FUTABA 8UHPS Instruction Manual page 87

ON or OFF
indicates
OFF
Start-Speed
switch
ON
position.
Switch G
14. You may also set up the speed mode presets
(SPEED, p. 90) for high-speed cruise between
thermals. Reflex (raise) the entire trailing edge
no more than 1/16" (1.5 mm), or you'll gain more
drag than penetration ability. Use no more than 5
or 10% for initial setup.
ON or OFF
indicates
ON
Start-Speed
switch
OFF
position.
Switch G
15. You can add aileron-rudder coupling (1-4
mixing is set up in PMIX-1, p. 70) for coordinated
turns. This setting is highly dependent on the
model configuration.
amount of rudder is needed, especially if a large
amount of differential is present, so start out with
10–15%. Carefully observe the direction of the
fuselage relative to the thermal turn the model is
making. If the nose points towards the inside of
the circle, the coupling is too high, and if it points
towards the outside of the circle, you need more
The chart on the next page describes the procedures that may be followed when trimming a new
sailplane. The flights for trimming must be made in near-calm conditions, and should be repeated several
times before making adjustments.
One of the most critical steps is the center-of-gravity (CG)/decalage testing (Step 3). Decalage is a
fancy way of describing the relative positions of the wing and horizontal tail. Although the control
neutrals have been set in Step 1, there are differing combinations of elevator trim and CG that produce
stable flight. In general, you get better performance by moving the CG aft, but at the same time you
reduce the stability and make the model more difficult to fly, or make it so that constant attention is
required. Moving the CG aft lessens the download on the model's tail and in some cases produces an
upload, which means the wing and tail are working together and not against each other as they do with a
forward CG. Many contest flyers use a CG position located between 35 and 40% of the mean wing
chord, which is near the aft limits for stability.
lack the performance of the aft-CG model.
You should also set differential and/or rudder coupling carefully. Incorrect settings will result in
needless increased drag, and may be checked fairly easily. If you practice keeping the fuselage straight
while gently rocking the wings back and forth, you'll learn how to coordinate turns and won't need
coupled rudder any more. You can also learn about the proper amount of differential or rudder coupling
by studying the figures of the model circling.
Whatever you do, be sure to spend a lot of time trimming your sailplane. If you have a nearby slope,
practice flying on very light days, where you can just barely keep the model airborne. It is under these
conditions that you learn if your model is really trimmed properly.
Usually only a small
coupling. When everything is set properly, the
fuselage will be tangent to the thermal turn circle.
Nose points outside circle :
increase coupling and/or
differential
While you are flying, watch for trim changes
during launch and butterfly control actions and set
the compensations to cancel them out.
You can also add other mixing types such as
elevator-to-flap mixing (ELE-FL, p. 75) to make
better pylon turns. You may wish to refer to the
sailplane trimming chart following. Whatever
you do, Enjoy!
A nose-heavy model will be easier to fly but will
84
Coordinated turn : fuse Nose points inside circle : too
lines up with turn direction much coupling or differential.
(don't change anything!) Reduce one or both.