Originally Posted by
Lonewolf_50
Cappy: are you referring to airspeeds as high as 80 kts being in the range of VRS?
At 80 knots in a Black Hawk you are well through translational lift, and not too far from L/D max (max fuel conserve airspeed, max power margin, of course DA/GW dependent) and pretty close to optimal autorotation airspeed (DA and GW dependent) with if memory serves a few knots to spare.
Was 80 knots a typo there? Your post confused me for multiple reasons, but that in particular makes no sense to me. What point were you trying to get across? In flight vibration levels, or something else?
(Memory banks are a bit foggy; while we flew most of our maintenance autos at ~80 KIAS, I seem to recall learning that the sweet spot was somewhere between 70 and 75 kts. I am sure Mr Dixson can fine tune that with his experiences in developing that helicopter).
I was looking at the chart wrong. I haven't looked at it in over a decade, so I followed the airspeed column up the approach angle lines when i should have went vertical. So, the range is up to 26 knots, and vertical descents from 1786FPM to 3383FPM will put you in VRS in a black hawk. That is a pretty large envelope compared to an R22 which is 14 knots and 927 fpm to 1756 fpm at gross weight. Or even a lightly loaded black hawk at 12,000 pounds which would be 20 knots, 1319 FPM to 2500 FPM
The higher the gross weight (higher disk loading), and the higher the altitude creates a faster downwash and a larger envelope which to avoid. Albeit, at a higher ROD which may make it easier to avoid. The lower the gross weight (lower disk loading), and the lower the altitude creates a slower downwash and a smaller envelope to avoid.
Main Rotor Radius 26.9
Disk Area 2273.28786006411
Weight 22000
Disk Loading 9.67761293520459
Air Desnity 0.002377
Vi 2707.10926827765
Vi min .66 1786.69211706325
Vi max 3383.88658534706
Vi Peak 14.6835315340503
Vi 1 26.6973300619097
Vi 2 53.3946601238194
Vi 3 80.0919901857291