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

with a control system actuated by a poner boost system. The syatsan we have
considered is shown in Pig. 1. Our cgr6tam consi8ts basicaUy of five parts.
Working from the stick to the control surface, from lef't to right on the
diagram, we have first a mechanical coupling system, between the stick and
the hydraulic power qystem. k here represents the compliance of the push
rod. or control cable from the stick to the input to the Wdraulic gyetm.
The damper fp aad lnrrsr % represent the impedance seen looking into the
input to the-bdraulic Getem from the output d of the control cable. In
our initial &udy of the qystm, ws have a 8 d that these parameters are
irdqandent of the gain of the Wdraulic system. I will have &re to say
ooneerning these oimplifying arsumptionr later.
The inprt to the hydraulic system is the displacsmsnt xp.
We consider
a singlbstage maulic system, with an output displacement + actuating
the bell crnk to give a deflaation of the control surface & . The normal,
or vertical aeceletration of the airplane, n, is detarmined by this deflection
through the aermcsl characteristics of the aircraft. The artificial
fael ~8'km Vb is the 8-108t po88ibh8 COM~S~* OW of the
bobweight of mas8 rmnll n. We do nat Imply that this is at all typical of
general artificial feel ayrtaw. Certainly our system probably should
include at least a spring. Howwer, we feel very strongly, as I shall txy
to point out later, that the desis of a witable artificial feel qpstsm
depends on consIdaration8 of dynamic &ability (and when I speak of stability,
I refer to dpadc stability) and the nature and characteristics of the pilot
in the closed loop system. We feel, and perhaps you will agree as wd continue,
that this simple bobweight system suffices as an emample of the general
prooeduree and ideas I hope to present to you. The introduction of a spring
does not, for e~mple, materially change our development.
Figures 2, 3, and 4 show the basic components of our syetem in more
detail. Figure 2 shows the aerodynamic axes a& basic equations, Plg. 3
the stick dynamics and Fig. 4 the hydraulic qystem. The pertinent equations
accontparUr the figures. A considerable portion of the &fort of the Purdue
group over the past year haa been spent in the aualyds of the bdraulic
system, the development of measuring techniques and the correlation of valve
configuration with static and dynamic characteristics. Homera today I would
like to consider the hydraulic valve as described simply by the flav-proportionalto-displacement
equation, which is an adequate deecription over the frequency
range of interest to usa and oadt any detailed disoussion of other possible
linear and nonlhear analytical descriptions of the system.
Referring again to figure 1, ue see that there are basically two feedback
eystcms to be designed-the &draulic system, ach is a closed-loop, positional
feedback ggstem, and the overall airplane control system which contains
the 4ydrauU.c loop ao one co~lponent. OPT initial interest at Purdue was
concentrated on the waulic system, but it rapidly became apparent that
this one component could not be intelligently designed or andlysed without
c~neideration of the overall qyatem. I mid like to speak briefly about the
stabilization of the maulic system and then consider in more detail the
desi- of the overall loop.