Aircraft specifically designed for short take-off and landing
(STOL) operations are particularly sensitive to atmospheric turbulence and
produce relatively high levels of vertical and lateral accelerations.
These acceleration levels cause discomfort, which is unacceptable in modern
transport aircraft. Such aircraft ought to have their dynamics improved by
the action of a ride quality control system (R.e.S.) which should effectively
reduce these accelerations thereby improving comfort.
Little attention has been given to date to the problem of
designing R.e.S. for executive jets. But with the developing use of such
aircraft which are increasingly of the STOL type the demand for an effective
R.e.S. has intensified. A few earlier studies used conventional theory to
derive the required control laws but so far the use of modern control theory
to derive laws based on a multi variable description of the aircraft responses
has not been widely tried.
Multivariable control theories can be applied to STOL aircraft
by making use of the active control technology (A.C.T.) concept. This
research has employed both A.e.T. and modern control theory to derive a
suitable optimal control system which uses several aerodynamic control
surfaces in such a way that the required reduction of the acceleration
levels can be achieved. The optimal control law used to provide ride
quality control involved the use of elevator, rudder and ailerons, in
conjunction with spoilers, and horizontal and vertical canards. The
subject aircraft chosen for this work was a specially-modified NASA
Jetstar. The uncoupled equations of motion of the aircraft, together with
disturbances due to atmospheric turbulence, were simulated on a digital
computer. Frequency response methods were also used to provide information
for comparison with results from conventional control.
The experimental investigations involved consideration of the
combination of surface activity, the effects of non-linearities in the
surface actuators and the dynamic response to both manoeuvre commands and
stochastic disturbances, The best results, expressed in terms of reduction
of the levels of the normal and lateral acceleration, were obtained when all
available controls were activated simultaneously and reductions of the order
of 40% were achieved. The effect of the optimal control law on the aircraft
handling qualities was also investigated and compared with idealised models
A Masters Dissertation, submitted in partial fulfilment of the requirements of the award of Master of Science of Loughborough University.