At a TAS of 185 at WOT, my IAS is well below Vno, which is 180 = the end of the green arc on my ASI. This is at around 8000?. At that speed and altitude, I?m indicating in the 160s (mph). Vno is an indicated airspeed. So I there is no problem with Vno either, at least not with my plane. Perhaps a constant speed prop makes a difference. Or my engine is underperforming. Maybe at higher altitudes it works out differently, but so far I haven?t seen it. It should be pretty simple: don?t exceed Vno in anything but calm air and don?t exceed Vne anytime. Whatever the risks of a 360, if any, the advantages are considerable: better short field performance, higher rate of climb, cruise at lower % rated power (less stress on engine), higher ceiling.
John,
This post is not made with the intent to pick at you personally, just to reemphasize the reason that the RV-9 has a maximum recommended engine HP of 160, and hopefully get more people like you to gain a proper understanding.
By your own admission, you were unaware that the engineering decision to limit HP to 160 was made primarily based on the Vno, limitation. That is not unusual. There are numerous long term RV-9 owners here in the forums that still mention only Vne when the max HP conversation gets revived.
Point being, that until this point, it sounds like you assumed you were fine as long as you are below Vne. That is not necessarily the case.
You mentioned that as long as you are below Vne, you are always below Vno IAS. This will probably be the case at higher altitudes like the 8000 ft example you gave, but a lot of the time not the case at lower altitudes. Down low, the actual IAS and TAS values start to converge and it is very possible to be operating in straight and level cruise within the yellow arc range (above Vno).
Your point about not operating above Vno in anything but smooth air is a good one, but in reality it is not realistic. Turbulance is not like speed bumps on a road. You can't see it ahead of time. It only takes one single acceleration event to overload the airplane.
The worst turbulence bump I have ever experience in 27 years of flying RV's was when my wife and I were over central TX headed west in our RV-6A, back towards PHX from S&F many years ago.
We had been in glassy smooth air for at least an hour. With zero warning we hit a bump that caused a major positive and then negative high G load event that put both out heads on the canopy (yes our belts were tight... no, the airplane didn't have 5th point crotch straps), and caused momentary loss of control. It immediately went back to glassy smooth for another hour. This whole event was over in less than 5 seconds.
I have always felt that it was probably caused by wake turbulence from a large aircraft that had crossed our path during climb from Dallas/ Fort Worth.
So to come full circle on the discussion.....
The largest recommended engine for the RV-9 was chosen because it is a high performance airplane (though many don't think of it that way since it is more at the bottom of the performance line up in RV models), and if higher HP is used, the typical pilot will probably at times be operating within a regime that is causing a reduction in safety ( this is in large part because a lot of pilots have experience in airplanes that would not come anywhere close to cruising in the yellow range regardless of what altitude they were flying).
In a nut shell.... Yes, if pilots properly control the speed (to do that they need to actually know what the limitations are) of their RV-9, then it doesn't really matter what engine is in it.
The scary thing though, (and these repeated discussions in the forums show it time and again) is that the majority of people (even those that have been flying big engine RV-9's for years and exclaiming things like "it hasn't fallen out of the sky yet"), don't have a full understanding of what the actual design limitations are.
If anything good could come out of these higher HP discussions, it would be that more people get educated on what the limiting factors are that people need to keep in mind, and possibly work to spread the word to others that don't know. Especially when they hear someone telling others that "as long as they keep it under Vne, they will be fine".