Abstract: Autonomous collision avoidance systems for unmanned aerial vehicles are disclosed. Systems illustratively include a detect and track module, an inertial navigation system, and an auto avoidance module. The detect and track module senses a potential object of collision and generates a moving object track for the potential object of collision. The inertial navigation system provides information indicative of a position and a velocity of the unmanned aerial vehicle. The auto avoidance module receives the moving object track for the potential object of collision and the information indicative of the position and the velocity of the unmanned aerial vehicle. The auto avoidance module utilizes the information to generate a guidance maneuver that facilitates the unmanned aerial vehicle avoiding the potential object of collision.

Abstract: An actuation system including a plurality of actuators; a plurality of position sensors coupled to the actuators, the plurality of position sensors providing rate feedback signals proportional to an actuator rate; a plurality of force sensors coupled to the actuators, the plurality of force sensors providing delta pressure signals; and a feedback control loop configured to receive the rate feedback signals and delta pressure signals and compute a difference in actual actuator rates and sum the difference with a computed difference in actuator forces to generate actuator positioning commands that equalize the actuator forces on a control surface.

Abstract: Disclosed are a method and device for attenuating vertical turbulence encountered by an aircraft during flight. Incorporated into the method and device is a wind determination device, which is used to determine a vertical wind component existing outside the aircraft. A severity level determination unit is used to determine a severity level of the vertical wind component determined by the wind determination device. A control unit calculates at least one control order based on the vertical wind component determined by the wind determination device. In addition, the control unit determines the actual existence of activation conditions determined according to the severity level determined by the severity level determination unit. Upon verifying the activation conditions, the control unit transmits the control order to at least one actuator of the at least one controllable movable member.

Abstract: A method for reducing yawing motions of an aircraft in-flight, wherein a spoiler adjustment drive of a spoiler and a regulating flap adjustment drive of a regulating flap of the same respective airfoil are adjusted in a time segment in such a way that the motion of the spoiler being adjusted and the motion of the regulating flap of the same airfoil deflect in mutually opposite directions in the time segment. The spoiler and the regulating flap are adjusted on the airfoil, on which the adjusted deflections counteract the respectively occurring yawing motion. Also provided are a computer program product for carrying out this method and an aircraft with a directional stabilization device for carrying out this method.

Abstract: Stable flight can be achieved without the need for a complicated throttle operation by a pilot even when part or all of control surfaces malfunction. A computation means (15) calculates a thrust control signal for controlling engine thrust and a deflection angle control signal for controlling control surfaces based on state information regarding an airframe and an operation command signal from an operation end. An engine driving means (17) drives an engine based on the thrust control signal. A control surface moving means (16) moves the control surfaces based on the deflection angle control signal.

Abstract: Present novel and non-trivial system, device, and method for generating altitude data and/or height data are disclosed. A processor receives navigation data from an external source such as a global positioning system (“GPS”); receives navigation data from multiple internal sources; receives object data representative of terrain or surface feature elevation; determines an instant measurement of aircraft altitude as a function of these inputs; and generates aircraft altitude data responsive to such determination. In an additional embodiment, the processor receives reference point data representative of the elevation of the stationary reference point (e.g., a landing threshold point); determines an instant measurement of aircraft height as a function of this input and the instant measurement of aircraft altitude; and generates aircraft height data responsive to such determination.

Abstract: Embodiments of the invention relate to a flight control system for controlling an aircraft during flight. The flight control system may include a primary controller configured to receive an input from a pilot and to output a primary control signal and a primary transmission path connected to the primary controller and configured to relay the primary control signal. The flight control system may also include a backup controller configured to receive the input from the pilot and to output a backup control signal and a backup transmission path connected to the backup controller and configured to relay the backup control signal. Additionally, the flight control system may include an actuator having a remote electronics unit configured to receive the primary control signal and the backup control signal and to determine if the primary control signal is available and valid.

Abstract: A present novel and non-trivial system, module, and method for constructing a flight path used by an avionics system are disclosed. A processor receives flight plan data and object data associated with terrain and obstacles. Free cells are extracted above the objects using a recursive space decomposition technique, and a reference path is formed through traversable free space determined from the availability of free cells. In an additional embodiment, threat data associated with hostile military weaponry and significant meteorological conditions could affect the availability of free cells. A genetic algorithm applying genetic operators which include mutators is employed with aircraft kinematic constraints to refine the reference path used to form a population of best path candidates. When a best path is reached after cycling through a re-generation process of path candidates, flight path data representative of the best path is generated and provided to at least one avionics system.

Abstract: This invention relates to an intelligence system on board an aircraft that detects an emergency, assesses the situation, and then acts on the situation in a pre-determined manner.

Abstract: A method and device of dynamically reducing the buffeting of an airplane. The method is carried out by detecting a risk of buffeting of the airplane in flight by a monitor. At least one control surface is turned by an actuator arranged at a trailing edge of each wing of the airplane. The control surface is turned, at a predetermined respective rate of turn, into a predetermined respective position to modify lift profile of the wing along a wingspan length to reduce lift in at least one buffeting-generating region of each wing.

Abstract: The invention concerns a method for improving determination of inertial navigation parameters (1) of a carrier (1) moving along modelizable kinematic movement components, the method including the following steps: (a) selecting, taking into account a kinematic model (13) of the carrier (1), at least one movement component whereby integration (11) of the inertial measurements (20) is assumed to give a predetermined value, (b) integrating (11) the inertial measurements (20) in accordance with the selected component(s), (c) determining (14) based on the component(s) a variation between the integration (11) obtained at step (b) and the predetermined value of step (a), (d) estimating on the basis of the variation(s) thus obtained a global inertial error resulting from internal errors associated with said modelizable components, and values to be updated of variable parameters of the kinematic model (13), (e) correcting said inertial navigation based on the thus determined global inertial error.

Abstract: The effects of IMU gyro and accelerometer bias errors are significantly reduced in accordance with the present teachings by a system or method for commanding an IMU or vehicle through a series of preprogrammed maneuvers. The maneuvers can be designed to minimize the effects of other gyro errors including scale factor errors, nonlinearities, cross coupling/misalignment, and scale factor asymmetries. A sample maneuver is provided which demonstrates performance based on a sequence of roll and yaw maneuvers resulting in zero build up of error at the end of a maneuver cycle period as a result of these errors. Modification of the system involves the addition of control logic to determine the maneuver period, maneuver rate, and vehicle orientation. No additional hardware beyond possible fuel required to perform the maneuver is required.

Abstract: Embodiments of a process and a program product are provided suitable for implantation by a flight management system (FMS), which is deployed onboard an aircraft and including a display device and a user interface. The FMS operable in a plurality of non-precision approach modes. In one embodiment, the process includes the steps of: (i) receiving data via the user interface designating an approach in a flight plan; (ii) enabling the pilot to utilize the user interface to select a non-precision approach mode from the plurality of non-precision approach modes if the designated approach is a non-precision approach; and (iii) placing the FMS in the selected non-precision approach mode during the designated approach.

Abstract: A method and device for generating a speed profile for an aircraft rolling on the ground. The device (1) comprises means (8) for automatically determining a speed profile which is suited to successive elements of a ground rolling trajectory and which complies with maximum speeds and particular constraints.

Abstract: In conformance with the invention, based on the incident conditions and velocity, the steering of the ailerons is weakly negative (b0) or corresponds either to the maximum sharpness of the aircraft (b1), or the optimal lift of the latter (b2).

Abstract: A hybrid helicopter includes an airframe provided with a fuselage and a lift-producing surface together with stabilizer surfaces and a drive system including: a mechanical interconnection system between a rotor of radius (R) with collective pitch and cyclic pitch control of the blades of the rotor and at least one propeller with collective pitch control of the blades of the propeller; and at least one turbine engine driving the mechanical interconnection system. The hybrid helicopter includes first members for controlling the angle at which the at least one pitch control surface is set as a function of the bending moment exerted on the rotor mast relative to the pitch axis of the hybrid helicopter, and second members for controlling the cyclic pitch of the blades of the rotor in order to control the longitudinal trim of the hybrid helicopter as a function of flight conditions.

Abstract: Embodiments of the invention relate to a flight control system for controlling an aircraft during flight. The flight control system may include a primary controller configured to receive an input from a pilot and to output a primary control signal and a primary transmission path connected to the primary controller and configured to relay the primary control signal. The flight control system may also include a backup controller configured to receive the input from the pilot and to output a backup control signal and a backup transmission path connected to the backup controller and configured to relay the backup control signal. Additionally, the flight control system may include an actuator having a remote electronics unit configured to receive the primary control signal and the backup control signal and to determine if the primary control signal is available and valid.

Abstract: Flight control systems have plural control subsystems with redundancies organized so as to provide continued but degraded control power over critical aircraft flight operating parameters even if any one complete control subsystem catastrophically fails. One example described in detail for a VTOL craft includes four groups of controls, each group comprising inputs relating to six degrees of freedom of the vehicle, at least one control computer and a plurality of actuators; each group utilizing 25% of required flight control power for the vehicle.

Abstract: A system and method of mitigating a force fight between hydraulically-operated actuators that are coupled to a single flight control surface is provided. The differential fluid pressure across each hydraulically-operated actuator is sensed. The position of a user interface is sensed using a plurality of user interface position sensors. Flight control surface position is sensed using one or more position sensors. The sensed differential pressures, the sensed user interface positions, and the sensed flight control surface position are used to generate a plurality of substantially equal actuator commands.

Abstract: A flight control system and method which determines an expected power required data in response to a flight control command of the at least one model following control law and utilizes the expected power required data to perform at least one action to control an engine speed.

Abstract: A flight control system for an aircraft receives a selected value of a first parameter, which is either the airspeed or inertial velocity of the aircraft. A primary feedback loop generates a primary error signal that is proportional to the difference between the selected value and a measured value of the first parameter. A secondary feedback loop generates a secondary error signal that is proportional to the difference between the selected value of the first parameter and a measured value of a second flight parameter, which is the other of the airspeed and inertial velocity. The primary and secondary error signals are summed to produce a velocity error signal, and the velocity error signal and an integrated value of the primary error signal are summed to produce an actuator command signal. The actuator command signal is then used for operating aircraft devices to control the first parameter to minimize the primary error signal.

Abstract: A system allowing for the controlled propulsion of aircraft, especially buoyant and semi-buoyant airships designed as a symmetric body of revolution, without the need for or use of aerodynamic control surfaces, comprised of a plurality of ducted fan thrusters placed both fore and aft, designed to ingest air flowing at less than free stream velocity. Fans are arranged such that when at standard orientation, the thrust from each is directed tangentially to an arc drawn along the hull from bow to stem. By defining multiple sets of thrusters based upon their location, differential thrust may be applied based upon set membership in order to affect translational and rotational maneuvering of the aircraft.

Abstract: Actuator systems and associated methods are disclosed herein. One aspect of the disclosure is directed toward an actuator system that includes a first structure and a second structure movable relative to the first structure. The system further includes an actuator apparatus and an actuator device coupled in series between the first structure and the second structure. The system can still further include a controller operably coupled to the actuator apparatus and the actuator device. The controller can be programmed with instructions to automatically actuate the actuator apparatus and the actuator device so that a position of the first structure relative to the second structure after the actuator apparatus and the actuator device have been actuated is at least approximately the same as a position of the first structure relative to the second structure before the actuator apparatus and the actuator device have been actuated.

Abstract: A smart servo controller that is operable to control a redundant configuration of servo motors corresponding to mechanical control surfaces of an aerial vehicle is described. The controller (i) outputs the necessary electrical signals that control the servo motors corresponding to each control surface, (ii) monitors those signals, (iii) monitors the positions of the servo motor shafts, and (iv) provides notification to a flight control computer upon detecting a servo malfunction.

Abstract: The invention relates to a method and a device for constructing a low-altitude flight path to be followed by an aircraft. The device comprises a database including a terrain profile concerning the terrain to be flown over by the aircraft, a set of data sources, first unit for determining a lateral trajectory of the flight path, and second unit for determining a vertical trajectory of the flight path, the second unit being formed so as to determine the vertical trajectory during the aircraft flight, successively as the flight proceeds, segment by segment, and including an element for retrieving from the database a profile section, and an element for determining a vertical trajectory segment, using the retrieved profile section, based on the climb-out and let-down performances of the aircraft derived from the set of data sources.

Abstract: A control device for aircraft for reducing the turbulence and gust influences on the flying characteristics is designed to generate an additional incidence angle drive signal for control surfaces on surfaces which generate an air force, in particular wing and/or tailplane as a function of an instantaneous bank angle (?) and sideslip angle (?).

Abstract: A method to assist the piloting of an aircraft in a non-precision approach during a landing phase may include a series of successive steps that are carried out interactively and automatically. The steps include verifying, in accordance with respective standards of operation, conditions relating to the correct functioning of a plurality of equipment of the aircraft and to the integrity and precision of measurements of parameters used for implementing the non-precision approach, based on information from the plurality of equipment. On the basis of the verified conditions, an appropriate approach category is selected and presented on a display screen.

Abstract: A flight control system is provided with one or more modal sensors that are each configured to measure the rate and possibly acceleration for a flexible body mode of the flight vehicle. The modal sensor's rate and suitably acceleration are subtracted from the rate and acceleration measured by the IMU such that the values provided to the flight controller more closely represent only the rate and acceleration of the flight vehicle's rigid airframe component. A piezoelectric modal sensor is capable of sensing a particular flexible body mode over variations in the modal frequency without inducing additional phase loss in the control loop in order to maintain suitable phase and gain margins. Sensors are suitably provided for at least and possibly only the 1st lateral bending modes in the pitch and yaw channels.

Abstract: Circuits and methods for use on a mobile platform including a flight control system, a structure, an aerodynamic surface, and an actuator operatively coupled to the surface to control the surface. The circuit includes a first and a second input, a summing element, and an output. The first input accepts commands from the flight control system while the second input accepts a vibration signal from the structure. The summing element communicates with the inputs and sums the signal and the command. In turn, the summing element controls the actuator with the summed signal and command.

Abstract: A method and system for preventing the control of an aircraft from the cockpit. In an exemplary embodiment, the system could be triggered externally. For example, an air traffic control (ATC) station could determine that the aircraft has deviated from its planned flight path. If personnel at the ATC station decide that the deviation is not attributable to the actions of the authorized flight crew, the personnel can transmit a signal to the aircraft that disables all normal cockpit control of the aircraft. Once normal flight controls are disabled, the aircraft may execute a preprogrammed emergency flight plan via its autopilot system, with or without the use of a flight management system (FMS). The emergency flight plan could cause the aircraft to fly to a sparsely populated area and enter a holding pattern, or it could cause the aircraft to land in a sparsely populated area or at an airport using an autoland system.

Abstract: A rotational position-adjusting system (6) for a vertical takeoff and landing aircraft (4). The system (6) includes multiple detectors (60) that generate rotor signals. The rotor signals are indicative of the position of each rotor (8) of the aircraft (4). The rotors (8) provide lift to the aircraft (4). A controller (24) is coupled to the detectors (60) and adjusts the rotational speed of one or more of the rotors (8) in response to the rotor signals.

Abstract: An adaptive control system is provided that scales both gain and commands to avoid input saturation. The input saturation occurs when a commanded input uc exceeds an achievable command limit of umax. To avoid input saturation, the commanded input uc is modified according to a factor ?.

Abstract: A method and a device reduces the vibration generated on the structure 17 of a helicopter 2 by the flow of air through the main rotor 5 and by the flow of air along the fuselage 3. The device 1 includes: at least one sensor 18, 19, 20 measuring the vibration generated on the structure 17; and computer element 30 responsive to the vibration measurements to determine variation in the angle of incidence of a tail fin 9 of the helicopter 2 suitable for generating an opposing force {right arrow over (T1)}, {right arrow over (T2)} for opposing the vibration, and transmitting the variation in angle of incidence as determined in this way to a control system 10 for controlling the angle of incidence of the tail fin 9.

Abstract: A flight control system and method which determines an expected power required data in response to a flight control command of the at least one model following control law and utilizes the expected power required data to perform at least one action to control an engine speed.

Abstract: A method and a device allow for reducing the vibration generated on the structure 17 of a helicopter 2 by the air flow through the main rotor 5 and by the air flow along the fuselage 3. The device 1 includes: at least one sensor 18, 19, 20 measuring the vibration generated on the structure 17; and computer element 30 responsive to the measurements to determine a variation in angle of incidence for a stabilizer 39 of the helicopter 2 that is suitable for generating a vertical opposing force {right arrow over (TZ)} for opposing the vertical vibration, with the variation in angle of incidence as determined in this way being transmitted to a system 10 for controlling the angle of incidence of the stabilizer 39.

Abstract: The present invention provides a diagnostics methodology and embedded electronic system that allows optimized low-frequency data sampling for EMA motoring subsystems in an operating vehicle. Each of the EMA motoring subsystems includes: an EMA; at least one motor for driving the EMA; and power controls for operating the motor, wherein the power controls includes a DSP controller for sampling and processing data at low-frequency sampling rates. The diagnostic methodology includes a method that has the steps of: determining an operational mode of the EMA motoring subsystem; selecting a sampling rate optimized for the determined operational mode; acquiring and processing data at the selected sampling rate; and analyzing the processed data to identify and classify a fault of the EMA motoring subsystem.

Abstract: An aircraft includes a fuselage, and first and second freewings. Each of the first and second freewings is separately mounted to the fuselage and independently freely pivotable about respective pivot axes. The aircraft includes an angular rate sensor configured to measure a roll rate of the fuselage and to output a first roll rate signal. The aircraft includes a controller in communication with the angular rate sensor and configured to receive a second roll rate signal from the pilot and to compare the first and second roll rate signals to generate first and second control surface control signals. The aircraft includes at least one control actuator in communication with the controller and configured to actuate a first control surface of the first freewing and a second control surface of the second freewing in response to the first and second control surface control signals, respectively, to control the roll rate of the aircraft.

Abstract: The present invention provides a practical method for UAVs to take advantage of thermals in a manner similar to piloted aircrafts and soaring birds. In general, the invention is a method for a UAV to autonomously locate a thermal and be guided to the thermal to greatly improve range and endurance of the aircraft.

Abstract: A flight control system for an aircraft is configured for receiving command signals representing commanded values of a location of a geospatial point and a radius about the geospatial point for defining a circular groundtrack. A sensor determines a geospatial location of the aircraft and provides a location signal representing the location of the aircraft. A controller for commanding flight control devices on the aircraft controls the flight of the aircraft and is configured to receive the command signals and the location signal. The controller uses the command signals and location signal to operate the flight control devices to control the flight of the aircraft for directing the aircraft generally toward a tangent point of the circular groundtrack and then maintaining a flight path along the circular groundtrack.

Abstract: In a vehicle, having a fixed supporting structure and a load movable relative thereto, a jam tolerant actuating system, a method for controlling this system including: Locating a physical coupling/decoupling mechanism between the load and an actuator assembly as close a practicable to the load; constructing the coupling/uncoupling mechanism to be reversible, and hence testable; and controlling the connection/disconnection via decision making electronics which will detect any system failure by monitoring, at a minimum: actuator main motor load and speed, and actuator output load. Also set forth are specific embodiments of pivotable rotary geared actuators as well as linear ball screw type actuators embodying the coupling/uncoupling mechanisms of this invention.

Abstract: A method for aiding a helicopter pilot to avoid a heat seeking missile includes the step of detecting a threat from a missile. The method also includes the step of reducing heat emanating from the helicopter's engine and rapidly reducing altitude. Then, when the threat has passed flight is resumed. A system for accomplishing the above is also described which simultaneously reduces engine temperature, deflects the exhaust gases, injects water into the exhaust gases, reduces altitude and launches a countermeasure.

Abstract: Aerospace vehicle yaw generating systems and associated methods are disclosed herein. One aspect of the invention is directed toward a yaw generating system that can include an aerospace vehicle having a fuselage with a first portion and a second portion. The system can further include a movable control surface coupled to the fuselage and extending generally in a horizontal plane. The control surface can be movable to a deflected position in which the control surface can be positioned to create a flow pattern proximate to the fuselage when the aerospace vehicle is located in a flow field. The flow pattern can be positioned to create a pressure differential between the first portion of the fuselage and the second portion of the fuselage. The first and second portions can be located so that the pressure differential produces a yawing moment on the aerospace vehicle.

Abstract: A method and system in an airborne aircraft to evade a heat seeking missile includes the steps of detecting the launch or “lock on” of a heat seeking missile and reducing the radiation from the aircraft's engine by reducing the engine speed to idle. The method may also include the steps of shutting down and restarting an engine and taking countermeasures to distract the missile or distorting its tracking system. In addition, a method and system for automatically shutting down an engine and/or injecting cooling water into the engine's exhaust port are disclosed.

Abstract: A method and apparatus for controlling a plurality of solar panels of a spacecraft is described. The method comprises the steps of providing a first step command to a first solar panel, and providing a second step command to a second solar panel at a time of a transient zero-crossing of a dynamic response of the spacecraft body to the first step command, wherein the second solar panel is disposed on an opposite side of the spacecraft from the first solar panel. The apparatus comprises a processor; a first solar panel driver, communicatively coupled to the processor, for providing a first step command to a first solar panel, and a second solar panel driver, communicatively coupled to the processor, for providing a second step command to a second solar panel at a time of a transient zero-crossing of a dynamic response of the spacecraft body to the first step command.

Abstract: Active and adaptive systems and methods to prevent loss of control incidents by providing tactile feedback to a vehicle operator are disclosed. According to the present invention, an operator gives a control input to an inceptor. An inceptor sensor measures an inceptor input value of the control input. The inceptor input is used as an input to a Steady-State Inceptor Input/Effector Output Model that models the vehicle control system design. A desired effector output from the inceptor input is generated from the model. The desired effector output is compared to an actual effector output to get a distortion metric. A feedback force is generated as a function of the distortion metric. The feedback force is used as an input to a feedback force generator which generates a loss of control inhibitor system (LOCIS) force back to the inceptor. The LOCIS force is felt by the operator through the inceptor.

Abstract: Active and adaptive systems and methods to prevent loss of control incidents by providing tactile feedback to a vehicle operator are disclosed. According to the present invention, an operator gives a control input to an inceptor. An inceptor sensor measures an inceptor input value of the control input. The inceptor input is used as an input to a Steady-State Inceptor Input/Effector Output Model that models the vehicle control system design. A desired effector output from the inceptor input is generated from the model. The desired effector output is compared to an actual effector output to get a distortion metric. A feedback force is generated as a function of the distortion metric. The feedback force is used as an input to a feedback force generator which generates a loss of control inhibitor system (LOCIS) force back to the inceptor. The LOCIS force is felt by the operator through the inceptor.

Abstract: A device for damping at least one rigid body mode and/or at least one elastic mode of an aircraft, especially for blast load reduction and increase of stability and comfort, in an airplane having at least one sensor, a regulation unit connected to the sensor, and at least one actuator controlling, guiding and/or regulating surfaces of the aircraft. The controller modifies the rigid body modes and/or the one or more elastic modes of the aircraft. With only one sensor signal of a sensor, which is preferably an acceleration signal, an arbitrary number and an arbitrary combination of rigid body modes and/or elastic modes, respectively, may specifically be modified, and the modes obtained are not influenced.

Abstract: The present invention provides a diagnostics methodology and embedded electronic system that allows optimized low-frequency data sampling for EMA motoring subsystems in an operating vehicle. Each of the EMA motoring subsystems includes: an EMA; at least one motor for driving the EMA; and power controls for operating the motor, wherein the power controls includes a DSP controller for sampling and processing data at low-frequency sampling rates. The diagnostic methodology includes a method that has the steps of: determining an operational mode of the EMA motoring subsystem; selecting a sampling rate optimized for the determined operational mode; acquiring and processing data at the selected sampling rate; and analyzing the processed data to identify and classify a fault of the EMA motoring subsystem.

Abstract: An unmanned helicopter includes an altitude control device for giving a command of a collective pitch blade angle based on an altitude change rate command, etc., and performing altitude control of an airframe and takeoff device, upon reception of a takeoff start command from the ground, for causing the airframe to take off and climbing the airframe to a first altitude while increasing the collective pitch blade angle without performing the altitude control of the altitude control device and then causing the altitude control device to start the altitude control. The unmanned helicopter further includes descending device for causing the airframe to descend to a second altitude while changing descent rate command of the altitude control device and giving a descent rate command smaller than the descent rate command to the second altitude to the altitude control device for causing the airframe to descend from the second altitude to the ground.

Abstract: Side-slip of an aircraft during flight is detected through a pair of pressure sensors fixedly mounted on opposite lateral sides of the aircraft fuselage. Pressure measurement signals at said sensors are fed to electronic circuitry within the aircraft for generating magnitude and frequency signals reflective of the side-slip that are applied to a pair of vibrators respectively mounted on the undersides of a pair of pilot foot pedals located within the cockpit. The foot pedals are connected by linkage to the tail rudder on the aircraft fuselage. The varying magnitude and frequency of vibrations applied to the rudder foot pedals by the vibrators enables the pilot to immediately sense side-slip through the feet on the pedals. In response to such side-slip sensing, one of the pedals may be timely depressed for side-slip corrective angular displacement of the rudder.