I posted this earlier...sorry if this wasn't understood. For clarity I posted:

JT2, Helilog -- No, I meant torque. G-SPAO had 2 Turbomeca Arrius 2B2 turboshaft engines each with a shaft out to the rotor. If one engine underproduces or fails then instead of providing a useful power, it becomes a drag on the working engine. A torsional strain gauge would show a reversal of torque on the dead, idling shaft. Instant output with very high reliability, proven third generation technology. I cannot see any reference to such an alarm in the flight manual either as an instrument or as part of a procedure -- indeed, the procedure suggests that there is no such alarm. Instead, it depends on the pilot sensing small corrections. Seems unnecessary and potentially dangerous when the workload is high.

Mushing?
 

Imposing sharp changes to the relative wind can sharply change the airflow over the disk, perhaps leading to a reduction in lift or a loss of control authority as different parts of the disk stall, and transient aerodynamic forces can overwhelm the power available. The interaction between changing airflow, course and power can be complex, especially since it's transient, and a steadier flow will be established. The different relative transient effects on the advancing and receding blades are also possibly relevant. It's an example of the richness of behavior that can be found with rotary wings: perhaps suitable fixed-wing analogies can only be found in the case of dramatic stalls during aerobatics, or with aileron reversal.

In the absence of concrete information, I don't think there's any indication these effects are relevant here.

Lemain, still not with you. If an engine lags or fails, the freewheeling unit operates, you don't have the good engine having to rotate the failed one. A failed engine disconnects from the gearbox (unless the freewheeling unit fails). Why would you need a drag torque warning? If an engine fails AND the freewheel, you are having a really bad day.
To clarify, a failed engine DOES NOT drag on anything, it disconnects that drive shaft from the gearbox

JT2 -- There will be some drag since the bearing isn't friction-free but don't let's dwell on that...if you looked at a torsional gauge, on reduction of engine 'power' the shaft torque will fall off and if/when the power out =0 the torque will be zero. An identical torsional gauge on the other shaft would allow the instrumentation to measure torque of both shafts, and the difference between them, providing a rapid indication of the failing engine.

I'm not suggesting that this was anything to do with the Glasgow tragedy - the report isn't available yet - but while we are discussing safety in general, it seems to me that something cheap, simple, proven and retro-fitable like two torsion torque gauges and a couple of channels in the instrumentation (simple, or at least as simple as anything can be simple in certified avionics) might reduce a load off the pilot at a time when he/she most needs it.

Free-wheeling units
 

require torque delivery to engage the driven side. No torque (failed power source), no engagement, no engine drag. One can reverse rotor rotation (often a pre-flight item) and drive the engine, but you're delivering torque.

Am I just thick or something? This is something we don't need and if we had it, wouldn't use. If an engine fails, an engineer could probably tell me there would be 0.000001% of nothing residual negative torque. The fact is, to all intents and purposes, the failed/slightly lower engine does not cause any problems.
I can tell which engine has failed by looking at the instruments, not rushing anything.

Why would a pilot possibly need yet another instrument reading torque for engine failure when the gauges already quite clearly show if its producing torque or not?

It just isnt necessary. More likely to add to confusion. An engine runs and produces torque or it doesnt, surely?

I agree, things can be hard enough to diagnose on a twin without adding another source of information to scan when time is critical.

here's a starter......lifting to the hover at night at MAUM in a confined and dark helipad.....at around 4 feet torque split...bad engine to zero tq, good engine giving all it's got (and more!)...what's your immediate action?

If the only eng is delivering all and "more" power the rrpm will drop and you will settle back to the ground before you have a rushing chance. When it comes to mind, the collective will be helping to cushion the landing.

thanks for responding. It's not a trick question but I did say the 'good engine' was giving all it had, rrpm was normal. The master caution was on and i was sharing my capacity between diagnosing the problem, trying to land without hitting the obstructions and warning the crew/passengers. Imagine my surprise when as I lowered the lever, the Nr rose rapidly.

As a 135 pilot you're probably now aware of the problem.

Just to complete the tale, it was a full FADEC FAIL on No1 engine.

My initial reaction was for engine failure, No2 engine was inside its 30 second limit so I tried to land, lowering the lever past the point of the frozen No1 fadec just swapped the driving engine so I was into a game of trying to land back on the pad to save the No2, but not overspeeding the rotor, at the same time trying to work my left hand up the collective to the No1 throttle to roll off the power as I touched down. Total flight time 22 seconds including 3 takeoffs and landings! To cap it all as I finally got it all secured the observer asked me if I needed the flight reference cards.

Did you have any caution light on CAD in the moment of failure (I mean on FADEC FAIL or sth like that)?

JR

Art of Flight:
Out of interest - what caused the FADEC to freeze? Was there any download following the incident?

AoF, you say the master caution was on, what did the CAD tell you?

Art, what was the Nr doing? After experience from instructing in a simulator I encouraged my students to use the term "engine malfunction" rather than engine failure. As we know, turbine engines can runaway up as well as down. The Nr is often a good clue, better than the engine gauges. A runaway up can be more dangerous than a rundown.

Captain to Crew, Engine Malfunction. Fly Aircraft, Check Nr/captions, Any Fire?, No? Relax, Nr Hi/Lo?, Diagnose, Pause, start again, confirm, Drills with FRCs.

AoF;Art, are you in the habit of cancelling the caution automatically and then diagnosing a problem without referring to the CAD?

Did it say ENG FAIL or FADEC FAIL ?

Apart from that 30 sec limit indication, did the VEMD indicate anything else, such as ENG FAIL ?

Were there any further indications of that diagnosed engine failure, such as the CAD also indicating ENG OIL P and GEN DISCON ?

I'm glad it stuck with some.... :cool:

Flying a Puma helicopter without a torquemeter fitted encouraged you to scan for information of engine problems. Two engine run ups and a freeze certainly showed how useful Nr was.
And yes, it did stick!

Nr, Gas Producer, N2, Torquemeter, Oil Temp, Oil Pressure, in that priority.