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57 Frost frost removal was conducted to determine the need for 33% changes or further approvals to accommodate the use of this procedure. Snow The primary literature and documents that were reviewed 56% and found pertinent to the use of spot deicing are listed below Other (a complete list of documents is contained in Appendix A): ZP 4% 7% Society of Automotive Engineers (SAE) guidelines in Figure 16. Worldwide deicing operations in various Aerospace Recommended Practice (ARP) 4737 and ARP precipitation conditions. 5149 that address procedures for spot deicing for frost removal; document industry regulations and practices related to Holdover time guidance material and documentation pub- spot deicing for frost removal; lished annually by Transport Canada and the FAA; and Conducting phone interviews with deicing service providers Association of European Airlines (AEA) Recommenda- and airlines; tions for De/Anti-Icing of Aircraft on the Ground. Developing a survey to gather pertinent information from a wider audience, including airlines, deicing service Laboratory Tests providers, deicing consultants, deicing instruction facilities, and regulators; Laboratory tests were conducted to collect data to support Designing and conducting tests to examine appropriate the development of guidance material for spot deicing of frost, fluid strength, temperature and quantities for spot frost specifically to provide procedural guidance on fluid strength, deicing applications; fluid temperature at application, and fluid amounts. Identifying if changes to any industry standards, recom- mended practices, or both are required and supporting Background the changes and/or development of guidance material as necessary; Frost can form in local areas on the wing surface by two dif- Developing a cost-benefit model; ferent mechanisms. Developing presentation aids to influence and aid decision The first is the ordinary type of frost that results from radi- makers; and ation cooling of the wing surface under a clear night sky. Not Preparing a technical report to document the work com- all areas on the wing surface cool to the same extent. For exam- pleted for this task. ple, control panels may cool to a lower temperature than the main wing due to their different construction and skin thick- ness. If they cool sufficiently, frost may form on these local Research Approach colder areas while the main wing remains frost-free. As morn- and Methodologies ing approaches, frost generation may cease, however the This section presents the research approach and method- affected areas remain frost covered. This is considered to be ologies employed to examine the current practices and regu- non-active frost. lations, opportunities, limitations, obstacles, and potential A second type of local frost condition is related to cold- benefits associated with the usage of spot deicing for aircraft soaked wings. Wing surface temperatures can be considerably frost removal. Four activities were conducted, and they are below ambient due to contact with cold fuel and/or close prox- addressed herein as follows: imity to large masses of cold-soaked metal in the wing struc- ture. In these areas, frost can build up. If localized frost patches Literature review; still exist at the departure time of the subsequent flight, the Laboratory tests; operator may assume that it is no longer active, and treat it as Focus group survey; and ordinary frost. However, if the fuel is still cold, as might be the Cost-benefit model. case for short aircraft ground-times, then frost generation could still be active. In the spot deicing procedure under examination, a heated Examination of Current Government deicing fluid would be applied only to the frosted areas, some- and Industry Regulations, Guidance times prior to departure. The equipment used for applying Materials, and Standards fluid could vary from portable sprayers, to fluid impreg- A review of current government and industry regulations, nated mops, to standard deicing vehicles. Accordingly, the guidance material, and standards related to spot deicing for fluid quantity and temperature could vary widely. As well, the

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58 interval from time of fluid application to flight departure could was developed prior to testing. This procedure involved filling vary considerably. aluminum boxes with Type I fluid that had been cooled to a Although spot deicing for frost is generally considered to temperature approximately 18F (10C) lower than ambient apply only to non-active frost conditions, its feasibility for temperature. Because the surface of the box was colder than active frost conditions is also of interest. If its application in ambient temperature, frost readily formed. active frost conditions is deficient, then field operators must be The aluminum boxes employed were the same wing-leading- cautioned that an unsafe condition may result from such use. edge thermal equivalent boxes used for measuring heated Because of this concern, test procedures were developed to Type I fluid endurance times in natural snow and for measur- examine spot deicing during both non-active and active frost ing Type I/II/III/IV fluid endurance times in simulated rain on conditions. cold soaked wing. The box upper surface consists of an alu- minum plate of the same dimensions (20 in. 12 in.) as a stan- dard fluid endurance test plate. For testing, the boxes were Objective placed on a test stand, at a 10 slope (Figure 17). The laboratory tests were conducted to collect data to sup- To simulate non-active frost conditions, the filled box was port the development of guidance material for spot deicing of exposed to the laboratory environment for one hour, then frost. The following work elements were planned: emptied of its cold fluid content, and kept open to bring the temperature of the air in the box close to ambient temperature. Examine whether fluid mixed to 18F (10C) fluid freeze The box top-surface temperature thus warmed to match that point buffer is adequate or whether full strength fluid is of the test chamber, and frost stopped accumulating. Simu- required to protect wing surfaces that are colder than out- lated non-active frost testing followed. side air temperature (OAT); To simulate active frost, the filled box was exposed to the Determine the fluid temperature at which fluid should be laboratory environment for one hour. Testing began immedi- ately with the box remaining filled as shown in Figure 18. The applied; ongoing temperature differential between box surface and Determine strength of fluid required at different tempera- ambient continued to generate frost throughout the test. This tures, especially at cold OATs; and test simulated the particular condition where frost is generated Gather data on amounts of fluid required for spot deicing by cold-soaked wings, as opposed to the condition where frost applications. is generated by radiative cooling of wing surfaces. The amount of frost that had accumulated on the test sur- Methodology face at the beginning of the test was determined from a paral- lel set of boxes, which were treated in the same manner as the Initial work to prepare for frost testing in natural frost con- test surfaces. The frost on the parallel boxes was scraped off, ditions was begun in March 2008. The limited outdoor tests collected and weighed as shown in Figure 19. conducted proved inconclusive due to insufficient frost accu- mulation occurring at the end of the 200708 winter. Test Surfaces, Fluids, and Application Techniques. Tests Alternate plans were subsequently made to conduct labora- were conducted on test surfaces that were subjected to both tory tests indoors with frost generated artificially on test plate surfaces. Tests were conducted at the National Research Coun- cil (NRC) Climatic Engineering Facility in Ottawa, Canada, from July 7 to July 10, 2008. In an effort to minimize the finan- cial impact of indoor testing, the tests were conducted at the same time as tests that were being conducted in the facility for a TC project. The advantage of the "pigging-backing" of proj- ects was that the costs for the test facility were shared; the dis- advantage was that the conditions available in the climatic chamber were not always optimal. A complete description of the laboratory test procedure is provided in Appendix B. This procedure is based on the nat- ural frost test procedure and includes the modifications required for indoor laboratory testing. A short description of the procedure is provided in the following subsections. Figure 17. Set-up for leading edge thermal General Methodology for Simulating Non-Active/Active equivalent boxes on test stands at NRC climatic Frost. A procedure to develop frost in laboratory conditions engineering facility.

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59 Figure 18. Active and non-active frost simulation Figure 20. Spray method for fluid application on a method. test plate surface. non-active and active frost conditions at various ambient applied according to the conventional test method with the use temperatures, including: -13F (-25C), 6.8F (-14C), 14F of a fluid spreader as shown in Figure 21. (-10C), 26.6F (-3C), and 33.8F (+1C). Type I Propylene Glycol (PG) fluid prepared at Standard Mix Equipment, Personnel, and Data Forms (63% glycol) and at a fluid freeze point buffer of 18F (10C) was used for these tests. Fluids were tested either heated to 86F The test procedure (see Appendix B) provides the detailed (30C) or cooled to the chamber's ambient test temperature. equipment and personnel required for testing. The procedure The selection of the 86F (30C) fluid temperature for the also includes copies of the data forms that were used. The data heated fluid tests was based on previous field tests on aircraft forms were used to record frost accretion, fluid strength, tem- that measured the actual at-wing fluid temperature for frost perature, and fluid endurance times. deicing sprays when the fluid temperature at the spray nozzle was 140F (60C). These tests showed a considerable drop in Tests Conducted fluid temperature between the spray nozzle and wing surface for the typical fan-shaped spray patterns used for defrosting. Eight sets of tests were conducted producing a total of A fluid application method was developed to represent the 75 individual tests. The test variables are described below. manner in which fluid is applied from a deicer spray nozzle in the field. The method consisted of spraying the fluid from a 1. Quantity of fluid used per test: 0.003 US gal (10 mL), standard push-spray bottle as shown in Figure 20. In addition, 0.005 US gal (20 mL), 0.011 US gal (40 mL), 0.021 US gal each test set included one test where the Type I heated fluid was (80 mL), and 0.042 US gal (160 mL); Figure 19. Scraping frost off test plate surface to Figure 21. Standard method for fluid application on measure rate. a test plate surface.

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60 Figure 22. Fluid brix measurements taken from Figure 23. Surface temperature measurements taken 6-inch line on test plate surface. from 6-inch line on test plate surface. 2. Fluid strength: 18F (10C) buffer or standard mix Two "baseline" tests were designated for each test set: (63% glycol); 3. Fluid temperature: 86F (30C) or ambient; 1. 0.1321 U.S. gal (500 mL) of fluid prepared at 18F (10C) 4. Method of fluid application, sprayed or standard buffer, poured at 68F (20C) with a spreader; and application; 2. 0.011 U.S. gal (40 mL) of fluid prepared at 18F (10C) 5. Ambient temperature of test chamber: -13F (-25C), 6.8F buffer, applied at 86F (30C) with a sprayer. (-14C), 14F (-10C), 26.6F (-3C) and 33.8F (+1C); 6. Active or non-active frost condition; and Baseline Test #1 was similar to the procedure used in hold- 7. Fluid strength and test plate surface temperatures: recorded over time testing in active frost conditions except the frost was progressively at 1 min, 5 min, 15 min, 30 min, 45 min, not removed from the test surface prior to fluid application. 60 min, 90 min, and 120 min after application as show in Baseline Test #2 was a baseline test for spot deicing, and Figure 22 and Figure 23. was based on results from preliminary tests conducted dur- ing outdoor active frost conditions. Test variables for the remaining tests were changed or modified in reference to Test Plan this baseline test. Table 38 presents the test plan used for each set of tests. Fluid The objective of all tests was to remove the frost accumulated strength was mixed to either an 18F (10C) below ambient on the test surfaces by spraying fluid at various strengths, temperature fluid freeze point buffer or at the standard fluid amounts, and temperatures. Success was indicated by complete mix as delivered. Eight sets of tests were conducted at a range frost removal without early freezing of the applied fluid. Fluid of temperatures as shown in Table 39. endurance time was also measured for tests in active frost. Table 38. Spot deicing test plan. 1 2 TEST # HOT spot 3 4 5 6 7 8 9 10 11 12 baseline baseline Plate # 1 2 3 4 5 6 7 8 9 10 11 12 Fluid Qty. (mL) 500 40 40 40 40 10 20 80 160 40 40 40 10 10 std. 10 std. 10 10 10 10 10 10 Fluid Strength std. mix buffer buffer mix buffer mix buffer buffer buffer buffer buffer buffer Fluid Temp. 20C 30C 30C OAT OAT 30C 30C 30C 30C 30C 30C OAT (C) non- non- non- Frost Event Type active active active active active active active active active active active active Method of Fluid pour w/ spray spray spray spray spray spray spray spray spray spray spray App. spreader