I get FEA of panels (FEA works...) , two parallel edges simply supported, two alternate edges not restrained (infinite length case). Reporting deflection at center of panel and a reserve factor based on ? I still can not tell. Tsai and Wu failure criteria cited has safe designs when criteria is less than unity. The makeup of the Reserve Factor is still not clear. Is it the inverse of a failure criteria?

The lack of reserve strength in some of the cases indicates that inflation alone will cause disqualification of some schemes.

I also still do not get the notation of loading in "kg per m^2 x 6" what is the "x 6" about? kg/m^2 seems quite complete to me.

Comments on the modeling and its impact:

FEA works when it is applied like the real system it is modeling;

The skin loadings as represented here are due to moving air outside and stationary air inside, not wing loading. Wing loading is the difference between the skin loading on the top vs the on the bottom. In fast airplanes, you can have very high skin loadings even at low lift, while in low speed airplanes, skin loadings are small.

Leaving two edges free is the case of the panel being infinitely long. According to Roark's Table 11.4 Case 1a (simply supported on all four edges), the infinitely long panel has 2.6 times the max stress of the square panel and the deflection is 3.2 times the deflection of a square panel. Stresses and deflections of real panels will be substantially smaller than for the illustrated panels.

Simply supported edges - where they are supported against translation, but not against rotation - might be appropriate in a case where torsionally soft members support a panel that ends at the supports. In composite wings this case will be present at the ends of each wing panel or where an access panel is attached. Where the skin is continuous across the supporting members, the fixed edges (Table 11.4 Case 8a) peak stresses and deflections similarly improve with transition from infinitely long panels to more nominal proportions, with max stresses being only slightly higher...

Then using curved panels shows further reductions in panel deflections and stresses.

In total, it appears that Stanislavz has picked the most severe cases to study, and should be secure, if somewhat overbuilt, using this method for sizing. Being as we have other loading issues to deal with besides inflation, it is good to have significant reserve strength under these issues.

Billski