DATCOM Release 2User's Manual______________________

Aleksey MatyushevRevision A

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Table of Contents

1.0 Introduction .................................................................................................................... 3 2.0 Requirements ................................................................................................................. 4

2.1 Hardware Requirements ............................................................................................. 4 2.2 Software Requirements .............................................................................................. 4

3.0 Feature Overview ........................................................................................................... 5 3.1 Running DATCOM through DR2 ............................................................................. 5

3.1.1 Importing an existing input file ......................................................................... 5 3.1.1.1 Preparing the import .................................................................................. 5 3.1.1.2 Reviewing the input file ............................................................................. 6 3.1.1.3 Reviewing the output ................................................................................. 7

3.1.2 Creating an input file ......................................................................................... 8 3.1.2.1 Preparing the build ..................................................................................... 8 3.1.2.2 Flight Conditions ....................................................................................... 9 3.1.2.3 Options Parameters .................................................................................. 10 3.1.2.4 Synthesis Parameters ............................................................................... 11 3.1.2.5 Body Parameters ...................................................................................... 12 3.1.2.6 Wing Parameters ...................................................................................... 13 3.1.2.7 Horizontal Tail Parameters ...................................................................... 14 3.1.2.8 Vertical Tail Parameters .......................................................................... 15 3.1.2.9 Terminating Parameters ........................................................................... 16 3.1.2.10 Reviewing the input file ......................................................................... 17 3.1.2.11 Reviewing the output file ....................................................................... 18

3.2 Building Aerodynamic Tables ................................................................................. 19 3.2.1 Assembling the input file ................................................................................. 19 3.2.2 Preparing the input file .................................................................................... 19 3.2.3 Reviewing the output ....................................................................................... 21

4.0 Acknowledgement ...................................................................................................... 22

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1.0 IntroductionThe United States Air Force (USAF) Stability and Control Digital DATCOM is a multi- purpose program written in FORTRAN that analyzes the stability and control of a given aircraft. Through basic geometric properties of the aircraft, along with the given flight conditions and propulsion elements, the DATCOM is able to compile coefficients which closely describe the performance and stability of the aircraft at the given conditions.

DATCOM was written in the 1970’s and due to the rapid development of technology since then, some aspects of the program are outdated. One of the key outdated features is the user interface. The input file (for005.dat) for DATCOM is written in a text document format for which the standard rules of FORTRAN apply. With these restrictions, it is time consuming to compile and troubleshoot the input file.

Another outdated feature is the use of the DOS command prompt to run the program. The DOS command prompt, although still an integral part of computing today, was replaced by more user friendly Operating Systems (OS) which are centered around easy to use Graphical User Interfaces (GUI) such as Windows. With the transition to more GUI intensive OS’s, the knowledge of DOS specific commands and their uses has become an archaic art.

DATCOM Release 2 (DR2) has been specifically developed to combat these two outdated features. DR2 is written completely in Sun Microsystems Java SE and uses the Java Virtual Machine (JVM) to interface with USAF DATCOM. The interface is completely coded into DR2; as a result, no modification to the original DATCOM code is needed.

DR2 uses basic GUI’s to allow the user to easily compile the input file, import an existing input file, and run DATCOM without any knowledge of DOS or the necessary FORTRAN formatting needed for the input file.

Another feature that was added to DR2, which the original DATCOM did not directly possess, is the compiling and export of stability and performance coefficients. This feature was added with the specific intention of compiling three dimensional stability tables which can be copied straight into the FlightGear (using the JSBsim flight model) open source flight simulator. This allows for an aircraft to be analyzed in DATCOM and its flight to be tested in FlightGear.

PLEASE NOTE: This document assumes that the user has had some basic exposure to the DATCOM program. For further reference on DATCOM please consult the Manual Volumes that are bundled with DATCOM. Also, this program is in BETA development stage and might have some bugs, as a result, please look through this manually carefully before using DR2 and it's features.

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2.0 Requirements

2.1 Hardware RequirementsDR2 is not a GUI or a processor intensive program, and therefore does not require large amounts of processing power or a top of the line graphics card. The following minimum hardware configuration is suggested:

• Intel Pentium III - 450 MHz or equivalent• 256 MB of RAM• 64 MB Graphics Card

It should also be noted that these hardware requirements are sufficient for the use of DR2 and DATCOM. For hardware requirements relating to FlightGear, please consult the FlightGear web page (www.flightgear.org).

2.2 Software RequirementsBecause DR2 is written in Java, it is technically OS independent. This means that the DR2 software can run on any operating system supporting Java technology. HOWEVER, DATCOM itself can only be run on the Windows operating system, as a result, the full extent of DR2 can only be utilized on the Windows OS.

If DR2 is ran on a Mac, or Linux OS, the only functionality which can be utilized is the building of the input file using the graphical interface, after which, the contents can be copied into a text document and ran on a Windows platform at a later time. If an attempt to run DATCOM from DR2 launched in Mac, or Linux OS platforms is made, DR2 will freeze.

The only two software packages needed for DR2 to operate are listed below:

• Java Virtual Machine (JVM) can be downloaded for free from (http://www.java.com/en/download/index.jsp)

• DATCOM (stored in the DATCOM folder attached to this distribution)• Microsoft Windows OS (tested on Vista and XP)

Once the JVM has been installed, the DATCOM directory needs to be placed somewhere on the file system. For easy use of DR2, and in general, it is recommended that it be placed on the “C:\” hard drive, so the DATCOM folder path should be “C:\Datcom”.

After the DATCOM directory has been positioned, DR2 should be placed somewhere on the file system as well. DR2 builds it's own path dependencies based on the file path of DATCOM; therefore, it does not matter where it is placed.

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3.0 Feature OverviewDATCOM has two main features after the input file (for005.dat) has been built: one option is for the user to simply run DATCOM, and the other option is to build stability tables (compiles multiple for005.dat files and runs them). Both of these features are described in detail below.

3.1 Running DATCOM through DR2

3.1.1 Importing an existing input fileThe easiest way to start using DR2 is to use it's IMPORT FUNCTION. This functionality allows the user to browse for an existing input file, review it, run DATCOM, and review the output (for006.dat) all from DR2.

3.1.1.1 Preparing the import

Figure 1: Main DR2 Screen

Figure 1 above, references the starting screen of the DR2 application. To import an existing input file, the user should select the “Browse” button first. A new window with a browser shall be shown allowing the user to select the appropriate input file. This input file can have ANY name, as long as the format of the input file's contents are in ASCII or UTF, the input should work. Following the selection of the input file, the user needs to press the OK button to save the file's path. The selected file's path shall be shown in the text box adjacent to the “Browse” button.

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After the selection of the input file has been made, the user needs to set the path to the DATCOM folder. This can be done by altering the text in the text box adjacent to the label “PATH”. The DATCOM directory path is the file system path of the folder containing the DATCOM program. If the user placed the DATCOM folder on the “C:\” drive and the folder is titled “Datcom” (so that the path is “C:\Datcom”), then the default file path can be left.

After the selection of the input file and the DATCOM directory path, a CASEID must be selected. The CASEID shall be the folder under the DATCOM directory path in which the input and output files will be placed. The CASEID needs to be a text value with no spaces or symbols; using numbers and underscores is allowed.

Following the selection of the input file, DATCOM directory path, and the CASEID, the “Import” button located towards the bottom of the screen needs to be selected.

3.1.1.2 Reviewing the input file

Figure 2: for005.dat Review Screen

Following the selection of the “Import” button (See Section 3.1.1.1), the for005 review screen is shown to the user. This screen displays the exact file the user chooses to import. Figure 2 above shows the layout of the review screen and a typical input file.

In this screen, the user has the option to edit any part of the input file before running DATCOM through DR2. The text shown will be exactly what is written to a for005 file

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under the path “Datcom Path\CASEID\”. When editing the for005 file manually from this screen, all standard FORTRAN formatting rules apply; therefore, care should be taken when editing this file manually.

After reviewing the for005 file and making sure everything looks correct, the button labeled “RUN DATCOM” towards the bottom of the screen needs to be selected.

3.1.1.3 Reviewing the output

Figure 3: for006 Review Screen

Following the selection of the “RUN DATCOM” button (See Section 3.1.1.2), the for006 review screen is shown to the user. When this screen is shown, the DATCOM command has been run on the previous file and the output files have been created.

The most common file that is reviewed from the output is the for006.dat file. For convenience, DR2 displays this file in a text area on this review screen. The text displayed is the exact replica of the for006.dat file located at “DATCOM Path\CASEID\for006.dat”. DR2 cannot write any changes to this file if any changes have been made in this review screen, as a result, the for006.dat file will never be altered.

Also, located at the bottom of this review screen is a “Back” button. This button allows the user to go back to the previous for005 review screen (See Section 3.1.1.2) which will show the input file used to run the current instance of the program.

After pushing the “Back” button, the for005 file can be altered in the review text area and the “RUN DATCOM” can be pressed once more. DR2 shall replace all the files in the

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“DATCOM Path\CASE ID\” folder and run DATCOM with the new for005 file. When the review for006 screen appears once more, it will have the updated output from the new for006 file.

3.1.2 Creating an input fileDR2 is also capable of creating for005 files compatible with DATCOM. This can be accomplished by inputting the variable data into a series of screens corresponding to each section of the DATCOM program. For a definition and a more detailed description of the variables available, the DATCOM manual should be consulted.

DATCOM provides a tremendous amount of variables and NAMELIST's. Not all of these variables and sections were integrated into this BETA stage of the program. The variables and sections included right now tend to be the most used and should provide sufficient capability.

If a variable or NAMELIST is needed and it is not available through the GUI building screens, the variable can simply be added into the for005 file through the review screen.

The following sections briefly describe the GUI screens which build the for005 input file.

3.1.2.1 Preparing the build

Figure 4: Main DR2 Screen

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Figure 4 above depicts the starting screen of the DR2 application. To start building a new input file, the PATH and CASEID fields need to be filled out.

The user needs to set the path to the DATCOM folder. This can be done by altering the text in the text box adjacent to the label “PATH”. The DATCOM directory path is the file system path of the folder containing the DATCOM program. If the user placed the DATCOM folder on the “C:\” drive and the folder is titled “Datcom” (so that the path is “C:\Datcom”), then the default file path can be left.

After the selection of the input file and the DATCOM directory path, a CASEID must be selected. The CASEID shall be the folder under the DATCOM directory path in which the input and output files will be placed. The CASEID needs to be a text value with no spaces or symbols; using numbers and underscores is allowed.

Following the setting of the DATCOM directory path, and the CASEID, the “Next” button located towards the bottom of the screen needs to be selected.

3.1.2.2 Flight Conditions

Figure 5: Flight Conditions Screen

The first screen following the basic configuration of the input file (See Section 3.1.2.1), allows the configuration of the flight condition parameters.

The flight conditions parameters need to be filled out with decimal numbers ONLY (Ex. “2.0”). If there is more than one number corresponding to a certain parameter, then the

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numbers should be separated by commas with no space between the comma and next number. When inputing multiple numbers, the last number should HAVE a comma after it (with specific reference to the ALSCHD parameter).

A brief description of most of the parameters listed on this screen can be found by holding the mouse over the parameter for a couple of seconds. For further explanation on these parameters, the DATCOM manuals should be referenced.

All fields do not need to be filled out, if one of the parameters is not to be utilized, the text field should simply be left blank and DR2 will not include it in the input file.

3.1.2.3 Options Parameters

Figure 6: Options Parameters Screen

The second screen following the flight parameters configuration of the input file (See Section 3.1.2.2), allows the configuration of the options parameters.

The options conditions parameters need to be filled out with decimal numbers ONLY (Ex. “2.0”).

A brief description of most of the parameters listed on this screen can be found by holding the mouse over the parameter for a couple of seconds. For further explanation on these parameters, the DATCOM manuals should be referenced.

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All fields do not need to be filled out, if one of the parameters is not to be utilized, the text field should simply be left blank and DR2 will not include it in the input file.

3.1.2.4 Synthesis Parameters

Figure 7: Synthesis Parameters Screen

The third screen, following the options parameter configuration of the input file (See Section 3.1.2.3), allows the configuration of the synthesis parameters.

The synthesis conditions parameters text inputs need to be filled out with decimal numbers ONLY (Ex. “2.0”).

A brief description of most of the parameters listed on this screen can be found by holding the mouse over the parameter for a couple of seconds. For further explanation on these parameters, the DATCOM manuals should be referenced. A screen from the DATCOM manual is included for easy reference.

All fields do not need to be filled out, if one of the parameters is not to be utilized, the text field should simply be left blank and DR2 will not include it in the input file.

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3.1.2.5 Body Parameters

Figure 8: Body Parameters Screen

The fourth screen, following the synthesis parameter configuration of the input file (See Section 3.1.2.4), allows the configuration of the body parameters.

The body conditions parameters text inputs need to be filled out MANUALLY following FORTRAN rules. As of the BETA DR2 release, no algorithms supporting dynamic BODY parameter creation have been developed.

A brief description of the parameters needed and their input format can be found in the DATCOM manuals.

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3.1.2.6 Wing Parameters

Figure 9: Wing Parameters Screen

The fifth screen, following the body parameters configuration of the input file (See Section 3.1.2.5), allows the configuration of the wing parameters.

The wing conditions parameters need to be filled out with decimal numbers ONLY (Ex. “2.0”). The NACA Airfoil Designation needs to be filled out based on the DATCOM user manual format.

A brief description of most of the parameters listed on this screen can be found by holding the mouse over the parameter for a couple of seconds. For further explanation on these parameters, the DATCOM manuals should be referenced. A picture is included for easy reference.

All fields do not need to be filled out, if one of the parameters is not to be utilized, the text field should simply be left blank and DR2 will not include it in the input file.

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3.1.2.7 Horizontal Tail Parameters

Figure 10: Horizontal Tail Screen

The sixth screen, following the wing parameters configuration of the input file (See Section 3.1.2.6), allows the configuration of the horizontal tail parameters.

The horizontal conditions parameters need to be filled out with decimal numbers ONLY (Ex. “2.0”). The NACA Airfoil Designation needs to be filled out based on the DATCOM user manual format.

A brief description of most of the parameters listed on this screen can be found by holding the mouse over the parameter for a couple of seconds. For further explanation on these parameters, the DATCOM manuals should be referenced. A picture is included for easy reference.

All fields do not need to be filled out, if one of the parameters is not to be utilized, the text field should simply be left blank and DR2 will not include it in the input file.

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3.1.2.8 Vertical Tail Parameters

Figure 11: Vertical Tail Screen

The seventh screen, following the horizontal parameters configuration of the input file (See Section 3.1.2.7), allows the configuration of the vertical tail parameters.

The vertical conditions parameters need to be filled out with decimal numbers ONLY (Ex. “2.0”). The NACA Airfoil Designation needs to be filled out based on the DATCOM user manual format.

A brief description of most of the parameters listed on this screen can be found by holding the mouse over the parameter for a couple of seconds. For further explanation on these parameters, the DATCOM manuals should be referenced. A picture is included for easy reference.

All fields do not need to be filled out, if one of the parameters is not to be utilized, the text field should simply be left blank and DR2 will not include it in the input file.

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3.1.2.9 Terminating Parameters

Figure 12: Terminating Screen

The eighth screen, following the vertical parameters configuration of the input file (See Section 3.1.2.8), allows the configuration of the terminating parameters.

The terminating parameters need to be filled out with decimal numbers ONLY (Ex. “2.0”). The NACA Airfoil Designation needs to be filled out based on the DATCOM user manual format.

A brief description of most of the parameters listed on this screen can be found by holding the mouse over the parameter for a couple of seconds. For further explanation on these parameters, the DATCOM manuals should be referenced. A picture is included for easy reference.

All fields do not need to be filled out, if one of the parameters is not to be utilized, the text field should simply be left blank and DR2 will not include it in the input file.

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3.1.2.10 Reviewing the input file

Figure 13: for005.dat Review Screen

Following the selection of the “Create for005.dat” button (See Section 3.1.2.9), the for005 review screen is shown to the user. This screen displays the exact file the user chooses to import. Figure 13 above shows the layout of the review screen and a typical input file.

In this screen, the user has the option to edit any part of the input file before running DATCOM through DR2. The text shown will appear exactly as written to a for005 file under the path “Datcom Path\CASEID\”. When editing the for005 file manually from this screen, all standard FORTRAN formatting rules apply, therefore, care should be taken when editing this file manually.

After reviewing the for005 file and making sure everything looks correct, the button labeled “RUN DATCOM” towards the bottom of the screen needs to be selected.

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3.1.2.11 Reviewing the output file

Figure 14: for006 Review Screen

Following the selection of the “RUN DATCOM” button (See Section 3.1.2.10), the for006 review screen is shown to the user. When this screen is shown, the DATCOM command has been run on the previous file and the output files have been created.

The most common file that is reviewed from the output is the for006.dat file. For convenience, DR2 displays this file in a text area on this review screen. The text displayed is the exact replica of the for006.dat file located at “DATCOM Path\CASEID\for006.dat”. DR2 cannot write any changes to this file if any changes have been made in this review screen, as a result, the for006.dat file shall never be altered.

Also, located at the bottom of this review screen is a “Back” button. This button allows the user to go back to the previous for005 review screen (See Section 3.1.2.10) which will show the input file used to run the current instance of the program.

After pushing the “Back” button, the for005 file can be altered in the review text area and the “RUN DATCOM” can be pressed once more. DR2 shall replace all the files in the “DATCOM Path\CASE ID\” folder and run DATCOM with the new for005 file. When the review for006 screen appears once more, it will have the updated output from the new for006 file.

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3.2 Building Aerodynamic TablesDR2's advanced features allow the user to build aerodynamic tables based on the DATCOM output. After DR2 has assembled the tables, they can then be integrated into FlightGear flight simulator.

The tables built by DR2 are three-dimensional in that the aerodynamic coefficient is based on the MACH number and the ALPHA (angle of attack). For this reason, these tables allow the JSBsim integrated with FlightGear to model the aircraft to a greater degree of detail.

The way DR2 builds the tables, is quite simple. DR2 re-runs the input file through DATCOM based on the MACH numbers and the ALTITUDES entered. The input file is evaluated first at a given ALTITUDE, for the given MACH numbers, after that it moves onto the next ALTITUDE and re-evaluates the same MACH numbers again.

Results are stored in MASTER text files which can then be copied into FlightGear. For information on assembling the aircraft XML files for FlightGear and JSBsim see their respective websites.

NOTE:Based on the number of ALTITUDES, MACH numbers, and the CPU speed it might take a while for DR2 to finish the table compilation. If DR2 does not display after a couple of minutes, check to see at which altitude it stopped (using the file explorer), and double check that the format for inputting the MACH and ALTITUDE numbers is correct.

The following two sections describe the procedure for building the aerodynamic tables using DR2.

3.2.1 Assembling the input fileThe input file is to be assembled through DR2 or imported into DR2. See section 3.1 for more details on how to accomplish this.

The only requirement when assembling or importing the input file, is that no “BUILD”, or “PLOT” commands be placed at the bottom of the input file. These commands change the format of the output file (for006.dat), making it impossible for DR2 to grab the parameters from the output file.

3.2.2 Preparing the input fileAfter arriving at the for005 file review screen (see the figure below), all the “BUILD”, “PLOT”, or any other command that changes the format of the output file (for006.dat) need to be taken out.

The for005 file must have only one MACH and ALTITUDE number entered. This allows the DR2 program to easily change those numbers.

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Figure 15: for005 Review Screen

Following the removal of the format changing commands and making sure only one instance of the MACH and ALTITUDE numbers are entered into the actual for005 file, the MACH and ALTITUDE numbers need to be entered into the “ALTITUDES” and “MACH'S” text boxes with these rules in mind (see Figure 15 above for an example):

1. Multiple MACH's or ALTITUDES need to be separated by commas

2. The last numbers MUST have a comma after them

3. All MACH numbers entered must have the exact same amount of characters as the MACH number entered into the for005 file. As an example, if the input MACH number is “0.23” in the for005 file, ALL the MACH numbers entered into the “MACH'S” text field must have 4 characters, such as “0.10”,”0.31”,”1.0”, etc..

4. All ALTITUDE numbers entered must have the exact same amount of characters as the ALTITUDE number entered into the for005 file. As an example, if the input ALTITUDE number is “10000.0” in the for005 file, ALL the ALTITUDE numbers entered into the “ALTITUDES” text field must have 7 characters, such as “100.000”, “2000.00”,”15000.0”, etc..

5. The MACH and ALTITUDE numbers actually placed in the for005 file will NOT be used in the building of the tables, they function as merely place holders when

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building the tables. If the user were to press the “RUN DATCOM” button, then these two values will be used.

6. The number of MACH and ALTITUDE numbers that can be entered into the “MACH'S” and “ALTITUDES” text fields is UNLIMITED. HOWEVER, it should be noted that the processing time increases with each MACH and ALTITUDE number entered.

Following these six rules above shall insure that no error shall occur during processing.

After the MACH and ALTITUDE numbers were entered, the “Build Tables” button needs to be pressed.

3.2.3 Reviewing the output

Figure 16: Reviewing Sample Output

If the tables were built successfully, then the user is presented with the sample output review screen (see Figure 16 above).

The most common file that is reviewed from the output is the for006.dat file. For convenience, DR2 displays this file in a text area on this review screen. The text displayed is the exact replica of the for006.dat ran for the last ALTITUDE number and last MACH number located at “DATCOM Path\CASEID\C3PO\LAST ALTITUDE\LAST MACH”. DR2 cannot write any changes to this file if any changes have been made in this review screen, as a result, the for006.dat file will never be altered.

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Also located on the bottom of the screen is the file path to the MASTER(meaning completely compiled) documents containing the aerodynamic tables. These tables can then be copied and pasted into FlightGear.

If the files are opened and the formatting seems to be inconsistent then either the text editor is not configured with the correct settings or is incompatible with viewing the output. Linux text editors always display the correct formatting. For the Windows OS, it is recommended that Notepad++(can be downloaded for free from http://notepad-plus.sourceforge.net/uk/site.htm) be used.

Also, located at the bottom of this review screen is a “Back” button. This button allows the user to go back to the previous for005 review screen (See Section 3.2.2) which will show the input file used to run the current instance of the program.

After pushing the “Back” button, the for005 file can be altered in the review text area and the “RUN DATCOM” pressed once more. DR2 will replace all the files in the “DATCOM Path\CASE ID\C3PO\” folder and run DATCOM with the new for005 file. When the review for006 screen appears once more, it will have the updated output from the new for006 file.

4.0 Acknowledgement The Datcom Release 2 BETA release was coded and developed by Aleksey Matyushev. Aleksey is currently a senior at Embry-Riddle Aeronautical University in Daytona Beach, Florida. Aleksey's main interests include aerodynamics and stability of aircraft as well as horizontal takeoff horizontal landing sub-orbital vehicles.

For obtaining a copy of DR2, feature requests, or bug reports, please contact Aleksey at the following email: alekseymatyushev@gmail.com .

The DR2 BETA release could not have been possible without the generous help of• Glenn Greiner• Kevin Russell• Anatoly Starikov• Bryan Lozick• Jason Williams• Andrew Viscovich• Jensen Joseph• Biana Moloksher

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