Europa Aircraft XS Monowheel Motorglider, Owner'S Manual

Page: 62 / 96

To provide this stick force a tab is fitted to the trailing edge of the tailplane
which is geared so that it opposes its movement (an anti-servo tab).
When the pilot pulls back on the control stick the trailing edge of the
tailplane moves upwards. The trailing edge of the tab also moves upwards,
therefore resisting the movement of the tailplane. The tabs attempt to
maintain the “status quo”. It is the force generated by the tab that the pilot
feels.
In the “stick free” situation, where the pilot has released the control stick,
the tab controls what happens to the tailplane. Firstly, the tab can be moved
independently of the tailplane to act as a pitch trim control. Secondly, if the
tailplane is upset by a sudden gust it is the tab that drives the tailplane back
to its original angle of attack.
Because the tab is attached to the trailing edge of the tailplane it has a
tendency to float slightly within the turbulent boundary layer of air. This
makes the tab less effective at damping out any oscillations of the tailplane.
To give the tab an immediate bite into the airstream the trailing edge of the
tab is thickened slightly. These areas of extra thickness are called Flettner
strips. Without these strips fitted to the Europa we found the aircraft
wandered slightly in pitch and had a different qualitative feel which led
some pilots to over control in pitch and get into a P.I.O. (pilot induced
oscillation) situation.
Fitting of Flettner strips to the tailplane tabs is mandatory. The entire
length of the anti-servo tab trailing edge should be thickened locally to a
thickness of between 7 and 10mm (1/4" — 3/8"). This can be achieved by
several methods:
November 2006 XS Monowheel Motorglider
Page 7 - 8 Issue 2 Owners Manual