NACA-ARR

Abstract

<strong>INTRODUCTION</strong> <br>The Shear webs employed in aircraft structures are frequently perforated with regularly spaced holes to lighten the web or to provide access to the interior of the structure. Round holes with flanges edges were used in airship girders before the metal monocoque structure came into general use for airplanes, and they continue to be the most common type of lightening hole. <br>The problem of computing the strength of a web with lightening holes by theoretical means offers formidable mathematical difficulties. There appears to be no published record of any attempt at a purely theoretical solution, the nearest approach being a general, but extremely laborious, method of computing the stresses in a web with plain holes. It has been necessary, therefore, to rely on tests for proving the strength of perforated webs. Individual tests are sufficient for the immediate purpose of proving the strength of a given design, but they furnish no information on the optimum design proportions. A sufficiently extensive series of systematic tests would furnish information on the optimum design proportions and would eliminate the need for many individual tests. Unfortunately, so many parameters are involved that a very large number of specimens would be necessary to cover the range of proportions; this obvious fact has acted as an effective deterrent for many years. <br>A fairly extensive series of tests was published by Schussler (reference 1), but his results have not been fully accepted by aeronautical engineers. A number of aircraft manufactures have been interested for some time in obtaining additional data; it was finally agreed that these manufacturers would furnish the test specimens and the NACA would do the testing. Each manufacturer was to use his standard dies for flanging but to provide a sufficient number of specimens to cover the range of variables as far as practicable. The specimens tested in the present investigation were furnished by the Bell Aircraft Corporation. Special acknowledgment is due this company for their willingness to cooperate by making a large number of test specimens at a time when unprecedented demands are being made on all production facilities. <br>The extensive test work involved was performed by Mr. S. H. Diskin of the NACA staff.