“Interactive Aircraft Design for Undergraduate Teaching” Omran Al-Shamma, Dr. Rashid Ali University of Hertfordshire Abstract: This paper presents new software package developed for Aircraft Design. It is intended primarily to be used for undergraduate teaching. The software does everything that is needed in preliminary design environment. It is able to predict the empty and maximum takeoff weights to an accuracy of better than 5%. The performance data computed by the software agrees very favourably with the published data of Airbus and Boeing aircraft, for a wide range of flight conditions. An interactive interface to the USAF DATCOM has also been developed to provide estimation of aircraft stability derivatives which can be used in flight simulation work to investigate the dynamic behaviour of the aircraft design under consideration. Introduction necessary for the manufacture of the aircraft. The second part is sometimes Aircraft design process can be divided into called production design where the three design phases: a- Conceptual, b- specialists determine how the aircraft will Preliminary, c- Detail. They can be be fabricated, starting with the smallest and summarized as follows: simplest subassemblies and building up to a- Conceptual design phase: The main the final assembly process. Detail design objective of this phase is to determine the phase ends with fabricating and testing the configuration layout (conventional or first prototype aircraft. novel) which are technically feasible and commercially viable. Teaching Aircraft design b- Preliminary design phase: The aim of this phase is to find the best optimum Many universities in UK, follow the configuration geometry for the aircraft that Problem Based Learning (PBL) approach achieves commercial operational in teaching aircraft design. PBL is a requirements. This design is done in concept used to enhance multidisciplinary parallel with the parametric studies to allow skills using planned problem scenarios. It is any desirable changes to the layout to be an active way of learning that teaches made. This phase is iterative in nature and students problem-solving skills while at the the design changes are made until all same time allowing them to acquire basic specifications are met. knowledge in aircraft design. In PBL approach, students work in small c- Detail design phase: It consists of two collaborative groups and learn what they parts. The purpose of the first part is to need to know in order to solve a problem. verify and refine the design to a greater The benefits of PBL have been explained level of detail and to produce data by Duch (1). Since, the aircraft design process is iterative, one or two semesters of software package RDS (7) which study is not enough time to fully cover the implements the approach described in his concepts of the aircraft design. Most book. Piano (8) is another complete aircraft universities present preliminary design design program developed by Simos. It is projects as coursework for this reason. It geared towards the design of commercial should be noted that these projects are not aircraft. Finally, CEASIOM (9) meant to provide a “fill in the blank” (Computerized Environment for Aircraft template to be used by current and future Synthesis and Integrated Optimization students working on similar design Methods) is meant to support engineers in problems, but to provide insight into the the conceptual design process of the process itself (2). The aircraft design aircraft. projects are undertaken students working in a group size comprising of 6-8 in number, and working to prescribed specifications as Limitations and Shortages set by the academics. The broad subject areas include Wing and Aerodynamics, Although some of the packages are Fuselage, Undercarriage, Systems, used for teaching purposes, the Propulsion & Performance, Project students need to know the Management, Materials and Manufacture philosophy of aircraft design and and Stability and Control. The students the influence of each variable. They work through a classical process of need to understand principles of preliminary design based largely on aircraft design before the packages textbook methods. Therefore, the need for a can be used. preliminary design tool (software) that Many assumptions need to be made helps the students to understand and in order to achieve the objectives. analyze their design process is necessary. Many programs are not truly interactive which makes them unsuitable for teaching purposes. Aircraft Design Software One of the important aspects in aircraft design is the dynamic Many software programs have been stability. Most of these programs developed in the last fifty years ago, lack it in their synthesis process. subsequent to the first optimized program (SYNAC II) coded by Lee, V. & et al (3) in 1967. In the early nineties, the AAA Software Scope (Advanced Aircraft Analysis) (4) program started out as a computerized version of The objective goal of the software is to Roskam's eight-volume text: Airplane develop a tool that can be used for teaching Design, Parts I-VIII (5), featuring a user- aircraft design. Therefore, it had to be friendly interface. Kroo (6) developed a highly interactive with friendly graphical system for aircraft design utilizing a unique user interface and easy to use. Addition of analysis architecture, graphical interface, parametric study Capabilities. in the and suite of numerical optimization software enables the students to learn and methods. In 1996, Raymer released his understand the influences of the various design variables. Therefore, the task uses a graphical user interface conforming becomes for the students to learn the standard software for teaching (10). processes which will take them from the first principles and concepts, through to the Figure 1 is a screen shot of a typical interaction form that allows the user to conceptual design and to the point where make the changes to the variables our software begins to guide them into associated with the wing design, and in interactive step-by-step approach enabling keeping with the interface requirements them to estimate, choose, and calculate the presented in (10). design variables, helping them to analyse, optimize, and evaluate the proposed design in less iterations. Synthesis Program The main synthesis program consists of many modules. These modules include: User Interface geometry, weight, aerodynamics, static Aircraft design involves a large number of stability, flight performance, cost design variables for a variety of estimation, and dynamic stability. The calculations. These variables are required aircraft geometry module calculates the for the estimation of aircraft mass, major geometries pertinent to aircraft aerodynamics, stability and control, components such as wing, fuselage, propulsion, and aircraft performance. Many empennage, flaps, and nacelles. In the design software packages use pre- weight module, which is one of the most configured input data files to define the significant module due to the fact that design variables. Alteration to the input accurate weight estimation at early stages is data is done through modification of these a hard and difficult process. The files. This configuration is very tedious and aerodynamics module evaluates: zero-lift is not intended for teaching. Thus, the need drag, aircraft lift, lift induced drag, for a user friendly graphical-user-interface compressibility effects, total aircraft drag, (GUI) becomes necessary. In the scope of and effects of flaps. In static stability this project an object-oriented- module, static margin constraint is programming (OOP) is used to create the evaluated and static margin in the datum GUI environment. The benefits of OOP are CG position for the proposed aircraft is also encapsulation, polymorphism, and reuse (or calculated. The dynamic stability module so-called inheritance). computes all the longitudinal and lateral stability derivatives and computes the The software uses more than 150 design properties of the modes of motion. The variables organised into eleven groups. flight performance module is used for flight These groups are: Wing, Fuselage, Tail, profile analysis and field performance, in Aerofoils, Flaps, Propulsion, Weights, the climb, cruise, and descent phases. Speeds, Stages, Weights, and Cost. This Detail changes in aircraft mass, air density, simplified configuration helps the students speeds, and time are calculated at the mid- to specify, alter and examine the effects of segment position. Time and fuel are the changes efficiently. Also, the software calculated using linear interpolation in each stage. In the climb stage the engines are at the maximum continuous climb rating, is equal to the accelerate stop whilst for the cruise segment engine thrust distance available (ASDA). is at a min fuel condition. The descent phase calculations are performed at flight idle setting. The field performance is Parametric Studies Module assessed using step-integration analysis of the equation of the motion of the aircraft A key feature that helps in understanding presented by Torenbeek(11) to determine the the philosophy of aircraft design is the balanced field length (BFL) requirements, interrelationship of variables. This module whereas Loftin(12) analysis is used to find consists of two options, either 1-to-1 or 2- the landing field length (LFL). Finally, the to1 i.e. changing one independent (design) cost estimation module evaluates the variable to one dependent (calculated)