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

coupling between the tm ends and through the line shown above the main
part of the figure. The output spring, shown in. the schematic is not
shown on the figure at the bottom of the page.
*
There are a number of other systems which accomplish essentially the
same results, but the difficulty of realizing a decent range of element
values has led us to consider a schane of this sort in s om detail. For
the stabilization of the control system with the numerical parameter values
used as an example during this paper, the spring and damper values for the
twin-T shown here coma out to be of order of magnitude yielding time constants
of about 1/10 secord. Specific values depd on the location in the ~ystem.
The element values can be readily determined'using the methods of network
synthesis well known in electrical engineering.
Clearly a findamental question is the proper location of thls twin-T or
any other form of compensation network in the overall loop. The answer to
thls westion depends on a number of theoretical factors (e.g., the effect
of loading at either end of the network on its characteristics, the effect
of the loading on the rest of the gystem produced by the network, etc.) as
well as such practical factors as space avadlability, effect of failure, etc.
One possible scheme is shown in Figure 19, where the compensation network
is inserted at the input to the hydraulic system.
Two comments are appropriate at this time concerning the stabilization
and compensation concepts discussed in the past few minutes. Eirst, it is
clear now, I hope, why we feel that the entire westion of artificial feel
is one which can not be divorced from the stability and control questions.
In the airplanes which have been discussed during the past few days, the
performance characteristics have been sufficiently low, in mimy cases, so
that the artificial feel system presented a more or less isolated problem.
However, as the satisfaction of performance specifications becomes more
difficult (and we do not envision this as being too far in the future) the
artificial feel system and the characteristics of the pilot (or at least
some generalized description of these characteristics) must be of basic
importance in determining system stability and controllability .
If the stability and controllability problams are to be resolved without
unnecessary difficulties, the feel system must be designed as part of the
overall loop.
The second comment I would like to make at'this time concern8 the effect
of nanlinearities in the various system components on the stabilization
procedures we have discussed. ~hese nonlinearities are, as I see it, of two
general types--the nonlinearities of specific hardware, as the hydraullo
system. Xe feel that nonlinearities of this type can be controlled and
kept small enough to make a linear analysis and -thesis at least a good
first order approximation. In the last analysis', final adjust~nent must of
couree be done axperbentally. The second type of nonlinearity is perhaps
more troublesome. I refer to the changing aerodfnamical coefficients Kith