Unmanned aerial vehicles (UAVs) have the potential of creating an ad hoc communication network in the air. Most UAVs used in communication networks are equipped with wireless transceivers using omnidirectional antennas. In this paper, we consider a collection of UAVs that communicate through wireless links as a mobile ad-hoc network using directional antennas. The network design goal is to maximize the throughput and minimize the end-to-end delay. In this respect, we propose a new medium access control protocol for a network of UAVs with directional antennas. We analyze the communication channel between the UAVs and the effect of aircraft attitude on the network performance. Using the optimized network engineering tool (OPNET), we compare our protocol with the IEEE 802.11 protocol for omnidirectional antennas. The simulation results show performance improvement in end-to-end delay as well as throughput.

Abdel Ilah Alshbatat

Liang Dong

Performance Analysis of Mobile Ad Hoc Unmanned Aerial Vehicle Communication Networks with Directional Antennas

The Routh criterion is used to assess longitudinal dynamic stability of a propeller-driven aircraft. Under a few plausible assumptions on possible ranges of the pertinent stability derivatives, it reduces to a pair of simple conditions imposing a traditional aft limit (the forward of the maneuver and the neutral-speed-stability points) on the center-of-gravity position and an upper limit on the longitudinal moment of inertia. It is demonstrated that most aircraft have sufficiently small inertia to remain stable as long as their center-of-gravity is properly placed. At the same time, sailplane-like aircraft (as, e.g., long endurance UAVs), with an engine installed at the rear extremity of the aircraft, may have sufficiently high inertia to become unstable regardless of their center-of-gravity placement.

Gil Iosilevskii

Longitudinal Stability Criteria for a Propeller-Driven Aircraft

Wind tunnel experiments were conducted on NACA-0015 airfoil model to investigate the effect of the reduced frequency (<svg style="vertical-align:-0.1638pt;width:72.837502px;" id="M1" height="11.125" version="1.1" viewBox="0 0 72.837502 11.125" width="72.837502" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"><g transform="matrix(.017,-0,0,-.017,.062,10.862)"><path id="x1D705" d="M484 406q0 -21 -22 -38q-10 -7 -18 -1q-15 11 -30 11q-30 0 -77.5 -37t-74.5 -67l79 -168q11 -23 19.5 -34.5t13 -14t10.5 -2.5q9 0 30 17.5t40 42.5l17 -23q-31 -45 -57.5 -69.5t-40.5 -29.5t-31 -5q-18 0 -32 13.5t-35 55.5q-34 71 -69 160q-36 -32 -59 -56&#xA;q-12 -27 -36 -158q-44 -7 -77 -15l-5 7l82 349q6 25 -2 25q-16 0 -72 -41l-14 22q44 41 89 69.5t66 28.5q19 0 19 -32q0 -16 -6 -43l-35 -160l146 143q94 92 136 92q20 0 33 -12t13 -30z" /></g><g transform="matrix(.017,-0,0,-.017,13.39,10.862)"><path id="x3D" d="M535 323h-483v50h483v-50zM535 138h-483v50h483v-50z" /></g><g transform="matrix(.017,-0,0,-.017,28.093,10.862)"><path id="x30" d="M241 635q53 0 94 -28.5t63.5 -76t33.5 -102.5t11 -116q0 -58 -11 -112.5t-34 -103.5t-63.5 -78.5t-94.5 -29.5t-95 28t-64.5 75t-34.5 102.5t-11 118.5q0 58 11.5 112.5t34.5 103t64.5 78t95.5 29.5zM238 602q-32 0 -55.5 -25t-35.5 -68t-17.5 -91t-5.5 -105&#xA;q0 -76 10 -138.5t37 -107.5t69 -45q32 0 55.5 25t35.5 68.5t17.5 91.5t5.5 105t-5.5 105.5t-18 92t-36 68t-56.5 24.5z" /></g><g transform="matrix(.017,-0,0,-.017,36.253,10.862)"><path id="x2E" d="M113 -12q-24 0 -39.5 16t-15.5 42q0 24 16 40.5t40 16.5t40 -16.5t16 -40.5q0 -26 -16 -42t-41 -16z" /></g><g transform="matrix(.017,-0,0,-.017,40.129,10.862)"><use xlink:href="#x30" /></g><g transform="matrix(.017,-0,0,-.017,48.288,10.862)"><use xlink:href="#x30" /></g><g transform="matrix(.017,-0,0,-.017,56.447,10.862)"><use xlink:href="#x30" /></g><g transform="matrix(.017,-0,0,-.017,64.607,10.862)"><path id="x31" d="M384 0h-275v27q67 5 81.5 18.5t14.5 68.5v385q0 38 -7.5 47.5t-40.5 10.5l-48 2v24q85 15 178 52v-521q0 -55 14.5 -68.5t82.5 -18.5v-27z" /></g></svg> to 0.5) and that Reynolds number (<svg style="vertical-align:-0.1638pt;width:84.637497px;" id="M2" height="11.375" version="1.1" viewBox="0 0 84.637497 11.375" width="84.637497" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"><g transform="matrix(.017,-0,0,-.017,.062,11.112)"><path id="x52" d="M631 18l-4 -26q-24 0 -35 1q-57 3 -92.5 23t-69.5 68q-21 30 -101 160q-13 22 -30.5 31t-54.5 9h-32v-159q0 -63 14 -77.5t74 -19.5v-28h-262v28q62 5 76 19.5t14 77.5v402q0 62 -13 76t-73 19v28h248q109 0 159 -34q67 -42 67 -131q0 -115 -127 -172q27 -52 89 -144&#xA;q49 -71 81 -104q31 -36 72 -47zM212 316h48q73 0 108 29q55 42 55 124q0 76 -42 112t-104 36q-41 0 -54 -10q-11 -7 -11 -44v-247z" /></g><g transform="matrix(.017,-0,0,-.017,10.653,11.112)"><path id="x65" d="M380 106l15 -22q-42 -52 -87 -74t-76 -22q-89 0 -142 62t-53 151q0 103 66 175q67 73 146 73h1q61 0 105.5 -46.5t44.5 -105.5q0 -16 -4.5 -22.5t-18.5 -9.5q-54 -10 -262 -17q1 -95 46 -143.5t104 -48.5q61 0 115 50zM225 412q-35 0 -64.5 -32.5t-40.5 -90.5q83 0 170 3&#xA;q14 0 19 4.5t5 15.5q1 41 -23.5 70.5t-65.5 29.5z" /></g><g transform="matrix(.017,-0,0,-.017,22.603,11.112)"><use xlink:href="#x3D" /></g><g transform="matrix(.017,-0,0,-.017,37.307,11.112)"><use xlink:href="#x30" /></g><g transform="matrix(.017,-0,0,-.017,45.466,11.112)"><use xlink:href="#x2E" /></g><g transform="matrix(.017,-0,0,-.017,49.342,11.112)"><path id="x32" d="M412 140l28 -9q0 -2 -35 -131h-373v23q112 112 161 170q59 70 92 127t33 115q0 63 -31 98t-86 35q-75 0 -137 -93l-22 20l57 81q55 59 135 59q69 0 118.5 -46.5t49.5 -122.5q0 -62 -29.5 -114t-102.5 -130l-141 -149h186q42 0 58.5 10.5t38.5 56.5z" /></g><g transform="matrix(.017,-0,0,-.017,57.501,11.112)"><path id="x1D438" d="M609 650l-19 -162l-30 -2q2 69 -14 94q-9 18 -28.5 26t-74.5 8h-88q-30 0 -37 -6.5t-12 -36.5l-41 -212h103q48 0 69 5.5t32 19t26 50.5h29l-40 -198h-30q2 58 -11.5 70.5t-85.5 12.5h-99l-30 -167q-17 -87 3 -101q18 -15 111 -15q59 0 89 7t54 27q8 7 15.5 16t16 21.5&#xA;l14 20.5t15 23.5t13.5 21.5l29 -10q-52 -129 -71 -163h-500l6 28q66 4 83 17.5t28 73.5l77 409q11 61 -0.5 75.5t-78.5 18.5l10 28h467z" /></g><g transform="matrix(.017,-0,0,-.017,68.244,11.112)"><use xlink:href="#x30" /></g><g transform="matrix(.017,-0,0,-.017,76.404,11.112)"><path id="x36" d="M137 343l67 33q37 17 63 17q79 0 129.5 -53t50.5 -131q0 -92 -58 -156.5t-147 -64.5t-147 68t-58 182q0 63 17 119t43 95.5t61.5 72t69 52t67.5 31.5q62 22 128 33l6 -32q-56 -11 -108 -35q-149 -71 -184 -231zM227 337q-47 0 -95 -27q-6 -23 -6 -70q0 -93 36 -155.5&#xA;t96 -62.5q53 0 78 45.5t25 105.5q0 68 -35 116t-99 48z" /></g></svg> to 0.7<i>E</i>06) on the aerodynamic characteristics and hysteresis behavior associated with the oscillating motion of the airfoil. 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Static and quasi-steady conditions are critically assessed in context of the existence of laminar separation bubble within the opted <svg style="vertical-align:-0.16379pt;width:17.950001px;" id="M6" height="11.375" version="1.1" viewBox="0 0 17.950001 11.375" width="17.950001" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"><g transform="matrix(.017,-0,0,-.017,.062,11.112)"><use xlink:href="#x52" /></g><g transform="matrix(.017,-0,0,-.017,10.653,11.112)"><use xlink:href="#x65" /></g></svg> regime. The flow separation was found to be trailing edge flow separation with existence of LSB upstream towards the leading edge with no evidence of unsteady flow reversals. Normal force defect and pitch damping factor are estimated for varied range of <svg style="vertical-align:-0.16379pt;width:17.950001px;" id="M7" height="11.375" version="1.1" viewBox="0 0 17.950001 11.375" width="17.950001" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"><g transform="matrix(.017,-0,0,-.017,.062,11.112)"><use xlink:href="#x52" /></g><g transform="matrix(.017,-0,0,-.017,10.653,11.112)"><use xlink:href="#x65" /></g></svg> and <svg style="vertical-align:-0.1638pt;width:8.7375002px;" id="M8" height="7.9499998" version="1.1" viewBox="0 0 8.7375002 7.9499998" width="8.7375002" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"><g transform="matrix(.017,-0,0,-.017,.062,7.675)"><use xlink:href="#x1D705" /></g></svg> within the quasi-steady conditions. Re effect is dominant at steady and quasi-steady regimes while the effect of reduced frequency is negligible in this domain. Minor hysteresis effect associated with the stalling and reattachment point is due to existence of weak stall flutter which is further restrained by the oscillatory motion of the airfoil. Laminar separation bubble traced during steady condition is conserved in quasi-steady domain as well.

Deepakkumar M. Sharma

Kamal Poddar

Investigations on Quasi-Steady Characteristics for an Airfoil Oscillating at Low Reduced Frequencies

Effects of amplitude and frequency of synthetic jet on the characteristics of induced jet are investigated. To estimate effects of the parameters, flow inside the synthetic jet cavity and orifice and the outer flow is simultaneously simulated using large-eddy simulation (LES). Comparison of the present LES result with the experimental data shows that three-dimensional LES of the flow inside the cavity is essential for accurate estimation of the velocity and velocity fluctuation of the synthetic jet. Comparison of the present results under various flow conditions shows that amplitude and frequency can control profiles of time-averaged vertical velocity and fluctuation of the vertical velocity as well as damping rate of the induced velocity and fluctuation.

Koichi Okada

Akira Oyama

Kozo Fujii

Koji Miyaji

Computational Study on Effect of Synthetic Jet Design Parameters

The paper deals with chemical contamination monitoring in phosphate-ester-based hydraulic fluids using nondispersive infrared (NDIR) optical absorption. Our results show that NDIR monitoring allows detecting the take-up of water into such fluids and their hydrolytic disintegration as these become additionally stressed by Joule heating. Observations on the O&#x2013;H stretching vibration band (3200&#x2013;3800&#x2009;<svg style="vertical-align:-0.12538pt;width:32.8125px;" id="M1" height="13.925" version="1.1" viewBox="0 0 32.8125 13.925" width="32.8125"  xmlns="http://www.w3.org/2000/svg">
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		</g>
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</svg>) are used for determining the free water content (0&#x2013;1.5&#x25;) and the Total Acid Number (0&#x2013;1&#x2009;mgKOH/g). Both quantities can be assessed by monitoring the strength and the asymmetry of the O&#x2013;H vibration band with regard to the free water absorption band centred around 3500&#x2009;<svg style="vertical-align:-0.12538pt;width:32.8125px;" id="M2" height="13.925" version="1.1" viewBox="0 0 32.8125 13.925" width="32.8125"  xmlns="http://www.w3.org/2000/svg">
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</svg>. As such optical parameters can be assessed without taking fluid samples from a pressurised hydraulic system, fluid degradation trends can be established based on regular measurements, before irreversible damage to the fluid has occurred. Therefore maintenance actions can be planned accordingly, which is very important for the airline, as unscheduled maintenance disturbs the flights organisation and often generates money loss.

Sumit Paul

Wolfgang Legner

Angelika Krenkow

Gerhard M&#252;ller

Thierry Lemettais

Francois Pradat

Delphine Hertens

Chemical Contamination Sensor for Phosphate Ester Hydraulic Fluids

Design and synthesis of a nonlinear generic supersonic flight vehicle longitudinal dynamics control for angle-of-attack, AOA, output tracking in the atmospheric flight is presented based on sliding mode control. A sliding mode observer is invoked to estimate AOA which is difficult to measure in practice. Large parameter uncertainties accommodation envisaged by designing adaptive mechanisms for both the control and observer and high chattering authority due to large deviations of aerodynamic coefficients arising from  wind-tunnel measurements are inhibited. The employed method enables the sliding mode control design to exhibit the desired dynamic properties during the entire output-tracking process. Simulations results are presented to demonstrate the performance, robustness, and stability.

M. Bahrami

B. Ebrahimi

G. R. Ansarifar

Sliding Mode Observer and Control Design with Adaptive Parameter Estimation for a Supersonic Flight Vehicle

The paper deals with the evaluation of the expected performance of aircraft approaches and landings operated with different navigation systems, both traditional and satellite-based. Flight dynamics characteristics and control authority of the approaching aircraft are considered in order to obtain an overall manoeuvre evaluation. The technique from the presented analysis applies to different operative conditions, taking into account aircraft requirements, navigation systems features, and environmental constraints. The aim is to offer a tool to be used in the very preliminary design phase for system performance analysis in different scenarios, such as airport ground systems adoption and air traffic control requirements compliance; later, the same tool can be tuned to complement and direct the required real flight trials to validate an already fielded solution. A numerical code referring to the presented analytical model has been implemented and some applications concerning the system&#39;s performance evaluation and planning are proposed to illustrate the algorithm capabilities. The tool and the proposed analysis technique indeed are successful in providing a quantitative assessment of the differences among several possible approaches.

Pier Domenico Tromboni

Giovanni B. Palmerini

Navigation Aids Performance Evaluation for Precision Approaches

This paper is concerned with modeling of ablation behavior of carbon-carbon composites used in hot spot areas of reentry space and hypersonic vehicles. Of the three modes of ablation (thermal, chemical and mechanical), the chemical (oxidation) is considered to influence the performance of the material. Aerodynamic heat flux need to be computed separately and is the input for this. The thermal field is obtained by 3D finite element method. Nonlinear transient thermal analysis is carried out, as the material properties are dependent on temperatures. Oxidation rates are computed using the analytical relations available in literature. The oxidation is divided into two regimes: reaction rate and diffusion rate controlled. Mainly the surface temperature controls the regime. The oxidation protected materials are considered by using the parameter &#x0201c;activation energy.&#x0201d; The variations of ambient temperature, pressure and oxygen concentration with altitude are taken into consideration. As the
recession takes place, newer surfaces are exposed to aerodynamic heating. Numerical examples are presented to show the effects of:
heat flux, altitude and oxidation protection on the recession characteristics. Change of regime from reaction to diffusion rate
control depends on parameters such as flow velocity and altitude. The latter has significant influence on ablation rate.

R. Palaninathan

Behavior of Carbon-Carbon Composite under Intense Heating

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<p><em>International Journal of Aerospace Engineering </em>serves the international aerospace engineering community through the dissemination of scientific knowledge on practical engineering and design methodologies pertaining to aircraft and space vehicles.</p>


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<p>Chief Editor, Professor Zhao, is based at the University of Canterbury and his research interests include applying theoretical, numerical and experimental approaches to study combustion instability, thermoacoustics and aerodynamics.</p>


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International Journal of Aerospace Engineering | Hindawi

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International Journal of Aerospace Engineering serves the international aerospace engineering community through the dissemination of scientific knowledge on practical engineering and design methodologies pertaining to aircraft and space vehicles.

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International Journal of Aerospace Engineering

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International Journal of Aerospace Engineering