Wills Wing Alpha 180 Owner's Service Manual page 23

fly the glider in smooth air, early in the morning or late in the afternoon. When you are well away
from the terrain, and well clear of other aircraft, look up at the wing tufts while you very gradually
reduce the speed of the glider. Note the speed at which the first tuft first begins to wiggle just prior to
blowing spanwise toward the tip. (If the tufts contain static electricity, they may not show this lat-
eral wiggle prior to reversal. However, you may get other clues to the beginning of separation, such
as slight flutter or rumble in the top surface of the sail.) This is your speed for minimum sink rate.
Familiarize yourself with the position of the control bar relative to your body at this speed, with the
sound and feel of the wind, with the reading on your airspeed indicator, and with the feel of the glider
in terms of pitch and roll pressures. Most of the time when you are flying it will not be practical to
look up for extended periods of time at your tufts. That is why familiarization with these other, more
accessible indicators is important.
After finding your minimum sink speed, experiment with roll control response at speeds just above
and just below this speed to find the value of MCA and the corresponding bar position and other
indicators for this speed. Realize that your effective MCA is going to be higher and higher as the air
becomes more and more turbulent; control response that is perfectly adequate in smooth air will not
be good enough in rougher air. Try flying the glider with the midspan tufts fully reversed; you will
probably find that the glider is somewhat controllable, but only with a lot of physical effort. Note that
both MCA and VMS come well before the glider actually "stalls" in the traditional sense, i.e. pitches
uncontrollably nose down. You may also be able to sense, or your vario may tell you that although the
glider has not "stalled" (pitched nose down) your sink rate has increased significantly. In this mode
the glider is "mushing."
Once you have familiarized yourself with the glider's characteristics in this range of speeds, you will
not need to look at the tufts very often. You will know from bar position and bar pressure, and from
the sound and feel of the relative wind when you are at your minimum sink / minimum controllable
airspeed. In general, you should not fly your glider below this speed. Be aware, however, that when
you are flying at minimum sink in thermal gusts and turbulence, you will experience gust induced
separation of the airflow which will periodically cause the tufts on your sail to reverse.
Of course in a turn, your minimum sink speed goes up because you are banked, and the bank effec-
tively increases your wing loading which increases your flying speed for any angle of attack. But note
this: The tufts indicate angle of attack, without regard to airspeed! Therefore, if you practice flying
various bank angles in smooth air (while well away from any terrain or other gliders) and watch your
tufts (on the inside wing, which will be at the highest angle of attack) you will get a feel for the way
your minimum sink speed varies at varying bank angles.
One final caution: from time to time a tuft may to stick completely to the sail, and fail to properly
indicate the direction of local flow. This may result from static buildup, or from the fine threads of the
yard becoming caught on a seam or some dirt or imperfection in the sail. The tuft may stick while in-
dicating normal flow, but most often it will stick after having reversed, such that the tuft will indicate
a stalled condition that does not exist. One clue in this situation is to note whether or not the tuft is
wiggling. Since flow reversal occurs during a turbulent separated flow, a reversed tuft should be wig-
gling rapidly. If it is not, it is probably stuck. A tuft indicating normal flow will not usually wiggle. An
occasional application of silicone spray to the tufts, and making sure that they are positioned so that
they cannot catch on any seam will minimize the problem of sticking.
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