Elsa M. Cárdenas

Stability and Performance of a Light Unmanned Airplane in Ground Effect

The objective of the present work is to understand the effect of ground proximity on the aerodynamic performance and stability of a light unmanned aerial vehicle. The flowfield around the airplane was computed by PAN AIR and Athena Vortex Lattice. The ground effect was simulated using the method of images. The stability coefficients and other aerodynamic characteristics were obtained at different heights above ground and in free flight. The results demonstrate that the airplane is lateral-directional statically stable, longitudinal statically stable in free flight and longitudinal statically unstable in ground effect. The dynamic stability characteristics of the airplane were obtained at different heights above ground. The phugoid mode is considerable influenced by ground effect and a divergent and non-oscillatory mode appears when the airplane is near to the ground. This is called non-dimensional height mode. The short-period, the Dutch roll, the roll and the spiral modes are slightly affected by ground effect. Significant differences were obtained when the z derivatives were neglected in the dynamic analysis for longitudinal motion. The present work demonstrates that the performance and stability of the unmanned airplane are considerably influenced by ground effect.

Design of an Unmanned Aerial Vehicle for Ecological Conservation

§The exploitation of petroleum can cause serious environment problems when oil leakages occur on the marine or lake surfaces. The constant vigilance over exploitation areas helps to minimize the adverse impact of such accidents by means of early detection. This article deals with the activities carried out at present in order to create an unmanned aerial vehicle designed to patrol the petroleum exploitation zones. Among these activities the preliminary design of the aircraft, the structural design of a prototype capable of accomplishing the assigned mission, and the aerodynamic optimization of such a design, are worth mentioning. A monoplane airplane, twin-boom configuration airplane, with a partially metallic structure was designed. The aerodynamic optimization process was realized applying theoretical and experimental methods. In conclusion, the designed vehicle will prove to be satisfactory for the mission for which it was created, and to be used as a tool for future research.

Increasing the Lift-Drag Ratio of an Unmanned Aerial Vehicle Using Local Twist

Recently published works predict that any planform shape may be optimized with twist to reduce the induced drag to an optimum value. When the twist is applied along the span of the airplane, the lift-drag ratio is lower than that with no twist. This can be corrected if twist is applied only in a specific portion of the span. The objective of this paper is to demonstrate that the local twist increases the lift-drag ratio using two different inviscid computational fluid dynamics codes and to describe the method employed to obtain the twist start line to increase the lift-drag ratio. The method was applied to an unmanned aerial vehicle designed for the early detection of oil leakages in the extraction areas, and a variation of 8 cm in the wing tip was obtained. The results show that the lift-drag ratio of the twisted wing is higher than that with no twist in conditions close to cruise flight. The lift-drag ratio increased 2.89 and 0.31%, estimated by Multhopps method and by the vortex-lattice method, respectively. The results demonstrate that the local twist may increase the lift-drag ratio when it is applied in the way explained in the present paper.

Stability and Flying Qualities of an Unmanned Airplane Using the Vortex-Lattice Method

The purpose of the present work is to evaluat e the static stability and open loop dynamic stability for un power ed condition of the Unmanned Aerial Vehicle for Ecological Conservation. Forces and moments were obtained by the vortex lattice method. These were computed for different values of angle of a ttack, sideslip angle, aileron, rudder and elevator deflection, and pitch, yaw and roll rates. Static stability and control derivatives were obtained and used for the analysis of airplane open loop dynamic stability and response. The longitudinal and later al –directional derivates show that the airplane is statically stable. The short period mode and phugoid mode correspond with damped mode. Dutch roll mode and roll mode of the airplane matches with damped mode and convergent mode, respectively. However, spi ral mode re spo nse prediction corresponds to a divergent mode. The airplane reaches flying qualities equal and better than those of Level 2

Stability of an Unmanned Airplane using a Low-Order Panel Method

The objective of the present work is to evaluate the static and dynamic stability of the Unmanned Airplane for Ecological Conservation using the inviscid panel code CMARC. This code is capable of analyzing three-dimensional steady and unsteady flow around a complete airplane. The longitudinal aerodynamics was studied by a half-model of 3.616 panels, assuming symmetrical flow conditions. The lateral-directional aerodynamics was investigated using the complete model supposing asymmetric flow conditions. The stability coefficients were calculated and it can be concluded that the airplane is statically stable. Using these coefficients, the longitudinal and lateral-directional equations of motion were written, in order to evaluate the dynamic stability of the vehicle. The eigenvalues for each mode of motion were computed showing a convergent response for each one. Excellent flying qualities were achieved, rating in Level 1 for the Cooper and Harper scale. A comparison was done between the data obtained in the present work and the values obtained by two vortex lattice method codes and an analytical-empirical method. The values associated with longitudinal mode calculated by the different methods agree fairly well, but those ones linked with lateral-directional mode have a poor correlation.

Dynamic Ground Effect on the Longitudinal Stability of Airplanes during the Landing

The objective of the work presented herein is to study the influence of dynamic ground effect on the longitudinal stability of airplanes during un-power landing by numerical simulation. A method was developed to design a landing control system which considers dynamic ground effect by the inclusion of the h derivatives in the longitudinal equations of motion. A case study was presented to illustrate with an example the influence of dynamic ground effect on the longitudinal stability using the Unmanned Airplane for Ecological Conservation. Open-loop flight simulations were performed considering dynamic ground effect using a program written in FORTRAN language. When the vehicle achieved heights lower than 2.5935 m during the simulations, an unstable response appears. A landing control system was designed using the methodology presented in this paper, and close-loop simulations were completed using a model created in Simulink. The control system drove the airplane to the runway, only when the h derivatives were included in the equations of motion. The unstable response produced by the dynamic ground effect has a strong influence in the flare manoeuvre, and for this reason, in the design of a landing control system, the h derivatives must be included in the longitudinal equations of motion.

Aerodynamic Analysis of the Unmanned Aerial Vehicle for Ecological Conservation

The present work has as objective to do a comple te aerodynamic analysis of the Unmanned Aerial Vehicle for Ecological Conservation. The panel method code PAN AIR is used to compute the inviscid flowfield. The viscous effects in drag are estimated by the classic Hoerner method, and the maximum lift coeff icient via the classic Valarezo and Chin method. The numerical aerodynamic forces of the complete airplane are compared to experimental data for validation. The spanload and wing pressure distribution are estimated for four configurations: wing, wing -body, wing -body -tail, and wing -body -tail with wing twist. The sources of induced drag for all configurations are achieved graphically via Trefftz plane. All the data were estimated at cruise flight, Reynolds number equal to 1.413×10 6

Aerodynamic Performance as a Function of Local Twist in an Unmanned Airplane

Recently published works predict that any planform shape may be optimized with twist to reduce the induced drag to an optimum value. The objective of this paper is to observe how the distance between the wing root and the twist start line is linked to the maximum lift –drag ratio and to the maximum lift co efficient on an unmanned aerial vehicle designed for the early detection of oil leakages in the extraction areas. The aerodynamic analysis was performed using a panel code to compute the inviscid flowfield, a viscous drag built to estimate the viscous drag , and the pressure difference rule to calculate the maximum lift coefficient. The results show that the maximum lift –drag ratio increases and the maximum lift coefficient reduces as the distance between the wing root and the twist start line decreases. The lift –drag ratio increases 1.51%, and the maximum lift coefficient decreases 3.55% respect to the value for the untwisted airplane. The twist start line was placed at 0.815 m as the greatest lift –drag ratio augmentation is located at this station. The res ults demonstrate that the maximum lift –drag ratio and the maximum lift coefficient are linked to the distance between the wing root and the twist start line.

Dynamic Ground Effect on the Aerodynamic Coefficients of a Wing using a Panel Method

A numerical investigation has been developed to evaluate the influence of dynamic ground effect on the aerodynamic coefficients of a wing using a panel method. This simulates unsteady flow by the time-marching method with a deformable free wake. The image method is used to model ground effect. Lift, induced drag, and pitching moment coefficients were obtained considering fixed height above the ground (static ground effect) and the wing in sink and flare maneuvers (dynamic ground effect). The results at static ground effect were compared with analytical and numerical results in order to verify and validate the created panel code, and they are acceptable. Lift and the absolute value of the pitching moment coefficients increase and the induced drag coefficient decreases as the height diminishes. Although the trends in static and dynamic ground effect are similar, the aerodynamic coefficients achieved in static ground effect are less affected than those ones calculated by simulations of the wing approaching the ground. Linear models of the wing in ground effect were developed by using the data of constant rate of descent and flare maneuvers. The sink rate produces significant variations in the aerodynamic coefficients of a wing.

Evaluation of the Flying Qualities of a Half-Scale Unmanned Airplane via Flight Simulation

The purpose of the present work is to evaluate the flying qualities of a half-scale radio controlled airplane based on the Unmanned Airplane for Ecological Conservation via flight simulation. The stability coefficients of the half-scale airplane were obtained by vortex lattice method using the code Tornado. The radio controlled aircraft simulator CRRCSim was used to perform the virtual flights. Aerodynamic, geometry, thrust and mass characteristics of the airplane were introduced to the simulator by a code written in C++. Virtual test flights were carried out and the flying qualities were obtained. It could be concluded that the half-scale airplane has excellent flying qualities, rating the aircraft in level 1. The simulator is recommended as a training tool for test pilots of the real model.