ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR PROGRESS REPORT NO. 19 A STUDY OF SPECIAL AND UNUSUAL CONDITIONS AFFECTING HIGH-SPEED AIRCRAFT AND MISSILES By, HE F. ALLEN Project M888 AIR RESEARCH AND DEVELOPMENT COMMAND, U. S. AIR FORCE CONTRACT AF 33 (08)-12235 November 1953

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN PROGRESS REPORT NO. 19 A STUDY OF SPECIAL AND UNUSUAL CONDITIONS AFFECTING HIGH-SPEED AIRCRAFT AND MISSILES PURPOSE This project covers theoretical analyses and laboratory tests to determine the type of tests necessary to substantiate the structural integrity of aircraft operating under elevated temperature conditions and to investigate methods of heating and load application. STATUS An AT-6 fin was subjected to light loads at 600~F for a period of 12 days. The eventual failure was similar to the room-temperature failure. A creep test of the deflection wires was carried out to determine if corrections were required in the long-duration tests. Two fins were tested to destruction at 500~F and 7000F respectively. THEORETICAL PHASE The write-up of the final report is continuing. ------------------------ 1

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN EXPERIENJTAL PHASE The first fin which was tested to destruction at 500F did not give representative results, as the loading system failed repeatedly, diue to the fact that rivnuts with improper grip lengths were inadvertently used at the load application joints, Consequently the test was repeated at a later date, using a different fin, Another fin was tested to destruction at 700'FX A steady-load test was carried out at 600~F in which the initial load corresponded to a stress of 2000 psi at the root. This load was applied for a period of 11 day and then removed to check recovery, which was negligible aside from elastic recovery,, The load was then doubled, and the fin failed after 1 additional day, The appearance of the fin during the test was observed periodically through the opening in the side of the oven, The first evidence of buckling at the point of failure appeared about 18 hours before failure, and, at the same time, the deflection began to increase more rapidly, Figure 1 is a photograph of the fin taken through the opening in the oven 4 hours before failure, and shows the wrinkles in the spar web and flange at the point of failure, and in the spar flange and compression skin in the area near the failure Figure 2 shows the same portion of the fin after failure. Fairly heavy weights are required on the ends of the deflection wires in order to coueteract the friction in the dial gages: Consequently, test was carried out to determine the amount of creep which takes place in the heated portion of the deflection wires This proved to be appreciable, and the measured deflections can be corrected accordingly, The fin deflectin are also corrected for jig deflection and rotation. The gheduled tests of AT-6 fins have been completed, and the remainder of the contract period will be used for data reduction and preparation of the final report, ----------------------.___ —--------------------— ___

Fig. 1. Appearance of AT-6 fin prior to failure at 6000F. Fig. 2. Appearance of AT-6 fin after failure at 600~F.

UNIVERSITY OF MICHIGAN 3 9015 02493 0219