Well, I'm getting closer. I've increased my MAUW to account for the many unexpected weight additions as the build progresses, and have now factored in wing loading, but still working with a cantilever scenario. I figure that if my results work for a cantilever wing, they will certainly work for a strutted one. Here's where I am at present.
View attachment 110425
If this is correct, then my 3mm shear webs are going to be fine, and I'm never going to stress the wings to 6 g's in a Flea anyway.
As for the 30mm gaps in the shear webs, won't the main stresses in the spar caps be almost purely in tension and compression? And they're capable of withstanding over two and a half thousand kg in tension/compression. Anyway, I'm going to finish the rear wing as is I think, and am thinking of a continuous shear web for the more heavily loaded front wing.
Duncan
Hi Duncan,
Here is a start on some calculations for the rear spar. Unfortunately I started before I saw the above post and I used 30% for the rear spar as you mentioned earlier. Nevertheless, I hope this will be of some value to you and others for the process if nothing else. I used a sort of graphical method to generate the shear and moment diagrams--they're not super precise but pretty close. Please beware that it is entirely probable that I have made errors and I would invite others who know what they're doing to offer their scrutiny. You will see on the first page (image below) that I have made some assumptions about the spar layout--it's probably not exactly the design you have. My drawing is not a suggestion--only a guess, but it is probably close enough as a first pass that could be cleaned up to dial in the precision. Sorry for the imperial units, but Bruhn and ANC and the FPL literature and charts use them and I'm more confident translating the basic dimensions at the start than trying to adjust all the literature into metric.
These pages deal with the basic scenario of a continuous shear web--the calculations for the rib slots will need to come after this. I have not yet checked the glue line shear strength, combined bending and axial stresses, or other load cases such as asymmetrical lift or the loads you get when the control surfaces (i.e. the entire wing panels) are deflected, which would need to be a part of a more complete analysis.
In this base case (cont. web, 30% weight on rear wing), it looks good so far (if not overdesigned). My guess is that increasing to 40% will erode the bending margin somewhat (current M.S. > 2) and that more shear strength may be needed (current M.S ~0.5). Of course the front wing will be a different animal, carrying more load and having a larger span.
I want to stress again (no pun intended) that the figures above in post #434 for web thickness are based on
average shear stress for a cantilever (not strut-braced) wing, and do not account for the
actual maximum stress, which is higher (but tempered by the fact that it's a strut-based design). You can see how this works in the attached file.
Yes, where the caps bridge the gaps, they will be in tension/compression due to the bending imposed from the portion of the wing outboard of the gap, but they will also have shear stress (and the axial stress imposed by the strut reaction needs to be added in as well).
I will see what I can do tomorrow night as time allows.
EDIT: I just saw that I made a dreadful mistake at the outset. I imposed the entire rear wing lift on just one wing panel. $%@!!! At least it means your wing is stronger than my calculations show. I believe the process is correct for demonstration purposes, but I'll need to correct this (I'll probably make a spreadsheet so that adjustments can be made more easily than this manual method, but it won't show all the steps).