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

precisely. The fir at demonstration of automatic pilot control of airplane
attitude war made by Lawrence Sperry in 1913. Note that thin "nboerdn
etabiliration, by the pilct or automatic pilot, de-aende on control. It ie
contrasted with %~tbooard"tabili~ation (8uch ae la provided by fixed
aerodynamic uurfacee) which intdferee with control.
The incqatibil ity cf outboard etabilization with control ha8
fortered the opinion that atability ie achieped only by racrificing
control. That this ie not neceeearily the cane may be illuetrated
by conridering the example of a rlmple poeitioning eervomechaniem,
(Figure 1). The first desim ie deficient in dynamic etability. The
output shaft reproduore the aagle of the input ahaft only after a
wdrly damped traneient har died out. The designer hae at leaet two
alternatiree. He may add mechanical dampiog to the output ahaft,
%utboardn. Thin waetee control power and opposes rapid and accurate
control of the output ahaft. (Such a ryetam has a eteady etate error
den eubjeated to a velocity input.) On the other hand the deeigner
may, Elnd usually doer, chooee to employ the derivative of error eignal
to etabilize the eyetan. UInboardn etabilization, accoqpSirhed at the
eimd level. doee not mete control power, and doer not reeult in a
eteady etate velocity error. In thie cam etability doee not interfere
with control. If anything, control of the output ahaft hae been enhawed
and refined by additional etability.
The aonaqt, illuetratal by this eimple example of e~taneous
etability ah control, can be carried over into the airplane handling
qualitiee field. Note, however, that both the etability and the control
shown here depend upon feedback.
Flight path etability, compoeed of attitude etability euperimpored
on relative uind etability, ie commonly achieved by the feedback
mechanisms known ae automatic pilote. These may be equipad with
pedeetal controllere vhich provide a meane of introducing control at
the eignd level. . Feedback for control purpoeee ie through the hurmrn
pilot 1s vioual referenore and. hle kineathetic emee for mall finger
and wriet moveplente.
We portulate that a euparior form of feedback to the Man pilot
ie force. There ie coneiderable logic and erne cuperimentd. widonce
to eubetantiate thie contention.
Aeauming -that the feel of the controls is .important to flight
path control and that compliance with the handling qualities qwificatione
inearee adequate feel characterietice, but poeeible only
marginal flight path etability chsracterietice, it is logical to
retain the f'miliar cockpit.controle'and their feel and add flight
path etability. This is the equivalent of eaying that it ie logical