Report of the Second Piloted Aircraft Flight Control System - Acgsc.org

INTRODUCTION
PARAMETERS FOR THE DESIGN OF HIGH- SPEED
HYDRAULIC SERVOMOTORS
by HAROLD GOLD
EDWARD W. OTTO
VICTOR L. RANSOM
of
National Advisory Committee for Aeronautics
Lewis Flight Propulsion Laboratory
Cleveland, 0.
The servomotor dealt Kith in this paper is a power amplifying,
positioning device of the type used in such applicatione as control
valve positioners, flight controls and power steering devices. The
hydraulic servomotor as a device has been known for approximately one
hundred years. Its application to high speed machinery, however, appears
to be relatively recent. There is consequently very little published
literature on the dynamics of *is servomotor in spite of its long history.
Nevertheless, when properly designed, the hydraulic servomotor is
particularly suited for high speed service because of the extremely high
force-mass ratios that can be obtained and because the device inherently
is heavily damped.
This paper is based on an experimental and analytical study of the
dynemics of the hydraulic servomotor recently completed by the authors
at Lewis laboratory and soon to be published by the NACA (reference 1)
The results of this study have shown that although the response of the
servomotor is essentially nonlinear and discontinuous, the response may
be closely approximated with relatively simple linear equations. The
present paper presents data demonstrating the nonlinear, discontinuous
nature of the dynamic response of the servomotor and inqludes a derivation
of the baeic analytical expressions for describing the response.
The derivations wfiieh are presented in the "Analysis" section of this
paper are essentially an abstract of the detailed derivations given in
reference 1.
The derived analytical expressions are summarized in the form of
charts. By means of these charts the rational design of the servomotor
to meet specifications on either the transient or the frequency response
characteristics is made possible.
DEFINITIONS AFSD IKMT& ASSUMET'IONS
Straight line servomotor. - The elements of the straight line
hydraulic servomotor are shown schematically in f imre 1. In the
nkutral position, the spool member of the pilot valve closes the paesages