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.

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.

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.

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.

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.

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.

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.

Is 'weather-vaping' anything like weather-vaning or is it a new term for those helos that are using e-cigarettes?;)

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.

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.

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'

"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!

Happy New Year to you too SAS:ok:

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;):)

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 :E)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 :ok:
That is the good thing that can come from 'Battle proven'.

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

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.

Following up a post by Industry Insider, can anyone explain the Sikorsky "HUMS Tail Gearbox Bearing Energy Tool"? Is it part of a routine ground station analysis? Does it gather sensor data independently of accelerometers?

Marv, (sorry)

It is a condition indicator looking at a spectrum of vibration at discrete frequencies or over a specific broad frequency range. As bearings fail or are loaded abnormally the discrete or broadband magnitude/energy increases. Unless the HUMS accelerometer is actually at the bearing these signs are not present and the fault is not detectable.

The Sultan

Don't write-off FSTDs just yet.
They can prove very useful if given the right data.
The problem of course is finding someone with a wheelbarrow big enough to carry the Cahoonas of the pilot carrying out the test program.
The recent developments in modelling wind turbulence is a good example in improving FSTD fidelity.

Thanks Sultan, do you know if there are conventional HUMS alerts (amber and red) associated with the tail rotor pitch change shaft bearing condition indicator? i.e. a way to categorize a bearing as 'normal' or 'abnormal'?
Marv

So it is two questions: are all operators following the OEM recommendation to use the HUMS tailrotor gearbox bearing tool, and would live or more frequent monitoring have caught this before the excitement on the deck.

How was the aircraft recovered to shore?