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Section 15: In-Flight Adjustments for
Once the fundamentals of launch, trim and control of the glider
are learned, it's time to consider getting the most out of the glid-
er's ability to perform. To do that, one must learn how to trim the
glider for maximum performance, whatever the current condi-
tions are at the time.
The key to trimming the glider for maximum performance is to
become knowledgeable of three key speeds. They are:
(1) Minimum Sink Speed, (2) Maximum Lift/Drag (L/D) Speed,
and (3) Best Penetration Speed.
These three speeds are what we call airspeeds, not ground
speeds (the glider's speed across the ground). Thus, the air-
speed of the glider is relative to the air mass surrounding it.
To determine the glider's airspeed, you will have to watch care-
fully for its pitch attitude. Pitch attitude can best be described as
the amount (degree) the nose of the glider is above or below a
line relative to the horizon.
Pitch Attitude
Longitudinal
Axis
Pitch
Attitude
Line Relative
to Horizon
Horizon
Minimum Sink Speed
Minimum sink speed is the speed at which a sailplane loses
altitude most slowly. As the term then implies, minimum sink
speed gives the glider the maximum amount of time aloft from a
given altitude. This is the speed to fly at when you are circling in
thermals, or whenever you need the maximum lift the glider can
produce. The pitch attitude will appear to be more nose up.
To determine what this speed is for your glider, you will need to
fly at a slow speed, slowing down until the glider just stalls, then
trim it to fly at a speed just above where it begins to stall.
Observe the pitch attitude at this speed. You will need to practice
flying at this speed without stalling so you can come back to it
whenever you want to when you're in a thermal or are trying to
maintain maximum lift.
34
Performance and Conditions
Nose
Center of
gravity
Maximum Lift/Drag (L/D) Speed
This is the speed at which you can fly the maximum distance for
a given altitude. It's used when you move from one thermal to
another, or when you need to cover the maximum distance over
ground. This will be a moderately faster airspeed than the mini-
mum sink speed. You will have to experiment by starting from
the minimum sink speed and add small amounts of down trim to
increase speed slightly. This is the speed the glider covers the
most ground, and the speed at which you will do most of your
flying. It will take practice until you're familiar with the
glider's attitude at this speed. Remember, you will be flying
slightly faster at a lower pitch attitude as compared to minimum
sink speed.
Best Penetration Speed
This is the speed at which the glider will travel forward against
the wind, as far and as quickly as possible. This speed will vary
with the conditions, such as windy situations. You will want to
use this speed to escape from sink or to get back up-wind. This
speed has a more pronounced nose down appearance, which
will vary with the conditions encountered. It will also not be a
consistent attitude, but vary with the strength of the wind.
Once you've learned to launch and control your glider in a
consistent manner, you will want to then proceed with practicing
these three speeds. Remember these are trim speeds, so you'll
be using your trim lever to obtain them.
The more you learn how to trim your Aspire for optimum
performance, the more fun you can have chasing thermals!
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