MINIMUM DRAG TRIM TECHNIQUE

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Editor : Copyright Ó Smartcockpit.com / Ludovic ANDRE version 01 Smartcockpit.com BOEING 737 BRIEFINGS Page 1 MINIMUM DRAG TRIM TECHNIQUE GENERAL The following procedure outlines the steps to be taken when correcting an out of trim condition: · Check for thrust asymmetry and adjust N1 as necessary to set even thrust. · Check for lateral fuel balance and, if required, control fuel feed to regain lateral balance. (A lateral unbalance will appear as a roll input). · Verify rudder and aileron trim is zero. · Autopilot engaged (preferred method): - Stabilize the airplane on a constant heading with HDG SEL - Trim the rudder in the direction of the down wing. - Apply rudder trim incrementally, allowing the bank to stabilize after each trim input. Large trim inputs do not give repeatable results. - The airplane is properly trimmed when the bank angle is zero as displayed on the ADI sky pointer. If the airplane is properly rigged, this should result in an approximately neutral wheel. - Disengage the autopilot. With the autopilot disengaged, hold the wings level with the control wheel using the ADI for reference. Trim out any control wheel forces using aileron trim. Note: Use of aileron trim with the autopilot engaged is prohibited. - If desired, re-engage the autopilot. · Autopilot disengaged (alternate method): - Hold the wings level with the control wheel using the ADI sky pointer for reference. - Use rudder trim to correct (stop) heading drift. For airplanes with IRS, display heading on the IRS overhead panel. Use the tenths of a degree window to zero heading drift. - Use aileron trim to remove any control wheel force. DRAG FACTORS DUE TO TRIM TECHNIQUE · If the control wheel is displaced more than approximately 1.6 units (10 degrees) spoiler deflection will be initiated and a significant increase in aerodynamic drag will result. · The following table above shows the effect of trim on airplane drag for a typical condition. The drag increase shown is based on a nominally rigged airplane. rigging deviation which results in early spoiler actuation will result in a significant increase in drag per unit of trim. · Effects of Trim on Drag