GRAUPNER MC-22S, Programming Manual

Page: 148 / 180

148 Programming examples – Fixed-wing models
still”. This is more or less the worst possible setting for
a power model, and might well result in the model te-
aring uncontrollably across the fl ying fi eld, represen-
ting a serious risk to pilots and spectators alike. For
this reason we strongly recommend that you should
at least set the motor to stop or throttle back, to avoid
precisely this risk; at the same time the undercarriage
should also be set to extend automatically. Once you
have carried out these settings, you should certain-
ly check them again once the model has been test-
fl own and trimmed out fully.
F A I L S A F E ( S P C M 2 0 )
P o s
h o l d
1 2 3 4 5 6 7 8
S T O
In the next section we consider the “battery fail-safe”
feature in PCM20 mode:
F A I L S A F E ( P C M 2 0 )
P o s i t i o n T i m e B a t t e r y F . S .
. 2 5 s - 7 5 %
S E L S E L S T O
The “Battery fail-safe” function, which is triggered
when the voltage of the receiver battery falls below
a particular point, moves the carburettor to a pre-set
value, which can be -75%, 0% or +75% of the thrott-
le servo’s travel. This forced throttle closure can be
eliminated again at any time simply by moving the
throttle stick, but don’t waste any time: you should get
the model down onto the ground as quickly as possib-
le and recharge the battery.
Since F3A models generally have two aileron servos,
it has proved useful to defl ect both ailerons “up” for
the landing. In most cases this causes the aircraft to
fl y slightly more slowly, and adopt a more stable atti-
tude on the landing approach.
To achieve this you will need to program mixers in the
menu ...
»Free mixers« (page 102)
Both ailerons are required to defl ect “up” to act as
a landing aid, in parallel with the movement of the
throttle stick, but only from the half-throttle setting in
the direction of idle. The further the stick is moved to-
wards the idle position, the more the ailerons de-
fl ect up. The reverse should occur when you open the
throttle: the ailerons / fl aps retract to avoid the model
suddenly ballooning up.
A little down-elevator must usually be mixed in to
ensure that the model does not climb when the aile-
rons / fl aps are extended.
To meet these two requirements you need the two li-
near mixers shown in the illustration below. The mi-
xers are activated using one and the same external
switch, e.g. switch No. “8”, which therefore has to be
assigned to
both mixers.
Move to the second screen page, and set the ap-
propriate mixer ratios. In both cases the mixer neu-
tral point should be left at the centre point of the Ch1
stick arc.
Select the ASY fi eld, set 0% for both mixers above
the centre point of the control, and the following set-
tings below the centre point, i.e. in the direction of
idle:
LinearMIX 1: -60% ... -80% and
LinearMIX 2: -5% ... -10% .
Example of LinearMIX 1:
L i n e a r M I X 1 C 1 5
M i x i n p u t O f f s e t
- 7 0 % + 0 % 0 %
®
O
U
T
P
U
T
- +
10
0
S T O A S Y S Y M C L R
This completes the basic set-up for a typical F3A mo-
del.
Correcting model-specifi c errors
It is an unfortunate fact of life that even very care-
fully built models exhibit minute faults and inaccura-
cies which have to be corrected using the mixers of a
computer radio control system. In this section we will
describe how to carry out these adjustments, but ple-
ase note the following points before we get started:
it is vital to ensure that the model is built as
accura-
tely as humanly possible, that it is balanced perfectly
around the lateral and longitudinal axes, and that mo-
tor downthrust and sidethrust are set correctly.
Rudder causes unwanted movement around the
longitudinal and lateral axes
It is often the case that a rudder command causes
the model to rotate slightly around the longitudinal
and / or lateral axes. This is particularly troublesome
in what is known as knife-edge fl ight, where all the
model’s lift is generated by the fuselage, aided by the
rudder defl ection. The result is that the model rota-
tes and changes heading slightly, as if the pilot were
applying aileron or elevator at the same time. These
tendencies have to be corrected with compensation
around the lateral axis (elevator) and around the lon-
gitudinal axis (aileron).
This can be achieved easily with the mc-22s, explo-
iting the facilities of the »
Free mixers « once again.
For example, if the model rotates to the right around
the longitudinal (roll) axis when the rudder is defl ec-