Originally Posted by
Agile
I have doubts that anybody understand the flow pattern on the tail of a rotorcraft. You got the induced flow from the main rotor, possibly the interacting flow from the tail rotor, and then the forward air flow. That sounds like a big whirlwind shake to me, Hills and the HX50 treat it with aerodynamics principle akin to a high performance glider, well I don't buy it. last time I heard, CFD on a rotor system is still a developing science due to the complexity of the flow interaction between blades (tip vortices) all that in a moving frame of reference.
The proof that nobody has understood anything is all these new horizontal stabilizer evolutions/modification, the H160 being a visible effort in that field.
The R66 just got it from the R44 that got it from the R22, I think you would be chocked to see how little thought went into it.
Agile: I tend to agree with your sentiments, though I can't be sure what level of sophistication of testing or computations there actually is at helicopter manufacturers, large or small. The Vertical magazine article at link above certainly shows that there are at least two universities in the USA that have more complex rotorcraft aerodynamics CFD analysis software in use that handle transient aerodynamic problems. Those may be standard CFD suites tailored to helicopter aerodynamics problems?? For the tail surface re-design, Robinson seems to be engaging such outside assistance, but clearly without an endless R&D budget. My feeling from the article is that this may in part have been motivated by NZ and other R44 accident investigation recommendations and a 'duty of care' on the part of Robinson to more fully understand what is occurring. If so, good.
As for H160 'bi-plane' horizontal stabilizer, my initial impression is that it is somewhat marketing gimmickry. But then again, there may be structural or other motivations we haven't grasped, for example:
https://www.geekwire.com/2023/boeing...ient-airplane/
Regarding the Hill use of fences on their stabilizers, I will bring that discussion over to the HX50 thread (with more details and link to video) as I am really quite interested to hear more about that feature, but so far I share your sentiment on this too.