Tail Volume Coefficients

Tail volume coefficients are used to determine the empennage reference areas, SH and SV. The definition of the tail volume coefficients is derived from the aircraft stability equations provided herein. The CG position (see Chapter 8) is shown in Figure 3.47. The distances from the CG to the aerodynamic center at the MAC of the V-tail and H-tail (i. e., MACvt and MACht) are designated Lht and Lvt, respectively, as shown in Figure 3.47. The ac is taken at the quarter-chord of the MAC.

H-Tail Volume Coefficient, Cht

From the pitching-moment equation (see Chapter 12) for steady-state (i. e., equilib­rium) level flight, the H-tail volume coefficient is given as the H-tail plane reference area:

Sht = (Cht)(Sw x MAC)/Lht, (3.46)

where Cht is the H-tail volume coefficient, 0.5< Cht <1.2; a good value is 0.8. Lht is the H-tail arm = distance between the aircraft CG to the ac of MACht. In general, the area ratio Sht/Sw & 0.25 to 0.35.

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