Bell 412 start and performance questions

[Aser]

helibuoy73, related thread about your last question:
http://www.pprune.org/rotorheads/189...pm-cruise.html

regards
Aser

[helibuoy73]

Aser,

Thanks. Very interesting.

HB

[TunaSandwich]

Does anyone know how much voltage is needed to activate the idle stop release?

Would it be possible to reach 12%N1 and there not be enough juice to activate the release?

Happy New Year

[Shawn Coyle]

Tunasandwich:
It has happened during start, and is the reason for the various start procedures.
You certainly wouldn't want to get caught with the throttle above the idle stop, at below self-sustaining speed, and no voltage.

[Droopy]

A certain West African location, 1986, 212....pilot does start checks which involve full and free on the twist grips, idle release back to shutoff etc. Except he forgot to do the idle release bit, operated the starter and cracked open the fuel from ground idle upwards.

I was on leave at the time but I was told it was quite spectacular

[212man]

I once had a total electrics failure after the second engine start - some kind of short circuit - and found myself unable to shutdown from the cockpit! After some shouting across the cockpit to the co-pilot, I got out and opened the idle stop solenoids manually, to close the throttles. It's a strange sensation when it happens.

[Torquelimited]

Basic common sense logic must prevail and simply one should always monitor VDC voltage when engaging the starter and if the value dips below 15VDC and does not immediately begin to recover then just do not induce fuel.

[before landing check list]

When I flew the UH1 we routinely set the throttle just below the idle stop, the 212 also.

[gittijan]

voltage needed

The real problem is with less than 14V the Battery relays open, and you now have no voltage at all. Same thing with APU only if it decides to quit delivering voltage and you do not have the Battery switches on.

[wazz'n'zoom]

The DHFS Griffins (Bell 412 EP) have adopted the new 'throttle closed start procedure' and so far in one month, no incidents of messed up starts. The 'ginger beers' have placed an orange mark on the throttle barrel that is just below(approx 5mils) the idle stop and once at 12% N1 the throttle is moved to that mark. This, for the students, is very akin to the AS 350 that they flew prior to this except that they used a white dot on the collective. It makes an impressive whoosh as the flame is lit and a at low light/night, a blue flame flicks out the exhaust.
However, the new Hyd and Electrics check doesn't exercise the hyd switchover valve correctly and the check of the DC emergency load switch is sporadically dumping U/VHF radio pre-sets.
Happy days.

[gowaz]

wazz and zoom; you in when its dark?

[ashfaq.ghori]

Target Torque

Hi,

I just want to know what is Target Torque; and how to apply in real world.

As per RFM 412
TARGET TORQUE: Available 2½ minute OEl torque of minimum specification engine, assured by satisfactory completion of power assurance check.

As per Charts at sea level 23 degree C target torque is 73% for PT6T-3D/DE/DF

Now just a case that during takeoff Mast Torque used is between 75-81 or ever more as Twin Engine Operation. To be most unlucky OEI occur, so other engine take over. So Eng Torque will be same as Mast Torque (say at that time mast torque is 80), So Eng Torque = 80.

Now Torque is past the 73% that mean Target Torque limit (OEI) are crossed.

In real world 412 will never come to hover with max allowed weight at 73%

So I think I am missing something. Pls correct and help me in building better understanding.

Regards
Ashfaq

[longtime lurker]

Target torque is the minimum power that should be available from an engine (at the 2.5 minute OEI rating) that has passed a power assurance check.

It is a factor of density altitude.

The relevance of it depends on how you are operating.

For example, if you are correctly loaded (and rigged) as per the Category A supplement the target torque should be sufficient to enable you to:

• Land back on the take-off area if the engine fails before TDP
• Continue the take-off if the engine fails after TDP
• Land at the intended landing area if the engine fails after LDP
• Fly away if the engine fails before LDP

(if flown in accordance with the relevant profiles).

Similarly, Class D external load operations make use of the target torque figure in establishing whether you can maintain an OEI hover.

[Shawn Coyle]

lurker:
To be perfectly correct, the target torque is a factor of pressure altitude and temperature - a 5,000' Density altitude can be 9,000 PA and -40C or about 2,000' PA and +40C. The Target Torque would be vastly different in those two conditions.

[longtime lurker]

You are quite correct, thank you for pointing that. My apologies to the initial poster for being lazy and therefore misleading/incorrect in my reply.

[helibuoy73]

Ashfaq,

Practical application of tgt torque IMHO. If you have an OEI at high torque settings, one of the first actions would be to lower collective to restore / maintain rpm.
Lower, but how much, to what setting?
Too less, rpm would drop. Too much, you are not making optimum use of the power available from the good engine.
Target torque gives you a good guideline of min torque to which you can safely lower collective (Min assured torque) and then maybe come up a little, N1, Rrpm and ITT permitting, if the engine is giving a better performance (than the minimum assured by passing the PA).

HB

[ashfaq.ghori]

Thanks longtime lurker, Shawn Coyle and helibuoy73....for correcting me as I was having impression that Target Torque is my ceiling(upper Limit) for the OEI 2.5 min rating.

Now my understanding is lower limit for 2.5 OEI has changed but max remain 81% . Anytime my torque is in

59 - 73% = 30 min OEI setting (taking 30 degree C at sea level)
73 - 81% = 2.5 min OEI

as against
59 - 77% = 30 min OEI
77 - 81% = 2,5 min OEI

Correct me if wrong.

Also
As per definition of Target Torque its ........
TARGET TORQUE: Available 2½ minute OEl torque of minimum specification engine, assured by satisfactory completion of power assurance check.

So what exactly is ...satisfactory completion of power assurance check
because some engine may have +ve, 0 or -ve value, so is their any range for pass and fail.

As per my case my result for P.A. give me +40 and +25 (+-5 up and down).

Regards
Ashfaq

[helibuoy73]

3odeg C, SL, assured max tq you can get from the eng - 73% Not 81%

The 30 min and 2.5 min are more like txn limits and not eng limits. The max tq eng is assured (guaranteed) to produce is tgt tq (SL 30deg C, 73% for DF eng).

[Matthew Parsons]

To be most unlucky OEI occur, so other engine take over. So Eng Torque will be same as Mast Torque (say at that time mast torque is 80), So Eng Torque = 80.

Keep in mind that mast torque is not the sum of engine torques. Engine torque includes losses due to driving tail rotor, electrical system, generators, etc. Mast torque is the torque actually applied through the mast.

The conversion factor between mast and engine torque is listed in the flight manual, but is slightly dependant on a number of factors.

[heole]

Lots of interesting arguments and Shawn is right as usual about the Pressure..
Why the `Target Torque``?
First, It is an Engine Torque value, not a mast torque value.
Second: During Category A manoeuvres, following engine failure, different limits can be reached: the OEI can be limited by the Torque, the ITT or the NG.
In order to decrease the pilot workload following the engine failure at the decision point, test pilots have elected to use a single parameter to target . (So, you can focus your attention on only one gage, instead of monitoring 3)
At the targeted value, the engine parameters will not exceed any of the OEI limits and performances will be met. This target torque is based on a minimum spec engine performance
Whenever possible, (Ie: at Vtoss), If there is still some power available, the pilot can adjust the critical parameter (Torque, ITT or Ng) to the 2 ½ OEI limit.