Automated Air Force Lug Analysis

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Discussion Overview

The discussion revolves around the analysis of Air Force lugs, specifically focusing on the challenges of automating the analysis using various software tools. Participants explore the reliance on empirical charts developed by the USAF in the 1960s and seek alternative methods or software solutions for accurate analysis.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant notes that the Air Force Lug Analysis method is comprehensive but relies on outdated charts, raising concerns about the precision of automated solvers based on these charts.
  • Another participant suggests that Peterson's Stress Concentration Factors may provide additional reference material, although it may not be as thorough as the Air Force reference.
  • There is a discussion about the lack of original empirical data for the charts, with one participant expressing a desire for curve fitting software recommendations.
  • One participant warns against curve fitting to empirically derived data of unknown quality, suggesting that Finite Element Analysis (FEA) could be a more reliable method for generating new data.
  • Another participant mentions a specific online calculator that utilizes the Air Force methodology and provides formatted reports, including equations and charts.
  • A different software option is recommended, which is said to be efficient and based on the USAF method, but assumes familiarity with lug analysis fundamentals.

Areas of Agreement / Disagreement

Participants express various viewpoints on the best approach to lug analysis, with some advocating for curve fitting and others recommending FEA. There is no consensus on the best method or the availability of original empirical data.

Contextual Notes

Participants acknowledge limitations related to the quality of empirical data and the potential inaccuracies in curve fitting methods. The discussion reflects uncertainty about the reliability of existing charts and the need for validation of any new data generated.

Who May Find This Useful

This discussion may be useful for engineers and researchers involved in structural analysis, particularly those interested in automated solutions for lug analysis and the application of empirical data in engineering contexts.

That_Intern
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Air Force Lug Analysis (section 9 here and summarized here) seems to be the best generalized method for comprehensive lug analysis. However, it relies on charts developed by the USAF in the late sixties. Every source I've found on the method uses those same images.

I'm trying to make an automated solver using MathCad (though excel, matlab, mathematica, etc could easily do it). But that relies on my code being able to read the charts or solve the underlying empirical equations.

Does anyone know what the source equations are for these charts or whether there is software that can solve them? The only thing I've thought of is plugging each curve into excel and then running through a best fit curve of each different equation type until I find something that fits well. This just doesn't seems precise enough to me.

Thanks in advance.

PS: any tips on how to improve the post are also appreciated

Edit: Attached is a first pass at 1/40 of the excel method. The original chart is underlain
 

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Peterson's Stress Concentration Factors has a section detailing lug analysis. Although it doesn't seem as thorough as the AF reference, it may give you a reference paper to follow-up on regarding any charts provided. I have found that some reference charts/curves in this book (and so possibly in the Air Force reference) are empirically derived, it may be there is no equation to solve unless you fit a polynomial curve to it...
 
Yeah I figured that was the issue I was just hoping someone had the original empirical data but realistically I just wanted to know if anyone had curve fitting software recommendations. I used http://arohatgi.info/WebPlotDigitizer/ but if I had MATLAB installed I'd probably use that
 
Curve fitting to empirically derived charted data of unknown quality is not a good thing to do .

You could use FEA to generate all new data which could be validated properly .

Personally though with FEA available I would just use it direct .

For frequent use and/or use by non FEA specialists it would not be too difficult to set up a parametric general model and have a simple spread sheet plus graphics front end for data entry and results display .

Some FEA software allows extensions to be embedded for specific applications . This would allow you to control the entire model generation , analysis and results display from a simple pull out data entry box on the standard FEA viewing screen .
 
Last edited:
That_Intern said:
Air Force Lug Analysis (section 9 here and summarized here) seems to be the best generalized method for comprehensive lug analysis. However, it relies on charts developed by the USAF in the late sixties. Every source I've found on the method uses those same images.

I'm trying to make an automated solver using MathCad (though excel, matlab, mathematica, etc could easily do it). But that relies on my code being able to read the charts or solve the underlying empirical equations.

Does anyone know what the source equations are for these charts or whether there is software that can solve them? The only thing I've thought of is plugging each curve into excel and then running through a best fit curve of each different equation type until I find something that fits well. This just doesn't seems precise enough to me.

Thanks in advance.

PS: any tips on how to improve the post are also appreciated

Edit: Attached is a first pass at 1/40 of the excel method. The original chart is underlain

The site that you linked to that summarized the Air Force Lug Analysis method includes a lug analysis calculator. The calculator is based on the Air Force methodology and uses all of the charts that you mentioned. This calculator is simple to use, and it generates a formatted report as part of the output which includes the equations used and the charts specific to your analysis. You can find the calculator here:
https://www.mechanicalc.com/calculators/lifting-lug-analysis/
 
I have been using the software available here:

www.lugcalc.com

The software assumes you are familiar with the foundation of lug analysis but is very efficient. The documentation indicates it uses the USAF method.

Best of Luck!
 

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