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The basic structure of the model is now complete.
Electrical connection, wing / fuselage
The alpha21/27 has up to four wing-mounted servos which
have to be connected to the receiver. They are connected at
the fuselage / wing transition using grey 5-pin MPX plugs
and sockets.
It is important that all the wing-mounted servo cables
should be fitted with separation filters. Cable sets including
all the parts required together with detailed instructions are
available under the following Order Numbers:
Cable Set UNI
Be sure to select the best quality connectors you can find.
Stick to genuine MPX connectors with gold-plated contacts!
Connect all the positive wires to a common connector pin,
and do the same with all the negative wires to a different pin.
A separate contact is required for each signal wire.
If you have to connect two servos for each wing you will
need to use four contacts of the 5-pin plug (1 x positive, 1
x negative and 2 x signal).
The connectors are installed "loose", i.e. the plugs (wings)
and sockets (fuselage) are not glued in place permanently.
Always grasp the connector by the plastic body when
disconnecting - don't pull on the wires!
Remember to mark the plugs and sockets L and R to avoid
confusion at the flying site (use a waterproof felt-tip pen).
Cut an opening for the cables at a suitable point in the
fuselage wing saddle. This is best done by drilling a series
of holes close together, then linking the holes with a
hacksaw blade and filing out to size. Avoid sharp or rough
edges, keep all radii large, and don't make the hole larger
than is necessary.
[Fig. 16]
Your model is now complete.
Nevertheless, there are a few important points to be checked
while you are still in the workshop:
Centre of Gravity (balance point) and longitudinal dihedral.
Provided that you get these two settings right you will
encounter no problems in test-flying your new model and
in general flying.
Successful test flying always boils down to good preparation.
At Multiplex the CG and longitudinal dihedral are first
determined theoretically, then confirmed by practical flight
testing.
Centre of Gravity:
alpha 21
alpha27
The easy way of checking this accurately it to use the Centre
of Gravity balance, MPX Order No. 69 3054.
A longitudinal dihedral of 2º has proved just right for these
models, and this can be checked using the incidence gauge,
MPX Order No. 69 3053.
We strongly recommend that you stick to these settings. The
control surface travels stated below have been established
as the ideal values during practical test flying, and have been
confirmed by several experienced model pilots. Set these
travels for the time being, and alter them as and when you
see fit. We are confident that you will never need to change
them.
8 5253 (2 x)
60 mm
70 mm
Control surface travels
All control surface travels are measured at the widest point
of the surface, and are stated below in millimetres.
Control surface travels, alpha junior
Rudder servo
Rudder
Elevator servo
Elevator
Aileron servos (optional) Ailerons
Landing flap servos (optional)
Control surface travels, alpha club
Rudder servo
Rudder
Elevator servo
Elevator
Aileron servos
Ailerons
Landing flap servos (optional) Landing flaps 90º
Now your alpha junior / club is ready for the air!
Preparing for the first flight
"Old hands" will now be waiting for the first opportunity to
take their new alpha21/ 27 to the flying site, where they will
test-fly it in the accustomed manner, carry out any minor
corrections required, and then, we hope, have many hours
of pleasure flying their new model.
The following is intended to help the less experienced
modeller to test-fly and trim the model correctly, and to
exploit the model's fine performance to the full.
Test flying
Every flying machine, from the humble chuck glider to the
full-size aircraft, has to be test-flown and trimmed after
completion; your alpha 21/ 27 is no exception. The slightest
inaccuracy in construction can lead to a minor variation in
the model's flight characteristics and control response. Test
flying is the process of optimising the CG, and of fine-tuning
the model's control response.
Avoid at all costs repeated hand-glides on a flat site. The
most dangerous time for any model is when it is close to the
ground, and hand launches are therefore by their nature
extremely hazardous. There is hardly any time to correct the
controls, and a hard landing can easily damage the model.
Range testing (for experts too!)
Ensure that your transmitter and receiver batteries are
freshly charged according to the battery manufacturer's
recommendations. Before switching on your transmitter
make certain that your channel is vacant. The channel
pennant on your transmitter aerial is obligatory, and shows
other pilots what frequency you are using. If there are other
pilots present, tell them loud and clear what channel you are
on, and find out what frequencies they are using.
Before the first flight you should carry out a range check, and
we strongly recommend that you repeat the test before the
start of every day's flying. Hold the model in such a way that
your body cannot influence the receiver aerial, i.e. hold it by
the fuselage nose.
Your assistant should collapse the transmitter aerial fully
(but leave it attached), then walk away from you carrying the
transmitter.
left / right mm
20
20
down / up mm
7
10
down / up mm
8
12
down / up
90º
0
left / right mm
20
20
down / up mm
7
10
down / up mm
8
12
down / up
0
15
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