Fenestron stall - Fact or Myth?
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To: Arkroyal
You asked,” Talking of the Lynx (which I didn't fly), can anyone confirm that when Westlands trialled the reverse direction T/R (Clockwise from the left instead of the earlier anti-clock), they forgot to alter the spiral groove oil feed to the outer bearing and seized the thing”?
This was the subject on another thread. My response at that time was that if Sikorsky could do it then I was sure that Westland could be guilty of the same error. During the design of the H 37, Sikorsky found that the tail rotor drive shaft was contacting a part of the primary structure. In order to correct this condition they had to lower the drive shaft. This involved putting an additional gear set on the main transmission causing the tail rotor to turn in the wrong direction. They modified the intermediate gearbox and the tail rotor gearbox by reversing the pitch on the gears. In the process, they forgot about the Archamedes (sp) pump on the outboard end of the tail rotor drive spindle and instead of delivering oil to the outboard bearing is actually took oil away from the bearing. In light of that, I would say that the Lynx story is true.
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The Cat
You asked,” Talking of the Lynx (which I didn't fly), can anyone confirm that when Westlands trialled the reverse direction T/R (Clockwise from the left instead of the earlier anti-clock), they forgot to alter the spiral groove oil feed to the outer bearing and seized the thing”?
This was the subject on another thread. My response at that time was that if Sikorsky could do it then I was sure that Westland could be guilty of the same error. During the design of the H 37, Sikorsky found that the tail rotor drive shaft was contacting a part of the primary structure. In order to correct this condition they had to lower the drive shaft. This involved putting an additional gear set on the main transmission causing the tail rotor to turn in the wrong direction. They modified the intermediate gearbox and the tail rotor gearbox by reversing the pitch on the gears. In the process, they forgot about the Archamedes (sp) pump on the outboard end of the tail rotor drive spindle and instead of delivering oil to the outboard bearing is actually took oil away from the bearing. In light of that, I would say that the Lynx story is true.
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The Cat
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Having been in a ******* in which the HP lost tail rotor control I think I have an idea on why this happened. The statements put forward by eden were borne out in this instance.
The HP was a young pilot (tw@t) who was not as good as he believed and who had a history of over-controlling. 2am over a well lit city to the W of GB ;-) We were hovering downwind (in limits, honest). Young chap decided to lose a bit of his limited concentration and sent us backwards. Wind crossed from one side of the tail to the other, then under the horizontal stab. The result was a spectacualr >360 which included a healthy dose of 80 deg nose down.
The next day he was heard spouting on about Fenestron Stall until it was pointed out that his poor handling had intitiated the whole sorry affair.
Regards PFL
The HP was a young pilot (tw@t) who was not as good as he believed and who had a history of over-controlling. 2am over a well lit city to the W of GB ;-) We were hovering downwind (in limits, honest). Young chap decided to lose a bit of his limited concentration and sent us backwards. Wind crossed from one side of the tail to the other, then under the horizontal stab. The result was a spectacualr >360 which included a healthy dose of 80 deg nose down.
The next day he was heard spouting on about Fenestron Stall until it was pointed out that his poor handling had intitiated the whole sorry affair.
Regards PFL
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In reply to Arkroyal, yes you are correct old chap, when the ex-garage door company first changed the Lynx tail rotor over the spiral oil groove forgotten about, causing an angle gearbox to fail, that was when the error was discovered.
As to Fenistron Stall, speaking from experience as a past and current Gazelle pilot, there is no such thing as Fenistron stall. Large and rapid imputs of right boot and high power settings can (if you try hard enough) cause a lack of directional control, its called gross miss handling! I managed it only once, that was during an "AAC Blue Ego's" pactice and yes, adrenaline is brown in colour.
As to Fenistron Stall, speaking from experience as a past and current Gazelle pilot, there is no such thing as Fenistron stall. Large and rapid imputs of right boot and high power settings can (if you try hard enough) cause a lack of directional control, its called gross miss handling! I managed it only once, that was during an "AAC Blue Ego's" pactice and yes, adrenaline is brown in colour.
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PurplePitot,
Speaking as a Crab who was on loan to the AAC around the time all this started, and speaking also as someone who was able to get the information as supplied by Eden from the other Crabs at CFS(H) - what's your point? Can't say I remember any fiendish Brylcreem-smeared plot to rid the forces of the chicken leg before its due date. Do enlighten us.
Oh yes, and I do remember having to take a Lynx Mk1 bombed-up with 8 (empty) tubes down to the <1 foot hover to get a nose-left turn going. Hat well and truly doffed to any HAS shipmates trying to get that lump onto a heaving deck in anything more than Mr Beaufort's size 5.
Speaking as a Crab who was on loan to the AAC around the time all this started, and speaking also as someone who was able to get the information as supplied by Eden from the other Crabs at CFS(H) - what's your point? Can't say I remember any fiendish Brylcreem-smeared plot to rid the forces of the chicken leg before its due date. Do enlighten us.
Oh yes, and I do remember having to take a Lynx Mk1 bombed-up with 8 (empty) tubes down to the <1 foot hover to get a nose-left turn going. Hat well and truly doffed to any HAS shipmates trying to get that lump onto a heaving deck in anything more than Mr Beaufort's size 5.
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Crudge and A Greenhall just 2 that I can think off who departed the fore and aft rather rapidly in the horizontal, with the Gaz piece. The former I believe, volunteered for it with the froggie TP's...
The TR was not altered in any way other than 'optimising' it. It seems pilots should have been aware of it if they were fully au fait with their flight envelope...as the rest of us are....no?
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Thermal runaway.
The TR was not altered in any way other than 'optimising' it. It seems pilots should have been aware of it if they were fully au fait with their flight envelope...as the rest of us are....no?
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Thermal runaway.
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TC: Andy G's was during a wingover from several hundred feet up - he showed me the pictures (of the wreckage he walked clear of) and spun the dit. He was very lucky and he knows it. Don't know about Crudge being the guy who did the Aerospat' tests - but thinking back - I recall that it may have been Paul Shawcross who went to AeroSpat' to do the exceptionally scary tests.
I am trying to trace the video .....???
I am trying to trace the video .....???
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I would like to agree with PFL,
I also have been involved in 2 cases of the famed Fenestron stall, once in exactly the same manner as described by PFL,
the other on a low approach downwind my pilot decided to pedal turn around instead of flying round, I was distracted with the maps and the first I knew we were in the C***, was as I heard 'you have control' during the 2nd 360, rapid application of the opposite pedal and a nose down attitude to regain airspeed, allowed us to walk away with only a dent in our pride as everyone on the the ground had seen our air display.
On both occaisions my pilots were straight out of MW and graded above average who thought they could do anything.
These were good lessons for both, about the effects of mishandling, and I am glad to say the experience years ago has possibly helped them earn that above average grading they now hold .
I also have been involved in 2 cases of the famed Fenestron stall, once in exactly the same manner as described by PFL,
the other on a low approach downwind my pilot decided to pedal turn around instead of flying round, I was distracted with the maps and the first I knew we were in the C***, was as I heard 'you have control' during the 2nd 360, rapid application of the opposite pedal and a nose down attitude to regain airspeed, allowed us to walk away with only a dent in our pride as everyone on the the ground had seen our air display.
On both occaisions my pilots were straight out of MW and graded above average who thought they could do anything.
These were good lessons for both, about the effects of mishandling, and I am glad to say the experience years ago has possibly helped them earn that above average grading they now hold .
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Yaw problems with fenestron equipped helicopters
Having survived a 'moment' with a 365N during which momentary loss of yaw control was experienced and the situation rectified by full application of opposite (right) pedal I reported the problem to the engineers just in case it was some sort of yaw AP problem (we had been having some problems with the yaw stab). The engineer came to find me the following day carrying a photocopy of a EC Service Letter dated about 10 years previously (so about 1990) drawing the pilots attention to a situation in which there could be a loss of yaw control when taking off with a wind from the starboard quarter. They implored the pilot NOT to take the aircraft flying in an attempt to regain control and instead suggested that he apply full opposite pedal and land as soon as possible.
I had landed and parked into wind but when we came to leave the wind was indeed from the starboard quarter. Never new about that problem until I read the Service Letter. Anyone else heard of it?
G.
I had landed and parked into wind but when we came to leave the wind was indeed from the starboard quarter. Never new about that problem until I read the Service Letter. Anyone else heard of it?
G.
I must admitt I don't understand such a big fuss about Fenestrons tail rotors....Having flown several thousands hours on helicopters types ranging from the SA341 to the AS365N3 on military, air transport or aerial work I only have experienced once what can be described as a "mild" LTE: it was on lift-off with an SA365C from an off-shore rig with a 15 kts front right wind....I just landed back and I never experienced this again later despite the great variety of wind/speed/power combinations.
It is true that we need a greater amount of anti-torque pedal to get the same affect as with a conventional tail rotor, but it should never be a great hasle if correctly informed or trained.
It is true that we need a greater amount of anti-torque pedal to get the same affect as with a conventional tail rotor, but it should never be a great hasle if correctly informed or trained.
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I have to admit, I had over two thousand hours in the Gazelle before I realised there was such a term as Fenestron Stall, I had never heard of it, and didn't know I didn't know.
I was sitting in the back of a Gazelle during a short flight on my QHI course when the HP very clumsily tried a lookout turn to the left. The strong wind caught the big tailfin and whipped us even faster to the left, his reaction was full-right pedal, and off we jollywell went. After about 3 revolutions, I thought the shaft had failed, I could see he had full right pedal applied and nothing was happening. He instinctively raised the collective to get away from the ground but this made things worse so he decided to land very heavily whilst in the spot turn.
On further investigation of the twisted Gazelle, there was nothing wrong with the anti-torque system. If you apply too much pitch to an aerofoil, eventually it will stall, he had applied the maximum possible pitch, very quickly, and I would say the fenestron had stalled.
The French TP's answer was to apply full left pedal to unstall then re-apply right pedal gently. I have no doubt that would work, but try doing it when you are spinning at 360 deg in 3 seconds and out of control with your ar$e biting the buttons off the seat cushion.
Call it what you like, I would say the fenestron had stalled.
Tam
I was sitting in the back of a Gazelle during a short flight on my QHI course when the HP very clumsily tried a lookout turn to the left. The strong wind caught the big tailfin and whipped us even faster to the left, his reaction was full-right pedal, and off we jollywell went. After about 3 revolutions, I thought the shaft had failed, I could see he had full right pedal applied and nothing was happening. He instinctively raised the collective to get away from the ground but this made things worse so he decided to land very heavily whilst in the spot turn.
On further investigation of the twisted Gazelle, there was nothing wrong with the anti-torque system. If you apply too much pitch to an aerofoil, eventually it will stall, he had applied the maximum possible pitch, very quickly, and I would say the fenestron had stalled.
The French TP's answer was to apply full left pedal to unstall then re-apply right pedal gently. I have no doubt that would work, but try doing it when you are spinning at 360 deg in 3 seconds and out of control with your ar$e biting the buttons off the seat cushion.
Call it what you like, I would say the fenestron had stalled.
Tam
Yes Hihover, but this case was initialy caused by a sharp yawing motion (caused by a wind gust on the fin) requiring a quick and wide pedal action to counteract. Don't you think a conventional tail rotor could have develloped an LTE in this situation as well ? Is it really typicall of a fenestron design ?
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Well, I would not like to comment on how a conventional tail rotor would have coped in the same situation but with the fenestron, the airflow is all going through the duct, and in this case, the blades in that duct had stalled. There is no way to regain control of the fenestron unless you unstall the blades and re-apply right pedal.
By definition, fenestron stall is LTE, but I do not believe it is the same thing when compared to a conventional tail rotor.
Gladly there were not too many cases like this one.
Tam
By definition, fenestron stall is LTE, but I do not believe it is the same thing when compared to a conventional tail rotor.
Gladly there were not too many cases like this one.
Tam
