THE SAGRES PROJECT - A NEW VERY LIGHT AEROPLANE Ivan A. Camelier * & Pedro V. Gamboa Department of Aerospace Sciences Universidade da Beira Interior Covilhã, Portugal Abstract This project aims at designing and constructing a complete new two-seat, very light aeroplane, bringing together the academic aspects of aircraft design, as taught in a normal Aeronautical Engineering undergraduate course, and the practical application of theory in the construction and testing of a real flying prototype. This paper presents an introduction with the philosophy of the project and a short historical perspective. It is followed by the main objectives set out for the project and a short description of the design methodology adopted in the Aircraft Design course which led to the layout and technical characteristics of the aeroplane. The construction of a prototype, undertaken by UBI (Universidade da Beira Interior) to familiarize the students with the real world, was initiated in 1996. The purchase of materials, the parts already assembled and those still to be fabricated and future work are also summarized in the paper. A very interesting approach to Aircraft Design teaching is resulting from the present combination of design followed by the making of a real engineering product. Introduction The course of Aeronautical Engineering at UBI started in the 1991/92 academic year. It consists of a five-year course in which the core subjects of the first two years are Mathematics, Physics and Computing. The third year is characterised by disciplines related to the engineering aspects of flight vehicles, such as Aerodynamics, Flight Mechanics, Aircraft Structures and Propulsion. In the second semester of the fourth year the students attend a very important course, Aircraft Design, where they learn the conceptual design of an aircraft and do the calculations necessary for sizing a new aeroplane. The work is continued in the first semester of the fifth year where further knowledge is gained and applied to enable the future engineer to participate in an aeroplane project team. Figure 1 The SAGRES aeroplane. In the academic year of 1994/95 UBI was required to teach Aircraft Design for the first time. In order to be prepared for that occasion, the Aerospace Sciences Department had established contacts in 1993 with the Department of Mechanical Engineering of UFMG (Universidade Federal de Minas Gerais) in Brazil. That university, through its Department of Mechanical Engineering, gives a course in Aeronautical Engineering since 1975, which has given them a large experience in Aircraft Design and enabled them to design and build several prototypes, two of them having been awarded Brazilian National Prizes. Under an agreement of co-operation between the two universities, a professor from UFMG came to UBI and taught the first Aircraft Design course assisted by a young member of the Aerospace Sciences Department staff. After six months at UBI the UFMG professor returned to Brazil but still supporting the teaching of Aircraft Design through a close contact with the assistant and the more experienced staff. During his stay at UBI, the UFMG professor together with his students, his assistant and some other professors, developed the concept for an * Head of the Department and Invited Professor. Assistant lecturing the Aircraft Design course. - 1 -
all new aeroplane, which was named SAGRES after the famous school which launched the Portuguese sailors to the discovery of new lands during the 15th century, including Brazil in April 1500. The objective of the SAGRES project was, initially, to teach the design (concept, design and calculations) of a complete new two-seat aeroplane under the VLA (Very Light Aeroplanes) requirements. Later it evolved to the construction, laboratory testing and flight testing of a real prototype. After the decision on the construction was made, the co-operation agreement with UFMG allowed us to bring another professor to UBI for a period of one year, from February 1996 to February 1997. The first steps in material procurement and purchase as well as in the construction of the SAGRES first components took place in this period. The construction is still going on, slowly as it should be for a process that counts only on a limited university budget, but lively enough to keep alive and well the enthusiasm of students and teachers of the Department of Aerospace Sciences at UBI and the Department of Mechanical Engineering at UFMG. Objectives To build one prototype of an aeroplane that performs as well as the best existing aircraft in its class yet being simple. To improve the Universidade da Beira Interior s Scientific and Technological Group expertise through the academic project of a manned aircraft. To master methodologies for constructing and testing aeroplanes by using appropriate techniques. To bring together interdisciplinary researchers in a project with a high degree of integration. To develop a well prepared human resource through the involvement of the Aeronautical Engineering students throughout all phases of a real aeronautical project. To learn how to manage an aeronautical project. To contribute to the country s know-how in designing and building light aeroplanes. To encourage local industries, through subcontracting during the project, to improve their technological capabilities so that they may become future suppliers in the field. To implement a strong relationship between Academia and Industry through collaboration of the parties involved in the project. The Design of the Aeroplane The SAGRES aeroplane has been conceived as a single-engined, two-seat (side by side) monoplane with high wing, conventional tail, tricycle fixed undercarriage, whose simplicity was mandatory. The powerplant will be a Rotax 912 rated at 80 hp at 5500 rpm mounted on the nose. It will be fitted with a three-bladed propeller whose pitch setting can be adjusted on the ground. The wing will have a single spar, a wooden box beam, with a fibreglass wingbox. The wing rib truss will also be made of wood. The fin and tailplane will have wooden ribs and spars and plywood and fabric skin. The fuselage will have a metal truss of welded steel tube and a composite skin. The tricycle landing gear is fixed, being the main legs made of steel spring whose elasticity will provide the suspension and the nose leg made of steel tube with spring coil for suspension. The concept of slenderness was applied to the fuselage cone to reduce the aircraft drag. The wing airfoil will be the HQ (DLR), which is currently considered one of the best performing sections world-wide. This aeroplane is aimed at basic pilot training, offering low fuel consumption and requiring low maintenance. It can also be used for other tasks such as agricultural applications, fire surveillance, road patrolling, executive transport, sports and leisure. In the current civil market, aeroplanes in this category are substituting older models, similar to the Cessna 152, in the training role and the other tasks mentioned. The Design The design process was a typical one 4,5,7,10 and consisted, essentially, on the following: Establish the specifications for the design based on the purpose of the aircraft and the VLA requirements 8. Comparison of several aircraft in the same category as the one being designed. Construction of tables and graphs to better visualize the data of the various aircraft. First sketch of the aeroplane with the general layout: wing position and planform, tail, fuselage shape, landing gear configuration, engine position. Preliminary calculations for determining wing area, tailplane and fin sizes and powered required. Choice of wing and tail sections. Ergonomics, cockpit layout and internal general arrangement of components. - 2 -
Various detailed calculations on aerodynamics, performance, weight and balance, loads, stability and control. Definition of materials, mechanisms, fittings, etc.. Structural sizing of various components: wing, tail, fuselage, engine mount, landing gear, etc.. Layout and fabrication drawings of the various components. The above items are presented in a logical and chronological sequence but most of them have some degree of interaction with the others, which required some feedback and updating. All this work was carried out by a professor, his assistant and some students. Load factor, n 6,0 5,0 4,0 3,0 2,0 1,0 0,0 0 25 50 75 100 125 150 175 200 225 250 275 300-1,0-2,0-3,0 Figure 2 no flaps with flaps V-n diagram. Speed, V [km/h) Fig. 2 shows one example of the results obtained in the analysis; the combined manoeuvre and gust V-n diagram which enabled the in-flight loads acting on the aeroplane to be determined, following to the appropriate requirements. Calculations A variety of calculations were carried out to define certain characteristics of the aircraft and to verify the results obtained. These calculations, again, required a great deal of iteration as they cannot be independent, and consisted of the following: Geometry. Weight and balance. Drag polar. Performance. Stability and control. Loading actions. Structural analysis. With the results obtained from the design one arrived at the SAGRES characteristics and performance data shown below. The aeroplane general layout is shown in Fig. 3. All calculations and drawings are kept in a dedicated set of dossiers. Basic SAGRES Technical Data & Performance External Dimensions Length overall... 6.370 m Height overall... 1.850 m Wheel track... 2.150 m Wheelbase... 1.450 m Propeller diameter... 1.630 m Propeller ground clearance... 0.230 m Wing Span... 10.000 m Chord (constant)... 1.275 m Aspect ratio... 7.840 Area... 12.750 m 2 Sweepback angle... 0.000 º Dihedral... 2.500 º Root incidence (no twist)... 1.500 º Flap relative chord... 0.200 Aileron relative chord... 0.200 Tailplane Span... 2.660 m Chord... root... 0.841 m tip... 0.550 m Area... 1.850 m 2 Aspect ratio... 3.825 Taper ratio... 0.654 Sweepback angle at 25 % chord... 3.800 º Dihedral... 0.000 º Root incidence... 0.000 º Elevator relative chord... 0.300 Vertical tail Height... 1.150 m Chord... root... 1.370 m tip... 0.600 m Area... 1.133 m 2 Aspect ratio... 1.168 Taper ratio... 0.438 Sweepback angle at 25 % chord... 7.000 º Rudder relative chord. root... 0.370 tip... 0.430 Weights and loadings - 3 -
Weight... empty...300 kg max. takeoff...510 kg Maximum wing loading...40.0 kg/m 2 Maximum power loading...6.4 kg/hp Limit load factors... +5.1/-2.3 Performance Max. level speed (SL, 80 hp)...240 km/h Cruising speed (SL, 75 % power)...210 km/h Stalling speed (SL)... flaps up...80 km/h flaps down...70 km/h Max. rate of climb (SL, 165 km/h, max. power)5 m/s Endurance (SL, 75 % power & 50 kg of fuel)..3 h Range (SL, 75 % power & 50 kg of fuel)...650 km Takeoff... run...150 m distance to 15 m...270 m that purpose come from the budget attributed to the department by the university. The construction period will be spread throughout several semesters to allow students at different levels in the course to participate. Work already done Specification and acquisition of machinery and tools. Specification and acquisition of materials. Fabrication of gigs for the ribs and spars for the vertical tail. Construction and primary assembly of fin and rudder. Fabrication of gigs for the ribs and spars of the horizontal tail. Construction of the ribs and spars for the horizontal tail. Setting up of the table for the fabrication of the wing main spar and the rig for the ribs that connect the wing to the fuselage. Construction of the wing main spar and the ribs that connect the wing to the fuselage. Work in progress Fabrication of the wing ribs. Construction of the horizontal and vertical tails. Acquisition of the steel tubes for the fuselage truss. Acquisition of materials and equipment for the aircraft. Work to be done Figure 3 General layout of the SAGRES aeroplane. Construction Work The construction work of the prototype of the SAGRES aircraft began in September 1996. This work was started by a professor from UFMG who passed some of his experience on aircraft construction to this university. Since then the construction has been undertaken by some members of the staff and some students. Construction of the auxiliary wing spar. Positioning of the wing ribs on the spar and covering with foam and fibre-glass. Fabrication of the wing tips. Definition, manufacture and installation of fittings and control systems in the wing. Fabric covering of the wing. Welding of the fuselage truss. Wing structural tests. Purchase of engine and instruments. The purchase of materials for the prototype is taking place without any hurry since the funds allocated for - 4 -
which, in the future, will contribute to their responsibility in the enhancement and strengthening of the aeronautical industry activities in this country. Figure 4 Construction of the wing main spar. References 1. Stelio Frati, L Aliante, Editore Ulrico Hoepli, Milano, 1946 2. Abbot & Doenhoff, Theory of Wing Sections, Dover Publications Inc, 1959 3. Cláudio Barros, Introdução ao Projecto de Aeronaves, Belo Horizonte - CEA/UFMG, 1979 Future Work After the prototype is complete, there will be a series of flight tests so that knowledge on the aircraft performance, flight qualities, safety and operation procedures can be gained. These tests will eventually lead to certification of the prototype as an experimental aircraft. Contact with DGAC (Direcção Geral de Aviação Civil) has been established in order to permit the certification. A series of wind tunnel tests will be carried out to verify the estimated drag polar of the aircraft and gain some understanding on the interference between the wing and the fuselage. These experiments will serve in the future for undergraduate laboratory work. Conclusion The experience gained with this project has been a very fruitful one. Teaching Aircraft Design to Aeronautical Engineering students is a real challenge to any teacher. The approach is a complex one and is always prone to discussion. 4. Egbert Torenbeek, Synthesis of Subsonic Aeroplane Design, Delft University Press, 1982 5. Darrol Stinton, The Design of the Aeroplane, 1983 6. L. Pazmany, Landing Gear Design for Light Aircraft - Vol. 1, Pazmany Aircraft Corporation, 1986 7. Daniel P. Raymer, Aircraft Design: A Conceptual Approach, AIAA Education Series, 1989 8. Civil Aviation Authority, JAR-VLA Very Light Aeroplanes, 1990 9. Jane s All the World Aircraft, 1995 10. L. Pazmany, Light Aeroplane Design, Pazmany Aircraft Corporation 11. Royal Aeronautical Society, ESDU Data Sheets The inclusion of a hands-on activity involving the fabrication and assembly of components of an aircraft designed during classroom work has been proving an efficient way of teaching and learning Aircraft Design. The opportunities created when establishing contacts with other universities, industries, material and equipment suppliers fully justify and do encourage the continuing effort to carry on this activity in the future. After the SAGRES prototype flight test program is complete it is intended that the detailed design and construction of a new aeroplane, picked from one of the projects being currently designed, will start. This will give our Aeronautical Engineering students the skills and encouragement - 5 -