Airplane Weight and Balance

There is a very good reason to pay close attention to the airplane weight and balance. If you don’t balance your RC airplane it is likely to crash!

A slightly tail heavy airplane will be very unstable and extremely sensitive to the slightest elevator input. If the airplane is more than slightly tail heavy it will be completely unflyable!

I made some repairs after a nasty landing once and forgot to re-balance the airplane. Due to the extra weight from reinforcing the rear of the airplane it became tail heavy. When the plane took off it went straight up! When I tried to correct it, it went straight down! After about three such cycles it smashed into the ground. Lesson learned! A tail heavy airplane is destined to crash!

An airplane is more stable when it is slightly nose heavy. An excessively nose heavy airplane will be very sluggish to elevator commands and will land very fast! It is not good to be more than slightly nose heavy, but its much better to be nose heavy the tail heavy! So if there is any doubt always err in the direction of a nose heavy airplane.

Airplane Weight and Balance from Nose to Tail

Mark the wing at the location indicated in the instruction manual. With the airplane facing towards you place an index finger on each wing exactly where you made the marks. Gently raise the airplane. If the airplane is perfectly balanced it will sit level on your fingertips with the nose just slightly downward. If the plane is tail heavy the nose will rise. If the airplane is nose heavy the nose will fall.

When balancing RC airplanes you always want to minimize the amount of weight you add. Many times airplanes can be balanced without adding any weight by moving the battery pack. If the airplane is nose heavy see if you have room to move the battery pack towards the rear of the airplane. For tail heavy airplanes move the battery pack forward. This is a trial and error procedure that requires you to remove and replace the wing each time you check the balance. When the airplane is finally balanced with nose slightly down be sure that you secure the battery pack as well as the receiver so that nothing moves during flight. This can be done by stuffing foam around the components. In addition to using foam it may be necessary to glue a couple pieces of scrap balsa wood on either side of the battery.

Depending on how heavy the engine is it may be necessary to add weight to the airplane to balance it properly. Any weight added needs to be as far away from the center of gravity as possible to minimize the amount of weight needed. If the airplane is tail heavy it is best to glue some weight on the firewall. If the plane is nose heavy add the weight as close to the end of the fuselage as possible.

Balancing tools such as this one to the left from Great Planes make balancing RC airplanes much easier. Instead of picking the airplane up with your index fingers after each adjustment you simply sit the plane on the tool. Sit the weight on top of the plane where you plan to glue it. Add or subtract weight until the airplane is balanced with nose slightly down. After you determine how much weight is needed, glue it down securely.

If you don’t have a balancing tool don’t worry! You can still balance your airplane, it will just be a bit more tedious. Add weight to either the rear or front depending on where it's needed. Use just enough glue to hold the weight from moving, then check the balance by lifting the plane with your fingertips. Repeat the process until the airplane is balanced. Then glue the weights securely to the airplane.

Any thing can be used for a weight. You can use nuts, bolts, fishing weights, or anything that can be fastened securely to the airplane. You can also buy weights designed specifically for balancing RC airplanes. When adding weight to the rear I like to tear a hole in the covering and glue the weight to the inside of the airplane so it can’t be seen. But there are stick on weights that can be added to the outside of your airplane.

You always want to fly your airplane the first time with the CG in the location dictated by the instruction manual. Once you are comfortable flying your airplane you can move the CG back slightly to make the airplane more aerobatic. If you decide to move CG back it is very important that you do it in very small increments of 1/8” at the most!

It is worth noting that balancing RC airplanes with low wings requires that the airplane be upside down. You can see this in the above picture of Great Plane's CG machine. This makes the process more accurate as low wing airplanes are most stable when upside down.

Airplane Weight and Balance Side to Side

This is quite easy to do. Simply put the airplane’s spinner on the work bench and hold the airplane up by the tail. Balance the tail on the back of your hand and observe which the airplane wants to roll. Do this several times. If it is out of balance it will roll to the same side each time. It will be obvious if you need to add weight. I personally have never had an airplane where weight was required to balance it side to side, but it's always good to check!

If you do need to add weight you want to add it as close to the wing tip as possible to minimize the weight. You could add weight to the outside of the wing but it would look much better if you tore a small hole in the covering and glued the weight where it won’t be seen.