How Can We Measure Weight and Balance Control of Different Aircraft?
Weight control is a critical element in aircraft safety, which is why there are several regulations pertaining to this topic. Whether it be a fixed-wing, rotor, powered parachute, or any other type of aircraft, each has its own requirements for managing weight and balance. In this article, we will discuss the weight control requirements for various aircraft in order to give you a better understanding of this important topic.
14 CFR part 23 requires fixed-wing aircraft manufacturers to provide information on the range of tolerable weights that a particular airplane can handle. While the section does not mandate weight and balance checks to be done as part of the preflight checklist, it has become a ubiquitous practice amongst pilots to ensure a safe flight. To accomplish this, pilots first check the operating manual of their aircraft to determine its weight when empty before adding the weight of passengers, fuel, and any other load-carrying objects. Next, they will multiply each item by the arm, which is the horizontal distance from an imaginary vertical plane called the datum that transects the aircraft. The pilot must then add all the weights together to get the total moment, then divide it by the gross weight to calculate the aircraft's center of gravity. Finally, they repeat this process to account for the shift in the center of gravity that occurs as fuel is expended.
The procedure for weight and balance calculations in a rotorcraft is very similar to that of a fixed-wing aircraft, yet it is more important due to narrower tolerances. Another pertinent consideration regarding rotorcraft is high-density altitudes, which can occur through various mechanisms, including temperature and weather fluctuations. Under normal conditions, the rotorcraft is assigned a maximum weight rating at which it can safely operate, but during high-density altitudes, it may no longer be safe to fly at the prescribed weight. Another consideration unique to rotorcraft is the lateral balance, which may fluctuate drastically based on the application. For example, a rescue helicopter performing hoisting operations is guaranteed to face a transient increase in lateral balance toward the side with the hoist.
Weight-shift control (WSC) aircraft are becoming more popular among hobbyists and others interested in aviation. The most widely known example of such aircraft is an ultralight trike, which lacks a tail and is controlled by a shift in weight. With this design, the flight controls directly influence the movement of an arm that connects to the wings at a single point. Since all the weight is put on a single point in (WSC) aircraft, the pilot must ensure that the center of gravity is close to being directly below this point. To accomplish this, the pilot may adjust the wing attach point to better match the varying center of gravity.
Powered parachutes also implement a single-point design with their wings. However, powered parachutes have suboptimal maneuverability compared to WSC aircraft because they lack aerodynamic pitch control. Regardless, the weight and balance calculations are identical to that of a WSC aircraft while also considering maximum takeoff weight. Finally, in a balloon, the center of gravity remains fixed, with the only other consideration being the maximum weight of all occupants.
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