Comparing C20R2 stalls/surges to a C20B

[5Blades]

I am interested in finding out what Operators, Pilots, or Engineers out there have had trouble if any with the C20R engine with particular interest in Compressor Stalls/Surges, if so what type of Aircraft, particle separator or mist eliminator installed? How did you eliminate the issue or are you still dealing with it? Also of interest are pilots who have experienced an compressor stall/surge in a C20R and also a C20B e.g. comparing the difference between the two. How it felt, noise, yaw, decrease in RRPM? The C20B sounds like it is a little more benign compared to the same issue in a C20R.

Genuine Questions so thanks for any info in advance.

[Shawn Coyle]

My only experience with the C20R was with a FADEC version of it under test with Allison and Agusta for the A109D (the version that was beat out by the A109E with PW engines).
We were flying with a rear wind of about 17-20knots and watched the TOT climb until there was one pop - the FADEC captured the condition and prevented further stalls.
The engineer and test pilot both from Agusta said that the 'normal' C20R would continuously compressor stall in these conditions. Later a Belgian Army pilot who flew their version of the A109 which had the 'normal', non-FADEC version of the engine confirmed the compressor stall issue.
I've never had a C20B compressor stall in all my years of flying JetRangers and OH-58Cs.

[Chris P Bacon]

From a Model 250 repair facility.
The majority of C20R surging/stalling can be atributed to the Turbine stage 1 nozzle.
The original Pt No 23038219 and then the replacement MAR-M version, Pt No 23062754 caused choking at the Turbine inlet. Rolls Royce agreed to us fitting the C20B engine stage 1 nozzle (Pt No 23062753) with a different flow area and this is just about standard now at all the RR approved facilities and has almost eliminated the problem. Also, to get the optimum performance, the C20B type stage 1 nozzle should be installed if you embody the power turbine enhancement.
One other area to look at is to have the Compressor bleed valve closing adjusted to the engine requirements, rather than the bleed valve test rig setting.