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National Advisory Committee for Aeronautics, Report - Drag and Cooling with Various Forms of Cowling for a 'Whirlwind' Radial Air Cooled Engine, I

The National Advisory Committee for Aeronautics has undertaken an inrestigation in the
20-foot Propeller Research Tunnel at Langley Field on the cowling of radial air—cooled engines.
A portion of the inrestigation has bee-n completed, in which sereral forms and degrees of cowling
were tested on a Wright “Whirlwind" J—b’ engine mounted in the nose of a cabin fuselage. The
cowli-ngs cariedfrom the one extreme of an entirely ezr-posed engine to the other in which the engine
was entirely inclosed. Cooling tests were made and each cowling modified, if necessary, until the
engine cooled approximately as satisfactorily as when it was entirely exposed. Drag tests were
the-n made with each form of cowling, and the efi'ect of the cowling on the propulsive eficiency deter-
mined with a metal propeller.

The propulsive efficiency was found to be practically the same with all forms of cowling. The
drag of the cabin fuselage un'th uncowled engine was found to be more than three times as great as
the drag of the fuselage with the engine remored and nose rounded. The contentional forms of
cowling, in which at least the tops of the cylinder heads and ualre gear are aposed, reduce the drag
somewhat, but the cowling entirely covering the engine reduces it 2.6 times as much as the best con-
eentional one. The decrease in drag due to the use of spinners proved to be almost negligible.

The use of the cowling completely covering the engine seems entirely practical as regards both
cooling and maintenance under service conditions. It must be carefully designed, however, to cool
properly. With cabin fuselages its use should result in a substantial increase in high speed orer
that obtained with present forms of cowling on engines similar in contour to the J-vb’.