What you have done is compute the thickness required based on the average shear stress. That gets you in the ballpark. But the shear stress is not distributed uniformly across the height of the shear web. The distribution depends on the shape of the beam.That gives us 5.639mm - the thickness of the ply required. It is so simple now.
what exactly do you predict?I predict that the wing will fail in testing at a rib to either side of the strut attachment, where maximum bending is encountered.
Sorry, Duncan, I just edited the post and removed that part--maybe take another look. I do still think it's correct that somewhere around the strut would be the location of the failure because it has the most bending and shear--but I want to analyze the slot areas for bending. What is your wingspan? Also, am I correct that this wing is only supporting 40% of the plane's weight? Don't scrap it just yet!Aaargh!
OK, I have more foam, so I'm going to cut two-piece ribs and cut a continuous shear web. BUGGER! This will be the 5th set of ribs I'm cutting...
When you say:
what exactly do you predict?
Hi Duncan,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.
You can mostly tell who took drafting before computers changed the industry by this skill alone.
Hand work like that takes me at least 3 iterations to make it readable for others. Generally two even if it is just me that needs to look at it next week.
Love my Excel.............
Actually................You can mostly tell who took drafting before computers changed the industry by this skill alone.
I am on the cusp for this so I understand. I took my first drafting/drafted descriptive geometry courses before computers entered the classroom. BUT I have essentially never formed a written idea outside a computer since I got my Apple II (with wordstar and visicalc) in 5th grade. My thought processes thus work best with infinite editing ability.Actually................
I started drafting when I was pre-teen. My grandfather was a very good architect and I too was/am pretty good at the paper, pencil and triangle drafting.
My problem is poor work flow planning for a small detail project like this - which I find kind of odd because I can visualize a building, or a plane, with all of it's subsystems and see how they relate and interact with the people that use them.
Excel is just a nice neat crutch. My paper versions tend to suffer from eraser abrasion fatigue.