Well, now that I've re-read what you passed on from Ron:

“… when flak started popping up in front of me …”
At this point you have few real options. The AA fire is likely radar-controlled, and is specifically designed for warplanes traveling a lot higher and a lot faster than a Huey. You cannot outrun it. You cannot climb high enough or fast enough to get away from it. Your only hope of salvation is to get under it. Quickly.

“Basically, you do a "quick stop" by pulling abruptly back on the cyclic to zero-out your airspeed...in other words, stand it on its tail.”
This kills the airspeed and gets you stopped.

“That puts the aircraft in a nose high attitude, … ”
As in, pointing straight up!

“ … at which time you kick in right pedal … “
This uses the engine torque to advantage to swap the tail and nose quickly, and puts the aircraft pointing nose straight down --- where you want to go.

“ … and roll off the throttle … “
Ahhh. An interesting wrinkle. More on this later.

“ … and lower the collective to enter autorotation. “
Ohh, boy. Grab something solid!

“This will point your nose straight down and corkscrew you towards the ground.”
No kidding. Whew.

This is not what I knew as a Corbin Spin, this power-off thing. It would really really be interesting to hear from some of the pilots between late 67 and late 69 and get their “spin” (please pardon the pun) on this. I, like many another, might want to think a little before rolling the throttle off. Everything I knew spin-wise was power-on. Which is partly why there were such large forces on the aircraft and the rotor system. Doing them power-off would greatly reduce these forces, but would also compromise the ensuing drop rate.

Traveling forward nose-down at 4000 fpm, it seems to me, would be similar to traveling forward at nose-level, except for the power required to maintain this speed. A little arithmetic shows that 4000 fpm is 414 miles per hour. This is somewhat greater than a Huey’s VNE (Velocity Not to Exceed) in powered flight, which is 120 knots? 140? My memory is dim, but I think a UH-1H’s VNE must be around 140. It relates to engine/rotor stresses transferred to the airframe that are greater than it (the airframe) is designed for. But in a gravity-driven power-off dive --- ? I’d like to go flying with Ron sometime and play with this.

It would appear to me that somewhere along the line, “we” decided to modify this spin somewhat to make it easier to enter, and easier to recover. Along the way, “we” made it more dangerous mechanically. Or else, I really did not know or use the Corbin Spin; which is certainly also possible. I sure wish some other pilots would get on board and help me out. I am running out of bullsh---, er, uh, I mean, technical talk and expertise.

Pickett