If you slam the collective down fast in an R22/R44 you will get a brief moment of negative G's,...and I mean brief, its barely one second.

However, I cannot think for the life of me why anyone would chop the throttle in a HOGE in a Robby. In all the years I was subjected to throttle chops never once was it done in a HOGE. Zero airspeed autos like that were always initiated with a smooth lowering of the collective followed by a slow rolling off of the throttle.

Agree with Robbiee.

First - RIP to the crew, professional investigation in time will tell what actually occurred - but we all wish it had never happened.

To add my bit to the conversation - I have been and still am instructing in the R22 since the early eighties - including original non tip weight blades - and have had no issues with rolling off the throttle for any simulated engine failure to the ground above 100 ft AGL on or outside the HV curve using the following process:

Students have heard all the scary furfies so its about leading them into it slowly following me through bit by bit to keep their confidence.
I do not "chop" the throttle as I do in B47 or other higher energy systems.
Always Student briefed that there will be no surprise throttle chop for their entry - always proceeded with "on the count of three" etc.
Student required to lower the collective at a rate which "splits the needles" - ie- full down - not too fast/not too slow.
Student does not shut the throttle - reasoning is that - in the real thing - there is no need and that a habit learnt at this point against throttle governor and detent spring might slow the lowering of the collective as the wrist action of closing takes nearly a full second of valuable time.
I have the throttle and shut it fully as their collective goes down - always guarding the collective/throttle and pedals.
Hover OGE above 500 ft AGL (HV curve)- nose always pitches down/wait one second for flow to build/ RRPM stabilises around 94% before pointing nose to ground and then building rapidly as airspeed increases. Never an issue.
Student identifies collective full down and calls RRPM at full down no matter entry configuration. Then fly the machine without fixating on RRPM.
Cyclic and pedal input depending on flight condition - through transition/not through transition.(No Low RRPM horn/light system as deactivated at full down collective)

Student to understand from day one that its Main Rotor RPM which holds us up in the air and therefore about learning and implementing the process to initially maintain rotor speed (energy)as much as possible and then complete process to the ground (control inputs) dependant on where positioned in relation to HV curve and environment (wind/landing zone etc)

I always strongly guard the pedals to ensure that if the student inadvertently pushes the left pedal - yes it does happen - it is restricted by right foot on the right pedal.

I guess that the above is what most in this forum do anyway.. but have heard the occasional interesting story such as -

I know of one R22 many moons ago which went inverted and fortunately came back to upright about 100 ft AGL when an instructor was giving a student a hard time and unannounced throttle chops.
At 70 kts and about 900 ft AGL the student caught the instructor by surprise when he put in full left pedal at the same time that the collective went down faster than a speeding bullet.
Nose dropped rapidly/RRPM decay/rolled hard left/went inverted before restored to normal flight / lucky boys.
Engine oil went out the breather and down the tail boom.

Fly safe :)

Crab, not saying that the RHC device doesn't respond to a lowering of collective by starting a descent, if you were powered, but if you had a power loss, then the matter is moot; there is no nicety in lowering the collective at all on the R-22, blade stall occurs by RHC's own analysis in 0.8 seconds, and my own recorded testing is consistent with that, where with an improved blade performance it is still a mind concentrating event. As the Nr collapses (this isn't the nice slow droop of the HH-3, this is more like a descent in a 269, the machine is on its way down, the choice is if you want to have tulip'd blades or want to still have a rotor system, and that requires a prompt lowering of the collective). John Anderson, once he regained his composure suggested that politely lowering the collective was undesirable to his health, that was my intro into whether there was any upper-speed limit in dropping the collective in an OGE hover loss of power.

The R-44 is much nicer to your health than the R-22, but the fundamentals remain the same, the loss of Nr is rapid and has to be responded to by prompt action. I would be more concerned with a case where the machine was not at a heavyweight, and in the power cut the student puts in the wrong pedal, more left instead of pressing right pedal (is USA) that will get a wild ride pretty promptly, and I would think it could compromise the TPP. As long as the rotor is still being driven in autorotation, the control system will function normally. A failure to lower the collective will definitely put the aircraft into zero-g quickly, as the rotor goes into the tulip until impact. As long as the collective is raised, the rotor will decelerate and the rate of deceleration is not trivial. RHC teaches failures every week at their school, and every RHC type trained pilot has experienced the same dynamics. OGE hovering is not for the slow of hand or unprepared driver. Personally, I avoid it whenever I can, happy to do all manner of torque turns, pedal stops etc, IGE failures, but OGE, ill keep the speed up unless there is a compelling reason to go well below ETL, and frankly, speeds above that give a great deal of recovery time as a cyclic loading of the disk trades off speed to Nr. Extremely high speed autorotations are another matter again, there you dont want to "dump a collective" on a robbie, just like you dont on a UH1, that will wind the blades up off the top of the tacho, and gets expensive, that ends up being a gearbox, head and rotor change out. The high speed entry also gives a considerable nose tuck, at the same time as the disk starts to flap back until autorotation is established, (now, that is a bit of maths worth looking at). I tested to 111% VMO at what was supposed to be 90% Nr, but ended up going a little beyond the speed and a little below the Nr. The system once established in autorotation will vibrate considerably in that case, but fly it does. Turning adds vibration depending on the direction of turn. About the only interesting thing in that was while measuring the torsion and bending loads on the rotor blades, and the pitch link strains, found that the entry into autorotation produces momentary loads on the blades and the pitch links that are only matched in the system at one other time, and that is as you touch down. No matter how softly the touchdown is, it is detectable as a load into the disk, which I found interesting. those loads were much more interesting than the steady-state, pitching or rolling loads in the system. That was done on my flight test program, not RHC, but the data says what it says. That was also for clarity, under Part 21 experimental category, with a parachute. Now, the good news is, when you want to work out how to bail out of a RHC, the removal of the blades has an obvious method, doesn't need explosive bolts, just a handful of collective and a twist of the throttle. Do recommend having a parachute on for that though.

Yes, the nose drops, but the TPP follows the control plane, unless there is a big input of cyclic. The thing that concerns me is someone hitting left pedal on entry while in a state of increased anxiety, which may well compromise the TPP/tail boom. A yaw rate from the wrong pedal can lead to the feedback through the control plane and result in an awkward motion of the rotor while the body is rotating underneath the mast, with an offset of the CG to the mast.

All of the above probably goes into the realm of Wayne Johnson to do the maths, or Gordon Leishman, or may be a topic for Shawn Coyle to comment on. Ray Prouty would have given a solution in short order too in small sentences.

Good news though, I'm done with PPrune, you guys fly safely and keep the blue on the top and the needles in the green.

Cheers,

fdr, very sad to read that you're done here, your musings were always one of the main reasons i (and probably many others) are reading these forums.

I don't have a lot to contribute other than anecdotes of my experience: an inadvertent left pedal stomp by the student on a simulated power loss in an R44 and R22 does put the machines into an absolutely hair-raising flight state, as you said. It happened to me once in each, during about 10 years of instructing on and off, and in both cases the attitude deviation and rotor RPM loss (mid to low 80s) was what I as a non test pilot would call "extreme". Despite my immediate intervention. I obviously survived both, and there was no damage found, but i can also easily imagine that a slightly different set of entry parameters could have caused structural failures. It would've been interesting to have had a camera in the cockpit, but no such luck.

The instructor in the accident machine has been identified, although i don't know if this information is public yet so i won't go into it. It is a very tragic affair. One thing that is perhaps relevant about the person is that they almost certainly attended the RHC factory safety course somewhat recently.

fdr, I know many share my sentiments that your contributions here are invaluable. Wisdom, experience, and a sense of humo(u)r are treasured commodities, not just on this website, but in life. You bring all three. We are, after all, pilots and friends who we look forward to meeting one day! I am certain that I speak for the membership when I ask you to reconsider.

- Ed

I’m wondering if use of the Vuichard recovery technique could have induced a mast bump.
When I used to teach VRS sometimes if you were “lucky” to find it she would sink very quickly, enough to give that sinking feeling in the stomach accompanied with zero or low g. With the power been low there was only a small amount of pedal used to keep the nose straight.
Using full pedal for the side slip on the Vuichard technique and if coupled with low/zero g might be the factor that introduces the roll, especially if the disk is unstable due to VRS.

There is a photo out there where you can clearly see the shear is about where the blade would strike. I assume that would rule out gearbox issue.

I was thinking along similar lines (only with low-rpm rotor stall). I just did my BFR in a 44 where we went over the dangers of not using enough pedal while doing that new recovery technique.

During one of our practice runs my instructor had me not use enough pedal and we started to spin. I lowered the collective and stopped the spin, but the wind was still making us a bit squirrelly and at one point (before I got everything back under control) the full throttle light came on.

,...and that's not the first time I've skirted with low rpm and the vortex ring state.

I fly only S300C so pls forgive my lack of Robbie knowledge, but I am curious about that hair-rising flight state mentioned above.
I'd guess : fast yaw to the left due to lack of torque to counter and increased decay of RNR caused by diverting the remaining rotational inertia of the MR to the tail rotor.

Hence: immediate spatial disorientation combined with RNR needle dropping fast, correct?

Bearing in mind that the video shows the aircraft travelling from left to right at quite some speed, I’m surprised that there’s so much discussion about VRS.

Or was it was a very badly botched recovery from a vertical descent which resulted in exceeding VNE and subsequent loss of main rotor control?

ShyTorgue are you referring to the video that starts when the aircraft is out of control with the TR severed or is there other footage showing prior to this.
I assume it’s the former in which case there is a lot that could have changed from the initial entry.

I have always been dubious with the Vuichard Technique. Positive forward cyclic to fast accelerating attitude I always found worked best at incipient stages.
Perhaps it’s a technique not suited to teetering hinges.

If you turn the video 90 degrees anti-clockwise, the power lines go from vertical to horizontal and the roof will be on the top instead of the right.

FYI: separate reports state the aircraft was in an OGE hover at the time of the incident. Supposedly the OGE hover was part of the training flight. The CFI was relatively new to the company and the student was an established fixed-wing pilot obtaining his rotor add-on. They've recovered the tail section and the link below shows several shots of it.

Yes, I've seen the later footage but the video evidence in the first post here shows it travelling at a relatively high speed and in level flight, or possibly even climbing, after the tail assembly had already separated.

Shy that video is deceptive it looks like the helicopter is moving left to right but the frame is 90degrees rotated anti clockwise so the actual path is substantially downwards (not left to right as it appears).

tail does not look chopped to me the break looks too vertical not diagonal slice you never know what happened in the cockpit did the student overpower the instructor? etc etc etc

Instructor was comms Director with Whirlygirls I see. https://m.facebook.com/whirlygirlsin...al/?__tn__=C-R

FYI: I believe if you measure distance at the break the M/R blade cut diagonally through only the upper half of the tailboom structure then the lower structure portion failed downward and tore off. And I think you are correct on the OP video that the aircraft motion is vertical due to the camera angle and optical artifacts. There are other reports that support a vertical decent from a hover after the incident.

Thanks, I see it now.

I just looked at an R-44. It appears that the boom separated exactly where an excessively downward flapping blade would contact it. Also, the footage showing the tail assembly being lifted seems to briefly show a sharp edged cut mark near the top of the boom.

Horrible to think about what the occupants must have experienced in those final few seconds.

Didn't this thread have three pages yesterday? :sad:

Thread creep - mod shifted a bunch of "off topic" to correct topic. You'll work it out.

Hard left yaw, combined with a strong right roll. I'm not going to make an attempt and estimate the roll angle, as i think those estimates are usually far off the mark, and i certainly didn't have time to look at an AI. The rotor decay was instant and likely caused by the disk being tilted forward into the air flow, due to the yaw and roll. I don't have good recollection of the recovery from the first time this happened, but the second time is still in my memory. The correct cyclic and pedal inputs to recover attitude were instinctive, so there was no confusion about the attitude we were in. Basically, full right pedal followed by lots of aft cyclic to recover the revs. Which in itself is not very effective because the extreme yaw really drops air speed, i think i had between 30-40kias left once straightened out. I also still remember the sound of the engine almost choking as i rolled the throttle all the way to the stop, and watched the needles labouring from horizontal back towards their normal position despite the collective being flat on the floor.

​​​​​​If i were to speculate, i think this scenario is one of many possible causes for this accident, but obviously there is no proof one way or the other so far.

Edited to emphasize, one of many possible causes.

For those instructing in these machines currently, you must guard the right pedal to prevent a student from shoving the left one forward. Unfortunately this is difficult to do effectively against a motivated student, especially considering all the other stuff you have to be ready for at the same time. In both cases, the autorotation was not a surprise throttle cut. The students also had done many dozens of autorotations prior, and were preparing for their commercial flight tests. Neither was a fixed wing pilot.