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Aviation History
1951
1951 - 2160.PDF
26 October 1951 * o a— o £?4 — —1 FC 11 1 T~ T 1 1— STEP —____^ CENTRC • r «EBODY FLATl.5O»beam) F Lf *- / / r / / / > — '— •• z* / 2 4 6 8 1O 12 FOREBODV LENGTH BEAM RATIO (lf/b) 14 height that could be attained through modification of trans- verse curvature. It was determined that a radius too small or abrupt would act only on the layer of water immediately adjacent to the hull, and that the inertia of the unaffected mass would carry it along the local curvature with little change in direction. Similarly, if exaggerated reflex flare were employed, the adjacent layer would actually rebound from the unaffected mass and rise higher than if no flare at all had been used. During the course of isolating the effect of downward 0 TOWING BASIN POWER-OFF X RADIO MODEL POWER- ON • FULL SCALE POWER-ON 5O 4O DESIGNED GROSS WEIGHT 2O 1O 1O MAXIMUM OVERLOAD (Left) Linear variation of deadrise forward of the step to maintain lower limit stability with increase in lengthjbeam ratio. (Above) Cross- sectional view of a blended-type hull, illustrating diagrammatically the action of the "spray dam." eventually concluded that further study was not necessary. The lecturer then dealt with the next phase of the research programme, in which were explored the possibilities of in- corporating turbojets into an efficient hydrodynamic con- figuration. Convair had just completed one of the first jet bombers to be built in the United States, the XB-46, and it appeared logical to start with this design and attempt to "water-base" it with a minimum of revision. Various approaches were made, using extreme length/beam ratios, light loading and other schemes; all of these configurations incorporated the basic elements of con- ventional hulls such as sharp chines and steps, and did not provide the static buoyancy or spray control required without incurring excessive frontal area and, hence, aerodynamic drag. At this stage, the early work with perpendicular spray strips was recalled and, deviating completely from established naval archi- tectural practice, a generous wing/hull fillet was added to the original XB-46. To keep the thickness ratio aerody- namically within reason, the plan form was faired generously into the bow and stern fuselage. Proceeding in this manner, a simple 20 3O FEET SO 4O NORMAL OVERLOAD deflection of the chine a simple expedient had been em- ployed. This consisted in attaching a metal strip to a hull without flare and then progressively deflecting this strip while recording the spray height. Beyond a few degrees of deflection below the horizontal, the reflected spray became steadily worse, as in the case of the exaggerated reflex flare. Following the course of many research investigations, the study was continued ad absurdum and upon the spray dam approaching a nearly perpendicular position an interesting Phenomenon occurred, in that marked reductions of spray height were noted. , It was concluded from these tests that the increased effec- tiveness was due to the sharp intersection of the strip with "W hull bottom which, in effect, acted as a dam. This Powerful effect was lost where the lowered chine was faired 7 ?S5n8 reflex flare or a fillet of any nature. Because of obvious structural limitations, this highly effective spray stripWa s not considered feasible for application to conventional nulls, aad in view of the outstanding success which had been observed through the use of a high length/beam ratio, it was 3O FEET (Left) The loci of maximum spray crests on the XPSV'-I, showing the correlation between model and full scale for design gross weight, normal and maximum overload. (Below) Typical hull lines and offsets for a transonic blended-hull configuration incor- porating high Mach number buttock sections. It can be ssen that there is no apparent dis- tinction between hydrodynamic and aero- dynamic functions.
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