For helicopters, there are usually 3 to 4 engine entries, usually entered in the UH-60_data.ini as:
[Engine3]
SystemType=PROP_ENGINE
InputName=THROTTLE_CONTROL
EngineID=3
SLPowerDry=158834.1
ThrustAngles=0.0,0.0,0.0
ThrustPosition=0.0,0.0,0.0
ThrottleRate=0.5
AltitudeTableNumData=10
AltitudeTableDeltaX=7000
AltitudeTableStartX=0.0
AltitudeTableData=1.0,1.0,1.0,1.0,1.0,1.0,1.0,1.0,1.0,1.0
TSFCM0=0.90
TSFCM1=1.26
SpinnerNodeName=Shaft
StaticPropNodeName=Rotors
SlowPropNodeName=SlowRotor
FastPropNodeName=SlowRotor
SlowPropRPM=500
FastPropRPM=1000
MaxPropRPM=1200
IdlePropRPM=300
BSFC=0.00298
ExhaustEmitterName=CleanExhaustEmitter
ExhaustPosition=-1.3053,-2.4138,1.8914
FireSuppression=FALSE
; new entries
AnimationID=
MaxPowerAnimationTime=-1
MinPowerAnimationTime=-1
PropRotationDirection=
ReversePropOrientation=FALSE
ConstantSpeedProp= FALSE
NumBlades=5
PropDiameter=5.0 <<--------------------------------------------------------------------- EDIT THIS Make sure this number is smaller than 8.0 or 8.1.
MomentOfInertia=2.25
PropEfficiencyAdvanceRatioTableNumData=7
PropEfficiencyAdvanceRatioTableDeltaX=0.2
PropEfficiencyAdvanceRatioTableStartX=0.0
PropEfficiencyAdvanceRatioTableData=0.041,0.40,0.70,0.82,0.78,0.50,0.00
I'm pretty sure you need to keep it under 8.1 for the rotors to begin working again. Also, this is subjective, but if you get sick of the disc looking fast prop animation (for when the rotor is at speed) look for these entries within the Engine 3 and 4 sections:
SlowPropNodeName=SlowRotor
FastPropNodeName=FastRotor <<----------- Change this to match the SlowRotor entry and you'll have rotors that spin without that rotor disc look. It's not important to do this, but you might find it looks better.