Aleksandar Simonović

This paper presents a quasi-dynamic experimental investigation of the tracer path of a 12.7 × 108 mm projectile, as well as the processing of collected signals using a developed supporting methodology and procedure. The aim of the presented methodology and accompanying procedure is to enable reliable, rapid, and safe verification of the quality of the tracer composition within the projectile, using a suitable device, without the need for an open firing range with a long firing line. The experimental procedure described allows for routine and swift factory quality control of tracer projectiles, reducing testing time and cost, improving data acquisition quality and overall test safety compared to conventional field tests, while achieving the desired repeatability of measurement conditions. The developed methodology, along with the accompanying procedure and device, enables the simulation of real flight conditions of a projectile along its trajectory. The experimental setup allows projectile rotation exceeding 100,000 rpm on the projectile carrier and includes an air-guiding system, a non-contact ignition system for combustion initiation, a spectrophotometer for light emission acquisition, and a PLC for experiment control and monitoring. The results confirm the potential of the developed experimental approach for application in the quality control and development processes of tracer ammunition across various calibers This work relates to the improvements of methods for testing pyrotechnic compositions that make up small arms ammunition tracers, as well as the tracer itself, to the development of contemporary experimental configurations for tracer functional tests, and to an attempt to establish quasi-dynamic testing conditions as an alternative to long-range firing range testing.

A novel concept of morphing airfoils, capable of changing camber and thickness, is proposed. A variable airfoil shape, defined by six input parameters, is achieved by allowing the three spinal points (at fixed axial positions) to slide vertically, while the upper and lower surfaces are determined by the lengths of the three corresponding ribs that are perpendicular to the spine. Thus, it is possible to find the most appropriate geometric configuration for a wide range of possible operating conditions often present with contemporary unmanned aerial vehicles. Shape optimizations for different Reynolds numbers and different cost functions are performed by coupling a genetic algorithm with simple panel method flow calculations. The obtained airfoils are presented and compared, whereas the proposed concept is validated by more advanced flow simulations. It appears that improvements in aerodynamic performance of nearly 20% can be expected at Re ranging from 0.05 × 10⁶ to 0.1 × 10⁶. The proposed methodology shows promise and can be applied to different types of lifting surfaces, including wing, tail or propeller blade segments. To check the viability of this method for producing airfoils that can be used in a practical sense, structural analysis of one of the obtained geometries using a simplified 1D finite element method as well as a more detailed 3D analysis are performed. The model is then 3D-printed on a fused deposition modeling (FDM) printer with a polyethylene terephthalate glycol (PETG) filament, and the capability of the airfoil to adequately morph between the two desired geometries is experimentally shown.

This paper presents the second stage of a tandem fixed-wing unmanned aerial vehicle (UAV) aerodynamic development. In the initial stage, the UAV was optimized by analyzing its characteristics only in symmetrical flight conditions. Posted requirements were that both wings should produce relevant positive lift, the initial stall must occur on the front wing first, the center of pressure should be close to the center of gravity, and longitudinal static stability should be in the optimum range. Computational fluid dynamic (CFD) analyses were performed, where the applied calculation model was derived from the authors’ previous successful projects. The eighth version TW V8 has satisfied all longitudinal requirements. Lateral-directional CFD analyses of V8 showed that the ratio of the lateral and directional stability at the nominal cruising regime was optimal, but both lateral and directional static stabilities were too high. On further development versions, the lower vertical tail was eliminated, a negative dihedral was implemented on the front wing, and four inverted blended winglets were added. Version TW V14 has largely improved lateral and directional stability characteristics, while their optimum ratio at the cruising regime was preserved. Longitudinal characteristics were also well preserved. Maximum lift coefficient and lift-to-drag ratio were increased, compared to the V8.

This paper presents the second stage of a tandem fixed wing unmanned aerial vehicle (UAV) aerodynamic development. In the initial stage, the UAV was optimized analyzing its characteristics only in symmetrical flight conditions. Posted requirements were that both wings should produce relevant positive lift, the initial stall must occur on the front wing first, the center of pressure should be close to the center of gravity, while longitudinal static stability should be in the optimum range. Computational fluid dynamics (CFD) analyses were performed, where applied calculation model was derived from the authors’ previous successful projects. The eight version TW V8 has satisfied all longitudinal requirements. Lateral-directional CFD analyses of V8 showed that the ratio of the lateral and directional stability at the nominal cruising regime was optimal, but both lateral and directional static stabilities were too high. On further development versions the lower vertical tail was eliminated, negative dihedral was implemented on the front wing, and four inverted blended winglets were added. Version TW V14 has largely improved lateral and directional stability characteristics, while their optimum ratio at cruising regime was preserved. Longitudinal characteristics were also well preserved. Maximum lift coefficient and lift-to-drag ratio were increased, compared to the V8.

The main aim of this paper was to determine the influence of different parameters of winglet design on overall Unmanned Aerial Vehicle (UAV) aerodynamics. Looking from an aerodynamicist's point of view, the main reason for using such wingtip devices is to reduce induced drag component, which noticeably contributes to total drag when flying both in cruising flight and on higher angles of attack at lower speeds. Significant benefits of using winglets on overall aircraft performance include reduced fuel burn, increased maximum range and endurance, and higher cruise altitude. Total drag of a simplified mock-up of an existing tactical UAV was calculated using hybrid approach. Parasite drag was obtained using analytical and semi empirical methods, while the induced drag and the lift in its linear domain were determined using inviscid CFD model based on a 3D vortex lattice method (VLM). Computational analyses were focused on determining the influence of winglet cant angle, root chord length, span, airfoil, and twist angle on lift-to-drag ratio of the UAV. Results obtained for different types of winglets (straight, blended and elliptical) were compared, and the best performing in the prescribed dimensions were the elliptical winglets. Their geometry was further optimized, finally providing an overall lift-to-drag ratio increase of 7% compared to the original UAV design without winglets, which represents quite remarkable improvement.

The main aim of this paper was to determine the influence of different parameters of winglet design on overall Unmanned Aerial Vehicle (UAV) aerodynamics. Looking from an aerodynamicist's point of view, the main reason for using such wingtip devices is to reduce induced drag component, which noticeably contributes to total drag when flying both in cruising flight and on higher angles of attack at lower speeds. Significant benefits of using winglets on overall aircraft performance include reduced fuel burn, increased maximum range and endurance, and higher cruise altitude. Total drag of a simplified mock-up of an existing tactical UAV was calculated using hybrid approach. Parasite drag was obtained using analytical and semi empirical methods, while the induced drag and the lift in its linear domain were determined using inviscid CFD model based on a 3D vortex lattice method (VLM). Computational analyses were focused on determining the influence of winglet cant angle, root chord length, span, airfoil, and twist angle on lift-to-drag ratio of the UAV. Results obtained for different types of winglets (straight, blended and elliptical) were compared, and the best performing in the prescribed dimensions were the elliptical winglets. Their geometry was further optimized, finally providing an overall lift-to-drag ratio increase of 7% compared to the original UAV design without winglets, which represents quite remarkable improvement.

Accurate aerodynamic coefficients and their derivatives are crucial for flight dynamics analysis and appropriate control definition. Even when the investigated geometry is simple (e.g. a revolution body, with simple control or stabilizing surfaces), determination of its aerodynamic derivatives, particularly at supersonic regimes, is rather challenging, and usually includes extensive computational and experimental campaigns. This paper computationally investigates quasi-steady or unsteady supersonic flows that include rigid body motion effects around the Army-Navy Finner geometry (a basic, revolution body with L/D = 10 fineness, slender, conical nose section, and wedge-section fins in × configuration). To elucidate the flow fields, the Reynolds-averaged Navier-Stokes equations are closed by k-o SST turbulence model. Roll and pitch damping are estimated by different approaches, and the obtained values are compared mutually, but also to the available experimental data. In addition, some representative flow visualizations are included.