On Thursday, July 16, 2020 at 3:57:52 PM UTC-4, wrote:
I just reread The Beautiful Mountain & her Sinister Trap, by Henry Combs, Soaring mag, Sept 1984. Henry’s friend crashed at 10:30 in the morning looking for earl lift flying alone a ridge line. Henry does an excellent job of explaining how a highly experienced pilot might get trapped on a ridge. Basically, he sets up the trap with a 5 knot thermal out away from the ridge with the sink and rolling away from the thermal, motion that everyone has experienced a thousand times. Only, this morning the sink is aligned with the face of the ridge.............here comes our highly experienced pilot flying along the ridge, looking for an early thermal........ he flies right into 5 knot sink and a rolling away motion of the thermal and the sink and rolling motion is confined by the ridge. Henry, an aeronautical engender states that it’s not hard to experience rolling motion that exceeds the capabilities of our sailplanes ailerons and in this case, the rolling motion is into the ridge!
The Sinister Trap snares someone every now and then........more than a half dozen times in my 50 year soaring experience!
JJ Sinclair

The question is: how to avoid this trap? What time of day and ridge geometry is conducive to this? What is a safe distance from the ridge and how does that depend on airspeed and thermal and wind conditions? How much airspeed (if any) would keep one safe (enough aileron authority)? When would you avoid circling (in a thermal near a ridge) and use figure eights instead (so as never approaching the ridge head-on), and is that enough to keep you safe (since that rolling motion may still get you even while flying parallel to the ridge)?