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  Partner: UNT Libraries Government Documents Department
 Collection: National Advisory Committee for Aeronautics Collection
Relation of rib spacing to stress in wing planes

Relation of rib spacing to stress in wing planes

Date: May 1, 1920
Creator: Zahm, A F
Description: The stress relations to the fabric and the rib consequent upon a change of spacing between ribs in a wing plane are discussed. Considering the wing plane as a static structure, and ignoring the question of aerodynamic efficiency, it appears that the unit stress in the rib and fabric will remain constant for constant p if the linear dimensions of both rib and fabric are increased alike, viz., if wing and fabric remain geometrically similar. Since the bulge and the structural dimensions remain geometrically similar, the whole distended plane remains so, and hence should have the same pressure distribution and efficiency. If therefore the Burgess rule of making the rib spacing always one-fifth of the chord of the plane be valid, it must be valid for all others that are mechanically similar in structure and covering.
Contributing Partner: UNT Libraries Government Documents Department
The six-component wind balance

The six-component wind balance

Date: January 1, 1923
Creator: Zahm, A F
Description: Dr. Zahm's report is a description of the six-component wind-tunnel balance in use at the Aerodynamic Laboratory, Washington Navy Yard. The description of the balance gives the mechanical details and the method of operation, and is accompanied by line drawings showing the construction of the balance. The balance is of particular interest, as it allows the model to be set up quickly and accurately in roll, pitch, and yaw, without stopping the wind. It is possible to measure automatically, directly, and independently the drag, cross-wind force, and lift; also the rolling, pitching, and yawing moments. It is also possible to make the balance self-recording.
Contributing Partner: UNT Libraries Government Documents Department
Stability equations for airship hulls

Stability equations for airship hulls

Date: January 1, 1926
Creator: Zahm, A F
Description: In the text are derived simple formulae for determining, directly from the data of wind tunnel tests of a model of an airship hull, what shall be the approximate character of oscillation, in pitch or yaw, of the full-scale airship when slightly disturbed from steady forward motion. (author).
Contributing Partner: UNT Libraries Government Documents Department
A study of wing flutter

A study of wing flutter

Date: January 1, 1929
Creator: Zahm, A F
Description: Part I describes vibration tests, in a wind tunnel, of simple airfoils and of the tail plane of an M0-1 airplane model; it also describes the air flow about this model. From these tests are drawn inferences as to the cause and cure of aerodynamic wing vibrations. Part II derives stability criteria for wing vibrations in pitch and roll, and gives design rules to obviate instability. Part III shows how to design spars to flex equally under a given wing loading and thereby economically minimize the twisting in pitch that permits cumulative flutter. Resonant flutter is not likely to ensue from turbulence of air flow along past wings and tail planes in usual flying conditions. To be flutterproof a wing must be void of reversible autorotation and not have its centroid far aft of its pitching axis, i. e., axis of pitching motion. Danger of flutter is minimized by so proportioning the wing's torsional resisting moment to the air pitching moment at high-speed angles that the torsional flexure is always small. (author).
Contributing Partner: UNT Libraries Government Documents Department
Tables for pressure of air on coming to rest from various speeds

Tables for pressure of air on coming to rest from various speeds

Date: January 1, 1930
Creator: Zahm, A F
Description: In Technical Report no. 247 of the National Advisory Committee for Aeronautics theoretical formulas are given from which was computed a table for the pressure of air on coming to rest from various speeds, such as those of aircraft and propeller blades. In that report, the table gave incompressible and adiabatic stop pressures of air for even-speed intervals in miles per hour and for some even-speed intervals in knots per hour. Table II of the present report extends the above-mentioned table by including the stop pressures of air for even-speed intervals in miles per hour, feet per-second, knots per hour, kilometers per hour, and meters per second. The pressure values in table II are also more exact than values given in the previous table. To furnish the aeronautical engineer with ready numerical formulas for finding the pressure of air on coming to rest, table I has been derived for the standard values specified below it. This table first presents the theoretical pressure-speed formulas and their working forms in C. G. S. Units as given in NACA Technical Report No. 247, then furnishes additional working formulas for several special units of speed. (author).
Contributing Partner: UNT Libraries Government Documents Department
Theories of flow similitude

Theories of flow similitude

Date: January 1, 1929
Creator: Zahm, A F
Description: The laws of comparison of dynamically similar fluid motions are derived by three different methods based on the same principle and yielding the same or equivalent formulas. This report outlines the three current methods of comparing dynamically similar motions, more especially of fluids, initiated respectively by Newton, Stokes (or Helmholtz), and Rayleigh. These three methods, viz., the integral, the differential, and the dimensional, are enough alike to be studied profitably together. They are treated in succession then compared. (author).
Contributing Partner: UNT Libraries Government Documents Department
The vector ruling protractor

The vector ruling protractor

Date: March 1, 1924
Creator: Zahm, A F
Description: The theory, structure and working of a vector slide rule is presented in this report. This instrument is used for determining a vector in magnitude and position when given its components and its moment about a point in their plane.
Contributing Partner: UNT Libraries Government Documents Department
Flow and Drag Formulas for Simple Quadrics

Flow and Drag Formulas for Simple Quadrics

Date: December 1, 1979
Creator: Zahm, A. F.
Description: The pressure distribution and resistance found by theory and experiment for simple quadrics fixed in an infinite uniform stream of practically incompressible fluid are calculated. The experimental values pertain to air and some liquids, especially water; the theoretical refer sometimes to perfect, again to viscid fluids. Formulas for the velocity at all points of the flow field are given. Pressure and pressure drag are discussed for a sphere, a round cylinder, the elliptic cylinder, the prolate and oblate spheroid, and the circular disk. The velocity and pressure in an oblique flow are examined.
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Flow and Force Equations for a Body Revolving in a Fluid

Flow and Force Equations for a Body Revolving in a Fluid

Date: December 1, 1979
Creator: Zahm, A. F.
Description: A general method for finding the steady flow velocity relative to a body in plane curvilinear motion, whence the pressure is found by Bernoulli's energy principle is described. Integration of the pressure supplies basic formulas for the zonal forces and moments on the revolving body. The application of the steady flow method for calculating the velocity and pressure at all points of the flow inside and outside an ellipsoid and some of its limiting forms is presented and graphs those quantities for the latter forms. In some useful cases experimental pressures are plotted for comparison with theoretical. The pressure, and thence the zonal force and moment, on hulls in plane curvilinear flight are calculated. General equations for the resultant fluid forces and moments on trisymmetrical bodies moving through a perfect fluid are derived. Formulas for potential coefficients and inertia coefficients for an ellipsoid and its limiting forms are presented.
Contributing Partner: UNT Libraries Government Documents Department
Horizontal buoyancy in wind tunnels

Horizontal buoyancy in wind tunnels

Date: November 1, 1920
Creator: Zahn, A F
Description: None
Contributing Partner: UNT Libraries Government Documents Department