Mechanically linked active sidesticks

Conventional column controls for aircraft flight control systems are replaced by active sidesticks which are connected to port and starboard aircraft mechanical, electrical or hydraulic systems by means of servo motors and cables. Movement of the active sidestick handles is detected and a signal generated to drive a servo motor in manner corresponding thereto, which in turn will drive cable assemblies which control aircraft flight control surfaces. Two sidesticks are provided, preferably with an electrical cross-cockpit interconnect to cause movement of one sidestick to result in a signal being transmitted to a second sidestick to cause the motor thereof to force the sidestick to track the movement of the first sidestick. In an alternative implementation, the sidesticks are employed in a fly-by-wire system with a conventional cable system as backup. The cable system is disengaged from the sidesticks by means of a disengage clutch whereupon failure of the fly-by-wire system, the clutch will engage the cable system and provide a mechanical backup to the fly-by-wire system in the event of failure thereof.

FIELD OF THE INVENTION 
This invention relates to the use of active sidestick hand controllers as 
replacements for columns employed in conventional column controlled flight 
control systems. More specifically, the invention relates to the use of 
the active sidesticks as an improved replacement for convention column 
controls, or alternatively, for use in a fly-by-wire system with a backup 
mechanical linkage between the sidestick and the flight control system in 
the event of failure of the fly-by-wire system. 
BACKGROUND OF THE INVENTION 
Conventional column-type flight control systems have typically included 
paired columns for a pilot and copilot. Each column includes handgrips on 
what can be termed a steering wheel. The columns are pivotable along one 
axis to control pitch of an aircraft and the steering wheel serves to 
control roll of the aircraft. 
Typically, the two columns are mechanically cross-linked and are connected 
to parallel mechanical systems (one for port side and one for starboard 
side) which control the aircraft flight control surfaces. Specifically, 
each system consists of cables connected by means of pulleys to the 
aircraft systems (e.g. mechanical, electrical or hydraulic) which in turn 
control the flight control surfaces in a manner corresponding to movement 
of the column or the steering wheel thereof. In the event of failure of 
one of the parallel systems of a corresponding column, the two columns 
which are mechanically cross-linked can be disconnected by means of a 
selective connection mechanism. 
A disadvantage in these types of systems is that they are often bulky, 
require significantly more space in an aircraft cockpit and involve 
addition of servo and trim motors connected to the cable system for 
autopilot backdrive and trim. Thus, it becomes desirable to replace such 
systems with active sidesticks, including servomotors, which are smaller 
and easier to use in controlling an aircraft then conventional column 
control systems. 
SUMMARY OF THE INVENTION 
In accordance with one aspect of the invention, conventional columns in a 
column controlled system are replaced with active sidesticks for a pilot 
and a copilot which link through means of servo motors to cables linking 
to the control systems of an aircraft. Thus, in one aspect, there is 
provided an active hand controller system which comprises a manual control 
stick moveable along a pitch axis (x) and a roll axis (y). Sensors are 
provided for detecting the movement and force of the manual control stick 
along at least one of the two axes for generating signals representative 
of the movement and force. Control electronic of the type disclosed in 
co-pending application Ser. Nos. 07/957,427, 07/957,278 and 07/957,216, 
serve to receive the signals from the sensors for generating a control 
signal in response thereto for controlling at least one servo motor per 
axis connected to the manual control stick. The servo motor is connected 
to the manual control stick and to cable linkages of the type in use in 
conventional column control systems, which are connected to an aircraft's 
mechanical, electrical or hydraulic flight control system. The servo motor 
when controlling the axis in response to the control electronics will also 
control the cable linkages which are connected to the aircraft flight 
control system. 
In a more specific aspect, the system of the invention includes two manual 
control sticks arranged in a dual cockpit configuration and having a cross 
feed of signals to also have the control electronics provide a signal from 
one control stick and cable linkages to the other to cause the other 
control stick and cable linkages to move in a manner duplicative of the 
manner in which the first control stick is moved. 
In an alternative implementation of the invention, there is provided an 
active hand controller for a fly-by-wire flight control system of an 
aircraft of the type disclosed in co-pending application Ser. Nos. 
07/957,427, 07/957,278 and 07/957,216, which disclosures are incorporated 
by reference herein. In this embodiment the manual control stick is 
electrically connected to the flight control system to provide a command 
signal from the control electronics as is disclosed in said co-pending 
applications. 
For the fly-by-wire implementation the cable system leading to the aircraft 
mechanical, electrical or hydraulic flight control system operates only as 
a backup with the control stick disengaged from the cable and linkages by 
means of a clutch which is in a disengaged condition when power is on, but 
which engages the cable system should there be a failure of the 
fly-by-wire system such that with or without the servo motors using the 
manual control stick, the pilot or copilot can maintain control of the 
aircraft. In the event power to the servo motors or the manual control 
sticks fails, the motors are selected to be backdrivable with forces 
applied to the control stick (e.g., forces on the stick will cause motion) 
so as to not obstruct movement of the cables as a result of a pilot or 
copilot applying force to the handle of the control stick.

DETAILED DISCUSSION OF THE INVENTION 
Prior to discussing the invention, the prior art conventional column 
systems as illustrated in FIGS. 1a, 1b and 2 will be discussed. As shown 
in FIG. 1a, the system for pitch control is generally designated by the 
numeral 10. Two columns 12 are arranged in a parallel arrangement and are 
pivotable in a manner shown by arrows A. The columns are interconnected by 
means of interconnect shaft 18 which includes a pitch mechanical 
disconnect which can serve to disconnect one column from the other by 
pulling handle 16. A conventional control column balance spring 20 
stabilizes movement and use of the column 12. As further illustrated in 
FIG. 1a, a link 22 to the forward quadrant pitch cable pulley assembly 24 
connects the column 12 to cable 26, which in turn leads to and is 
connected to the aft quadrant 30 of the system 10. The connection at the 
aft quadrant 30 leads to the mechanical, electrical or hydraulic system of 
the flight control system through load limiters 34 for control thereof. 
Since the columns 12 are connected to the flight control system by means 
of cables 26, the "feel" of a mechanically linked system is not 
ordinarily maintained at the column for the users thereof. In order to 
ensure such "feel," as shown by the dashed line, there is connected to the 
cables 26 a pitch feel simulator unit 32 of conventional construction, as 
shown in FIG. 1b. An autopilot servo 28 serves to provide movement to the 
column in a manner corresponding to control pitch of the aircraft by the 
autopilot when the autopilot is engaged. 
FIG. 2 further illustrates the roll control assembly 36 of the prior art 
column controlled system. The steering wheel 38 is connected to cables 12a 
and is shown connected by means of forward quadrant 44 to cable assembly 
52 which serves to control roll as connected to port and starboard aileron 
controls of an aircraft. There is provided a roll disconnect mechanism 40 
which enables the cables 12a to be disconnected from each other by merely 
pulling at handle 42 which then disconnects the two columns at the roll 
mechanical disconnect 46. Balance springs 50 are arranged in a 
conventional configuration to maintain balance between the parallel 
systems of cables 12a. The cables 52 lead to the aft quadrant (not 
numbered) and are connected in a conventional configuration to a trim 
mechanism 54, trim actuator 56, and as in the case with the pitch control 
system of FIGS. 1a and 1b, there is provided an artificial feel unit 58 to 
provide artificial feel to the steering wheels 38. An autopilot servo 60 
serves to provide movement to the wheel in a manner corresponding to 
control roll of the aircraft by the autopilot when the autopilot is 
engaged. 
FIG. 3 schematically illustrates in partial transparent and perspective 
view, a mechanically linked active sidestick 62 of the type employed in 
the present invention. The active sidestick 62 includes a handle 80 which 
is moveable about a pitch axis (x) and a roll axis (y). The handle 80 
includes connected thereto at least one motor on each axis generally 
illustrated by the number 76a for the pitch axis and 76b for the roll 
axis. Although one motor is shown numbered for each axis, it will be 
appreciated that more than one can be employed, depending on the redundant 
configuration. 
Connected to motor 76a is a pitch interface link 68 which has connected 
thereto a push rod 70 which leads to the forward quadrant cable pulley in 
both embodiments of the present invention. Connected to the motor 76b, is 
a roll pulley assembly 72 including cable 74, also implemented in both 
embodiments of the present invention. The roll cable 74 and the push rod 
70 are connected to the forward quadrant in a manner similar to that 
illustrated in FIGS. 1a-2. 
A mother board 66 interconnects the control electronics 64 sensors 
connected (not shown) to handle 80 to detect movement and force thereof 
and generate a signal, typically a position signal, or even a force signal 
as a result of force applied to and movement of handle 80 caused by a 
user. The operation of the control electronics through the sensors as well 
as the motors 76a and 76b will not be detailed further herein but is as 
described in co-pending application Ser. Nos. 07/957,427, 07/957,278 and 
07/957,216. The control electronics serve to control the operation of the 
motors in response to a pilot's use of the handle 80 to cause the motor to 
drive the pitch and roll linkages and cables as well as to drive movement 
of the handle 80 in response to any external control signal being received 
by the electronics, which are then processed and transmitted to a 
respective motor 76a or 76b to move a respective handle 80. The motors 76a 
and 76b provide the "feel" to the system during piloted operation. 
Specific implementation of the gimbal configuration for the roll and pitch 
implementation will require consideration of decoupling motion of the 
innermost gimbal from the outermost gimbal. One option is with roll as the 
innermost and pitch as the outermost, then a decouple mechanism can be 
implemented similar to that achieved on previous purely mechanically 
linked systems such as the commercially available military Cobra 
helicopter forward sidestick configuration. This decouple mechanism has 
been implemented in prior art and as such is not a subject matter of this 
invention. 
A first embodiment of a pitch control system in accordance with the 
invention is generally illustrated at FIG. 4. In FIG. 4, the pitch control 
system mechanically connected to the aircraft flight control system is 
essentially the same as illustrated in FIG. 1a without the mechanical 
interconnect shaft, and in addition, a disengage clutch 86 for pitch is 
configured so that the active sidesticks 62 are disengaged from the cables 
26 when power is on. Thus in this configuration, the system is employed in 
a fly-by-wire system wherein the aircraft flight control surfaces are 
controlled by electrical signals transmitted through lines 88 from the 
respective active sidesticks 62. 
Movement of the handles 80 results in position and force signals being 
transmitted and processed by control electronics 90 to be transmitted to 
the respective motor 76a, and such movement also results in a direct 
signal for control of the fly-by-wire system being transmitted through 
lines 88, depending on which handle is moved as is described in said 
above-referenced co-pending applications. 
Thus, movement of the pilot handle 80 on the left side of the drawing will 
result in a control signal being transmitted on its line 88, as well as a 
torque signal for electronic coupling being transmitted by means of switch 
84 when closed, to the control electronics 90 of the copilot, i.e., right 
side, to result in a signal being fed to motor 76a to cause the handle 80 
to move in a manner corresponding to that of the pilot handle 80 on the 
left side. As may be appreciated, also shown is a center command control 
line 92 for inputting a number of different signals, for example, for 
signals from an autopilot system and for signals in response to the flight 
control surfaces being forced to move by external forces. Such an applied 
signal results in a corresponding movement of both handles 80 caused by 
being driven by the respective motors 76a. 
As will be appreciated, upon failure of the fly-by-wire system, a number of 
things can occur. First, a complete system shutdown may occur (e.g., power 
loss), in which case the clutches 86 will close allowing the handle 80 to 
be driven to drive the cables 26 to maintain control of the aircraft 
flight control system. In the case of total system failure including 
failure of power to motors 76a, the motors are backdrivable and as such 
will not impede movement of the handle 80 and cables 26. Thus, the handles 
80 are moved based on pure physical strength of pilot and copilot alone 
resulting in degraded pilot "feel". An alternative failure can occur when 
there is a failure of the electronics of the fly-by-wire system, but power 
is maintained to motors 76a. In this scenario the motors 76a drive the 
cables in a manner where not much force is required of the pilot or 
copilot in moving the control stick handles 80. 
One alternative configuration of the embodiment of FIG. 4 can include a 
mechanical interconnecting cross-link similar to that of FIG. 1a 
connecting the copilot and pilot active sidesticks 62 not only 
electrically by means of switch 84 but also mechanically with a shaft 
similar to interconnect shaft 18 also having a mechanical disconnect 14 
for pitch as shown in FIG. 1a. The clutches 86 will allow engagement of 
the mechanical linkage flight control system as presented or independently 
engage or disengage the mechanical cross-link interconnecting shaft. 
A second alternative configuration of the embodiment is to mechanically 
cross-link the pilot and copilot sidesticks only without the use of the 
electrical cross coupling torque signal. The clutches 86 can be used to 
engage or disengage either the flight control system or the mechanical 
interconnection. 
The roll control system of this embodiment of the invention is shown in 
FIG. 5 in a manner similar to that of FIG. 4. It will be appreciated that 
the control electronics is likewise similar to that disclosed in 
co-pending application Ser. Nos. 07/957,427, 07/957,278 and 07/957,216, 
and need not be disclosed in greater detail herein with reference being 
made to said co-pending applications for the details of said electronics. 
In the roll control system, a roll clutch 94 serves to disengage the 
mechanical system and cables 52 at the forward quadrant roll cable pulley 
assembly 44 from the active sidesticks 62. The active sidesticks are 
typically connected and interfaced to the forward quadrant pulley 44 
through a roll output pulley 45. A control signal in the fly-by-wire mode 
is typically generated by movement of the handles 80 by the sensor thereof 
and transmitted through lines 96 to the fly-by-wire control system. 
As in the case with the pitch control of FIG. 4, the torque coupling 
signals are interconnected by means of a switch 98 which serve to transmit 
cross signals between active sidestick assemblies 62 to ensure that they 
track each other in movement by processing the cross signals in the 
respective control electronics 90, which are then transmitted to motors 
76b to drive the handles 80. Likewise, a center command or autopilot 
signal is also transmitted to the roll axis of the system by means of an 
input line 100 as illustrated in FIG. 5. 
As will be appreciated, first and second alternative variations of both 
mechanical and electrical interconnection between the pilot and copilot 
roll control systems will be effected in the same manner as discussed with 
reference to FIG. 4. First, a mechanical cross-link can be provided 
similar to that of roll interconnect shaft 48 of FIG. 2 in addition to the 
electrical interconnection. Secondly, the connection through switch 98 
between the torque coupling signals can be such that there is no 
connection resulting in only the mechanical interconnect shaft 48. 
Having thus described the pitch and roll control system employing active 
sidestick 62 in accordance with this first embodiment of the invention as 
implemented on a fly-by-wire system with a mechanical backup, the second 
embodiment of the invention will be discussed with reference to FIGS. 6 
and 7. 
The embodiment of FIGS. 6 and 7 contemplates the use of the active 
sidestick 62 as a direct substitution for the conventional mechanical 
column 12 of FIGS. 1a, 1b and 2. Specifically, as will be appreciated from 
the drawing, since the sidesticks of 62 of necessity employ motors 76a and 
76b and electronics electrically cross-linking them, there will be some 
electronics involved similar to that disclosed in the co-pending 
application Ser. Nos. 07/957,427, 07/957,278 and 07/957,216, but there is 
no electrical connection to a fly-by-wire system as generally illustrated 
by lines 88 and 96 of FIGS. 4 and 5. 
Further simplification in the embodiments illustrated in FIGS. 6 and 7 from 
FIGS. 4 and 5, is that flight control is achieved through the cables 26 
and 52 respectively connected to the aircraft mechanical, electrical or 
hydraulic flight control system. The clutches 86 and 94 of FIGS. 4 and 5 
for the fly-by-wire implementation are eliminated in the preferred 
configuration shown in FIGS. 6 and 7 for pitch and roll control 
respectively for flight control with a mechanically linked sidestick. The 
systems illustrated in FIGS. 6 and 7 have the advantage of the servo 
motors 76a and 76b driving the cables 26 and 52, wherein not much force is 
required of the pilot and copilot in moving the control stick handles 80. 
Additional benefits are achieved because the servo motors 76a and 76b are 
used to achieve the functions of FIGS. 1a and 2 autopilot servo 28 and 60 
with associated mechanisms and the FIG. 2 trim servo 56 with associated 
mechanisms, thereby simplifying the mechanical control system reducing 
complexity and weight. 
FIG. 6 generally illustrates the connection of the active sidesticks 62 in 
a manner similar to that of FIG. 1a and including an interconnect shaft 18 
with a pitch mechanical disconnect mechanism 14 which is activated by 
handle 16. As in the case with FIG. 1a, the system for pitch control is 
connected by means of cables 26 through forward quadrant pulley 24 which 
is in turn driven by the link 22 to the forward quadrant. 
As may be appreciated, the active sidestick 62 handle 80 may be driven to 
result in signals picked up by sensors and transmitted to control 
electronics 90. The control electronics 90 translates the signal into a 
motor control signal which is transmitted to motor 76a. The motor 76a as a 
result drives the linkage 22. As may be appreciated, the motor 76a is 
selected to be of a type sufficiently powerful and effective to drive the 
linkage 22 to control the cables 26 which in turn drives the aircraft 
mechanical, electrical or hydraulic systems for control of the flight 
control surfaces. 
The active sidesticks 62 are also electronically interconnected through 
switch 84 such that, for example, when the left side pilot handle 80 is 
moved, a torque signal for electronic coupling is transmitted by means of 
switch 84 when closed to corresponding control electronics 90 of the 
copilot sidestick 62 to result in an augmented signal being transmitted 
from the control electronics 90 to motor 76a to drive handle 80 in a 
manner corresponding to the movement of the other handle 80. The 
electronic disconnect switch 84 for the electronic coupling can be 
simultaneously controlled by the disconnect handle 16 when mechanical 
cross-cockpit disconnect mechanism 14 is selected. The cross-cockpit 
tracking between the pilot and copilot sidesticks will be dominantly 
controlled by the electrical interconnection through switch 84 because of 
the inherent backlash and compliance in the mechanical interconnection via 
shaft 18 and associated mechanisms. Likewise, the system can be configured 
to include an electrical input through line 92 from external sensors 
detecting the movement of flight control surfaces or, for example, from an 
autopilot system which would ensure that the handles 90 track the movement 
of the flight control surfaces or the commands of the autopilot system to 
the flight control surfaces. 
As may also be appreciated, making reference to the embodiments of FIGS. 4 
and 5, an alternative interconnect between the two active sidestick 
systems 62 from FIGS. 6 and 7 can be achieved. The first alternative from 
FIGS. 6 and 7 may be configured such that only electrical signals are 
transmitted between sidesticks 62. With this alternative, the complete 
electrical interconnect can be maintained but the mechanical interconnect 
through shaft 18 can be eliminated. The second alternative from FIGS. 6 
and 7 is to eliminate the electrical interconnection 84 between the 
sidesticks and maintain only the mechanical interconnect through shaft 18. 
The specifics are a matter of design choice for the particular aircraft 
involved. 
FIG. 7 illustrates the roll control system in a manner similar to that of 
FIG. 5 and FIG. 6. In this case, there is also no control signal line to a 
fly-by-wire system but the active sidesticks 62 are interconnected 
electrically through switch 98 in a manner similar to that of FIG. 6. The 
roll control mechanical interface is via the roll control pulley 
illustrated using the number 45 again. There is a direct link by means of 
forward quadrant pulley 44 to the cables 52 which in turn control the roll 
flight control surfaces, i.e., ailerons, of the aircraft. As in the case 
with the pitch control of FIG. 6, lines 100 serve to provide an electrical 
input which is reflective of either movement of the flight control surface 
or is a signal from an autopilot system to ensure tracking between the 
handle 80 and the autopilot system. 
Likewise, as in the case with FIG. 6 various permutations can be set up 
wherein the mechanical cross link can be eliminated or the electrical 
cross link can be eliminated between the active sidestick 62. 
Having generally described the invention in detail, the same will be better 
understood from the following claims which set forth the invention in a 
non-limiting manner.