Vendetta Final Proposal Part 2 - Cal Poly

10 Stability and Control
To initially size the horizontal tail, tail volume coefficients from historical aircraft were analyzed. This was done
in an attempt to determine the rough size of the horizontal and vertical tail surfaces prior to addressing stability and
control issues. The tail volume coefficients are unitless parameters defined by geometric values relating the size of the
empennage surface to the aircraft. The horizontal and vertical tail volume coefficients are defined in the following
equations.
V
H
SHTL
=
c S
W
HT
W
V
V
SVT
L
=
b S
W
VT
W
Because the demands for most supersonic cruising aircraft are considered similar to a certain extent, the historical
values of tail volume coefficients are used to back out the planform areas for the horizontal and vertical surfaces.
Similar aircraft and their tail volume coefficients are presented in Table 10.I.
Table 10.I - Historical Aircraft Tail Volume Coefficients
Tail Volume Coefficients
Aircraft
V H
Boeing SST (2707-300) 0.36 0.049
Concorde n/a 0.080
GD F-111A 1.28 0.064
Rockwell B-1B 0.80 0.039
TU-22M 1.11 0.087
TU-144 n/a 0.081
Average 0.58 0.067
Using the average tail volume coefficient for these similar aircraft yielded a horizontal stabilizer area of 386 ft 2 .
This is rather large and may be attributed to the fact that these vehicles require large robustness in CG travel without the
use of a flight control augmentation system (CAS). Likewise, the vertical tail would require 196 ft 2 of area. This
number is driven slightly larger due to the fact that some of the larger historical tail volumes are inflated because these
aircrafts’ verticals are mounted on booms which extend aft. These booms allow for greater moment arms and make the
vertical more effective.
The effects of horizontal tail area on longitudinal static stability were looked at in an attempt to determine what
the driving factors for horizontal tail area are. A Roskam class II method was used to see how the increased weight of a
bigger horizontal affects the longitudinal static margin. It became apparent that as the tail grows, the CG of the entire
configuration shifts aft. This also shifts the effective neutral point (center of pressure) of the aircraft aft at a faster rate
than the CG shifts aft. At approximately 108 ft 2 of horizontal area the Vendetta has a neutrally stable static margin at
V V
47