Hi all.
I've read a lot of interesting stuff in this thread about Autopilots, SAS and ATT modes. I've a little experience with French Autopilots, and with the older Bell Sperry types. (say about a thousand hours).
Most of these had an Autopilot disengage plate on the cyclic. There is another thread about whether to fly "through the AP" that is , against the cyclic force, after trimming the helicopter for level flight, or to use the hat to trim. (
http://www.pprune.org/rotorheads/834...med-turns.html) It was a very interesting discussion, especially because I have had different instructors telling me to do the exact opposite of each other, depending on what they'd been used to flying. Those flying the Russian Mi-s would insist on using the FTR and the ones trained on the SeaKing in the UK would be ready to throw you out of the cockpit if you ever touched the FTR button on the cyclic. In the Russian APs, there was no 'coolie hat' trimmer, and the only way to change the attitude was by the use of the FTR. This was also essential when you needed to get the 'ball' in the centre.
I understand from the Trimmed Turns forum that the 'fly through' or not, has a lot to do also with the way the particular Autopilot is designed. Nick says in his post that " The type that Sikorsky generally builds uses a "fly through" concept, where the pilot can move the stick against trim, and some degree of smooth acceptance by the autopilot keeps things stable". I have had this experience in the French APs including the one in the Alouette III - it was called AP146, and did a pretty good job. The Bell , on the other hand, tended to react pretty badly if one ever tried to fly through the AP. In the Simulator, I had a high time Bell 412 pilot telling me to "Tap-Tap-Tap" when in a turn. It took me some time to understand that he was asking me to tap on the FTR switch on the cyclic in the turn - and all the time, I was flying against the pressures!
Another difference I notice is that most Autopilots are meant to be switched off when taxying on the ground. Any idea why some are not? In some of the Agusta models, there is no Quick Disengage plate on the cyclic, and one has to pull the switches into the off position. Couldn't get any satisfactory answer at the Factory too. I have seen a kind of Camel ride on a Bell 212 where the Pitch channel had a problem. Disengaging the SAS and re-engaging it without the Pitch channel worked wonders.
Now, my question is this... You're flying VMC, good weather and all, with the basic stab ON, (no higher / upper modes or holds engaged), and you encounter some clear weather turbulence (say flying over hills and the like). The turbulence is a bit disconcerting, and of course sends the ball all over the place too. Would it be better to fly with the Force Trim off? This way, with hands-on flying, perhaps the ride would be smoother, in particular with the rudder control. Finer control of the attitude and roll in turbulence would be smoother by hand. My experience is that the ride did turn out smoother. Of course, it is a personal observation, and I may be only perceiving an improvement in ride quality!!
(Many high-time Bell pilots I understand, prefer to fly with the Force Trim off in all cases, unless of course in IFR.)
Any takes on this?