TM 1-1520-238-10 2-45 2.37.4  Trim Feel. CAUTION Use of the pilot FORCE TRIM REL switch in the force trim off position with the heli- copter on the ground is not authorized. Inflight  operation  with  the  pilot  FORCE TRIM  REL  switch  in  the  force  trim  off position is authorized when briefed and the  force  trim  off  selection  is  acknowl- edged by both crewmembers. Either crewmember can trim the cyclic and pedal controls. A lateral, longitudinal, and directional trim feel magnetic brake and spring assembly is incorporated into each con- trol system. Setting the pilot FORCE TRIM REL switch to the on position will engage the magnetic brakes in the lon- gitudinal, lateral, and directional flight controls. The spring assemblies will hold the cyclic stick and directional pedals in trim. Movement of the cyclic or directional controls, by either the pilot or CPG, with FORCE TRIM REL switch on, will cause the spring assemblies to compress and provide feel to the controls. When control pressure is released, the controls will return to their trimmed position. Retrimming is accomplished by a TRIM pushbutton on the CPG cyclic stick or by a FORCE TRIM REL switch on the pilot cyclic stick grip. Pressing the button or pressing up on the switch releases  the  magnetic  brake  and  allows  the  springs  to travel to the new control position. Additionally, this action also allows the SAS actuators to recenter, if necessary. Releasing the button or switch will then allow the magnetic brake to engage and hold the springs at the new position. The pilot may press the FORCE TRIM REL switch to the full down position to disable trim feel entirely. For the CPG, trim feel is lost in the affected axis when the respective SPAD shear pin is broken or if mechanical linkage  severance  has  occurred  between  the  pilot  and CPG stations. With the pilot FORCE TRIM REL switch in the down posi- tion, the ATTD/HOVER HOLD and SAS actuator center- ing capabilities of the DASE are inoperative. The capabili- ties will return when the switch is returned to the center position. The full down position of the pilot FORCE TRIM REL switch may be used momentarily to unlatch the mag- netic latch of the ATTD/HOVER HOLD switch on the ASE control panel (fig 2-27). The DASE capabilities of the pilot FORCE TRIM REL switch remain unaffected in the event of a trim system failure such as with the magnetic brake or spring capsule. Trim feel is operable throughout all ranges of cyclic stick or pedal travel. The trim system receives 28 vdc from the emergency dc bus through the TRIM circuit breaker on the pilot overhead circuit breaker panel. 2.37.5  Flight  Control  Servos. The  four  primary  flight control servos are tandem units that use hydraulic pres- sure from both the primary and utility hydraulic systems. The primary and utility sides of the servos are indepen- dent of each other which provides redundancy in the ser- vos. If one hydraulic system fails, the remaining system can drive the flight control servos. If both systems fail si- multaneously  during  flight,  either  crewmember  can  use stored accumulator hydraulic pressure to provide limited hydraulics for safe landing. Section VI contains a detailed description of the emergency hydraulic system. The pri- mary side of each flight control servo has two electrohy- draulic solenoid valves. One responds to DASE computer signals for stability augmentation. The second electrohydraulic solenoid valve responds to DASE computer inputs for BUCS. 2.37.6   Digital  Automatic  Stabilization  Equipment (DASE). The  DASE  augments  stability  and  enhances maneuverability of the helicopter. DASE includes and/or controls the following: stability and command augmenta- tion  in  pitch,  roll,  and  yaw;  attitude  hold;  heading  hold; hover  augmentation;  turn  coordination;  and  the  BUCS. Major  components  include  an  ASE  control  panel  (fig 2-27), a DASE computer, eight linear variable differential transducers  (LVDT),  two  26  vac  transformers,  and  four hydraulic servo actuators. a.   DASE Computer. The DASE computer receives 28 vdc from the No. 3 essential dc bus through the ASE BUCS circuit breaker and a stepped down 26 vac refer- ence voltage from the No. 1 essential ac bus through the ASE AC circuit breaker. Both circuit breakers are on the pilot overhead circuit breaker panel. The DASE computer automatically  disengages  a  mistrack  of  more  than  35% and lights the ASE FAIL indicator on both caution/warning panels;  concurrently,  the  PITCH,  ROLL,  and  YAW switches on the ASE control panel will drop to OFF. The squat  switch  on  the  left  main  landing  gear  disables  the YAW CAS function during ground taxi to prevent overcon- trol  of  the  helicopter.  The  YAW  channel  circuitry  in  the DASE computer receives sideslip data from the air data sensor which provides turn coordination above 60 KTAS.