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 $C_{Y β}$ , $C_{n β}$ , $C_{L q}$ , and $C_{m q}$ 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
Plotting Drag Polar Moments
Plotting Pitching Moments

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')

Documentation