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OK-10-0876 Acceleration in Aviation: G-Force Acceleration in Aviation: G-Force Human beings are adapted to live and survive within the ever-present, accelerative force of gravity. While on earth, this is a constant, and we live and function with it from the day we are born until the day we die. As an infant learning to walk, we learn very quickly that a misstep will ultimately lead to a painful gravity-induced incident with the ground that we call “a fall.” As we develop and start to solve problems, we learn that a cookie jar falling off the counter will accelerate all the way to floor with shattering results. Many hours of our youth are spent determining the results of gravity on spherical objects of various shapes and sizes to our advantage in competition. We became accustomed to gravity at the standard 1 “G-force.” When we pilot an aircraft, all that we have learned about gravity and have become comfortable with sudden changes. Flight—in its purest definition—is overcoming gravity to ascend through the air. Just as when we where learning to walk, a primary goal of every flight should be to avoid painful, gravity-induced incidents with the ground. These encounters are called aircraft accidents and mishaps, and they can be destructive, even fatal. What Goes Up Must Come Down The force of gravity on earth causes a constant acceleration of 32 feet-per-second squared. An object in freefall will accelerate at an ever-increasing speed toward earth until it impacts the earth or reaches terminal velocity—the point at which the force of aerodynamic drag acting on the object overcomes the force of acceleration induced by gravity. Acceleration is described in units of the force called “Gs.” A pilot in a steep turn may experience forces of acceleration equivalent to many times the force of gravity. This is especially true in military fighter jets and high-performance, aerobatic aircraft where the acceleration forces may be as high as 9 Gs. Air race pilots in a tight pylon turn also experience high G-forces, but the important thing to remember is that any aircraft operated in a maximum-performance profile will subject the pilot to acceleration that is greater than the 1 G acceleration encountered on the ground. Pilots need to understand this in to successfully master flying. Types of Acceleration There are three types of acceleration. These types are Linear, Radial, and Angular Acceleration. Linear Acceleration—reflects a change of speed in a straight line. This type of acceleration occurs during take-off, landing, or in level flight when a throttle setting is changed. Radial Acceleration—is the result of a change in direction such as when a pilot performs a sharp turn, pushes over into a dive, or pulls out of a dive. Angular Acceleration—results from a simultaneous change in both speed and direction, which happens in spins and climbing turns. G Forces During flight, a pilot may experience a combination of these accelerations as a result of input to the flight controls. These accelerations induce G-forces on the body that may be described as Gx, Gy, and Gz. Gx—is described as force acting on the body from chest to back; +Gx is experienced, for example, during the take-off roll as the throttle is advanced. This is the force that pushes the pilot back into the seat as the aircraft accelerates. –Gx is described as force from back to chest, and it is encountered during landing as the throttle is closed. This force pushes the pilot forward into the shoulder strap. Naval pilots flying from aircraft carriers feel the extremes of this type of G force. During a catapult launch, the aircraft accelerates to 160- plus mph in just under two seconds. During landing, the aircraft will decelerate to a complete stop in just a few feet. Carrier pilots have adapted and successfully functioned with these extreme Gs for decades. Gy—is a lateral force that acts from shoulder to shoulder, and it is encountered during aileron rolls. Aerobatic pilots routinely encounter this type of G force and can still safely and precisely maneuver their aircraft. Gz— is a gravitational force that is applied to the vertical axis of the body. If it is experienced from head to foot, it is termed (positive) +Gz. This happens when a pilot pulls out of a dive or pulls into an inside loop. –Gz (negative) travels from foot to head, and it is experienced when a pilot pushes over into a dive. Physiological Effects of High G Forces www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：Pilot Safety Brochures飞行员安全手册
