In Army flight school in the late 60's at Fort Wolters TX., many of the Southern Airways instructors were willing to WOW the young student pilot with an occasional backup auto in a Hughes 269A.
I went back to Wolters after RVN and did a few in the 269 myself.
Went to Fort Rucker and tried to demonstrate one in a UH-1H to my students one day. After all, a Vietnam warrior, high-speed instructor who was as good in an H1 as I should have no problem with a maneuver he had done several times in a "lesser" aircraft.
Worked fine till enough air got on top of the Sync Elevator to pitch the nose up abruptly. One of the oddest ways to enter a hammerhead you might imagine.