Control Wheel Steering (CWS)

[TotalBeginner]

One of the PA28's at our flying club has a CWS button on the yoke. What function does this have? I can't find any reference to it in the POH.

I know it has something to do with the Autopilot. Does it simply disconnect the servos while it is pressed to allow you to hand-fly, or does it have a more sophisticated fuction like CWS on the 737 for example?

[BackPacker]

It stands for Control With Stick (yoke in your case). It indeed temporarily disconnects the autopilot servos so that you can control the aircraft manually, without resetting the autopilot. As soon as you let go of the CWS knob, the autopilot engages again.

[IO540]

The CWS (control wheel steering) button varies on the actual implementation but basically it enables the AP to be overrided and the plane to be controlled manually.

With some autopilots it has other functions too. For example with the KFC225 if you are flying in PIT mode then the CWS button can be used (together with a manual pitch change) to modify the pitch which the AP will be maintaining when CWS is released. Similarly with altitude hold - the altitude which was current at CWS release will be the new target altitude (IIRC).

[JW411]

I realise that it might not be too helpful to this discussion but the DC-10 automatics had a CWS (Control Wheel Steering) mode.

Putting it simply, when CWS was selected then the control wheel was connected to the automatics and it was just like flying the aircraft manually. In other words, the pilot made a control input which signalled the autopilot to make the same control inputs to the control surfaces as demanded by the pilot.

Not many pilots that I ever met used this function but I did hear of one Far East airline that used to take-off and land in CWS. I could never work out why. Perhaps they were not very well fed!

[TotalBeginner]

Putting it simply, when CWS was selected then the control wheel was connected to the automatics and it was just like flying the aircraft manually. In other words, the pilot made a control input which signalled the autopilot to make the same control inputs to the control surfaces as demanded by the pilot.


Mmmm strange, what benefit or use does this have?

[linedriva]

I use CWS in the 737 during climbout in turbulent conditions. It seems to ride out the turbulence better than the full autopilot or no autopilot. From what I understand, airbus operate in CWS or something similar all the time.

LD

[Dr Eckener]

Mmmm strange, what benefit or use does this have?
It will hold pitch/bank for you. So you pitch 10 degrees nose up in CWS and when you let go it will hold 10 degrees nose up. Similarly for bank angle, depending on how many axis are covered by the autopilot.

For your PA28 you need to find the autopilot manual, assuming that it actually works.

[TheChitterneFlyer]

CWS is qute simple... you twiddle the knobs on the autopilot and the aeroplane responds appropriately... the 'knobs' in this case are at the end of your arms and legs!

Turb Mode drops the autopilot from CMD to CWS, thus reducing the 'gain' and stops the autopilot chasing the Alt Hold, thus maintaining attitude in turbulence. I can't imagine a CWS system being fitted to a PA28... why would you?