Courtney, believed head size of F35 pilots is of course infinite....
I do detect a head size limitation design parameter here, I am assuming, no doubt erroneously, that all the special display bits that take over the role of the HUD are a one size solution. Looking at various motorcycle helmets in my house, the outside is rather larger for the one worn by the rider with a large head size..... Hence my thoughts that no big heads can be F35 pilots. Could of course be that only big headed pilots need apply as a small headed pilot would have too much liner to pad out the helmet, it would vibrate too much....