'============================================================================
' Calculate descent rate of a parachute given diameter and load.
'============================================================================
'
'This is a public domain program which you are encouraged to copy and give
'to your friends. A complete rocket design program which takes into account
'real, commercially available engines and real aerodynamic drag is available
'from:
'
' Cambridge Group
' 1921 N Gaffey #D
' San Pedro
' CA 90731
' (310) 832 8836
'
' The program allows you to design your own engines and handles supersonic
' flight. It comes with a manual describing some innovative and radical
' design possibilities.

' Print header page
CLS
PRINT "Another public domain shareware program by:-"
LOCATE 5, 32
PRINT "CAMBRIDGE GROUP"
LOCATE 7, 16
PRINT "AUTHOR OF CAMBRIDGE GROUP ROCKET DESIGN PROGRAM"
LOCATE 8, 10
PRINT "All you need to predict rocket performance - high altitude, low"
LOCATE 9, 10
PRINT "altitude, multi stage, supersonic - you name it."
LOCATE 11, 10
PRINT "We provide source code in Quick Basic - easily moved to another machine"
LOCATE 15, 10
PRINT "1921 N Gaffey #D"
LOCATE 16, 10
PRINT "San Pedro"
LOCATE 17, 10
PRINT "CA 90731"
LOCATE 25, 1
PRINT "Hit any key to continue";
DO
LOOP WHILE INKEY$ = ""


CLS
PRINT "RATE OF DESCENT OF A PARACHUTE. SUGGESTED VALUES:-"
PRINT "Barometric Pressure = 29.921. Altitude = 0."
PRINT "Temperature = 59."
PRINT "Cd = 0.8 (Paratech) 1.0 (Standard) 1.2 (Mylar)"
DO
   INPUT "Barometric Pressure (inch), Altitude (MSL)"; Baro, alt
   INPUT "Temperature (deg F)", Tf
   'Compute the density altitude. This is the altitude at which a
   'standard atmosphere would have the same density as the actual
   'atmosphere through which the parachute descends.

   'Convert to degrees absolute
   K = (Tf - 32) * (5 / 9) + 273.15

   'Compute pressure in mm of mercury
   P = Baro * 760 / 29.921 - alt * .02647

   'Compute density in kg/m3
   'Density of air at 0 deg C = 1.2928 kg/m3
   'Density of air at 15 deg C = 1.2256 kg/m3
   Rho = 1.2928 * (273.13 / K) * (P / 760)
  
   'Compute density altitude
   Densalt = (1 - Rho / 1.2256) * 35474
   PRINT USING "Density Altitude = ###### ft"; Densalt
  
   'Get parachute data
   INPUT "Weight (lbs), Parachute Diameter (in), Cd"; W, Dia, Cd
  
   'Compute area in sq meters
   A = 3.14159 * ((Dia * .5 * .0254) ^ 2)
  
   'Compute mass in kg
   m = W / 2.24

   'Compute descent rate
   v = SQR(2 * m * 9.8 / (Rho * Cd * A))
   PRINT USING "Descent Rate = ###### ft/sec"; 3.281 * v

LOOP