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Aviation History
1954
1954 - 0444.PDF
204 FLIGHT BEAVER IN MEXICO ... to lunch at the businessmen's club at Pachuca. After making arrangements to meet the official party again at the airport at 2.45 p.m., we had lunch and returned at 2.30 p.m., only to find the Governor and his party had been at the appointed place at 2.15 p.m., and had since started for Mexico City (too many interpreters, I guess). We took off and Doug flew full speed at tree-top height along the highway, eventually overtaking the Governor's station wagon, which was barrelling along with siren going and red fender light blinking. We circled the car a couple of times and then landed at an abandoned military strip, fortunately only about half a mile away. Paddy Kissack and I exchanged places with the Governor and his daughter. They took off in the Beaver and we also took off (literally) in the station wagon, which was driven by the chief of police, complete with .45 and sub-machine.gun. I enjoyed that ride to Mexico City; I was sure everyone we passed thought we were either important officials or political prisoners. A couple of days later I returned to Toronto. Doug Givens and the Beaver continued the tour, flying over most of Northern Mexico and visiting and demonstrating at some of the highest airstrips in the country, including Tobica (8,900ft a.m.s.l.), Uruapan, Guadalajara, Tepic, Mazadan, St. Ignacio, Tayalitito, Cerliacan Bamoa, Los Mochis, Chihuahua, Torreon, Gomex Palacio, Saltillo and Monterey. At take-off from these places with crew of two, baggage and full tanks, the Beaver's gross weight was about 4,200 lb. BEAVER FOR EUROPE How the Alvis-engined Series 2 was Developed THE experiences with the D.H.C. Beaver 1 recounted in the preceding article add particular interest to the following account, from information provided by the parent de Havilland company, of the development of the design into the Series 2 ver sion with more powerful Alvis Leonides engine. This machine has even better short landing and take-off characteristics than the P. and W.-powered version demonstrated in Mexico. Some comments on the handling of the Series 2 prototype, written by the Editor, were printed in our August 21st issue. Brief comparative data are given below. The Series 2 development was undertaken with a view to producing a "European" version. With the Beaver's world-wide usefulness its application in Europe tended, obviously, to become a question of economics. The modification, therefore, centred upon introducing a European engine into the basic airframe, and enhanced performance was an additional result. The engine selected was the 550 h.p. Alvis Leonides 502/4 with a de Havilland three-bladed airscrew. Initial studies showed that maximum gross weight would thus be increased to 5,100 lb, and that landing and take-off performance would show an im provement over that of the Beaver 1 despite the increase in power-plant weight. Before the English engine and airscrew arrived in Canada, initial modifications were undertaken, aimed primarily at improv ing the landing performance in readiness for the increase in weight. Two measures were successfully applied. Firstly, the incidence of the wing was increased from zero to +2 deg by modifying the rear wing-root attachment fittings. Secondly, the wheel brakes were improved—this had to be done in any case, in order to hold the increased thrust of the Leonides during ground running at full power. The brakes themselves were felt to be adequate for the new loads, and it was a question of "stiffening" the brake circuit and achieving maximum brake power with less pedal deflection. To this end, a mechanical connection was installed which positively linked the left and right rudder pedals. The results of these modifications were highly satisfactory. Pilots found it possible, in landing, to stall the aircraft neatly onto three points with no danger of touching tail-first. The increased wing incidence gave greater drag during the ground run, and the flap and drooping-aileron high-lift system of the Beaver 1 was not interfered with. Further braking effect was expected from the increased windmilling drag of the new three-blade airscrew. The next line of development clearly centred round the fin and rudder arrangement. It had been found in the Beaver 1 that it was tiring to maintain a set heading during protracted stage- lengths, especially in the seaplane version. The prototype Otter also showed a tendency to yaw due to engine torque, which at times was sufficiently pronounced to cause fin stall. To improve weathercock stability, as well as to allow for the increased torque of the Leonides, a new fin and rudder were designed, providing an area increase of no less than 65 per cent over the original, yet still using the same mounting points. A rudder tab was incor- Though a demonstration take-off picture of this kind is not necessarily proof of performance, the Series 2 beaver has, in fact, an exceptional ability for getting away in lively fashion, even at full load. porated to allow for asymmetric external loads, and the rear fuselage was strengthened to accommodate increased side-loads. The incidence and brake modifications were first flown in Decem ber 1952, and tests on the new fin were carried out in January 1953, both on the D.H.C. factory's own experimental Beaver. In February the engine and airscrew arrived from England and were weighed. It was found that the new combination would entail an increase of 96 lb in empty weight, although subsequent modifications might reasonably be expected- to reduce this penalty. The Leonides, 100 h.p. more powerful than the Wasp, weighed some 107 lb more, while the airscrew was 10 lb lighter, despite its three blades and 6in greater diameter. The addi tional 100 lb in the nose caused no e.g. troubles. At full load, the e.g. of the Beaver 1 was in any case near the after limit, and could be allowed to travel forward without adverse effects. In the half-loaded condition, the slight risk of nosing over on using full brake during landing could conveniently be counteracted by the addition of a small quantity of ballast, or by the weight of such radio equipment as a customer might specify. A set of cowlings had been made before the Leonides arrived, and as soon as the engine mounting (of welded steel tubes) had been constructed the power-plant was fitted. Some difficulty was experienced with pipe connections, since the engine had English threads and the airframe American. Adaptors were, however, quickly produced. The accessory-compartment cowl ing and the induction system were finally added, with carburettor intake ducts so arranged that air could be drawn direct through an under-engine scoop, or alternatively through a filter or between the cylinders, as required. While this was being done, extensive instrumentation was installed, complete with auto matic recording camera. Early test flights revealed no major snags. It was found, however, that the engine ran slightly hot during the standard five-minute climb at take-off power. Wool-tufting revealed poor airflow from under the cowling immediately forward of the windscreen; this section was therefore blanked off and the lateral openings slightly extended. The tufts, incidentally, were photographed from another Beaver flying in close formation. Although as lightly loaded as possibleg the photographic machine had difficulty in keeping up with the Beaver 2 on the climb. These engine tests had shown that a slightly smaller vertical tail would suffice. One was accordingly constructed, and was fitted at the end of the test programme. Stability tests (for which a large boom with swivelling pitot-head and yaw-and- pitch vanes was fitted, as well as extensive instrumentation) raised no snags. The only criticism was that the aircraft tended to roll to the right at the stall before developing a definite nose-down pitch. This was remedied by slightly off-setting the fin; thereafter the normal coarse use of rudder corrected wing- drop at the stall. The Canadian Department of Transport's approval tests followed immediately on the company's own flight tests, and only 23 weeks after the beginning of the Series 2 development the aircraft was fully tested and approved. As noted in these columns last year, the Beaver 2 then came to England and was demonstrated at the S.B.A.C. display at Farnborough. Beaver Series 1 and 2 Performances at 5,100 lb a.u.w. Series 1 Series 2 Max. cont. weak cruising 133 m.p.h. 138 m.p.h. S.I climb max. power (S min) 1,100ft/min 1,4«0ft/min Service ceiling 19.500ft 23,000ft Range, cruising, 1,000 lb payload, with fuel reserves 600 st. miles 600 st. miles Min. take-off to 50ft 300 yd 250 yd Min. landing from 50ft 0 yd 300 yd
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