Design ProjectBackgroundProject DescriptionCompetition Objective Function and ConstraintsTeam ResponsibilitiesSoftware, Resources, Experience/KnowledgeCost Estimation16.810 IAP 2005 Engineering Design and Rapid Prototyping Dept. of Aeronautics & Astronautics Prof. O. de Weck Massachusetts Institute of Technology C. Graff, A. Bell December 31, 2004 Version 2.1 Design Project A hypothetical Indy racecar manufacturer seeks bids for a new wing design for their 2005/2006 model year vehicles. The rear-mounted wings are intended to maximize downward force (negative lift), while at the same time minimizing incremental drag and weight added to the vehicle. The wings have to conform to regulations (constraints) and be designed and manufactured in an economical fashion. Teams comprised of two students (one aerodynamicist, one structural engineer) will conceive, design, implement and operate a prototype wing and compete for the bid during a 4-week period in IAP 2005. I. Background The challenge for each Indy Car Team is the same every year. Design and develop a race car that is safe, durable, and competitive in different racing conditions (Fig.1 left). A major competitive element in race car design is efficient aerodynamic design [1,2,3]. Team designers consider aerodynamic efficiency to be the most important element in developing a competitive race car. Roughly speaking, aerodynamic design is concerned with two primary elements: reducing drag (D) and increasing downforce (negative lift, L). The principles, which allow aircraft to fly, are also applicable in car racing. The main difference being that the wing or airfoil shape is mounted upside down producing downforce instead of positive lift (Fig.1, right). DL Fig.1: rear wing detail [3] Downforce is necessary in maintaining high speeds through the corners and forces the car to the track. In actual race car design there are complex interactions between the aerodynamics of the 1front wing, rear wing and the main chassis as all three main components (in addition to the tires) contribute to both drag and downforce. In this project we will focus on the isolated design of one component of the race car: the rear wing. II. Project Description The project for IAP 2005 is for the students to design and build a wing section, its supports, and then test the wing in the wind tunnel. The students will be given some boundary conditions and a nominal operating condition. The main focus is on carrying out an end-to-end conceive-design-implement-operate (CDIO) process and to learn from that experience. The maximum design envelope for the wing and its support structure is 20” x 20” x 40” (width, height, span). The wing model can be created as an extrusion of a 2D wing section, thus limiting the aerodynamic analysis to 2D section airfoils. There will be no taper or dihedral, thus simplifying the analysis further and allowing for easier manufacturing. However, taper or dihedral are not explicitly forbidden in the final design. The design task also includes developing an attachment method of the wing to the supports and load cell. The support fixture attachment points to the wing strut are pre-defined. This will allow quickly mounting and comparing wing designs produced by different teams. An example wing support strut is drawn below (Fig.2); a drawing such as this will be due as a deliverable. Fig. 2: Sample wing mounting structure (CAD drawing) 2Dimensions: There are two support brackets located 39.75 (+/-0.5) inches apart, from inside surface to inside surface. The two bolts holes (5/16th O.D.) on each end of side the supporting fixture are 16.0 inches apart, and 1.0 inch above the lower plane of the design envelope. The support fixture is shown in the 3D view below (Fig.3). This support structure will interface with the hypothetical race car and the wind tunnel load cell. Fig. 3: Wing lower support structure and attachment points These brackets are the boundary conditions for the support struts, which the student teams will design. The design of the support strut to the wing is left open to the student design teams. The material available for students for the support struts/structure is either: A. 24 x 24 inch Aluminum 6061 plate, 0.125 inches thick B. 24 x 24 inch Aluminum 6061 plate, 0.25 inches thick. Note that the 0.25 inch thick Aluminum plate is roughly 3 times as expensive as the 6061 plate, and this will have to be taken account for in the student’s manufacturing reports and cost estimations. Wing/Strut Interface: The attachment of the wing(s) to the support structure can be done via epoxy. The wing might also need to be fiberglassed for strength. Another option is to include a supporting spar (a hollow aluminum rod, inside the wing). This option would involve cutting through the wing, span wise, to incorporate a hollow aluminum rod for support. This is an option students may have in case fiberglass is not available or desired, but note that there will be a penalty involved in costs associated with time to cut the wing and complete the assembly. Students will need to make an informed design decision with regards to fiberglassing, using a support rod or other innovative interface method. The 3D view below (Figure 4) is an example of a completed wing assembly that students will be fitting to the test fixture. A similar 3D model for the wing and support structure will also be due 3as a deliverable. The example below is not meant to limit designer’s imagination, but provides a rough idea of what the completed product might look like. Note that the design shown in Figure 4 has not been optimized or refined, but that it will be entered as the official (staff) contribution in the design competition. Fig.4: Isometric view of 3D CAD model – baseline rear wing design III. Competition Objective Function and Constraints The hypothetical race car manufacturer will compare all bids entered into the design competition. The winner of the competition will maximize the following objective function: Objective Function: ma x 3 5FL D W=−⋅−⋅ Where L = measured downforce (negative lift) at speed vo [N] D = measured drag at speed vo [N] W = total weight of the assembly (w/o support structure shown in Fig. 3) [N] The nominal speed is vo = 60 [mph]. Any change from this nominal condition will be announced within the first week of IAP. The actual objective function value for