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7-4 X X X X X X X XX XXXX XXXXXX X X X X X X X X XX Y Y Y Y Y Y Y YYYYYYYYYYYYYYY Y Y Y Y Y Y Y Z Z Z Z Z Z ZZ ZZZZ ZZZ ZZZZZ Z Z Z Z Z Z Z Z Z A A A A A A A A A A A A AA AA A A A A A AAA A A A A A A A A A A A A A C C C C C C C CC CC CCCCCCCCCC C C C C C C C C D D D D D D D D D D DD DDD D DDDDD D D D DD D D DDD D D D D D D Angle (deg) SPL (dBA) 0 10 20 30 40 50 60 70 8090100 110 120 130 140 150 160 170 180 -20-20 -10-10 00 1010 BACK FRONT A319 A320 A310 A340 B717 B737A B737B B747 B757 B767 B777 CRJ DC-9 X Y Z A C D FIGURE 7-3 Directivities of US Fleet jets with curve fits of their weighted average. The directivity adjustment for taxiing jet aircraft, DIRTXJ (in decibels), is computed as a function of azimuth angle and provided as Equations 7-1 (forward directivity) and 7-2 (aft directivity). For Jet aircraft, the forward directivity as a function of ï± between 0o and 90o is: )00000002996.0( )0000017203.0()0051454.0()19853.0(4325.5 4 32 ï± ï±ï±ï± ï ï«ïïïïïï«ï½TXJDIR Eq. 7-1 For Jet aircraft, the aft directivity as a function of ï± between 90o and 180o is: )60000004231.0( )00025536.0()051706.0()2362.4(73.120 4 32 ï± ï±ï±ï± ï ï«ïïïï«ïïï½TXJDIR Eq. 7-2 The coefficients of determination and standard error of the estimate for the curve fit between 0o and 90o are 0.997 and 0.15 dBA, respectively. The coefficients of determination and standard error of the estimate for the curve fit between 90o and 180o are 0.998 and 0.21 dBA, respectively. It is important to note that the curve fit and associated statistics refer to how the fit matches the average of the weighted directivities, and not how well the curve fit matches the data from which the average directivity was derived. The resulting directivity pattern represents the U.S. fleet mix average for taxiing jet aircraft. 7.2. Turboprop Aircraft To find a directivity pattern for taxiing turboprops, the same data set used for finding the US fleet mix above was analyzed for propeller aircraft. Of the aircraft for which there are measured directivity patterns, it was found that four aircraft accounted for 57% of the fleet mix. Table 7-3 contains a list of those aircraft. The procedure for finding a curve fit to the directivities was similar to that used for the turbofans above; however, the directivity patterns for three of the four empirical prop aircraft come from
7-5 the Madrid data set. As was shown in Figure 7-1, the Madrid data set does not have information in the front or rear of the aircraft; thus, there is only data for angles from 20 to 160 degrees. NOISEFILE data was obtained from static measurements and includes acoustic directivity measurement data directly behind and in front of the aircraft. Table 7-3 Fleet Mix Used as Weightings for Taxiing Turboprops Aircraft Number of ops % of Total Fleet Normalized Weighting (%) ATR 72 946650 16% 29% Beech 1900 697613 16% 22% DHC 8 1354843 22% 42% Fokker 50 237242 4% 7% A fifth order polynomial was fitted to the weighted directivity patterns for the aircraft in Table 7-3 from 20 degrees to 160 degrees. The polynomial was then extended forward to 0 degrees and aft to 180 degrees. This extended fit was compared with the empirical NOISEFILE data in these regions. Figure 7-4 contains a polar plot of the resulting curve fit based upon a weighted average of the four US fleet mix aircraft, the Madrid propeller aircraft directivity, and all of the propeller aircraft from NOISEFILE (Military aircraft in NOISEFILE do not appear in the US fleet mix used to generate the final INM/AEDT propeller directivity equations, however they were examined in order to evaluate general propeller directivity shapes). The fifth order polynomial was chosen because it agreed best with the directivity patterns of the propeller aircraft in NOISEFILE. X X X X X X X X X X X X XX XXX XXXXXXXX X X X X X X X X X X X X Y Y Y Y Y Y Y Y Y Y Y Y YY YYYY YYYYY YY Y Y Y Y Y Y Y Y Y Y Y Y Z Z Z Z Z Z Z Z Z Z Z Z Z Z ZZ ZZZZZ Z ZZZZ Z Z Z Z Z Z Z Z Z Z Z C C C C C C C C C C C C CCCCC C C CCCC C C C C C C C C C C C C C D D D D D D D D D D DDD D DDDDDDDDD D D D D D D D D D D D D D D A A A A A A A A A A A A A A AA AA AAA A A A A A A A A A A A A A A A O O O O O O O O O O OOO OO OO OO O OOOOOO O O O O O O O O O O O P P P P P P P P P P P P PP PPPP PPPPP PP P P P P P P P P P P P P T T T T T T T T T T T TT TT T TT TTTT TTT T T T T T T T T T T T T H H H H H H H HH HHHHHHHHHHHH H H H H H H H H F F F F F F F FF FFF FFF FFFF F F F F F F F F F F R R R R R R R RR RRRRR RRRRR R R R R R R R R R R Angle (deg) SPL (dBA) 0 10 20 30 40 50 60 70 8090100 110 120 130 140 150 160 170 180 -20-20 -10-10 00 1010 CurveFit AC123K BEECH1900 C118 C119L C121 C130AD C130E C130HNP C131B C7A KC97L OV10A JPATS P3A T29 U4B DHC8Q001 FOK50001 ATR72001 X Y Z C D A O P T H F R FIGURE 7-4 Directivities of NOISEFILE Turboprops compared with the curve fit of the US fleet-weighted average.
