AS350 crash due to Jack Stall...
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Surely some Whirlwind experienced Pilots had some exposure to that.
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.
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 hangar 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.
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.
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.
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.
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...!
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...!
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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!
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!
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"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
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
Sycamore - very interesting background on the Gazelle jacks and jackstall response - never heard that before
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
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
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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 !
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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.
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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!
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...
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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.
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.
This accident in Norway in 2011 claimed 5 lives
https://aviation-safety.net/wikibase/137259
https://aviation-safety.net/wikibase/137259
Onehunglow - yes plenty of opportunities in Snowdonia to do that - sometimes when you didn't want to
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.
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.
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.
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.
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
Last edited by Agile; 2nd Dec 2023 at 09:39. Reason: added respective hydraulic pressures
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
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