w_n, I once had a problem with our KFC150 in that the servo motors brushes were worn out and the Bonanza went into Bonanza mode – rocking up and down because the pitch attitude signal input into the servo was not adequately matched by servo movements. Pressing the CWS button eliminated the problem.
When I fly (much less complex than multicrew) I use the CWS for two things: 1) before first engaging the AP in climb, I press CWS button quickly to make sure the AP gets the actual pitch and doesn’t use old pitch information from the previous flight and 2) I use it to divert the flight path quickly or or adjust the direction when approaching.
That’s basically it. But usefull nonetheless.
RobertL18C wrote:
I was trying to come up with reasons why the designers had thought of CWS, and to understand whether any SOPs actually use it.
Flightsafety don’t teach use of it on the Mustang.
The Cirrus never had CWS, not with the S-TEC autopilots, nor with the Avidyne DFC90 or Garmin GFC700. If I needed to react quickly I would therefore disconnect the autopilot.
Alexis wrote:
not with the S-TEC autopilots
Interesting, the S-TEC 55X has it but it is a “funny” variant of it. While I don’t use it much, it has it’s moments where it’s useful.
The older SR22s also use the 55X, but without the CWS button. I have no idea why that is.
Possibly something to do with this and especially post #4.
If the autopilot is driving only the trim, there is no way to implement the CWS function. It can be done only in a system where the pilot, having pressed CWS, is not just moving the control linkages but also rotating the servos (which will rotate freely since their clutches have been disengaged) so that when they re-engage they start at the new position. And a trim can’t be thus forced because it is a jackscrew arrangement (usually).
The DFC90 autopilot uses both the trim AND the pitch servo in the SR22.
You mean that the roll servo in the Cirrus does not have the necessary clutches for CWS? I have to check how that works in the SR22.
Flightsafety don’t teach use of it on the Mustang.
Their instructors for “my” C550/560 line suggest to use it under special circumstances only. For example when reacting to a TCAS/RA. Hold the TCS button, climb or descend according to the TCAS display and release the button when clear of conflict so that the aircraft can return to what it was doing before. One big advantage of using TCS instead of disengaging the autopilot for brief periods of manual flying is that the flight director will remain engaged. So in case of that TCAS event one can still follow the lateral guidance of the flight director. Similar for an emergency descent.
