AEROFOIL AND WING PITCHING MOMENT COEFFICIENT AT ZERO ANGLE OF ATTACK DUE TO DEPLOYMENT OF TRAILING-EDGE DOUBLE-SLOTTED OR TRIPLE-SLOTTED FLAPS AT LOW SPEEDS
INTRODUCTION This Item provides a method to obtain the increment in pitching moment coefficient at zero angle of attack due to deployment of trailing-edge double-slotted or triple-slotted flaps at low speeds@ either on an aerofoil or on a wing. For aerofoils the method predicts the centre of lift position@h2@1 @ h2@2 and h2@3 @due to deployment of each element of a double-slotted or triple-slotted flap@ based on the thin-aerofoil theory of Derivation 19 and modified to obtain correlation with the experimental data of Derivations 3@ 5@ 6@ 7@ 8@ 10@ 13@ 17 and 18. Each centre of lift position is combined with the increment in aerofoil lift coefficient for the corresponding element calculated from Item No. 94031 (Derivation 2) to estimate the total pitching moment coefficient increment. When applied to a multi-element flap@ thin-aerofoil theory represents each element as an ??equivalent' single-element flap (of chord cet1 etc.@ see Sketches 1.2 and 1.3)@ and their moment contributions are summed. For wings with full-span flaps@ factors@ dependent on planform geometry@ are applied to the pitching moment coefficient increment on a section that is representative of the wing@ to allow for three-dimensional effects. Derivations 20 and 21 are used as the basis for these factors@ with some adjustment to the simple theoretical assumptions. For wings with part-span flaps@ additional factors are introduced that are dependent on taper ratio@ aspect ratio@ sweep and spanwise extent of the flap. Section 3 describes the prediction method and Section 4 discusses Mach number and Reynolds number effects. The applicability and accuracy of the method are addressed in Section 5. The Derivation and References are given in Section 6. Section 7 provides worked examples illustrating the use of the Item for an aerofoil and a wing.