Document Type: Technical Research Report Authority: Government Military (authoritative reference) Document Number: Air Service Information Circular (Aviation) Vol. V, No. 436 (dated May 1, 1923), based on McCook Field Report Serial No. 2079 (October 20, 1922).

Scope: Airplane Section Report prepared by Leslie MacDill [Major, possibly Chief Engineering Officer] and F. W Herman of the Engineering Division, Air Service, McCook Field. MacDill was a 1922 graduate of MIT with a Doctorate of Science in Aeronautical Engineering.

Contents: "OBJECT OF STUDY. The selection of the most suitable engine, wing section and wing loading to obtain the most desirable performance for single-seater, low-altitude, water-cooled, pursuit airplanes.

SPECIFICATIONS. General Mitchell, in a letter of July 10, 1922, proposed the following specifications: Military load..............................................pounds.. 450 Fuel supply...............................................hours.. 3 and 1/4 Ceiling......................................................feet.. 20,000 Velocity at 15,000 feet...................miles per hour.. 155

This analysis, however, was made on the basis of a military load of 525 pounds, corresponding to that previously used, and fuel supply sufficient for running one-half hour full speed at the ground and 3 hours full speed at an altitude of 15,000 feet.

CONCLUSIONS. To increase the speed of the airplane (even at 15,000 feet) it is necessary to sacrifice a certain heighth of ceiling. The best compromise is obtained by use of minimum parasite area, light wing loading (less than 8 pounds per square foot) and thin wing sections. The Fokker D-8 tapered wing section, however, gives very good performance, and structural considerations might make the selection of this wing section more suitable. Thick untapered wing sections, contrary to the often expressed belief, do not give as good a performance at altitude as the thin wing sections. Likewise the tapered U. S. A. 35 did not give a satisfactory performance. The reason for this is that the thick wing sections have such a high minimum drag that it is much better to use strut and wire construction, and the consequent increase in parasite drag, than to increase the minimum drag of the wing by use of the thick wing section, because the additional parasite drag of struts and wires is not so great as the additional minimum drag of the thick wing section.

The Curtiss D-12 is theoretically the best engine if consideration is given the low parasite area demanded by this engine. A performance at altitude was assumed in the calculations of at least the same efficiency as the Wright H-2 motor. No altitude chamber tests have as yet been run for the Curtiss D-12, so exact figures are not obtainable.

The results are summarized in figure 1, where ceiling is plotted against velocity at 15,000 feet, for various wing loadings and wing sections. Calculations are based upon model results, no allowance being made for scale. How-ever, in order to arrive at some idea of the performance to be expected, the performance of the MB-3 is calculated by the same method and plotted against actual performance, showing that the performances indicated by the chart are conservative for the parasite areas assumed (smaller than that of the MB-3) and may actually be obtained.

The conclusions above apply likewise to airplanes built about the Wright H-2 and Liberty engines."

Further detailed analysis follows.