I'm not a pilot, just asking out of curiosity. What is the typical descent rate for a helicopter when landing? I found the answer of 300 feet per minute on the web, but I want to confirm this. If this is true, than a helicopter descending from 2400' to land would take 8 minutes. Is this correct?
That is of course dependent on airspeed at approach, and the approach angle. I have a flight manual of an older type helicopter, I cannot reproduce the contents, but it shows True Airspeed on the horizontal axis, Rate of Descent on the vertical, and a set of inclined lines for the angle of Descent.
In the Emergency Procedures - Normal Approach, an Angle of Descent of 8 - 10º is specified, and a typical TAS of 65 knots. This amounts to a Rate of Descent between 800 and 1100 ft/min. Maximum allowable ROD at that speed is 1600 ft/min which is marked as Approximate Autorotation.
The 300 feet per minute rate is the maximum descent rate for a hover. In helicopters, it is the rotor that is providing airflow downwards to keep the helicopter in the air. The air that has traveled through the rotor, downwards, keeping the helicopter aloft has become very turbulent air with a downward velocity. This means that it until it settles, it is not going to provide lift. If I'm in a hover, and I descend at a rate higher than 300fpm, then I can potentially descend into my own down-wash, and then the rotor stops providing lift. This is known as vortex ring state, or sometimes settling with power (Vortex Ring State is more precise, settling with power can occur for various reasons and in different conditions). If I'm traveling in some direction at a reasonable speed, I'll be moving away from the turbulent air that just went through the rotor, and the low descent speed no longer applies.
The calculations from the earlier post are reasonably accurate for an emergency descent. In an emergency landing (an autorotation, or power-off landing), the R22 emergency procedures state to establish your glide at 65 knots, with your vertical descent being controlled by what is required for me to keep the rotor spinning.
In a normal descent, my forward airspeed would be closer to 90 knots, and 8-10 degrees would be on the higher end for descent rates.