Bell 412 start and performance questions
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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.
For Perf Cl 1, the limiting factor should be segment 1 ie; pickup - hover - OGE - TDP (Rotation). Therefore the RTOW should be linked to hover capabilty (almost) with OEI, and this shlould be linked to the Target Torque?
HB73,
the first segment is between achieving Vtoss and 200 ft, when OEI. It is certainly not the limiting segment for the 212. For the Clear area Cat A profile, the TDP is 56 kts at 35 ft and this is then the subsequent Vtoss in the event of an engine failure. The predicated rate of climb is 100 ft/min using 2.5 minute power. However, 56 kts is also Vy - the speed at which the second segment is climbed at. This segment requires a 50% increase in rate of climb but at a reduced power setting - MCP OEI. There is no drag reduction from raising undercarriage either, unlike wheeled types.
Obviously, then, the second segment is the limiting factor for Class 1 Performance (using the clear area procedure.)
the first segment is between achieving Vtoss and 200 ft, when OEI. It is certainly not the limiting segment for the 212. For the Clear area Cat A profile, the TDP is 56 kts at 35 ft and this is then the subsequent Vtoss in the event of an engine failure. The predicated rate of climb is 100 ft/min using 2.5 minute power. However, 56 kts is also Vy - the speed at which the second segment is climbed at. This segment requires a 50% increase in rate of climb but at a reduced power setting - MCP OEI. There is no drag reduction from raising undercarriage either, unlike wheeled types.
Obviously, then, the second segment is the limiting factor for Class 1 Performance (using the clear area procedure.)
Fly the damm thing, it's just a helicopter.
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Cat A
The RFM does not say that for Perf Class I, the limiting factor is Segment 1. I was just saying what it defines 'Segment 1' as.
Power / Torque required is max in Segment 1, that is why I think that should be the limiting factor for RTOW and not segment 2 (Perf Cl 1). And this in turn should be linked to the target torque!
Power / Torque required is max in Segment 1, that is why I think that should be the limiting factor for RTOW and not segment 2 (Perf Cl 1). And this in turn should be linked to the target torque!
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Originally Posted by Offcourse
Fly the damn thing, it's just a helicopter
There is a good deal of difference between 11,000lbs and 11,900lbs.
I am astounded at the lack of knowledge being illustrated by some on this thread (and have stayed off for that reason); you might improve your understanding of offshore profiles by reading the following thread (it also explains why PC1 is not always possible offshore):
http://www.pprune.org/rotorheads/405...-offshore.html
It would appear that only Bell use the three segment classification, most other manufacturers define: the first segment (100ft/min climb at Vtoss up to 200ft); the acceleration segment (level acceleration from Vtoss to Vy); and second segment (150ft/min climb from 200ft to 1000ft at Vy) - all at the appropriate power settings.
For offshore operations the first segment (as used by other than Bell) is never limiting as the departure sector has to be free of obstacles (operations with exposure might not use the CAT A procedure). The second segment climb is a constant for all procedures (and for PC1 and PC2).
Apart from the second segment climb, the manufacturer may configure any of the other elements to suit the operator's constraints - that includes: the defined manoeuvre to TDP (which can be horizontal, vertical or oblique and can be operated with a target Tq, a delta Tq or a target ROC); the rejected take-off distance; the take-off distance; and the first segment climb (the Vtoss can be defined by the manufacturer). Any of the elements of the profile may be limiting as they have to be calculated with respect to the obstacle environment of the operating site (which has to be known/surveyed).
A CAT A procedure only becomes 'an operation in PC1' when the environmental aspects of the operating site have been taken into account and the mass calculated/adjusted. It is the Operational Rule that sets obstacle clearance criteria, the CAT A data is used only to satisfy those rules!
Jim
http://www.pprune.org/rotorheads/405...-offshore.html
It would appear that only Bell use the three segment classification, most other manufacturers define: the first segment (100ft/min climb at Vtoss up to 200ft); the acceleration segment (level acceleration from Vtoss to Vy); and second segment (150ft/min climb from 200ft to 1000ft at Vy) - all at the appropriate power settings.
For offshore operations the first segment (as used by other than Bell) is never limiting as the departure sector has to be free of obstacles (operations with exposure might not use the CAT A procedure). The second segment climb is a constant for all procedures (and for PC1 and PC2).
Apart from the second segment climb, the manufacturer may configure any of the other elements to suit the operator's constraints - that includes: the defined manoeuvre to TDP (which can be horizontal, vertical or oblique and can be operated with a target Tq, a delta Tq or a target ROC); the rejected take-off distance; the take-off distance; and the first segment climb (the Vtoss can be defined by the manufacturer). Any of the elements of the profile may be limiting as they have to be calculated with respect to the obstacle environment of the operating site (which has to be known/surveyed).
A CAT A procedure only becomes 'an operation in PC1' when the environmental aspects of the operating site have been taken into account and the mass calculated/adjusted. It is the Operational Rule that sets obstacle clearance criteria, the CAT A data is used only to satisfy those rules!
Jim
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Jim,
Thanks for the link pointer. A very enlightening thread indeed!
If you could just indulge me a little longer- Shouldn't an increase in Tgt Tq result in an increase in RTOW/RLW for PC1?
HB
Thanks for the link pointer. A very enlightening thread indeed!
If you could just indulge me a little longer- Shouldn't an increase in Tgt Tq result in an increase in RTOW/RLW for PC1?
HB
If you are talking about an offshore procedure, target/delta Tq is associated with the deck-edge clearance (as discussed in the thread shown) - this target/deltaTq will provide the vertical acceleration (ROC) that results in the energy for the rotation/deck-edge clearance manoeuvre.
In the limited winds and high temperatures associated with India, deck-edge clearance is unlikely to be the limiting condition, it is more likely to be the drop-down (which is associated with single-engine power).
As the wind increases (for a given engine setting) drop down decreases until the limiting condition becomes the second segment climb. None of this is entirely predictable because the helicopter/engine combinations are configured to favour one or another of the power setting.
The engine manufacturer can also 'make available' an additional power mode - this has already been discussed on this thread because the PT6 can come with a 30 minute power setting (or it can be limited just to the max continuous). Not all manufacturers provide the '30 second'/'2 minute' power modes - staying instead with a single 2.5 minute power setting.
So, in answer to your question; not necessarily!
Jim
In the limited winds and high temperatures associated with India, deck-edge clearance is unlikely to be the limiting condition, it is more likely to be the drop-down (which is associated with single-engine power).
As the wind increases (for a given engine setting) drop down decreases until the limiting condition becomes the second segment climb. None of this is entirely predictable because the helicopter/engine combinations are configured to favour one or another of the power setting.
The engine manufacturer can also 'make available' an additional power mode - this has already been discussed on this thread because the PT6 can come with a 30 minute power setting (or it can be limited just to the max continuous). Not all manufacturers provide the '30 second'/'2 minute' power modes - staying instead with a single 2.5 minute power setting.
So, in answer to your question; not necessarily!
Jim
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Thanks Jim,
Your explanation confirms my understanding.
As I understand, PC1 offshore, with ltd winds and high temps, average drop down from low floaters to 90-100 ft, the RTOW/RLW limiting factor is likely to be single eng capability. Tgt Tq, again linked to single engine capability. So both are directly/indirectly linked.
The increased tgt tq with same AUW, if nothing else, provides us with additional safety (albeit carrying load less than max perhaps possible PC1)
HB
Your explanation confirms my understanding.
As I understand, PC1 offshore, with ltd winds and high temps, average drop down from low floaters to 90-100 ft, the RTOW/RLW limiting factor is likely to be single eng capability. Tgt Tq, again linked to single engine capability. So both are directly/indirectly linked.
The increased tgt tq with same AUW, if nothing else, provides us with additional safety (albeit carrying load less than max perhaps possible PC1)
HB
Not quite - the RTOM/RLM are part of performance planning and have to be in accordance with: the procedure; deck-edge clearance; drop-down; and climb performance. The mass calculation could be from one graph or several.
The AEO target/delta Tq is associated with the necessity to produce an ideal set of conditions in the vertical climb - i.e. to ensure deck-edge clearance from rotation.
If an engine fails at or after TDP, the good engine will accelerate to topping (or, if there is a FADEC, the single engine limit) regardless of the AEO Tq set (if the target Tq is high, there will be rotor droop - which will have to be controlled); from that point the drop-down, continued take-off and climb segments will be with one-engine-inoperative.
The setting of that engine will have to be in accordance with the defined limits. With a modern FADEC controlled engine and a failure at the worst time, the 30 second limit will (likely) take the aircraft to the beginning of the first climb segment (if drop-down has been scheduled - into the water if not); the first climb segment (200ft at 100ft/min) will use up the two minute limit; leaving the second climb segment to be flown at the next level of limits.
With powerful aircraft like the AW139 or the Bell 429 it is likely that they could (in a temperate climate) reach 1000ft before the 2 minute power setting is exhausted.
All of these descriptions are with the failure at the worst time (which is one second before TDP when the Pilot Intervention Time (PIT) is set to that interval). Descriptions are general; your aircraft/engine type specific profile and procedures may differ in some way.
To conclude I would emphasize once again that PC1 is not always possible offshore (because of environmental conditions) and should not be part of any regulatory regime.
Jim
The AEO target/delta Tq is associated with the necessity to produce an ideal set of conditions in the vertical climb - i.e. to ensure deck-edge clearance from rotation.
If an engine fails at or after TDP, the good engine will accelerate to topping (or, if there is a FADEC, the single engine limit) regardless of the AEO Tq set (if the target Tq is high, there will be rotor droop - which will have to be controlled); from that point the drop-down, continued take-off and climb segments will be with one-engine-inoperative.
The setting of that engine will have to be in accordance with the defined limits. With a modern FADEC controlled engine and a failure at the worst time, the 30 second limit will (likely) take the aircraft to the beginning of the first climb segment (if drop-down has been scheduled - into the water if not); the first climb segment (200ft at 100ft/min) will use up the two minute limit; leaving the second climb segment to be flown at the next level of limits.
With powerful aircraft like the AW139 or the Bell 429 it is likely that they could (in a temperate climate) reach 1000ft before the 2 minute power setting is exhausted.
All of these descriptions are with the failure at the worst time (which is one second before TDP when the Pilot Intervention Time (PIT) is set to that interval). Descriptions are general; your aircraft/engine type specific profile and procedures may differ in some way.
To conclude I would emphasize once again that PC1 is not always possible offshore (because of environmental conditions) and should not be part of any regulatory regime.
Jim
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Jim,
I think there is a difference in the Tgt Tq that we're discussing.
The tgt tq I'm talking about is the OEI tgt tq. The tq that the healthy engine is guaranteed to provide, if the eng satisfies the Power assurance check.
It is the tq that the pilot is advised to set initially in case of an OEI.
It should therefore have nothing to do with the deck clearance or AEO ROC.
However, when the tgt tq availability graph was revised upward last year, I was expecting the RTOW also to increase correspondingly.
HB
I think there is a difference in the Tgt Tq that we're discussing.
The tgt tq I'm talking about is the OEI tgt tq. The tq that the healthy engine is guaranteed to provide, if the eng satisfies the Power assurance check.
It is the tq that the pilot is advised to set initially in case of an OEI.
It should therefore have nothing to do with the deck clearance or AEO ROC.
However, when the tgt tq availability graph was revised upward last year, I was expecting the RTOW also to increase correspondingly.
HB
helibuoy73,
I see I have been guilty of not reading the thread thoroughly. I missed Buitenzorg's comment that clarified exactly what you have just said:
If you are using a CAT A helideck procedure in offshore operations, the RTOM is probably derived from two parts; the WAT part which covers the take-off profile (deck-edge clearance) and includes the first and second segment climb performance (no need to correct for obstacle clearance as the take-off segment has to be clear of obstacles) and that part which deals with the drop-down. It is likely that the drop-down portion will include wind accountability (which might have a cut-off value to prevent you exceeding the mass for the second segment climb, by using wind accountability to raise the mass).
As was previously explained, the deck-edge clearance part of the profile depends almost entirely of the energy provided by the AEO acceleration (and the higher Nr used in the take-off profile). Because the AEO Tq will be higher than the permitted OEI Tq, any failure will cause the remaining engine to go to topping - resulting in a rotor droop. Containing (restoring) the Nr will keep the engine at topping until you have reached a safe flying condition (usually just before the bottom of the descent - sometimes called Vt or target speed) at which time the engine is set to a lower limit (if 30 second power has been available) and a climb at Vtoss achieved.
Apart from adjusting the power to remove any condition of exceedence (caused by the engine moving away from its correct topping setting), the first time you have to adjust the setting will be to move from 30 second to 2 minute power (or, if there is no 30 second setting, from 2.5 minute to the next setting).
However, this still does not answer your question and that is because I can see no relevance of a Tgt Tq (as described by Buitenzorg) to an offshore profile. Perhaps your best bet then is to approach your Bell rep (there will be one in India) and pose the question to him/her.
You give the impression (from your comments) that in spite of the fact that you claim to be operating to PC1, you are not adjusting the masses for drop-down. Is that a correct assumption?
Jim
I see I have been guilty of not reading the thread thoroughly. I missed Buitenzorg's comment that clarified exactly what you have just said:
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.
As was previously explained, the deck-edge clearance part of the profile depends almost entirely of the energy provided by the AEO acceleration (and the higher Nr used in the take-off profile). Because the AEO Tq will be higher than the permitted OEI Tq, any failure will cause the remaining engine to go to topping - resulting in a rotor droop. Containing (restoring) the Nr will keep the engine at topping until you have reached a safe flying condition (usually just before the bottom of the descent - sometimes called Vt or target speed) at which time the engine is set to a lower limit (if 30 second power has been available) and a climb at Vtoss achieved.
Apart from adjusting the power to remove any condition of exceedence (caused by the engine moving away from its correct topping setting), the first time you have to adjust the setting will be to move from 30 second to 2 minute power (or, if there is no 30 second setting, from 2.5 minute to the next setting).
However, this still does not answer your question and that is because I can see no relevance of a Tgt Tq (as described by Buitenzorg) to an offshore profile. Perhaps your best bet then is to approach your Bell rep (there will be one in India) and pose the question to him/her.
You give the impression (from your comments) that in spite of the fact that you claim to be operating to PC1, you are not adjusting the masses for drop-down. Is that a correct assumption?
Jim
Last edited by JimL; 27th Sep 2010 at 07:48.
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Jim,
Thanks for the detailed reply.
We are adjusting RTOW/RLW for drop down ht, as advocated by the RFM CatA supplement.
Drop down ht 90Ft or more, std WAT graph for Cat A Part A (elevated helipads) applies :- which gives say 30degC, SL, Nil winds - RTOW 11,000lbs. (Increases with head wind component).
If drop down less than 90ft, the reduction in RTOW is calc from dedicated graph for different drop down hts (less than 90Ft) which results in a even lesser RTOW.
A second question (I have a faint idea about the ans but not sure if it is correct)
Why do we beep up the Nr to 103% before takeoff / landing in CatA profiles?
As I understand, we are on the wrong side of the L/D ratio, so inc in Nr actually increases the Drag (therefore torque / power reqmt) more than the Lift. So what is the benefit? Is it just more reserve of Nr in case of an OEI?
HB
Thanks for the detailed reply.
You give the impression (from your comments) that in spite of the fact that you claim to be operating to PC1, you are not adjusting the masses for drop-down. Is that a correct assumption?
Drop down ht 90Ft or more, std WAT graph for Cat A Part A (elevated helipads) applies :- which gives say 30degC, SL, Nil winds - RTOW 11,000lbs. (Increases with head wind component).
If drop down less than 90ft, the reduction in RTOW is calc from dedicated graph for different drop down hts (less than 90Ft) which results in a even lesser RTOW.
A second question (I have a faint idea about the ans but not sure if it is correct)
Why do we beep up the Nr to 103% before takeoff / landing in CatA profiles?
As I understand, we are on the wrong side of the L/D ratio, so inc in Nr actually increases the Drag (therefore torque / power reqmt) more than the Lift. So what is the benefit? Is it just more reserve of Nr in case of an OEI?
HB
Chief Bottle Washer
Why do we beep up the Nr to 103% before takeoff / landing in CatA profiles?
As I understand, we are on the wrong side of the L/D ratio, so inc in Nr actually increases the Drag (therefore torque / power reqmt) more than the Lift. So what is the benefit? Is it just more reserve of Nr in case of an OEI?
As I understand, we are on the wrong side of the L/D ratio, so inc in Nr actually increases the Drag (therefore torque / power reqmt) more than the Lift. So what is the benefit? Is it just more reserve of Nr in case of an OEI?
When you are TQ limited it also improves the TQ margin - for a given hover power the TQ will decrease as Nr rises. I'm not sure that the L/D ratio does rise - the induced drag will decrease with the reduced pitch setting.
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Mmmmmm ....
And with the 412EP the increased Nr also gives you more T/R authority ... as well as improving the rotor disc area ... the 412 with 'slow' (read old) governors will cause a fair bit of coning which in turn can cause all sorts of RPM and therefore Tq oscillations (which the yaw SAS then tries to cure) ... the result is usually an 'Over Torque' !!
And with the 412EP the increased Nr also gives you more T/R authority ... as well as improving the rotor disc area ... the 412 with 'slow' (read old) governors will cause a fair bit of coning which in turn can cause all sorts of RPM and therefore Tq oscillations (which the yaw SAS then tries to cure) ... the result is usually an 'Over Torque' !!
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When you are TQ limited it also improves the TQ margin - for a given hover power the TQ will decrease as Nr rises. I'm not sure that the L/D ratio does rise - the induced drag will decrease with the reduced pitch setting.
Secondly, with all these benefits of 103% Nr :- Reserve Nr for droop, inc disc surface, inc TR effectiveness; are there any drawbacks too? Otherwise why have this for Cat A only? This additional safety, why not have it for all operations?
HB
