6. ENGINE CYCLE DESIGN PROGRAMS and DESIGN … Guides/AEDsys User Guide 2.pdfENGINE CYCLE DESIGN PROGRAMS and DESIGN STEPS . ONX - Parametric Engine Analysis determines the change

Copyright 2002 - 2017 - Jack D Mattingly, Ph.D.

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6. ENGINE CYCLE DESIGN PROGRAMS and DESIGN STEPS ONX - Parametric Engine Analysis – determines the change in an engine’s uninstalled performance with changes in the engine design parameters (a design parameter like compressor pressure ratio). ONX can also calculate the performance of a reference engine (each design parameter set to one design value) and output a reference data file (*.ref) for later input into the AEDsys program. The ONX program can be started from the File pull-down menu of AEDsys’ Engine Model Data window or the Program List (Start button). Each start of the ONX program starts a new program run. If you want to use a previous run of the program, select the ONX task located in the Task Bar along the bottom of the computer screen. AEDsys - Performs constraint analysis, contour plots, mission analysis, and engine test – can input reference data for an engine obtained from ONX program or create its own reference engine (from Engine Data window) and fly this engine through the mission; run engine performance calculations [variation in an engine’s uninstalled performance with changes in engine flight conditions (altitude and Mach number) and engine throttle (Tt4)]; perform constraint analysis; and generate contour plots. When an AEDsys data file (*.aed) is saved with a reference engine, the reference data for that engine is saved inside the AEDsys data file (*.aed). Data Files – There are three data files (see below) used for these design steps. The files with the file extension of “onx” are input data files for the ONX program. The files with the file extension “ref” are created by the ONX program and are used as input of an engine design into the AEDsys program.

Programs Data Files Name ONX On-Design Input Data File *.onx Reference Data File *.ref (output of ONX program and input to AEDsys program)

AEDsys AEDsys Input Data File *.aed It is very important to keep very good records of the data within each data file. Students have found it very useful to name the files with sufficient information so that they know what is within that file. For example, a file named “Student1_Engine1_CPR26_FPR_3.ref” would refer to a reference file generated by the ONX program for Student1’s first engine with a compressor pressure ratio of 26 and fan pressure ratio of 3.


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Basic Steps 1. Run ONX program using its Carpet

Plot feature to determine candidate engine designs. Remember to correct default input data or read in a previously generated ONX data file. Print resulting plot (see example below) for use in selecting candidate engines. Make sure to save the ONX input data file (*.onx) used to generate this plot. Using the ONX carpet plot, select several candidate engine designs – for example, compressor pressure ratio (CPR) / fan pressure ratio (FPR) values of 26/2.5, 26/3, and 24/3 have fuel consumption much less that the line at 0.85.

2. Design a candidate engines using the ONX program at a single design point (remember to put in correct values of design choices in data window, correct cycle, and correct component data) and save the resulting Reference Engine Data file (*.ref) for later use. Also save the ONX input data file for this reference engine (*.onx).

3. Using the AEDsys program, select Cycle Deck under Engine Model pull-down menu or press the Engine Data button of AEDsys program to display the Engine Data window. Read in the ONX Reference Engine Data file (*.ref) by selecting Input under the File pull-down menu. Update Engine Control values and accept automatic update of Tt4 and Tt7 in Mission Analysis data. For Installation Loss Model, select Constant Loss for Each Leg. See Engine Data window shown below. Save the AEDsys data file (*.aed) which includes the installed engine with an appropriate file name.


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4. Run Constraint Analysis to determine the required thrust loading (TSL/WTO) for the selected wing loading (WTO /S). If required, update data on Mission Analysis window. Run Mission Analysis and determine fuel used. If engine is too small for any flight condition, increase the system TSL/WTO as required and rerun the Mission Analysis. Note that the engine is automatically scaled (TSF) in accordance with required TSL at the start of the Mission Analysis. See example first page Mission summary result shown below.

5. Repeat steps 3 and 4 for each engine design until desired engine design is reached. See detailed Search Results for the Air-to-Air Fighter (AAF) on pages 181-184 in Chapter 5 of textbook.


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Size Inlet and Nozzle for each selected engine design (see upper 2/3 of Fig 6.E2 on page 212 of textbook): 6. Review second summary sheet of Mission analysis and find largest required A1 and A10 for the mission (see

example page below). For this example mission, the largest A0* and A9 are 7.570 ft2 and 11.187 ft2, respectively.

Check other regions of the aircraft flight envelope to see if larger values are required (see pages 206-208 of Chapter 6, note that Cold Day performance can require larger values of A1 and A10). If needed, run Engine Test over range of Mach numbers at different altitudes to obtain required A1 and A10. For the example cold day data at 40k ft altitude shown below, the largest A0 and A9 are 8.363 ft2 and 17.422 ft2, respectively.


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7. Select Chapter 6 Installation Model in Engine Data window of AEDsys. Input design A1, A10, and nozzle length

(L). See example input data shown below.

Perform Constraint Analysis with this Chapter 6 installation loss model. If either the required thrust loading (TSL/WTO) or wing loading (WTO /S) change, input new values in Mission Analysis window. If engine thrust at sea level (TSL) changes, accept the automatic updating of the inlet and nozzle input data (otherwise you’ll need to do steps 6 and 7 over again). Perform Mission Analysis and check results to see if the Aircraft System Weight needs to be changed. Note the resulting Thrust Scale Factor (TSF).

Resize an Engine (see bottom of Fig 6.E2 on page 212 of textbook): 8. Input the number of engines into the tab page shown above. For the reference engine, calculate the correct input

engine mass flow rate using the value for Thrust Scale Factor (TSF) and the previous reference mass flow rate. For example, ( ) ( )0 0correct previous

m TSF m= × Input this new value of the mass flow rate into the edit field on the

Reference Engine Design tab of the Engine Data window and the following window is displayed to recalculate the Thrust Scale Factor (TSF). If the reference mass flow is sized correctly, the new value of the Thrust Scale Factor is 1.000.

9. Save the reference data file using the Save As item in the File pull-down menu of the Engine Data window. It is recommended that you add “sized” to the file name.


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7. ENGINE CYCLE DECK MODEL – ENGINE DATA WINDOW

Selecting the Cycle Deck from the Engine pull down menu on the AEDsys main window opens the Engine Data window (with three tabs), shown below, and permits design of reference engine or input of engine reference data from the ONX program (select Open in File pull-down menu). The Reference Engine Design tab is used to input data for the flight conditions, design limits, and design variables of the reference engine.

This window has three pull-down menus: Engine File, Engine Cycle, and Gas Model. Each of these menus are shown below. Current selected engine cycle and gas model have a check mark to their left.


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Selecting Open in the File pull down menu opens a dialog window like that shown below to input an engine reference data file created by this program or the ONX program. A similar window is opened when Save As is selected from the File pull down menu for saving reference engine data file.

The Fuel/Gas Prop., Comp. Efficiency tab, shown below, is used to input data for the fuel and gas Properties, bleed and coolant air, power takeoff, exhaust nozzle, and component figures of merit (total pressure ratio, polytropic efficiency, and component efficiency).

The Level of Technology button brings forth a window that presents that data from Table 4.4 of Aircraft Engine

Design, Second Edition to help the user select appropriate input data.


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The Controls, Install Model, # of Engines tab, shown below, is used to input data for the Engine Control limits, Installation Loss Model, and Number of Engines.

The results for the reference engine are calculated as the data is entered into the data fields. Once the user has entered

the data for their reference engine, we suggest that you save the data using the Save item in the File pull down menu. As shown below, the user is asked if they would like to update the maximum engine temperature(s) {Tt4 and Tt7} in

each mission leg with the value(s) contained in the engine reference file. If either the maximum temperature at station 4 or the maximum temperature at station 7 is changed in the above window, the user is asked if they would like this new value to be used in all mission legs.

After a reference engine calculated or its data file has been loaded into the AEDsys program, this engine’s reference

data is used in the engine performance model for all analyses and the Engine Data button and Engine Test button are added to the AEDsys Main window as shown below to facilitate navigation.


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Selecting the Component Interface menu item at the top of the Engine Data window opens the Component Interfaces window. Press the Calculate button to display the component flow properties based on the user input Mach number data (initial estimates) at the top of the window and the Thrust Scale Factor as shown below. The resulting annular flow areas are used in Engine Station Test Results calculations within the Engine Test window.

Selecting the Scale Thrust menu item at the top of the Engine Data window will scale the engine mass flow so that the thrust from the number of engine will equal that specified on the Mission window and the resultant Thrust Scale Factor (TSF) is 1.00.


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8. ENGINE CYCLE DECK MODEL – ENGINE TEST WINDOW Pressing the Engine Test button on the AEDsys main window opens the Engine Test window, shown below, and

performance analysis of the reference engine. Pressing the Test button causes the performance analysis software to calculate the engine performance at the percent thrust set in the % Thrust data field and update results on the right side of the Engine Test window.


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After performing a test, press the Summary of Test Results button in the Engine Test window to open the Results window and display a comparison of engine performance at the reference and test points as shown below.

Press the Engine Station # button on the Engine Test window to display a sketch of the engine showing engine station numbers as shown below.


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After performing a test, press the Engine Station Test Results button in the Engine Test window to open the Engine Station window and display the component interface flow properties as shown below. These are based on the annular flow areas calculated using the Component Interface button within the Engine Data window. If the Component Interface button has not been pressed and the annular flow areas calculated, then only the mass flow rates, ratio of specific heats, and total properties are shown for each engine station.


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The engine performance can be calculated at full throttle (military and maximum power) and plotted using the lower left of the Engine Test window as shown above. After the Perform Calcs button is pressed, the Results window is opened and the predicted engine performance displayed as shown below. The program saves the variation of the engine performance with the independent variable for later plotting. The status of the saved plot data is updated in the Engine Test window. Up to 21 plot lines can be plotted.


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As an example of a performance plot, the performance of the AAF Final Engine is calculated at maximum power over the range of Mach numbers listed for each altitude listed below for a standard day atmosphere.

Altitude (kft) Min Mach Max Mach

0 0 1.2 10 0.4 1.4 20 0.5 1.5 30 0.6 1.6 36 0.6 1.8 40 0.6 1.8

Once these calculations were done, the uninstalled thrust was plotted and is shown below. The uninstalled thrust

specific fuel consumption (S) is shown on the next page.


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Similarly, the partial throttle performance of an engine can be calculated and plotted using the lower right of the Engine Test window (shown below). Press the Partial Throttle button to calculate the uninstalled performance of an engine from 100% down to the minimum thrust entered in the Min % Thrust data field (minimum value is 4%). The results are displayed in a Throttle Hook results window as shown on the next page.


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Once the partial throttle has been calculated, the partial throttle plot buttons become visible in the lower right of the engine test window as shown below.


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As an example, the partial throttle performance was calculated at the following altitude/Mach number conditions in a standard altitude: 0 kft/0.0M, 30 kft/0.9M, and 30 kft/1.5M. The uninstalled throttle hooks (thrust specific fuel consumption versus thrust) and the fan operating lines are displayed below.


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In addition, the overall uninstalled engine performance (thrust and fuel consumption) can be calculated over a range of Mach number and altitude and plotted as a carpet plot. Press the Performance Carpet Plot vs Alt-Mach button at the bottom of the Engine Test window and the following window will display.

Input the desired range of Mach and Altitude (combined maximum of 22 plot lines) followed by the Calculate button. Press the Plot button when calculations are done and a plot like the following is displayed.


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A similar plot can be made for this engine with the afterburner off by first turning the afterburner off (set Tt7 to zero) on the Engine Test window.

Note on Separate Exhaust Turbofan Engine The engine performance can be calculated with the fan exit area different than that of the reference engine by entering a value for Area18/Area18R in the engine controls setting (see below).

Area18/Area18R setting


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9. ENGINE CYCLE DECK MODEL – MISSION ANALYSIS Once a reference engine data has been input into the AEDsys program and the installation loss model selected in the

Engine Test window, mission analysis can be performed of the reference engine installed in the aircraft. Pressing the Mission button on the AEDsys main window opens the Mission window, shown below. Note that the mission leg data now has maximum Tt4 (and Tt7 when applicable) for each mission leg. This data needs to be set to the appropriate maximum(s) for each mission leg. Maximum Tt4 for each mission leg can only be greater than or equal to the Maximum Tt4 value set in the Engine Controls data on the Engine Data or Engine Test windows.

For engines with convergent-divergent exhaust nozzles, an exit area (A9/A8) schedule can be input versus Mach number during the exhaust nozzle design (see example in Chapter 10 of Aircraft Engine Design, Second Edition). It is not recommended to select the A9/A8 schedule until that phase of the design. When the A9/A8 Schedule check box is not selected (see below), the mission analysis assumes that the exit pressure (P9) equals the ambient pressure (P0). See page 41 for the case when the user wants to specify the A9/A8 schedule,


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The mission summary for a cycle deck engine has two pages. The first page (shown below for a constant installation loss model) is similar to that of the simple engine models. Information about the number of engines, thrust scale factor, and engine controls is now included in the header. In addition, a column listing the uninstalled thrust (F) has been added to the right of the previous columns of data.

The second summary page lists the required A0* (or A0) and A9 areas, TSFC, installation loss, control limit, maximum engine temperatures, etc. This area data is very useful for sizing the inlet (A1) and the afterbody (A10).


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The mission performance of a cycle deck engine with the inlet and afterbody sized using the methods of Chapter 6 can be determined similar to the above analysis for constant installation loss. Based on the previous type of mission analysis, the Chapter 6 model inlet and afterbody data is first entered into the appropriate data fields on the Engine Test window (see below) before the mission analysis is performed.

The first page of the results and the top of the two summary pages now display the inlet and afterbody information as shown below for the first results page. The Results window for each mission leg now gives the data used to calculate the installation losses and the results.

The first and second mission summary pages for the installation loss model of Chapter 6 is very similar to those of the constant installation loss model with the exception of the additional information in the header. The second mission summary page is presented below for the AAF showing the variation in installation losses with flight condition.


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Exhaust Nozzle Area Schedule: For engines with convergent-divergent exhaust nozzles, the program assumes the exhaust pressure (P9) equals the ambient pressure (P0) when the exhaust nozzle area ratio is not specified (A9/A8 Schedule check box not checked). Mission calculations are performed for this matched exit pressure requirement (P9 = P0) and the resulting exhaust nozzle exit areas (A9) are given on the second mission summary page (see above). After reviewing these mission results, the desired exit area ratio (A9/A8) can be input to an exhaust nozzle schedule that is a function of the aircraft Mach number (M0). Checking the A9/A8 Schedule check box, enables the A9/A8 Data button (see below). Pressing the A9/A8 Data button opens the Exhaust Nozzle Schedule window (see below). Up to 11 data points can be entered into the schedule and the data needs to be entered in increasing Mach number.

6. ENGINE CYCLE DESIGN PROGRAMS and DESIGN … Guides/AEDsys User Guide 2.pdfENGINE CYCLE DESIGN PROGRAMS and DESIGN STEPS . ONX - Parametric Engine Analysis determines the change

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