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Aviation History
1953
1953 - 0012.PDF
12 FLIGHT, 2 January 1953 Honningstad Finnmark Amphibian Ingenious Dowty-designed Skij Wheel Undercarriage DESIGNED by Mr. Birger Honning stad, the company's technical mana ger, the Finnmark amphibian is built by Norsk Flyindustri A.S., of Fornebu, near Oslo, Norway. The prototype now flying is designated Finnmark 5A, but an improved version will be known as the 5A-II. The Finnmark was designed to suit the special climatic conditions prevailing in Northern and Arctic regions, and is powered by two Pratt and Whitney Wasp R-1340- S1H1 engines. We are informed by Mr. Honningstad that the machine has success fully completed about 150 hours' test-flying and has shown very good handling qualities both on sea and land. The combined ski/ wheel undercarriage "works according to plan" and has no noticeable effect on the exceptionally good seaworthiness inherent in the sponson-equipped type of flying boat, of which the Finnmark is an example. The sponsons serve not only to provide lateral stability on the water but to accommodate the special retractable ski/wheel assemblies. The undersides of the skis fit snugly into the sponsons when the gear is raised and form a flush surface, except for part of the landing wheel, which protrudes slightly below the ski. Al though in the accompanying photograph no tailwheel ski is seen in place, this is, in fact, being installed for a new series of trials. The undercarriage was designed and built by Dowty Equipment, Ltd., working in close collaboration with the Honningstad design staff. Each half consists of a main leg, the lower end of which incorporates a lever-type liquid-spring shock-absorber, and which is attached to the front spar of the sponson. Retraction is rear wards and a hydraulically operated linkage system is provided for up and down positive locking. The skis are equipped with trimming struts, which ensure a controlled aligning of the skis during undercarriage retraction, and maintain them at a pre determined setting on the ground and in the air. Under the influence of air or ground forces, however, they allow the skis When this photograph of the Finnmark was taken the tailwheel ski had not been installed. to deflect or rotate on their pedestals. This displacement is positively restricted until a predetermined moment is applied to the ski—a moment sufficient to prevent any ski movement due to air and inertia forces. Thus the skis are kept truly aligned and absolutely stable in the air, though on the ground they are subject to sufficiently great forces to cause them to move and thus allow them to "ride" on uneven snow or ice. The principle of the undercarriage has been the subject of patents in Norway, Sweden and Canada. "You will undoubtedly have concluded," Mr. Honningstad writes, "that a combined ski/wheel undercarriage on a flying-boat is a rather heavy weight penalty. However, the purpose of this type of aircraft must be taken into consideration. It ought to be able to perform its duty as a rescue/ambulance/freight or expedi tionary aircraft where no other type of ordinary aircraft can be used with advantage." The general layout of the Finnmark may be studied in the illustrations. There are two passenger cabins with seats for twelve, one main or baggage compartment in the bow of the hull, and one toilet or baggage compartment in the rear. Cubic capacity of the two passenger cabins amounts to 388ft. Dual controls are provided for the crew of two. The power plants are interchangeable, and each Wasp drives a Hamilton Standard Hydromatic three-blade airscrew. There are four welded aluminium fuel tanks, with a combined capacity of 3co gallons, in the outer part of the wing centre-section. Dimensions are : span, 62ft 6in; length, 46ft 4m; wing area, 522 sq ft. The following data apply to the Finnmark 5A-II arranged as an amphibian with retractable ski/wheels (the machine can readily be arranged as a normal flying-boat either with sponsons or wing-tip floats): weight empty, 9,966 lb; gross weight, 13,100 lb; maximum speed, 190 m.p.h.; cruising speed (65 per cent METO power at 6,200ft), 156 m.p.h.; rate of climb at METO power at sea level, i,iooft/min; still-air take-off distance from water, 2,080ft. Below is the Finnmark''s patented combined wheel and ski undercarriage, designed and built by Dowty Equipment, Ltd., in collaboration with the Honningstad design staff. R.Ae.C. s NEW BADGE nTHE Christmas number of the Royal Aero Club Gazette—a •*• worthy effort on which Editor H. J. Cooper deserves congratu lation—has a new cover on which is prominently displayed the revised version of the Club's badge. The caduceus (Mercury's winged staff), with its "contra-rotating" serpents, now bears larger wings; and it is now vertically placed on the burgee, with the crown above it. The change was made in order to avoid confusion with the Aesculapius, the well-known medical emblem, which the former R.Ae.C. insignia to some extent resembled. As from the January, 1953, issue, the Gazette committee will consist of the following members : S. Kenneth Davies (ex-officio, as R.Ae.C. chairman); Capt. K. J. G. Bartlett (chairman of Gazette committee); Geoffrey Dorman; Alex Duncan; F. H. W. Lucas; Col. R. L. Preston (ex-officio, Secretary-General R.Ae.C.).
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