One contributing factor to the reduced stability will be that the higher
fuselage perimeters resulting from the modification has shifted the
aerodynamic centre of the wing / fuselage combination forward. This then
reduces the longitudinal static margin (distance between CG and AC) and as a
result the aircraft will be less stable in pitch.
Frans
Both the original High Top (with the high cowl) and the new version
(lowered
cowl, bigger screen) the difference in max speed and cruise speed (for
a
fixed power setting) is too small to measure given the other variables
such
as weight and very small build differences.
The only thing I have noticed since we completed testing is that the
new
(64b) setup seems to be very slightly less stable in pitch. Having
modified
the aircraft we cannot go back to the original to get a real
comparison.
The new deeper screen seems to generate a little more lift from the
fuselage. Flying "hands off" in gusty conditions, and directly into
wind,
the nose will hunt up and down very slightly with a period of about 10
seconds. This is so slight that the original High Top may have been
the
same but we did not notice until we started to look carefully for
differences. If you have your hand on the stick you damp this out.
Most of
this testing was done with the TruTrak autopilot on to maintain the
heading
and this could be the cause.
Has any other high top owner noticed anything similar?
David Stanbridge
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