Document Type: Technical Research Report Authority: Government Military (authoritative reference) Document Number: Air Service Information Circular (Aviation) Vol. V, No. 444 (dated May 1, 1923), based on McCook Field Report Serial No. 2094 (dated December 11, 1922). Document includes 1 sheet (2 pages) of "Air Corps Information Circular Vol V, No. 444 Change No. 1" dated April 9, 1929)

Scope: Report prepared by J. A. Roché of the Airplane Section, Engineering Division, Air Service, McCook Field.

NB: Change No. 1 (dated April 9, 1929) corrects equations 4 and 5 on page 8 of the original Air Service Information Circular.

Contents: "INTRODUCTION The main purpose of this report is to set forth some clear and simple methods for the analysis of glider performance on different kinds of winds. The value of gliders to aeronautics, the effect of topography on soaring, and a few different types of gliders are discussed. An appendix gives the criteria for the selection of a soaring site.

VALUE OF GLIDERS. Gliding has been firmly established as a sport in European countries, and gliding should be studied and encouraged in this country because of its value as a means of popularizing and advancing aeronautics. A few arguments in favor of the usefulness of gliding follow.

TECHNICAL. Gliders, being designed for flight with minimum power, present aerodynamic problems similar to those encountered in all types of airplanes, with the only exception of the purely racing types, and even then the arrangements of wings and body which give best results on gliders are very likely to give best results in any type of airplane. Stability problems can be studied and solved more thoroughly by the use of gliders than by means of the wind tunnel alone. A glider may be used to determine the lift and drag coefficients of wing sections, providing still air be available. Results so obtained will not require scale corrections.

MILITARY. A glider will make an excellent observation post, when wind is available, by flying it as a kite. It requires less storage space than a balloon and no cumbersome equipment in the way of winches and gas supply. Its vulnerability is much lower than that of a balloon; its risk of damage through storm and fire and its first cost are likewise lower. For use in conjunction with vessels, the advantages mentioned above are greater than for land use. A light glider dropped from a balloon will make a cheap and realistic target for antiaircraft fire and machine guns from an airplane; dropped from 10,000 feet, it will take a glider about one hour to reach the ground. Its stability can be controlled so it will fly a straight path, a spiral, or will perform a series of phugoid oscillations. Gliding, practiced as a sport, will give young men preliminary training in the handling of aircraft at small expense; such training, however, should be properly supervised to minimize accidents. The following table, listing the chief characteristics of foreign gliders, has been prepared to act as a guide as to what aspect ratio and wing loadings are likely to give satisfactory results at the start:"

[Table includes data about these gliders: "Vampyr Harth S-12 Espenlaub II Espenlaub I Stuttgart Harth S-10 Berlin Feldberg Segler Feltzner Devoitine Peyret Handaysyde Brokker"]

"AERODYNAMICS OF GLIDERS. Although the same aerodynamic laws apply to airplanes and gliders, the performances of the two can not be represented conveniently by the same diagrams. A special diagram has been developed for the glider which gives its velocity and path slope in still air for all values of incidence. This diagram requires for its construction either a model test or an estimate of its resistance and airfoil characteristics, preferably the former. The indications of this diagram will be subject to the same errors as the performance estimate curves of an air-plane, with the exceptions of those errors which result from the power plant, propeller, and slipstream. Assume a characteristic polar curve obtained from a model test, such as Figure 1, then the values required for plotting a gliding diagram can be obtained by the process exemplified in the following table."