Fuselage and Strake Effects
Strakes or leading-edge extensions and, to a lesser degree, fuselages tend to shift the aerodynamic center so that the location of the aerodynamic center of the wing/fuselage combination is not at the same as for the wing alone. The effect of strakes and leading-edge extensions may be estimated by treating them as additional wing panels, using (6.14) to locate the aerodynamic center of the strake by itself, then calculating a weighted average aerodynamic center location, with the areas of the strake and wing providing the weight factor:
 (6.15)
The effect of the fuselage on the aerodynamic center is approximated using an expression obtained from extensive wind tunnel testing1:
Figure 6.13 Geometric and Graphical Determination of the Mean Aerodynamic Chord
 (6.16)
where  has units of 1/radians, wf is the maximum width of the fuselage, lf is the fuselage length, and  is the distance from the nose of the fuselage to the aerodynamic center of the wing/strake combination. From (6.15) and (6.16) it is apparent that strakes, leading-edge extensions, and fuselages all tend to move the aerodynamic center forward. A look at (6.10) confirms that moving the aerodynamic center forward is destabilizing. As a result, increasing the size of an aircraft’s fuselage and/or strakes would require a commensurate increase in the size of the horizontal tail, if the same aircraft stability is to be maintained.
Share with your friends: |
