Show heat and cold aid in giving planes strength new boik two ies dry ice fee and electric furnaces can be thanked for the ibe tremendous strength which has bag been built into the modern airplane says a bulletin of united air lines commemorating comme on features of construction st in the GO CO three mile a minute multi motored hoeing boeing planes it now has on its routes these are the first high speed all metal transports eer built by taking klets from a 1 degree heat treating bath to sub freezing temperatures pera tures of dry ice containers the nging aging of rivets Is definitely retarded by heat treating metal the tensile strength Is more than doubled dura irminus being raised from the normal strength of pounds per square inch to approximately pounds per square inch the steel used in the landing gear of the planes has a tremendous tensile strength of pounds per square inch because of heat treating and the landing gear can withstand nn an emergency impact of 32 tons |