That kind of limitation is not unknown; for example my IO540-C4 has one here (note the shaded area) but that one is torque (MP is a proxy for torque) related.
To have a straight min figure for RPM is curious and I bet very few people know that. Mind you, they do say “CMI will continue to evaluate any counterweight releases reported to CMI in an attempt to establish a root cause, including any possible connection with power settings.”
Also: how many decades have these engines been around?
Also I am surprised there is a possible physical process which would de-tune the counterweights below 2300rpm and which would take any significant time to do it; if there was an issue then it ought to take place within a fraction of a second.
It is also interesting because it removes a key option for getting more MPG: fly LOP and with a low rpm.
WingsWaterAndWheels wrote:
I don’t know the 400, but most airplane flies a lot slower once upside down !!!!
Not everything has inverted fuel/oil systems to cope with an extended inverted flight 
aart wrote:
A combination of 1 and 2 works too of course.
What about adding 3. flying in the wake turbulence of the PA28 in front?
The slowest the PA28 goes the more poser you need on C400, so the whole formation has a natural tendency to stay tight, tough abit inspired from swapping luggage load
Since we are being creative, why not flying inverted? I don’t know the 400, but most airplane flies a lot slower once upside down !!!!
Here’s two more out-of-the-box ones
1. Forget 100 kts, let the whole squadron slow down to 80. This way the Col400 will be behind the power curve, needing lots of power.
2. Load the Col400 up, as far forward as possible. Guess with what.. The bags of the other ones, making these faster, and the Col slower
A combination of 1 and 2 works too of course.
If nobody is impressed by my creativity this early in the morning, well at least i am 
There are no figure for % of power at 100kts on the C400 (POH quotes 30% power on 136kts), but I think with a rough extrapolation at 100kts it probably around 18% of power (power % =
(100/230)×(100/230)), I don’t that will give you that much oil temperature…
It doesn’t work that way, due to the engine needing a lot of power just to turn it at the required rpm. An engine is an air pump which happens to share the pistons etc with the bit which produces the power. It takes a lot of power to pump all that air. And all the mechanical friction. See this for example and extrapolate the axes backwards.
Also the pumping losses increase (relatively) at low power because the pump is sucking against a nearly closed throttle,
It’s kind of puzzling why people ask questions instead of trying things. There is only one way to find out if this works, and that is by trial (and error).
It is a perfectly good question to ask, especially as it will work (otherwise, as I wrote earlier, the plane could not land) but there could be issues with doing it for some hours, and it is better to ask than to end up with a bunged-up engine.
Karl_Acht wrote:
The Q was if the engine can cope with slow flying
I don’t see why not. Get the RPM up and the oil will keep circling around as usual, and if the temps are within normal limits it should run forever IMO. Why not just try it first, and see how the engine behave? I also think the oil could possibly be too cool, but try it and find out.
It’s kind of puzzling why people ask questions instead of trying things. There is only one way to find out if this works, and that is by trial (and error).
There are no figure for % of power at 100kts on the C400 (POH quotes 30% power on 136kts), but I think with a rough extrapolation at 100kts it probably around 18% of power (power % =
(100/230)×(100/230)), I don’t that will give you that much oil temperature…
The Q was if the engine can cope with slow flying. The answer is simple. If the oil temperature remains above 80 deg celsius or at least 70 and the CHTs over 150 deg C the engine is happy. The test is not a big deal and I expect the necessary sensors are in the 400. I normally fly at 160kts with 65% (but not a 400) and 100kts is too slow for me to keep the temps up. Whether or not its convenient to fly a 400 at 100kts over hours is another Q. Dont know the lower AP limit and how loose your formation is
Thread drift
