Adnan Maqsood

Optimization of Hover-to-Cruise Transition Maneuver Using Variable-Incidence Wing

A = disc area of the propeller D = drag g = acceleration due to gravity J = cost/objective function L = lift L=W = lift-to-weight ratio m = mass of the aircraft T = thrust Tmax = maximum thrust T=W = thrust-to-weight ratio T=W max = maximum thrust-to-weight ratio u = horizontal velocity u = control variable vector ut = terminal horizontal velocity V = freestream velocity wi = ith weight coefficient vt = terminal vertical velocity W = weight w = induced velocity aft of the propeller x = horizontal acceleration yi = altitude at ith discretized calculation instant z = vertical acceleration fus = fuselage and inboard wing angle of attack prop = angle of attack of the propeller wing = outboard wing angle of attack _ wing = rate of change of outboard wing angle of attack = flight-path angle = air density _ = rate of change of variable , d dt

Aerodynamic Estimation of Annular Wings Based on Leading-Edge Suction Analogy

A NNULAR wings belong to the class of nonplanar wing configurations and have gained significant popularity recently [1–5] among the designers of unmanned air vehicles (UAVs) and micro air vehicles (MAVs). The lift increment of the annular wing from any planar configuration of same aspect ratio is well known. Moreover, for small aspect ratios, a significant improvement in L∕D max is observed. Not surprisingly, the increased popularity of annular wings has been driven by their application in ducted-fan UAVs. Annular shroud around the fan helps to increase the static and dynamic thrusts produced, and when the shroud is designed as an annular wing, it also acts as a lifting surface in the forward flight. Typical examples of UAVs with annular wings are the Honeywell MAV by AVID, LLC [1,2], the Singapore Technologies (ST) fantail system [3], and the GoldenEye UAV [4]. The application of the annular wing on passenger aircraft has also been conceptualized. Although the work related to annular wings can be traced back to [6] in 1947, the generic theoretical aerodynamic models of such wings have not been fully studied and have not received significant attention from technology protagonists beside its recognized advantages. Ribner [6] analytically derived the lift characteristics of annular wings and concluded that their lift-curve slope is twice that of the flatplate elliptical wings of the same aspect ratio. The seminalwork in [7] represented the first formal experimental investigations on annular wings by a varying aspect ratio and comparing their lift-curve slope with various theoretical models. The investigation included the longitudinal aerodynamic characteristics of five annular wings of aspect ratio AR 1∕3, 2∕3, 1.0, 1.5, and 3.0 with equal projected areas and theClark-Yairfoil cross section (thickness-to-chord ratio of 11.7%). The Reynolds numbers of the experiment varied, Re 0.704–2.11 million, due to the variation in the root chords of the wings. The results indicated that the lift-curve slopes of the annular wings were about twice that of the lift-curve slopes for planar rectangular wings having the same aspect ratio, which confirmed the findings of [6]. Recently, Traub [5] has revisited the topic by carrying out the experimental investigation on the baseline annular wing aerodynamics and studied the effects of gap and aspect ratio. The findings for aspect ratio variation coincide with the results in [7], but no analytical approximation of the lift behavior is attempted. Demasi [8] has developed a theoretical model of the minimum-induced drag prediction for annular wings based on the lifting line theory and the small perturbation acceleration method. A simplified concept of leading-edge suction analogy was proposed in [9] for the low-aspect ratio planforms (specifically delta wings) in the late 1960s. The aerodynamic surfaces at moderate angles of attack suffer from flow separation at or near leading edge, which significantly alters the pressure distribution on the upper surface. The approach assumes that the total lift in the prestall regime can be calculated as the sum of the component of lift from potential flow (based on fully attached pressure distribution) and the other component associated with the separated leading-edge vortices. The total force on the wings (prior to stall) associated with the pressure required to stabilize the separated vortices is equivalent to the leading-edge suction force to keep the flow around the wings attached. This theory was extended in [10] to other planform shapes, such as rectangular wings in subsonic and supersonic regimes. Suction analogy for the side-edge vortices was also proposed in this work. Recently, this approach has been used to study the aerodynamic characteristics of different low-aspect ratio planform shapes at the low Reynolds numbers in [11,12]. Specifically, the aerodynamic effect of pressure-induced forces and vortex-induced forces are parameterized and can be observed explicitly for various planform shapes and aspect ratios. The vortex generated from leading-edge flow separation is also observed in the annular wings. In [5], during the surface flow visualization, a significant region of separation is observedon topof the annular wingwith an increasing angle of attack. The lower surface also showed evidence of large scale separation in the vicinity of the stall. Such separation leads tovortex generation and, consequently, a suction force that will contribute to lift as in the planar wing. Therefore, the influence of leading-edge separation on overall pressure distribution can be approached similarly using the Polhamus-like method. The key factor in the development of the Polhamus-like formulation for the annular wings is to properlymodel the division of overall lift contribution from fully attached (potential) flow and vortex-induced flow. This is achieved by comparing a set of different theoretical models to the experimental data of the annular wing with Received 22 February 2012; revision received 2 July 2012; accepted for publication 25 August 2012; published online 26 November 2012 Copyright

Study on Aerodynamic-Assisted Transition Control Technique for Versatile UAV

In this paper we present preliminary results of a study on an aerodynamic-assisted transition technique for a ducted-propeller Vertical Takeoff and Landing Unmanned Aerial Vehicle from hover to forward flight and vice versa. The technique utilizes a variableincidence wing, whose pitch orientation with respect to the ducted propeller is a control variable. A fourth-order point-mass model is used for the modeling of the aircraft dynamics in the study. For the dynamic analysis, the aerodynamic forces and moments database is developed both in pre-stall and post-stall regime using a three-dimensional vortex lattice code. Then a parametric optimization of the thrust, pitch angle, and wing incidence during the transition maneuver is studied. The objective is to achieve a transition scheme with minimal variation in altitude, reduced transition time and reasonable thrust-to-weight ratio. The results indicate that with proper scheduling of the pitch angle and wing incidence, the objective can be achieved. Based on the parametric analysis results, nonlinear constrained optimization based on energy approach and Sequential Quadratic Programming (SQP) algorithm is performed to generate the transition trajectories. A trade-off within the defined objectives of the transition is also discussed. The results obtained can be used as a benchmark for future closed-loop transition controller development.

Longitudinal flight dynamic analysis of an agile UAV

Purpose – The purpose of this paper is to describe the longitudinal dynamics of a hover‐capable rigid‐winged unmanned aerial vehicles (UAV) under various equilibrium flight conditions. The effects of the variable‐incidence wing in comparison with the fixed in‐incidence wing on the dynamics of UAV are also discussed.Design/methodology/approach – The aerodynamic modeling of the vehicle covers both pre‐stall and post‐stall regimes using a three‐dimensional vortex lattice method incorporating viscous corrections. The trim states across a velocity spectrum are evaluated using a nonlinear constrained optimization scheme based on sequential quadratic programming. Then linearized dynamic analysis around trim states is carried out in order to compare the characteristics of the conventional platform with the modified platform incorporating variable‐incidence wing.Findings – It is found that with the variable‐incidence wing, the longitudinal equilibrium flights can be achieved with reduced thrust‐to‐weight ratio dem...

Study on the design improvement of an indoor ceiling fan

Ceiling fans are frequently used in tropical areas of the world for low cost indoor comfort. An incremental work in improving energy efficiency of ceiling fans can directly reflect in substantial energy conservation across Pakistan. In this paper, computational modeling and simulation of the ceiling fan rotating inside the room is performed. The computational model is validated by the experimental data collected at Fan Development Institute Gujrat, a subsidiary of Pakistan Electric Fans Manufacturing Association. A parametric study of ceiling fans is carried out with the objective to improve flow field variables and fan efficiency. The performance indicators such as velocity profile, mass flow rate, torque, rated air delivery and service value are calculated. Different cases of rake angles are considered and compared to the baseline geometry. The study concluded that six degree rake angle show enhanced performance.

Parametric Studies and Performance Analysis of a Biplane Micro Air Vehicle

This paper presents the experimental investigation of a biplane micro air vehicle. The effects of geometric parameters, gap, stagger, and decalage angle are investigated at low Reynolds number (~150,000) in a low-speed wind tunnel. A rigid flat plate with an aspect ratio of one and square planform shape is used to evaluate all three geometric parameters. The side dimension of the single flat plate is 0.15 m. The goal is to find an optimal biplane configuration that should exceed monoplane performance by generating high lift and flying as slow as possible, in order to capture high-quality visual recordings. This configuration will directly help to fly at a lower velocity and to make tighter turns that are advantageous in restricted environments. The results show that the aerodynamic performance of the biplane MAV is significantly enhanced through the combination of gap and stagger effects. A performance comparison demonstrates the superiority of the optimal biplane configuration compared to a monoplane in cruise and glide phases. Moreover, no significant compromise is found for the range, endurance, and climb performance.

Optimization of dynamic soaring maneuvers to enhance endurance of a versatile UAV

Dynamic soaring is a process of acquiring energy available in atmospheric wind shears and is commonly exhibited by soaring birds to perform long distance flights. This paper aims to demonstrate a viable algorithm which can be implemented in near real time environment to formulate optimal trajectories for dynamic soaring maneuvers for a small scale Unmanned Aerial Vehicle (UAV). The objective is to harness maximum energy from atmosphere wind shear to improve loiter time for Intelligence, Surveillance and Reconnaissance (ISR) missions. Three-dimensional point-mass UAV equations of motion and linear wind gradient profile are used to model flight dynamics. Utilizing UAV states, controls, operational constraints, initial and terminal conditions that enforce a periodic flight, dynamic soaring problem is formulated as an optimal control problem. Optimized trajectories of the maneuver are subsequently generated employing pseudo spectral techniques against distant UAV performance parameters. The discussion also encompasses the requirement for generation of optimal trajectories for dynamic soaring in real time environment and the ability of the proposed algorithm for speedy solution generation. Coupled with the fact that dynamic soaring is all about immediately utilizing the available energy from the wind shear encountered, the proposed algorithm promises its viability for practical on board implementations requiring computation of trajectories in near real time.

Shape optimization of non-linear swept ceiling fan blades through RANS simulations and Response Surface Methods

Ceiling fans are the most used resource for providing indoor thermal comfort in hot climates because of factors like low cost, easy availability and less electric consumption compared to air conditioning units. The fan industry of Pakistan is well-renowned on the national scale. In this paper, the features of the flow field generated by the ceiling fans under different geometric shapes are discussed. Specifically, the effect of forward elliptic sweep angle is studied on the performance of ceiling fans. Other geometric variables considered are tip width, root and tip angle of attack. The response variable considered for parametric analysis as well as optimization studies is the rated air delivery. The benchmark design is the reference blade being sold in market. By applying Design of Experiment (DOE), sixteen experiments are designed for new blades. These new blade designs are simulated through Reynolds-Averaged-Navier-Stokes (RANS) commercial flow solver. The computational model is developed around the same experimental facility and validated with experimental data. Subsequently, statistical tools are used to study the effect of individual parameters as well as their interactions. Finally, Response Surface Methodology (RSM) is used to find the optimal solution in the design space.

Quantitative evaluation of Security and Privacy perceptions in online social networks: A case study

The growth in technology has transformed our socio-economic system to socio-techno-economic dimension. The usage of online social media for formal / informal interactions has added complexity to our existing communication networks and lifestyles. As a consequence, the security and privacy of individuals / information is now more vulnerable. Security and Privacy of social networks act as means to develop counter-terrorism strategies. Development of appropriate security layers in online social media requires enormous time and financial resources. However, the awareness of such complex issues in Pakistani society is still under-developed. In this study, we have focused on extracting the existing awareness state in the society about privacy, security and information sharing in social media. The study is based on a questionnaire filling. Data has been collected from National University of Sciences & technology, (NUST) Islamabad, Pakistan. Correlations between variables and usage / awareness levels of security settings in social networking sites are evaluated. The results of this study will help in evaluating current user perspective and futuristic interventions required for development of awareness programs and design of security procedures / layers in social media system.

Aerodynamic Evaluation of Wing-Strake Modification by Higher Order Panel Method

In this paper we present the preliminary aerodynamic evaluation of enlarged wing-strake and increased wing-sweep modification of an underdevelopment multi-role supersonic fighter aircraft. In this study, higher order panel method is employed in order to explore the high subsonic and supersonic regimes. For this purpose the shareware version of PANAIR code is used. The effect of the wing-strake modification on aerodynamic characteristics of the aircraft is evaluated by comparative study of the original (unmodified) and the modified configurations. The results, for both subsonic and supersonic regimes, indicate reduced static longitudinal stability, increased static lateral stability and increased lift for the modified configuration. Reduction in wave drag is indicated in supersonic regime while an increase in induced drag is predicted in the subsonic regime for the modified configuration. These computed results are quantified in terms of difference in various non-dimensional aerodynamic forces and moments between the modified and original configurations.