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Helicopter crash Kenya

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Helicopter crash Kenya

Old 18th Oct 2020, 04:53
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Helicopter crash Kenya

Video of the incident yesterday here.
https://sendvid.com/vt7rrmrj

News reports indicate there were 4 adults on board and all survived. It may be relevant that the site of the incident (Narok) is at around 6,000' MSL.

I know nothing about helicopters, but it sure looks like it was overloaded/underpowered, but undeterred by the obvious basic problem, they tried to get away by building-up a load of airspeed at zero feet.
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Old 18th Oct 2020, 06:00
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A couple of news items:



This is full of ads, which you can skip, but has a bit more detail of the wreck. Amazing that they all survived looking at the impact.

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Old 18th Oct 2020, 07:17
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So sorry! Looked very much doable. But then ground effect disappeared when his take-off path took him over the long grass. Then dynamic roll-over to the front, as the skids got entangled in the dense, strong and wet grass.
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Old 18th Oct 2020, 07:41
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“they tried to get away by building-up a load of airspeed at zero feet.” It’s called a cushion creep. Designed for low power margins on take off. Not very well executed on this occasion. The “ tussock” nature of the grass probably didn’t help.

Last edited by Globocnik; 18th Oct 2020 at 07:54.
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Old 18th Oct 2020, 07:49
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Yep, that crash always looked doable. Just a case of were to have it.

Another ineptly flown R44, clearly out of its performance envelope and CofG.

Bet that low RRPM horn was going off way before the pilot was committed to the crash, then he had no power or aft cyclic to avoid it. What a complete numpty
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Old 18th Oct 2020, 08:39
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Looks like he didn't realise that the max power requirement on a cushion creep take-off is just before you get ETL because you have to get through the roll-up vortex created by the downwash.

He would have lost most of the benefit of ground effect shortly after he initiated the transition.
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Old 18th Oct 2020, 08:44
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There were two missing elements to that cushion creep: The cushion and the creep.
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Old 18th Oct 2020, 09:08
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Another +1 to this year's Robbie sales figures.
No wonder they can’t make them fast enough.
They should save everyone some time and just make them disposable
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Old 18th Oct 2020, 09:31
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Would appear to be these guys https://www.karenblixencamptrust.org.../conservation/
Not good news for the protection of wildlife in the area.
Suppose the wealthy yank donors will just get them a new one.
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Old 18th Oct 2020, 09:37
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Originally Posted by Bell_ringer View Post
Would appear to be these guys https://www.karenblixencamptrust.org.../conservation/
Not good news for the protection of wildlife in the area.
Suppose the wealthy yank donors will just get them a new one.
You are right.

I suspect the wealthy yank donors will be asking why their machine was being used to fly a politician to a funeral.
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Old 18th Oct 2020, 09:42
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I could have prevented that crash if I’d been a passenger because I’d probably have been the one passenger who volunteered to get out after it ran out of power during the first attempt. If the aircraft had been less heavily loaded, the pilot might have got away with it.

Was the second departure attempt into wind because it didn’t look like it? It was carried out almost 180 degrees away from the first one. It’s possible to hear the rotor rpm drooping due to over pitching almost as soon as the aircraft set off.

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Old 18th Oct 2020, 09:48
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Originally Posted by ShyTorque View Post
I could have prevented that crash if I’d been a passenger because I’d probably have been the one passenger who volunteered to get out after it ran out of power during the first attempt. If the aircraft had been less heavily loaded, the pilot might have got away with it.
Indeed, there is a certain irony that one of the passengers was a bodyguard who could have best protected his principal by not being there.

I would bet the pilot was pressured to take more weight than he was comfortable with by politicians who are used to their every whim being indulged.
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Old 18th Oct 2020, 10:07
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Dunno what model Robinson this is and it has been 10 yrs since I flew one but I seem to remember that the OGE on the R1 was only around 3500' at 30 degrees Celsius at MAUW. Surprised me whenI was a noob and learning to operate one professionally. If they were at 6k with 4 on board in Africa it was never going to end well was it? Unless it was a very cold day!
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Old 18th Oct 2020, 12:12
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Well, for a running take off you only need IGE capability (not OGE). It was definitely doable, as evidenced by the fact that he was perfectly able to hover IGE. A bit more creep (as others have already noted) and a bit more “runway” before he lost ground effect, and he would have been fine.

Of course he should have been able to set here down safely, even in the long grass. The fact is, he committed too early to the take-off. He tried to pull her out with more pitch, instead of stick back, slow down, level, land.

I don’t think the first lift-off was an attempted take off. He was simply backtracking in order to get more “runway” in front of him.

Most likely that the PIC got arm-twisted in taking an additional pax without updating his CoG, MTOW, and performance calcs. You see him settling after his first attempted lift-off, as if he was surprised by the fact that he didn’t have enough power to just climb out.

Difficult to say where the wind was blowing from. Clearly he took off downhill, which makes sense. But if that meant he had to deal with a tailwind, it would have further complicated the running take-off.
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Old 18th Oct 2020, 12:29
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Originally Posted by Torquetalk View Post
Yep, that crash always looked doable. Just a case of were to have it.

Another ineptly flown R44, clearly out of its performance envelope and CofG.

Bet that low RRPM horn was going off way before the pilot was committed to the crash, then he had no power or aft cyclic to avoid it. What a complete numpty
Nailed it, TT! Much cringing here in the first few seconds of that video, it was hanging so badly nose low, almost certainly had to be past the forward CG limit, and possibly over gross as well. Had the exact same thoughts as you about the horn.

Both the elephant nuts on FB and the news folks are reporting "mechanical failure". The only mechanical failure was in the Mark 1 Neural Network Computer located on top of the pilot's shoulders

5Y-MEP is reported as a Raven II elsewhere on the interweb. FWIW performance data follows. It didn't look too warm there based on how folks were dressed. The data speaks for itself.





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Old 18th Oct 2020, 14:44
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If you look at the first video, in the first seconds you can see the crops/gras moving to the right. Not much but when heavy, every bit of wind from the correct direction helps.
So his first hover was into wind. Then his transition was downwind, downhill over tall gras and looking at the guys that came out of the R44, possibly out of CG.
Good they all got out without injuries.
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Old 18th Oct 2020, 15:01
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Originally Posted by aa777888 View Post
Nailed it, TT! Much cringing here in the first few seconds of that video, it was hanging so badly nose low, almost certainly had to be past the forward CG limit, and possibly over gross as well
You mean something along those lines...?



4 pax; half fuel. Able to lift IGE, but > MTOW, and CoG too much forward

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Old 18th Oct 2020, 15:21
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always sad to see a machine get wadded up. At least in helo's more often than not, the soft filling gets to walk out of the wreck or carried.

Wind: the video shows negligible wind in the grass near the camera (phone..). What there is, appears to be from the left of the viewpoint, in the direction of the first translation. The 1st translation was reasonably undertaken and doesn't look like it was intended to be a take-off that was aborted, it looks like positioning for the turnaround. Only the pilot knows for certain, but it looks like positioning for the actual take-off.

Path: The final flight path looks like it went over a descending field, which also had a transition from short grass to long grass. For a running take-off, the disk height needs to be as low as is possible until achieving ETL, with the power requirement increasing rapidly with even small changes of the disk height from the ground. In the image, it appears that the flight path did not follow the terrain to maintain a constant level of the disk, so power requirement would have increased just because of the height above the ground. The path went from short grass to long grass, and that results in an increasing demand for hover power, The change is due to the attenuation of ground effect by the surface material, so the absolute change is dependent on the effect of the grass height, but as the helicopter is translating across the changed conditions, the rate of change is dependent on translation speed.

CG: 4 onboard and some gas will give a forward CG, heavy dudes in the front will bring it well forward. In the hover, absent wind, a CG outside of limits would be evident as a low nose condition, and if the cyclic limit is reached, then translation will occur that cannot be checked. To achieve a case like that, you are well outside of the CG envelope, but that is what happens. In this case, the helicopter first translates and then stops, pedal turns, and then sets off again, suggesting that the CG was not a significant factor. For a semi-rigid rotor (OK, one with a hybrid coning/teeter head...) A CG at a limit won't make a whole lot of difference to the power required. Within reasonable body pitch angles, the TR arm isn't going to shift a whole lot; a forward CG will induce a slight roll component increase, but not much, and the lateral cyclic demand isn't much. Power required won't change any significant amount.

Running take-off with increasing skid height below ETL; The terrain falling away seems to have let the driver enter an increase in his skid (disk) height, and the outcome suggests that they were likely still under ETL. That would have increased power requirement. The ground falling away would have required an increase in forward cyclic to maintain a constant height. Going from zero speed towards higher speed, the cyclic demand for level accelerating flight follows a reverse "S" shape, (with all motion forward), the flap back even at low speed, results in an increase in forward cyclic and if not made, e.g., a constant longitudinal cyclic is held, then the helicopter longitudinal acceleration will reduce. Nothing new in any of these issues, but coupled with ground contour falling away, a lot of things are occurring that happen to need care in handling to avoid an increase in power. For most take-offs, we don't get to the absolute limits of power required, which is a good thing, as when it starts to go bad, the problems compound quickly. (Mason tells the story of a messed up slick running takeoff that ended up in the razor wire inside a minefield, lots of stuff can happen...)

RPM: Low RPM sucks, and shows up in the coning angle if observed, and rapidly decaying TR authority, reducing cyclic authority, and some other stuff related to inertial-aero effects, most giving degraded HQ's. As the engine power output is dependent on RPM, low RPM really sucks. Recovery from low RPM in the hover is one thing, recovery below ETL is another, the translating case is going to have some interest in the surface conditions/contour etc... and the cyclic inputs at all times.MIlking the collective works like a hot dog in a hover, in a messed up running takeoff, lots of other dynamic stuff will come up rapidly and limit any effective gains from that technique.

Turns; a gentle turn to the right with minimal lateral cyclic, and a reduction in the left pedal will recover power, and RPM, but needs clear terrain, and judicious control on the rates, but the reduction in tail rotor power required will recover available power to the main rotor.

Leaving the bodyguard on the ground would have been a good start to a happy day flying.

This incident happened when someone answered the phone and accepted the task, the planning allowing weight above IGE is not reliable in the outcome in the field.

Helicopters, every flight an adventure into physics.







Last edited by fdr; 18th Oct 2020 at 15:32.
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Old 18th Oct 2020, 16:44
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If he was downwind then he committed the cardinal sin I warn my students about - don't imagine your power required in the hover is the max you will need for a downwind cushion creep - that will come at the zero airspeed condition when you have lost any help from the wind behind you and you have positive groundspeed but zero airspeed.

Downwind limited power transitions are an accident waiting to happen.
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Old 18th Oct 2020, 22:00
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Some of the sentiment being expressed here is a little concerning. With takeoff power set and you find yourself barely bobbing at 2 foot on a bubble of air you are too heavy. Simple as that. Nothing more to think about. Lower the collective to flat pitch, kick somebody out, and try again. This talk of running take-offs is utter bollocks. Save your running take-offs for when you have 1000+ feet of flat level asphalt or concrete in front of you, on your annual check-ride. This is not something to be tried in the circumstances we see here.
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