Ideally you want to run your engine just above the peak power so that as it loads up the revs drop and the power increases. Curtis also recommends this on his website. I like to run about 50rpm headspeed above the peak power rpm. This equates to 425 engine rpm @ 8.5 gear ratio. The ideal head speed would then be 2050 for an engine speed of 17 425.
The control loop in the GV1 will always try to return the headspeed to its setpoint and is probably underdamped for a faster response. This means it will slightly overspeed before settling back to setpoint. You might not hear this as the RPM involved are low. An engine should also not be overspeeded. The GV1 manual recommends setting the headspeed 50 rpm below that for maximum engine revs to protect the engine. The OS 50 Hyper is specced at 20 000 RPM practical maximum so a headspeed of 2100 and engine speed of 17 850 (@8.5 gear ratio) should not be a problem for the engine! 20 000 rpm equates to a headspeed of 2350 rpm - any takers?
The amount of energy stored in the rotor blades goes up with the square of head speed so a 5% increase in headspeed (2000 to 2100) results in 10% more energy in the head. As you pull collective or cyclic the stored energy goes into the extra drag causing a drop in rpm. The governer catches the drop in rpm by adding more power. The more energy available in the head the smaller the rpm drop when the head loads up. This leads to smoother flight and more constant head speed.
If we move too far out of the engines power band then the head will sag more. So we have to find the ideal balance between higher head speed for energy, protecting the engine & rotor head (from overstressing) and being in the right place on the engine power band.
I think I'll try the 2100 headspeed on the 50SE!!
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