4.* t\r, SUMMARY Cf A STUDY Of TEMPERATURES ATTAINED IN A DUMMY AIRGRAF1 WING DURING THE SUMMER AT MADISON, WISCONSIN January 1943 ■ affecting RESTRICTED CLASSIFIED DOCUMENT This document contains classified i^m|UU affecting the National Defense of the I' n^A tMJj'^ witn 'n the meaning of the Espionage^Ju, SWB.Jft^l and 32. Its transmission or the j*wPfcB$» of* its contents in any manner to an uruj^Knoidp person is prohibited by law. Information^ jrfk^fcswn^cPmay be imparted only to per- sons in^^ tfrflB^JPf and naval Services of the United StaiAiDfcwj^rTOte civilian officers and employees of ^HrafeSpd Government who have a legitimate interest ■rajsllf and to United States Citizens of known loyalty and discretion who of necessity must be informed thereof. THIS REPORT IS ONE Of A SERIES ISSUED TO AID THE NATION'S WAR PROGRAM No. 1343 -A u,, UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wisconsin summary of a study 0? tz:. -^:..-~3 attai15d i1c a t AIRCRAFT V/I.. - .'..I. ■ I - Z'.^-ZuR at MADibQi:. y:s:. :: - By F. L. BROWIJE, Princ4pal Chemist DOi: LAUGHKAH, Associate Technologist BRUCE r,. HEEBIlOv, Associate Technologist HERBERT 0. FLEISCHER, Junior Forest Products Technologist The material herewith presented comprises a summary of the principal results of a more extensive report issued by the Forest Products Laboratory as Mimeogr fo, 13435. Reference should be made to the extensive report for details of test procedure and results. Because of the poor ventilation of the enclosed air spaces and the dark camouflage paints with which military aircraft are painted, seme - t - work "becomes heated to temperatures far above those cf the surrounding air when the craft are on the ground in bright sunshine. The e. nts dis- cussed here vere made ts give an indication cf the magnitude cf the tempera- tures that may be attained and some of their consequent effects or. the mois- ture content of the woodwork. Phases of the study included (l) the effect of r upon internal wing t : tures; (2) the effect of temper.- tures upon the glue usee, to c: struct lywood; (3) the relation between temperature and moisture c I of the wing interior; and (<*) the effect of the reflective power of differ- finishes upon the internal temperatures attained. 1. — Dummy aircraft wings consisting of wood framework ooverea 3/32-inch aircraft plywood were constructed and exposed at Medisc. such a way as to permit the sun to shine directly on 1 or surfaces. Thermocouples suitably olaced permitted readings cf the tern] -ratures reached at various times throughout the daylight hours during July and August, 1942. When exterior surfaces vere finished Leal olive drab camoufla h is one cf a series of ass reverts issued a Pore Products Laboratory to further the • r effor - . suits here . ted are preliminary and may be revised as additional dat; available. Mimeo. So. 1343 A -1- finishing system, it was f«und that the upper painted surface and the #uter glue line in the plywood sometimes reached 180° F. or slightly more at times when the temperature of the outside air was no higher than 85° F. The tem- perature of the air proved to be a much less important factor than the angle of incidence of the sun's rays, which changes with the time of day and the season of the year, the velocity of the wind, cr the presence or absence of clouds to dull the sun's rays. As a rule, maximum surface and glue-line tem- peratures occurred when the sun reached meridian, although the maximum out- side air temperature might not be reached for another hour or two, by which time the surface and glue line had begun to cool off noticeably. Mere pas- sage of a cloud over the sun promptly cooled both surface and glue line, although the air temperature remained essentially unchanged. Windy days never produced surface and glue-line temperatures as high as those observed when there was little rr no wind, even though the windy days were often fully as warm as the still days. Temperatures in the enclosed air spaces within the dummy wings followed not far behind those at the upper surface, reaching temperatures as high as 170° F. when the outside temperature was 90° F. Glue lines in the plywood on the bottom tf the dummy wing reached temperatures as high as 135° F, Presumably still higher temperatures are attainable in other parts of the world where the intensity of' sunlight is greater than it is at Madison, Wis. Even at wadison, higher temperatures might have been tbserved if the tests had been started by the middle of June, when the sun reaches its maximum angle. 2. — The temperatures reached in the glue lines »f the upper plyw%cd under the conditions of the test apparently were high enough to soften the thermoplastic glue used, because opening of joints and delamination attribut- able tc "creep" of the glue were observed, TT, nere thermosetting phenolic- resin glue was used in making the plywood a few slight cracks developed at joints, but there was no evidence of "creep" ^r delamination. 3. — To study changes in moisture content in woodwork within the dummy wing resulting from the marked rises in temperature during sunny days, two spruce specimens representative *f small braces in ribs were inserted in one • f the air spaces in such manner as to permit quick removal fjir weighing an'.~» reinsertion, One specimen was left unfinished and the other was protected with a very generous coating of a typical aircraft sealer. Starting with the specimens in the oven-dry condition, it was found that the unfinished specimen came tc approximate equilibrium with the environment within 2 days but the finished specimen required approximately one week. Subsequently, the unfin- ished specimen fluctuated in moisture content as much as 1.3 percent within a single day, whereas the finished specimen experienced daily fluctuations of at mere than Q.6 percent. During August the unfinished specimen fluctuated between 7.6 and 5.4 percent, the finished specimen between 6„ 8 and 5,7 percent moisture content. For both specimens, the over-all average moisture conte:.' for the mid-summer season seemed to be abcut the same, roughly 6.5 percent. For the period under crnsiderati#n, the spread from maximum t» minimum mois- ture content was 2.2 percent for the unfinished and 1,1 percent for the fin- ished specimen. In stretches ^f bright, sunny days, the finished specimen Mimeo. No. 1343A -2- usually contained more moisture, and in stretches of cloudy days it contained BS moisture than the unfinished specimen. (Although this report is concerned with the summer season only, the observations have "been continued. With the passing cf summer weather, both specimens slowly increased in moisture content until by the middle of December they attained approximately 15 percent moisture content. ) . — Experiments were made in a second dummy wing, in which the neigh- boring sections between ribs were finished With exterior paints differing in ^r and reflective power for infrared radiation. It was I surface, glue-line, and interior air space temperatures were developed, - e infrared reflectance of the paint. Highest temperatures were i under a blue camouflage paint cf 5 percent reflectance, and lowest temperatures were recorded with a glossy yellow enamel of 80 percent reflc ance. The order of difference in temperature at 1:3C p.m. en August 28, w.\ the outside temperature was 90° J . , is indicated in the following table: Variations in temperature with different finishes Teupert ture in degrees F, Bection paintc 1 — Loci * ion of ilue cam- ^live drab : Olive drab : RLossy ;'ellcw thermocouple ouflage camouflage : camouflage : enamel cf 80 paint of 5 paint of : paint cf : perce percent 10 perc< : 50 perce. reflectance reflectance: reflect- ance : reflect- ' ance Glue line in upper 157 i plywood Glue line between oor plywood and rib cap 159 156 145 136 El closed air s^ace 146 138 133 129 Glue line between : lower plywood ! rib cap 128 123 r 12C 116 . Figure l.--The dummy wing partly assembled, showing some of the wiring for the thermocouples. 115170 p UNIVERSITY OF FLORIDA i nun ii in 1 1 3 1262 08925 4352