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Tim H wrote: ↑Fri Oct 22, 2021 12:03 am
One thing I noticed is the RPM seems to be higher in colder temps. Does the temp impact max RPM and if so if the prop is adjusted in cold weather then it won't make max RPM in warm weather and if its adjusted in warm weather then it might overspeed in cold weather?

Is it time for a governor overhaul since the adjustment is at the max RPM and I'm not making max RPM?

Mine tends to want to be a bit higher when the oil is “cold”. That is, the initial takeoff of the day. But it doesn’t vary wildly. Since yours has shown itself considerably low for over a decade it wouldn’t seem to be governor wear. I can think of two things:

1. There is an adjustment screw in the hub that restricts how “flat” the blades can possibly go. This should be properly set at manufacture and/or overhaul. A way to see if this is the limit is put the plane in a bit of a dive with the prop lever full forward. If the RPM increases substantially this is probably a factor.
2. This is a little trickier to explain, but the travel of the lever that rotates the control shaft of the governor may need “reclocking”. It’s a spline joint. By repositioning the lever on this spline one can bias the entire setting range to higher RPM. So the max limit is now higher.

Rich wrote: ↑Fri Oct 22, 2021 12:38 am

Tim H wrote: ↑Fri Oct 22, 2021 12:03 am
One thing I noticed is the RPM seems to be higher in colder temps. Does the temp impact max RPM and if so if the prop is adjusted in cold weather then it won't make max RPM in warm weather and if its adjusted in warm weather then it might overspeed in cold weather?

Is it time for a governor overhaul since the adjustment is at the max RPM and I'm not making max RPM?

2. This is a little tricker to explain, but the travel of the lever that rotates the control shaft of the governor may need “reclocking”. It’s a spline joint. By repositioning the lever on this spline one can bias the entire setting range to higher RPM. So the max limit is now higher.

Has your governor ever been overhauled? After mine was, I couldn't get more than 2620 RPM even with the adjustment screw backed all the way out. I called the shop that overhauled it, and spoke to the tech that actually did the work. It turns out that different versions of the IO360 have different prop governor drive ratios, and he used the incorrect one when 'clocking' the lever on the splined shaft - it was off by one tooth. After 're-clocking', the adjustment screw is in the middle of its travel, and my max RPM is right at 2700.

The governor has never been overhauled (since I've owned it) and I don't see a record of an o/h in the logs.

My mechanic adjusted the "clocking" two splines and now I get 2690 static RPM, so that appears to have been the issue.

Thanks for your suggestions.

Tim H wrote: ↑Fri Oct 22, 2021 11:19 pm The governor has never been overhauled (since I've owned it) and I don't see a record of an o/h in the logs.

My mechanic adjusted the "clocking" two splines and now I get 2690 static RPM, so that appears to have been the issue.

Thanks for your suggestions.

Tim:

I would watch your RPMs carefully during the takeoff roll. The 2700 max RPM figure for our engines is exactly that, an absolute maximum. Generally RPM increases anywhere from 30-50 during the takeoff run from static max RPM.

Thanks for posting this information. I am new to the DA40 and some of the techniques that are taught for operating, although they may not be harmful, are not necessary. Keep up the great work. This forum is a VALUABLE source of information!

Here are some other articles I have found on the forum re IO-360 performance and leaning. Trying to pull them together with the AFM, STCs, engine manual etc for our own ops guide. Additional pointers are appreciated.

Advanced Leaning Mike Busch
2200 or 2400 Cruise
Preferred Power Settings
How do you fly cross country
IO-360 Lean During Cruise Climb
Maximizing Climb Performance

The 2700 max RPM figure for our engines is exactly that, an absolute maximum

FWIW, my mechanic says that as long a its just a blip over 2700 it's fine. I see 2710 for a split second during a takeoff roll with a smooth throttle advance.

dant wrote: ↑Tue Jan 18, 2022 8:41 pm

The 2700 max RPM figure for our engines is exactly that, an absolute maximum

FWIW, my mechanic says that as long a its just a blip over 2700 it's fine. I see 2710 for a split second during a takeoff roll with a smooth throttle advance.

Understood. Mine goes to 2710 very occasionally, and that is not a problem. Tim, however was reporting 2690 static RPM, which would typically result in 2740 max RPM during takeoff, and I wouldn't recommend that.

I have the VM1000 engine monitor that records maximum RPM for each flight. I “download” the number manually with a pen and paper during cruise so that I know what the max t/o value was. My numbers range from 2630 to 2720. They have been greater than 2670 since it turned cold in December. I have only seen > 2700 twice but these were in September when it was warm. I cycle my prop 2x during my run-up. My governor was overhauled a year ago and I didn’t notice a change, except that on my test flight the RPM’s were < 2600 and I asked for an adjustment. I’ve checked my VM1000 tach against a TruTach II digital optical tachometer and it’s accurate. My impression is that because the governor is a mechanical/analog system it’s control over the prop speed isn’t that great, especially when it is trying to respond quickly to changes in power and load that occur during take off. I’m not sure I really needed the overhaul. It was $1K when done with the prop.