56 A I R C R A F T E N G I N E E R I N G February, 1939 Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Committee, Reports and Technical Notes of the U.S. National Advisory Committee for Aeronautics and publications of other similar research bodies as issued Th e maximum normal accelerations recorded The effect of the roughness of the afterbody was US. A. were 2g in take-off and 4·5g (in bow and centre found to be negligible except at high trims. NATIONAL ADVISORY section) in a stalled landing. Th e model data were extrapolated to full size by Th e maximum angula r acceleration was 1½ radian s COMMITTEE FOR AERONAUTICS th e usual method that assumes the forces to vary pe r (sec.)2, the maximum difference between bow according to Froude's law and, in the case of the TECHNICAL NOTES an d tail accelerations was l·6g and the maximum smooth model, by a method of separation that (Secretary, N.A.C.A., Washington) difference between hull an d centre section was 0·9g. take s into account the effect of scale on th e frictional I n some landings the correction for angular acceler resistance. It was concluded that the effect of Technical Note No. 655. Principles atio n was insufficient to bring the bow and tail rivet heads on the take-off performance of a accelerations to th e same value as the acceleration Involved in the Cooling of a Finned and relatively high-powered float seaplane is of little amidships and this shows that the hull distorts. consequence, but tha t it may be of greater import Baffled Cylinder. By M . J. Brevoort. I n the majority of landings there was a distortion ance in th e case of more moderately powered flying An analysis of the cooling problem for a finned of the centre section similar to tha t recorded on a boats . cylinder is made on the basis of the known funda Singapore IIc seaplane when dropped into water. mental principles of heat transfer from pipes. Th e records from the four accelerometers of Technical Note No. 658. Generalized Experimental results tha t support the analysis are different frequencies showed good agreement. The Analysis of Experimental Observations in presented. The results of previous investigations higher frequency instruments gave more oscillatory on the problem are evaluated on the basis of the Problems of Elastic Stability. By Eugene E. records, were less easily analysed and gave only a analysis and the results. An illustration of the small increase in accuracy. Lundquist. application of these principles to a specific problem A generalized method of analyzing experimental is included. R. & M . No. 1830. December 21, 1936. observations 111 problems of elastic stability is Stressed-skin Structures. Compression Tests presented in which the initial readings of load and Technical Note No. 656. Hydrodynamic deflection may be taken a t any load less than the of Panels with Tubular Stiffeners. By I. J. critical load. This analysis is an extension of a and Aerodynamic Tests of Models of Floats Gerard and B. G. Dickens. (Price 4s. od.) method published by Southwell in 1932, in which for Single-Float Seaplanes, N.A.C.A.. Models Tests of complete cylinders and quadrants had it was assumed tha t the initial readings are take n a t 41-D, 41-E, 61-A, 73 and 73-A. By J. B. revealed that in order to obtain constructions com zero load. bining maximum stiffness and strength for a given Parkinson and R. O. House. weight, the stiffeners must not only be flexurally Tests were mad e in th e N.A.C.A. tank and in the GREAT BRITAIN stable but they must also be torsionally stiff. A N.A.C.A. 7- b y 10-ft. wind tunnel of two models of preliminary series of compression tests of panels AERONAUTICAL RESEARCH transverse-step floats and three models of pointed- with tubular stiffeners gave results considerably step floats considered to be suitable for use with COMMITTEE bette r than had been obtained using stringers single-float seaplanes. The models were designed formed from sheet strip. (H.M. Stationery Office, London) a t th e N.A.C.A. tank as par t of a programme having Th e present report is principally concerned with for its object the reductions of th e water resistance th e estimation of the failing bending moments of R. & M. No. 1827. January 29, 1938. and spray of single-float seaplanes without reducing complete circular cylinders stiffened longitudinally The Use of the Principle of Minimum Potential th e angle of dead rise believed t o b e necessary for th e b y uniformly spaced tubular stiffeners. The failing Energy in Problems of Static Equilibrium. By satisfactory absorption of the shock loads. bending moments have been estimated from tests The form of N.A.C.A. model 41-D is similar to D . Williams. (Price 2s. 6d.) of small duralumin samples of the variou s construc tha t of the Navy Mark V float (N.A.C.A. model Th e application of the Principle of Minimum tions. These samples took th e form of panels about 41-A), but ha s more gradual fore-and-aft curvature Potentia l Energy to problems of static equilibrium 1 ft. square, each incorporating two tubular stiff of th e buttoc k lines near th e stop s and a lower angle ha s received little attentio n in th e pas t as compared eners. They were tested in longitudinal compres of afterbody keel. N.A.C.A. model 41-E is a with tha t given to its application in clastic stability sion. Comparative tests of constructions using modification of model 41-D, the rear step having tubula r and extruded angle section stringers are also problems. Its possibilities in the former field were been eliminated. N.A.C.A. model 61-A has a quoted . therefore considered worth investigating. pointed step with a horizontal afterbody similar to I t is shown how th e difficulties usually associated As a necessary step in the interpretation of the N.A.C.A. model 35-13. N.A.C.A. model 73 is a wit h variational methods of finding a minimum may panel test results the load-carrying capacity of flat refinement of the pointed-step form, in which a b e circumvented by an approximate method that an d curved unstiffened sheet was investigated. fairing has been fitted above and behind the step. depends upon expressing the deformation of a Constructions incorporating solid drawn tubular N.A.C.A. model 73-A is a modification of model 73, structur e in terms of an arbitrary function of the stiffeners are lighter for a given strength or stronger the chine being wider and higher near the bow for co-ordinates and certain undetermined constant for a given weight than constructions incorporating greater seaworthiness in rough water. multipliers. The importance of choosing a suit stiffeners formed from strip material. All th e models were tested in the N.A.C.A. tank able form for the assumed deformation is demon Comparativ e tests of panels with tubular and free to tri m a t one gross load. The results indicated strated , and consideration is given to boundary extrude d angle stringers indicate that constructions tha t all the models have less resistance and spray conditions. For illustration, th e metho d is employed using tubular stringers are 15 pe r cen t more efficient tha n the model of the Mark V float and that the t o solve a problem that is intractable by standard on a strength/weight basis tha n constructions using pointed-step floats arc somewhat superior to the methods . extruded angle section stringers of similar material transverse-step floats in these respects. Models Comparison is made between the energy method an d weight. 41-D, 61-A and 73 were tested by the general an d certain other approximate methods. Withi n the present range of tests, it has been method over a wide range of loads and speeds ; the Th e method has importan t possibilities in dealing shown that for a given skin thickness, pitch and results are presented in the form of curves and wit h highly redundant structures and is straight weight of rings, an increase in th e weight of tubular charts for use in design calculations. forward in application. For static problems it stiffeners produces a directly proportional increase The aerodynamic drag of the models was deter compares not unfavourably with other approximate in the failing bending moment of the complete mined in the N.A.C.A. 7- by 10-ft. wind tunnel at methods . cylinder. angles of pitch from —10 deg . t o 16 deg . Models Fro m the results given, it is possible to estimate (61-A and 73 have the lowest minimum drag wit h reasonable accuracy the bending strength of R. & M. No. 1829. June 18, 1937. coefficient and model 73-A has the highest. The circular cylinders of any radius and skin thickness Measurements of Accelerations at Different difference between models 41-D and 41-E is stiffened by an y of th e sizes of tubes included in th e negligible. Parts of a Boat Seaplane during Take-off and presen t series at any given circumferential pitch, Landing. By G. C. Abel. (Price 2s. 6d.) provided the rings or transverse stiffeners are Technical Note No. 657. Tank Tests to adequat e in stiffness and strength and of 12-in. pitch. Measurements of acceleration at selected parts of Th e results of a few test s on constructions incorpor a seaplane structure during take-off and landing Show the Effect of Rivet Heads on the Water atin g one size of tubular or extruded angle stiffener were required to provide further knowledge of Performance of a Seaplane Float. By J. B. structur e loads. indicate tha t 25 per cent and 50 per cent increases Parkinson. in the pitch of rings produce relatively small Take-offs and landings were made in calm and A 1/3·5 full-size model of a seaplane float con decreases in failing stresses. choppy water. The landings were made deliber structed from lines supplied by the Bureau of ately heavy in order to give an upper limit to the Th e stress developed in unstiffened curved dural Aeronautics, Navy Department, was tested in the factors required on seaplane structures. umin sheet is given by the simple relation :— N. A.C.A. tank, first with smooth painted bottom Th e normal acceleration was measured at seven Stress in tons/sq . in. = 1,040 thickness of skin/ surfaces and then with round-head rivets, plate positions and the longitudinal acceleration at two radiu s for values of thickness/ radius u p t o 0·003. laps and keel plates fitted to simulate the actual of these positions. At one position four accelcro- Th e method of panel test procedure (which is bottom of a metal float. The percentage increase meters of different frequencies were fitted. A gyro defined in detail) appears suitable for use in all in water resistance caused by the added roughness pitc h recorder was fitted to record the change of normally equipped test laboratories and should be was found t o be from 5 t o 20 per cent at the hump attitud e during impact and from this record the a valuable aid t o designers in estimating th e strength speed and from 15 to 40 per cent at high speeds. angula r acceleration has been deduced. in bending of complete stressed-skin components.
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Feb 1, 1939