Monocoque FBH requirements (FSG)
Hey guys,
I've seen some different FBH designs for monocoqoues by now and am wondering if I misunderstand the requirements in the (FSG) SES because of the huge differences.
One team has had an aluminium FBH with around 0.8 - 1mm skin thickness both innerskin and outerskin plus 25/30mm aluminium core. Another uses CFRP plus 25mm aluminium core and another uses a few mm of CFRP whith ultra slim core (or none at all, wasn't too clear in the picture) and others have to go for a 4mm CFRP skin plus 1mm aluminium sheet on top still using 20mm alu core and a cfrp innerskin.
Since the rules do not state a specific number for e.g. the shear strength unlike for the SIS (7.5kN) I am unsure what leads to these very different designs. I mean, clearly a thin aluminium sheet cannot be compliant, yet it has been used and approved before (probably a few years old, maybe different rules back then). With our reference tests our panels would have to achieve a shear strength of >25kN and >15kN in the 3-point bending test with a gradient of >5000 N/mm. These numbers are quite far above the other required forces stated in the rules and I cannot imagine that those are the intended numbers.
Do you guys have to achieve similar forces or am I just stupid right now? It would be a great help, if you could give me some reference numbers and point me in the right direction.
Thank you in advance!
Posted Feb 26, 2021, 4:52 PM UTC
Use the Excel Sheet and don't assume that every design makes sense
Well I kinda have to assume that, since they are being used and approved. I am not asking for solutions or anything, just if my numbers are way off. I know those depend on the baseline tests but the heavy differences in what's ok and what's not make me unsure.
Even if you see them at an event, that dosn't mean much. The SES correctors kinda miss a lot, or let teams go with it for a year.
And again, I Just checked. There are fixed values for stiffness and pss. You should try to understand the spreadsheet better, cause you don't.
I'm not trying to be rude, but missing this kinda, stuff can mess up the whole car.
The shear value you need is in C13 of page T3.13 T3.5 Ft Bulkhead. The stiffness is C27, same page. But the formula for the monocoque stiffness is a mess because of T3.13.2