AS350 crash due to Jack Stall...

[BigMike]

Interesting video...
Apologies if posted before.


https://www.youtube.com/watch?v=P44VxgI20H8

[Ascend Charlie]

Speed, weight, and vigorous cyclic movement = soiled underwear at the minimum.

[hargreaves99]

The cyclic movement/pushover didn't look that vigorous to me? Is this something that the AS350 is particularly prone to?

[Agile]

Speed, weight, and vigorous cyclic movement = soiled underwear at the minimum.
you forgot "Altitude" into the mix, VNE goes down 3 knots for every 1000ft, if they are at 6000ft (judging from the tree line) VNE is close to 130Kts.

[SLFMS]

I’m not really familiar with the 350 but know it’s susceptible to Jack stall. I don’t know enough about that to comment.
When watching my initial thought was it’s retreating blade stall, he’s obviously high, he’s gets a lot of speed in the dive then pitches up and rolls right at the moment he aggressively pulls the cyclic back.
Lucky to be alive looks like the deep snow save them

[ShyTorque]

All I can see is the deep snow.

Either that, or the page is blank.

edit: The link appeared when I clicked on “quote”.

A similar scenario to the Colin McCrae accident, by the looks of it.

[hargreaves99]

Looking again at the video he seems to push the cyclic abruptly forward at 1:05, (speed increases, passengers woop for joy) then cyclic back and right roll at 1:15

[212man]

I’m not really familiar with the 350 but know it’s susceptible to Jack stall. I don’t know enough about that to comment.
When watching my initial thought was it’s retreating blade stall, he’s obviously high, he’s gets a lot of speed in the dive then pitches up and rolls right at the moment he aggressively pulls the cyclic back.
Lucky to be alive looks like the deep snow save them

I think the symptom are similar

[Cornish Jack]

If I was going to put money on it, RBS would be my choice. The occupants (assuming that they all survived), are very lucky.! One of my early jobs on S&R was recovering the personal effects of my predecessor from the remains of an RBS induced crash on the South coast which killed three. - deep snow is useful !

[Rotorbee]

If I have got all the informations right, that accident happened in 2016 and the accident report is already out. It was servo transparency aka. jack stall. The Company was TRK helicopters. Everybody walked away.

[Stuart Sutcliffe]

This appears to be the accident in question:

"Summary
On 16 March 2016, at 1618 Pacific Daylight Time, the TRK Helicopters Ltd. Airbus Helicopters AS 350 FX2 helicopter (registration C-FBLW, serial number 2955) departed from the base of a ski run approximately 82 nautical miles northwest of Smithers, British Columbia, on a day visual flight rules flight to the base camp (located approximately 7 nautical miles south-southeast of the ski run), with the pilot and 6 passengers on board. Approximately 1 minute after takeoff, while operating at low altitude, the pilot initiated a descent into a ravine. During the descent, the helicopter's airspeed increased rapidly. Moments later, the helicopter abruptly rolled to the right, pitched up, and collided with terrain on a steep snow-covered slope. There were no injuries, and all 7 occupants egressed the aircraft. The helicopter was substantially damaged. There was no post-impact fire and the emergency locator transmitter did not activate."

https://www.tsb.gc.ca/eng/rapports-reports/aviation/2016/a16p0045/a16p0045.html

[[email protected]]

What doesn't gel with the RBS/jackstall theory (they are so similar it's difficult to tell them apart) is the low Nr horn - that sort of disc loading produces high Nr not low.

[[email protected]]

Shy - great tip about hitting quote to see the link - I have been having this problem with my browser for ages.:ok:

[Two's in]

...while operating at low altitude, the pilot initiated a descent into a ravine.

So, primary cause, servo transparency, secondary cause, lack of imagination.

[RVDT]

What doesn't gel with the RBS/jackstall theory (they are so similar it's difficult to tell them apart) is the low Nr horn - that sort of disc loading produces high Nr not low.

The same horn also provides aural warning of low or high main rotor speed, that is, when the rotor is between 250 and 360 rpm (continuous sound) and above 410 rpm (intermittent sound).

​​​​​​​Have another listen - sounds like it worked as advertised.

[albatross]

RTFM!

[RVDT]

The reason for it - elastomeric bearings - i.e. the spherical bearing.

https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/640x426/elastomeric_bearing_6404261hab_875cf9db971e7219e034747fb33d1 fa4b75c8245.jpg
This bearing is multiple steel spherical cups separated by thin layers of rubber material. Not unique to the AS350.
It can bend and twist but not move so much in compression. Distorting the bearing takes some effort. The maximum effort is naturally at maximum pitch i.e. the retreating side and is always there.
In forward flight some of the disk is constantly stalled and even going backwards with regard to flow. Stall creates a shift in centre of lift aft on the blade and creates an additional feedback which is cumulative with speed and loading further outboard on the disk where it matters.
The forces are quite high and affect fatigue life and ultimate strength, I think the weak point is the PCL's which will possibly bend. Hence the HYD system was designed to be not strong enough to let this happen.
As it is at the edge or slightly outside of the certified flight envelope and marginally before RBS it seems to be acceptable.
Dual HYD aircraft in the same family which will not yield to feedback have a load cell (flat spring and microswitch) on one servo which will warn with a LIMIT caption to avoid overloading the control system.

There are warnings and limitations in the RFM. "Forewarned is forearmed" but maybe not communicated readily.

"Grey" 355 style wide chord blades may be more susceptible than the old "Blue" B model blades but even a B model is susceptible.

[SASless]

This discussion has been had before....probably a couple of times.

Refresh my fading memory as to why just making stronger PCL's and marginally stronger hydraulic jacks would prevent the problem although allowing honest to goodness RBS?

I recall one wonderful old Sikorsky and a venerable Bell product that with youthful indiscretion could both demonstrate RGS for the young and dumb. (Hand raised!).

In those aircraft with correctly turning rotor heads, the nose would pitch up and roll left....and the airspeed would bleed off till the RBS abated or ceased....and assuming one was wise enough to reduce Collective to a reasonable cruise setting....normal flight returned.

Surely some Whirlwind experienced Pilots had some exposure to that.


In the early CH-47....A Models being grossly over weight could provide occurrences of reactions very similar to RBS but in both heads....and with contra rotating rotors....;think about how those symptoms were manifested!

[[email protected]]

Have another listen - sounds like it worked as advertised.

Good point RVDT, I didn't realise it had a high Nr warner as well.

[jimjim1]

Shy - great tip about hitting quote to see the link - I have been having this problem with my browser for ages.:ok:

This is a well known pprune problem and fix (reply). I seemed to fix mine by resetting the pprune cookies.

It went something like:-

Turning down/off ad blocker
Making sure cookies were enabled
Closing pprune
Clearing pprune cookies (will delete saved password)
loading pprune
logging on (needs password)
accepting cookies
Turning up/on ad blocker

[ShyTorque]

Surely some Whirlwind experienced Pilots had some exposure to that.


Yes. Almost 45 years ago, when I was a basic rotary student, my RAF QHI decided to carry out a “spirited arrival” at the unmanned Chetwynd airfield in Shropshire, first thing one fine morning. He descended to very low level at what was very close to Vne (not fast in a Whirlwind 10) and pulled the aircraft round in a hard turn. All I remember is being at close to 90 degrees to the ground, the aircraft wobbling slightly, then us being suddenly placed straight and level at a much reduced speed, alongside some 100’ high cables near the airfield. I was shaken rather than scared (the innocence of youth) but more intrigued to know how he’d done it. There was a nervous laugh from the other seat and he explained we’d just inadvertently experienced retreating blade stall. The aircraft did it, rather than himself.

So, very similar to the situation under discussion, although as far as I know, the Whirlwind reached RBS rather than jack stall/servo transparency, whatever we’d prefer to call it. It makes little difference to the symptoms. Had we been in a left turn, the aircraft might have put us inverted and I might not be here.

Sadly, said QHI was killed in a terrible motorcycle accident a short while afterwards whilst travelling on RAF duty.

[Georg1na]

My memories of my own flick roll in the Culdrose SAR Whirlwind 7. It was not a good day for flying, a howling north westerly wind, so strong that we had to start up and engage in the hanger as we were out of limits to engage outside. Probably frowned upon today but it did get the dust out of the rafters!

We taxied out and took off to look for a fisherman who was missing from below the cliffs near St Agnes, up to the North West. The only way to progress was to fly very low indeed to try to keep out of the gale as our ground speed otherwise would have been even more pathetic than normal. After what seemed like an eternity we arrived close to the scene at very low level and balls out.

As we crossed over the cliff edge those of you with even a rudimentary knowledge of aerodynamics will know what happened next. The upflow of the gale over the cliff edge suddenly and dramatically increased the angle of attack on the blades – the retreating blade stalled – the aircraft flicked rolled to the left – reared enormously nose up – and hurled itself with little control from me across the ocean. I sat there bemused for a very short while, as the unamused SAR crew in the back were flung across the cabin to the port side along with their kit.

After what seemed an age as I was jostling with cyclic, rotor rpm, collective and so on this hunk of aluminium sorted itself out and flew on as though nothing had happened.

We never did find the fisherman and the trip back to Culdrose was at supersonic speed – well for a Whirlwind 7 it was.

Happy days.

[Cornish Jack]

The summary in #11 and Shy Torque's Chetwynd 'event' are,essentially pointing at the same sequence - the direction of divergence being opposed, down to the preferred 'National' rotor rotation direction.
Shy - your QHI was my guide and mentor on my first Whirlwind ride ... which included a Chetwynd visit for sloping ground ... but no RBS demo ! His accident was a huge shock.
I only experienced jack stall as a demo on my first trip at Boscombe (in a Gazelle) and (from memory) it was something of a non-event.

[sycamore]

It is also worth noting that the W-Wind Mk7 RRPM was normally 207,whereas the Mk9/10/12 was normally 219-220,and also had the `beefed-up` dinner-plate` rotating swashplate,and Vne95 kts..!

In fact ,I think that the WW Mk3 we had at B-D, RRPM was normally 203...

During my early Gazelle flights at Marignane ,as Project pilot,we flew early `development` Gazelles,which had stiffer fuselages,only 2doors,and no /small roof transparencies,solid u/c,low skids,and short-backed seats.During `tactical ALAT `Spectrum` flying(flight envelope) ,at `jack-stall` in both left and right turns,the aircraft would roll back towards level flight,in a `self-righting manner.
Sometime later,myself and my CEV ALAT Pilot were requested to fly new mods,as these had to be `Joint` agreements.The hyd system had been modified,and different `jacks` fitted to a different airframe,also ,more plastic roof panels and side doors. So,`orf we went to `explore the envelope,and soon found that hard rolling and pulling produced the expected roll towards level in left hand turns at the jack-stall,to an initial `eye-watering` further roll in right hand turns,The cockpit was full of the usual expletives,both in French ,and English,until control was returned to normal.!! Further investigations into why the jacks had been changed was never fully explained by SNIAS/A`spatiael, just a `c`est la vie`...However,it was fully agreed that,whilst not `dangerous`,handling at the point of jack-stall,had to be fully explained in the Flight Manual ,and fully demonstrated on aircraft conversion,...at a safe height...!

[ShyTorque]

I remember carrying out Range Autos in the Whirlwind 10. The parameters were 180 RRPM & 80 kts (reduce Nr and increase the IAS from a normal one).
You could actually see the individual blades going round, which was a bit disconcerting, but the old lady picked up her skirts and really glid well!

[Georg1na]

"It is also worth noting that the W-Wind Mk7 RRPM was normally 207"
Actually I think it was 210 normally and 213 in the hover. The crewmen in the back would look up between ones legs and make a very loud noise if the rrpm dropped below 213 in the hover over the sea. It seems amazing now that just the loss of a few rrpm could cause one to ditch. Ah - the manual throttle - didn't we just love it! And cartridge starters - clutch pumps - high energy button for starting and so on. If you had to do a manual start, and yes it had a starting handle! it was 82 turns of the handle for one revolution of the engine. Had to do that once during the P1127 trials on HMS Bulwark. D

[[email protected]]

Sycamore - very interesting background on the Gazelle jacks and jackstall response - never heard that before:ok:

Georg1na - a very similar experience happened to a Valley Wessex SAR pilot in about 1989/90 - he came into our crewroom next door looking for a QHI to ask if it was possible to lose control of a helicopter in the hover.

He described an almost identical winching scenario on Tryfan in very strong winds and updraughts and fortunately they hadn't deployed the winchman when the aerobatics started - I told him I was pretty convinced it was RBS

[Cornish Jack]

Shy - re the 180 RRPM - Bill McE, , when he was 'boss' at Valley training, took a 10 out to South Stack on a very on-shore windy day, went manual and took the revs back to 190-ish and slope-soared ! Produced some ridiculous consumption figures !

[ShyTorque]

CJ, I once experienced a similar thing in a SK-76. I was tasked as a favour by the RAF to pick up some British Army soldiers from a rocky offshore outcrop in the South China Sea (obviously, there's a bit of a story behind why they were there and why the RAF couldn't do it themselves), in the teeth of an incoming typhoon. The headwind on the way out and on arrival was somewhere over 70 kts, even at low level. The only place to pick the pax up was from an into wind, steeply sloping rock platform. The slope caused a strong updraught and every time I tried to fully lower the lever, the aircraft autorotated well above the surface and the Nr kept rapidly going to the top limit (doesn't take much with the 76's slippery blades). It took quite a few attempts to get even one wheel on the ground. Thankfully, the soldiers were very keen to leave their precarious perch as they were almost being blown off into the sea and beginning to get rather wet. As soon as the one wheel touched, they leapt on the aircraft like rats up a drainpipe. On our way back to base the indicated ground speed showed 223 kts.

[212man]

ST, was that the same typhoon when the drilling rig under tow was evacuated and then sank? Sadly, taking the hapless divers still in saturation with it!

[sycamore]

Georg1na,you forgot to carry `sixpences`,in case the safety disc `blew`...anyway ,the Mk3 had a `Cyclone`,so it was an electric starter...not so many `prayers and incantations,burning of `joss-sticks`,etc,to get it going...

[ShyTorque]

ST, was that the same typhoon when the drilling rig under tow was evacuated and then sank? Sadly, taking the hapless divers still in saturation with it!

No, different typhoon! :(

[onehunglow]

Crab...I remember at Valley it was possible on certain wind direction and w/v (around 20-25kt) days to take a Wessex out to Snowdowia and find a near vertical cliff face with updraughting air,

Sit in the hover along side the cliff face at just over half power, in the hover, zero airspeed showing.....then over a period of about a minute or less, slowly have to pull to max power to maintain position, before having to dive away lowering the lever and gaining fwd airspeed to recover. It was repeatable over and over again.

[rotorrookie]

This accident in Norway in 2011 claimed 5 lives
https://aviation-safety.net/wikibase/137259

[[email protected]]

Onehunglow - yes plenty of opportunities in Snowdonia to do that - sometimes when you didn't want to:)

[Rotorbee]

There you go. One accident in Switzerland with a lot of details and explanations. Even pictures.
https://www.sust.admin.ch/inhalte/AV-berichte/2265_e.pdf

[PlasticCabDriver]

Crab...I remember at Valley it was possible on certain wind direction and w/v (around 20-25kt) days to take a Wessex out to Snowdowia and find a near vertical cliff face with updraughting air,

Sit in the hover along side the cliff face at just over half power, in the hover, zero airspeed showing.....then over a period of about a minute or less, slowly have to pull to max power to maintain position, before having to dive away lowering the lever and gaining fwd airspeed to recover. It was repeatable over and over again.

I remember one occasion doing similar in the Wessex, sitting in the hover over a ridge in Snowdonia with lever full down. For a few seconds anyway, before the simultaneous realisation from the two of us up front that this probably wasn’t a great idea, and escaping quickly before the wind suddenly dropped.

[albatross]

What a positive Whirlwind of posts.
Anyhoo as I have posted previously a few years ago.

IMO if you encounter Jack Stall you have, , with the exception of actual servo failure, already exceeded the G limits of the helicopter for some reason be it overloading, over torque or overenthusiastic maneuvering.

Many seem to think that when you encounter Jack Stall the controls lock. This is NOT the case.

The controls will move and work as designed but you will feel feedback and need to apply force to move the controls.
Manipulate the controls as required to lower the G Load back within limits by reducing bank angle, lowering the collective ect.
If you don’t have space to do this before ground contact bad things will happen.

We used to demonstrate this in training on the AS350D and the 355F in a very controlled manner. Note: with the Twinstar we just pulled to the Limit Light not to actual Jack Stall which, due to the dual hydraulics, have been very bad practice. Because all the pilots getting checked on the 355 already had lots of 350 time that was all that was required on the 355.

When the 350 first came into service a lot of pilots gained knowledge by pushing the button on the tip of the collective, thereby bypassing the accumulators and turning off the hydraulic system suddenly and completely. They sometimes even did this at high-speed cruise. The ensuing exhilarating rapid, high G, nose up roll to starboard really got their attention. Fortunately they usually did this when going somewhere solo and doing as pilots new to an aircraft sometimes do “Humm What happens when I push this?” After things were returned to normal that stunt usually went into the “Not Going To Do That Again” file.

[Agile]

IMO if you encounter Jack Stall you have, , with the exception of actual servo failure, already exceeded the G limits of the helicopter for some reason be it overloading, over torque or overenthusiastic maneuvering.

I like your logic, but I had understood that he got overenthusiastic in the dive, overspeed past VNE, got blade stall, and consequently jack stalled.

Note: with the Twinstar we just pulled to the Limit Light not to actual Jack Stall which, due to the dual hydraulics, have been very bad practice. Because all the pilots getting checked on the 355 already had lots of 350 time that was all that was required on the 355.

just my personal reminder note: its an error to think that dual hydraulic have twice the actuator thrust power, two piston on the same shaft (with pressure equaly regulated for the two pistons), does not double the thrust.
only higher hydraulic pressure can do that and actually the dual hydraulic version has a slightly inferior hydraulic pressure.
single hydraulic: 40 bars
dual hydraulic: 35 bars

[212man]

just my personal reminder note: its an error to think that dual hydraulic have twice the actuator thrust power, two piston on the same shaft (with pressure equaly regulated for the two pistons), does not double the thrust.
only higher hydraulic pressure can do that and actually the dual hydraulic version has a slightly inferior hydraulic pressure.
single hydraulic: 40 bars
dual hydraulic: 35 bars

Please explain. Force equals pressure x area. So if you have two pistons of the same surface area being acted on by the same pressure, you’ll have twice the force. It’s a simple way to keep the set is light and compact compared to having one large servo (plus redundancy). If you lose a hydraulic system there are normally RFM limits on speed and angles of bank - because you have less servo power.

[Agile]

Please explain. Force equals pressure x area. So if you have two pistons of the same surface area being acted on by the same pressure, you’ll have twice the force. It’s a simple way to keep the set is light and compact compared to having one large servo (plus redundancy). If you lose a hydraulic system there are normally RFM limits on speed and angles of bank - because you have less servo power.

that video explain it better than me:
https://www.youtube.com/watch?v=lJZ-ml75dF0
its because both pressure have two different regulator, kind of the series versus parallel concept

[212man]

that video explain it better than me:
https://www.youtube.com/watch?v=lJZ-ml75dF0
its because both pressure have two different regulator, kind of the series versus parallel concept
Not able to watch right now, but I have been mulling it over and I suspect the answer is twice the power and not twice the force. With two actuators with the same force moving the same distance each in the same period, that’s double the work done in unit time. I’ll look later.

[RVDT]

that video explain it better than me:
https://www.youtube.com/watch?v=lJZ-ml75dF0
its because both pressure have two different regulator, kind of the series versus parallel concept

I think Archimedes just rolled over in his grave!

[albatross]

I like your logic, but I had understood that he got overenthusiastic in the dive, overspeed past VNE, got blade stall, and consequently jack stalled.

just my personal reminder note: its an error to think that dual hydraulic have twice the actuator thrust power, two piston on the same shaft (with pressure equaly regulated for the two pistons), does not double the thrust.
only higher hydraulic pressure can do that and actually the dual hydraulic version has a slightly inferior hydraulic pressure.
single hydraulic: 40 bars
dual hydraulic: 35 bars

That may well be but the jack stall would be symptomatic of exceeding the G-limit not the cause. You would still have control of the aircraft but may be in a position from which you have neither time nor space to recover.

As an aside the RFM of the Astar 350D stated that if you encountered it you had reached the G limit and how to recover from same.
Because of the dual hydraulics on the 355 this was indicated by the illumination of the limit light. This was also in the RFM. No jack stall would be present, Hence we only demonstrated it momentarily to point out that you had reached the G limit, the light was on, no Jack Stall was present but they should recover immediately by reducing bank angle, lowering collective ect. As jack stall had already been demonstrated in 350 training there was no reason to do anything more in the 355 than a steep turn to illuminate the light and recover from that.

I am a little mystified by the video, it is counterintuitive that the heavier, more powerful 355 would require only 35 Bar of Hyd. Pressure vs the 45 Bar required on lighter, less powerful 350D. That is not what I recall being taught on my original factory course on the 355 in the early 80s.
Don’t have the RFM to hand but wonder what the ECL for a single Hyd. failure on a 335 or 350 with dual hydraulics states.

. Never flew a 350 with dual hydraulics and have had the sore arm to prove it. I experienced 3 Hyd failures in the 350D.

Many, many moons since I flew either one. Freely sprinkle, therefore, all the grains of salt you may feel are required

[admikar]

that video explain it better than me:
https://www.youtube.com/watch?v=lJZ-ml75dF0
its because both pressure have two different regulator, kind of the series versus parallel concept
Nope. Servos are parallel, not in serie.
That's why 355 has limit light, otherwise you will ovestress rotor system before you overstress hydraulics. Even with lower pressure, individual servo might have less power than single system one, but together they exert more force.

[SquirrelDev]

The servos are in series. In parallel both cylinders would be side by side, while here they are facing each other.
35 / 40 bars says nothing about the available force without mentioning the surface on which that pressure applies. Same about the power if the flow provided by the pump(s) is unknown.

[JimEli]

Most are trying to describe the same thing with confused terminology and reasoning. The resultant of 2 identical colinear forces is double the individual force.

However, the AS350 dual hydraulic system does not produce twice the force of the single system because they operate at different pressures (and presumably with different piston sizes).

The above video simply states that the two independent systems don’t result in double pressure.

The AS350 dual system is not a traditional series nor parallel hydraulic system. Customarily, a series hydraulic system is where the hydraulic outflow of the first piston is fed as input to the second piston. And typically, a parallel system has a single pump feeding separate pistons. The AS350 is a hybrid parallel system utilizing two pumps (operating at the same pressure) that feed separate pistons that happen to be connected (colinear) to one another via the same shaft.

Grain of salt: The 2 cylinders of the dual system are not identical due to the construction of the actuator which shares the same shaft. The upper cylinder incorporates a liner which serves to reduce that system’s piston area to be comparable with the lower system.

[albatross]

Found this: https://youtu.be/U7sc2BodDHo?si=tarmuSmLTeGFKQYi

As an aside: In the video it is mentioned that VNE of 155 KTS is to reduced 3 KTS per 1000 ft.
Therefore at 10,000 a VNE of 125 KTS would apply. A darn important thing.

I mention this because, and I kid you not, I have had to listen to pilots bitch, gripe, whine and complain about this on many helicopters. (especially on the 212 where some develop a nervous twitch at anything below 100 KTS IAS. (Fun to Watch). Strangely they sometime complain at the same time about how rough the aircraft is while they blithely exceed VNE as they seem unaware that the VNE placard is in Hd NOT Hp) providing they looked at it at all.

Just a reminder to some, a small group I am sure, that while you may think you are crawling over the landscape at such a speed that you will reach retirement age before your destination.

Let’s look at flight 1000 ft in a standard atmosphere. Temp 13c Vne would be 152 KTS
Using a lapse rate of 2 C/1000 ft 10000 ft Temp should be +- -5C VNE is 125 KTS

But lets look at our True Airspeed
Using the numbers above and your Handy Dandy all Doing, all Telling Computer. ( Old School )
Or looking at your “No thought required Glass Panel” ( New School )

You TAS at 1000 feet is 153 KTS VS the 152 KTS calculated VNE indicated on the gauge.
Your TAS at 10,000 is 144 KTS VS the snail like 125 KTS Calculated VNE on the gauge .
See you will make it home in time for Beer Call!
Everybody Happy Now?

In any case fly safe and avoid unplanned, inadvertent Airframe / Planet interface……the Planet always wins.

[RVDT]

Found this: https://youtu.be/U7sc2BodDHo?si=tarmuSmLTeGFKQYi

As an aside: In the video it is mentioned that VNE of 155 KTS is to reduced 3 KTS per 1000 ft.
Therefore at 10,000 a VNE of 125 KTS would apply. A darn important thing.

I mention this because, and I kid you not, I have had to listen to pilots bitch, gripe, whine and complain about this on many helicopters. (especially on the 212 where some develop a nervous twitch at anything below 100 KTS IAS. (Fun to Watch). Strangely they sometime complain at the same time about how rough the aircraft is while they blithely exceed VNE as they seem unaware that the VNE placard is in Hd NOT Hp) providing they looked at it at all.

Just a reminder to some, a small group I am sure, that while you may think you are crawling over the landscape at such a speed that you will reach retirement age before your destination.

Let’s look at flight 1000 ft in a standard atmosphere. Temp 13c Vne would be 152 KTS
Using a lapse rate of 2 C/1000 ft 10000 ft Temp should be +- -5C VNE is 125 KTS

But lets look at our True Airspeed
Using the numbers above and your Handy Dandy all Doing, all Telling Computer. ( Old School )
Or looking at your “No thought required Glass Panel” ( New School )

You TAS at 1000 feet is 153 KTS VS the 152 KTS calculated VNE indicated on the gauge.
Your TAS at 10,000 is 144 KTS VS the snail like 125 KTS Calculated VNE on the gauge .
See you will make it home in time for Beer Call!
Everybody Happy Now?

In any case fly safe and avoid unplanned, inadvertent Airframe / Planet interface……the Planet always wins.

Video shows a 355N roll left at about 70 knots? Wut?

https://youtu.be/Ttkf8DUEtWY?si=z2y0NSUw_KgeA3Hv

[albatross]

Well I don’t know about the cause of that accident shown in the video above, however, since the discussion is about Jack Stall, Servo Transparency, ect.
It would be possible to enter that area of the Flight Envelope in a left as well as a right turn. Especially if you were at a high gross weight and maneuvering enthusiastically.
It is not necessary to be near, at or over VNE to encounter it.

[JimEli]

Video shows a 355N roll left at about 70 knots? Wut?
Servo hardover? See NTSB report NYC97LA058 (https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/39330/pdf) for a similar occurrence in a 355. Although, Airbus Helicopters makes much ado about the jam-proof double rotary distributor valves.

[JimEli]

FWIW, older versions of the AS350 RFMs define the maneuver limitation as:

Do not exceed the load factor corresponding to the servocontrol reversibility limit.

Which is an odd way to put it, since pilots wouldn’t have a genuine way of knowing where the limit is until after exceeding it (Maybe it was a Frenglish artifact).

The latest versions state:

Continued operation in servo transparency (where load feedback is felt in the controls) is prohibited.

However, this version possibly reduces the respect servocontrol reversibility is due and gives the impression it's okay to tickle it now and then.

[Agile]

You TAS at 1000 feet is 153 KTS VS the 152 KTS calculated VNE indicated on the gauge.
Your TAS at 10,000 is 144 KTS VS the snail like 125 KTS Calculated VNE on the gauge .

The interesting thing about VNE in "level flight":
1/ at sea level there is not enough power to get to 152kts; at 10,000 ft there is not enough power to get to 125kts.
2/ at 10,000ft the vibration level that you get, the colective position, they all come in a way that 125kts feels like 152kts.
unless you are thick and only look at the indicated speed, its not such a pitfall.

[albatross]

The interesting thing about VNE in "level flight":
1/ at sea level there is not enough power to get to 152kts; at 10,000 ft there is not enough power to get to 125kts.
2/ at 10,000ft the vibration level that you get, the colective position, they all come in a way that 125kts feels like 152kts.
unless you are thick and only look at the indicated speed, its not such a pitfall.

Trust me there are some thick people around sometimes through no fault of their own but the hapless victims of substandard training.
Also some folks have been happily flying an airframe at sea level in a cool environment for years and thousands of hours with an altimeter that has never indicated over 2000 feet being thrust into a high altitude, high temp environment and expected to do wonderful things.

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When demonstrating jackstall on the Gazelle, it was shown in two different conditions - a left turn and a dive to VNE.

A Gazelle could normally tolerate a 2g sustained turn - 60 deg AoB - albeit sacrificing speed through the manoeuvre. So a harder pull was required to get it to jackstall, at which point it would pitch up and roll right - exactly why we did it in a left turn and not a right one.

The dive to VNE used the conditions of the day to calculate the DA and therefore the VNE at 1500' agl. From 2500' agl you dived to VNE with MPS set (14.5 deg collective pitch), usually somewhere between 160 and 168 Kts and then pulled aft cyclic - it usually went into jackstall fairly easily in that condition compared to the turning state.

In both scenarios, you could hold the aircraft in the jackstalled state to show how the aerodynamic back loads on the retreating blade (and therefore lateral jack) had to be reduced before the jack would un-stall.

The AS365 had a LIMIT light and audio warning which we also demonstrated in a left turn but never pulled past that - the two side of the hyd jacks had different cross sectioned pistons so the upper half would 'collapse' before the lower half, making a microswitch on the jack and illuminating the LIMIT light and giving the audio 'bong'.

It seems to have been a design philosophy in Aerospatiale/Airbus helicopters.

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I have only flown one aircraft that had a g meter and that was the Lynx for aerobatics - since the manufacturers don't quote g limits you can't be criticised for exceeding something you don't know and couldn't measure anyway.

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We used to refer to the max speed in level flight that could be obtained at max power as VMax since it was usually lower than VNE but that may be because military release to service limitations were usually lower than the manufacturers limits.

[212man]

We used to refer to the max speed in level flight that could be obtained at max power as VMax since it was usually lower than VNE but that may be because military release to service limitations were usually lower than the manufacturers limits.
The civilian term is Vh - maximum speed in level flight using maximum continuous power.

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The civilian term is Vh - maximum speed in level flight using maximum continuous power.
I knew there was a grown-up V something for it, just couldn't recall it and too lazy to google:)

[oldbeefer]

When demonstrating jackstall on the Gazelle, it was shown in two different conditions - a left turn and a dive to VNE.

A Gazelle could normally tolerate a 2g sustained turn - 60 deg AoB - albeit sacrificing speed through the manoeuvre. So a harder pull was required to get it to jackstall, at which point it would pitch up and roll right - exactly why we did it in a left turn and not a right one.

The dive to VNE used the conditions of the day to calculate the DA and therefore the VNE at 1500' agl. From 2500' agl you dived to VNE with MPS set (14.5 deg collective pitch), usually somewhere between 160 and 168 Kts and then pulled aft cyclic - it usually went into jackstall fairly easily in that condition compared to the turning state.

In both scenarios, you could hold the aircraft in the jackstalled state to show how the aerodynamic back loads on the retreating blade (and therefore lateral jack) had to be reduced before the jack would un-stall.

The AS365 had a LIMIT light and audio warning which we also demonstrated in a left turn but never pulled past that - the two side of the hyd jacks had different cross sectioned pistons so the upper half would 'collapse' before the lower half, making a microswitch on the jack and illuminating the LIMIT light and giving the audio 'bong'.

It seems to have been a design philosophy in Aerospatiale/Airbus helicopters.

My instructor on my QHI course in 1976 decided to do the descending turn demo in a 60 degree RIHT HAND TURN.. The aircraft flicked though inverted and came out almost straight and level. I didn't fly with him again.