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To Trim or Not to Trim


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RDM, It''s been a while since I''ve flown the Puma and those were C''s and L''s with the original french autopilots, HDG, ALT and A/S hold only. If I remember correctly the list of prohibited maneuvers was on the first page of the "Limitations" section. If there is a different autopilot installed in your machines it might not have the same limitations.

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  • 33 years later...
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For those of you flying twins, I started a rather heated debate over on pprune re: trimming your turns.

 

It started when an ex-mil guy gave me some grief over using the hat for turns. The belief is, should you feel some vertigo, let go of the stick and she''ll right herself. I believe that you''re saturating the channel and getting very little aid from the AFCS throughout the turn, and fighting the system, contrary to its intended design. Sikorsky agrees with this but it does come down to personnal preferance. Apparently the US Navy fight the force trim and the Army boys trim. Whadayathink?

 

 

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Depends on the aircraft and autopilot system. Some will attempt to counter your input and would cause more trouble.

 

Personally, I like to trim for what I''m doing, and I fail to see how letting go and rolling wings-level will solve your problem with the leans - it might make your workload increase when ATC starts asking you what the **** you''re doing.

 

That''s why there are two of you in the office.

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Bladestrike - what was the general consensus on your inquiry? I assume we''re thinking along the same lines?

 

Sorry, I don''t frequent the other forum much anymore, read - at all. Too many egos masquerading as experts.

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Nick Lappos, Senior Sikorsky Test Pilot, agrees. He was on the design team for the 76 AFCS. It comes down to the design of the system. The intent was to make life easier, and most AFCS systems, if you recenter the stick into a turn, or trim the turn, the AFCS will provide full stabilization as intended around the stick position. If you move the cyclic against the trim, you near saturation of the AFCS and could negate its affects (although this varies on some newer systems). The other side use the force trim as an autoleveler. You let the springs give you an indication of the turn and if you get vertigo, you let go and the bird will right itself. While most dismiss that you would actually let go of the stick if disorientated, this is the way most military guys are taught. The design was to make life easier, and trimming a turn is much easier than fighting the springs. Try a 45 degree bank near Vmini with and without trimming the turn and see the difference. I don't see much sense in fighting the system for something that rarely if ever happens. If I'm trimmed in a rate one turn and get vertigo, I'll still be in a rate one turn. There's not much chance of losing control. Apparently its an arguement that has been going on since the inception of the force trim and even the US military don't agree. Army trims, navy doesn't. Most North Sea guys fight the trim, but then again, most of them are ex-mil and thats the way they were taught. In Canada in general, HeliJet trims, Cougar doesn't, the CAF doesn't, and there isn't a consensus among the boys with the red chicken. It generated quite a reponse.

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Bladestrike. As stated above, by CTD I think, it does depend on the aircraft and the AFCS or autopilot installed. If I recall correctly, one of the eleven "prohibited" maneuvers (sp?) in the Super Puma Flight Manual is trimming into turns. Flying a turn against the trim in the Puma worked well and was quite easy. The S76 on the other hand it doesn''t really seem to make much difference either way. I just got back from flying the Ch-146 simulator and it gives you an "autotrim" warning light if you attempt to fly against the trim. Go figure!

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Reddog,  having a look and can not find it in the FM, thought it was in the SOP''s , although I do not have the full FM home with me, will check later today.

 

I would say about 50 50 here with regards to trimmimg,

 

Like CTD said, that is why there is two in the office

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