January 6, 2014
An aircraft established in its flight attitude with power and pitch, followed by careful trimming, will maintain its set flight condition—whether level flight, a climb, or descent—with no need for the pilot to hold pressure on the yoke or stick. The trimming takes a fine touch. Then the pilot should resist temptation to fuss with the trimmed condition during flight in choppy air, or after making minor power adjustments.
Mastering this task is a sure sign you are developing a knack for aircraft control. But that’s not the whole story of trim: During rapid changes of power setting or configuration (gear/flaps), it is often necessary to overpower trim momentarily to prevent unintended pitch changes.
That’s known as rough trimming. It can be critical to aircraft control. For example, during a go-around from a power-off glide, adding climb power may induce an excessive nose-up response as the aircraft attempts to maintain its trimmed airspeed.
In that scenario, the pilot may have to apply strong forward yoke pressure to control the pitch attitude—perhaps more forward pressure than the pilot can deliver. Trimming toward a more nose-down attitude can relieve some of that physical burden and avoid an extreme nose-up condition. In this case, the goal of trimming is simply to help the pilot maintain a safe angle of attack during the rapid transition from gliding descent to power-on climb. Fine trimming of the aircraft for the climb back to pattern altitude awaits stabilization of the climb at the intended airspeed.
A similar but opposite use of rough trim to effect a quick transition may be appropriate during a simulated (or real) engine failure during cruise flight. In this situation, the pilot’s goal is best-glide airspeed and reaching an off-airport landing site. Usually that pitch change and rough-trimming will be toward a more nose-up condition. Again, fine trimming follows when glide airspeed stabilizes.
"Don't waste time. Rough-trim the elevator as necessary and move to the next step while airspeed is decreasing toward the speed that these attitudes will generate," advises this Flight Training magazine article on forced landing techniques.
Practice go-arounds and engine-out scenarios frequently! Doing so will save you time during quick transitions, and enhance safety by teaching you to anticipate—not just react to—your aircraft’s responses to big power changes.
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