I will have a total of 7 ribs by wings,all compression ribs from 3/4" to 7/8" thick .The thickness of each spruce spars is 11/16" .
As Boku said,i am wonderind about the shear from the skin into the spars...and the skin will be very thin,around 5/32" .
BJC. Standard S1SS airfoils,spruce spars with pultruded carbon caps,Compression ribs with spruce capstrips ans carbon skin.The goal,better tortional strength to handle the bigger ailerons and get a better roll rate..above 360° per seconde espected.
Billsky .I did start to have a look at the PVC and Rohacell core....Of course,i could to the skin in one step using them and the infusion method ...and there is more area glued from the carbon to the core compared to the Nomex Honeycomb...May be using a thinner core,let say 2 mms and a thicker outer layer of carbon will be better.
RSD. I had a look to that video ,thank you
I am having a difficult time with this. It sounds like you are building a pretty much standard Pitts wing with a few adjustments - wood spars with a little carbon reinforcement, only a slight reduction in the number of ribs, and compression ribs? Are you trying to build a stronger wing by adding some carbon to the spars and ribs, then put on carbon fiber skins? This may get you stronger than the stock wing, but it will not take weight out. I expect it will gain weight...
Then there is the little issue of load is distributed according to the stiffness of the pieces. A wooden beam (spars and ribs are beams) with some of its most effective area (near the top and bottom) routed away and replaced with graphite fiber becomes a graphite cap beam with a wood core. Wood is heavy compared to a graphite web laminated on both sides of a foam core. Yeah, you will have to replace foam with plywood or phenolic at the places where struts and the like mount and add a couple plies to the laminates there too, but this is still way lighter than the wooden spar with graphite reinforcements.
In composite structures, many of us abhor what we call "aluminum thinking". That is where you design a composite structure as it it were sheetmetal. It makes for heavy, difficult to build structures. Much better to start with what the structure has to carry load wise and scheme out an efficient composite structure.
In the case of swapping the stock Pitts wings for new set of graphite wings, this drives a few constraints - The attachment points for hanging the wings and struts and flying wires need to be in the same places, which drives the spars to the same places. There will be openings in the skins for the various attachments, so you add a couple plies locally around the openings. You will have to add some access panels for inspection and assembly/diassembly.
Now for how I would design those wings.
The spars would go from wood to extruded graphite rod caps and graphite webs with foam web cores. Even designing the spar and skin set (together) to 24 g you will save substantial weight over the standard spruce spar with some graphite rods inlet into the spruce.
The wing skins will be structural - they will contribute to bending stiffness and strength and will provide most of the torsional stiffness too, so why not include those contributions and do the calcs with that in mind? You can do some optimizing trading wing core thickness against number of ribs. You likely omit a bunch of ribs. There is math to be done to check that the skins are OK with large rib spacing to make sure, but once you get stiff skins, most of that internal stuff can go away.
Compression ribs? What for? Once you have a stiffer spar and structural skinset, you wing is set. Compression ribs are there in a fabric covered wings to keep the spars apart and the wing stiff against wracking and torsion. You now have structural skins that do all that, so the cross brace wires and their mounts and the compression ribs are superfluous. Gone with them...
Once you have graphite sandwich wing skins that will stand the aero loads, graphite sparset/skinset that will stand the bending and shear and torsion, and ailerons hung, you may find you have raised your max g and lowered your weights. Then you can run the numbers with similar outer facings on a massive core wing with built-up sparset internal to the massive foam and see if that saves you some more weight.
By going with either of these options, I suspect you will add a lot of strength and stiffness while taking some real weight and roll-axis inertia out of the plane.
But to keep the sparset, most of the ribs including the compression ribs and then hope to not add too much wieght in the skins, well it seems like immense effort to buy a weight gain...
Billski