 similar law stress heat wing similar law stress heat wing differenti equat heat plate larg temperatur gradient plate constant temperatur proper modif thick load isotherm plate fact lead result stress heat plate calcul measur strain unheat plate seri relat call similar law applic analog theori solid wing aerodynam heat discuss detail load unheat analog wing complic involv novel concept feedback bodi forc load problem stress heat box-wing structur solv analog method discuss 