I'm guessing that only one of us read those papers?
It was good few years ago now ... happy to be corrected!
From CAA Paper 2009/002:
1 CG / Thrustline offset. The recommendation that the vertical location of the centre
of mass is within 2 inches of the propeller thrust line is a result of the study and
therefore is reported as such. CAA accepts that closer alignment of the CG and the
thrustline is a sensible design aim to achieve pitch dynamic stability (phugoid
mode) but also has flight test experience of a gyroplane design that achieves good
stability but is well outside of the 2 inch criteria. CAA Flight Test Specialist
qualitative assessment implies that pitch dynamic stability may not be solely a
function of CG/Propeller Thrust alignment for all types of Gyroplane. It is
appreciated that in paragraph 8.3.1 (page 152) of the report it is stated that other
factors can affect the phugoid mode.
MPD 2005-08 was issued 24 August 2005 mandating, in part, restrictions on pilot
experience, VNE and wind/gust speeds for single seat a/c. These could be removed
if acceptable evidence was presented to show that the CG/thrustline offset was
within ± 2 inches. However other restrictions noted in the MPD would still apply.
Advisory material to BCAR Section T.23 now includes ± 2" criteria.
2 Effect of tailplanes. The report also concludes that horizontal tailplanes are largely
ineffective in improving the long term response of pitch dynamic stability (phugoid
mode). This is the result of studies primarily on narrow tandem cockpit enclosures.
A CAA Flight Test Specialist qualitative evaluation of the effects of a horizontal
tailplane on a single side-by-side configuration gyroplane type indicated a degree
of improvement in the phugoid characteristics at higher speed. It is appreciated
that in paragraph 8.3.1 (page 152) of the report it is stated that other factors can
affect the phugoid mode.