De Havilland Canada Chipmunk

Description
Shortly after the end of the Second World War, the RAF had a need to replace the ageing Tiger Moths initially issued to the numerous post-war Reserve flying Schools and University Air Squadrons. Studies of the needs of these units led early in 1948 to the issue of Specification T.8/48 for a new elementary trainer of more advanced monoplane design, and two contenders emerged, the Fairey Primer and the de Havilland Chipmunk, both based on existing aircraft.

The Fairey submission was a development of the Tipsy M, which had been built by their Belgian subsidiary company, Avions Pairey SA, at Gosselies, to the design of E.O. Tips, who designed a series of Tipsy light aircraft both before and after the war. Hopeful of an order, Faireys brought over the first prototype OO-POM, which with manufacturers marking G-6-1 was flown briefly before being dismantled at the Hayes factory, where jigs were then made for its intended production.

The position at de Havillands was somewhat similar, their Canadian subsidiary having already built an elementary trainer as an intended replacement for the Tiger Moth in service with the Royal Canadian Air Force, By the time the Air Ministry Specification appeared, early examples of this machine were already in Britain.

The Ministry of Supply invited tenders on the basis of a minimum order for 100, with provision for further orders up to a possible ultimate 750, Both tenders were submitted in mid-late 1948, and Faireys offered to build 100 Primer airframes at £2070 each, this price reducing to £1405 each for the next 150, £1360 for a further 250 and £1320 for a final 250. The firm proposed delivery of the first batch within l3-l4 months of a contract being signed,

De Havilland's first bid. submitted around the same tirne, was considerably more expensive. They could provide an initial l0O machines for £4400 each, deliveries commencing in April 1949 and ending in March 1950. If the order was increased to 250 machines, this could be completed within three years and the price for each machine would drop to £3135. An increase to 500 machines over four years would reduce the unit price to £2750, and an order for 750 over five years would bring a final reduction to £2620 each, The quotation in each case would include £100 per machine to help their Canadian subsidiary recover its design and development costs, These prices did not take into account fitments, such as engines, propellers, instruments, radios and harnesses, all of which would have to be provided by the Ministry

Early in June, having learned that they were in danger of losing this contract, de Havillands had second thoughts, They wrote to the Ministry suggesting that they had not appreciated that their quotations were intended to be taken as a competitive tender, and said they were not yet in a position to put in a firm price. They asked for an opportunity of reviewing their costs of manufacture to see if this could produce a lower production figure.

The outcome was a fresh letter to both companies in late july inviting formal tenders in competition. Before the tenders would be considered, however, an example of each machine, equipped to RAP standards, had to be provided for comprehensive evaluation and tests. De Havilland accordingly made available the tenth Canadian production machine G-AJVD. This was still to specification T6/48, but it was decided to issue a fresh specification, T17/48, for the Primer, the machine submitted being G-ALEW. which had the manufacturer’s marking G-6-5, and was fitted with a l55-hp Blackburn Cirrus 3.

ln the meantime both firms had taken a fresh look at costings, and Fairey had now increased theirs slightly, ranging from £2150 each for the first 100 down to £1380 each for the last 250. De Havillands, however, had evidently realised that their original pricing put them in danger of losing this prized contract, and were now quoting a much-reduced flat rate of £2100 each for 100 upwards, irrespective of the size of the order.

Both machines were delivered in November 1948 to the Aeroplane and Armament Experimental Establishment at Boscombe Down for an urgent test programme, and the evaluation reports were ready by mid-December. It emerged from this that the Chipmunk had a slight but definite superiority in both handling characteristics and ease of maintenance, though the Primer scored slightly in ease of repair. The only real criticism of the Chipmunk was that it would not spin very easily, but it was thought that this could be cured by a simple modification to the rudder.

De Havilland's costings still remained at £2100 per machine, but Faireys had in the meantime substantially revised their tender upwards, to give a new price, ranging from £2590 each for the first 100. dropping to £1750 for the last 250. Over a lengthy production run this would still work out less than the Chipmunk, but by now the initial need was seen as only 200 machines, at which number the Chipmunk came out substantially cheaper. Combined with the more favourable evaluation report this left no doubt as to which firm would win the contract, and on 25 February 1949 an order was placed for 200 Chipmunks T.l0s.

The Chipmunk owed its origins to an idea by an exiled Polish designer, Wsiewolod 1. Jakimiuk. He had been responsible before the war for a number of designs built by PZL, the Polish National Aviation Establishment, and had also worked on the de Havilland D.H.95 flamingo. ln June l940 he was offered to the Canadian Government by the Polish Government-in-exile, and accordingly joined de Havilland Canada. By 1943 his desk carried a model of an idea for a low-wing monoplane trainer to replace the Tiger Moth.

With the end of the war in sight it was possible to devote design time to this concept. The first prototype Chipmunk, as it had become, flew at Downsview, Toronto on 22 May 1946 in the hands of Pat Fillingham, a test pilot sent from the parent Hatfield company. Registered CF-DIO-X, it was of all-metal stressed-skin construction. and had a typical de Havilland elipticalshaped fin and rudder, similar to that of the Mosquito. The first flight was uneventful, and it looked from the start as if the firm had a potentially successful machine on their hands.

A few relatively minor problems were experienced. The metal fuselage was found to respond to the frequency of the engine, but the resulting vibration was cured by fitting firmer rubber engine mountings. A slight aileron over-balance was cured by a quarter-inch droop. The top was cut off the rudder at one stage to improve stability. but this idea was soon abandoned. After several attempts to improve stalling characteristics, stall bars were fitted immediately under the leading edge of the wings, After modification, the prototype was shipped to England. and on 15 January 1947 flew at Hatfield, being later re-registered G-AKEV.

Further modifications were incorporated in the British version. ln place of the original D.H. Gipsy Major lc engine, the RAF specified a 145 hp Gipsy Major 8 with a Coffman cartridge starter, Two 12 volt batteries were fitted in a special compartment aft of the luggage locker, and redesign of the panel and coaming was necessary to enable a standard RAF blind flying panel to be fitted. These alterations resulted in the Centre of Gravity moving forward, and there was now some tendency to ground-loop and stall recovery was inadequate. These problems were overcome, however. by raking the undercarriage forward three inches, increasing the rudder area, and fitting spinning strakes.

Initial deliveries to the RAF began in February 1950, but a second order had already been placed in May 1949 for a further 100 machines. The first units to receive them were the Oxford and Cambridge University Air Squadrons, quickly followed by No 22 Reserve flying School at Cambridge, and by the end of 1951 most units of these two types had been re-equipped. Due to expansion of the RAF as a result of the Korean War, five Basic flying Training Schools were set up in 1951 and 1952, and these too adopted the Chipmunk as standard equipment. Aircraft were also required for a rejuvenated Rhodesian Air Training Group, and further orders were consequently placed, eventually bringing total RAF production orders to 740 aircraft. The final order was placed in December 1951, though many became surplus when all the Reserve flying Schools were closed during 1953 and 1954 for economy reasons. Four members of the Royal Family have so far flown solo on the Chipmunk - Princes Philip, Charles, Andrew and Michael of Kent.

In addition to RAF service, small numbers have served with both the Army and the Navy. When the Army Air Corps was set up in September 1957, the Elementary flight at Middle Wallop received 25 Chipmunks, and this unit still exists under the title Basic Fixed Wing flight. The fleet Air Arm did not get Chipmunks until 1966, however, when the Britannia flight of the Britannia Royal Naval College at Dartmouth received l2 Chipmunks, these aircraft being still based at Roborough, Plymouth, giving air experience to naval officers.

The type was slowly phased out of service beginning in the late 1950s, although in the ab initio elementary training role, this did not happen in the Royal Air Force until 1996, when it was replaced by the Scottish Aviation Bulldog.

Many Chipmunks that had been in military use were sold to civilians, either to private owners or to companies, where they were typically used for a variety of purposes, often involving the type's excellent flying characteristics and its capability for aerobatic manoeuvres. More than 70 years after the type having first entered service, hundreds of Chipmunks remain airworthy and are in operation around the world. The Portuguese Air Force still operates six Chipmunks, which serve with Esquadra 802.