Robbiee

Actually (according to the DA chart in my Robbie POH) 6,000' PA and 40 degrees is only 10,000' DA. To get to 14,000' DA at 40 degrees you'd have to take it to just above 9,000 PA and at 30 degrees you'd have to go up to around 10,000 PA to get to 14,000 DA.

The R44 NO FLIGHT area checks out ok with everything being at or above 14,000 DA, but the R66 chart does not at 6,000' or 8,000' PA and 40 degrees where NO FLIGHT is below 14,000' DA.

TwinHueyMan

I stand corrected... There's also a limit on closing the throttle above 10k DA "to prevent engine flameout", and an ISA+35c / 50c temp limit in section 2 of the POH.

Mike

chopper2004

So many congratulations And celebrations to Robinson on this milestone..

https://robinsonheli.com/news/robins...l-number-1000/

Cheers

CRAN

An amazing achievement indeed. I fly the 66 regularly and as an all round practical personal helicopter nothing beats it.

Well done Kurt & Team.
CRAN

bellblade2014

Anyone flown this yet?

https://verticalmag.com/news/how-rob...w-tail-design/

helispotter

bellblade2014: I see nobody had so far given any feedback to your question from last September. I certainly can't comment as a non-pilot, but that Vertical Magazine article sure seems quite comprehensive in its coverage of the re-design of the R66 tail surfaces. Of course the test pilots at Robinson Helicopters would presumably be able to respond in detail.

I came across your question while checking if this modification had already been the subject of discussion on PPRuNe as I only just read about it now also becoming available on new R44's with option to retrofit existing R44's, see:https://www.flyingmag.com/new-robins...ennage-design/

I hadn't been aware it was already being fitted to the R66 until reading that article.

This is where it gets interesting: During initial flight testing, the Bell 505 Jet Ranger X originally had a tail surface configuration which seemed quite similar to the R22, R44 and R66 in that it had a horizontal stabilizer projecting only to one side of the vertical stabilizer. The vertical stabilizer looked similar in overall shape to that on the original Jet Ranger. See image below found on web:



However at a later stage of flight testing and for production, the horizontal stabilizer was removed and a larger symmetrical (left and right) stabilizer was 'strapped' below the tail boom:


This brought the 505 back to a tail configuration much more similar to its Bell 206 predecessor, though the horizontal stabilizer now looks like an after-thought rather than its integrated form on the Bell 206 where the stabilizer effectively 'passed' through the tail boom. I am sure this comes at a price of additional interference drag compared to the 206 implementation. There is some old discussion on one Rotorheads thread about the horizontal stabilizer implementation on the Bell 505 in which the need for the larger 206 stabilizer had already been anticipated by one writer.

So while some tail elements of the 505 may have originally been modelled off the Robinson, in the meantime the Robinson now has elements off the current 505 tail! Perhaps all helicopter designers should first look to the 206 for inspiration!

Also interesting to note the Hughes 500, having started life as the competitor to what became the Jet Ranger, originally had an asymmetric V-type vertical and horizontal stabiliser combination (in the 500C). But the design later changed to a T-tail configuration in the 500D. Perhaps Hughes realised the benefit of a symmetrically arranged horizontal stabilizer as well?

A final observation: In one of the Hill Helicopters videos on the HX50, Jason Hill makes mention of the use of what I would call a 'fence' fitted to the horizontal stabilizer just outboard of the tail boom and indicates this is all about improvement of the flow characteristics over the stabilizer (or words to that effect). It seems complicated to me, but I haven't seen the CFD analysis they have no doubt undertaken to come up with this detail. Still, it is surely a less draggy stabilizer implementation than what is now on Bell 505, R44 and R66?

If David Smith reads this post, I would be interested in hearing his take on the topic if he is open to speak about it. From the Vertical Magazine article, I guess he has more experience than most on this subject now.

PhlyingGuy

The mounting of the Bell 505 stab is significantly cheaper than the special type of welding that would have been required to integrate it into the tailboom.

Agile

I have doubts that anybody understand the flow patern on the tail of a rotorcraft. You got the induced flow from the main rotor, posssibly the interacting flow from the tail rotor, and then the forward air flow. That sounds like a big wirlwind shake to me, Hills and the HX50 treat it with aerodynamics principle akin to a high performance glidder, well I buy don't 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.

helispotter

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.

DavidSmithHeli

I had comparatively little to do with the recent Robinson tail as I joined the company well after the project started in earnest. I just helped to share the background in the article you linked and the associated podcast. It’s a very good story of modern tools helping to improve understanding of a very complex phenomenon. The industry’s understanding for decades has been incomplete regarding the primary contributors to the rolling moment of helicopters during low-g flight. Now we have a much more complete picture of the aerodynamic factors and a way to reduce the rolling phenomenon. That is what drove the new Robinson tail. Please avoid low G flight! No matter what tail you have low G flight can be hazardous with a teetering rotor.

The 505 change was made for an entirely different reason related to the stability of the aircraft in hover and the pitching moment of the aircraft as it transitions from high to low speed and low to high speed. it turns out that the horizontal stabilizer, when it is located inside the hover downwash like on the 505, offers a helpful stabilizing effect to make the aircraft easier to control. It was hard to tease this out during the testing but had nothing to do with low G roll. I imagine if the 505 had not made the change early in the program, it might have seen similar roll moments in low-G.

I hope this helps. Feel free to message if you are curious about this topic.

helispotter

Yes, I appreciate the production cost would be lower. But Bell did (and still does) produce countless helicopters with the 'traditional' configuration of horizontal stabilizer. While I have read that they needed to design the 505 to a reasonable budget, I see the solution implemented as being the easiest fix to reconfigure the tailboom and tail surfaces from their original prototype arrangement, else it may well now look like that of a 206?

Agile

Exactly right, I think Georgia Tech and another university in Maryland, I had and application filled to both of them to do grad study there, but eventually went somewhere else that was 30 years ago, California was more atractive for a young guy.
(Head of R&D at airbus helicopter is from that Maryland Campus)

Georgia Tech has a nice Video about the state of the art in helicopter CFD, check 25 minute mark to start to feel how involved it is and 54+ minute mark to see how messy it is on the tail.

14,000 compute hour per simulation run !!! ouch, cloud computing bill must be hot.