Preliminary design The focus of preliminary design is to determine approximate dimensions, weight, power, load limit and other physical characteristics for an optimum aircraft, which best maximise scores for competition. The main areas of concern were wing area, span and empennage size. The entire routine is modelled based on the conceptual design, with carefully considering the specific requirement of the competition. 1. Critical design parameters and sizing trades Based on results obtained in the conceptual design phase, the critical design parameters are revised to reflect on the performance parameters considered most influential to the overall score. These include main wing dimension, power plant, ménage dimensions and load factor limit. Wing area Since the weight of the structure is approximated in the conceptual design stage, and the payload weight is specific by the competition organisation, the total weight at level flight can be found. Since no vertical acceleration applies during level flight, and fuel consumed can be neglected in comparison with the total weight, thus, L W 4.5 9.8 Equation 1 From the definition of lift produced in flight: L 1 / 2V 2 SC l Equation 2 From the studies of existing RC planes, it is sensible to assume the plane flies at 200m, =1.22kg/m^3, V=25m/s, and the aircraft flies at an angle of attack at 5 degrees. The lift coefficient of the whole aircraft can be found from the wing tunnel test. In order to find out the minimum area required, it is assumed that CL is at maximum. The MAX (Cl) equals to the Cl of the Clark Y aerofoil. From the NACA full-scale wind tunnel test result, we found the lift coefficient at the same flow condition is approximately equals to ---------. Due to the box-wing configuration from the wing tunnel testing conducted by Mississippi state university, the Cl can be doubled if the distance of separation is greater than the chord length. Therefore, the minimum plan form area required is about 1.01 m^2. Due to vortices and flow separation the maximum Cl would decrease and it would result in increasing the plan form area. Assuming the efficiency of the box-wing to be 0.9, the minimum plan form area required is approx. 0.22m^2. Figure 1 The lift curve slope depicted in Fig. 5 shows that the nonplanar configurations have much greater slope than monoplane allowing the nonplanar wings to produce the same amount of lift at much lower angles of attack Wingspan The wingspan can be found from the aspect ratio of the plane since the minimum plan form area is known. Using results from regression method, existing bi-planes have a typical aspect ratio of approx. 6.8. Since the efficiency factor of box-wings is approx. 5% hight than that of bi-planes, a reasonable aspect ratio of 6.5 can be used. Hence the span of the main wing equals to 17.1 cm.