Wing Aspect Ratio Optimization Problems for Transport Turbojet Airplanes

The paper concerns the conceptual design phase: definition of the airplane configuration according to the standard requirements. The aim is the optimization of the payload and of fuel consumption which are fundamental elements in the design of a transport airplane. These are required in relation to the external configuration in order to define an optimum wing aspect ratio value. In detail, the work starts out from Breguet's formula, modified for jet airplanes, and develops it as a function of the different parameters. Calculations were performed for different cruising height values, selected from the flight levels usually utilized. The solutions are given as functions of the range, of the cruise flight attitude and of the cruise height. A simple formula is introduced in the flight performance equations for estimating the wing weight. Obviously, for the purposes of this optimization, the fuel consumption during the climb must be taken into account; this evaluation was performed using an energetic method. The computation program consists of a matrix of the variables and parameters, and determines the variation of each one with respect to the others. The results are presented in the form of diagrams and all quantities are represented as variables or parameters. This method, which is a development of that already proposed by the authors for turboprop airplanes, is very easy to use and permits the optimum solution for economy utilization to be found. This situation is determined by certain values for payload and fuel consumption. The external configuration of the airplane may be defined in this way following the most suitable criterion: optimization of the payload, or optimization of the fuel consumption.