2034. Drive System Weight Optimization

Paper

Abstract

The drive system of a VTOL aircraft can vary from 8 to 20 percent of the weight empty. There are several parameters, which, when combined in the proper way, will affect the weight of the drive system. Some of these parameters are: RPM reduction stages, tooth pressure angle, and Hertz compressive stress. This paper presents a way, through the efficient use of a Lotus spreadsheet, to optimize the weight of a VTOL aircraft’s drive system. Using two SAWE papers: Paper No. 1120 ”A Method for Estimating the Weight of Aircraft Transmissions” and Paper No. 651 ”A Simplified Method for Calculating the Weight of Aircraft Transmission Drive Shafting,” both by Arling H. Schmidt, retired from Boeing Helicopters, a typical drive system for a single rotor helicopter is optimized using various trade studies. The trade studies used are: Gear mesh architecture Hertz stress levels Gear pressure and helix angles Types of transmission lubrication systems Supercritical versus subcritical drive shafting Main rotor shaft material and mounting configuration This paper also discusses the programming capabilities of Lotus 123 and its use for mass properties analysis. Through the use of this Lotus spreadsheet, it is possible to carry out several different trade studies to optimize the weight of a drive system quickly and efficiently. It is a very effective tool in preliminary design.