Bell 412 start and performance questions
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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,
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,
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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.
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.
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
Turkey
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"
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.
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.
Another version I've seen called "canadian start"
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.
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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
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
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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. 
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.
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.
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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.
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.
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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.
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.
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.
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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.
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.
Last edited by zudhir; 18th Jun 2008 at 06:42.
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So at sea level around 30 deg C what limit would i hit first? No performance graphs let me analyse this.
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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.
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.
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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.
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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
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
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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?
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?
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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!
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!
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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
Ouch!!
JHR