Documentation

## Digital DATCOM Data

### Digital DATCOM Data Overview

The Aerospace Toolbox product enables bringing United States Air Force (USAF) Digital DATCOM files into the MATLAB® environment by using the `datcomimport` function. For more information, see the `datcomimport` function reference page. This section explains how to import data from a USAF Digital DATCOM file.

The example used in the following topics is available as an Aerospace Toolbox example. You can run the example by entering `astimportddatcom` in the MATLAB Command Window.

### USAF Digital DATCOM File

The following is a sample input file for USAF Digital DATCOM for a wing-body-horizontal tail-vertical tail configuration running over five alphas, two Mach numbers, and two altitudes and calculating static and dynamic derivatives. You can also view this file by entering `type astdatcom.in` in the MATLAB Command Window.

``` \$FLTCON NMACH=2.0,MACH(1)=0.1,0.2\$ \$FLTCON NALT=2.0,ALT(1)=5000.0,8000.0\$ \$FLTCON NALPHA=5.,ALSCHD(1)=-2.0,0.0,2.0, ALSCHD(4)=4.0,8.0,LOOP=2.0\$ \$OPTINS SREF=225.8,CBARR=5.75,BLREF=41.15\$ \$SYNTHS XCG=7.08,ZCG=0.0,XW=6.1,ZW=-1.4,ALIW=1.1,XH=20.2, ZH=0.4,ALIH=0.0,XV=21.3,ZV=0.0,VERTUP=.TRUE.\$ \$BODY NX=10.0, X(1)=-4.9,0.0,3.0,6.1,9.1,13.3,20.2,23.5,25.9, R(1)=0.0,1.0,1.75,2.6,2.6,2.6,2.0,1.0,0.0\$ \$WGPLNF CHRDTP=4.0,SSPNE=18.7,SSPN=20.6,CHRDR=7.2,SAVSI=0.0,CHSTAT=0.25, TWISTA=-1.1,SSPNDD=0.0,DHDADI=3.0,DHDADO=3.0,TYPE=1.0\$ NACA-W-6-64A412 \$HTPLNF CHRDTP=2.3,SSPNE=5.7,SSPN=6.625,CHRDR=0.25,SAVSI=11.0, CHSTAT=1.0,TWISTA=0.0,TYPE=1.0\$ NACA-H-4-0012 \$VTPLNF CHRDTP=2.7,SSPNE=5.0,SSPN=5.2,CHRDR=5.3,SAVSI=31.3, CHSTAT=0.25,TWISTA=0.0,TYPE=1.0\$ NACA-V-4-0012 CASEID SKYHOGG BODY-WING-HORIZONTAL TAIL-VERTICAL TAIL CONFIG DAMP NEXT CASE```

The output file generated by USAF Digital DATCOM for the same wing-body-horizontal tail-vertical tail configuration running over five alphas, two Mach numbers, and two altitudes can be viewed by entering `type astdatcom.out` in the MATLAB Command Window.

### Data from DATCOM Files

Use the `datcomimport` function to bring the Digital DATCOM data into the MATLAB environment.

`alldata = datcomimport('astdatcom.out', true, 0);`

### Imported DATCOM Data

The `datcomimport` function creates a cell array of structures containing the data from the Digital DATCOM output file.

```data = alldata{1} data = struct with fields: case: 'SKYHOGG BODY-WING-HORIZONTAL TAIL-VERTICAL TAIL CONFIG' mach: [0.1000 0.2000] alt: [5000 8000] alpha: [-2 0 2 4 8] nmach: 2 nalt: 2 nalpha: 5 rnnub: [] hypers: 0 loop: 2 sref: 225.8000 cbar: 5.7500 blref: 41.1500 dim: 'ft' deriv: 'deg' stmach: 0.6000 tsmach: 1.4000 save: 0 stype: [] trim: 0 damp: 1 build: 1 part: 0 highsym: 0 highasy: 0 highcon: 0 tjet: 0 hypeff: 0 lb: 0 pwr: 0 grnd: 0 wsspn: 18.7000 hsspn: 5.7000 ndelta: 0 delta: [] deltal: [] deltar: [] ngh: 0 grndht: [] config: [1x1 struct] cd: [5x2x2 double] cl: [5x2x2 double] cm: [5x2x2 double] cn: [5x2x2 double] ca: [5x2x2 double] xcp: [5x2x2 double] cla: [5x2x2 double] cma: [5x2x2 double] cyb: [5x2x2 double] cnb: [5x2x2 double] clb: [5x2x2 double] qqinf: [5x2x2 double] eps: [5x2x2 double] depsdalp: [5x2x2 double] clq: [5x2x2 double] cmq: [5x2x2 double] clad: [5x2x2 double] cmad: [5x2x2 double] clp: [5x2x2 double] cyp: [5x2x2 double] cnp: [5x2x2 double] cnr: [5x2x2 double] clr: [5x2x2 double]```

### Missing DATCOM Data

By default, missing data points are set to 99999 and data points are set to NaN where no DATCOM methods exist or where the method is not applicable.

It can be seen in the Digital DATCOM output file and examining the imported data that ${C}_{Y\beta }$, ${C}_{n\beta }$, ${C}_{Lq}$, and ${C}_{mq}$ have data only in the first alpha value. Here are the imported data values.

```data.cyb ans(:,:,1) = 1.0e+004 * -0.0000 -0.0000 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 ans(:,:,2) = 1.0e+004 * -0.0000 -0.0000 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 data.cnb ans(:,:,1) = 1.0e+004 * 0.0000 0.0000 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 ans(:,:,2) = 1.0e+004 * 0.0000 0.0000 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 data.clq ans(:,:,1) = 1.0e+004 * 0.0000 0.0000 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 ans(:,:,2) = 1.0e+004 * 0.0000 0.0000 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 data.cmq ans(:,:,1) = 1.0e+004 * -0.0000 -0.0000 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 ans(:,:,2) = 1.0e+004 * -0.0000 -0.0000 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999 9.9999```

The missing data points will be filled with the values for the first alpha, since these data points are meant to be used for all alpha values.

```aerotab = {'cyb' 'cnb' 'clq' 'cmq'}; for k = 1:length(aerotab) for m = 1:data.nmach for h = 1:data.nalt data.(aerotab{k})(:,m,h) = data.(aerotab{k})(1,m,h); end end end```

Here are the updated imported data values.

```data.cyb ans(:,:,1) = -0.0035 -0.0035 -0.0035 -0.0035 -0.0035 -0.0035 -0.0035 -0.0035 -0.0035 -0.0035 ans(:,:,2) = -0.0035 -0.0035 -0.0035 -0.0035 -0.0035 -0.0035 -0.0035 -0.0035 -0.0035 -0.0035 data.cnb ans(:,:,1) = 1.0e-003 * 0.9142 0.8781 0.9142 0.8781 0.9142 0.8781 0.9142 0.8781 0.9142 0.8781 ans(:,:,2) = 1.0e-003 * 0.9190 0.8829 0.9190 0.8829 0.9190 0.8829 0.9190 0.8829 0.9190 0.8829 data.clq ans(:,:,1) = 0.0974 0.0984 0.0974 0.0984 0.0974 0.0984 0.0974 0.0984 0.0974 0.0984 ans(:,:,2) = 0.0974 0.0984 0.0974 0.0984 0.0974 0.0984 0.0974 0.0984 0.0974 0.0984 data.cmq ans(:,:,1) = -0.0892 -0.0899 -0.0892 -0.0899 -0.0892 -0.0899 -0.0892 -0.0899 -0.0892 -0.0899 ans(:,:,2) = -0.0892 -0.0899 -0.0892 -0.0899 -0.0892 -0.0899 -0.0892 -0.0899 -0.0892 -0.0899```

### Aerodynamic Coefficients

You can now plot the aerodynamic coefficients:

#### Plotting Lift Curve Moments

```h1 = figure; figtitle = {'Lift Curve' ''}; for k=1:2 subplot(2,1,k) plot(data.alpha,permute(data.cl(:,k,:),[1 3 2])) grid ylabel(['Lift Coefficient (Mach =' num2str(data.mach(k)) ')']) title(figtitle{k}); end xlabel('Angle of Attack (deg)')```

#### Plotting Drag Polar Moments

```h2 = figure; figtitle = {'Drag Polar' ''}; for k=1:2 subplot(2,1,k) plot(permute(data.cd(:,k,:),[1 3 2]),permute(data.cl(:,k,:),[1 3 2])) grid ylabel(['Lift Coefficient (Mach =' num2str(data.mach(k)) ')']) title(figtitle{k}) end xlabel('Drag Coefficient')```

#### Plotting Pitching Moments

```h3 = figure; figtitle = {'Pitching Moment' ''}; for k=1:2 subplot(2,1,k) plot(permute(data.cm(:,k,:),[1 3 2]),permute(data.cl(:,k,:),[1 3 2])) grid ylabel(['Lift Coefficient (Mach =' num2str(data.mach(k)) ')']) title(figtitle{k}) end xlabel('Pitching Moment Coefficient')```

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