Various control options, using both conventional and novel control motivators, may be available to the designer of a second-generation supersonic commercial transport (SCT) aircraft. A number of tradeoff studies using conventional control surfaces have already been addressed and, more specifically, the low-speed performance benefits deriving from a second pitch control surface quantified. However, a combination of limited rudder control power together with the continuing need to improve overall aircraft performance through reduced fin and control surface sizing has resulted in this assessment of alternative methods of control power generation. Specifically, using the foreplane asymmetrically to generate yawing moments for directional control and deflecting the engine exhaust nozzles for thrust vector control (TVC) about all three rotational axes. At low-speed the effectiveness of TVC will be enhanced due to the high engine thrust required by an SST to overcome the large lift-induced drag generated at approach angles of attack where, conversely aerodynamic control power will be at a minimum due to low dynamic pressure.

This paper begins with a statement of the technical background to the work together with an overview of TVC and its current applications. This is followed by a description of the aerodynamic mathematical model, thrust vector control implementation and the accompanying flight control system. A comparison of aerodynamic and thrust vector control at low speed is then made using established manoeuvres about all three rotational axes. Aircraft speed, take-off performance and the effect of fin area reduction are also addressed. Finally, the major results are summarised and conclusions drawn on a selection of control options and the associated implementation issues. It should be noted that issues relating to high speed and supersonic cruise are not specifically addressed nor are the implications of engine failure conditions.

Exact expressions for the frequency equations and mode shapes of an idealised whole aircraft are derived using the symbolic computation package REDUCE. The aircraft is idealised as a bending-torsion coupled beam for the wing with the associated mass and inertia of the fuselage, tail-plane, fin and rudder assembly being concentrated at the root. The governing differential equation of motion of the aircraft is then solved in its most general form. The analysis is split into symmetric and anti-symmetric cases to formulate the equations from which the natural frequencies and the corresponding mode shapes of the unrestrained aircraft are derived. The analytical approach used here is of great significance, particularly from an aeroelastic optimization point of view, for which repetitive calculations of natural frequencies and mode shapes are often required. The application of the theory is demonstrated by numerical results. These results have been compared with those obtained from the dynamic stiffness and finite element methods.