Some good thoughts here. Of course, the right answer is to not put yourself into a bad situation, if you can avoid it.
In general, I think of the autorotation in three phases: entry, sustained, landing. Each has its own peculiarities that we could all talk about for days. When you get into any low level situation, then you may have to omit the sustained portion.
For example, zero speed 500' AGL, lower collective and dive for airspeed, you should be able to attain your normal sustained parameters, so all is simple.
The entry and the landing both have airspeed changes and height changes. I think of the landing phase as a graph of speed and height, start high and fast, end at 0/0. If the entry speed and height approaches the landing speed/height line you just switch from entry phase to landing phase, allowing time and energy for the transition. Sounds complicated, but its really not.
Change the example to 200' and zero speed, you lower collective and dive. At 100' you have ~40knots (made up numbers), you haven't attained your sustained parameters, but your speed/height combination looks just like the middle of your normal landing phase, so you raise the nose to your decelerating attitude, allow the rpm to build a bit and continue with the landing you've trained.
topendtorque,
#1 I agree you don't want to lose all rpm or collective at the tree tops, but you also don't want to hit the trees at max speed. Seen the effects of that. I'd rather take my chances on a 35' foot fall, with a small cushion available than a 2000fpm descent into lumber. My plan if I don't think foliage will cushion me is to zero speed and minimize descent just above the tree tops, then dump collective to try and recover rpm on the way down, cushion at the bottom. Of course, that would be pointless if I thought the trees were going to destroy the blades so this is all situationally dependant.
This gets a bit more difficult on the West Coast of Canada. 200' trees that are greater than 5' diameter at the base, and with foliage not always dense enough to stop or slow your descent. Reliable engines and/or prayer is the best alternative we could come up with.
#2 Trade airspeed for altitude. Same as above, you start in the entry phase, but in this case you approach the landing phase from below. When you flare on entry, you made need to raise collective to control rpm, but that is type and situation dependant. When your altitude & height intercept the landing phase, it gets easy again.
Last edited by Matthew Parsons; 29th Oct 2011 at 16:29.