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Air Data System

Airspeed Subsystem Calibration

The following are fundemental air data equations for subsonic flight written in a classic FORTRAN flow format to illustrate the procedure for calculating the various elements.

Air Data Calculations

COMPRESSIBLE DYNAMIC PRESSURE

QCI=29.92126*(((1.+.2*(VI/661.48)**2)**3.5)-1.)

AMBIENT PRESSURE CALCULATIONS

IF (HPI-36089.24)1,1,2

1 CONTINUE

PSI=29.92126*(1.-.00000687535*HPI)**5.2561

GO TO 8

2 CONTINUE

XI=1.0/EXP((4.80637/10.**5)*(HPI-36089.24))

PSI=29.92126*0.223360*XI

8 CONTINUE

PTI = PSI + QCI

CLI=WT/(SW*QCI*70.73)

MACHI2=5.*((QCI/PSI+1.)**0.28571-1.0)

MACHI = SQRT(MACHI2)

LAG HERE IF OPTION REQUESTS

IF(LAG)82,83,82

82 CONTINUE

TAMA=(FATI+273.15)/(1.0+0.2*RF*MACHI2)

AMUMU=(TAMA/288.15)**1.5*(398.15/(TAMA+110.4))

XAA=AMUMU*29.92126

XLMDS=SLAG*XAA/PSI

XLMDT=TLAG*XAA/PTI

PSIL=PSI+(XLMDS*DPSDT)

PTIL=PTI + (XLMDT*(DPSDT + DQIDT))

QCIL=PTIL-PSIL

MACHIL2=5.0*((QCIL/PSIL+1.)**0.28571-1.0)

MACHIL = SQRT(MACHIL2)

QEL=0.7*70.73*MACH2*PSIL

CLI=WT/(QCIL*SW*70.73)

GO TO 84

NO LAG HERE

83 CONTINUE

PSIL = PSI

PTIL = PTI

QCIL = QCI

84 CONTINUE

DPC=GIRC(CLI,XT,YT,NX,1)

POSITION ERROR HERE

IF (IFIG-1)439,307,439

307 CONTINUE

LK=1

L=LL

GO TO 205

If Mach incremental correction needed

308 CONTINUE

DPM=GIRC(MACH2,XT,YT,NX,1)

GO TO 306

43 CONTINUE

DPM=0.

306 CONTINUE

9 CONTINUE

DP=(DPC+DPM)*QCIL

PAM=PSIL-DP

QC=QCIL+DP

IF (QCI)486,486,485

486 CONTINUE

MACH = 0.

GO TO 487

CALCULATE MACH

485 CONTINUE

MACH = (((QC/PAM+1.)**0.28571-1.0)*5.0)**0.5

CALCULATE FATC

487 CONTINUE

FATK = (FATI+273.15)/(1.+.2*RF*MACH**2)

FATC = FATK - 273.15

CALCULATED VKTAS

VKTAS = 38.968*MACH*(FATK**0.5)

CALCULATE VC

IF(QC)604,604,605

604 CONTINUE

VC=0.

GOTO 8007

605 CONTINUE

VC =661.48*((((QC/29.92126+1.)**.28571-1.)*5.)**.5)

8007 CONTINUE

CALCULATED VE

DELTA=PAM/29.92126

THETA=(FATC+273.15)/288.15

VE=VKTAS*(DELTA/THETA)**.5

CALCULATE HPC

DELTA=PAM/29.92126

IF(DELTA-.223360)4,5,5

5 CONTINUE

HPC=145447.*(1.-DELTA**.190256)

GO TO 8003

4 CONTINUE

HPC=36089.24-20806.*ALOG(DELTA/.223360)

8003 CONTINUE

CALCULATE QE

QE=70.73*(0.7*(MACH**2)*PAM)

CALCULATE CL (Bypass for low speed)

IF (QE)1200,1201,1200

1200 CONTINUE

CL=WT/(QE*SW*70.73)

GO TO 8005

1201 CONTINUE

CL=0.

8005 CONTINUE

89 CONTINUE

HPC=HPC + DH

PT = PAM + QC

IF(HPC-36089.24)23,23,24

23 CONTINUE

PAM=29.92126*(1.-.00000687535*HPC)**5.2561

GO TO 26

24 CONTINUE

XI=1.0/EXP((4.80637/10.**5)*(HPC-36089.24))

PAM=29.92126*0.223360*XI

26 CONTINUE

QC = PT - PAM

IF (QC)600,600,601

601 CONTINUE

VC=661.48*((((QC/29.92126+1.)**.28571-1.0)*5.)**.5)

GO TO 58

Bypass for zero and low speed value overflow

600 CONTINUE

VC=0.

58 CONTINUE

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