There are three subjects that deserve discussion concerning the prerotator function of the Nano. There is the hydraulic pump flat belt and its two adjustments. There is the hydraulic motor with its cog belt with tensioner adjustment with the focus on preflight of hardware for remaining tight and in place. And lastly, technique applied to get the most efficient output of the system.
Flat Belt Adjustments-This is a trial and error process with the goal of no belt slippage as engine rpm is raised to attain the goal rrpm. You will know the belt is not tight enough when the erpm races up telling you the load on engine has gone away and is creating damaging heat on the belt as well. You will need to make two adjustments. The wire of the cable is squeezed tight by two 10 m nuts. And the cable housing is adjusted to allow the full 90 degree throw of the engagement lever. Will too much tightness damage belt long term? And too much heat generated by unneeded slippage? Don't know, but changing that belt does not look simple.
Technique- This is my opinion developed after many practice and not fly exercises of engine and rotor rpm. I place erpm at 2500 and move prerotator knob down at a rate that almost kills the engine. I engage and back off as needed and soon there is full lever down with engine stable at 2500 rpm. This technique involves moments of slippage but cannot be helped. Now the erpm is advanced at 200 rpm increments while observing the response of rrpm. There is a judgement as to the rate of movement of the two rpm that experience will teach. As you advance beyond 3500 rpm, the rate of rrpm may slow. If you reach the ideal goal of 200 rrpm, then your good to go. However, be on alert for the snap sound which is the cog belt jumping sprockets on the small hydraulic motor gear. Do not let the snap continue as you are only damaging the belt and will not gain any higher rrpm. In my opinion, the weak link in this system is the width of the cog belt. A belt cut to fit the entire width of the large sprocket would spread the loads of the higher erpm. This would require a hardware change of the drive gear. If you do not need more than 175or 180 to safely launch on your runway, then its not a real problem
I would hope that folks would join in on this discussion. And don't worry about hurting my feeling. I have learned to thrive of rejection.
