tailieunhanh - Aircraft Design: Synthesis and Analysis - part 5

Thang máy trên hệ thống cánh thân máy bay được tính toán từ các xoáy trường xa, vì vậy hiệu quả khoảng là: e = 1 - d2 / b2. Trong thực tế, một trong những hiện không đạt được điều này nâng nhiều trên thân máy bay. Giả sử một thân máy bay dài tròn và tính toán thang máy dựa trên hình ảnh, kết quả tăng kéo gây ra là khoảng hai lần giá trị lý thuyết đơn giản, vì vậy: s = 1 - 2 d2/b2. | Airfoil Design Methods The process of airfoil design proceeds from a knowledge of the boundary layer properties and the relation between geometry and pressure distribution. The goal of an airfoil design varies. Some airfoils are designed to produce low drag and may not be required to generate lift at all. Some sections may need to produce low drag while producing a given amount of lift. In some cases the drag doesn t really matter - it is maximum lift that is important. The section may be required to achieve this performance with a constraint on thickness or pitching moment or off-design performance or other unusual constraints. Some of these are discussed further in the section on historical examples. One approach to airfoil design is to use an airfoil that was already designed by someone who knew what he or she was doing. This design by authority works well when the goals of a particular design problem happen to coincide with the goals of the original airfoil design. This is rarely the case although sometimes existing airfoils are good enough. In these cases airfoils may be chosen from catalogs such as Abbott and von Doenhoffs Theory of Wing Sections Althaus and Wortmann s Stuttgarter Profilkatalog Althaus Low Reynolds Number Airfoil catalog or Selig s Airfoils at Low Speeds . The advantage to this approach is that there is test data available. No surprises such as a unexpected early stall are likely. On the other hand available tools are now sufficiently refined that one can be reasonably sure that the predicted performance can be achieved. The use of designer airfoils specifically tailored to the needs of a given project is now very common. This section of the notes deals with the process of custom airfoil design. Methods for airfoil design can be classified into two categories direct and inverse design. Direct Methods for Airfoil Design The direct airfoil design methods involve the specification of a section geometry and the calculation of pressures and .