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Aviation History
1942
1942 - 1257.PDF
JUNE IITH, 1942 FLIGHT 597 B3 = 525 also and so B = V5.25 B = 1.74ft. D = 1.74ft. L = 4 x 1.74ft. = 7.06ft. It will not be necessary to use a step on our floats as steps are seldom fitted to small designs. The float heel should be upswept to prevent it " digging in " when the boat drifts backwards, and the bows of the float should be raised to ensure getting clear of waves. The decking should be well curved to shed water and spray, and the bottom should, of course, be vee-d, flaring out towards the bows. The float should be set so that when the c.l. of the flying boat is vertical, the float should be clear of the water by about 4m. to minimise roll before restoring moment is applied. lji. Float Attachment.—The simplest form is by means "fcjf'xivo struts, one from the front spar and one from the rear, to strong bulkheads in the float. These struts can either be braced or cantilevered. We will choose the cantilever type to reduce drag and the number of bits and pieces. 19. Weight Estimate.—We have now reached the stage when we need a provisional weight estimate: This is necessary in order to check our layout drawing for correct disposition of everything in relation to the centre of pressure of the wing section. Our limiting weight of 10,000 lb. is made up as follows :— lb. Hull, 12% A/U (all-up weight) ... .. 1,200 Wing, 20% A/U . . . . .. .. 2,000 Tail unit, 2.5% A/U.. .. .. .. 250 Controls, 1.0% A/U . . .. .. . . 100 Wing tip floats, 1.3% A/U . . .. .. 130 Engine nacelles, 1.6% A/U .. .. 160 Marine gear, 2.5% A/U .. .. .. 250 Instruments, 2.0% A/U .. .. .. 200 Wireless .. •.. .. .. . . 200 Equipment at crew stations ' . . .. 70 Engine equipment : Cowling, airscrews, controls, starting, gear, etc. . . .. 240 Engines, dry wt. at 750 lb. each .. .. 1,500 Oil, 10 galls, at 9 lb./gall. x 2 .. .. 180 Oil tanks Fuel, 150 galls, at 7.5 lb./gall. X 2 .. 2,250 Fuel tanks 15° • Crew at 200 lb. each (4) . . . . . . 800 Total . . 10,000 20. The C.G.—Now that we have a provisional weight listvperhaps the most tricky part of the project can proceed. AM the components and equipment, including engines, t'rew, fuel and oil, must be so disposed as to bring their combined C.G. to a position coinciding with the centre of pressure range of the wing section of the main wing. The C.G. is found by taking moments about a reference line placed preferably well forward of the stem of the boat, on the drawing (for fore and aft position of C.G.) and about a base line placed well below the keel (for the vertical position of the C.G). Note here that in order to reduce the metacentric height, and also to minimise the likelihood of porpoising troubles, the C.G. should be kept as low as possible. We usually find that quite a fair amount of juggling is needed in order to satisfy the centre of pressure—centre of gravity—main step position, demands. 21. Load Water Line.—It is necessary to mark on the layout the water line at the design load of 10,000 lb. To do this accurately, reference would have to be made to the hull lines, but as these will not be available at this stagey of the work, a quick way is as follows : Find the len«f'?>. nf +h» 1.nil 0.67^W)4 0.O7 X (-^io.ooo)4 L = g = 6 — 28.84ft. approx. Now mark this distance on the inclined line joining the C.G. with the main step heel (see para. 8), so that half (14.42ft.) is forward of the line and the other half behind. It is better to mark the 28.84ft. on a straight line drawn upon a separate piece of transparent paper, spotting on its mid-length. Then move it up the datum line, at 90 deg. to it, until it cuts the forebody and afterbody ; mark this interception, and join up the two points and this will give the load water line position. 22. Concluding Details.—There are certain other points which merit attention in the project stage. A bow com partment complete with hatch in the top decking, should be provided, to facilitate picking up moorings, etc. Marine gear should be stowed here, such as boat hooks, anchor, mooring lines, etc. Access to the bow compartment should be as easy as possible from the interior of the hull. An entry hatch should be provided either well above the water line aft of the wing trailing edge, or preferably in the top decking. There is some likelihood of the boat being wet inside if the entry door is in the hull side. Having located the C.G. satisfactorily, it will be possible to form an idea as to where strong frames, water-tight compartments, etc., can be stationed. The structure at the main step, rear step, stern frame, wing fixings and tail unit attachments, can also be considered provisionally. 23. Conclusion.—It must be appreciated that from this stage the design, both aerodynamic and structural, really begins. It is almost certain that every point we have discussed will be rearranged and the basic project type bear little resemblance to the finalised design. The method of setting out on the design, i.e., choosing a certain wing loading and working outwards, may be open to criticism, as many would prefer to adhere to the method of choosing a lift coefficient CL equal to something or other and building the wing design around the W or L = CL|/>AV8 expression. There are other equally tricky ways of drafting out a project, but since the whole shooting match has to be changed once, changed twice, and changed again, any quick, easy method is looked upon favourably. Although performance does not really concern us on the board, it is interesting to form an idea of what our boat could achieve in stalling speed, top speed, rate of climb, ceiling (service) and ceiling (absolute). As a rough guide to the top speed, the following formula may be used. F-iJ/w Top speed = — at sea level. A In which " F "= a factor based upon analysis of known performances of similar boats and is equal to 140. 10000 = wing loading = 15.4 lb./sq. ft. 650 10000 power loading = —= *= 12.5 lb./h.p. Then Vmi = 140^15.4 = 140^/1.23. = 149.94, say 150 m.p.h. Since the top speed is usuallv about three times the stalling 156.8 speed, the V ST. = = 52 m.p.h. Using the charts and methods contained in M. Langley's " Seaplane Float and Hull Design," this design would appear to have an absolute ceiling of 15,000ft., a service ceiling of 13,000ft. and an initial rate of climb of 835ft./min. Non-stop A.T.C. 'TWO cadets of the Samford, Suffolk, Squadron A.T.C. -*• cycle from Harwich three times a week to their instruc tional classes, a distance of 14 miles each way, and have never missed a parade. The Samford Squadron covers an area of 25 small and scattered "front line" villages, where local buses, cycles, and even shanks's pony are essential links in the cadets' communications. "Yet," their CO. says, " despite the transport problems the cadets are rarely late, wet or fine."
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