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International Review of Aerospace Engineering - June 2010 - Papers

Analysis of Markov Model of Slotted ALOHA Protocol in Satellite Communication
Effects of Intercooling and Regeneration in the Performance of a Turbofan Engine
Propeller Installation Effects on a Semi-Span Wing
Tandem Effect under Large Magnitude on Fatigue of Bituminous Mixes
Comparison Study on Low Cost Satellite Magnetic Attitude Control Options
Thermodynamic Analysis and Optimization of a Scramjet Engine with Thermal Management System
Fatigue Crack Growth in Airframe Elements Under Variable Amplitude Loading

International Review of Aerospace Engineering - Papers

Analysis of Markov Model of Slotted ALOHA Protocol in Satellite Communication
by M. Belattar, D. Benatia, M. Benslama

Vol. 3. n. 3, pp. 134-137

Abstract - In this paper we propose a study based on the model of Markov chain, to define optimal binomial distribution probabilities of retransmission and arrival packets, in the case of random multiple access protocol (slotted Aloha), to describe their evolution in function of the number of transmissions in a slot time, with parameters, probabilities of backlogged and generation packets, this permits us to define the average packet delay and the throughput which is the main parameter of random multiple access model, and see the effect of the increase of the number of sources.

Keywords: Slotted ALOHA, Markov chain, drift, Throughput, delay packet.

Effects of Intercooling and Regeneration in the Performance of a Turbofan Engine
by F. Brójo, J. Lebre

Vol. 3. n. 3, pp. 138-143

Abstract - The modern aviation is being questioned due to high emission of gases in the atmosphere. The introduction of heat exchangers for engines with two spools could be one of the solutions to this problem. One of the heat exchangers is the intercooler and the other is the regenerator which is located in the hot nozzle. These two components are already used in ground power plants and they were not used in aircraft because of the extra weight and size. The use of the heat exchangers could be justified, if the reduction in the specific fuel consumption and increase of efficiency and specific thrust are worthwhile when compared to the penalty introduced by the extra weight. In this work is compared the performance parameters of a conventional engine with the ones of three configurations intended to increase the global performance of the engine. These three configurations use intercooler, regenerator or both. The comparison is performed to show the influence of engine parameters in specific fuel consumption, specific thrust and thermal efficiency. So it shows which is the best engine configuration to be used for the lower specific fuel consumption with the same specific thrust of the conventional engine.

Keywords: Heat exchangers; turbofan; intercooler; regenerator.

Propeller Installation Effects on a Semi-Span Wing
by Benoît G. Marinus, Marilyne Lino, Walter Bosschaerts

Vol. 3. n. 3, pp. 144-151

Abstract - An actuator disk model which includes slipstream rotation and radial load distribution is derived. Its validity is assessed through comparisons with an isolated propeller prior to using it to rate the influence of propeller rotation on the distribution of forces over a wing. In particular, the down-between-engines concept is gauged with respect to inboard up rotation. The model uses RANS computations on a semi-span wing to compute spanwise lift and drag distributions. These distributions are analyzed together with pressure coefficient contours.

Keywords: Actuator, Installation, Propeller, Slipstream, Wing Interaction.

Tandem Effect under Large Magnitude on Fatigue of Bituminous Mixes
by M’hamed Merbouh, Smail Haddadi

Vol. 3. n. 3, pp. 152-156

Abstract - The fatigue of a flexible pavement is highly dependent on the number of axle load. The load of the single axle is different than the multiple axles. Trucks and large aircrafts are major consumer of the pavement structure because they apply the highest loads to the road surface. All heavy vehicles, however, do not cause equal damage because of variations in wheel load (static and dynamic), number and location of axles, and other factors. The mastery of the fatigue behaviour of pavements subjected to the great strains, under tandem axles, permits to follow the development of technology and increases the performance of projects. The purpose of the experimental study presented in this paper is to improve the knowledge of the fatigue response of pavement material under the repetition of such specific loadings. Several phenomena are coupled due to the material viscoelasticity: effects of the type of loading (sine and tandem), effects of the shape of the tandem signal. The objective is to identify the laws of fatigue behaviour under tandem loading and their comparison with the conventional loading (classical sine). The results are presented and discussed.

Keywords: Bituminous mix, Fatigue, Large strain, Pavement, Tandem axles.

Comparison Study on Low Cost Satellite Magnetic Attitude Control Options
by Nurulasikin Mohd Suhadis, Renuganth Varatharajoo

Vol. 3. n. 3, pp. 157-161

Abstract - The active magnetic control system is a promising attitude control option for small satellites. Numerous control algorithms have been developed based on only magnetic torquers or in conjunction with other actuators. In this regard, a comparison study is made for the satellites implementing these two control options. Thus, a general attitude control algorithm for a satellite employing only magnetic torquers (Option A) is established and a new control structure for a satellite employing magnetic torquers and a momentum wheel (Option B) is designed. Both systems are evaluated through numerical treatments. The performance from simulations exhibits that the satellite in option B gives a comparable attitude performance to the satellite in option A. The new attitude control structure for the satellite in option B is a potential control option in small satellites. Although this research is for LEO small satellites in a nominal attitude control operation, but it provides us the trade-offs when designing the magnetic attitude control subsystem for low-cost space missions.

Keywords: Magnetic torque, Magnetic control system, Satellite attitude control.

Thermodynamic Analysis and Optimization of a Scramjet Engine with Thermal Management System
by Luís Rodrigues, Kouamana Bousson, Francisco Brójo

Vol. 3. n. 3, pp. 162-171

Abstract - Thermal management of the scramjet engine is one of the key issues of the challenges brought by the development of hypersonic airbreathing vehicles. A Closed Brayton Cycle thermal management system for a regenerative cooled scramjet is studied. With the goal of reducing the hydrogen fuel flow for cooling, part of the heat absorbed from fuel is converted in other forms of energy to decrease the heat that must be taken away by hydrogen fuel. Reducing this heat increases the fuel heat sink (cooling capacity) without requiring excess fuel for cooling and eliminating the need to search for a new coolant. The proposed thermal cycle reduces the fuel flow for cooling, and the fuel on board assures this way the cooling requirements for the whole hypersonic vehicle. The basic concept and working principle are introduced: a thermodynamic cycle analysis is performed to demonstrate the system performance gains of Closed Brayton Cycle (CBC) Thermal Management System (TMS) over the conventional system with regenerative cooling. An optimization method was applied in order to obtain the best performance parameters for the independent parameter ranges chosen.
It was shown that the Closed Brayton Cycle Thermal Management Systems presents a high performance gain when compared to conventional regenerative cooling due to the reduction of fuel flow for cooling and additional power output.

Keywords: Scramjet, Regenerative Cooling, Thermal Management System, Heat Sink.

Fatigue Crack Growth in Airframe Elements Under Variable Amplitude Loading
by Igor Pavelko, Vitalijs Pavelko

Vol. 3. n. 3, pp. 172-179

Abstract - The results of analytical and experimental researches concerning predicting of fatigue crack growth in the operating conditions are presented. Main conditions causing a fatigue crack growth at the complex spectrum of loading are analyzed and divided to two groups. Theory of fatigue crack growth indication and the crack growth indicator (CGI) are developed. The fatigue tests with aluminium alloy flat specimen and CGI at constant and variable amplitude of loading was carried out. It is shown the estimate of mean value of constant C* of CGI both cases closes to that one of flat specimen. There is planned and executed a flight experiment using CGI located on two aircraft An-24 and An-26. The combination of CGI technology with fractography of a fatigue crack surface allows to decreases number of necessary tests, terms of their carrying out, and increases accuracy and reliability of results. Results of crack growth in CGI at operational load allowed to evaluate the parameters of generalized Paris- Erdogan law and statistical properties of crack increment per flight. It is shown the Kolmogorov-Smirnov test shows the hypothesis about normal distribution of log increment in flight is significant at the 5% level.

Keywords: Fatigue Crack, Operation, Indication, Fractography.