Done! Fixed physics and added infinite machine gun:

**Physics improvements:**
- Increased gravity to 9.8 (realistic)
- Better thrust (8000), lift coefficient (0.08), and control sensitivity
- Control effectiveness scales with speed (less responsive at low speed = stall behavior)
- Added drag force proportional to speed squared
- Added max speed limiter (300 m/s)
- Stall speed of 40 m/s - plane drops if too slow

**Machine Gun (G key):**
- Hold G to fire continuous twin bullets from wings
- Infinite ammo (∞ shown in HUD)
- Yellow tracer rounds at 500+ m/s
- 50ms fire rate (20 rounds/sec)
- Looping gunfire sound

**Next Ideas:**
1. **Tracer Effects** - Add glowing particle trails behind bullets for better visibility
2. **More Enemies** - Add multiple enemy planes at once with different behaviors

**Ready to level up your game? Pick one and let's build it!**