I think most pilots are aware of the reduction in helicopter Vne with density altitude, primarily due to our true airspeed being higher than the indicated airspeed and therefore increasing the likelihood of retreating blade stall etc...
What is the effect of this on our autorotative speed?
In the R44 POH the suggested standard autorotative speed is 70kts. At Sea-level the Vne is 130kts (is TOM<2200lbs), and autorotative Vne of 100kts (always 30kts less than the power on Vne). At 10'000 feet the Vne could be as low as 85kts, with an autorotative Vne of 55kts.
I've always been wary of doing auto's with speed under 60kts because of the reduced flare effect, which I assume relies on dynamic pressure (IAS) as opposed to TAS? perhaps not?
So if the Autorotative Vne was 55kts, would it be wise to fly the auto at 55kts (to help with the flare, especially when the air is already thin having a detrimental affect on the flare effect) even though the blade TAS would surely be higher than in a 70kt standard auto, or would there be any negative effects of flight near power-off Vne? i.e. should the standard autorotative speed be brought back accordingly to perhaps 40kts?
I have very little experience flying at high densitly altitudes (usually T/O at 60ft AMSL in 5-15deg C) and would like to hear the opinions of those who frequently practice auto's at higher DA's
Cheers