At the request of the Department of National Defence, Air Service, static load tests were conducted on two Harvard II starboard mainplanes in the High Angle of Attack and Centre of Pressure Back conditions. The object of these test was to observe the conditions in which wrinkling occurred in the upper skin of the mainplane and the nature and permanence of the wrinkles. For purposes of comparison, the tests were conducted on two wings, one new and one which it was suspected had been overloaded in flight manoeuvres. It is concluded from these tests that the wrinkling phenomena in both wings is normal for a stressed skin structure and that the wings comply with current airworthiness requirements for the conditions examined.
National Research Council of Canada. Division of Mechanical Engineering