The aim of this document is to provide guidance to designers and stress engineers. The directions and recommendations in this document reflect the airworthiness regulations, industry best practices and the general experience of the author across several FAR part 23 & 25 metallic and composite aircraft programs.
The general approach for all analyses is shown below:
Figure 1.5.1‑1: General Analysis Approach
It must be noted and understood that all analysis methods, whether a simple or a complex hand analysis or simple or a complex finite element solution, are just mathematical models of the real world. All analysis results require checking and correlation to representative testing prior to the engineered product being used for any critical application. All analysis methods should be applied with skepticism and caution.
The applicability of all analysis methods must be understood before an assessment of their likely accuracy is made. Where reference is made back to testing in the cited source material, does the tested range cover the configuration you are analyzing? If the testing is not directly applicable to your engineering problem is it reasonable to assume the method is applicable? Do you have access to any other specific company, proprietary or public domain test results to confirm the suitability of the method? Is there a subject matter expert available to consult and advise? We supply the original references so that you can check on the range of applicable situations the method does applies to. Do not take anything for granted!
If the method you have chosen for the analysis is applicable, have you applied the method correctly? Is it error free? Sanity checking of your own work and peer review is essential. Just because you have a result you expect or wanted it does not mean that it is correct. An applicable modified idiom could be “The road to hell is paved with wishful thinking”. In the author’s experience, it is important to trust your instincts, if you obtain an analysis result that gives you cause for suspicion or is too good to be true, trust your instincts and go back and check, reanalyze and be sure you are correct.
In the end, the analyst must have confidence in the accuracy and applicability of their selected methods. In this document, we have tried to give cited sources for all critical aspects. We encourage everyone who uses this document to go to the original sources and understand the specific limitations of each analysis method. If you think that we have misinterpreted or misrepresented any of the source material, please let us know. If we make a change to a subsequent issue of the book we will give you footnote credit for helping us all better understand the analysis method.