Integrated Noise Model Accuracy for General Aviation Aircraft (2014) / Chapter Skim
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Pages 52-60
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From page 52... ...
8 Potential Solutions As shown in Sections 4 through 7, the INM standard departure profiles for GA jet aircraft produce discrepancies in noise levels and have steeper ascents than those observed for actual operations. The general cause for these discrepancies is the use of maximum thrust departures as standard INM input.
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From page 53... ...
Both of these processes were evaluated using the GIV and Lear35 INM types and used as a check on the validity of each method when compared to the measured results and radar profile data described in the earlier part of this report, Sections 4 through 7. The ATM2 method was also used to evaluate the CNA560E INM type and compared to radar data.
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From page 54... ...
Figure 30 CNA560E departure altitudes: all radar data, ATM2 profile and polynomial fit 8.2.1 Using Specific Profile Definitions from Operator and Manufacturer Surveys (ATM1 profiles) This method for introducing reduced thrust for an INM aircraft departure involves changing the thrust coefficient given in INM "Thrust Jet"30 database where, as described in INM 7.0 User's Guide Section 9.11, the thrust for a given jet engine is described as: Equation 1 INM Thrust Jet πΉπ πΏ = πΈ + πΉππ + πΊππ΄ + πΊππ΄2 + π»π Where: β’ πΉπ is the Net thrust per engine in pounds; β’ πΏ is the ratio of the atmospheric pressure to sea-level standard pressure; β’ E is the coefficient equal to the static net corrected engine thrust at sea level pressure; β’ F is the airspeed correction coefficient; β’ πΊπ and πΊπ are altitude correction coefficients; and β’ H is temperature correction coefficient.
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From page 55... ...
Adjustments to the speed coefficients (πΊπ , πΊπ ) in theory are also required; however a new regression analysis using complete performance data for aircraft flying ATM profiles would be required to derive these speed coefficients and is outside of scope of this project.
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From page 56... ...
Completion of ATM1 for GIV To complete development of ATM1, the appropriate cutback thrust and associated altitude for the change to climb thrust was required. Standard INM GIV procedure profiles have a significant thrust cutback around 400 ft.
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From page 57... ...
determine the corresponding thrust level. We accepted this reduced thrust level as equivalent to an ATM thrust and can be used to create an updated ATM Thrust Jet entry where the E coefficient from Equation 1 is equal to the ATM thrust determined from Equation 3.
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From page 58... ...
The base INM case for this study used a Temperature of 59.9βF based on an average of the six study airports where the elevated temperatures evaluated will start with this as their base. GIV Aircraft ATM Case Temperature Adjustment The best fit GIV ATM profile as shown in Figure 28 was achieved with an assumed temperature of 107βF.
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From page 59... ...
Table 25 describes the final Thrust, Altitude and noise values for the GIV for the Standard and ATM profiles. With the ATM profiles in place there is now agreement within 20ft of altitude and less than a half dB in Noise compared to greater than 600 ft discrepancy in altitude and a 3dB discrepancy in noise.
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From page 60... ...
CNA560E noise level comparisons and considerations: As described in Section 8.2 no additional profile modifications beyond the thrust reductions were needed for the CNA560E. Table 27 describes the final Thrust, Altitude and noise values for the CNA560E for the Standard and ATM2 profile where with the ATM profile in place there is now a high agreement in altitude and less than a one dB difference in noise.
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