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Old 1st Jan 2017, 01:25   #21 (permalink)
 
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I always wondered what would lure Sultan out of hiding.....and once again wonder what works effectively to send him scurrying off with his tail between his legs yet again.

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Old 1st Jan 2017, 02:42   #22 (permalink)
 
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"I suggest you move over to another forum. This one is for professional pilots."

Since when? That not what the forum heading says.
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Old 1st Jan 2017, 10:37   #23 (permalink)
 
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Quote:
Originally Posted by Apate View Post
Two fatal accidents (L2 & EC225) with full independent investigations do not find a root cause. The latest EC225 accident also highlights that HUMS did not provide any indications of an issue, yet resulted in a catastrophic failure with no chance of any survivors.
Once you wiped the Foam off your Mouth you should see that there is a very serious failure mode that hasn't been properly fixed. This is a serious issue and shouldn't be taken too lightly. The S-92 has proven to be apparently very difficult/impossible to control with a failed Tailrotor (Cougar accident). They were at low power setting and prepared that something might be bound to fail plus they were over water and still the result was an accident with only one survivor. This is probably due to a pretty big and boxy Fuselage and a rather small tail. Weather vaning effect likely pretty small. So the Tail rotor is extremely critical on this type.
Sikorsky needs to fix this ASAP. We don't need another predictable fatal accident.


Does it warrant immediate grounding? Possibly not. Does it warrant highest urgency on the side of the Manufacturer plus rigorous and tight inspections on the active fleet? Absolutely.
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Old 1st Jan 2017, 11:04   #24 (permalink)
 
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This failure was potentially very serious, especially as it appears to have manifested itself to the crew after committal to landing on a deck. Loss of control (fixed pitch) of the tail rotor is something crews practice regularly in the simulator, but not when landing on helidecks.

Other than the event itself, there's very little information out there. We don't yet know the root cause, whether the AD was complied with, how long the bearing has been installed, whether HUMS picked up anything, etc. Hopefully these answers will be available soon.

henra - the Cougar accident was a loss of tail rotor drive, a very different failure to this one. Immediate entry into autorotation is the only way to recover from loss of tail rotor drive. They were not at a low power setting as the Captain decided to increase speed to normal cruise power despite the co-pilot suggesting it was not a wise thing to do. To draw parallels between this current issue and the Cougar accident is not appropriate.
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Old 1st Jan 2017, 11:48   #25 (permalink)
 
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Originally Posted by Variable Load View Post
henra - the Cougar accident was a loss of tail rotor drive, a very different failure to this one. Immediate entry into autorotation is the only way to recover from loss of tail rotor drive.
I know. I wanted to point out that the S-92 is probably even more difficult to handle with a problem on the tail rotor than some other types due to relatively small vertical area behind cg.

Quote:
To draw parallels between this current issue and the Cougar accident is not appropriate.
Agreed, they are technically not directly comparable. But the Cougar accident gave an indication about the criticality of the tail rotor for the S-92 (or any other big Transport Heli. To avoid any suspicions: The 225 or any other of the big Transport Helis won't behave much different they all have massive fuselages and small tails - The only one with a chance of a somewhat more benign behavior might be the Blackhawk). They had to be prepared that something might break, yet they didn't manage to go into Autorotation quickly enough to make it survivable.
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Old 1st Jan 2017, 12:02   #26 (permalink)
 
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Only some TRPCS were affected by the 2 ASBs. Neither of the ASBs were applicable to this TRPCS. Sikorsky recommends specific emphasis on utilization of the HUMS Tail Gearbox Bearing Energy Tool. This Tool will detect a PCS bearing that is experiencing degradation.
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Old 1st Jan 2017, 12:38   #27 (permalink)
 
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It's all very well practicing TR malfunctions in the sim but is the software modelling in the sim completely representative of the handling of the real aircraft? It is possible to get lulled into a false sense of security by a relatively benign sim - it is, after all, just a big computer game.
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Old 1st Jan 2017, 13:16   #28 (permalink)
 
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Originally Posted by industry insider View Post
Only some TRPCS were affected by the 2 ASBs. Neither of the ASBs were applicable to this TRPCS. Sikorsky recommends specific emphasis on utilization of the HUMS Tail Gearbox Bearing Energy Tool. This Tool will detect a PCS bearing that is experiencing degradation.
Interesting.

From that, I gather that this pitch change shaft (and bearing) was presumably beyond the 80FH which meant there was no inspection requirement. That will clearly need readdressing if so.

If they have a tool to monitor this specific failure mode, I would have expected it to pick up on something. From that, I draw a few conclusions.

The system is ineffective and give no prior warning.

The system is effective and did give a prior warning but was missed or wrongly diagnosed by the staff at CHC.

The system is partially effective and give a very late warning, i.e, only an hour or two notice.
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Old 1st Jan 2017, 17:56   #29 (permalink)
 
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Name one "Large" helicopter that does not have problems "weather vaping" after a Tail Rotor gives up its assigned tasking?

When One considers all possible Power Demands, Torque Moments, and Airpeeds....I doubt any large helicopter can be shown to be able to cope with such problems.
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Old 1st Jan 2017, 18:47   #30 (permalink)
 
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None that I know of ...fixed pitch yes....loss of tail rotor drive..No.
I assume someone will be along to dispute this.
Taking cover...you may fire when ready.

I would think that folks would wait for additional info on what actually occured before making expert comments on this particular event. Glad everybody was OK after a shower and underwear change.
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Old 1st Jan 2017, 21:31   #31 (permalink)
 
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Originally Posted by SASless View Post
Name one "Large" helicopter that does not have problems "weather vaping" after a Tail Rotor gives up its assigned tasking?

See my SWAG conclusion that the only 'big' Helicopter where I see a tiny chance that it might remain controllable to some extent might be the Blackhawk when lightly loaded and in minimum power cruise.
Between the 'uncontrollable' ones there might be minor differences how many seconds (if any, depending on phase of flight and weight) remain to enter Auto before it goes pear shaped.
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Old 1st Jan 2017, 22:30   #32 (permalink)
 
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Is 'weather-vaping' anything like weather-vaning or is it a new term for those helos that are using e-cigarettes?
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Old 1st Jan 2017, 22:42   #33 (permalink)
 
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The UH-60 series helicopter has in fact a very small vertical stabilizer surface and any sort of t/r drive failure calls for engine shutdown and auto. You can't sustain straight and level flight without t/r drive.
An interesting feature are the t/r pitch centering springs that allow for in trim forward flight at a certain weight and either 40kts or 125kts in case of a t/r control failure.
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Old 2nd Jan 2017, 01:55   #34 (permalink)
 
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T/R Pitch Centering Springs

Hello Mast Bumper. May I provide some more specific information on this design feature. BTW, this design feature is incorporated into the basic S-92 as well.

Actually, the nomenclature you applied is misleading. In the vertical tail structure of the S-70, and prior to the cables being attached to the tail rotor servos, the two tail rotor control cables are attached to opposite sides of a control quadrant. Each side also has a spring capsule. The idea is that in case one cable is shot away anywhere over the cable run from up forward in the machine, the other cable side of the quadrant remains in tension, against the spring force afforded by the spring capsule on the other side of the quadrant. The output side of the quadrant feeds the servo inputs. Full tail rotor authority remains. A switch in the failed cable side of the quadrant illuminates a cockpit warning capsule. The same basic arrangement is found in the basic S-92 design. It has been combat proven on the S-70.

I might add another design feature of the cross beam tail rotor design in both helicopters: As assembled, the cross beams are of course flat, BUT, the airfoils as attached to the beams do not have their zero lift lines coincident with the flat surface of the beams. The airfoils do incorporate twist, and the built in positive angle of attack of the design facilitates flight between 40 KIAS and 120 KIAS with a reasonable amount of sideslip, with no control input. We flight tested the S-70 with both stages of the tail rotor servos depressurized at the same time, and that was the result. We were almost able to come to a hover ( with rather a lot of force on the left pedal (that force is actuated thru the servo control follow-up link ), but not quite, hence the emergency procedure to perform a run on landing if that dual failure were to occur. For non S-70 pilots: the S-70 TR servos are pressurized by the No. 1 and the Backup Hydraulic Systems ( the backup being the same pump as the main No 1 and No 2 systems, but electrically driven ).

Anyway, as you can see, the tail rotor quadrant and spring capsules are probably not a factor in this event, at least as far as the information posted so far indicates, and I am not privy to any other.

Last edited by JohnDixson; 2nd Jan 2017 at 02:00. Reason: Additional information
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Old 2nd Jan 2017, 03:04   #35 (permalink)
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Quote:
Originally Posted by SASless View Post
Name one "Large" helicopter that does not have problems "weather vaping" after a Tail Rotor gives up its assigned tasking?

When One considers all possible Power Demands, Torque Moments, and Airpeeds....I doubt any large helicopter can be shown to be able to cope with such problems.
I know of an instance where an AH-64D has the entire tail rotor blade assembly depart in flight, the aircraft was flown to an airfield and made a roll on landing with no further damage. Just sayin'
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Old 2nd Jan 2017, 12:29   #36 (permalink)
 
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Quote:
Originally Posted by crab@SAAvn.co.uk View Post
Is 'weather-vaping' anything like weather-vaning or is it a new term for those helos that are using e-cigarettes?
"Vaping" is autocorrect for "vaning".

Were you unable to make the intellectual leap to figure that out without a colored pencil Briefing?

By the way.....Happy New Year! Fly Safe when you have to leave that notorious Recliner you are reported to wear out when on shift and not engaged in service to the Realm!
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Old 2nd Jan 2017, 13:27   #37 (permalink)
 
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Happy New Year to you too SAS

Don't do shifts any more, which is wonderful - back to 9-5 instructing.

What a strange auto-correct you have - I thought it was just your age and eyesight letting you down
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Old 2nd Jan 2017, 19:12   #38 (permalink)
 
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Quote:
Originally Posted by Mast Bumper View Post
The UH-60 series helicopter has in fact a very small vertical stabilizer surface and any sort of t/r drive failure calls for engine shutdown and auto. You can't sustain straight and level flight without t/r drive.
Among the current generation of bigger Transport Helicopters it still has about the largest vertical Tail especially if you include the smooth transition to rear part for the fuselage that should also produce some Weather van(/p )ing or at least reduce obstruction of airflow to the Tail.

@John Dixson: Are there possibly known cases where it was possible to keep the S-70 at least somewhat controllable in a cruise at least for some time with a failed T/R drive? Personally I would consider that potentially possible? Am I too optimistic?


P.S.: Very interesting information about the clever backup solution for the Tail Rotor control
That is the good thing that can come from 'Battle proven'.
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Old 3rd Jan 2017, 00:59   #39 (permalink)
 
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Quote:
We flight tested the S-70 with both stages of the tail rotor servos depressurized at the same time, and that was the result. We were almost able to come to a hover ( with rather a lot of force on the left pedal (that force is actuated thru the servo control follow-up link ), but not quite, hence the emergency procedure to perform a run on landing if that dual failure were to occur.
Very true John. We used to do the same for training students on the S70 back in the early 90's before we had access to simulators. Pull the APU C/B and then fail the the #1 Hyd system......

Result - both T/r servos without Hyd power.

It worked a treat. Built huge confidence in instructors/students alike in the capability of the S70. Directional control as you got below 40KIAS got far more dependant upon wind/cross wind and gusts than simulators can hope to predict.

You learnt quickly that airspeed was your friend in T/R malfunctions....providing you have a fin with descent camber on it.

Speed/attitude control as speed decayed and the pedals got heavier, was essential. Amazing how only a matter of a couple of knots could make the difference in accurate directional control and a straight and totally manageable landing.

Its this amazing and variable effect that happens in real life that simulators sadly can't faithfully reproduce as Crab said earlier. With fear of being called a heretic, perhaps we need to start to recognise the shortfalls of simulators in realistic training in particular for helicopters and low manoeuvres and adapt training accordingly.

Back to the original thread........Excellent design without a doubt......

As an aside and ref loss of tail rotor drive; I had heard an anecdotal incident back in the late 80's of a UH60 losing total tail rotor drive and his #2 (in the formation) calling the incident as the tail rotor (of lead) came to a complete stop. Lead entered a shallow descent and had a slight right hand turn on to maintain better control. But as I remember they landed OK but am uncertain of the finer points of the termination of the incident. But I was talking to a member involved in the incident....so it couldn't have been too messy.

cheers
RG
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Old 3rd Jan 2017, 16:32   #40 (permalink)
 
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Questions raised by Henra and RG:

Let me add some background ( think I've covered this before but probably in a PM. If so, apologize for the repetition ).

The US Army Request for Proposal for UTTAS had a requirement that the vehicle be able to fly at the speed for best endurance in level flight and at a sideslip angle that was 20 0r 30 degrees ( and I cannot remember which ). Tough requirement, and if you recall the pictures of the huge ( and very cambered ) original vertical tail, that was the reason. After getting the flight envelope opened up, we attacked verifying the tail allowed us to meet the requirement. ( Aside: SA flight test had done a similar program on the original S-58 design. That tail rotor had flapping hinges, which allowed the determination of zero tail rotor thrust to be done fairly easily ). A very long story short, with a good number of frustrating flights, meetings, different technical/instrumentation approaches etc left us unable to determine when we were at precisely zero thrust with the rigid, crossbeam tail rotor. That, in addition to the fact that the huge tail incurred a list of penalties that was significant, led us to make the decision to take a proposal non-compliance on that requirement*. As the company strategy was to take zero exceptions, that was a serious internal issue. Result was that we cut the tail down significantly to what it is today. For those who espouse the position that a tactical helicopter can never have too much tail rotor thrust ( I am in that number ), it was the correct compromise.
*I can't say this with surety, but from the size of it, the Boeing UTTAS did not appear to be configured to meet that requirement either.

Now to Henra's and RG's question. I believe that the data that we did generate during the unsuccessful testing, in addition to a few incidents in the field over the years, the answer is that I am not aware of anyone achieving stable level flight ( yes, with a significant sideslip ) following a TR thrust loss, and thus am of the opinion that the existing emergency procedure ( not aware it ever changed ) is correct. RG, I will bring your note to the attention of the now retired test pilot who took over the UH-60 program and who has an excellent memory. Perhaps we can close that loop.

Good posts.
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