TR3,
there are two beeper trim mod states.
The standard Bell one is a single rocker swith on the collective which adjusts the N2 datum within a nominal 4% range (+/-2%). It energises a linear actuator which is connected in series with the droop compensation mechanism, so directly changing the settings on the N2 governors by the same degree.
Normally, the single engine beep range is 95-99%, and the twin beep from 97-101.5%. Normal power on range is 97-100%.
However, there is a high power mod state (TB138/145)which allows an increased take- off torque rating of 104.3% for 5 minutes. At this power the torque matching/sharing side of the torque control unit is not stable enough for it to be properly used. This is why the TCU normally limits torque to 102-104%; it improves stability. So, Bell isolate the torque sharing part of the TCU and add a separate N2 actuator for the number 2 engine and the rocker switch has a lateral movement added to it as well.
The pilot can then set a twin N2 datum and use the No2 engine beep to keep the torques matched at high settings.
Make sense? I hope that helps.
(Not sure what your background is, but you will find all turbine helicopters with a simple hydro-mechanical governing system use beepers)
[ 09 July 2001: Message edited by: 212man ]