NACA-WR-L-489

Abstract

INTRODUCTION <br>Tests have been made in the NACA full-scale wind tunnel on 11 single-engine military airplanes to investigate methods for increasing their high speed. The airplanes were tested for the Navy Bureau of Aeronautics and the Army Air Corps, and separate reports have been for-warded to these agencies. Repetition of similar inefficient design features on many of the airplanes indicated the desirability of analyzing and combining all of the results into a single paper for distribution to designers. The data for the various airplanes are not consistent in scope since the extent of the tests depended on the possibility of making alternations to the particular airplane and the time available for the tests. <br>The discrepancies between the computed high speeds for ideal airplane arrangements and the speeds actually reached by standard military types are well knows, and it is largely the purpose of this paper to indicate the sources of these differences. The compromises involved in the engineering design of the airplanes that were tested often lead to disadvantageous of combinations of their basic components. The advantages of elegant refinements to the basic aerodynamic elements in other cases were nullified by inattention to detail, and established aerodynamic principles were violated to simplify structural problems. In the tests the modifications were usually limited to those which practically could be applied to the existing airplanes, and the gains that were realized were by to means the maximum. Changes were guided by fundamental information obtained from studies throughout the laboratory on cowlings, ducts, etc. It will be possible to utilize some of the data directly in design; however, it is believed that the results are of greater importance in indicating errors to be avoided. As a guide, comparisons are made wherever possible between the test arrangements and the ideal. <br>The investigations included numerous studies of cooling and cowling arrangements for air and liquid-cooled power plant installations. Scoops for carburetor intakes, for intercoolers, for Prestone radiators, and for oil coolers were tested on many of the airplanes. Measurements of the wing drag by the momentum method were made for each of the airplanes, and measurements of the transition point and the critical compressibility velocity were included to aid in evaluating the wing drag at high speeds. Considerable data were also obtained on the drag of retracted and partially retracted landing gears, wind-shields, cockpit enclosures, aerials, air leaks, and armament installations. <br>The crag increments were measured at tunnel speeds between 60 and 100 miles per hour. Increased performances predicted by the tunnel tests from modifications of several of the airplanes were later substantially verified in flight tests.