@212Man - logic...
Hey 212Man, I see what you are saying and why it may seem that way, but I let me try to explain why I still think it is right.
Firstly - lets be very clear - this is JUST talking about why the number is 57 knots - this is not a discussion on if you should be flying at 10,000 ft at 30C or what you or I do personally when flying in turbulence - this is just about the FAA approved number in 2-15 of the Limitations section of the R22 POH.
So lets run a couple of scenarios:
#1
4,000' PA, 0C
Vne is 102 kts. We are flying along at 100 kts when we come across moderate turbulence - according the POH 2-15 we reduce airspeed to between 60 kts and 71 kts (102 Vne x 0.7).
#2
8,000' PA, 30C
Vne is 69 kts. We are flying along at 65 kts and hit moderate turbulence again - doing the math we should be flying between 60 kts and 48 kts (69 Vne x 0.7) but wait, 48 is lower than 57 kts and the POH section 2-15 says "...but no lower than 57 KIAS..." - so it should be between 57 kts and 60 kts.
#3
10,000 PA, 30C
Vne is 57 kts (the lowest Vne on the chart) so although we may be flying along at 57 kts, we should not go any faster as we would be exceeding limitations and likely soon experience retreating blade stall. Lets say we flying along at 53 kts (best climb speed), trying to get max performance to be able to stay up at 10,000....Now we hit moderate turbulence again (been a bad day for it) and we do the math - between 60 kts and 40 kts (57 Vne x 0.7). 40 kts is lower than the minimum 57 kts mentioned and we shouldn't be going 60kts as that is above Vne, so according to the limitations we should speed up to 57 kts.
Does that make sense as far as number go?
If that still doesn't make sense and you want a better explanation, give Robinson Helicopter a call. I spoke to a guy called Pat Cos (not sure of the spelling).Let us know what you hear.
Like I said this is just a discussion of where the 57 comes from - in reality I don't think I would be trying to fly an R22 at 10,000 at 30 C.
p.s. I am referencing those numbers from the latest R22 POH - available at robinsonheli.com/r22_poh.html