Understanding the weight of fuel is an important aspect of aviation, impacting aircraft performance and flight safety. Unlike many liquids measured by volume for everyday use, aviation fuels are often considered by their weight. This distinction arises because fuel density can change, meaning a given volume might not always have the same mass.
Understanding Avgas Weight
Aviation gasoline, commonly known as Avgas, is a specialized fuel powering piston-engine aircraft. Avgas 100LL (low lead), typically dyed blue, is the most widely used type for smaller aircraft. At standard temperature and pressure (STP), which is 15°C (59°F) and 1 atmosphere of pressure, Avgas 100LL weighs approximately 6.02 pounds per U.S. gallon. For practical weight and balance calculations, this figure is often rounded to 6 pounds per gallon.
Specific gravity describes Avgas density. It is the ratio of a substance’s density to that of a standard substance, usually water. For Avgas 100LL, its specific gravity is typically around 0.71 to 0.72 at standard conditions, indicating it is less dense than water. This lower density means Avgas floats on water, a useful property for identifying water contamination during pre-flight checks.
Factors Influencing Avgas Density
Avgas density is not constant and can fluctuate with environmental conditions. Temperature is the primary factor affecting its density. As Avgas heats up, it expands, decreasing its density, so a gallon weighs slightly less. Conversely, when it cools, it contracts and becomes denser, weighing slightly more per gallon.
Pilots and fuel handlers consider these variations, especially in extreme temperatures. This is because the actual weight of the fuel loaded can differ from the standard value. Careful attention to density charts or temperature corrections is required to ensure accurate fuel calculations.
Operational Significance for Pilots
Knowing the precise weight of Avgas is important for safe aircraft operations. Accurate fuel weight calculations are necessary for an aircraft’s weight and balance assessment. This assessment ensures the aircraft’s total weight remains within its maximum limits and its center of gravity stays within the approved range. Exceeding these limits can compromise the aircraft’s structural integrity and make it difficult to control.
Inaccurate fuel weight can significantly affect aircraft performance characteristics. An overweight aircraft requires a longer takeoff distance and has a reduced climb rate. It can also impact cruising speed and overall range. Every pound matters in aviation, and precise fuel weight calculations are important for predictable performance, regulatory compliance, and flight safety.