飞机总体方案设计例子

飞机总体方案设计例子内容摘要：

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。 10     222 2 12 12 1 t a k e o f ft a k e o f fc r u i s ec r u i s ee VghVghVghh Equation 10 where h is altitude, g is the gravity constant, and V is speed. Note that Vtakeoff is calculated as times stall speed. This is conservative since it does not consider the acceleration that will occur as the plane climbs to the 50 foot altitude accounted for in the takeoff fuel weight fraction equation. The average climb speed is calculated using the Raymer’s equation : 02limDbc CKSWV   Equation 11 where W/S is wing loading (an input parameter), ρ is air density at sea level, CD0 is the zero lift drag coefficient, and K is the aerodynamic constant. CD0 was calculated to be in the aerodynamic analysis. K was calculated using the equation: eARK  1 Equation 12 Where AR is the aspect ratio and e is the Oswald Efficiency Factor. The Aspect ratio is an input parameter which was chosen through the use of carpet plots (discussed later) and the Oswald Efficiency Factor was determined as a function of aspect ratio via a curve fit of CMARC analysis data for the plane which yielded the equation: 4 3 5 2 6  ARe Equation 13 34WW represents the fuel weight used during the cruise segment and is calculated using the Breguet range equation (also Raymer ): DLVCRWWii ex p1 Equation 14 where R is range (less the distance traveled during climb), C is SFC (same as before), V is cruise speed, and L/D is the lift to drag ratio at cruise conditions. Distance traveled during the range segment is calculated by subtracting the average climb velocity multiplied by the time it will take to reach 8000 ft at a climb rate of 700 fpm from the design mission’s range of 600 nmi. Cruise speed is set at the design cruise speed of 150 kts. Cruise L/D was calculated in the same manner as it was for climb, except that the density and speed used were the cruise condition values, and not those of climb. 45WW represents the fuel used during descent and is assumed to be . This was approximated by estimating the fuel usage per minute and multiplying it by an estimated time to descend. Team V。 11 56WW represents a missed approach and climb to a 2020 ft divert altitude. It is calculated in the same manner as the fuel used to climb to cruise altitude 23WW . 67WW represents a divert distance, however, the team opted to use a 45 minute loiter/divert segment, thus this fuel fraction is 1. 78WW represents the fuel used during the 45 minute loiter/divert segment and is calculated using the loiter equation (also Raymer ): DLCEWWii ex p1 Equation 15 where E is endurance time (in hours), C is SFC (same as before), and L/D is the lift to drag ratio at cruise conditions. The endurance time is specified as 45 minutes to acmodate IFR regulations and the L/D used in the loiter/divert segment is the same as that for cruise. 89WW is another descent segment and is assumed to be equal to45WW which should be conservative considering the aircraft is descending from a lower altitude. Finally 910WW represents the fuel used during landing and is assumed to be . This is based upon Raymer’s equation which simply states it should be between and [10]. The Wcrew and Wpayload were taken from the design requirement of having a 600 lb payload including crew. Once all of these sizing equations were piled together, it was possible to place them inside of two for loops. The first of these loops varied aspect ratio through a specified range。 the other varied the wing loading. This made it possible to plot a curve of GTOW vs. wing loading for each aspect ratio. Using this for loop approach allowed the team to rapidly generate numerous data points which (with a small enough wing loading increment) could be linearly connected to adjacent points to form a smooth curve. 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 ex。