Mountain Models Magpie
19
Setting the Center of Gravity
The Center of Gravity (CG) will affect how the airplane recovers from a nose up or nose
down condition (pitch stability). With the CG too far forward, the plane will be quite stable,
but require a lot of up elevator to fly level. This will result in an increased low end speed. On
the other hand, too far back and the plane will be hard to control, requiring constant input
to keep the plane flying straight and level. Set the CG .25”-.5” behind the rear of the wing
spar. You adjust the CG by moving the battery as follows.
Attaching the Battery
1.
With the battery resting on the wing, adjust the battery fore and aft to find where it will
need to be positioned to achieve the correct CG.
2.
Attach the Velcro to the side of the fuselage below the wing such that the battery will be
centered on the Velcro.
3.
Attach the soft side of the Velcro strip to the side of your battery pack.
Setting the Control Throws
You need to adjust your radio trim so that the elevator, rudder, and ailerons are all level.
The throws are as follows:
Low Rates
High Rates
Elevator
+-.5 inch
+-1 inch
Rudder
+-.75 inch
+-1.25 inch
If you are new to flying, set up your controls so that the maximum deflections measured
from the furthest point back on the control surface, are what is specified in the low rates
column. The plane will be fairly gentle set up as such. If you are brand new to flying and
will be teaching yourself, you might want to set the rudder throws to +- .5” and the elevator
to about 3/8”. These soft controls will help to keep you from over controlling.
Setting the Lateral Balance
The lateral balance is along the length of the airplane. If you mount the battery on one side
of the fuselage, the balance will be off. You can easily check the balance by resting the
propeller shaft on a finger and gently lifting the rudder with your other hand such that the
airplane is completely off the ground. If the plane rocks to one side, the balance is off. I
found that, on my Magpie, a quarter and a nickel on the wingtip opposite the battery was
required when I used 1200mAH Lipoly cells. I cut a slip in the wingtip and pressed the coins
in the slit then taped the slit shut.
A word on activating the camera shutter
Because of the many types of cameras, I can’t advise on how to activate your camera
shutter. If you are lucky, you may have a camera that has an aftermarket radio activated
shutter control available. Some are available for the Pentax S5 and some Nikons. If a
remote shutter control is not available, it will be necessary to rig a servo such that the servo
can press the shutter button. A search on
www.rcgroups.com
in the AP forum will show a
number of creative ways to use a servo.
