Aircraft Loading and Performance
Before any flight, we must consider various factors that might influence flight operations. The material condition of our equipment, properly charged batteries, and the weather are just three variables we thoroughly examine to ensure conditions are favorable for a safe and efficient flight. Another crucial factor to consider before launch is the Weight and Balance of the Air Vehicle (AV).
An overweight or improperly loaded aircraft can lead to significant problems. Improper loading decreases the performance and endurance of the AV. An overweight aircraft might not even take off, or worse, once airborne, it may be subjected to forces and stresses it is not designed to handle. This can lead to the AV coming apart in flight or during landing, risking loss of equipment and potential injury or damage to personnel or property in the operational area.
Weight and Balance Terminology
As a Remote Pilot in Command (PIC), it’s imperative to be familiar with the terms related to the AV’s weight and balance:
- Arm: The horizontal distance from the reference datum to the center of gravity (CG) of an item. Arms are referred to as (+) if measured aft of the datum or to the right side of the center line when considering a lateral calculation. The algebraic sign is minus (-) if measured forward of the datum or the left side of the center line when considering a lateral calculation. The arm is typically measured and expressed in inches.
- Ballast: Removable or permanently installed weight in an aircraft used to bring the center of gravity into the allowable range.
- Center of Gravity (CG) Limits: CG limits are specified longitudinal (forward and aft) and/or lateral (left and right) limits within which the aircraft’s center of gravity must be located during flight. The area between the limits is called the CG range of the aircraft. The limit information can be found in the Aircraft Manual.
- Moment: The force that tries to cause rotation and is the product of the arm. The further an object is from this point, the greater the force it exerts. Moment is calculated by multiplying the weight of an object by its arm and is generally expressed in pound-inches.
- Reference Datum: A reference plane that allows accurate and uniform measurements to any point on the AV. The location of the reference datum is established by the manufacturer and is defined in the aircraft flight manual. The horizontal reference datum is an imaginary vertical plane or point, placed along the longitudinal axis of the aircraft, from which all horizontal distances are measured for weight and balance purposes. There is no fixed rule for its location, and it may be located forward of the nose of the aircraft.
Weight
We’ve learned how weight affects aerodynamics in earlier lessons. Weight is a major force that must be respected when designing and building aircraft. Excessive weight reduces the performance and efficiency of an AV, thus reducing the ability to respond in emergencies if they arise. It is important to remember that for Part 107, aircraft must weigh less than 55 pounds.
When AVs are built, they are designed to be as light as the required structure will allow. The lifting bodies (wings/rotors) are then designed to carry the maximum allowable weight. When weight is increased, the lifting bodies must increase the amount of lift to achieve flight. The airframe must also support the additional static load of the AV and the dynamic loads imparted on it during flight maneuvers. For example, an AV weighing 50 pounds must have wings that support 50 pounds in straight and level flight. However, during a turn utilizing a bank angle of 60°, the wings must support a dynamic load of 100 pounds.
An overweight AV can have a variety of problems:
- Fixed-wing aircraft need a higher takeoff speed, resulting in a greater takeoff distance.
- Rate and angle of climb are reduced.
- Service ceiling is lowered.
- Cruising speed is lowered.
- Endurance/Range is lowered.
- Maneuverability is decreased.
- Longer landing distances due to increased landing speed.
- Airframe stresses, specifically on landing gear, are increased.
Aircraft can only perform to their specifications when they are operated and maintained as designed. Ensuring strict weight and balance configuration management is largely responsible for the safety of flight. To ensure safe and efficient flight through weight and balance, three critical elements must be strictly managed:
- Weighing the Aircraft.
- Maintaining meticulous weight and balance records.
- Proper loading of the AV.
Each of these elements is equally crucial to overall safety. If there is an error in any one of these elements, the weight and balance are flawed, and the AV is at risk.
Balance and Stability
Balance control depends on the location of the CG of an AV. This directly impacts stability, which is a major factor in flight safety. Balance along both the lateral and longitudinal axes is important, but the primary concern is longitudinal balance, or lengthwise through a fuselage. Rotary aircraft are more affected by lateral imbalance than fixed-wing aircraft; if the load is not properly balanced (such as a gimbal or battery), it could make the AV unsafe to fly. It is also possible that an external load carried in an out-of-balance position could result in large lateral displacement, making effective flight control limited.
