What is aircraft trim

The major part of the lift comes from the wings, but the horizontal stabilizer and elevator also produce lift which can be varied to maneuver the aircraft. The average location of the weight of the aircraft is the center of gravity cg. Any force acting at some distance from the cg produces a torque about the cg. Torque is defined to be the product of the force times the distance.

A torque is a "twisting force" that produces rotations of an object. In flight, during maneuvers, an airplane rotates about its cg.

But when the aircraft is not maneuvering, we want the rotation about the cg to be zero. When there is no rotation about the cg the aircraft is said to be trimmed. On most aircraft, the center of gravity of the airplane is located near the center of pressure of the wing. If the center of presure of the wing is aft of the center of gravity, its lift produces a counter-clockwise rotation about the cg. The center of pressure for the elevator is aft of the center of gravity for the airliner shown in the figure.

In addition to heavy rudder application, rudder trim can help alleviate some of the pressure required to keep the airplane coordinated, though additional rudder pressure from the pilot will likely still be required. Ailerons control the roll of the aircraft. For airplanes equipped with aileron trim, the ailerons sometimes have an aileron trim tab pictured below that creates opposite air deflection to the aileron and pushes it in the desired direction.

For some aircraft like the Cirrus SR22, aileron trim will actually just move the entire aileron similar to trim on a stabilator or some rudders and do not have trim tabs. Because the two main wings are actually one wing, if one wing rises and the other must fall. For this reason you may see aileron trim tabs on only one aileron or sometimes they will be on both if the aircraft was designed that way.

Even in single installations, the aileron trim still affects both wings simultaneously. Aileron trim can be used whenever the aircraft will not maintain straight flight. Sometimes airplanes can develop slight roll tendencies to one side or the other for a number of reasons minor dents, stretching and re-rigging of the control surface cables, change of onboard equipment and will require slight but perpetual aileron trim to correct it.

The larger need for aileron trim comes from the weight and balance of the aircraft passenger, crew, and fuel loading and configuration. The need for aileron trim could also change during the course of the flight as fuel is burned off and the weight and balance of the aircraft changes.

A safe and accurate way to trim an aircraft elevator, rudder, or aileron is to achieve the desired flight attitude with the yoke or stick and then slowly trim the aircraft until the yoke pressure is no longer needed to maintain the same attitude. In other words, set the airplane in the desired attitude and then use trim to hold the airplane in that attitude where your input is no longer required. It is important to not use the trim adjustment wheel, crank handle or other device to force the airplane to fly as you want.

Critically, the order of application for all movable trims such as this is to use the pilots own effort to get the aircraft in the correct yaw, pitch and bank attitude, then use the trim to relieve the trim pressures required, checking and adjusting always in this same order.

The proficient and consistent use of aircraft trim is a useful and often necessary tool for all pilots, and especially for those pilots who fly at night, in heavy traffic areas such as Class C or B airspaces or in IMC where pilot workloads can quickly become overwhelming. Aircraft trim is designed to ease that workload while also adding to the efficient, safe and fun operation of your aircraft.

I've been flying since I was 14 years old and have loved every minute of pursuing aviation ever since. Particular highlights include my seaplane rating in Talkeetna Alaska in a Super Cub on floats, getting my instrument rating, taking mountain flying courses in the Idaho backcountry, and purchasing my first airplane a Cessna P in Aviation is my biggest passion and Airplane Academy is my outlet to continually research aviation tips, tricks, and FAQs and present them in a helpful way both on this website as well as our YouTube channel.

You can read more about my story here. I recently had a phone call and email exchange with an air traffic controller named Mike, who has worked in several different ATC roles in the San Antonio, Texas region. He is currently an approach Nearly all of the topics I most commonly get asked about flight training, all in one place, for free. Skip to content Pilots often have a lot to do when flying and aircraft trim helps pilots manage that workload and keep the aircraft moving in the right direction.

Table of Contents. Continue Reading. If you wish to access the latest content from the SKYbrary team, please visit and bookmark www. Trim Systems are considered to be a "secondary" flight control system. By definition, to "trim" an aircraft is to adjust the aerodynamic forces on the control surfaces so that the aircraft maintains the set attitude without any control input.

While all axes of rotation are affected by aerodynamic forces, not all aircraft types are capable of being trimmed in all three axes.