Technology developments in radar frequency simulators of the type used to verify the performance of complex electronic warfare systems are described. The successful verification of this performance prior to combat use is a necessary pre-requisite of military platform survivability and mission success. These simulators and associated modelling and analysis tools have enabled a major shift during the last 15 years from expensive and limited flight trials to repeatable laboratory and anechoic chamber tests, although they will never totally supplant those trials. Most limitations of the early days of many-channel simulators, 25 years ago, have been resolved or adequately and – as importantly – affordably mitigated, largely enabled by computing power increases. Limitations remain that will, within affordability constraints driven by Defence Ministries worldwide, prevent perfect simulation (‘emulation’) and the attendant, tantalising but utopian goal of laboratory and chamber test results that precisely match those from flight test and combat.

This paper describes an experiment which was performed using an offshore transport helicopter to investigate the impact of the rotor blades upon Global Positioning System (GPS) reception.

The test aircraft was fitted with two separate GPS antennas which were positioned to isolate the effects caused by the main and tail rotors. Testing was undertaken with the aircraft on the ground and this allowed an assessment to be performed at different rotor speeds with accurate control over the relative geometry between the antenna, rotors and satellites.

Recorded data from a measurement system incorporating three dissimilar GPS receivers (including a technical standard order (TSO)-C129() compliant aviation unit and a custom research receiver) was analysed to identify the effect of the rotors at the correlator level and to determine the impacts upon ranging accuracy, the availability of ranging measurements, and the receivers’ signal level estimates.

Correlation data was used to demonstrate that the rotor blades were capable of generating both destructive and constructive interference effects, and the periodic nature of these oscillations was shown to correspond directly to the blade passing frequency. It was identified that signal degradation was not limited to satellite signal paths which intersected the rotor discs.

No evidence was found for any increase in code measurement error due to the rotor interference, but it was demonstrated that there could be a significant impact upon a receiver’s ability to maintain continuous tracking of the satellite signals. The overall effect of this availability problem for a given installation and type of operation will be dependent upon satellite geometry and other factors which are beyond the scope of this study.

The ability of a receiver to identify the presence of rotor interference was investigated by examining estimates of carrier-to-noise, and this revealed inconsistencies between the results from different receivers implying differences in the estimation algorithms employed. It was also identified that two alternative ‘textbook’ estimators do not give identical results in the presence of rotor interference and it is suggested that such data should therefore be interpreted with caution.

In many engineering applications (e.g. helicopters, turbines, compressors), lifting surfaces experience unsteady motion or are perturbed by unsteady incoming flows. Horizontal axis wind turbine rotors experience large time dependent variations in angle-of-attack as a result of control input angles, blade flapping, structural response and wake inflow. In addition, the blade sections encounter substantial periodic variations in local velocity and sweep angle. Thus, the unsteady aerodynamic behaviour of the blade sections must be properly understood to enable accurate predictions of the air loads and aero elastic response of the rotor system.

The aircraft industry, as a whole, is striving to limit its impact on the environment. Improved engine design and operation may offer a reduction in emissions of a few percent. More efficient air traffic control (ATC) may offer a limited reduction in overall fuel burn. Improvements in aerodynamic design and materials available (e.g. on A350XWB, B787) might achieve a few percent increases in efficiencies. The use of alternative fuels is some way off. The ACARE objectives present a stiff challenge.

Our recent studies have shown that air-to-air-refuelling (AAR), well established in military circles, introduced to civil aircraft operations would provide fuel savings of the order of 30% – 40%. AAR will allow smaller (3,000nm range), more efficient (greener) aircraft, operating from shorter runways, to fulfil long-range route requirements. In addition, the ‘safety-net’ afforded by the availability of AAR will enable a host of hitherto borderline technologies to be accepted and utilised in future aircraft designs. Laminar flow will provide fuel savings and increased efficiency in its own right provided it is enabled within a civil AAR environment. Similarly, supersonic transport becomes an acceptable economic option.

In this paper, a theoretical study of the turn manoeuvre of an agricultural aircraft is presented. The manoeuvre with changeable altitude is analyzed, together with the, effect of the load factors on the turn manoeuvre characteristics during the field-treating flights. The mathematical model used describes the procedure for the correct climb and descent turn manoeuvre. For a typical agricultural aircraft, the numerical results and limitations of the climb, horizontal and descending turn manoeuvre are given. The problem of turning flight with changeable altitude is described by the system of differential equations which describe the influence of the normal and tangential load factors on velocity, the path angle in the vertical plane and the rate of turn, as a function of the bank angle during turning flight. The system of differential equations of motion was solved on a personal computer with the Runge-Kutta-Merson numerical method. Some analytical and numerical results of this calculation are presented in this paper.