Techtalk: Moth Handout-1

BRINGING BRITISH COLUMBIA’S AVIATION PAST INTO THE FUTURE CCAANNAADDIIAANN MMUUSSEEUUMM OOFF FFLLIIGGHHTT TTEECCHHTTAALLKK:: DDHH TTIIGGEERR MMOOTTHH The Canadian Museum of Flight is presenting a series of informal technical talks on aircraft in its fleet. These talks will cover topics ranging from the history of the com - pany; the history of the aircraft type; its development; production methods and places; the history of the engine and its development. Also covered will be the challenges in maintaining and flying these classic aircraft in today’s environment; how the mechanics find the parts and how the pilots keep current on flying a 70 year old flying machine designed before the dawn of the jet age. This will be followed by details of how the aircraft is prepared for flight; how the engine is started; followed by an engine start and flight. During the procedings a draw will be conducted entitling the lucky winner to a flight in the aircraft being discussed (some conditions apply). 2 The History of the de Havilland Moth family By 1931 the basic wooden DH60 Moth had evolved into an aircraft with a welded steel tube fuselage and 120hp engine, a combination more than capable of satisfying a growing requirement for initial training aircraft with added ca - pacity for actual or pseudo military aggression. Bearing this in mind the de Havilland Aircraft Company decided there was still potential development to be wrung out of their current airframe and even more from the engine. On 10 July 1931, an aircraft identified as a ‘DH Training Moth T1’ fitted with a Gipsy ll engine, was weighed at the de Havilland factory at Stag Lane. In most re - spects she was identical with the final specifica - tion of another aircraft which had been tested using identity E.3, DH60T G-ABNY (1724), one of three destined for China, fitted out with bomb racks and provision for wireless, electrical gener - ation and camera guns. The exception was that Training Moth T1 was fitted with swept main - planes, the top set staggered forward of the lower wings. Her centre of gravity in this configuration was closely compared with No 1724 and found to be further forward, the difference noted as being due to an increased tare weight and ‘the forward shift of petrol.’ The prototype DH60 Moth The increase in tare weight was accounted for by the addition of ‘a controlled slot locking device’ and ‘a (four) drop door fuselage.’ The petrol tap was described as being ‘cockpit controlled’ rather than positioned on the cabane where it could not have been reached from the rear cockpit. With the addition of petrol, oil and crew the Training Moth T1 was 11lb over the then maximum permitted aer - obatic weight, a detail in need of attention. According to Richard Clarkson, the solution adopted in the case of three similarly afflicted DH60Ms supplied to the Royal Danish Navy in February 1931 as Type LB Ill, 1682-1684, was simply to select the lightest components, a practicality which resulted in a saving of 18lb per machine. The new configuration of the T1 Moth had been achieved by moving the whole of the cabane structure forward of the front cockpit, removing the petrol tank from immediately above the occupants head, thus satisfying both the cur - rent views of the Canadian Government who had already declared its opposition to purchasing more aircraft in the old configuration, and as importantly, compliance with the Air Ministry’s latest trainer specification 15/31. Sweeping the wings was viewed as the most practical and economical method of recovering some of the inevitable loss of balance. It is most probable that the T1 Moth was in fact No 1705 (G-ABKS), which carried the test marks E.4 and was flown by production test pilot Jack Tyler on 21 July and by Hubert Broad later in August. E.4 never qualified for a Certificate of Airworthiness before, in this period of intense experimentation, initiative and progress, as a cob - bled together test specimen, she was declared re - dundant and dismantled. To comply with a further Air Ministry require - ment, any prospective training aeroplane had to be given a name, one beginning with the letter ‘T’ (for Trainer), and de Havilland chose the name previously applied to their experimental DH71 monoplane: Tiger Moth . The first new aircraft built with swept wings to be designated a DH60T Tiger Moth was No 1726, fitted with an inverted Gipsy lll engine and registered G-ABNI to the de Havilland DH Training Moth T1 with unswept wings Aircraft Company Ltd. on 25 June 1931. Sales Director Francis St. Barbe was concerned about the new Canadian trainer specifications of which he had been advised during an extended visit to the Dominion at the beginning of the year, a country still suffering from the effects of the Depression and with a government counting the pennies and demanding quality aircraft manufactured against very precise operational requirements. In August G-ABNI was despatched with haste to the de Havilland Company works in Toronto where her arrival was greeted with anything but enthusiasm. The second DH60T Tiger Moth, G-ABNJ (1727), wearing identity E.5, was delivered by Hubert Broad to the Aeroplane and Armament Experimental Establishment (A&AEE) at Martlesham Heath on 18 August, where the general impression gained from the trials which began four days later was favourable, except that in the opinion of her test pilots, landing in a crosswind put her into-wind wing tip perilously close to the ground and that when taxying across uneven territory, any down-aileron was liable to make contact with the surface. At Stag Lane, DH60T Tiger Moth G-ABPH (1732), was re-rigged to accept additional dihedral on the lower wings 3 D.H.82A 4 only, adequately solving both problems. Hubert Broad flew her to Martlesham Heath on 3 September from where it was reported that the change in rigging had created no adverse effect on handling. In this new configuration the A&AEE’s report cleared the aircraft as a military trainer of a type which would be acceptable to the Air Ministry. In sup - port of a prospective order from the Portuguese Government, in December, Hubert Broad delivered G-ABPH to Carlos Bleck, the Company’s agent in Lisbon, where she was sold to the gov - ernment and absorbed into the military. The Design Department at Stag Lane decided that a sufficient num - ber of major alterations had now been embodied in the basic DH60 for a new Type Number to be applied to the Tiger Moth. This was not a hasty decision, for all design and stress calculations, modification summaries and flight test reports collectively formed the aircraft Type Record held by the Design Authority. A change of Type Number usually signalled an entirely new design of aircraft requiring a new Type Record to be estab - lished, a time consuming and expensive exercise. By October 1931 the inevitability of a change of Type Number was accepted within the Com - pany and the next available was DH82. However, to avoid cost and ex - cessive administrative effort, the Type Record for the DH82 Tiger Moth continued to be referenced to the key type, the DH60X, under whose The DH82 employed a modified upper wing protection it has remained. de Havilland D.H.82 Tiger and Menasco Moths in Canada Following its incorporation in March 1928, de Havilland Aircraft of Canada operated in a sales and service role for its parent company’s products and undertook modifications to make them more suitable for Canadian operating condi - tions. In 1935 the company attempted to sell British-built D.H.82A Tiger Moths to the Canadian Government but with no results, and on 2 October, 1936, P. C. Garratt, DHC’s new manager, proposed building D.H.82As in Canada if a minimum order for twenty was received. This is the first known instance of a proposal to start manufacturing opera - tions by DHC. A contract was shortly awarded for twenty-five D.H.82As to DND specification C/18/36, and they were required to be built in Canada with changes that the RCAF called for to meet its operating conditions. The D.H.82A was the final development of the highly successful D.H.60 Moth, which had originally been fitted with the 60 hp A.D.C. Cirrus engine, later with the more powerful D.H. Gipsy I and II, and finally with the inverted 120 hp Gipsy III. When the D.H.60T with the inverted Gipsy was tried out by the RAF, improved access to the front cockpit was asked for and was achieved by sweeping back the wings. This new version was given a new type number, the D.H.82, and the name Tiger Moth. The original D.H.82 had the Gipsy III engine and when the Gipsy Major I was fitted the type became the D.H.82A. On 22 March, 1937, a meeting was held with the RCAF to agree on details of the design changes and on 14 May a set of drawings arrived from England. New buildings were started, and the British-built D.H.82A CF-AVG (c/n 3348) was dismantled and stripped to serve as a master pattern. The changes required were: Fuselage. A 2-inch (5-cm) thick foam rubber crash pad was to be fitted around the instruments. A cockpit canopy, dimensionally similar to those already installed by DHC on five British-built D.H.82As, to be constructed similarly to the Fleet 7’s. A cockpit heating system was to be installed consisting of a hot-air muff around the ex - haust pipe and suitable ducting.

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