ao-tools: Add ao-fakeflight

[fw/altos] / ao-tools / ao-fakeflight / ao-physics.c

diff --git a/ao-tools/ao-fakeflight/ao-physics.c b/ao-tools/ao-fakeflight/ao-physics.c
new file mode 100644 (file)
index 0000000..114b9e0
--- /dev/null
+++ b/ao-tools/ao-fakeflight/ao-physics.c
@@ -0,0 +1,53 @@
+/*
+ * Copyright © 2014 Keith Packard <keithp@keithp.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
+ */
+
+#include "ao-fakeflight.h"
+
+/* Density of dry air in kg/m³ for a given pressure and temperature. */
+double
+density_air(double pressure,           /* Pa */
+           double temperature)         /* °C */
+{
+       return pressure / (GAS_CONSTANT * (temperature + 273.15));
+}
+
+/* Area of a circle */
+double
+area_circle(double diameter)
+{
+       double radius = diameter / 2;
+       return M_PI * radius * radius;
+}
+
+/* Force due to drag (N) */
+double
+force_drag(double      speed,          /* m/s */
+          double       rho,            /* kg/m³ */
+          double       cd,             /* unitless */
+          double       area)           /* m² */
+{
+       return 0.5 * rho * (speed * speed) * cd * area;
+}
+
+/* Force due to gravity (N) */
+double
+force_gravity(double   mass,           /* kg */
+             double    altitude)       /* m */
+{
+       double  distance = altitude + EARTH_RADIUS;
+       return GRAVITATIONAL_CONSTANT * EARTH_MASS * mass / (distance * distance);
+}