Analysis of Cooling Limitations and Ef'fect of Engine-cooling Lwroveau3nts on Level-flight Cruising Perforl~wnce of Four-engine Heavy Bomber

The I \ ~ . C . ~ has delleloped means, including an injection impeller and ducted head h f l e s , to improre the cooling charact ee t i c s of the SS60-cubieinchdisplacement radial engines installed in a four-engine h a z y bomber. The improrements afforded proper cooling of the rear-row exhaust-ualre seats for a wide range of ~(~101-jhp angles, mixture strength, and airplane speeds. The results offright tests math this airplane are used a8 a ha& for a study to determine the manner and the eatent to which the airplane performance was limited by engine cooling. B y means of this analysis for both the standard airplane and the airplane with engine-cooling modifiations, comparison of the specijc range at particular conditions and comparison of the cruising-performance limitations were made. The analysis of lerd$ight eruiaing performance of the airplune urifh both the standardand the modqijied-engine installuEions indicated that the maximum cruising economy i s atiained at the minimum brake spee23c fire1 consumption when engine cooling under these conditions is possible. Operation at lean mixtures, high altitudes, and large gross weights m s limited for the standard airplane by engine cooling at the point where larger cowl-gap openings increase the power required for lerel flight at such a rate thut the additional cooling air amilable i s i m f i i e n t to cool the engine when deceloping the additional power. 1T7hen cooling becomes impossible at the minimum brake speci'c fuel conaumptwn, the maximum cruising economy i s obtained with a cowl-frap angle of approximately 6 ' and with the leanest mixture (abore the stoichiometric value) g i~ ing satisfacdory engine cooling. Compa~ison of the calculated pet.fomanee of the atandard and the modified airplane indicated thut cooling improrements increased the marimurn spmj(;c range as much as 58 percent for operation where wide courb$ap angles and. enriched mixtures are required to cool the standard airplane. Corresponding increases in cruising range were calculated for$ights i n which conditiom allowing large increases in' cruising economy were encountered. The cooling improrements a l l m either an increase of more than 10,000 feet in operating alfitude at a giren airplane wight or a gross-weight increase of from 10,000 pounds af sea lerel to 86,000 pounds at all operating altz'tudes cabore 10,000 feet. INTRODUCTION