An exact expression for the flow variables through a viscous shock wave is obtained from the Navier-Stokes equations. The Prandtl number is taken to be ¾, which is close to the value for air, and the viscosity is assumed to be given by Sutherland's formula.

By considering the limit as the viscosity tends to zero, it is shown that the solution to the Euler equations has an entropy spike at the shock wave. This explains certain, hitherto considered spurious, features of shock waves captured by numerical solutions of the Euler equations.

The conversion of the Hercules aircraft for flight refuelling necessitated the installation of a small drogue box on the lower surface of the rear fuselage. This produced a long flow separation and unacceptable rear fuselage and elevator buffeting at the drogue towing speeds required.

The flow separation was stabilised, and the buffeting eliminated, by the installation of strakes and the provision of a small bleed flow through the drogue box.

For the computer simulation of bodies moving through real fluids input data about the aerodynamic and inertial forces and moments developed on them are required. It has long been known that under appropriate conditions the apparent masses of the body can play an important role in the determination of dynamic characteristics and this is certainly the case with parachute systems. In the past, because of inadequate experimental investigations, not all of the implications of apparent mass for this system have been fully appreciated. The current objective is therefore, in the light of experiments conducted on the measurement of apparent masses for some parachute canopies, to derive the relevant equations of motion for the parachute and store system and thus to determine the effects of various parameters on the dynamic characteristics of fully-deployed parachutes. In this system the store has been assumed to be rigidly connected to the canopy.

By introducing experimentally-obtained apparent mass components into the relevant equations of motion, performance characteristics of descending parachutes have been obtained which so resemble those observed as to give an appropriate basis for performance prediction. The effects on pitching oscillations caused by certain changes in system physical parameters; the size of the parachute canopy, the length of the rigging lines and the store mass, have all been considered as well as the effect of parachute altitude. For good stability in pitch the significant ratio of physical parameters is that of store mass to effective canopy mass, inclusive of apparent mass.

The normal practice for achieving some specified degree of reliability in automatic flight control systems has been to use methods which employ several identical feedback channels. The use of such methods requires additional sensors and other hardware components. Since such an approach has become increasingly expensive to implement, and attracts operational costs, owing to the increased weight arising from the extra equipment, any method is attractive which achieves the same degree of reliability through the use of only a single hardware path for each feedback channel. This implies the employment of special software techniques for both detecting any channel failures and reconstructing the feedback signals, which are then missing as a result of those failures. Such a scheme is presented and discussed in the paper and a number of results obtained from digital simulation are also presented to illustrate the effectiveness of the scheme for a wide variety of sensor failure conditions. The sensitivity of the scheme to initial errors in the estimation process, to the dynamic nature of the motion sensors, and to errors in the mathematical model of the aircraft dynamics, is also illustrated and discussed.