(NACA-TN-3781, 1957) is the best available reference (again) and gives a simple rational method for how to account for the presence of cladding.
![](https://www.abbottaerospace.com/wp-content/uploads/2019/08/60.png)
![](https://www.abbottaerospace.com/wp-content/uploads/2019/04/DOCUMENT-e1572009841677.png)
The reducing in buckling due to the presence of cladding depends on two ratios:
![](https://www.abbottaerospace.com/wp-content/uploads/2019/08/61.png)
For different loading conditions and stress level the following terms apply.
![](https://www.abbottaerospace.com/wp-content/uploads/2019/08/62.png)
![](https://www.abbottaerospace.com/wp-content/uploads/2019/08/63.png)
![](https://www.abbottaerospace.com/wp-content/uploads/2019/04/DOCUMENT-e1572009841677.png)
![](https://www.abbottaerospace.com/wp-content/uploads/2019/08/64.png)
![](https://www.abbottaerospace.com/wp-content/uploads/2019/04/DOCUMENT-e1572009841677.png)
This method is available in this spreadsheet:
Note that in some circumstances, particularly for panels with low buckling allowables, a cladding reduction factor of greater than 1.00 can occur. In this circumstance a maximum value of 1.00 should be used.