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Aug. 13, 1,963
s._ s. osDER
FAIL-SAFE CONTROL SYSTEMS FOR AIRCRAFTv
'
Filed nec.- 2s, 1960
A7' OR/VEY
Patented Aug. i3, i963~
„
- i ,
`s 1008561
~IS‘AIlL-SAli‘lí) CÜNTRGH’J SYSTEMS FOR AHQCRAFT
Stephen S; Ostler, Phoenix, Ariz., assigner to Sperry Rand
Corporation, Great Neck, NX., a corporation of Del
aware
»
.
Filed Dec. 23, 1960, Ser. No. 77,959
8 Claims. (Cl. S18-489)
.
2
stead, the attitude rate signal. Since the attitude rate sig
nal is representative of the rate thatv the craft departs
from its reference attitude, it is essential to the prevention
of dangerously rapid departures from the reference latti
tude. It is for this reason that the attitude rate signal is
preferentially handled, as .described-above, and applied
always Ito either one for the other of the serv-os.
Under
normal operation with both the stability augmentation
The Vpresent invention relates generally to control sys
servo and the displacement servo operating properly, the
tems for aircraft ‘and more particularly .to fail-safe 'auto 10 control surface is moved, «as before, in response to the
matic 'flight control systems. '
`
Ordinarily, in a system `for controlling the movement of
a craft about one of its taxes, signals are provided which
represent both the displacement of the craft from a refer
sum of the displacement and attitude rate signals. In the
event that the displacement servo fails to operate, the
stability »augmentation servo will operate to» prevent dan
gerously rapid :departures of the craft from its reference
ence attitude and the rate'that the craft changes its at 15 attitude. However, in theevent the stability augmenta
titude; these signals are added algebraically to produce a
tion servo fails to operate, the servo malfunction detec
sum signal which is applied to a servo, the servo being
tor will respond immediately to apply the attitude rate
operable with a control surfacelon the craft to cause the
signal to Ythe displacement servo, thereby as mentioned
craft to assume lthe reference attitude.
.
above, preventing dangerously rapid departures of the
As presently practiced, there are two general ways in 20 craft from its reference attitude.
which the above-described flight control system may be
By providing separate servos to which the displacement
made fail-safe: In theiirst of these ways, the above-men- `
and attitude rate signals are applied respectively, the ap
' tioned sum signal is ‘applied ’to two >separate channels,
paratus of the present invention, as will be Idescribed later,
each of which has a servo. .One of the servos receives
the sum signal directly and, when operating properly,
moves the control surface.
' is adaptable readily to the following lmodes of operation:
«a semiautomatic flight control mode in which short term
The >second servo, on the
attitude corrections are «automatically provided and long
term attitude corrections are provided by manipulation
tive only when the first servo fails to operate. When
of the craft control stick; an automatic flight control
operating, the second servo, likewise, moves the control
mode as described above; and a standby automatic ñight
surface. As is readily apparent, the above-described fai 30 control mode.
safe technique, to its disadvantage, does not make full
A. principal object of the invention is to provide an
use ofjall of its components, i.e. it maintains a fully
automatic flight control system having fail-safe features.
operative servo in a standby, non-operating condition as
. Another object of the invention is to provide a flight
other hand, is normally inoperative and. becomes opera
long as the .other servo ‘operates properly.
In the- sec
control system |wherein separate servos are provided for
ond of the above-mentioned rfail-safe techniques, the 35 the displacement and attitude rate signals, and wherein
sumsignal is applied simultaneously‘to two servos, each ` the attitude rate signal is preferentially handled.
of which has its gain so .disposed that it contributes half
Sti-ll another object of the invention is to provide a flight
of the force necessary to move the control surface. The
control system having normal automatic, standby auto
outputsofy the two servos Iare then summed by a differ
matic, and semiautomatic modes of operation.. .
ential linkage which moves the Vcontrol surface. In the> 40
The invention will be described with reference to the
event one ofthe servos fails, automatic lcontrol is pro
figures wherein:
vided by the operating servo; however, since one-half of
FIG. -1 is .a block diagram of apparatus embodying the
the force required to move the ’control surface is lost when
present invention,
~
one of the servos fails, the automatic control provided
FIG. 2 is »a schematic diagram of a circuit adapted to
by the operating servo is only suiiicient enough to pre
provide a specie of the invention, and
.
vent dangerous craft maneuvers.’ 'llo increase the auto
FIG. 3 is a schematic diagram of a circuit which, when
v matic control provided by the single operating serv-o, its
employed with the apparatus of FIG. 1', provides that ap
gain may be increased; however, this too has undesirable . paratus with several modes of operation.
aspects. For example, since each servo :is designed to
. Referring to FlG. 1, a ilight control system, eg. a sys
have optimum performance when it has a certain level of 50 tem for, controlling the pitch attitude of »a craft, has a
gain, lany change in Igain yfrom that level deterioratesthe
pair of sensors 10and112, each of which produces a signal
performance of the servo.
'
`
representing the rate that the craft chan-ges its pitch at
The apparatus «of the present invention overcomes the
titude. The attitude rate sensors 10 land 12 are, as present
attendant disadvantages of the prior art by employing two ` ly preferred, integrating yaccelerorneters which apply their
normally operating servos which, together or singly, prop
erly control the flight of the craft I'and which, also,'never
Vrrequire'modification in any form. Generally, the appa
.ratus of the present invention applies the signal represent
output signals respectively to .amplifiers v1‘4- and .16. The
-amiciliiiers'i‘l> and 16 apply their .output signals to a sum
ming device 18` which operates. to produce a composite at
titude 'ra-te signal. The output signal hom. _the ‘amplifier
ing .the craft displacement from a reference attitude to
Mis also applied .as -a Ibias «tothe amplifier 116; likewise,
one- servo and the signal'representing the Acraft rate of 60 the amplifier 16 applies its «output signal as a Ibias Ito .the
change yof @attitude to a different servo, this technique be
the amplifier 14. As a result of .this mutual biasing of
ing in contrast to the prior artiapplication of these sig
the amplifiers, Ithe output signal 'from the summing de
nals toa summing device. The outputs of the two servos
vice ~l8 always represents the rate that the craft changes
are' then summed by a differential linkage'which moves
its attitude. For example, in the event that the signal
65
the control surface. A servo malfunction detector, oper
at the output of the amplifier 14» has Ia magnitude less
able with the servo adapted to receive the attitude rate
than .that which properly represents the rate that the craft
signal, hereinafter called lthe stability augmentation servo,
operates to detect failures in that servo and, when a fail
ure is detected, operates Yto remove the displacement sig
is `chan-ging its attitude, the bias applied to the amplifier
lr6 will be reduced correspondingly, hereby causing: (l)
«the _amplifier .16 output signal to have an enhanced mag- `
nal from the other servo, hereinafter called the -displace 70 nitude, and (2) the summing device l8r output signal to
ment servo, and to apply to the displacement servo, in
be unaffected Iby changes in the output signals from `the
3,100,861 i
,
5A
6 .
have been used are words of description rather than of
displacement from said reference attitude, summing means
limitation and that changes within the purview of the ap-`
receiving said displacement and displacement rate signals
pended claims may Ibe made without departing from the
producing a signal representing their algebraic sum, first
true scope and spirit of the invention in its broader aspects.
:What is claimed is: ,
servo` means, second servo means, switching means for
selectively applying said displacement rate signal to said
`
l. Apparatus for controlling the attitudeY of an aircraft
Yfirst servo means and no signal to said second servo- means,
comprising means producing a signal representing the craft >
displacement froma reference attitude, means producing
a signal representing the rate that said craftvchanges its
attitude, first «and second servo means adapted to receive
-respectively said displacement and attitude ratesignals,
means connected to both said yservo -means responsive to
vary a control »member on said craft in accordance with
or said displacementrate signal Iand saiddisplacenrent sig
nal respectively to said first »and second Iservo means, or
said sum signal to each ‘of said servo means, and means
connected to said ñrst and second servo means to operate
a control 'member on said craft in proportion to the alge
braio sum lof the outputs of said first and second servo
the sum of the respective outputs of said servo means, and
6. A control system for use with a dirigible craft com
means responsive to malfunctions of said second servov
15 prising means producing a signal representing the dis
means to apply said attitude rate signal to said first servo
lmeans instead of said displacement signal.
2. A control system for use with a dirigible craft com
prising means producing a signal representing the displace
ment of `said craft from a reference attitude, means pro
ducing a signal representing the craft‘rate of change of
displacement from >said 4reference attitude, switching
, means, first and second servo means, said `second servo
means being adapted -to receive the signal representing
` the craft rate of change of displacement and said ñrst
servo means being adapted to receive the displacement
t signal through said switching means, means responsive to
malfunctions in said second servo mea-ns to operate said
placement of said craft from a reference attitude, means
producingk a signal representing the craft rate of change of
displacement from said reference attitude, summing means
receiving said displacement and displacement rate signals
20 producing ya signal representing their algebraic sum, first
servo means, second servo means, switching means for
>selectively applying said displacement rate signal Ito said
ñrst servo means and no signal to said second servo means,
or said displacement rate signal and said displacement
signal respectively to said first and second 'servo means,
or said sum signal to each of said servo means, means
connected -to said first and second servo means to oper
ate a control member on said craft in proportion to the
switching means and apply said displacement rate signal
,to said first servo means instead of said displacement sig 30 algebraic sum of the outputs of said first «and second servo
means, and means responsive to failures insaid first servo `
nal, and means coupled. to said first and "second Vservov
means Ito remove the signal being applied to said second
means to operate a control member on said craft 1n pro
servo means and apply thereto instead the »signal being
portion to the sum of the respective outputs of said servo
applied to said first servo means.
means.
Y
7. A control system for use with a dirigible craft com
3. Automatic pilot rapparatus for dirigible craft com
prising means producing 'a «signal representing the cra-ft 35 prising means producing a signal representing the displace
ment of said craft ‘from a reference attitude, means pro
`displacement from a reference attitude, means to produce
ducing -a signal representing the craft rate of change of
a signal representing the’rate that said craft changes its
displacement from said reference attitude, said means pro
attitude, first servo means responsive solely to said idis
placement rate signal, relay means, second servo means, 40 ducing a signal representing the rate of change of displace
means responsive to‘malfunctions in said first servo means
nrent comprising a multiplicity `of means sensing the rate
of change of displacement, a multiplicity of amplifiers each
of which is operable respectively with-a sensing means,
summing means adapted to’ receive the output signals
rate signal or said displacement signal to said second
servo means when said relay means is respectively operated 45 from each of said amplifiers producing a composite dis
placement rate signal, and means responsive when one of
or not operated, and means operable with a control ele
said amplifiers fails to have an output signal to increase
ment on said craft summing the respective outputs of said
proportionately the gain of said other amplifiers, thereby
first and second servo means.
Y
preventing the composite signal from being affected by
4. Apparatus for controlling the attitude of an aircraft
comprising means producing `a signal representing the craft v5.0 the failure of amplifiers land sensing means, summing
means receiving said displacement »and composite dis
displacement from a reference attitude, means producng
placement rate signals producing a signal representing
a signal representing the rate that said craft changes its
their algebraic sum, first servo means, second servo means,
attitude, said> means producing a signal representing the
to disable said first kservo means Iand operate said relay
A means, said relay means applying either said displacement
rate of change of attitude comprising a multiplicity of >
switching means for selectively ‘applying said composite
means sensing the rate :of change of attitude, a multiplicity 55 displacement rate signal to said -first servo means and no
signal to said second servo means, lor said composite dis
iof amplifiers each of which is operable respectively with
placement rate signal and said displacement signal respec
a sensing mean-s, summing means adapted to receive the
tively to said first and second servo means, or said sum
output signals from each of said amplifiers producing a
signal to each |of said servo means, means connected to
composite attitude rate signal, and means responsive when
one of‘said amplifiers fails to have an output signal to 60 said >first and'second servo means to 'operate a control
member on said craft in proportion to the algebraic sum
increase proportionately the gain v«of said other amplifiers,
of the outputs of said Afirst and second servo means, and
thereby preventing the composite »signal from being af-`
means responsive to failures in said first servo means to
fected bythe failure of ampliñersand sensing means, first
remove the signal being applied to said second servo
and second servo means adapted to receive respectively
said displacement and composite signals, means connected 65 means and apply thereto instead the signal being applied
to both said servo means responsive to vary a control
member on said craft in accordance with the sum of the
to said «first servo means.
respective outputs lof said servo means, and means respon
prising means producing a signal representing the displace
sive to malfunctions of said second servo means to apply
ment of said craft from a reference attitude, means pro~
8. A control system for use with a dirigible craft com
said composite signal to said first servome-ans instead 70 ducing a signal representing the craft rate of change of g
Y of said displacement signal.
displacement from said reference attitude, summing means
5. A control system for use with a dirigible craft com
receiving said displacement and displacement rate signals
prising means producing a signal representing the displace
producing a signal representing ‘their algebraic sum, first
ment of said craft from a reference attitude, means pro--
servomeans, second servo means, switching means for
ducing a signal representing the craft rate of change of 75 seiectively applying said displacement rate signal to said
,
first servo means and no signal to'said second servo means,
or Lsaid displacement VrateV signal and said displacement
Y
8
'
l
second servo means and apply theneto instead the signal
being applied to said first servo means.
'
signal respectively to' said first and second servo means,
l or said sum signal to each of said servo means, means
connected rto said iirstand second servo means fto operate
adcontrol member .on said crafty in proportion to the alge
References Cited in the iile of this patent
UNITED STATES PATENTS
braic sum of the outputs of said `first and second servo
2,642,554
MacCallurn __________ __ June 16AI 1953
Ymeans, and means comparing the input signal to said ñrst
2,665,086
Moog et al. _____ _-_ ____ _„ Jan. 5, 1954
servo means with a signal representing fthe output of said
first servo means responsive when there is a difference lO
therebetween to remove the signal lbeing applied to said
2,820,935
Kleason _____________ __ Jan. 21, 1958
2,835,861
2,862,167
Eckhardt _". __________ __ May 20, 1958
Curry _______________ __ Nov. 25, 1958
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