飛機(jī)總體方案設(shè)計(jì)例子-全文預(yù)覽
【正文】 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。 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。 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 plot a curve through these data points. The cruise speed was calculated by using Matlab’s fsolve function to solve the following equation for V: 2m i n __202 221 ???????? ??? ??????????? d r a gLDp CSV WKCSVVbhp ??? Equation 16 In Equation 16, ηp is the propeller efficiency, bhp is the horsepower of the engine (200), V is the cruise speed, ρ is the air density at cruise altitude, S is the area of the wing, CD0 is the zero lift drag coefficient, K is the aerodynamic constant, W is the aircraft GTOW, and CL_min_drag is the coefficient of lift which corresponds to the minimum drag coefficient. ηp, V, K, and CD0 were previously discussed. CL_min_drag is based upon the drag polar generated by the aerodynamic analysis and S is calculated by dividing the GTOW by the wing loading. It can be noted that the factor of in Equation 16 signifies that this velocity will be the cruise speed at 75% power. Climb rate is calculated using the Raymer’s equation : W VDWbhpV bcpv ????? lim_550 ? Equation 17 Where ηp_climb is the propeller efficiency during climb, bhp is the horsepower of the engine (200), V is the cruise speed, W is the GTOW, and D is the drag force of the aircraft during climb. ηp_climb is assumed to be based upon the propeller analysis (discussed later) and other than D all other parameters have been previously discussed. D is calculated using the equation: ?????? ???? 02 3421 DCSV? Equation 18 Where ρ is the density at sea level, V is the average speed during climb, S is the wing area, and CD0 is the zero lift drag coefficient. All of these values have been previously discussed. Takeoff distance was calculated using Raymer’s equation [10]: ?????????????????????????????????????????slavo b s t a c l ebcL UWThCg SWGB F L???lim_ Equation 19 Team V。 9 G TO WWT p???? 550200 Equation 4 where ηp is the propeller efficiency, which is assumed to be based upon the propeller analysis discussed later. The SFC was calculated from the brake horsepower SFC (BSFC) which was calculated for the aircraft’s engine to be . Engine selection and SFC calculation is discussed later in this report. The equation used to calculate SFC from BSFC is: pVB S F CS F C ???? 550 Equation 5 where V is speed and ηp is the propeller efficiency. 12WW corresponds to the fuel used during takeoff and is also calculated using Equation 3 with 100% thrust. Duration for the takeoff segment is assumed to be one minute as specified in Raymer’s chapter 19 [10]. 23WW represents the fuel weight used in climbing to the cruise altitude of 8000 ft. It is calculated using Raymer’s equation : ?????????????????? ??????TDVhCWW eii1e xp1 Equation 6 where C is SFC (same as previously discussed), Δhe is the change in height energy, V is the average climb speed and D/T is the average drag divided by the average thrust during climb. It should be noted, however, that D/T is not actually calculated within the code, and is instead replaced by: 1??????? ?? WTDLTD Equation 7 In Equation 7, L/D is calculated implicitly by calculating CL/CD. CL is calculated using the equation: 221 VS WqSWC L ?? ???? ? Equation 8 where W/S is wing loading (an input parameter) and ρ is air density at sea level. CD is calculated using the curve fit for the plane’s drag polar: 0 2 0 7 2 ????? LLD CCC Equation 9 Δhe is calculated using Raymer’s equation : Team V。 6 Proposed Concept Team V’s proposed concept is shown in Figure 1. The Barn Owl is a low wing, conventional tail, single engine, tractor prop, 4 seat general aviation aircraft. Figure 1 Concept 3 View Team V。 3 Table of Contents Introduction .................................................................................................................
公司管理相關(guān)推薦
鄂ICP備17016276號(hào)-1