The effects of aspect ratio on elliptical sonic jet decay at different levels of under-expansion has been studied experimentally. Elliptical sonic jets from orifices of same area with aspect ratios (AR) 2, 4 and 6 at nozzle pressure ratios 2 to 5 in steps of 1 have also been studied. A circular jet from an orifice with an area equal to that of elliptical orifice was also studied for comparison. Jet centreline pressure decay, spread and waves present in the jet core were analysed. The results show that the mixing of the elliptical jet is superior to the circular jet, at all the nozzle pressure ratios of the present study. Also, the aspect ratio of the elliptical orifice has a strong influence on the jet mixing. Elliptical jets of aspect ratio 4 and 6 experience a significantly higher mixing than the aspect ratio 2 jet, till the under-expansion level corresponding to Mach disk formation. For higher under-expansion levels, the mixing of AR 4 and 6 jets become inferior to that of the AR 2 jet.

Elastomeric and Fluidlastic® absorbers are proposed to be embedded in blade cavity to reduce troublesome second harmonic flap-wise blade loads of rigid rotors. A simple model of a blade with a flap-wise dynamic absorber is derived to investigate centrifugal force effects on the absorber's rotating frequency. The system's dynamic equations of motion indicate that centrifugal force has no effect on absorber's frequency under rotation. Aeroelastic simulation of the coupled rotor and absorber system based on an elastic beam model in generalised force formulation is used to explore load reduction extent and dynamic absorber behaviour. At a forward speed of 200 km/h, the elastomeric absorber reduces the second harmonic flap-wise root-bending moment by 88.8% for unacceptably large stroke; the Fluidlastic® absorber reduces the moment by 78.5% with a stroke 4.26% of blade chord length. Results indicate that placing an embedded Fluidlastic® absorber in the blade's flap-wise direction has potential for reducing load in different flight states with relatively small strokes. Increasing tuning port area ratio or Fluidlastic® absorber mass can distinctly decrease strokes without increasing loads. However, deviation from normal rotor speed significantly lowers Fluidlastic® absorber performance.

This paper presents a study of the W3-Sokol main rotor equipped with Gurney flaps. The effect of the active Gurney is tested at low and high forward flight speeds to draw conclusions about the potential enhancement of the rotorcraft performance for the whole flight envelope. The effect of the flap on the trimming and handling of a full helicopter is also investigated. Fluid and structure dynamics were coupled in all cases, and the rotor was trimmed at different thrust coefficients. The Gurney proved to be efficient at medium to high advance ratios, where the power requirements of the rotor were decreased by up to 3.3%. However, the 1/rev actuation of the flap might be an issue for the trimming and handling of the helicopter. The current study builds on the idea that any active mechanism operating on a rotor could alter the dynamics and the handling of the helicopter. A closed loop actuation of the Gurney flap was put forward based on a pressure divergence criterion, and it led to further enhancement of the aerodynamic performance. Next, a generic light utility helicopter was built using 2D aerodynamics of the main aerofoil section of the W3 Sokol blade along with a robust controller, and the response of the rotorcraft to control inputs was tested. This analysis proved that the 1/Rev actuation of the Gurney did not alter the handling qualities of the helicopter, and as a result, it can be implemented as a flow control mechanism for aerodynamic enhancement and retreating blade stall alleviation.

The certification process plays an important role in aircraft safety and operation, assuring a high degree of confidence in accomplishing their objectives. Unfortunately, in the field of Unmanned Aerial Vehicles (UAV), there is not enough information to enable an acceptable decision-making process regarding compliance with certification requirements. To overcome this limitation, a methodology was developed based on morphological analysis principle, taking advantage of the knowledge and behaviour of similar items and affecting them with the necessary corrective factor in accordance to the differences in design, operation and environment. The objective is to establish an initial maintenance program as an important requirement to operate any kind of aircraft. This paper presents the methodology and the obtained results for a UAV under development concerning the establishment of a maintenance program regarding its certification process.

The ionosphere is one of the main factors affecting the accuracy and integrity of satellite-based augmentation system positioning systems. This paper presents the results of a 30-day study of the accuracy and integrity of the European Geostationary Navigation Overlay Service (EGNOS) conducted at the EPOD airport belonging to the Aeroclub of Warmia and Mazury in Olsztyn, in northeastern Poland (the area until recently considered as the edge of EGNOS coverage). Analyses of the parameters characterising the accuracy and integrity of positioning were performed in three calculation variants/modes: with the original EGNOS ionospheric correction, with correction determined by means of Klobuchar algorithm, and finally with modified ionospheric coefficients developed by the CODE. Studies have shown clearly that the original EGNOS ionospheric model gives the best integrity and accuracy results allowing to use EGNOS for approach with vertical guidance procedures, while the Center for Orbit Determination in Europe and Klobuchar models could only be used for non-precision approach operations.

The modification of aerofoils with structural morphing in order to enhance aerodynamic efficiency is an active field of research. The required forced and induced displacements are, usually, out the current developments on shape memory alloys, piezoelectric actuators or multi-stable structures for commercial transport aircraft applications. This work aims to present studies for obtaining an optimum rudder structure which morphs to a pre-defined curvature that can sustain aerodynamic and internal loads in a critical certification load case for a commercial transport aircraft. It also includes the feasibility of a morphing rudder based on a zero Poisson skeleton, or close to a zero Poisson ratio panel geometrical configuration that has no transverse deformation when perpendicularly loaded and which is produced with an additive layer manufacturing process.

This paper presents a multi-disciplinary analysis methodology for a box-wing aircraft configuration optimised for a given mission scenario. This conceptual design methodology and associated toolchain combines well-established vortex lattice analysis and a newly developed structural analysis tool called WingMASS, allowing the design space to be explored from a combined aerodynamics and structural design perspective. For a given mission scenario, the method optimises a box-wing configuration and compares it with an equivalent conventional configuration. This study shows that, for a given mission, a box-wing configuration can lead to a fuel burn reduction of up to 5% by optimising aspect ratio, horizontal and vertical wing separation.

Steven Ford was omitted from the list of authors in the article by Murrieta-Mendoza(1). The correct authorship is:

A. Murrieta-Mendoza, R. Mihaela Botez and S. Ford

The article has now been updated with the correct authorship; this change has been made to the online version only.

The authors were listed incorrectly in the article by Botez(1). The authors should have appeared in the following order:

A. Koreanschi, O. Sugar-Gabor and R.M. Botez

The article has now been updated with all authors listed in the correct order; this change has been made to the online version only.