Dave,
from your site:
The pitch-flap coupling introduces an aerodynamic spring that increases the effective natural frequency of the flap motion.
That means that the blade will move into position sooner in the cycle, following a cyclic input. Therefore, the rotor begins its tilt a fraction of a rev sooner. I doubt this would be very noticeable.
You state elsewhere that delta-3 makes for a SLOWER response. I think by this you mean slower for the rotor tip path plane to come into complete alignment with the control plane. This may be true, but the rotor actually flaps into position faster in the initial cycle and thus the rotor tilts into position earlier. Granted, its tilt will be phase shifted by a few degrees, but it will be mostly tilted in the desired direction on that first cycle. The remaining cross coupled component will wash out in a couple of revolutions as the tip path plane aligns with the swashplate and the overall effect is of a crisper response. Anyway, that's my take on it.
Here you talk about the stick tracking:
It is assumed that the right-hand graph represents a teetering rotor with delta-3, such as the Robinson. In this situation, the phase lag has biased the teetering to left. Therefor at moderate speeds there is a need for a small amount of right lateral cyclic, whereas at fast forward speeds there is a need for a small amount of left lateral cyclic.
I'd like to quibble slightly with your interpretation of how delta-3 adds "bias". The graph is probably not for a R22, but the point is, Delta-3 in the R22/44 counteracts a right tilting tendency of the rotor from coning. It provides a left tilting bias which gets greater as the flapping angle gets greater, i.e, as forward speed increases. At low speed, the delta-3 is not doing much of anything to left bias the rotor.
Delta-3 only acts when there is a *changing* stick input and/or during flapping.
At these times the tip path plane is not lined up with the control plane. Note that this occurs continually during flapping and a rearward flapping blade will tend to constantly tilt left slightly with delta-3(up flapped blade flaps into position early, which means its high point is in the forward right quadrant.)
At one particular airspeed, right tilt from coning is exactly countered by left tilting tendency.
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The excerpt below, taken from a patent, alludes to a potential problem with delta-3 on multi-blade rotors, which is flap-lag instability, a growing problem in this permissive society.
"Large positive values of delta-3, however, will cause the flapping frequency to increase and approach the rotor inplane mode frequency. This can lead to a rotor flap/lag instability at high speed. Likewise large negative values of delta-3 will improve the rotor flap/lag stability by preventing coalescence of these two rotor modes." -United States Patent 6616095