Aircraft Weight And Balance: How Do They Affect Flight?
Aircraft weight and balance play an important role in flight, and knowing these two factors can help ensure a safe and enjoyable flight.
Some general aviation passengers are taken aback when asked how much they weigh as the pilot prepares for flight, or if the first officer takes a look at a pile of luggage and announces that some of it (or maybe even a passenger) has to stay behind. If that big aircraft can make it into the sky, what does one bag matter?
The aircraft weight and balance are both important factors in ensuring a safe flight. When it comes to pre-flight planning, it is vital to know the approximate weight of an airplane’s load, how much it can safely carry, and how to best distribute it.
Center of Gravity
Every craft that moves through air, space, and water is affected by gravity. Even those designed to fly and space and return to Earth, such as the Apollo spacecraft, must take gravity into consideration. If you have seen the movie “Apollo 13,” you might remember a scene in which the astronauts’ trajectory back into Earth’s atmosphere was at a dangerously shallow angle.
Because they never landed on the Moon as originally planned, the spacecraft was returning without heavy lunar samples. Their weight and balance was off and while this was not issue in deep space, when the crew returned to the full force of Earth’s gravity, they had to compensate. They resorted to turning to a low-tech solution by shifting equipment, trash, and video cameras into one end of their crippled spacecraft and it worked.
Shifting aircraft weight and balance is rarely that dramatic, however it is just as necessary. All aircraft have maximum landing weights; these must account for fuel, passengers, cargo, and the airframe itself. Center of gravity (CG) limits state how much weight is allowed in the lateral (left to right) and longitudinal (also known as forward and aft) axes of the aircraft. On smaller airplanes, this sometimes means shifting bags or moving passengers to other seats. Experienced pilots know that the center of gravity can become redistributed as the airplane burns fuel over longer flights.
While aircraft weight and balance are important, it is not as trivial on large airplanes built for stability, such as airliners than it is for small custom aircraft constructed for performance. These airplanes like aerobatic craft and jet fighter are designed for maximum speed and agility. They are easily set off balance because they sometimes require the ability to flip upside down or turn quickly. Their function is to dodge enemy aircraft or defy gravity as dazzlingly as possible. A training aircraft like a Cessna or a large passenger jet meant to comfortably transport large amounts of people over long distances, have a different mission so its weight and balance are not so easily over set.
Pilots can find information about their aircraft’s weight and balance in the operating manual. The pilot in command is responsible for verifying its accuracy and adjusting accordingly. Trying to cheat the weight and balance of an aircraft for by attempting to carry more cargo than the aircraft was designed can result in:
- Inefficient fuel burn
- Overloaded engines
- Takeoff rolls which are longer than usual
In flight, imbalanced weight to the front of the airplane might make it challenging to keep its nose up. If the weight is overloaded to the back, the pilot might have difficulty recovering from a stall.
Calculating Aircraft Weight and Balance
The Federal Aviation Administration (FAA) publishes a “Weight and Balance Handbook” which details what pilots should calculate and how. Learning how to accurately figure aircraft weight and balance is an important part of a student pilot’s training and it is not unreasonable to expect to see it on the FAA Knowledge Test.
Additional weight or improperly distributed cargo, not only potentially stresses the airframe beyond its capabilities; the flying characteristics of the airplane can also become affected. Even if a pilot has flown an aircraft hundreds of times, they might be taken by surprise in the air when gravity has its say. In addition, unexpected equipment in the cabin, such as a large wheelchair, service dog, or hospital bed, might make for necessary weight and balance shifts.
The weight and balance calculations involve the gross weight of the airplane and its cargo and using a chart to ensure these are within acceptable ranges. Most often, pilots use an app to confirm these numbers. However, it is always important for pilots to understand how to figure out aircraft weight and balance distribution on their own in the event of an electrical problem or a malfunctioning smartphone or tablet.
Changes in Weather, Season, and Elevation
Student pilots are taught to understand the impact of weather on their flight. This not only affects their ability to take off, cruise, and land safely, it also affects their weight and balance calculations.
Airplanes cannot take off or move through the air without lift. Bottom line is air needs to flow over the wing in order for this to happen. If it moves too slowly, not enough lift is generated; moreover, engines and wings are less efficient when the air density is less dense. This means that humidity, temperature, and fuel amount must all become part of the picture. It might not always be possible to place a person in each seat and completely fill the cargo hold. Pilots adjust for the amount of bags and what might be in them whiles taking in consideration situation like winter weather which often means heavier baggage as passengers cram in warm coats, sweatpants, and boots.