Don’t know if you folks have had this feeling before. Like some intuition or idea is building in the back of your mind but you can’t yet sit down to figure it out… then you get out of bed one morning and it’s crystal clear. You write it down immediately and, presto, it’s so simple and it fits on 3 pages.
What am I talking about?
For the past year - in fact ever since I started the job I started in June last year, I’ve been managing a 3rd party contractor working on the structural analysis of a new product design. The new product was already sold, delivery due 2026, drawings released to production, just some last details to tidy up with the analysis. The analysis sub-contract was signed just before I arrived. The week of my arrival, they had the initial data load. The week after, the first problems cropped up. The story really hasn’t changed since then.
To be clear, the contractor is doing excellent work. They are diligent Finite Element Model builders, and have insight into joint analysis and material failure that I’ve come to trust in our regular discussions about their progress with the analysis. We handed them the working FEM models of the product that our company had developed over the previous years, and they’ve transformed them into high-fidelity representations of how our system works. Ask a question and they’re very quick with the answers. I will recommend them to people in the future.
To be frank, and I’m glad I have a fairly anonymous handle on a fairly obscure forum here, the problems are primarily of my own company’s making. This “discovery” process, where weekly or monthly this contractor discovers a new error that my predecessor made some time in the past, has profoundly undermined my ability to bond with the engineering team I’m working with. It’s difficult to trust people who make mistakes like ones they have found in our FEMs. Incorrectly applied loads, incorrect safety factor, incorrectly contact stiffness, incorrect mass properties, incorrectly place reactions, incorrect models of the surrounding airframe. Many examples of both oversimplification of some structures (unrealistic behaviour) and excessive elaboration of other parts, bogging down the computing.
Why am I mentioning this now?
This morning I woke up with the whole thing sorted out in my mind. The free-body diagram was finally in focus, the math in all 3 coordinates added up. I think I have finally seen enough of the load cases, structural reactions, and aerodynamics, that even before writing it down I had the first few equations worked out in my head.
2 hours later (yes, a Sunday morning wasted on work) I had my 3 pages and a free-body diagram that illustrates the result. It concisely demonstrates that there was NEVER any possibility that the proposed design would work. The free-body diagram and the sum of forces & moments I used is all first-year engineering school stuff.
The complexity of these sophisticated FEM models with 100,000 elements and 100 load cases has concealed from our designers and engineers the INSIGHT they need to make a sound design.
I feel a little guilty, not focusing myself on this solution months ago, especially when the flaws with the design just wouldn’t go away. What a lot of trouble I could have saved if I’d given myself this insight 6 months ago.
OTOH, most (not all) members of my engineering team also went to engineering school, and my predecessor had a very high standing in the company, and in the local engineering realm beyond our company. For all of them to not attempt this evaluation before embarking on the design… again my ability to trust suffers.
I’m not asking a question, I’m just getting something off my chest. What a way to remind myself that the tried-and-true methods still work, even in a world of fast computers and high-fidelity models. All I needed was a pencil, drawing paper, and pocket calculator.