DRDO Science Spectrum, March 2009, pp. 4-11 DRDO SCIENCE SPECTRUM 2009 © 2009, DESIDOC
Aircraft Performance Improvements-A Practical Approach
Centre for Military Airworthiness and Certification, Marathalli Colony, Bangaluru- 560 037 ABSTRACT An aircraft is designed based on various wind tunnel testing, computational analysis, previous design experience etc. In most of the aircraft programs the design objective could not be met with the first prototype design itself. Before the induction into the service the aircraft could have undergone many design improvements in order to meet the desired performance. These performance improvements can be achieved by improving the original design in the area of aerodynamics, structure (weight reduction), propulsion and systems (like flight control system, avionics, fuel system etc.). This could be by modifying the original design or introducing new concepts in the design. Due to the obsolence of many technology and growing demand many aircraft program undergone an upgradation program and meets the higher performance demands. Many successful modifications were retrofitted in all their earlier aircrafts and followed in other aircraft programs also. Keywords: Aircraft, aerodynamics, performance improvement program, PIP, propulsion systems
Performance Improvement Program (PIP) is inevitable in almost all the aircraft programs worldwide. Always there is a scope for improvements. An attempt has been made to bring out and consolidate the successful aircraft modifications in other countries. And this paper brings out the many modifications envisaged in our country’s prestigious indigenous aircraft programs Tejas and HJT-36 also. Even though the modifications are in the field of aerodynamics, structure, propulsion and other systems the general modifications are pertained to aerodynamic configuration change and propulsion, i.e. engine upgradation. The weight reduction methods followed in many aircraft programs also brought out in this paper. 2. SUCCESSFUL AIRCRAFT PERFORMANCE IMPROVEMENT METHODS WORLDWIDE
Due to the increasing pollution, cost and demand there is a need to improve the aircraft airframe and its power plant. From the first flight of Wright brothers in 1903 to Airbus 380, the aircraft industry underwent various technology challenges. During this phase there was lot of improvements in the airframe, propulsion and other systems. The following are some of the design changes or inventions which makes great impact in the aircraft performance improvements. 2.1 Winglets in Boeing-737 The unmodified 737 model wing, originally designed in the early 1970's, is derived from wings developed at a time when aircraft flew at low Mach numbers, and a primary goal was to produce low skin friction drag. At high Mach 4
number, such as those achieved by the 737 model aircraft, strong shock waves form on the upper wing surface of the unmodified wing. This causes the following deficiencies: a) relatively high lift-induced drag; b) rapid increase in drag with increased Mach number (early drag rise); c) early onset of wing buffet at typical cruise Mach numbers; and d) appearance of pronounced nose-down pitch at relatively low Mach numbers. The winglet at the wing tip along with the flaps and aileron droop reduces these deficiencies. Winglets are small lifting surfaces attached to the outboard end of an airplane wing, commonly at or near to a vertical angle from the wing structure. Winglets function to relocate the tip vortex of an airplane wing further outboard and above the unmodified location. In flight, the substantially inward pointing load carried by the winglets relocates the wing tip vortex. Due to pressure differentials between wing surfaces at a wing tip, air tends to flow outboard along the lower surface of a wing around the tip and inboard along the wing upper surface. When winglets are added, the relocated wing tip vortex caused by the winglets...
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