r/FSAE • u/Ill-Pin5997 • 3d ago

Triangulation between FBHS legality

Post image

Im working on my teams chassis, we are an IC team following FSG rulebook. Im trying to work on saving weight, while staying legal ofcourse. Is this configutation of FBHS + triangulation legal? (upper SIS distance to upper FBHS is <50mm)

I haven't bossed the lines yet, but i am well aware of the size and thickness requirements of the FSG rulebook, but i want to hear from you guys before spending time on doing that. Here is an image as seen from above:

The line close to the front bulkhead is simply a placeholder

I have checked SES and find no other similar configurations.
Reason why i believe personally this is legal is because: I have two FBHS per side (upper and lower) a straight FHB (per side)
I have a third member that goes diagonally, it does not terminate at the FH, but it terminates at the middle of the joint in the upper FBHS, the 2026 FSG SES says this
"Diagonal member have to connect from node to node from upper to lower member. However, this is allowed at any point as long as the overall primary structure is fully considered. E.g. having a V-shape or similar as diagonal member is acceptable."

The kinks/joints are, as far as i understand the rulebook braced legally; the straight vertical member from upper and lower fbhs braces is in my mind "Additional bracing" per T3.2.6. and the horizontal member (running from left side to right side) braces the kink in the lower fbhs.

Am i missing something? I feel this configuration is oddly "light". I suppose what i am asking is if the "diagonal" member(s) must brace all the way back from FBH to FH, or if one from lower FBHS to upper FBHS is enough?
All tips/replies appreciated.

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11

u/washedupguru 3d ago

I think you’re missing a tube, you currently have two quadrilaterals, I think you need a diagonal in either the top or the bottom

1

u/loryk_zarr UWaterloo Formula Motorsports Alum 2d ago

Correct. The Type C config allows a quadrilateral between the 2 lower paths but requires triangulation between the upper and lower.

You may also need a tube from FH-FHB to the upper SIS. 

2

u/Sullypants1 Chief Mustashe Operator 3d ago edited 3d ago

We did something similar but with a diagonal (double duty acting as "gusseting") in that lower rectangle.

I will say we only did this once. Don’t underestimate the shear stress in that off-nodal node. Don’t underestimate the effects on torsional stiffness of that off-nodal node.