26" wheels won't fit even if it's square, i think? 26"+26"=52, leaving 10" for depth... but the wheels have to have the axles next to each other or nothing else will fit.
We appear to have two diverging lines of discussion. I agree Jur, that it is highly unlikely that a large wheel, folding bike would fit in a “legal” suitcase. However, the comment about the wheels is off point. My S&S coupled (not folding) 29er fits in a 26” x 26” x 10’ hard case. It is necessary to deflate the tires, but removal from the rims is not necessary. They nest side by side with the two frame parts intermingled. And there is room for a helmet.