When to flare?
When I teach autorotations in a 300C I have the students start the flare between 50 - 60 feet. I have them slowly apply aft cyclic and have them level the aircraft between 5 - 10 feet no mater what the ground speed is. After several auto's they develope the idea of how much to flare and how long to hold it. It will vary depending on wind conditions, etc.
"disclaimer"
DO NOT TRY THIS WITHOUT A FLIGHT INSTRUCTOR ON BOARD!
When you enter the autorotation and have established a steady state auto increase the collective slightly to bring the rotor RPM to the lower part of the green. 300C 410-420RPM. You will see the rate of descent is slower than when the rotor is in the middle to upper part of the green.
When you flare the RPM will raise to the upper part of the green in the rotor rpm gauge, and you are less likely to overspeed the rotor in the flare. Always try to be in a level attitude by 5 - 10 feet.
DO NOT TRY THIS WITHOUT AN INSTRUCTOR. LOW ROTOR RPM WILL KILL YOU.
I have done this with commercial students (175 hrs - 200 hrs) learning touchdown auto's and found that it made the decent and flare less dramatic at the bottom. The instructor has to stay on his toes to insure rotor RPM does not decay below limits.
skycop9
"never let your education interfere with your learning"