Bell 412 start and performance questions
 

For the 412 drivers out there; a couple of questions please.

Why is it on the start procedure, at 12% N1 the throttle is opened past the idle detent all the way open then back to the idle detent, the idle solenoid activated then the throttle is set just below idle? Why not just go to idle, activate the idle detent then set just below idle? Does it have anything to do with the inner workings of the fuel control unit?

My second question is what is the best angle climb speed and where is it written? I have been quoted 45kts however no reference. This speed seemed a little slow to me, given best rate of climb is 70kts.

Thanks very much for your help.

Cheers,

WBS,

I believe the throttle use on start is to first ensure you're at the idle stop. Once there you don't want to be stuck there if you lose electrical power, so you roll the throttle back to just behind the stop and you can shut down even with a dead battery.

Best angle of climb is not well defined for a helicopter. For a fixed wing, it considers the vertical component of your thrust vector. A helicopter can climb at 0 airspeed, making an angle of climb of 90 degrees. For the Bell 412, if you're on instruments, keep the speed at 60KIAS or higher (its a limitation) and that will be pretty close to your best angle of climb.

Matthew.

Q. "Why is it on the start procedure, at 12% N1 the throttle is opened past the idle detent all the way open then back to the idle detent,..."

A. Don't know, never heard of that procedure, never seen it done like that before...all the way open??? why????

I've (inadvertently) had the throttle ever so fractionally slightly past the idle position before when it's lit off and it went very hot very quickly...reckon if I'd followed the procedure suggested here (throttle opened all the way then back to idle detent) then my tail boom would probably have been a molten mass of metal pooled on the ground. Now I start it with the throttle slowly being opened at 12% and it lights off nicely before you even get to the idle stop position. Then steadily wind it on a bit more as you go past the 2nd ITT peak. No need to back off the throttle at all.

Yep...we advance the throttle open then back to the idle detent...there was a reason but bugger me if I can remember it... Never had a start even looking like being hot and I have seen guys in classics EPs etc use the same technique. Someone must know something!

Turkey

yep, 12% then full open and then back to just behind the detent. Bell412 classic

gulliBell:
You missed the throttle check before start-up then(also all the way to full-then all the way to close), not a problem with the start procedure sugested here.

Another version I've seen called "canadian start" :E is when you are low on battery, just doing the full open-close to idle and set just below idle BEFORE engaging the START switch, works fine.

Aser,

what you call the "canadian start" is actually standard starting procedure on the Sikorsky S-58T, which uses the same turbine as 412's. If it works fine in one machine, why shouldn't it work fine on the other?

Regards

The best angle airspeed is zero, or the windspeed, whichever results in a 90 degree climb, straight up. That's the best angle you can get, unless you consider a backward climb better. :8 This of course assumes enough available power for an OGE climb.

The only reason I know of for taking the throttle to full open is to insure that you know where the throttle is being set, and that there is no binding throughout the range. You want it under the idle stop before engaging the starter so you can take it to full off in the event of an electrical failure. If the battery gets too low during the start, and the temp starts going too high, you risk not having enough battery voltage to engage the idle stop solenoid, thus not being able to stop the fuel, resulting in a hot start. Below the stop, you can take the throttle to full off with no electrical power. But I've never heard of going to full throttle at 12% N1. You do that before initiating the start.

In the flight manual under the starting procedure is is Engine 1 Throttle --open to idle at 12% GAS PROD RPM (N1) minimum.

Engine 1 ITT --Monitor to avoid a hot start. ITT limits for different models not to exceed ITT limits If ITT continues to rise, abort start by activating idle stop release and rolling throttle fully closed. Starter should remain engaged until ITT decreases.

rcapiloto,

Then you well know that on the S58T there is a mechanical stop, ground idle before you advance it through the mechanical detent when it becomes the flight idle stop. The Bell 412 EP doesn't have the same engines (though the 412 does) and all the 412s as with the 212 have an electrically activated idle stop release, so the systems are not quite the same. It's a shame Bell never adopted the Sikorsky system.

WBS,

As has been mentioned, the best angle of climb speed for any helicopter is 0 knots groundspeed, i.e., a vertical climb. However, in most cases this is not practicable as much of the time you will not have the power reserve to achieve it. In most twin engine helicopters, when they are being operated to performance class one limitations, the 2 speeds which are relevant are the best rate of climb speed which, as you say, is 70 knots for the Bell 412 and the take off safety speed, which for the Bell 412 is 45 knots. This is only relevant during the initial phase of the take off and is basically the speed at which the aircraft will maintain a rate of climb of 100 feet per minute and remain clear of obstructions by the prescribed amount in the event of a single engine failure after TDP up to 200 feet. At this point, the aircraft is accelerated to Vy for the remainder of the climb. Depending on which RFM you're using (FAA/JAA/UK) it's in the Category A or Class 1 supplement.

Big Guy has it, as per the RFM.
It's a good idea (indeed, see RFM para 2-5) to check the throttle for full and free BEFORE the start, to note the 'engine' legend position of the throttle at the idle stop and then to open it to just below the idle stop at 12% or above, and with indications of engine oil pressure. (212 is the same, but rotors will also normally start to move before the throttle.) That way if you do get a voltage drop or have to close the throttle in a hurry, it's easy. Remember too, that on both the 212 and 412, if you are holding the throttle back against the idle stop, friction may result in the plunger not retracting when you operate the idle stop (solenoid) release. (As Note in RFM.)
Incidentally, I would advocate the same procedure for the AS350 with collective throttle and for the EC120.
As for 412 angle of climb, see the Class 1/Perf A segment at 45 KIAS, as someone else has pointed out.
Now I'm exhausted....all this 'idle stop' chat. (And no, the soubriquet has nothing to do with 212/412!)
Idle Stop.

Thanks for all your responses guys.

WBS

Bell 412 OEI Performance
 

Hi. I'm a recent 412 convert. Tend to draw parallels to my previous helo- the ALH (Dhruv). I have a few queries. Grateful if anyone could help.

1. The 412 EP RFM in the Cat A supplement gives a graph that gives "Target Torque" which, say at 30 deg Sea Level, gives a target torque at 2.5 min rating of 65%. However in the limitations section, the OEI torque limit is supposed to be 81%. So what torque would I need to pull? And what is Target Torque???

2. For various ratings, there would be ITT, N1 and Torque limits. I presume the limit you hit first would be the limiting factor for that rating. So, at sea level around 30 deg C what limit would i hit first? No performance graphs let me analyse this.

ITT always (940 degrees C on later p/n guages 920 degrees on earlier)

I am with Mattew on this one. The reason why it is recommended to open the throttle all the way is that it is the only way you can be absolutely positive that you are passed the detent. Many experienced 412 pilots just open the throttle a tad on the right side of the detent and wait for the lightoff to prevent for getting stuck on the wrong side of the detent at the wrong time.

Note: I personally don't wait for the proverbial 12% to introduce gas. I do it as soon as I see positive oil pressure on the gage. It will happen always above 12% and it is a more critical start-no start decision item.

Putting the throttle just below idle detent is the way I was taught, and the way I've always done it. If the battery dies on you during the start, and you're above the idle detent, you'll melt the engine, because you can't close the throttle. I've always opened the throttle full open, back to idle, check where that is, close the throttle, and then initiate the start, and at 12% open it to just below where you saw it at idle. With experience, you can open the throttle there without even looking, doing it by feel. PT6s start very benignly, and the exact location of the throttle isn't critical, unless the battery dies. And 412 batteries have been known to die during start.

Climb angle speed
 

WBS,
Regarding climb angle speed, you remember the basic power curve? The tangent to the power required curve from the origin of the power available line gives the best climb angle speed. What this means is that:
1. The best climb angle is irrelevent when power available is more than power required. i.e. the best speed will be zero.
2. When power available is lesser, then the best speed will actually depend upon how much lower the power available is- lower the power avbl, higher the best climb angle speed

Target Torque
 

Hi! Picking up an old thread.
At Sealevel 30degC, I thought the chances would be brighter for a drop in Nr as a result of N1 topping before anything else. Otherwise Tgt Tq of 67 or 73% wouldn't make sense?

One year back, the tgt tq graph was revised shifting the entire thing right. The tgt tq for say Sea level 30deg now has become about 73%.

I have a couple of queries based on this revision:

1. Now with the increased target torque available, shouldn't the chart giving the max permitted wt to hover with Single Engine also change / increase?

2. Consequently, should'nt the WAT graphs for Cat A operations also change and permit an increase in allowable AUW?

During my initial SIM training, I was taught the start procedure of full open at 12% then back all the way to just inside the idle stop.
Being new I asked the instructor why and he said it was purely a Bell directive. Didn't go into details though and I didn't think to ask! :ok:

412 Start
 

During the mid 90's I flew with a Bell flight instructor in a BH212. His technique was to set the throttle just below the idle detent prior to engaging the starter. His explanation was it takes at least 12% N1 speed for the engine driven fuel pump to develope the required pressure to activate the fuel flow divider and primary start fuel nozzels. The company I work for has been using this start technique without a problem on both 212's and 412's for the last 17 years. I have witnesed another operator have a engine hot start using the Bell flight manual technique. After engaging the starter the throttle was rolled open above the idle stop, the battery voltage was to low to complete the start and to low to open the idle stop and abort the start.
Ouch!!

JHR

Mmmm ...

212s & 412s(with -3B engines) and 412 EPs (with -3D?) engines certainly do start differently.

In the early days the so called 'Okanaghan' start was used because of the problem with the idle stop solenoid activation.

I understood that Bell in their wisdom modified the solenoid so it would operate reliably at a lower voltage but could be jammed by friction of the mechanism if an inexperienced pilot has an issue with the start routine.

After so many years and thousands of hours in the beasties ... (particularly with the 412EP) I now just do a check prior to start to ensure that the throttle IS in Idle Cut Off then hit the starter .... at >12% N1 gently roll the throttle to modulate the start ... the lightoff is gentle very much like with the -3B and under normal conditions acceleration good .... (if the battery or starter dies ... then there is no panic I just roll off back to ICO and all is well) as the monster goes through about 35-40% with a reasonable rate of acceleration I roll thru the stop to the idle position and at >55% disengage the starter .... simple ...


212 Vy was 54 Kts and the 412 around 70 Kts depending on Gross weight etc.


;)

I keep hearing all of the stories about how another operator had a problem with the batteries resulting in a hot start. Would really like to see an incident report that actually says that...

If you do not go above the idle stop and then release the stop and resest the throttle just below the idle stop, then you do NOT KNOW where the throttle is set. You are just guessing....

Unless you have the delicay of a gorilla, the throttle cam pushing the idle stop is easy enought to feel and there should be no need to go past it.

Spinwing - the 212s I flew had a Vy of 56 kts :ok:

see these?
Quiz Cards

The ******* Way
 

Engine starts


Bell Helicopters Textron has devised an alternate Engine Starting technique which has been adopted on all ******* operations. During the start procedure at 12%N1 with Engine Oil Pressure indicating, roll the throttle to slightly below the Flight Idle position (approx. 20 degrees - NG of ENGINE uppermost). If the ITT should rise rapidly during the start, control or "modulate" the temperature with the throttle. At approximately 45% N1, the throttle will need to be advanced slightly to increase the N1 to 61%.
This technique allows a pilot to abort a start at anytime with a simple "off" movement of the throttle to the cut-off position, even if electrical power fails.
Pilots must ensure correct internal battery or external power limitations prior to start.

Trog.

P.S Helibuoy - why would you worry about the WAT graphs for the FM Category A Runway (Part C) profile? you wouldn't ever consider using those - would you?

:8

The only 'incident' I've ever heard of for the 'Throttle pre-positioned to just below idle before hitting start switch' method was when a very new-to-turbine engines pilot was partway through the start and had a loud buzzing noise in his headset. He immediately shut off the start switch without shutting off the throttle.
My friend sitting in the copilot seat watched the TOT go through the roof, and later picked up bits of melted engine off the tarmac. Needless to say, pilot was not long with the company.

CAT A Ops
 

No, not Part C. My concern is Part A (Elevated helipads) for offshore ops.

Shawn, would the outcome not have been the same using any of the aforementioned methods?.

I wish Bell would clarify this issue, it seems every company I work for has a different start method, and then every pilot has his/her preferred method. I think just to say "refer to the 212/412 RFM" is unhelpful as this does not tell you 100% which side of the idle stop you are at. Two major companies I've worked for use the full open then back to just below idle stop method and I never heard of any problems. But listening to the reasoning of the alternative methods then the argument seems valid. No wonder there are issues with Hot starts, it can be very confusing for newly rated pilots being shown three different methods.

Of the three methods discussed, the only one that really makes sense to me is the so called "Canadian start". Apart from Shawn's example, does anyone know of any reason that this could not be used as standard?

TS

CAT A Ops
 

My understanding is that for say Sea Level, 30deg C, deck at or above 90 ft ht when tgt tq was 67%, max Restd AUW was (and is) 11000 lbs.

Now that the tgt tq has increased to 73%, shouldn't there be a corresponding inc in Restd AUW?

Cat A Part A?
 

Helibuoy,

The WAT Graph is only relevant for the climb segment above 200 feet and should not affect your Deck Operating weight.

Compare the graphs for the 3D, 3DE & 3DF engines on the EP - the WAT figures vary but the 2 and a half minute OEI parameter is the same for all 3 variants and this is the parameter used for segments 1 and segment 2 of the profile. Segment 3 (200 feet to 1000 feet) relies on the Max Continuous OEI for the 3D and the 30 minute OEI for the 3DE & 3DF which is why the WAT graphs differ.

For Offshore Ops most Operators use Twin Engine Hover out of Ground Effect (HOGE) graphs to calculate Landing and take-off Mass although the profile flown is similar if not identical to Cat A Part A.

We comply with Performance Class 2 and this is perfectly acceptable to all the Major Oil Companies that I have come across.

2 Engine HOGE for Unrestricted Decks (fully compliant with CAP437/ICAO Annex 14) gives the following figures:

For a basic 412 or 412SP with C Box Torque indication only your MTOM at 30 Deg C is 11400lbs.

For the 412HP or 412EP with Mast Torque indication your MTOM is 11900 at 30 Deg C.

For restricted decks - i.e. not fully compliant due to a whole range of factors we use HOGE minus 500 lbs to give extra power in hand.

Hope this is of some use.

Trog

Cat A
 

Thanks a ton Trog,

The basic difference is that where I'm operating right now ie; India, the DGCA has mandated that all offshore ops have to be Performance Class I (in vogue for more than 4yrs now).

Therefore Cat A, Part A kicks in restricting your load to WAT for Cat A Part A, which works out to 11000lbs (SL, 30deg C) for the EP with DF engines.

I guess this should be directly linked to the tgt tq (the tq that each DF eng is guaranteed to deliver OEI)?

Logic Free Zone 2
 

Helibuoy,

What a waste of a 412 EP.

I haven't been too concerned with the CAT A (Part A) mainly cos' we don't have to be but I still as you do suspect the graphs.

I'll dig a bit deeper in the meantime.

Are you still doing your medical every morning? - What a place!

:ugh::ugh::ugh:

take care

Trog

Trog,

Yeah Medical every mng (at least on paper) ;)

I'm looking for other places, but not been able to get my foot in, so far!

helibuoy

Cat A
 

From what I have gathered so far the whole exercise of Performance Class I of DGCA is to talk Cat A but call it another name....unlike what most Oil companies worldwide follow as 'exposure time' during take off from Rigs etc ...to be able to climb away following a OEI condition..and maybe a similar exposure time during landings Offshore.
True Cat A capability for various machines like S-76 , AW-139 involves a great deal of concept definations,performance issues, helicopter configuration ,training for both Pilots from both seats(to land or take off from Offshore rigs based on obstructions etc ) which probably the DGCA would not like to address or is incapable of analysing with its present members .., nor would the helicopter Operators...so using part of the supplement for Cat A of the Bell 412 ,some details are reduced to some numbers that work for all concerned. I guess a similar number works for the Dauphin N3 or other such machines that operate Offshore.
Serious Regulators would go the extra mile to fully investigate , understand and legislate Cat A issues coz they are liable to legal recourse in many countries not only by the aggreived parties concerned ,but by Insurance companies as well... if they are found wanting .

Cat A
 

Absolutely!
My question remains, if the tgt tq has been revised (upwards), shouldn't there be a corresponding revision in the permissible RTOW?

Cat A
 

Can you explain target torque and its origin ?...as in the Bell-412 Flight Manual ..Supplement details etc .
One could take a relook and try to understand what you say or question... else just quote verbatim all you see / cut - paste the whole page to better understand what the Bell company allows you to do or wants you to limit yourself to ?? Any data outside of the Bell Manuals I hope you understand is not legal .. except those which are introduced by Operators or Regulators to make Operations safer ?

Prehar:
I'm sure there's something you'd like to know, but I'm afraid I don't understand your question!

Cat A
 

Shawn,
You are the right person to help on the issue of Bell 412 Offshore Operations !!
I tried picking up an earlier post here.. of 18 Jun where Zudhir and helibuoy were trying to understand what is a 'target torque' and related MTOW issues in the Cat A supplement of the Bell 412 ....I don't readily have one so I can't fully understand their apprehensions .
Thanks
Prehar

Cat A
 

Shawn & Prehar,

Well here goes:

I had raised a query with Bell in Feb2009 as follows:

Based on this query, I believe, the Tgt Torque graph was revised last year in Jul2009, shifting the entire graph right and also increasing the max limit to 81%.

With the revised graph the tgt tq has increased (ex 30deg C SL the fig has inc from 67% earlier to 73% now) and so on.

My quest is, with this inc in tgt tq shouldn't there be a corresponding inc in the RTOW for Cat A ops?

Helibuoy

As Troglodita has already answered you:

No.

The target torque is Bell’s poor man’s equivalent to a FLI (first limit indicator). Dependant on ambient conditions the first OEI limit the engine is expected to reach, whether engine torque, ITT or N1, is “translated” into a calculated torque value, so in case of an engine failure the pilot has only one power instrument to monitor at what will be a pretty busy time.

This target torque value represents the first OEI 2½ minute limit to be reached.

As Troglodita pointed out, the climb segment between 200 and 1000 ft AGL is the limiting segment in determining Cat A/PC1 RTOW, and this is flown/certificated at OEI MCP (-3D engines) or OEI 30 min. limits (-3DE and -3DF engines). So the target torque value has nothing to do with the power settings during the “weight limiting” segment of the Cat A profile.

Hope this answers your question adequately.