January 14, 2014
By Dan Namowitz
A trainer is rolling down the runway for takeoff. The student pilot is holding right rudder to keep the airplane tracking straight ahead, and a little aileron into a gentle left crosswind, as the moment of rotation nears.
Suddenly, well before the airspeed arrives at that value, the aircraft’s nose rises abruptly, and the student pilot finds the trainer airborne in mushy, semi-stalled flight. What’s going on here?
Later, the experience will go down as an important learning experience. But for right now, a combination of instinct and stall-awareness training takes over, and the trainee lowers the pitch with one hand and quickly rough-trims the trainer with the other, to relieve the strong yoke-forward pressure that was required to get the nose down promptly.
That use of trim also provides the key clue to the nature of the problem: The aircraft was mis-trimmed for takeoff—in this case, trimmed excessively nose-up.
How did this scenario come about? More than likely distraction or sloppy use of the before-takeoff checklist kept the pilot from noticing the trim condition. But if the pilot who had flown the aircraft previously had used a large dose of nose-up trim for the final landing, the setting would likely have needed a significant adjustment for the next takeoff.
Why? The aircraft would have been trimmed to maintain an airspeed at or near its power-off stall speed. On the next takeoff run, when the aircraft passed through that airspeed while accelerating, the nose would have risen in an attempt to maintain an airspeed at or near Vso.
You may get a taste of the same kind of aircraft response, to a lesser extent, during touch-and-go practice. After you touch down, the usual drill is to retract the flaps, add takeoff power, and retrim while holding enough forward yoke pressure to keep the nose from rising prematurely.
Fortunately, a trainer with modest power and unhurried acceleration will pitch up less aggressively than a more “gutsy” aircraft would. But a surprise is a surprise—and critical phases of flight are no place for the unexpected.
After such an experience, there is little doubt that you will be more trim-conscious next time. But don’t declare your analysis of the situation complete without determining how you came to overlook the pre-takeoff checklist item "Elevator trim – TAKEOFF" before pronouncing yourself ready to fly.
Dan Namowitz is an aviation writer and flight instructor. He has been a pilot since 1985 and an instructor since 1990.
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