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Aviation History
1919
1919 - 0207.PDF
FEBRUARY 13, 1019 THE CHRISTMAS 5TRUTLESS BIPLANE * SEVERAL attempts have been made for years by experimenters to perfect an aeroplane with flexible wings, or following closely the flexibility of the wings of a bird. The biplane designed by Dr. W. W. Christmas appears to have met with much success in the structure mentioned, and his theories of flexing wings have shown more practicability than most rigid-wing adherents were apt to believe possible. The British and French Governments have manifested considerable interest in this machine, probabh because of reports of the great speed accredited to it. by the resiliency of the wings. It would seem that such con struction would result in a low factor of safety, but the designer claims a safety factor of seven throughout. When at rest on the ground, the wing droops in a negative dihedral of -17 degrees. In flight the wing tips have a range of flexibility of 3 ft. ; that is, the wings can assume positive or negative dihedral measuring iS in. from the horizontal in either direction. It has been demonstrated that the wings carry a load no greater than necessary to sustain the machine in flight, and THE CHRISTMAS " BULLET."—Front view showing the absence of struts and bracing wires. A most radical departure from what has heretofore been believed to be necessary practice is the entire elimination of struts, cables, and wires in the bracing of the wings, as well as the absence of wiring in the internal structure of the wings. The wing curve is one developed by Dr. Christmas, and is of fairly deep section between the main wing beams, but tapering off sharply aft of the rear beam, and merging into a fiat thin, flexible trailing edge. The effect of the section is to maintain a high angle of incidence as the machine is travel ling at low speed, and a low angle as the machine gathers speed, flattening out the wing and presenting very little resistance. Upper and lower wings have the same aspect ratio. Upper wing has a thickness of 5 in. Patents are pending on the wing construction, and full details cannot now be given of these features. With the wing section used. Dr. Christmas has succeeded this load is carried regardless of wind puffs or extra strains due to increased wind pressure above or below the wing. The principal specifications of the Christmas " Bullet" are as follows :— Span, upper plane .. .. 28 ft. Span, lower plane Chord, upper plane .. Chord, lower plane . . Area, upper plane Area, lower plane Length overall Weight, machine empty Weight, fully loaded Minimum speed Maximum speed Cruising radius Ceiling 12 ft. 5 ft- 2 ft. 6 in. 140 sq. ft. 30 sq. ft. 21 ft. 1,820 lbs. 2,100 lbs. 50-60 m.p.h. 175 m.p.h. 550 miles 14,700 ft. E E m The Christ mas " Bul let": Three- quart e r view T from front. • ; • H HE E B E E E E E E E E E E E in obtaining a 72 per cent, lift on the upper surface, a higher vacuum than found on any other section. Winp are set at an incidence of 3J degrees. > As the wings are not braced transversely, flexibility is also obtained in that direction. Puffs of wind or sudden changes of direction, do not sharply affect the machine's progress, for the shock is transmitted only after being partially absorbed • Courtesy Atrial A ge, M.Y. A Liberty " 6 " is used, giving 185 h.p. at 1.400 r.p.m. ; the machine attains 170 miles at three-quarter throttle. The weight fully loaded is with 50 gallons of gasolene and ""5 gallons of oil, sufficient for a sustained flight of three hours. The " Bullet *' was originally designed as a single seater fighter. The pilot has an unobstructed range of vision, as his eyes are at the level of the upper plane and the lower plane has such a narrow chord that it offers but very little 207
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