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A theoretical investigation of hydrodynamic impact loads on scalloped-bottom seaplanes and comparisons with experiment

Description: An analytical method is presented for calculating the hydrodynamic impact loads and motions experienced by seaplane floats and hulls with scalloped (fluted) bottoms. The analysis treats vertical impact at zero trim in addition to the more general problem of the step impact of a seaplane at positive trim where the flight path is oblique to the keel and to the water surface. Also considered are the transformations required to represent impacts into waves.
Date: January 1, 1947
Creator: Milwitzky, Benjamin
Partner: UNT Libraries Government Documents Department

A Generalized Theoretical and Experimental Investigation of the Motions and Hydrodynamic Loads Experienced by V-Bottom Seaplanes During Step-Landing Impacts

Description: Note presenting a theoretical investigation made of the motions and hydrodynamic loads experienced by V-bottom seaplanes during the course of a step-landing impact. In the analysis, the primary flow about the immersed portion of a keeled float or hull is considered to occur in transverse flow planes and the virtual-mass concept is applied to calculate the reaction of the water to the motion of the seaplane. The results are presented in the form of dimensionless curves which may be used to predict the behavior of V-bottom seaplanes at all instants during an impact as well as at the particular instants of maximum acceleration, maximum draft, and rebound.
Date: February 1948
Creator: Milwitzky, Benjamin
Partner: UNT Libraries Government Documents Department

A Generalized Theoretical Investigation of the Hydrodynamic Pitching Moments Experienced by V-Bottom Seaplanes During Step-Landing Impacts and Comparisons With Experiment

Description: Note presenting a theoretical investigation made of the hydrodynamic pitching moments experienced by V-bottom seaplanes during step-landing impacts. The entire immersion process is analyzed from the instant of initial contact until the seaplane rebounds from the water surface.
Date: June 1948
Creator: Milwitzky, Benjamin
Partner: UNT Libraries Government Documents Department

Generalized Theory for Seaplane Impact

Description: "The motions, hydrodynamic loads, and pitching moments experienced by V-bottom seaplanes during step-landing impacts are analyzed and the theoretical results are compared with experimental data. In the analysis, the primary flow about the immersed portion of a keeled hull or float is considered to occur in transverse flow planes and the concept of virtual mass is applied to determined the reaction of the water to the motions of the seaplane. The entire immersion process is analyzed from the instant of initial contact until the seaplane rebounds from the water surfaces" (p. 953).
Date: October 30, 1952
Creator: Milwitzky, Benjamin
Partner: UNT Libraries Government Documents Department

An Impulse-Momentum Method for Calculating Landing-Gear Contact Conditions in Eccentric Landings

Description: An impulse-momentum method for determining impact conditions for landing gears in eccentric landings is presented. The analysis is primarily concerned with the determination of contact velocities for impacts subsequent to initial touchdown in eccentric landings and with the determination of the effective mass acting on each landing gear. These parameters determine the energy-absorption requirements for the landing gear and, in conjunction with the particular characteristics of the landing gear, govern the magnitude of the ground loads. Changes in airplane angular and linear velocities and the magnitude of landing-gear vertical, drag, and side impulses resulting from a landing impact are determined by means of impulse-momentum relationships without the necessity for considering detailed force-time variations. The effective mass acting on each gear is also determined from the calculated landing-gear impulses. General equations applicable to any type of eccentric landing are written and solutions are obtained for the particular cases of an impact on one gear, a simultaneous impact on any two gears, and a symmetrical impact. In addition a solution is presented for a simplified two-degree-of-freedom system which allows rapid qualitative evaluation of the effects of certain principal parameters. The general analysis permits evaluation of the importance of such initial conditions at ground contact as vertical, horizontal, and side drift velocities, wing lift, roll and pitch angles, and rolling and pitching velocities, as well as the effects of such factors as landing gear location, airplane inertia, landing-gear length, energy-absorption efficiency, and wheel angular inertia on the severity of landing impacts. -A brief supplementary study which permits a limited evaluation of variable aerodynamic effects neglected in the analysis is presented in the appendix. Application of the analysis indicates that landing-gear impacts in eccentric landings can be appreciably more severe than impacts in symmetrical landings with the same sinking speed. The results also indicate ...
Date: January 1, 1952
Creator: Yntema, Robert T & Milwitzky, Benjamin
Partner: UNT Libraries Government Documents Department

Analysis of landing-gear behavior

Description: From Summary: "This report presents a theoretical study of the behavior of the conventional type of oleo-pneumatic landing gear during the process of landing impact. The basic analysis is presented in a general form and treats the motions of the landing gear prior to and subsequent to the beginning of shock-strut deflection."
Date: 1953~
Creator: Milwitzky, Benjamin & Cook, Francis E
Partner: UNT Libraries Government Documents Department

Evaluation of the reduced-mass method of representing wing-lift effects in free-fall drop tests of landing gears

Description: Report presenting an investigation of the validity of the reduced-mass method of representing wing-lift effects in free-fall drop tests of landing gears by means of tests of a small landing gear in the impact basin. The free-fall drop tests with full weight produced excessive values of load factor, impact period, strut stroke, mass travel, and impact energy.
Date: July 1951
Creator: Milwitzky, Benjamin & Lindquist, Dean C.
Partner: UNT Libraries Government Documents Department

Effect of interaction on landing-gear behavior and dynamic loads in a flexible airplane structure

Description: The effects of interaction between a landing gear and a flexible airplane structure on the behavior of the landing gear and the loads in the structure have been studied by treating the equations of motion of the airplane and the landing gear as a coupled system. The landing gear is considered to have nonlinear characteristics typical of conventional gears, namely, velocity-squared damping, polytropic air-compression springing, and exponential tire force-deflection characteristics. For the case where only two modes of the structure are considered, an equivalent three-mass system is derived for representing the airplane and landing-gear combination, which may be used to simulate the effects of structural flexibility in jig drop tests of landing gears. As examples to illustrate the effects of interaction, numerical calculations, based on the structural properties of two large airplanes having considerably different mass and flexibility characteristics, are presented.
Date: January 1, 1956
Creator: Cook, Francis E & Milwitzky, Benjamin
Partner: UNT Libraries Government Documents Department

Analysis of Landing-Gear Behavior

Description: Note presenting an analytical study of the behavior of the conventional type of oleo-pneumatic landing gear during the process of landing impact. The basic analysis is presented in a general form and treats the motions of the landing gear prior to and subsequent to the beginning of shock-strut deflection.
Date: August 1952
Creator: Milwitzky, Benjamin & Cook, Francis E.
Partner: UNT Libraries Government Documents Department

A summary of ground-loads statistics

Description: From Summary: "This paper briefly summaries the more important statistical data obtained by the NACA on the subject of ground loads. The information presented relates primarily to landing-impact and taxiing loads; however, some limited data are also presented on one phase of ground-handling loads, namely, braking friction. A number of experimental and theoretical papers dealing with various aspects of the subject are listed in the bibliography."
Date: May 1957
Creator: Westfall, John R.; Milwitzky, Benjamin; Silsby, Norman S. & Dreher, Robert C.
Partner: UNT Libraries Government Documents Department

An experimental study of applied ground loads in landing

Description: Results are presented of an experimental investigation made of the applied ground loads and the coefficient of friction between the tire and the ground during the wheel spin-up process in impacts of a small landing gear under controlled conditions on a concrete landing strip in the Langley impact basin. The basic investigation included three major phases: impacts with forward speed at horizontal velocities up to approximately 86 feet per second, impacts with forward speed and reverse wheel rotation to simulate horizontal velocities up to about 273 feet per second, and spin-up drop tests for comparison with the other tests. In addition to the basic investigation, supplementary tests were made to evaluate the drag-load alleviating effects of prerotating the wheel before impact so as to reduce the relative velocity between the tire and ground.
Date: August 18, 1955
Creator: Milwitzky, Benjamin; Lindquist, Dean C. & Potter, Dexter M.
Partner: UNT Libraries Government Documents Department

An experimental investigation of wheel spin-up drag loads

Description: Report presenting some information on landing-gear applied drag loads and on the nature of the wheel spin-up phenomenon in landing, based on a program of tests under controlled conditions in the impact basin. Results regarding fundamentals of the wheel spin-up process, comparison of the maximum loads in various types of tests, variation of coefficient of friction, and effect of prerotation are provided.
Date: September 1954
Creator: Milwitzky, Benjamin; Lindquist, Dean C. & Potter, Dexter M.
Partner: UNT Libraries Government Documents Department

An experimental investigation of wheel spin-up drag loads

Description: Report presenting information on landing gear applied drag loads and the nature of wheel spin-up in landing based on testing in the Langley impact basin. Particular attention is paid to the nature and variation of the coefficient of friction between the tire and runway during the wheel spin-up process. Results regarding the fundamentals of the process, comparison of maximum loads, variation of coefficient of friction, and effect of prerotation are provided.
Date: June 8, 1953
Creator: Milwitzky, Benjamin; Lindquist, Dean C. & Potter, Dexter M.
Partner: UNT Libraries Government Documents Department