feat(flight): enhance flight model with transonic drag and vortex lift features

src/main/java/dev/lumareth/improvedAerodynamics/flight/TransonicDrag.java

@@ -0,0 +1,33 @@
+package dev.lumareth.improvedAerodynamics.flight;
+
+/**
+ * Rise of zero-lift drag around the speed of sound: shock waves build up from Mach 0.8, drag peaks at Mach 1.05 and
+ * settles to a lower, still high, level once the flow is fully supersonic from Mach 1.3.
+ */
+final class TransonicDrag {
+    private static final double DRAG_RISE_START = 0.80;
+    private static final double PEAK = 1.05;
+    private static final double SUPERSONIC_START = 1.30;
+
+    private TransonicDrag() {
+    }
+
+    /**
+     * @param mach           airspeed divided by the speed of sound
+     * @param peakDrag       multiplier at the peak
+     * @param supersonicDrag multiplier once fully supersonic
+     * @return factor for parasitic drag, 1 in subsonic flight
+     */
+    static double multiplier(double mach, double peakDrag, double supersonicDrag) {
+        if (mach <= DRAG_RISE_START) {
+            return 1.0;
+        }
+        if (mach < PEAK) {
+            return 1.0 + (peakDrag - 1.0) * ImprovedAero.smoothstep(DRAG_RISE_START, PEAK, mach);
+        }
+        if (mach < SUPERSONIC_START) {
+            return peakDrag + (supersonicDrag - peakDrag) * ImprovedAero.smoothstep(PEAK, SUPERSONIC_START, mach);
+        }
+        return supersonicDrag;
+    }
+}