Balancing Act

The predominant factor that determines how an aircraft of the same design will perform and handle is the center of gravity (CG). Without getting into aerodynamics, the effects of CG are as follows:

Forward CG

• Increased longitudinal (pitch) stability

• Increased stall speed

• Decreased cruise speed

Aft CG

• Decreased longitudinal (pitch) stability

• Decreased stall speed

• Increased cruise speed

• Poor stall/spin recovery

As you may have guessed, trainers and many scale models benefit from a forward CG. Aerobatic pilots tend to favor an aft CG due to the increased maneuverability. Of course, if taken too far, the plane can become so unstable as to be uncontrollable or unrecoverable from a stall/spin. No doubt, experienced pilots have their own method of determining the sweet spot for their particular flying style. Pilots just getting into aerobatics may not know where their plane falls in the CG range. The method that I (and many others) use to get a quick check on the CG is simple (assuming you can fly inverted for a short distance): At 3/4 throttle, pull into a slight climb and roll inverted, and see what the plane does. If it immediately starts descending, it is on the noseheavy side. If it continues on the same path or it climbs, it is on the tail-heavy side. Most pilots feel the most comfortable when holding a slight amount of forward-elevator pressure when inverted.