From 1d081cdd9328cdcbb74a16e9442a2597f6aa0014 Mon Sep 17 00:00:00 2001
From: ehofman <ehofman>
Date: Sat, 2 Oct 2004 13:34:06 +0000
Subject: [PATCH] Move the calculations of Mach to the base class.

---
 src/AIModel/AIBallistic.cxx |  1 -
 src/AIModel/AIBallistic.hxx |  1 -
 src/AIModel/AIBase.cxx      | 16 +++++++++++++++-
 src/AIModel/AIBase.hxx      |  3 +++
 4 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/src/AIModel/AIBallistic.cxx b/src/AIModel/AIBallistic.cxx
index 5bfadf48b..2a9f97e73 100644
--- a/src/AIModel/AIBallistic.cxx
+++ b/src/AIModel/AIBallistic.cxx
@@ -36,7 +36,6 @@ FGAIBallistic::FGAIBallistic(FGAIManager* mgr) {
     gravity = 32;
 //  buoyancy = 64;
     no_roll = false;
-    Mach = 0.4;
 }
 
 FGAIBallistic::~FGAIBallistic() {
diff --git a/src/AIModel/AIBallistic.hxx b/src/AIModel/AIBallistic.hxx
index 83231bcf3..82309ea2b 100644
--- a/src/AIModel/AIBallistic.hxx
+++ b/src/AIModel/AIBallistic.hxx
@@ -67,7 +67,6 @@ private:
     bool wind;              // if true, local wind will be applied to object
     double Cd;              // drag coefficient
     double mass;            // slugs
-    double Mach;
 
     void Run(double dt);
 };
diff --git a/src/AIModel/AIBase.cxx b/src/AIModel/AIBase.cxx
index 935d5c660..db566a1ef 100644
--- a/src/AIModel/AIBase.cxx
+++ b/src/AIModel/AIBase.cxx
@@ -98,9 +98,23 @@ void FGAIBase::update(double dt) {
     }
 
     rho = p / (1718 * (T + 459.7));
+	
+	// calculate the speed of sound at altitude
+	// a = sqrt ( g * R * (T + 459.7))
+	// where:
+	// a = speed of sound [ft/s]
+	// g = specific heat ratio, which is usually equal to 1.4  
+	// R = specific gas constant, which equals 1716 ft-lb/slug/°R 
+	
+	a = sqrt ( 1.4 * 1716 * (T + 459.7));
+	
+	// calculate Mach number
+	
+	Mach = speed/a;
+	
+//	cout  << "Speed(ft/s) "<< speed <<" Altitude(ft) "<< altitude << " Mach " << Mach;
 }
 
-
 void FGAIBase::Transform() {
     if (!invisible) {
       aip.setPosition(pos.lon(), pos.lat(), pos.elev() * SG_METER_TO_FEET);
diff --git a/src/AIModel/AIBase.hxx b/src/AIModel/AIBase.hxx
index f8728561d..5cc92b5b4 100644
--- a/src/AIModel/AIBase.hxx
+++ b/src/AIModel/AIBase.hxx
@@ -182,6 +182,9 @@ public:
     double rho;
     double T;                             // temperature, degs farenheit
     double p;                             // pressure lbs/sq ft
+	double a;                             // speed of sound at altitude (ft/s)
+	double Mach;                          // Mach number
+	
     static const double e;
     static const double lbs_to_slugs;