon Rapide, or Dominic, with a pair of 200-hp engines; the Dragonfly; and the four-engine DH-S6. Then the Mosquito's direct ancestor appeared on the air racing scene.

Specially designed for the MacRobertson Race commemorating the Melbourne centennial in 1934, a trio of de Havilland Comets were produced, one of them, Grosvenor House, won in record time with C W A Scott and T Campbell Black at the controls. The Comet had a thin stressed-skin wooden wing of sharp plan taper, was the first British plane designed around the combination of variable pitch props, flaps and retractable undercarriage. Americans may take some pleasure from the fact that the Comet first carried the Hamilton hydraulic props produced under license by de Havilland.

Proved successful in the Comet, the stressed-skin wood wing was subsequently developed in the 23-passenger Albatross, which in 1938 reduced the London-Paris schedule to less than an hour. This 205-mph passenger plane had four de Havilland Gypsy Twelve engines rated at 525 hp, plywood and balsa fuselage, amazing economy because of cleanliness of line. Built in substantial quantities for European and trans-Continental airline operation, these ships are still serving on routes of British Overseas Airways Corporation. However, de Havilland ingenuity of 1939 was not concentrated exclusively on wood aircraft and the all-metal Flamingo appeared about this time with two Bristol Perseus sleeve-valve engines. A high wing monoplane with inherent loading advantages, the Flamingo was built in quantity for BOAC, still serves that corporation in civilian dress while wearing camouflage in military versions.

This, briefly, is the de Havilland company up to the birth of the Mosquito two years ago. With Capt Geoffrey de Havilland, young Geoffrey de Havilland, the late John de Havilland, Peter de Havilland, and Major H de Havilland all sharing actively in the firm's operation under wartime conditions the Mosquito's family tree has only begun to grow. In military affairs today, civil and sport flying tomorrow, the company which started inauspiciously three decades ago expects to multiply its previous ninety-five designs a hundred-fold. Chances are better than even that Capt Jeff or one of the younger de Havillands will have a hand in the drafting-room legerdemain.

Part Two: The Mosquito Family Tree
Mosquitos sting at night

by William S Friedman

Few weapons were conceived in as desperate an hour as the de Havilland Mosquito. Winston Churchill, with a bulldog growl surveyed the wreckage at Dunkerque and said "and if this island should fall, we shall fight from our Empire beyond the seas." Careful plans had been laid for the mining of British aircraft plants to make sure that Hitler got only ashes and rubble if he came to claim the plants that built such magnificent aircraft. Thanks to "the few" flying Hurricanes and Spitfires, the hour for destruction never came. Out of that desperate moment, an airplane was born which almost compensates for the horror of those hours.

The possibility of losing England, building aircraft in out-of-the-way places posed a unique engineering problem. What material was universally available throughout the Empire, which could be converted into aircraft with a minimum of skilled labor? Wood was the answer. Native timbers in Canada, Australia, New Zealand and India could be shaped into planes by their own people if a proved, competent design was provided. Even if the island stood, there was a need for a multi-purpose design, a swift, low-altitude bomber that could dart under a fighter-screen and knock out a possible invasion armada. This plane would have to be built of materials that were not already in use in other airplane manufacture.

The answer again pointed to wooden airplanes, and straight to the house of de Havilland. This company, whose experience reached back to the flying industry's toddling years, had the most recent experience in the building of wooden ships. In 1934, they had built two high-speed racers for the MacRoberts race from London to Melbourne. Four years later, they turned out a 23-place plasti-plywood four-engined transport that carried passengers from London to Paris in less than an hour.

Once saddled with this job, the de Havillands put their best engineering brains to work on the project. Besides the collective skill of the entire de Havilland family, R M Clarkson, crack British aerodynamicist, and R R E Bishop, world famous structures expert, went to work on the problem. They had to design a plane that would match or surpass the combat planes which would be current when it was completed. It would have to be built almost entirely of wood, of native materials in virtually any part of the continent by workers who had never worked on aircraft before, some of whom may have thought planes to be instruments of the devil. The airplane had to be a basic airframe, convertible for many purposes, simple to maintain and easy to repair, If necessary, the single type would have to pinch-hit for an entire air force, doing virtually every job on the books.

The de Havillands took a deep breath, and during the fall of 1939, trotted out the Mosquito prototype. The Air Ministry clocked the results — "Top speed, 417 mph!" — rubbed its eyes, checked its instruments and went back to convince the chairborne members of the RAF that they weren't fooling. The Mosquito was nothing short of incredible.

By the time they were ready to produce Mosquitoes in numbers, the military situation had been evened out a little. The problem was no longer an invasion one. It was now a matter of keeping Germany's industrial and military time-table sufficiently upset while the United Nations prepared for the invasion of Festung Europa. The prototype Mosquito whose wing-span was several feet shorter than the final production type, vanished. In its place came an all-purpose airplane affectionately called Mossie by the RAF, and "that damned armed sp1inter" by the Luftwaffe.

The Mosquito, as it finally faced the enemy, has a wingspan of 54.2 feet and a length of 40.5 feet. Its power plant varied a little with modification and purpose, but most of them were powered by Rolls-Royce Merlins of various marks, producing in the neighborhood of 1405 hp at takeoff.

The fuselage is as close to the true monocoque or stressed-skin structure as has been attempted in modern military aircraft. The trick in building a fuselage is not only to have a light, strong structure, but a rigid one as well. In metal aircraft, this is solved by building a series of transverse bulkheads and stiffeners to establish form, connecting them with longerons and stringers and covering the frame with a riveted metal skin. This process, while unquestionably successful, has several disadvantages. First, hundreds of man-hours are spent cutting, shaping and riveting. If ordinary button or brazier-headed rivets are used, they stick out into the air stream like so many half peas, sacrificing many valuable mph in top speed through increased drag. The metal skin itself is not totally rigid, and, particularly in broader surfaces, tends to wave a little between fastening points. This waviness or "tincanning" also slows the plane down.

The Mosquito's fuselage is all wood, a complete structure, formed into one piece without the aid of screws or rivets. The basic material, a standard wood veneer, is built up into shaped plywood on either side of a balsa core. The balsa has no structural strength of its own, but is used to stabilize the veneer, turning the entire unit into a single continuous box spar. The veneer which actually carries the stress is spruce, birch, mahogany or certain native woods which have been tested and found suitable for Empire production.

The fuselage is built by the bag-molding process, one that was pioneered in the United States by Eugene Vidal, Virginius Clark and other experts. These men, remembering the success of wooden planes like the Lockheed Vega, realized that structural and operational failures attributed to wood were usually traceable to the glues that were used. Milk-based casein glues were dissolved and softened by water, while the blood-albumen or hot glues were subject to bacterial decay. When plastic glues, phenol and urea resins were introduced, they made possible the creation of weather- and decay-proof wood structures of great reliability.

The process of bag-molding worked something like this: first a mold was cast for the part. In the case of the Mosquito, the first master-molds were made of wood. Then the dimensions of these patterns were recast into concrete, and the production molds carefully finished to find tolerances by power tools. These molds contained slots into which the plies for building up bulkheads and stringers, as well as the general surface for supporting the skin.

All of the wood stock used in the building of the airframe was treated with the plastic glue. The strips for the bulkheads were dropped into the proper slots. This was followed by the inner skin, layer on layer of mahogany and spruce, less than 1/32" thick, wrapped in opposing spiralled laminations for strength. This was followed by the balsa planking, with solid ash gussets at doors, windows and fitting points where the extra strength was needed. Then the outer skin was applied in the same manner as the inner one.

In the Mosquito, the two fuselage halves are completely fitted with seats, instruments, control wires, etc., before the longitudinals are assembled by heat-bonding to make a whole fuselage. Once this is done, it needs only to be fitted to the wing and power plant and have the tail assembly attached.

The Mossie's wing is a simple, one-piece full-cantilever structure, built up of two box spars. These are made up of spruce flanges, connected by a birch web. These are connected by simple compression members and built-up plywood ribs. The lower surface of the wing is a simple sheet of plywood screwed and glued to the ribs. The upper surface is a preformed surface, a double plywood skin separated by hardwood spacers. This turns the entire upper section into a strong, stress-bearing unit of great strength and absolute stiffness. This is vitally important in the wing surface, as tin-canning here costs a lot of performance at high speed.

Ailerons are the only metal part of the airframe. They are conventional light frame structure, sheet-alloy-covered. The slotted flaps are of the same balsa-core plywood as the rest of the airframe.

The Rolls-Royce engines are mounted on welded steel-tube mounts, bolted to the front spar. Radiators are installed in the leading edge of the wing, between the engine and the fuselage. The retractable landing gear swings backward into each of the underslung engine nacelles. Internal tanks are self-sealing, and adequate armor is provided for the cockpit and vulnerable parts of the engine.

All Mosquitoes are two place planes, but the crew's jobs vary with the ship's function. Most Mosquitoes in current use are day fighters, built to blitz Europe, concentrating particularly on railroad and motor traffic. These are Mark II Mossies, with a solid nose, carrying 4 20-mm Hispano cannon and 4 .303 Browning guns. These babies roam up and down the continent, with the aid of a couple of disposable wing tanks, shooting up locomotives, small coastwise vessels, knocking operational crews from canal locks, shooting up radar stations and keeping tired AA crews on their posts at all hours. A recent bit of captured correspondence, picked up in Russia from a Luftwaffe pilot stationed in France, stated that if those d—d armed splinters would stay home once in a while, the boys could occasionally get home on pass.

The next most important job is that of bombing. The Mossie's first appearance was the transparent-nosed bomber version. In 1941, they dropped in on Oslo to help Vidkun Quisling open a convention. The Mossies adjourned the meeting — to the air raid cellar. These same ships pushed Herman Goering off the air on the tenth anniversary of the Munich Putsch and have raised enough hop to make the Luftwaffe madder at the 'skeeter than at the Lancasters.

The full bomber version carries 4 500-lb bombs in a belly bomb bay. It flies unarmed, depending on its speed and climb for getaway. Once it drops its bombs, it slips into the pursuit class for top speed. On some of the bomber missions, fighter Mossies go along just to confuse the Luftwaffe. There is a fighter-bomber version of the Mosquito which carries 1000 lbs of bombs and 4 20-mm cannon. This type was used in Africa, Malta, and was quite successful against surface vessels and even subs. In the bomber-conversion, the pilot flies the ship, the observer drops the bombs, runs the radio, navigates and keeps an eye out for the enemy. In the fighter-bomber, the pilot also handles the guns. In the straight fighter version, the observer's job is chiefly navigation, as the high-speed Mossie can get lost in a hurry if someone doesn't watch the terrain.

The night fighter version of the Mossie carries a lot of radio and ranging equipment, and has done more about clearing the air over England of night intruders than any other ship. Recent reports indicate that the "armed splinter” may be dropping the flares that light the target for some of the RAF's recent block-buster raids over German industrial targets.

Photo reconnaissance is one of the top 'skeeter jobs. Packing up to three cameras, the little ship has slipped into such places as the Reich's main experimental station at Reichlin, taking air views of their hush-hush planes, while the Ack-Ack blaze away in vain.

There are a couple of more jobs for the Mossie which do not bear discussion. However, it might be some post-war indication of the ship's usefulness to point out that recently, a Mossie was completely demilitarized and put into fast mail and courier service. One of the most vicious of the twin-engined types is to date a prospective useful citizen in the post-war world of air commerce.

This two-part history article was originally published in the January and March, 1944, issues of Air News magazine: Part I, vol 3, no 6, pp 22-25, 46; Part II, vol 4, no 2, pp 46-48.
Part I includes a portrait of Captain Geoffrey de Havilland, a photo of the Mosquito, and a three-page foldout chart (PNG, 3.8MiB).
Part II includes 26 photos.
Photo credits:
    Part I: Air News drawings by Perry Fuller, photos not credited;
    Part II: British Information, International, deHavilland, Rudy Arnold Photos.