Documentation of the Linear Statistical Discrete Gust method’

Department of Transportation in the interest of information exchange. The United States Government assumes no liability for the contents or use thereof. The United States Government does not endorse products or manufacturers. Trade or manufacturer's names appear herein solely because they are considered essential to the objective of this report. This document does not constitute FAA certification policy. Consult your local FAA aircraft certification office as to its use. The Statistical Discrete Gust (SDG) method is an alternate procedure for estimating and predicting severe gust and severe turbulence loads. This method claims to have the potential to replace the combined Power Spectral Density (PSD) Model of Title 14 Code of Federal Regulations (CFR) 25.341(b) and the Tuned Isolated Discrete Gust (IDG) of 14 CFR 25.341(a), which jointly ensures that an airplane has sufficient structural strength for encounters with continuous turbulence (PSD) and discrete gusts (TDG) of design-level intensity. The SDG method provides such a specification in a form that takes into account the non-Gaussian statistical structure of the more intense turbulence fluctuations and the manner in which these interact with the dynamic response of a flexible aircraft. This report documents the development of the method, as applied to the response of a linear aircraft, in the following order: historical development, evidence that severe and extreme gust encounters are characterized by short-duration bursts evidence for the 1/6 scaling law examples of calculated loads and comparisons with models in existing requirements, and advantages and limitations of current SDG models. The SDG method was developed over a period of over 30 years, and during its development, many in industry, research institutions, and academia have expressed divergent viewpoints regarding the suitability of using the SDG method for the derivation of design gust loads. Consequently, the Federal Aviation Administration has invited three experts to express their views and comments, which have been included as an addendum in the documentation of the SDG method contained herein. PREFACE The Federal Aviation Administration has supported the development of the Statistical Discrete Gust (SDG) Method, for use as an alternative procedure of estimating severe gust and turbulence loads. This report reviews and documents the SDG methodology. This methodology was reviewed by a group of international Gust Specialists, who met approximately yearly during a 15-year period. Aircraft design must ensure sufficient structural strength to survive extreme cases of encounters with atmospheric turbulence, thus requiring a mathematical model of turbulence to …