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

Equations (21) and (22) are written in terms of transient response parameters
but apply to frequency redponse parameters by replacing S and E
with St and El, respectively. The corresponding equations for the
varioue sizes of a rotary servomotor in terms of the various design
parameters may be obtained from equations (9) and (10) in a similar
menner .
Equation (21) expresses the relation between the motor inertia ( roportional
to 9)
I
and the various response parameters. Equation (22
expresses the relation between the input inertia (proportional to RW
and the various response parameters. The motor inertia and the input
inertia are signif icant factors in the design of high speed servomotors .
The following paragraphs will diecues methods for aiding in the selection
of optimum designs to meet specifications on either the transient or
frequency response characteristics.
Determination of Design Parameters
Load mass. - The value of M in the design equations includes the
mass of the output part of the servomotor as well as the load mass. In
high-speed applications the motor mass may be a significant percentage
of the total mass. For this reason the estimated mass of the output part
of the motor should be added to the known load mass. It is obvious from
the character of the response of hydraulic servomotors of this type that
the, responee~,characteristics for a given size are always improved by
reductions in the load mass.
Pressure differential across servomotor. - In general the size of a
servomotor for a given response is reduced by an increase in pressure differential.
The reduction in weight, however, is modified by the need for
larger sections to withstand the increased pressure. The determination
of the optimum pressure' is beyond the scope of this paper. The no-load
time constant varies' inversely as the square root of the pressure differential'whereaa
the inertia index is independent of the pressure diff
erential. Therefore in a given servomotor the break frequencies. (f
and f3) are proportional to the sqwe root of the pressure differential,
and the rise time is approximately inversely proportional to the square
root of the pressure differential.