PpruneFan#1,
1) If you have a copy of that accident report, please share it with me. I have no idea what the weight is, frankly. But I can say with some certainty the hover weight was more than the available power would support!
2) The maximum design rate of descent for an H-3/S-61 main gear design is 8 feet per second, which varies a very little with gross weight. Combined with the yaw at touchdown (symptomatic of excess torque, saturating the tail rotor) and the bank, the gear failure is predictable at somewhere near 500 or 600 fpm. The fuselage stayed intact, showing that the rate was not too much greater.
3) The downwash velocity of an H-3 is about 80 feet per second (4800 fpm), so we need at least 50% of that to get close to VRS, and 75% before we see any real torque spikes and the like. Thus, the machine had to be dropping at more that 2400 fpm to be anywhere
near VRS.
See:
http://www.ae.gatech.edu/people/dsch...201%20Aero.ppt slide 33 for a nice discussion of the downwash velocity and how to calculate it. Remember, the Vortex that forms the ring is running down away from the rotor at that velocity, and you have to drop fast enough to catch it if you want to form a VRS.
See:
http://www.enae.umd.edu/AGRC/Aero/vring.html for a great VRS resource site. Leishman did great work helping define where VRS actually happens (because of the notorious V22 accident) and modeled for the first time the actual vortex reingestion. He shows that no significant power rise occurs until 50% of the downwash speed, based on experiment and modeling.
Here is a movie of his very accurate modeling of the vortex ring. The film shows a rotor as it is accelerated downward, showing the vortex forming as the descent rate increases. Unfortunately, he didn't run a device to show the rate of descent as the vortex forms, but his paper shows that the first vortex touches the rotor at aboyt 60% of the downwash speed ((3000 fpm for that S-61!)
http://www.enae.umd.edu/AGRC/Aero/images/wake1.gif