On my 9A I've got an IO360 and Whirlwind RV200 prop with their Jihostroj governor. Over the last couple days doing taxi testing prior to first flight I've been doing some progressive higher power runs, including sudden full-throttles, mostly to see if I could make the engine stumble or miss or do anything else that would concern me if it happened in the air. For this purpose I was being intentionally "ham-handed" with the throttle and throwing it around rather quickly, much more so than would normally be done in a non-emergency scenario. As I said, I was trying to make the engine do something bad.
Well, the engine played nice-nice through it all, and this morning I'm perusing my datalog from the Dynon Skyview, which was set to record all parameters at 1/4 second intervals. One thing that I was looking at was RPM stability versus manifold pressure, and I found that on those occasions where I would absolutely slam open the throttle, then engine would speed up and the governor let the RPM overshoot a bit before pulling it down. In several cases I saw two consecutive datasets (1/2 second) in the mid-upper 2700 rpm range, and 3 times I saw a single dataset (1/4 second) above 2800. The highest I saw was 2850 rpm. In all cases the governor stabilized in the upper 2600's within the span of a full second, usually within 3/4 second. I think it's likely this has been happening to all of us with C/S props for about 60 years, and only recently do we have data collection good enough to see it.
I called Whirlwind and spoke to an engineer there named Greg, discussed this situation, and he expressed surprise that the governor actually captured the target speed as quickly as it did, considering the rapid change that was being asked of it. He advised first off that I not be so hamhanded with the throttle (which I won't normally, this was testing) and second that these minor overspeeds are expected and accepted within some range of RPM. He wouldn't tell me what they considered the upper range of acceptable, but did say they have tested to 3100RPM without problems as long as it is a simple short excursion. They are much more concerned with sustained overspeed in the several-second to minutes range. My governor seems to be quite happy stabilizing at 2650-2670 rpm, and he actually suggested I dial that up just a hair for a target of 2700, but I think I will leave it right where it is for the moment. The power production of the IO360 at that RPM gives an acceleration that I am more than comfortable with and I don't see the advantage of chasing that small detail just yet, during early Phase I.
Anyway - just a datapoint on Whirlwinds view of minor overspeeds - thought I would share that. The whirlwind manual says no action is needed for an overspeed up to 110% of normal redline.
Well, the engine played nice-nice through it all, and this morning I'm perusing my datalog from the Dynon Skyview, which was set to record all parameters at 1/4 second intervals. One thing that I was looking at was RPM stability versus manifold pressure, and I found that on those occasions where I would absolutely slam open the throttle, then engine would speed up and the governor let the RPM overshoot a bit before pulling it down. In several cases I saw two consecutive datasets (1/2 second) in the mid-upper 2700 rpm range, and 3 times I saw a single dataset (1/4 second) above 2800. The highest I saw was 2850 rpm. In all cases the governor stabilized in the upper 2600's within the span of a full second, usually within 3/4 second. I think it's likely this has been happening to all of us with C/S props for about 60 years, and only recently do we have data collection good enough to see it.
I called Whirlwind and spoke to an engineer there named Greg, discussed this situation, and he expressed surprise that the governor actually captured the target speed as quickly as it did, considering the rapid change that was being asked of it. He advised first off that I not be so hamhanded with the throttle (which I won't normally, this was testing) and second that these minor overspeeds are expected and accepted within some range of RPM. He wouldn't tell me what they considered the upper range of acceptable, but did say they have tested to 3100RPM without problems as long as it is a simple short excursion. They are much more concerned with sustained overspeed in the several-second to minutes range. My governor seems to be quite happy stabilizing at 2650-2670 rpm, and he actually suggested I dial that up just a hair for a target of 2700, but I think I will leave it right where it is for the moment. The power production of the IO360 at that RPM gives an acceleration that I am more than comfortable with and I don't see the advantage of chasing that small detail just yet, during early Phase I.
Anyway - just a datapoint on Whirlwinds view of minor overspeeds - thought I would share that. The whirlwind manual says no action is needed for an overspeed up to 110% of normal redline.
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