Table of Contents
Advertisement
them in the wing in any position you like. This makes
building your model easier because both servos don't
have to be mounted in the same direction. Lastly, mixing
your throttle servos electronically allows you to start one
engine, run it up and tune it as needed, then set it at idle
(by turning the mixing off) and start the other engine while
the first engine stays at idle. This method of mixing
requires a mixing function that can be used with a trim so
you can use your throttle trim as you normally do. Most
mixing functions do not automatically have a trim
assigned—you have to activate a trim yourself.
Following are guidelines on how to set up your radio so
you can mix your servos electronically. We recommend
you set up your radio on your workbench first with your
throttle servos out of the model. We also recommend
you refer to the owners manual that came with your
radio as you proceed.
Connect the right throttle servo to the throttle output
(usually No. 3) in your receiver. This will be the master
servo. The reason your right servo (and right engine) is
the master is because when you get to the flying field,
you will start the left engine (the slave ) first. With the mix
on, run up and tune the left engine. You can use the
ATV for that channel. Once the left engine is warmed up
and tuned, turn the mix off. This will hold the left engine
at idle while you start and tune the right engine.
Check the direction your master servo moves. If it
moves the wrong way, use your servo reversing to
change the direction.
Connect the left throttle servo to an available channel.
This will probably be channel seven because your gear
is probably on channel five and your flaps are probably
on channel six.
Assign the mix to a switch so you can turn the mix on
and off. You won't be using this switch during flight so it
doesn't have to be easily accessible.
Relocate the offset of your master channel to high
throttle (forward stick) on the throttle stick (most offsets
are factory set to begin at center stick). Now, the slave
servo will be mixed to the master servo through the
entire range of throttle stick movement (while the mixing
switch is turned on).
Set your mix to +100%. Observe the direction of the
slave servo. If the slave servo moves in the wrong
direction, change the mix to -100%.
Now you have to deactivate the control (it will be either
a knob or a switch) that operates the slave because you
won't be using it. If your radio does not allow you to
deactivate the control, mix the slave to itself at 100% in
both directions testing to make sure the control (the
knob or switch) no longer operates the slave servo.
One last thing; if your radio has a throttle cut switch, you
must mix the switch to the slave servo (at this time, the
throttle cut switch is mixed only to the master servo). To
do this, use yet another mix to mix the throttle to the
same channel as your slave (channel seven in this
case). Use the throttle cut switch as the switch that
activates this mix.
Now your mix is setup correctly and you may adjust
your ATV's to set the idle and full throttle for both
servos independently.
PREFLIGHT
IDENTIFY YOUR MODEL
No matter if you fly at an AMA sanctioned R/C club site
or if you fly somewhere on your own, you should always
have your name, address, telephone number and AMA
number on or inside your model. It is required at all
AMA R/C club flying sites and AMA sanctioned flying
events. Fill out the identification sticker included with
this kit and place it on or inside your model.
CHARGE YOUR BATTERIES
Follow the battery charging procedures in your radio
instruction manual. You should always charge your
transmitter and receiver batteries the night before you
go flying and at other times as recommended by the
radio manufacturer.
BALANCE YOUR PROPELLERS
Carefully balance your propellers before you fly. This is
especially important on a twin engine model. An
unbalanced prop is the single most significant cause of
vibration that can damage your model. Not only will
engine mounting screws and bolts loosen, possibly with
- 63 -
disastrous effect, but vibration may also damage your
radio receiver and battery. Vibration can also cause
your fuel to foam, which will, in turn, cause your engine
to run hot or quit.
We use a Top Flite Precision Magnetic Prop Balancer
(TOPQ5700) in the workshop and keep a Great Planes
Fingertip Prop Balancer (GPMQ5000) in our flight box.
SYNCHRONIZE YOUR ENGINES
In order for your DC-3 to fly correctly and handle well, it
is important that your engines are synchronized—they
both should turn the same R.P.M. This is especially
critical at full throttle where you will be doing most of
your flying (and takeoffs). There can be a considerable
variance in the pitch between different propellers of the
same size and brand. Don't assume that if you have two
Brand "X " 10 x 6's they will turn the same R.P.M. The
variance in propeller pitch from prop to prop will greatly
affect the R.P.M. a given engine can turn. A variance of
no more than 500 R.P.M. is acceptable.
So, because of the importance of synchronized engines
and the variance between propellers, you should own a
tachometer to check this. Select propellers by checking
the R.P.M. of each one. To do this, mount a propeller on
one of your engines, open the throttle all the way and
read the R.P.M. on your tachometer. Record the R.P.M.
of that propeller on a note pad or write it directly on the
propeller with a felt tip pen. Do this for all of your
propellers on the same engine, then make pairs that
have the closest R.P.M.'s (did we mention earlier that you
should be glad you're not building a B-17?).
After you have selected a matched set of propellers, use
your tachometer to check the R.P.M. of both engines.
Tune your engines as necessary so they both turn the
same R.P.M. at full throttle.
™
- Quick Links:
- Engine Selection
Hide quick links:
Advertisement
Table of Contents
