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Aviation History
1920
1920 - 0320.PDF
in resistance, running angle and stability was very satis- factory. Results obtained in trial flights with America and P/5 machines have also confirmed isolated detail predictions based on tank experiments, and warrant the use of model results for estimating work. 17. Wing Floats.—These are secured to th« under-side of the lower wing, immediately below one of the struts. When planing at high speeds, both wing floats should be well clear of the water. The chine line at main step will then be slightly lower than the general water level, and the bottom of the wing floats should be at least 2 ft. to 3 ft. above this- level for a machine of about 10,000 lbs. weight and above.' In small machines, this clearance might lead to undesirable inclinations ; when at rest the transverse inclination should not exceed 30 to 40, and less clearance has to be accepted in their case. VT,.~- .^ ^ ;„_;,•.-..._ • .-_,."" :- :•;.--- .-v.v v- MARCH 18, 1920 TABLE V.—Some Types of Flying-boats Designed and constructed by the firms named. The speed given is that for leaving the water, normally slightly above the minimum speed for the machine. "j* '„""'*' Dimensions in Feet and Lbs. • - 'Mt^:'X:'s:/,,:• :_::,jry- Type ^••"••^T:- - a.o . t Vt- \ A is THE: LOAD DISPLACEMENT V is THET&ETTING OFF"SPEED -C.E.I.TYPE = AMERICA =FS. LOAD ON WATER = F RESISTANCE " R FIG. 3. ; -X: SPEED IN KMOTJ Fig. 3—Resistance and efficiency curves for various types . When lying at rest, with one wing float in the water, the tip of the after edge of the wing should be 2 ft. to 3 ft. above the water to be clear of the waves. If the machine is to be an- chored out, there should be such a reserve buoyancy in the wing float that, with a heavy cross wind, the leeward wing should still be above ordinary waves. For the purpose of calculating the required reserve buoyancy it has been assumed at the Tank (1) that the machine has pitched to an angle of about 120 on the wing chord (or about 70 above the " at rest " angle) ; (2) that a 25-knot breeze produced a lift on the wings of ao 3 Designed and made by Displacement lbs. normal cargo B.H.P. No. of propellers Speed, getting off in knots.. Hull Length (overall) ..Length (stem to step) ..Beam Messrs. Vickers, Son and Maxim 3,200 18,300 101,000 270 1,300 5,200 1 2 4 Supermarine Aviation Co. 2,300 — Sopwith Avn. Co. 2,150 100 1 48 49-5 About Attained 50 128 on trial. 30-2 53-0 120-0 26-0 — 10 -7 4-0 21 -6 9-0 42 9 20 -o 18-o II -2 4-0 Phoenix Cork has the hull called P/5 in the paper. Channel four-seater is somewhat similar to the A.D. type. The Sopwith Bat Boat started from the sea and settledon the land, and started from the land and settled on the sea in 1913. The Super-marine Baby was looped twice in February, 1918. 2 -5 lbs. per sq. ft., and (3) that the centre of pressure of both wings on the windward side was one-third their length from the tip, and on the leeward side one-third their length from the hull. Knowing the wing surface the tipping moment for a 25-knot breeze can be obtained, and the buoyancy required at the wing float position is then easily obtained The clearance of the wing tip, when the wing float is immersed, to give this extra buoyancy would depend upon the service and size of the machine. Consistent with satisfying these requirements, its cross section area should be kept as small as possible, so as to avoid wastage of wing surface (shrouded by the float) and head resistance. 18. Stresses on the Float Hull due to Water Action.—To determine the stresses coming on a hull as a whole, the ordinary bending moment calculations have been made for a hull supported on wave crests at each end, and with the wave hollow amidships just touching the keel. Expressed in terms of the length (L) and displacement (A), this gave a bending moment of . If pitching takes place, dipping by the bow increases the virtual weight of all the parts for-ward and decreases at the stern. The line of action of the virtual gravity force of any weights w at y feet above or belowthe centre of gravity, is such as to give a horizontal component w d^8 d^ti of + —V-Tn' where ^ is the angular acceleration. Taking this to be -4 radians per sec, the calculation has been made for the above machine in waves. The additional bending moment is not more than 1 or 2 per cent, in this case, but may amount to 17 per cent, with other waves. If the machine is heaving so that it just does not leave the water, the water force will vary from nil to twice its steady value, and the vertical loads will be correspondingly increased, giving a B.M. of — AL. When heaving with longitudinal motion, although local forces may be increased, the general B.M. is less. This statement is based on a calculation for the above machine at 20 knots, moving with a maximum vertical motion of 3 f.s. The actual angle of attack of the planing bottom varied from 140 to 40, its normal angle at this speed being 90. The forces at various immersions, and relative motions, have been calculated, and the B.M. obtained in this way was A of AL. The worst B.M. likely to be met is of the order of 1/5 AL. NO general system of calculating these stresses on the hull has been adopted so far, and it would appear that until further knowledge has been obtained, the worst B.M. may be taken as twice that 320
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