Well whaddya know, something we *do* agree on! That is, the definition of "trim."
Okay, first things first, Nick:
I don't have the time to answer each of your points, but you are basically incorrect if you think that pushing pedal does not cause a turn, if the wings are level. (This is not the basic subject here, as I contend some bank will happen, and you have to supress it with cyclic). If the ball is out and the wings are level, you are turning, that's why the ball is out! I won't go thru a tome here. If you disgree, then tell us why the ball is not centered.
I do disgree. Nick, it must be a long time since you flew anything smaller than an S-76. (Say, how does the S-76 fly at 140 knots with all the SCAS stuff turned off? Do you even remember?) Not all helos fly alike. General statements like "helicopters exhibit positive dihedral effect" are just misleading. I do not wish to be mean, but maybe we need Shawn to weigh-in here on how small helicopters fly, because he seems to have more "street cred" than a lowly line pilot who's spent a lifetime at the controls wondering how to make the machine do the things I need it to.
Small helos. Those are the ones I fly. They do not have artificial rotor or yaw stability added. And they are perfectly capable of flying along on a straight track with the rotor unbanked and the trim ball slammed hard against one or the other side of the race, especially on approach. Don't believe me? Ask any of my early instructors. Fly sideways? That's what helicopters do!
If the ball is out and the wings are level, you are turning, that's why the ball is out!
Contrary to your contention that if the ball is not centered then the aircraft
must be turning, in the helicopters I fly (206's and the like at 105 - 110 kts), the turn needle is the primary indicator of a rate of turn, not the yaw trim ball. In fact, a 206 flies a little better with the ball displaced slightly out to the left (ask Prouty, he'll explain it). This does not mean that the rotor is banked. In fact, it is level and it is the fuselage that is slightly banked. But you know that. You even know that we don't even have any way of knowing the actual pitch or bank angle of the rotor; only that of the fuselage. And in a helicopter with a teetering rotor, those angles can be very different. Yes, an airplane can skid it's way around a turn with the wings level. The rudder, firmly connected to the fuselage and hence to the wings will see to that. A helicopter won't. In fact, I'd love to see a helicopter that could turn with the rotor unbanked. That'd be a neat trick!
If you contend that helicopters exhibit a positive yaw/roll coupling, why did you say that bit about the 212 shark fin? And I quote:
Phoinix, I wasn't clear enough. It counteracts the roll left with right pedal, which is unstable, and not allowed for IFR flight.
If I were silly enough to climb into my 206, start out from a hover and translate into protracted left sideward flight, I would find that the helicopter would tend to bank
more to the left as the speed increased, even though I was holding (probably full) right pedal. It's not hard to see why (the drag of the fuselage). At some point, the flapping limit of the hub would be reached.
If what you said was true, the helicopter would quickly tend to roll back to the right, in the direction of the pedal I was pushing. In reality, this simply does not happen. In fact, it would not happen with even as little as a 45 degree out-of-yaw-trim condition, or even a small out-of-yaw-trim condition in cruise flight. This is very easy to demonstrate. Most pilots do unconsciously tend to counteract the small rolling moments, but if they held the cyclic extremely steady (through friction in the 206) they would see what I mean. Anyone can go up and do it for themselves. I'd love to be proven wrong.
(Good idea, chaps. Post your results here on this forum...who's going to be the first to make a fool of PPRUNE FAN#1! -Ed.)
What I have observed in 11,000 hours of driving these little buggers around is that many helicopters exhibit little or no positive dihedral effect at all. You seem to disagree, although your various thoughts on the subject are confusing at best. Oh well.