Development of a Software for Aircraft Preliminary Design and Analysis

Transcription

1 Development of a Software for Aircraft Preliminary Design and Analysis Fabrizio Nicolosi and Giuseppe Paduano Department of Aerospace Engineering(DIAS) - University of Naples Federico II Via Claudio 21, Napoli - ITALY fabrnico@unina.it Ph: Fax : Keywords: Aircraft preliminary design, Educational software, Aircraft Performances Abstract The present paper deals with the description of a software called ADAS (Aircraft Design and Analysis Software) that has been developed at DIAS (Dep. of Aerospace Eng.) by the authors during the last 5 years. The paper gives an overview of all main modules and used procedures and approaches that have been built and implemented in the software. ADAS code has been originally intended as an educational tool, but after many improvements carried out during the past years, can be used as a research tool and it can be of some relevance also for some industrial applications. All the aerodynamic characteristics used for stability, control and aircraft performances calculations are estimated mainly through semiempirical laws integrated with more sophisticated approaches like the use of aerodynamic tools like Multhopp or Weissinger to estimate wing lift spanwise distribution. The software is extremely user-friendly and can represent a valid teaching tool for aircraft design courses. 1 Introduction In the last years many attempt have been made in order to develop and deliver to the aerospace research and teaching community some software or tool that can be used with the aim to perform preliminary design of airplanes. One of the most known software, developed by J. Roskam(one of the main scientist and researcher in this field) and his collaborators, is the Advanced Aircraft Analysis (AAA) software (see that is the industry standard aircraft design, stability, and control analysis software. AAA is installed in over 55 countries and is used by major aeronautical engineering universities, aircraft manufacturers, and military organizations worldwide. The AAA software is based on the well known aircraft design book written by Roskam, i.e. [1],[2], [3], that presents several semi-empirical methodologies and fast approaches for aircraft preliminary sizing and aerodynamics analysis, mainly derived and copied by USAF Datcom [4]. During the last ten years many other software have been written and also some very well known books have been introduced in the attempt to allow to many people, often without the deep and solid experience of an old aircraft designer, the 702

2 possibility to carry out the preliminary design of an aircraft, mainly at teaching level, but sometimes also with some features typical of industrial tools. Among them it is worth to point out the book proposed by D. Raymer [5], famous aircraft designer, and the software[6] RDS, Integrated Aircraft Design and Analysis ( ml) that is also widely used in the aerospace academics for aircraft design teaching. Another interesting effort in this direction has been made by Prof. I. Kroo from Stanford University. The digital textbook and the associated examples of calculations made by several java applets (see ml) represents a good example of a very effective teaching tool that allow students the comprehension of aircraft design theory and the possibility to play and see the results of parametric analysis. The ADW software (see distributed by Desktop Aeronautics is an example of extremely user-friendly application for aircraft design activities, performed at teaching level. The ADW program was developed as an interactive museum exhibit that allows the user to investigate the trade-offs involved in the design of a commercial transport aircraft. Another software, also developed by I. Kroo and Desktop aeronautics is PASS(see The software PASS is a conceptual design tool that is capable of evaluating all aspects of mission performance. Rapid analyses are coupled with optimization tools to quickly achieve realistic aircraft designs. Configuration design is not limited to meeting a singular performance goal. PASS ensures that designs satisfy a wide range of appropriate, real-world constraints such as FAA field length, climb gradient, and community noise requirements. PASS was developed for general applicability to conventional aircraft, but has been customized to do analysis of non-conventional aircraft such as supersonic business jets, oblique flying wings and blended wing bodies. The software is an advanced tool and maybe represents a complex tool to be used as teaching application in aircraft design courses. Other examples of aircraft design software often used at industrial level are ACSYNT software ( PIANO software ( developed in UK by Lissys Limited, the ADS software ( developed by OAD SPrl in Belgium and used by several general aviation companies. All the last examples represents some complex software that becomes extremely hard to use for non-expert students, especially if the aircraft design course does not allow (due to short period of lectures, i.e. 80 lecture hours in 2-3 months) the students to go deeply in some specific aerodynamic problems and to have a deep comprehension of the problems. The development of the software by the authors at the Department of Aerospace Engineering of University of Naples started in 2005 as an effort to give some support to the students in the development of aircraft design exercises carried out by students in the aircraft design course. Other authors like Martinez-Val [7] and T. Young [8] have recently emphasized the importance of aircraft design course as a fundamental milestone in an aerospace student curriculum (to develop synthesis attitude and to build multidisciplinary links). It is evident that such a course can be of relevant effectiveness only with some practical exercises or better with the development by the students of the complete preliminary design of an aircraft. 2 ADAS Software structure ADAS software has been originally intended as an educational tool, but after many improvements carried out during the past years, can be absolutely used as a research tool and it can be of some relevance also for some industrial applications. The approach to estimate all aircraft characteristics has been the use of classical semi-empirical laws (like those one proposed by Roskam [1-3] or ESDU or USAF Datcom[4]) integrated with more sophisticated approaches like the use of aerodynamic tools like Multhopp or Weissinger to estimate wing lift distribution along span and wing stall path. 703

3 One of the main goal that was fixed in the development of ADAS software was to obtain a very user friendly platform that should be easily used also by students, with many graphical helps and with many output graphs and figures, including 2D and 3D drawing of aircraft parts under development. The software is split in modules. In fig. 1 the main software dialog window (main menu) is shown. The classical approach and first part of the software starts with the preliminary estimation of aircraft weight (both empty and maximum take-off) and required wing area and engine thrust/power under specified design requirements [1]. In this phase all FAR/CS 23/25 performance requirements have been automatically implemented based on aircraft weight. After the preliminary phase the user starts designing all aircraft parts. The main dialog window allow the user to enter and carry out the design of each airplane part (fuselage,, nacelle, wing, aileron and flap, taiplanes). Each module (fig. 1) can be used as independent module, but is linked with the other modules if an airplane design activity is developed. Figure 2 shows the classical flowchart of design/analysis steps that the designer can carry out in sequence. The drag polar and main flight/ground performance estimation can be accomplished also with a first preliminary sizing of tailplanes (fig. 2). The tailplane design and analysis modules allow a detailed and accurate design and analysis of horizontal and vertical taiplanes, performing also the aircraft stability and control analysis up to non-linear conditions. The wing module allows to design the wing and to obtain all wing aerodynamics characteristics, including lift, moment and drag. The estimation of spanwise lift coefficient distribution and wing stall path are also included and gives to the user the possibility to check the assumed wing twist and to make a preliminary estimation of wing bending moment. The wing module is linked with the fuselage module to estimate the body longitudinal instability contribution which depends on wing induced upwash and downwash. The wing analysis is also coupled with the modules for high-lift and aileron analysis. The aileron analysis and design module allow also the estimation of aircraft roll performances with the prescribed propulsive system. The software has one module dedicate to the accurate estimation of aircraft drag polar and a module for aircraft flight and ground performances. Other very important modules deal with aircraft tail sizing and aircraft longitudinal and lateral-directional characteristics. The modules are really userfriendly and allow a fast calculation of all required information. Finally the user can have the drawing of the designed aircraft. The software allow the preliminary design and analysis of a transport aircraft in less than 1 hour. The software has been recently also presented in previous conferences[9]. Other similar software are under development in other European Universities, like that one developed by D. Scholz [10] and this demonstrate the relevance and the importance of such applications, both for teaching and for some applied industrial case. Jenkinson has written an educational book [11] that put in evidence the importance for students of performing aircraft design activities and examples. 3 Description of software modules As already outlined the software is organized in separate modules. Each module can be run separately, but the necessary link between modules are built to allow the user to perform the preliminary design of an aircraft. In this paragraph the paper present a general description of each module and each part of the software, trying to put in evidence the main characteristics and capabilities of the software. 3.1 Weight estimation The first part of the software deals with the preliminary estimation of aircraft weight (both empty and maximum take-off). The classical approach suggested by Roskam[1] and Nicolai [12] is used. The design requirements must be fixed by the user. In particular the aircraft weight is estimated on the base of some assumed parameters (cruise aerodynamic efficiency, fuel consumption, propeller 704

4 efficiency) and especially on the base of the imposed and expected mission fundamental to calculate the required fuel fraction. The mission includes all the flight phases like take-off, climb, cruise and descent. In fig. 3a is shown the table that reminds to the user the assumed value for the imposed mission and the result of the two-equation system for weight calculations. Figure 3b shows the output graph of the software with all the aircraft weights (empty weight, gross weight, fuel weight, etc.) reported in different unit (kg and lb). 3.2 Aircraft preliminary sizing One of the first modules is the general aircraft sizing, or the estimation of required wing area and engine thrust/power under specified design requirements [1]. In this phase all FAR/CS 23/25 performance requirements have been automatically implemented based on aircraft weight. This module allow the preliminary sizing of jet and propeller driven aircraft. The preliminary choice of wing loading and engine thrust to weight ratio (for a jet) is made on the base of design and regulation requirements and in particular take-off distance, landing distance, climb requirements and cruise requirements. The module is very fast and with user-friendly interface. An example of the final graph for preliminary sizing of a 150 seats jet transport aircraft is shown in fig. 4. The graph reports all the limitations imposed both by the design specifications and by the regulation requirements. The user can also add some point representative of existing aircraft (i.e. the Airbus A320) and can make its choice. 3.3 Fuselage design After the preliminary phase the user starts designing all aircraft parts. One of the first component that need to be defined is the aircraft fuselage. The fuselage is designed with the classical approach from the inside to outside. The fuselage module allows the design of the fuselage, starting with cabin interior required space up to the final shape in which the sections can be modified to account for classical squared-like sections. The section shape can be modified directly by the user with the mouse and using classical curves like nurbs or splines as weel described in [5]. The internal dimensions are calculated on the base of the assumed seat pitch and seat width. Some important guidelines for this module have been taken from some representative aircraft design books [2, 3, 13, 14]. The user can play with this dimensions (that defines the internal comfort) and look at the effect on fuselage dimensions (length, width, fuselage wetted area) and fuselage aerodynamic characteristics(fuselage drag, body aerodynamic longitudinal instability). The fuselage module allows calculation of all fuselage geometrical characteristics (i.e. wetted area) and all aerodynamic characteristics, like fuselage moments and fuselage drag. The aerodynamic fuselage moments (both longitudinal and directional) are estimated with classical strip method proposed by Munk and with the implementation suggested by Multhopp[15]. This last approach and other semi-empirical alternative analysis [3, 16] have been also implemented. The software allows an easy and fast link between components, with very fast choice of wing-fuselage relative position with the real-time calculations of the effect of this parameter on fuselage negative stability and on aircraft cg position in percentage of mean aerodynamic chord. An example of some output and interface windows from fuselage design module are shown in fig Wing Analysis and Design The wing module allows to design the wing and to obtain all wing aerodynamics characteristics, including lift, moment and drag. The semi-empirical approach is based on formula and suggestions reported in [3,4,17,18]. The effect of fuselage on wing lift [17] and wing induced drag (see ml) has been also taken into account. The aerodynamic calculations have been extended in non-linear condition and the wing maximum lift coefficient is estimated through both semi- 705

5 empirical and wing stall path approaches. In the wing module Multhopp (non swept wing) and Weissinger (swept wing) methods have been both implemented to estimate wing span load, wing stall path and to estimate also wing shear and bending moment due to aerodynamic loads. Many comparisons with available results and literature have been done and the code seems to give reasonable and reliable results. Figure 6 shows the wing design dialog window. All main geometrical characteristics (mean aerodynamic chord, aerodynamic centre) and aerodynamic parameters are estimated. Figure 7 shows some results concerning the aerodynamic analysis and some output graphs showing relevant aerodynamic data. The wing module is coupled with the high-lift module where all the aerodynamics (mainly lift and pitching moment) of wing with high-lift device are estimated. The module is very easy and allows the design (in terms of choice of required flap chord ratio and flap span extension for required lift increment). In figure 8 the high-lift system design dialog window is shown. The user can define all main flap and slat geometrical characteristics (flap chord, flap span extension, flap type and flap deflection) and can immediately estimate the aerodynamic effect on the wing lift curve. The semi-empirical approach that has been used is based on effect of high-lift system on [14]. Figure 9 shows the aileron design dialog window. The user can define aileron geometrical data and the software can estimate in real time the aircraft roll capabilities, also according to the chosen propulsion system characteristics. 3.5 Aircraft Performances A very important software module is the performance analysis module. This module allow the calculation of aircraft flight and ground performances based on the aircraft drag polar. The wave drag (compressibility effects) is taken into account and the user can chose between different airfoil type (from peaky up to aggressive supercritical airfoil) and estimate different wave drag aerodynamic effects on aircraft drag. The user can chose different propulsion system(piston engine, turboprop engine, turbofan with low by-pass-ratio and high by-pass-ratio). A very deep analysis has been made in order to built these different engine models. Many indications have been taken from [19, 20] and [21] and from the Aircraft Design digital textbook available from DesktopAeronautics( 41/AircraftDesign.html). Some examples of aircraft flight performances calculations of a typical jet transport are shown in fig Tailplane design. Stability and control As well known in all aircraft design textbook the tailplane design and associated stability and control(both longitudinal and directional) characteristics of an aircraft are crucial elements for the quality of the designed aircraft. ADAS software has some modules dedicated to the preliminary design of tailplanes and also for a deep stability and control analysis which can take into account also non-linear effects (like non-linearity of lift curve slope, non linearity of wing downwash, pendular stability). Figure 11 shows the main horizontal stabilizer design dialog window. The user through the definition (made very fast by the use of interface boxes and sliders) of some assumed characteristics (tailplane position, tailplane sweep angle, taper ratio) and with the calculated characteristics of the wing-body combination, can estimate some relevant limit curves in a carpet plot showing stability and longitudinal control limit. Accurate estimation of wing downwash angle[22] extended in non-linear conditions has been implemented. After a preliminary design, the user can also investigate the aircraft longitudinal characteristics including also non-linear effects. The vertical stabilizer is designed mainly with the constraint of minimum control speed for multi-engine aircraft. The vertical tailplane aerodynamic lift can be estimated both with the approach suggested by Roskam [3] and USAF Datcom [4] and with the alternative approach suggested by ESDU [23]. The two methodologies often lead to different results and the user, based on the acquired experience should use the most suitable method. Figure

6 shows the vertical tailplane design dialog window for a medium-range transport aircraft. The user has to assume some geometrical characteristics and the module helps the user in finding the best vertical tail area. 4 Drawings and export capabilities In the software some drawing features have been implemented. The final designed aircraft shape can be also exported in general CAD format. Figure 13 shows the final aircraft layout and 3-view drawings as produced by a dedicated module in the software. 5 Conclusion The paper has presented some capabilities and features of ADAS software. The importance of such tool for teaching and for fast estimations has been highlighted. The importance of a very user-friendly interface for such tools is crucial. An important extension and improvements for the code is the inclusion of some automatic optimization procedure to help the designer with some computer-guided decision strategies. References [1] Roskam J., Airplane Design: Part I, Preliminary Sizing of Airplanes, 1 st Ed., Roskam Aviation and Engineering Corporation Ottawa, Kansas, [2] Roskam J., Airplane Design: Part III, Layout Design of Cockpit, Fusolage, Wing and Empennage:Cutaways and Imboard Profiles, 1 st Ed., Roskam Aviation and Engineering Corporation Ottawa Kansas, [3] Roskam J., Airplane Design: Part VI, Preliminary Calculation of Aerodynamic, Thrust and Power Characteristics, 1 st Ed., Roskam Aviation and Engineering Corporation Ottawa Kansas, 1985 [4] Hoak, D.E., et al, USAF Stability and Control Datcom, Flight Control Division, Air Force Flight Dynamics Laboratory, WPAFB, Ohio, , 1978, revised. [5] Raymer D.P., Aircraft Design: A Conceptual Approach, 1 st Ed., American Institute of Aeronautics and Astronautics Washington D.C., 1999, Chaps. 12, 13. [6] Raymer D P., RDS-STUDENT: Software for aircraft design, sizing, and performance. American Institute of Aeronautics and Astronautics Inc., Reston, [7] Martinez-Val R., Perez E., Airplane Design: A must in Aeronautical Engineering Education, ICAS th ICAS Congress, Anchorage, (Alaska, US), September [8] Young T M. Aircraft design education at universities: benefits and difficulties. Aircraft Design, Vol. 3, No. 3, pp , [9] Nicolosi F., Paduano G., Development of a Software for Aircraft Preliminary Design and Analysis, 10 th European Workshop on Aircraft Design Education (EWADE), Dipartimento di Ingegneria Aerospaziale University of Naples, Naples, May 2011 [10] Scholz D., PreSTo The Aircraft Preliminary Sizing Tool, 10 th European Workshop on Aircraft Design Education (EWADE), Dipartimento di Ingegneria Aerospaziale University of Naples, Naples, May 2011 [11] Jenkinson L.R. and Marchman J.F. III, Aircraft design projects: for engineering students. American Institute of Aeronautics and Astronautics Inc., Reston, [12] Nicolai, L.M., Fundamentals of Aircraft Design, METS inc., 6520 Kingsland Court, San Jose, CA, [13] Jenkinson L.R., Simpkin P., Rhodes D., Civil Jet Aircraft Design, 1 st Ed., Arnold, a member of the Hodder Headline Group London, 1999 [14] Torenbeek E., Synthesis of Subsonic Airplane Design, 1 st Ed., Delft University Press, 1982 [15] Multhopp H., Aerodynamics of the fuselage, NACA TM 1036, Washington, Dec [16] Perkins C.D., Hage R.E., Synthesis of Airplane Performance, Stability and Control, 1 st Ed., John Wiley & Sons Inc., New York,1976 [17] Anderson Jr J.D., Aircraft Performance and Design, 1 st Ed., McGraw-Hil, New York, [18] Abbott I.H., Von Doenhoff A.E., Theory of Wing Sections, Dover Pubblications New York, [19] Roskam J., Lan C.T.E., Airplan Aerodynamics and Performance, 1 st Ed., DARcorporation Lawrence Kansas, [20] McCormick B.W., Aerodynamics, Aeronautics and Flight Mechanics, 1 st Ed., John Wiley & Sons Inc., New York New York, [21] Hartman E.P., Bierman D., Report No 640, The Aerodynamic Characteristics of Full Scale Propeller Having 2, 3 and 4 Blades of Clark Y and A.F. 6 Airfoil Sections NACA, [22] Hartman E.P., Bierman D., Report No 648, Design Chart for Predicting Downwash Angles and Wake Characteristics Behind Plain and Flapped Wings. NACA, [23] ESDU 82010, Contribution of Fin to Sideforce, Yawing Moment and Rolling Moment Derivatives Due to Sideslip, in the Presence of Body, Wing and Tailplane.. 707

7 Development of a Software for Aircraft Preliminary Design and Analysis Fig. 1 ADAS Software Main Dialog Window (main menu) and displayed design/analysis modules Mission Specification ADAS 1.0 Weight Estimation Sizing Requirements Airplane Drag Polar Wing Analysis High-Lift Devices/Aileron Design Performance Evaluation Fuselage Nacelle Sizing Stability And Control Fig. 2 ADAS Software Analysis and Design modules and flowchart of possible design sequence 708

8 Fig. 3a Weight estimation module. Flight mission data table Fig. 3b Weight estimation results. Weight breakdown in different unit. Fig. 4 Example of final graph of Preliminary Sizing Module (150 seats medium range transport jet) 709

9 Fig. 5 Example of interface windows of fuselage design module. External dimension and general fuselage characteristics (left) and wing-fuselage integration (example of a 150 seats medium range transport jet) Fig. 6 Wing design dialog window. Definition of wing geometrical and main airfoil characteristics. 710

10 Fig. 7 Wing aerodynamic analysis results. Lift curve (left) and lift coefficient spanwise distribution and stall path (right) Fig. 8 High-lift system design dialog window. Definition of flap/slat characteristics and estimation of effects on lift. 711

11 Fig. 9 Aileron Design dialog window and aircraft roll performances calculations. Fig. 10 Flight Performances calculations. Necessary and available thrust (left) and flight envelope (right). 712

12 Fig. 11 Horizontal tailplane design. Dialog and interface window and output results. Fig. 12 Vertical tailplane design. Dialog and interface window and output results. 713

13 Fig. 13 Final designed aircraft 3-view drawings. 714