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Aviation History
1931
1931 - 0081.PDF
FLIGHT, JANUARY 23, 1931 [SOME ASPECTS OF THE DESIGN OF SEA-GOING AIRCRAFT By A. GOUGE, B.Sc, A.F.R.Ae.S., General Manager of Short Brothers Being a lecture delivered before the Royal Aeronautical Society on January 8, 1931 [Concluded from page 64.) ! The Range of a Large Flying-Boat SO much has been written of late regarding long-rangeflying-boats, that is may not be out of place here if I giveyou the actual figures that have been obtained on a large ; flvin" boat recently completed by the firm with which 1 am , connected. This flying-boat, which was not built entirely for range purposes, has normal civil safety factors at the weight under consideration. In other words I consider it useless to talk of range obtained by reducing the safety factors below ; those required for a normal certificate of airworthiness. On Fig. 16 will be found the range of this boat plotted j against useful load exclusive of fuel. ' From the curve it will be noted that the absolute maximum1 range is approximately 2,400 miles, the whole of the useful load being fuel. At a range of 2,000 miles the useful load | apart from fuel is 4,000 1b. and finally the total useful load 'is lfi.fiOO lb., which represents 44-5 per cent, of the total1 weight of the flying-boat. From the above it appears that it is possible to fly from 1,500 to 2,000 miles in still air in one hop, carrying a fair amount of paying load, but I am afraid the charge per lb. would have to be high to make such a flight a paying proposition. Single-Strut Engine Mounting and Absence of Chine Struts A glance at the front view of the flying-boat in the photo- graph will, at once, suggest two further points in design, which, having received due attention and consideration, have resulted in a considerable cleaning up of the air frame and consequent increased overall efficiency of the machine in the air. I refer to : (1) The installation of the power unit. (2) The absence of struts from under the engine strut to the chine of the hull. I 1 a ft 8 : S e r 0° FIG.10 — — EFFECT OF NOSE-DIVING MOMENTS ON PUNNING ANG DISPLACEMENT 2I.QQD LBS. -- • —_ - — \ / r ! i (8 19 20 21 ULL 5I2E SPEED IN KNOTS 22 21 2" Dealing with (1), it has for long been recognised that the usual methods of strutting engines between the wings, with their attendant vibratory struts, etc., results in considerable interference with air flow around the adjacent wing structure, entailing excessive air drag. A satisfactory attempt has now been made to overcome this difficulty by installing the power unit in a monocoque nacelle into which is built, either integral with it or separate, one very robust vertical member between the wings in the P-ane of each front and rear spar. As an additional refine- ment this member may be tapered, being widest at the junction with the nacelle. Suitable fairings are incorporated0 n °use all necessary pipings, wires, etc. In the tandem arrangement shown these members are stayed horizontally ray another much smaller member carried" to the caban'eracl °£- Tne stress assumptions imposed upon the vertical members were : four times engine weight horizontally plus torque and thrust reactions, and flying loads from various cases. In addition, periods of vibration of both vertical and horizontal members were investigated for comparison with engine periods. The monocoque nacelle itself is cut down to its minimum frontal area consistent with efficient cowling of the engine and general accessibility to parts requiring frequent attention, such as engine pumps, magnetos, plugs, etc. TANK TESTS ON '/a" SCALE MQDE.I OF SINGLE IL0A1 fc»TECT Of NOSE-DIVING M0ME.NT5 ON RUNNINO ANGLL r / _l FIG.II i 1 // s (2 13 (^ 15 FULL SIZE SPEED ti KNOTS The resulting structure is satisfactorily rigid under all running conditions of the engines, entailing very little addi- tional weight and making for increased simplicity, eliminating the attendant trouble of vibration on a large number of pins and bolts to such an extent that maintenance required on the structure itself is nil. On later installations this vertical member has been used for supporting the radiator above the nacelle, and has thus reduced another source of interference with the wing. Dealing with (2), chine struts have always been trouble- some by reason of liability to damage by attendant boats and resistance and interference with the neighbouring wing. Hence, an endeavour has been made on the aircraft, as shown on the photograph, to substitute a structure in lieu of these external members. This has been done, and the structure faired over by gradually " blowing up " the wing section from its junction with the main plane to its point of contact with the hull framing. This " blow-up " is carried out on chord as well as depth, and at the hull the section is approximately twice the normal depth of wing. The resulting shape between the two spars is ideal for fuel tanks, inasmuch as it is possible to extract every gallon of fuel from the tank in any normal attitude of the machine without the necessity of employing any elaborate sump arrangements. This scheme of bracing is, however, slightly heavier than the normal type of chine strut, but the increased weight is more than compensated for by the overall gain in efficiency to the machine. Undoubtedly, these two points alone have had a marked influence towards improving the I-/D of the complete structure. THE DISCUSSION In opening the discussion, WING. COMM. CAVE-BP.OWNE- CAVE said that he would feel very glad if Mr. Gouge could com- pare the efficiency of the single float seaplane or the single hull flying-boat with that of the twin float seaplane or twin hull flying-boat. He questioned whether this was entirely a matter of float interference. He then queried whether Mr. Gouge's suggested remedy of moderately supercharged engines for assisting the take-off in tropical climates under conditions of varying atmosphere and density was entirely sound. He felt that in many cases a fall in density was due to a rise in temperature and in such conditions he doubted whether a supercharged engine would be a sound remedy. Commenting upon the tests in the tank carried out by Mr. Gouge, he said 83
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