R44 inflight breakup story - TV NZ
 

I don't know when that report was made, but that Coroner's recommendations of not flying in turbulence and slowing to 70kts have been in the R44 POH since '98, and the safety course has warned us about flying in those conditions since at least 2006 (the first time I attended).

As for, "Should Robinsons be flying in New Zealand?" Well,...maybe not.

Program was screened last night.
The inquiry findings were published recently.
https://www.rnz.co.nz/news/national/...-pilots-deaths
https://www.stuff.co.nz/national/129...d-two--coroner

On many levels, "the last flight" is worth watching.

Following the avoidable deaths of 4 NSW scientists in a post impact fire caused by a landing incident, the CAA Australia, demanded R44s be fitted with more robust fuel tanks.

The subsequent reduction in the incident rate of post crash fires of R44s has enabled investigations, such as this one on NZ, to have a better understanding of the crash sequence.
And now, more information will be available from in-cockpit witness cameras ( mentioned in the tv programm)

It is worth noting that the improved fuel cell and the in-cockpit witness cameras appear not to have be driven by the manufacturer.
Why?

I ponder, had fuel bladders been fitted to the R44 from day one, would the manufacturer now be in a stronger financial position?
​​​​​Mjb

I have huge sympathy for the poor woman but how can an apparently very experienced heli pilot not know that many many robinsons have broken apart mid air over the years? Aus and NZ have a huge database of this?
I knew it 25 years ago and it has remained enough evidence for me to stop me ever getting in one. I also have personal experience of the result of a robinson r22 mastbump with the fatal consequences!
Helicopters are wonderful and I love them. But they have an ability to bite even the most experienced guys very hard occasionally. Why would you choose to diminish those odds by a considerable amount volentarily?

well that might bugger Robinson sales in NZ !!!

Possibly, which can be adverse as well to the industry, the RHC product fills a niche and sales suggest it is a needed part of the industry.

Since the advent of teeter rotor systems there have been issues with mast bumping, low-g, turbulence and push over maneuvers. The RHC rotor head itself, as designed by Frank is not itself any worse than any other teeter system in this regard, so long as the tensions on the teeter hinge and the coning hinges are correct.

The SN of interest have been out for a long time, and no one that trains on a RHC helicoper should be unaware of the need to maintain a load on the rotor head at all times.
Turbulent conditions call for lower speeds to reduce the probability of unloading the rotor. However, what appears to not be mentioned is that while that is necessary, the control system of the helicopter introduces a flexible component in the control system, that is the pilots right arm. The body of the pilot is not rigid, nor are the limbs that connect from the pilot to the cyclic... the response of the body to reduced g will result in uncommanded motion of the extremities, exacerbating the reduced g load on the underslung mass of the helicopter. The control of the teeter head relies completely on there being a load under the teeter hinge and down to the swash plate. When there is a possibility of turbulence, it is conceivable that the pilots do not consider that the condition may get to zero g, which is severe, however, the inadvertent arm movement in low g may induce a forward cycle input that will lead rapidly to mast bump events.

Low speed is certainly called for; bracing your right arm to your body may also assist in reducing unwanted cyclic motion.

RHC makes a fine, minimalist device, they are fantastic when flown with care, but they need constant awareness of the risk involved in any part of the operation from pulling them out of the hanger to putting them back inside afterwards. The faster you are going in the machine, the higher the potential for achieving a low g condition though a surprise or any condition that results in an instinctive or accidental reaction.

It begs a question if a control loading could be added that was responsive to speed and low g, to add an aft cyclic input if a low g condition is sensed at speeds above ETL. The response rate would have to be pretty quick, the blades are at ~7Hz, 2 blades, so the response time is pretty short... but the good news is the very low control loads would not require a large input force. Most of my time on the RHC was involved in doing odd things with them, and so the preparation for every flight was comprehensive, the instructor in the field will have more familiarity but less time to consider each aspect of the flight and to determine the risk related to each phase of flight. For my R22 and R44 we avoided high speed operations unless called for in a flight profile, and then they were subject to a full THA. Irrespective of that, every flight at high speed needs to be conducted with caution, and that is within the normal envelope, the helicopter can bite back.

I thoroughly enjoy flying the RHC products, the R-22 remains one of my favorite machines, it is the Pitts S-1 of the helicopter world; it talks back to the pilot for every error they make.


https://cimg6.ibsrv.net/gimg/pprune....ffa49e2de4.png
https://cimg7.ibsrv.net/gimg/pprune....38584b173e.png

FDR - the only problem I could foresee with a system that automatically applies some aft cyclic when low g is sensed is if the g is reducing rapidly due to turbulence and the head is starting to unload - that aft cyclic could well be the thing that chops off the tail.

The answer, obviously, is not to fly them in turbulence.

As a fixed-wing pilot who is interested in all things technical, please could someone briefly explain what helicopter mast bumping is, and why teeter head unloading is dangerous on the R22/44.

Would a simulated engine failure and subsequent auto-rotate landing dangerously unload the head?

Thanks in advance.

henra explains it better

A teetering head is a Rotor Head, which has a central undamped teeter hinge which freely connects the Rotor mith the mast and subesquently the cabin. This means the cabin is just suspended freely underneath the disc and it can act as a pendulum. In contrast to that rigid rotor systems or fully hinged rotor systems do transfer moments between disc and mast/cabin (due to excentricity of the hinge points). When the rotor disc is tilted (due to cyclic input or external force) it will apply a moment on the mast/cabin forcing it to tilt into the same direction. A teetering rotor does not. It lets the disc freely tilt while the cabin stays as it is. To limit this tilting on the ground and while starting up there are mechanical stops on the teetering head which contact the mast when a certain tilt angle is achieved. In flight the cabin is kept vertical simply by gravity (or centrifugal force when in a turn). If a low G situation occurs, this centralising effect of the weight of the cabin 'hanging' underneath the teeter hinge will be reduced/gone and the rotor being unloaded it will produce less lift, i.e. also produce less horizontal force opposing any sidewards force from the tailrotor. Now disturbances (like the tail rotor pushing sideways on an axis higher than the cg) are able to push the cabin out of the vertical, If now the pilot wants to counteract this tilting of the cabin by opposite cyclic input the disc can and will unopposed and easily tilt against the direction of the cabin without applying any force to take the cabin with it. That is up to the tilt angle where the teeter stop hits the mast. So there is a sudden change from no moment to 'rigid' force transfer. This in many cases happens so violently that the thin rotor mast will receive a massive dent and in many cases finally sheer off. That said the angle at which this happens is so big that combined with the coning hinge travel plus elasticity of the blades the excursion will be sufficent for the blades to chop through the cabin and/or the tail boom.

In case of a (simulated) engine failure a 'typical' way to get to mast buming in an R22/44 is idfferent to what I described above. Normal procedure in an engine failure would be to lower collective and move cyclic aft. The latter will ensure continued loading of the disc.
Especially the R22 has a second feature that may lead to critical situations in case of (simulated)engine failure. It has a low inertia rotor. This means that Rotor RPM will drop off quickly in case of (simulated)engine failure. If lowering of the collective and aft cyclic isn't applied quickly enough, Rotor RPM will drop quickly to a point where progressive retreating blade stall (noth the whole balde will stall at once - it will start at the inner part and progress outward) will occur. As you know from fixed wing a stall means massively increased drag and reduced lift. This will further reduce RRPM down to the point where the rotor blade will stall over a wide span on the retreating side while the advancing side still happily produce lift. This will massively tilt the disc towards the rear on the side of the retreating blade. Again this can develop to a point where a blade would hit the teeter stop and slice through the tail.

The relevant accident and its associated report can be found here: ASN - Robinson R44, ZK-IPY

The subject accident of this thread, ZH-IPY has a couple of oddities to it;

1. the conditions at the time were unlikely to be conducive to severe turbulence at all,
2. if the winds aloft were strong, then the resultant GS suggests the CAS was not that high, which is not conducive to a low g event from environmental causes,
3. the IP was an experienced pilot with multiple RHC safety courses completed,
4. the red blade exhibited a fracture near the chord extension, however this was not in the region where fatigue has previously occurred, and the TAIC assessed the failure to be overload which does appear to be appropriate.

low g occurred almost certainly, however turbulence was unlikely to be the cause in this case, either the winds were light, and NZL is not known for thermals (other than really good gliders), orographic effects etc may occur but then the GS suggests there is a trade between the wind or CAS/TAS, take your pick, the low g due environmental is not likely.

I made comment before reading the latest version of SN-32; RHC makes appropriate note on the potential for motion of the pilots arm, and that is a factor worthy of awareness.

There is no doubt that the divergence occurred, and the pitch links have failed under overload which is consequential to not due to divergence. The divergence is unlikely to have occurred from environmental conditions. Divergence to the front and left side is not likely to come from a left pedal input, there is a fair authority at cruise speed, but the damping from the tail is fairly high then too. About the only thong that would be conclusive is a video of the cockpit at the time of the event, it is somewhat more like the Concorde event than most of the other known low g/turbulence cases.

There are some benefits from having zero hinge moment rotor systems, there are also some definite drawbacks.

NZL certainly is oversubscribed with bad days with the RHC, from 275 odd copters a 5% in flight break up rate would upset the Sqn in 1943... Time for a full time local RHC safety course maybe...




https://cimg5.ibsrv.net/gimg/pprune....2521fc81b4.png

Only if you have a FW pilot flying it since the natural reaction is to push the nose down to maintain speed - if that is done harshly as the collective is being lowered smartly, you can very quickly generate a low g situation.

FDR Agreed, that T handle arrangement isn't conducive to being able to 'damp' your arm using thigh or body contact. If it was LHS flying it as a demonstration on a training sortie with the RHS holding his side of the cyclic normally, the LHS pilot would have his arm up in the air - unless he was holding it 'centre-stick style' - with obvious possibility for PIO.

There could be some impacts there, it is an uncomfortable position to hold as an IP, your arm is not supported at all. There was an STC to add a conventional stick to the R-22, not sure about the 44. Could be worthwhile doing a statistical review of how many bad days occurred with dual controls fitted. IIRC the Concorde one was dual. RHC would have the data to hand, and anything that may improve confidence in franks design is worth the effort.

there was a conversion kit for the r22, probably not available anymore

more here:

https://helicopterforum.verticalrefe...c-for-the-r22/

https://cimg8.ibsrv.net/gimg/pprune....2c52a10169.jpg
https://cimg0.ibsrv.net/gimg/pprune....05f12973e7.jpg

The real preventive solution is to get SAS installed. At its simplest (without autopilot) it acts basically as a fancy trim system, though based on aircraft attitude rather than control position. But to oversimplify, it keeps the cyclic at basically one position and you can counteract it but you'll feel resistance. Aside from increasing flying comfort, it significantly increases safety as it will not do a forward pushover like a pilot might. I bought an R44 without it and then added the SAS and autopilot a couple of years later. It's a great system.

Ummmm, that might be overselling artificial stability additives. E,g., one fine day in Japan at the end of a demonstration mission, returning south from Hokkaido. Sunny day with a wind from the west, which resulted in fairly frequent sharp edged excursions ( the reason I have recalled that flight-the turbulence was notably sharp edged-sort of like a square-wave, if you will ) between +2 to zero G. Machine was a standard UH-60A with SAS and AFCS ( attitude/heading hold ). Wasn’t any special turbulence warning from the weather-guessers when filing at Chitose.

Uplinker, for you. :ok: