XFLRR5

XFLRR5 is an open sourced subsonic aerodynamic design and analysis software. It's been a trusted design software both among amateurs and professionals alike. It's the perfect software for designing your own fixed wing UAV platforms. The best part is, it's completely free and open sourced.

XFLR5

techwinder has a great series on the introduction and basics of using XFLRR5. It does have a steeper learning curve than most other software programs, but it's well worth the time.

XFLRR5 is based off of Xfoil, the original subsonic airfoil analysis software. In case you're interested, it is still available:

https://web.mit.edu/drela/Public/web/xfoil/