GB2192163A - Rotorcraft automatic autorotation entry device - Google Patents

Abstract

During the first few seconds after an engine failure, autorotation is established automatically by an Automatic Flight Control System, thereby avoiding undesirable transients and allowing the pilot time to react. The system has collective, pitch, roll, and yaw channels and receives engine failure signal, and signals of rotor speed, a rotor speed reference value for autorotation, rotor acceleration, load factor limit for the helicopter, a load factor as measured, pitch rate, airspeed, roll angular acceleration, yaw acceleration, yaw reference signal of desired yaw attitude during autorotation. <IMAGE>

Description

SPECIFICATION Rotorcraft automatic autorotation entry device Background of the invention The trend towards using lower inertia rotor systems in modern helicopters reduces the level of kinetic energy stored in the system and makes the rotor more susceptible to large variations in rotational speed during rapid maneuvers. Therefore, it is generally known to provide integration of control and propulsion.

This is discussed, for instance, in an article which appeared in Technology Today, Viol.30, No.6, entitled "Rotorcraft Flight-Propulsion Control Integration". Despite this general awareness, there are many specific problems yet to be addressed. The invention addresses but one.

During high speed flight, the engine is transmitting maximum levels oftorque to the rotor. The failure of one engine in a multi-engine arrangement or, more significantly, the failure of all engines causes a rapid decay in rotor speed - so rapid, in fact, that the pilot is unable to initiate autorotation to preserve rotor speed.

The loss of power also eliminates the requirement for tail rotor anti-torque balance. Consequently, the aircraft yaws rapidly and, because of roll/sideslip couplings, a rapid roll ensues.

Disclosure ofthe invention Therefore, it is an object of this invention to initiate automatic control inputs that counteract the unfavorable aerodynamic effects immediately following engine failure, thereby providing for automatic entry to autorotation and attitude control more quickly than a pilot could react. Following the automatic entry into autorotation, the pilotwould resume control and fly an autorotative landing in a normal manner.

According to the invention, during the first few seconds after an engine failure, autorotation is established automatically by providing collective, pitch, roll, and yaw commands to an Automatic Flight Control System so as to trim collective to maintain a desired rotor speed, to control pitch so as to remain within stress limits, to control roll so as to avoid roll atitude changes, and to control yaw so as to avoid an undesirable yaw transient which would otherwise result from an engine failure (no more antitorque required). Existing rate and attitude signals are processed to provide the aforementioned commands to theAFCS.

Other objects, features, and advantages ofthe invention will become more apparent in light ofthefollow- ing description thereof.

Briefdescription ofthe drawing The Figure is a blockdiagram ofthe control scheme ofthis invention.

Best mode for carrying out the invention The figure shows an Engine Failure Detector 10, such as is disclosed in U.S. Patent No.4,454,754 (Zagra- nski et al, 1984). A signal indicative of an engine failure is provided on a line 12. The output of the detector is provided to four switches 14, 16,18,20, which arms a logical check to implement the following automatic autorotation entry logic.

In closed-loop fashion, the following parameters are monitored according to known sensing techniques: NR- rotor speed; NR- rotor acceleration; Nz- load factor; Q - pitch rate; v - forward velocity (airspeed); P - roll angular acceleration; and R - yaw acceleration Ashaping circuit 21 is responsive to rotor speed (no), rotor acceleration (no), and to a pilot-seiected desired rotor speed 22 to provide a collective command signal (Oc) on a line 24,through the switch 14 when armed,to the collective channel of an Automatic Flight Control System (AFCS) 26 for automatically adjusting the collective pitch of the rotor so as to maintain a desirable autorotation rotor speed, such as 100% NA.

A shaping circuit 28 is responsive to load factor (Nz), pitch rate (Q), airspeed (v), and to a reference 30 indicative of load factor limit to provide a longitudinal cyclic (pitch) command signal (Bls) to the pitch channel of the AFCS 26 on a line 32 through the switch l6so as to control pitch attitude during entry to autorotation, thereby avoiding overstressing the aircraft during this maneuver.

Ashaping circuit34 is responsiveto roll angular acceleration (P) and to a roll reference 36 equal to zeroto provide a lateral cyclic (roll) command signal (Als) on a line 38 to the roll channel of the AFCS 26, through the switch 18, so as to maintain "wings level flight during entry to autorotation.

A shaping circuit 40 is responsive to yaw acceleration (R) and to a yaw reference 42, nominally equal to zero, to provide a yaw command signal (our) on a line 44to the yaw channel of the AFCS 26, through the switch 18, so as to control tail rotor collective pitch and to prevent an erroneous yaw correction during entry to autorotation, as discussed previously.

The automatic control described above stabilizes the aircraft and initiates autorotation undercircumstances (engine failure) where the pilot could not react fast enough and provides control inputs similarto those that the pilot would provide given less demanding circumstances. The control inputs are quicker than a pilot, but are well within the limits of known automaticflight or stability systems.

A shorttime after autorotation is established, for instance 2-3 seconds, the command signals (Oc, B15, A5, OTR) from this system could be eliminated or washed out so as to yield affirmative control to the pilot.

Claims (2)

1. An automatic autorotation entry control system for a helicopter having an automaticflightcontrol system including collective, pitch, roll and yaw channels, comprising, means (10) for providing a engine failure signal indicative of an engine failure; means (22)for providing a rotor speed reference signal indicative of a desired autorotation rotor speed; means for providing a rotor speed signal (NR) indicative ofthe actual rotor speed; means for providing a rotor acceleration signal (NR) indicative of the change in speed ofthe rotor;; means (21) for providing a collective command signal (#o) to the collective channel of the AFCS as a func- tion of the rotor speed reference signal, the rotor speed signal, and the rotor acceleration signal so asto maintain the rotor speed at the desired autorotation rotor speed in the presence of the engine failure signal; means (30) for providing a load factor limit signal indicative of a stress limitforthe helicopter; means for providing a load factor signal (NZ) indicative of the stress of the helicopter; meansfor providing a pitch rate signal (Q) indicative ofthe pitch rate of the helicopter; means for providing an airspeed signal (v) indicative ofthe airspeed of the helicopter;; means (28) for providing a pitch command signal (bus) to the pitch channel ofthe AFCS as a function ofthe load factor limit signal, the load factor signal, the pitch rate signal, and the airspeed signal so as to control pitch attitude to avoid overstressing the helicopter in the presence of engine failure signal; ofenginefailure signal; means for providing a roll angular acceleration signal (P) indicative of the roll angular acceleration ofthe helicopter; means (34) for providing a roll command signal (Als) to the roll channel of the AFCS as a function oftheyaw acceleration signal so as to maintain a desired roll attitude in the helicopter in the presence of the engine failure signal; means (42) for providing a yaw reference signal indicative of a desired yaw attitude during autorotation; means for providing a yaw acceleration signal (R) indicative ofthe yaw acceleration ofthe aircraft; and means (40) for providing a yaw command signal (#TR) to the yaw channel ofthe AFCS as a function ofthe yaw acceleration signal so as to eliminate erroneous yawing during autorotation in the presence ofthe enginefailure signal.

2. Apparatus according to claim 1 wherein the collective command signal, the pitch command signal,the roll command signal and the yaw command signal are washed out a short time after the provision ofthe engine failure signal.