1927. Simplified Weight Evaluation Methodology for VTOL Aircraft

Paper

Abstract

This methodology was developed to fill the need for a simplified weight estimation methodology for use in preliminary sizing and proposal evaluation of VTOL aircraft. The preliminary sizings are based upon the weight empty fraction of the type of vehicle proposed. The fraction is then adjusted for discriminating features, new requirements, technology improvements, and mission oriented items to arrive at a revised weight empty fraction. A fuel fraction is then added to the weight empty fraction to determine the fraction available to carry the required payload. The projected gross weight solution is determined by dividing the payload by the available payload factor. This process is then iterated as required by adjusting the fuel fractions for the gross weight change. Refinements of the preliminary estimates are made using curves such as wetted area vs. design gross weight, change in fuel fraction vs. design gross weight, change in gross weight vs. speed, and change in weight empty fraction vs. technology and requirements. Using this preliminary evaluation methodology, the weight empty fraction for a typical air vehicle to do a specified mission can be developed with reasonable accuracy. To illustrate a projected new mission gross weight from an existing aircraft, an example using the CH-53E Marine transport aircraft is included. A second part of the paper discusses a review of the weight validity of the major subgroups, once the aircraft size has been evaluated and any differences resolved. Weight trend charts showing major weight subgroups as a function of design gross weight support the fraction weight projection. Weight empty fractions and design gross weights for a large sample of helicopters and compound vehicles are provided for information.