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ANP Folder

Overview

GRAPE comes with integrated support for directly importing the ANP database into a study. Download and unzip the ANP database into a local folder on your computer and then import it via Edit->Import->Database->ANP. All .csv import rules defined in the CSV Files section must be respected.

Info

An exception is the variable units. GRAPE assumes that all units are in the original ANP format, and does not interpret them based on column names.

The following files must be found in the selected folder:

  • aircraft
  • jet_engine_coefficients
  • propeller_engine_coefficients
  • aerodynamic_coefficients
  • default_approach_procedural_steps
  • default_departure_procedural_steps
  • default_fixed_point_profiles
  • spectral_classes
  • npd_data

The file matching is case insensitive, and the file name must merely contain the names above. This means that the files

Aircraft.csv
my_aircraft.csv
AiRcRaFt_strange.csv
would all be recognized as being the ANP aircraft file. The default_weights file is currently ignored.

Limitations

The Doc29 data structure in GRAPE, into which the ANP database is imported, does not currently support all of the ANP data. This is mostly due to the more restrictive nature of the data structure in GRAPE.

Thrust Rating

The jet and propeller engine coefficients in the ANP database are necessary to apply the equations B-1, B-4 and B-5 of the Doc29 Volume II, which allow to estimate thrust based on a thrust rating and the aircraft state. While in the ANP database the thrust rating can be anything (the most common ones being MaxTakeoff and MaxClimb), GRAPE only supports the thrust ratings in the following table:

GRAPE ANP
Maximum Takeoff MaxTakeoff
Maximum Takeoff High Temperature MaxTkoffHiTemp
Maximum Climb MaxClimb
Maximum Climb High Temperature MaxClimbHiTemp
Idle IdleApproach
Idle High Temperature IdleApproachHiTemp

This restriction enables two functionalities in GRAPE:

  • Doc29 departure procedural profiles do not need to specify the thrust rating for each step. Instead only the step at which thrust cutback is performed needs to be specified. All steps before are assumed to use the Maximum Takeoff rating, and all steps after the Maximum Climb rating. The high temperature ratings are automatically used if present and the temperature is above the engine breakpoint temperature (which can be defined for each aircraft). If high temperature ratings are not present, equation B-4 of Doc29 is used.
  • For departure flights, thrust reductions can be specified for the Maximum Takeoff and Maximum Climb phases of flight, which will be directly applied when using the Doc29 performance model, without modifying the underlying Doc29 profile description. One of the examples in the examples folder demonstrates this use case.

For the ANP version 2.3, the following thrust ratings and the applicable aircraft will not be imported:

Thrust Rating Aircraft
ReduceTakeoff GII, GIIB
ReduTkoffHiTemp GII, GIIB
ReduceClimb ECLISPE500, GII, GIIB
ReduceClimbHiTemp ECLISPE500
MaxContinuous 727QF
MaxContHiTemp 727QF

Given the relatively low number of aircraft to which the alternative thrust ratings apply, the tradeoff was made for the added functionality described above. GRAPE will log an error when importing these thrust coefficients from the ANP database.

Warning

The ANP database additionally provides General thrust coefficients for most of its aircraft. These coefficients are intended to be used with equations B-2 and B-3 of the Doc29, which require knowledge of the engine state (Engine Pressure Ratio or N1 value). GRAPE currently does not support these and will silently ignore the General thrust coefficients.

Noise Thrust Parameter

In GRAPE, a performance output will always contain the Corrected Net Thrust Per Engine for every point. The Doc29 noise data in GRAPE follows this principle, and the required Noise-Power-Distance (NPD) tables to apply the Doc29 noise model always have the thrust parameter in Corrected Net Thrust Per Engine. GRAPE parses the aircraft and npd_data tables of the ANP database, and the following cases can occur:

  • Aircraft Power Parameter is either Pounds or CNT (lb): if not yet existent, the corresponding NPD data and spectral classes will be imported into a new Doc29 Noise entry named with the NPD ID, without modifications.
  • Aircraft Power Parameter is either Percent or CNT (% of Max Static Thrust): a new Doc29 Noise entry will be created, named with the NPD ID followed by the ANP aircraft name. The NPD power parameter will be converted to Corrected Net Thrust Per Engine by multiplying the existing parameter with the aircraft maximum sea level static thrust. The spectral class data will be imported without modifications.
  • Aircraft Power Parameter is anything else: GRAPE does not support other types of thrust parameter, both aircraft and noise data will not be imported.

For the ANP version 2.3, this limitation excludes the following aircraft and NPD data from being imported into GRAPE:

Aircraft Thrust Parameter NPD ID
CNA206 Other (RPM) IO540
CNA20T Other (RPM) TIO540
PA28 Other (RPM) O320D3
PA31 Other (RPM) TIO542

Again the number of affected aircraft is relatively low, and all general aviation aircraft. The tradeoff of not supporting this type of aircraft, in order to have a coherent representation of the thrust state of each aircraft for all performance outputs was made. This enables for fuel flow, noise and emissions models to be applied independent of the databases used to achieve the performance output.

Noise Metrics

GRAPE currently only supports A-Weighted noise metrics. For single events this correspond to the A weighted maximum level (LAmax) and sound equivalent level (SEL). The ANP database additionally contains EPNL and PNLTM data in the NPD tables. It is part of the roadmap to develop support for these metrics in GRAPE. Currently, this ANP data is simply ignored.

Warning

When importing the ANP database, the EPNL and PNLTM data of the NPD tables will be silently ignored.