【正文】 19 2D Aerodynamics In order to improve the performance of the aircraft, it was suggested that a new laminar flow airfoil be designed specifically for the Barn Owl. The goal of the design is to use optimization methods to create an airfoil that has lower drag during cruise than the NACA fourdigit series airfoils used on some GA aircraft, while simultaneously maintaining good performance at high angles of attack and under fully turbulent conditions. Methodology The optimization procedure is shown in Figure 7 as a flow chart. First, the Matlab optimizer generates a vector of design variables with information regarding the xy location of control (or “handle”) points the airfoil’s surface needs to pass through, as well as the tangency and curvature at the trailing and leading edges for both halves of the airfoil. The number of control points can be changed within the call script that runs the optimizer. The design vector is fed into the objective function, which fits a spline curve through these “handle” points and the tangencies provided at LE and TE (see Figure 6). The spline curve is converted into data points and saved as the airfoil coordinate input file for XFoil. 0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6 0 . 7 0 . 8 0 . 9 1 0 . 7 0 . 6 0 . 5 0 . 4 0 . 3 0 . 2 0 . 1Co ntro l “ h an d l e ” po in tsSmoo th spl i ne curveCo nstra i n re gio ns Figure 6 Il。 was needed for takeoff. Thus, the fuselage and landing gear were arranged so this rotation angle was possible (see Figure 4). Figure 4 Takeoff rotation Engine Mounting Room Using an engine CAD model obtained from the engine manufacturer website, the engine was integrated into the plane CAD model to determine if its position as required by the center of gravity and stability requirements would interfere with the fuselage. It was found that the nose of the aircraft has adequate room for the engine and all related ponents. Figure 5 Mounted engine Fuel Volume Concerns were raised that there might not be enough room inside the wing for 54 gal of fuel. Calculations from the Catia model showed that the wing had enough room for 240 gal. 15176。s E f f i c i e n c t F a c t o r 0 . 6 7 0 4 2 Team V。 16 It can be seen in Figure 3 that the lowest GTOW is approximately 2610 lbs which corresponds to a wing loading of lbs/sq ft and an aspect ratio of approximately . For the final design, Team V chose to use a wing loading of and an aspect ratio of to allow room for error. Also note that in Figure 3 the climb constraint plotted is for a climb rate of 1350 fpm, not the 700 fpm climb rate used for the design mission. This was done so that the climb constraint would appear on the carpet plot, as 700 fpm was too far to the left. Plugging this wing loading and aspect ratio back into the sizing/carpet plot code gave the final sizing numbers. These can be seen in Table 3. It should be noted that our 75% power cruise speed is not our designed cruise speed, thus the power required to fly at 150 kts during cruise was calculated to be approximately 61% using Equation 16 above. Team V。 14 Landing distance was calculated using a summation of approach distance, flare distance, ground roll distance and a two second frictionless roll at stall speed to account for the time before the pilot applies the brakes. Approach distance was calculated using Raymer’s equation : ? ?bc TRobstaclec hhS limtan ? ?? Equation 25 hobstacle and γclimb have been previously discussed. hTR was calculated using Raymer’s equation : ? ?? ?bcTR Rh limc o s1 ??? Equation 26 where R is calculated using Raymer’s equation : stallVR ?? Equation 27 where Vstall is a design parameter equal to 57 kts and is explained in further detail later. Flare distance was calculated using Raymer’s equation : DLWTST 1?? Equation 28 where T/W is the thrust to weight at idle speed (20%) and L/D is the lift to drag ratio with full flaps which is assumed to be 5 based upon the aerodynamic analysis/engineering judgment. Ground Roll distance is calculated by using Raymer’s equation : ???????? ?????????? ??? 2ln2 1 iAT TAG VKK KKgS Equation 29 where g is the gravity constant, Vi is the initial speed (assumed to be stall speed at touchdown). KA and KT are calculated using the following 2 equations: ???WTKT Equation 30 ? ?? ?202 LDLA CKCCSWK ?????? ?? Equation 31 All of the above values have been previously discussed except for μ which was estimated to be based upon Raymer’s Table [10]. Best range cruise speed was calculated using Raymer’s equation which is seen above in Equation 11. Best range cruise distance was calculated using equation of Raymer: ???????????? fibhp p WWDLCR ln550 ? Equation 32 Where ηp is the propeller efficiency, Cbhp is the BSFC, L/D is the minimum drag lifttodrag ratio and Wi/Wf is the weight ratio of the segment. The minimum drag lifttodrag ratio is calculated Team V。 12 In order to find the optimal aircraft design (. the one with the minimum GTOW), Team V calculated and plotted various constraints along the aspect ratio curves. The constraints used were stall speed, cruise speed, climb rate, takeoff distance, and turn load factor (n) value. For each aspect ratio and wing loading bination, cruise speed, climb rate, takeoff distance, and the turn load factor (n) value were calculated as discussed below and placed into an individual matrix for each constraint. Then for each row in the matrix (which corresponded to a constant aspect ratio) the value above and below the desired value was found. Next, a linear interpolation was used to find exact GTOW that corresponded to the desired value for that aspect ratio. Finally, all that had to be done to create the constraint lines was