# The Vertical Tail without Interference

To evaluate the above equations, the lift slope dciyjday must be known for the interference-free vertical tail. Basically, this can be computed with the methods of three-dimensional wing theory. Since the shapes of the vertical tails are in most cases quite asymmetric, this task is particularly complicated. Hence, wind tunnel measurements are indispensable for the acquisition of these aerodynamic quantities of the vertical tail. An attempt has been made in Fig. 7-37 to represent the measured lift slopes of single-fin assemblies with partial fuselages as a function of a uniquely defined aspect ratio Ay = b2v/Av. The meaning of Ay and by is obvious

Figure 7-37 Measured lift slopes of an interference-free vertical tail with partial fuselages from DYL measure­ments and Koloska [13].

from the sketch in Fig. 7-37. The aspect ratios Ay he between 1 and 2. Fuselages of round and rectangular cross sections and with horizontal and vertical tail edges were investigated as well as systems with and without horizontal tails. The ratio of the fuselage height hp to the span by of the vertical tail was limited by hplby = 0.35 and 0.5. Curve 1 of Fig. 7-37 shows the theoretical trend for the lift slope as in Fig. 3-32. It represents approximately the test points for vertical tails with circular fuselages and with horizontal tails. For such vertical tails, the lift slope follows the relationship

=——- 2яЛу— (7-58)

da. v 4 + 2

Curve 2, lying considerably lower than curve 1, represents a vertical tail with fuselages of rectangular cross section and without horizontal tail surfaces. Between these curves Me, as curve 3, the results for systems of circular fuselages without horizontal tails and those of rectangular fuselages with horizontal tails. Additional measurements for vertical tail assemblies with two fins are given in [35]. Theoretical studies of the lift slope of a vertical tail with a horizontal tail have been conducted by Rotta [31].

It is almost impossible to give generally valid data for the aerodynamic coefficients of vertical tails at compressible flow.