Aviation what is trim

The most common trim is elevator trim which we can find in many aircraft regardless of age, manufacturer or type of aircraft. The elevator is a control surface on the tail that raises or lowers the nose of the aircraft. Elevator trim helps reduce the amount of control pressure needed to keep the elevator in a certain position.

For aircraft equipped with stabilators, the trim actually moves the entire stabilator and is not a separate trim tab. What is interesting and counterintuitive about how elevator trim works is that the trim tab actually creates opposite deflection to the direction of the elevator. To point the aircraft nose upward, this would require upward deflection of the elevator that pushes the tail down and the nose up.

To accomplish this through trim, the trim tab would actually have downward deflection to push the elevator upward. The trim tab here is shown deflecting a small amount of passing air downward so that reciprocal effect while flying will be for the trim tab to push the rear of the elevator up, pushing the tail down and the nose up.

Note that while flying, this upward deflection of the trim tab would cause the elevator to deflect downward, thus pushing the tail up and the nose down. Elevator trim can be used as much as needed to relieve the amount of control pressure needed to keep the elevator in a certain position. Aircraft will typically have a desired elevator trim setting for takeoff. This is called runaway trim and if this happens in flight it can be a difficult situation.

A climb typically begins when the pilot pulls back on the yoke and deflects the elevator upward, pushing the tail downward and raising the nose of the aircraft. Applying nose-up trim see image above takes the place of the pilot physically applying back pressure to the elevator. It reduces the physical workload on the pilot but also reduces mental workload. With the airplane now climbing on its own, the pilot is also mentally freed up to focus on other pertinent tasks.

When the climb first begins, the airplane has more inertia from straight and level flight, and does not need significant elevator input for the climb because there is more air flowing over the control surfaces. As the aircraft climbs and slows, more elevator deflection and thus trim will be required to maintain the climb. As the aircraft enters less dense air with higher altitude, more trim may be required to maintain the climb as well.

But overall, elevator trim can help the airplane to nearly climb on its own with little input from the pilot. Elevator trim is extremely useful during the cruise phase of the flight to maintain level altitude without the pilot needing to touch the yoke. Aircraft equipped with electrim trim and an autopilot might autotrim the aircraft to reduce servo pressures on the control surfaces. Some autopilots like the STEC will notify the pilot that more manual upward or downward elevator trim is required to reduce servo input, but will not actually adjust the trim automatically.

As cruise continues, the pilot might need to slightly retrim the aircraft to compensate for weight and balance changes due to fuel burn. Trimming the aircraft during descent is similar to climb. The pilot can set a desired descent rate and appropriate power setting and the appropriately trimmed aircraft will fly itself during the descent. Possibly the most helpful use of trim is during the landing phase of the flight.

They're stalls caused by adding full power when flying with substantial nose-up trim, without proper forward pressure on the controls to prevent a high pitch attitude as full power is added.

Imagine flying a perfectly trimmed, hands-off approach to the runway. Elevator trim stalls are supposed to replicate what would happen during a go-around with this kind of trim setting and not enough forward pressure on the yoke. Because of the risk for an elevator trim stall, some instructors don't recommend trimming at all on final approach.

But does this make sense? Just because the nose will pitch straight up during an elevator trim stall, doesn't mean we shouldn't use trim on final approach. It just means you need to apply forward control pressure and begin rolling trim forward on go-arounds as soon as practical.

Having a little bit of nose-up trim on final approach is a great way to ensure you're able to flare without your nose touching down before the main wheels. Once again, trim preferences divide sharply at this point, and there's no definable "correct" way to do it. Like steep turns, some points prefer flying final approach with heavier control pressures, while some don't.

But for most pilots, trimming on final is a what you should do. Trim will help you fly more stabilized, on-speed approaches. And doing that almost always results in better landings. Trim is important, and you really should use it to reduce your workload. But you should not fly the airplane using trim alone. Some pilots have a tendency to use trim, especially electric trim, to initiate climbs and descents.

Don't use trim to point the nose where you want it to go. Instead, think of trim as a piece of tape. First, use your hands on the controls to set the airplane in place, then add trim or tape where you want it to stick, and let go.

There's no "perfect way" to trim an airplane. But using trim is an excellent way to reduce your workload in the cockpit, and make your flights more comfortable. Practice trimming during every phase of flight, as well as maneuvers like steep turns, and see what works for you. Become a better pilot.

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Elevator deflection is fastest but requires a pilot force which is uncomfortable for longer periods, that is why the forces can be trimmed out to make the new stick position the neutral force one.

Trim is the control that adjusts the trim tab. Wiki gives a nice description of it , this is for elevator control but the same applies for all control surface trim. Elevator trim frees the pilot from exerting constant pressure on the pitch controls. Typically, when this trim control wheel or lever is rotated or moved forward, the nose is held down; conversely, if the trim control is moved back, the tail becomes "heavy". Many newer aircraft, especially jet aircraft, have electric trim controls.

There is a nice article on it here as well as here. The trim is generally adjusted any time the aircraft transitions flight phase climb to cruise, cruise to decent etc or when the power setting is changed or periodically in cruise if the CG is greatly effected.

For example if you climb out at full power, reach your cruising altitude of ft. In this case you would trim off the control pressure by rolling the wheel forward until you no longer needed to apply control pressure to keep the plane level. At this point you could fly "hands off". Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams?