Spar Connector Development
May 2022 - October 2023
Structures and Material Science team
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The SAE AERO Regular Class competition 2023 and 2024 ruleset saw a requirement that no component on the plane may be longer than 4' in length along any primary axis. Since the most optimum wingspan for the regular class competition was 18' in 2023 and 15' in 2024, this required the wing (and fuselage) to separate into multiple sections. This page goes over the iterative process that led to the connector we have today, which has an 80% reduction in assembly time and 50% reduction in connector weight.
2023 Experimental Plane (XP1) Connector:
Initially, requirements were simply focused on strength. In that, they succeeded. However, we quickly found out that they were exceedingly tedious to assemble, because it required 20 screws and nuts, along with 2 connecting plywoods and two webbing connectors per spar connection. Once everything was connected, it further required small wing spanners to be added in order to cover the gap in the wing where the connector was. In total, putting the whole plane together took over 3 hours.
This was a sharp realization that usability was a requirement as well.
2023 Competition Plane (CP1) Connector:
So, it was time to learn about Design for Assembly. The key takeaway for the connectors was to reduce part count as much as possible.
Our destructive testing indicated that the connector was at least as strong as the spar it was a part of, so we could afford to make it more minimal in favor of ease of use.
We designed plywood fingers to specifically take the shear load, and aluminum tabs to take the bending load, which at the top and bottom of the spar equates to simple tension and compression. Having dedicated components allowed us to optimize each for their specific load (i.e. the fingers take shear only and the tabs take bending only).
Furthermore, not having to manually connect components on the webbing allowed us to make the outtermost ribs sit flush with the connection, eliminating the wing spanners as well.
Overall this was a big improvement, with an assembly time reduction to ~30 minutes.
2024 Experimental Plane (XP1) Connector:
With the new season came a new opportunity to further revise the connectors. I wanted to eliminate any screws on the bottom of the wing, since those required crawling around on your back to access. Furthermore, I wanted to achieve the ultimate minimum part count, which was simply one.
To accomplish this, I came up with a hinge connection mechanism where the bottom spar has a pin which fits into an opposing hole, and the whole spar rotates in.
Since the biggest force on the wing will always be lift, I could afford to make the spar connector more minimal on the top. Hence, I put only one screw. During destructive testing, the connector survived sufficiently high loads and lasted longer than the spar, which indicated it was acceptable for use.
This resulted in an assembly time of ~15 minutes for the plane, a big improvement from where we started.
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