Let's read what Brother Dixon had to say.....I am quoting from his Post. The Bold Print is mine and I have split up his post into individual sentences to make it easier for some to read and comprehend.
The aero guys at SA in answer to an internal query on an accident investigation some decades ago, did some simulation and opined that there is an Nr number, where at least from the lift vector and angle of attack calculations, the Nr can reach a point where the decay is unrecoverable, and hence ( and this was assumed at full low collective ) you need to put the throttle(s) forward or use your chute.
That Number was in the 60% range.
So there is some margin between where the qualification test crews operate and the point at which the situation turns really dangerous.
With an Nr decay rate of 10%/second, though, one does not have all day.
Since either the FAA or the cognizant military test organization gets copies or witnesses all of this testing, the actual Nr behavior is anything but a " deep dark secret ".
As to the H-V subject, I think Nick has said it all.
Hard to comment on other manufacturers/models H-V diagrams, but I and Nick have more than a passing relationship with the UH-60, SH-60, all S-76 models and the S-92 models, and for those, I will pass on that the H-V tests were flown to the required structural limits of the machine by pilots who had experience doing that stuff.
If one wants to ignore their validity, as at least one poster suggests, have at it, but do have an adequate supply of band-aids on hand.
Now let's read what Nick Lappos had to say. Again the bold print and highlighting is my work as is splitting some of his paragraphs.
This is a great thread, as it makes us think. Why I weighed in is very simple: Today especially there exists a certain kind of distrust of some of the fundamentals of our existence, think born out of the intellectual freedom the web excites (a very good and powerful thing!)
This thinking that goes something like this:
"Those idiots who make XXX (insert a term like: vaccines, evolution textbooks, public laws, medical procedures, missions to the moon, reports on assassinations, flight manual procedures, investigations of 911 acts. ......) are all YYY (insert a term like: too stupid, on the take, drunk with power, ......) and I know because ZZZ (insert term like: I saw a youtube video, my cousin's Aunt's brother told me, a great web site proves otherwise, Glenn Beck told me,....).
The thing that makes me laugh is that within 100 meters of my desk are world class experts who have spent 20 years of so studying, designing, building and testing helicopter stuff. They (like their peers in France, Russia, Texas, Philadelphia, and Yeovil) have become very expert in ways that operators cannot fathom, any more than they can appreciate what a night rig approach is like.
When I read of a person who basically says "that page in the operating limits section of the flight manual is just bull****, do it this way and you will be so happy you will pee your pants!" I react.
Ppruners, do what you will, but while you do, please respect the flight manual, and those who wrote it. Trust them, they know so much more than you can fathom about the machine, because it is their job. That is not an arrogant statement, it is a simple fact. It take nothing away from your expertise, it is a simple statement of how we are a team, and that we rely on each other to stay safe and productive.
No one should be insulted by what was said by either of the guys. They both said to operate within the Limits set by the RFM. Brother Dixson clearly is warning against operating outside the established Limits and Nick says the same thing as a Real Helicopter Pilot talks.
I see absolutely nothing wrong with what they said or how they said it.
That is their words pulled from earlier posts.