Boelter, L. M. K.; Martinelli, R. C.; Romie, F. E. & Morrin, E. H. An Investigation of Aircraft Heaters 18: A Design Manual for Exhaust Gas and Air Heat Exchangers, report, August 1945; (https://digital.library.unt.edu/ark:/67531/metadc279599/m1/1/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, digital.library.unt.edu; .