INTRODUCTION
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| High Wing RC Plane resting on CG Machine |
A properly balanced rc airplane is a top priority for a number of reasons. Number one if we consider the balancing process from a safety standpoint, it quickly becomes a major factor.
An incorrect CG or improperly balanced rc plane can be a handful to control, which can lead to a crash or even worse someone being struck by the model.
An old saying that has been around for awhile, a nose heavy plane flies poorly, but a tail heavy plane only flies once.
All rc airplanes ( and all aircraft for that matter) have a specific CG point or position, this is the point at which the plane balances fore and aft accurately.
CG points are determined during the design phase by the manufacture of the airplane and properly displayed on a plan for your reference. If you have purchased an RTF or ARF model the included instruction manual will more than likely give you the CG point, which normally is a distance measured from the leading edge of the wing or sometimes from the nose of the plane.
If you have built your model from a set of plans or kit the CG position should be clearly marked on your set of plans.
An accurately balanced rc airplane is easier to fly and control, and more importantly, it is safer. A correctly balanced airplane will not need much trim set on the transmitter.
BALANCING PROCEDURE
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| Low Wing RC Plane on CG stand |
1. When balancing a plane with an engine, check to make sure the fuel tank is empty before attempting to balance the plane.
2. Place a mark on the wing with the pre-determined CG location found in your manual or on your plans if you have built your model from a kit.
With the model facing towards you, place your index finger on each wing half precisely where your mark was made.
3. Raise the airplane gently. When your model is correctly balanced it will set level on your fingertips with the nose very slightly downward. (Your model will be more stable if slightly nose heavy)
Remember if it is to nose heavy the airplane will be sluggish and slow to respond to elevator control inputs and will land extremely fast.
Balancing RC Planes with Low Wing
In order to correctly balance these airplanes, it will require that the plane be positioned upside down (See photo above)
The balancing process is more accurate because low wing models are typically more stable when inverted (upside down)
When balancing rc airplanes a high wing airplane is balanced right side up.
(See the top photo above)
Attempt to Balance without adding Weight
When balancing rc airplanes you will want to minimize any additional weight if at all possible while attempting to balance your model.
This can be done by moving components fore or aft like the battery pack. If your plane is nose heavy and you have room, try moving the battery pack back, if your plane is tail heavy attempt to move the battery pack forward in an effort to balance your airplane correctly.
This may require positioning components a few times until the plane is correctly balanced. After the plane is properly balanced make sure you secure all the components before flying your model.
Adding Weight to Balance Airplane
Sometimes when balancing rc airplanes the plane cannot be balanced without adding weight. It is important that the added weight be placed and secured as far away as possible from the CG (center of gravity) to minimize the amount of weight to be added.
Tail Heavy - secure weight on the firewall.
Nose Heavy - Secure weight as close to the end of fuselage as possible. (On or under horizontal stabilizer is always an option) Or you may want to cut a small area near the rear of fuselage covering in order to place the weight on the inside where it cannot be seen, then reseal the covering.
Obtaining weight for you Model
You can purchase balancing weight from your local hobby shop or online websites. (Note: The sticky pad on the back of weights purchased from hobby shops can vibrate loose, I recommend using epoxy or glue to secure them).
Other Weight Options-you can also use nuts, bolts, lead fishing weights or anything that can be securely fastened to the airplane.
Balancing Plane from Side to Side
This balancing procedure is not as critical as the nose to tail balance. It is always good to check it though to ensure the plane performs well while doing any aerobatic maneuvers.
Place the spinner on a table or workshop bench bench, then while holding the airplane up by the tail, place the tail on the backside of one hand, and see if it tends to roll one way or the other. You will want to do this several times, if it rolls the same way numerous times the wing is out of balance. Finding a wing out of balance is not something that occurs very often.
Adding Weight to an out of Balance Wing
You will want to position added weight as close to the wing tip as possible to minimize the added weight. Securing the weight to the outside will not look very good, I recommend cutting an access hole in the covering on the underside of the wing, then secure the weight with glue or epoxy, and reseal the covering.
CG Adjustments
After you have test flown your model rc airplane with the CG in the recommended location listed in your model or on your building plans, and are comfortable with the handling of your airplane, small adjustments can be made. You can move the CG back slightly, which will make the plane more aerobatic.
If you prefer to do this make sure that your adjustments do not exceed 1/8".
Final Thoughts
Balancing your rc airplanes is important and relatively easy, even for beginners.
If you have rc airplanes constructed of foam, stick pins and small nails can easily be pushed into the fuselage or wing to add weight, and are easily hidden from sight.
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