What is the most helpful way to report bugs?
On OS X 10.9.2 there is a fairly reproducible problem after some heli crashes, particularly into the terrain past the wind sock in the default scene. The frame rate drops to roughly half of the usual 60 frames/sec. There is also an odd sound in the background.
If I select the "Load model" menu option, after clicking the "Load" button the problem is resolved.
I could capture a profile via the OS X Activity Monitor or send along logs if that would be helpful.