Sikorsky S-92: From Design to Operations
Mast
Gee I do not know. Maybe the excessive flair angle, the fact you had two trained test pilots doing it on a hard strip after working up to it for awhile and that is the best they can do.
If all agree that auto is safe to do into rough seas then you are left with the "fact" that the S-92 can not survive a loss of tail rotor drive. Something else for the FAA to look at.
The Sultan
Gee I do not know. Maybe the excessive flair angle, the fact you had two trained test pilots doing it on a hard strip after working up to it for awhile and that is the best they can do.
If all agree that auto is safe to do into rough seas then you are left with the "fact" that the S-92 can not survive a loss of tail rotor drive. Something else for the FAA to look at.
The Sultan
1. Does the S92 have a Cat A Helipad profile approved for take off and landing from ground level AND elevated helipads?
2. If so what is the minimum size helipad required?]
2. If so what is the minimum size helipad required?]
Geoff, the procedure is being certified as we speak. I believe it it has been tested with a 1D (20.88m) pad. Obviously National regulators my require 1.5D for Public Transport operation.
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I don't understand why it's not possible to create a MGB transmission that can "run dry" for 30 minutes. I thought of a way to do this, and rely on my fellow ppruners to critique this idea. Surely I'm not the first to think of this.
Why not use an automatic grease system to lube the bearings and gears for 30 minutes after loss of MGB oil? It would consist of several light weight tubes (inside the transmission) running to nozzles that apply an appropriate grease (heavier than the normal MGB oil) to critical gear and bearing areas. The application device could be some small electronic (aircraft battery powered?) device that runs a pump activated at predefined intervals once started (by a switch in the cockpit?), that could run at least 30 minutes or until the grease runs out. The grease could be contained in cartridges, that are easy to load and unload. I don't think the whole system needs to weigh more than about 30 lbs or so, and would be pretty simple.
The technology for this already exists. Grease is cartridges exist, small grease pumps (pressure and demand sensitive) already exist, and the control device (in some form) already exists. Each nozzle tip on the end of a tube, could be properly sized and shaped (point, fan, etc) to distribute the grease correctly, and proportionately between the various nozzles. Also, there would be torque increase with grease (compared to oil), but far less I would think than the latter stages of running dry. I also think this system would work better than a melting wax system.
Why not use an automatic grease system to lube the bearings and gears for 30 minutes after loss of MGB oil? It would consist of several light weight tubes (inside the transmission) running to nozzles that apply an appropriate grease (heavier than the normal MGB oil) to critical gear and bearing areas. The application device could be some small electronic (aircraft battery powered?) device that runs a pump activated at predefined intervals once started (by a switch in the cockpit?), that could run at least 30 minutes or until the grease runs out. The grease could be contained in cartridges, that are easy to load and unload. I don't think the whole system needs to weigh more than about 30 lbs or so, and would be pretty simple.
The technology for this already exists. Grease is cartridges exist, small grease pumps (pressure and demand sensitive) already exist, and the control device (in some form) already exists. Each nozzle tip on the end of a tube, could be properly sized and shaped (point, fan, etc) to distribute the grease correctly, and proportionately between the various nozzles. Also, there would be torque increase with grease (compared to oil), but far less I would think than the latter stages of running dry. I also think this system would work better than a melting wax system.
Flight Safety
MGB oil does of course provide lubrication, but for most of the gearbox at least, its to lubricate roller or ball bearings, rather than the plain bearings that you would find in a car crankshaft etc, and gear teeth meshing. Unlike car crankshaft bearings, such bearings and gear teeth continue to be lubricated by residual oil even after loss of all oil from the sump. I think the primary issue is cooling not lubrication. Consider how much heat is expelled via the oil cooler and how that heat, if left localised in the gear teeth and bearings, would affect the materials. The oil does a good job of being a heat transporter, something grease could not do.
And to answer your initial question, it is possible to create an MGB transmission that can "run dry" for 30 minutes, its just that so far Sikorsky decided not to do that for the S92.
Sultan - I seem to recall that there was mention of 20g at touchdown for the Cougar aircraft. The video looks like max 2 g or so, so although an engines off landing might cause damage, I don't think the video shows that it would be in the same ballpark for catastrophe as the Cougar event.
HC
MGB oil does of course provide lubrication, but for most of the gearbox at least, its to lubricate roller or ball bearings, rather than the plain bearings that you would find in a car crankshaft etc, and gear teeth meshing. Unlike car crankshaft bearings, such bearings and gear teeth continue to be lubricated by residual oil even after loss of all oil from the sump. I think the primary issue is cooling not lubrication. Consider how much heat is expelled via the oil cooler and how that heat, if left localised in the gear teeth and bearings, would affect the materials. The oil does a good job of being a heat transporter, something grease could not do.
And to answer your initial question, it is possible to create an MGB transmission that can "run dry" for 30 minutes, its just that so far Sikorsky decided not to do that for the S92.
Sultan - I seem to recall that there was mention of 20g at touchdown for the Cougar aircraft. The video looks like max 2 g or so, so although an engines off landing might cause damage, I don't think the video shows that it would be in the same ballpark for catastrophe as the Cougar event.
HC
Sultan - you clearly don't know much about EOLs, especially in large aircraft - you need a big flare to stop a 10-ton helo and it will never look pretty at the bottom unless you are very light and into a strong wind.
On the water, all you care about is making it survivable and that means reducing water entry speed as much as possible, even if it means putting the tail in first (which if you did have a functioning TR would probably trash it anyway).
On the water, all you care about is making it survivable and that means reducing water entry speed as much as possible, even if it means putting the tail in first (which if you did have a functioning TR would probably trash it anyway).
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HC, did you see the photos of the ring and pinion gear of the TR drive from the Cougar S92? Hard to say whether the grinding of the gear teeth was caused by the lack of lube to the teeth, or the failure of the bearings that have to hold a ring and pinion in near perfect alignment (or both). I would point out however that ring and pinion arrangments place a great deal of pressure on the gear teeth surfaces, and thus require lubrication to survive.
No heat is transferred after the loss of MGB oil anyway. Grease by its nature isn't normally used in flowing or recirculating applications, and therefore isn't normally used for heat transfer. Grease always lubricates in place, and is quite heat resistant. I think some basic testing would show whether the idea has any merit or not.
No heat is transferred after the loss of MGB oil anyway. Grease by its nature isn't normally used in flowing or recirculating applications, and therefore isn't normally used for heat transfer. Grease always lubricates in place, and is quite heat resistant. I think some basic testing would show whether the idea has any merit or not.
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Geoff, the procedure is being certified as we speak. I believe it it has been tested with a 1D (20.88m) pad. Obviously National regulators my require 1.5D for Public Transport operation.
So what are the requirements for 1D v. 1.5D pad?
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Helipad Ops - S92
I think JimL can provide an answer to that question ........ are you there Jim? Funnily enough we were just discussing that point but I won't steal his thunder.
G
G
As simple as adequate visual cueing. Whilst this may not be an issue with ground level helipads, it surely is for elevated.
Take for example a helicopter which has a dynamic vertical procedure with plenty of power in reserve; if the engine failure is recognised at just before TDP of say 30ft, the aircraft will continue to accelerate upwards (some to higher than 60ft).
If the elevated helipad were only 1D, sight of the landing surface would in all likelihood be lost and the reject would be problematical (not for those test pilots who do this every day but for the average pilot).
For this reason, AC 29-2C has a provision that:
This is exactly the problem for those pilots who fly from rooftop helipads or from wellhead platforms where there are no obstructions topside.
One of the issues is that test flying for helipad procedures is sometimes conducted from a square painted on the runway; this provides no problem for hitting the target on rejects as there is sufficient peripheral visual cueing.
A further issue is the designation of elevated helipad; in JARs (not sure about other regulations) this is when the operating surface is 3m above the surrounding surface (triggering the higher requirement). This has been recognised in JARs and there is a facility to apply for a derogation (to the lower limit) based on an assessment of the pad and the visual cues.
The issue is more serious with larger helicopters with less than optimum Fields of View (FOV); with smaller helicopters the pilot tends to sit close to the door - where the visual cues can be maintained for longer. The best vertical procedure I have seen is the one which is provided for the Bell 427/429 where the pad can still be seen at a height of 120ft with the disc at the back and side of the pad (a very steep vertical/oblique). This profile could obtain a 1D CAT A approval.
Jim
Take for example a helicopter which has a dynamic vertical procedure with plenty of power in reserve; if the engine failure is recognised at just before TDP of say 30ft, the aircraft will continue to accelerate upwards (some to higher than 60ft).
If the elevated helipad were only 1D, sight of the landing surface would in all likelihood be lost and the reject would be problematical (not for those test pilots who do this every day but for the average pilot).
For this reason, AC 29-2C has a provision that:
Conduct of the Test. Vertical takeoff profiles should be flown from a pad simulating operational conditions because the sight picture may be critical to successful OEI operations, particularly for elevated heliports. At all points on the vertical takeoff flight path up to the TDP, the pilot, with reasonable head movement, shall be able to keep sufficient portions of two heliport boundaries (front and one side) or equivalent markings in view to achieve a safe landing in case of engine failure...
One of the issues is that test flying for helipad procedures is sometimes conducted from a square painted on the runway; this provides no problem for hitting the target on rejects as there is sufficient peripheral visual cueing.
A further issue is the designation of elevated helipad; in JARs (not sure about other regulations) this is when the operating surface is 3m above the surrounding surface (triggering the higher requirement). This has been recognised in JARs and there is a facility to apply for a derogation (to the lower limit) based on an assessment of the pad and the visual cues.
The issue is more serious with larger helicopters with less than optimum Fields of View (FOV); with smaller helicopters the pilot tends to sit close to the door - where the visual cues can be maintained for longer. The best vertical procedure I have seen is the one which is provided for the Bell 427/429 where the pad can still be seen at a height of 120ft with the disc at the back and side of the pad (a very steep vertical/oblique). This profile could obtain a 1D CAT A approval.
Jim
Flight Safety
Its hard to say whether the tail drive failed from overheating or lack of lubrication, most probably it was a bit of both. What I was alluding to was the fact that its dealing with the overheating that is the primary issue, dealing with lubrication is secondary and this is why the aircraft I fly has a system whereby synthetic glycol is sprayed onto the hot parts. The tank holds sufficient to last 50-odd minutes, though its only certified to run for 30 minutes following complete loss of oil. As far as I am aware, the glycol does not really lubricate well, it just transfers the heat away. If you used grease, it would get very hot very quickly to the point that it might vapourise and I am not sure it would do much of a lubrication job. It would certainly make a lot of smoke!
HC
Its hard to say whether the tail drive failed from overheating or lack of lubrication, most probably it was a bit of both. What I was alluding to was the fact that its dealing with the overheating that is the primary issue, dealing with lubrication is secondary and this is why the aircraft I fly has a system whereby synthetic glycol is sprayed onto the hot parts. The tank holds sufficient to last 50-odd minutes, though its only certified to run for 30 minutes following complete loss of oil. As far as I am aware, the glycol does not really lubricate well, it just transfers the heat away. If you used grease, it would get very hot very quickly to the point that it might vapourise and I am not sure it would do much of a lubrication job. It would certainly make a lot of smoke!
HC
Crab
EOL's have been a routine part of my existence, so I do know what I am talking about.
As to S-92, the pictures of G-TIGK shows that other designs can do it with much more tail damage.
The Sultan
EOL's have been a routine part of my existence, so I do know what I am talking about.
As to S-92, the pictures of G-TIGK shows that other designs can do it with much more tail damage.
The Sultan
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Thanks Jim. Great info, but I'm still confused about the 1D v. 1.5D bit. While the guidance material talks about sight picture/visual cueing, I would think that 0.5D would make very little difference from a high TDP (say >75').
Great point about the larger Part 29 aircraft and their field of view. Do the ops rules have a say? Seems like operators would need to have some 'ground rules' for how large an aircraft they can use at a given facility...
Great point about the larger Part 29 aircraft and their field of view. Do the ops rules have a say? Seems like operators would need to have some 'ground rules' for how large an aircraft they can use at a given facility...
Hullaballoo, it is the 'ops rules' that specify the 1.5D. You will find them in ICAO Annex 6, Annex 14 and the ICAO Heliport manual. Obviously not all regulators follw these guidelines, so they may not apply to all operators.
Hullaboo,
In fact the ICAO Annexes (6 and 14) defer to the Flight Manual, specifying only in the absence of limits.
My remarks were directed towards the issue of adequate visual reference using '1D' only as a general example. Flight Manuals tend to provide their limitation in specific units of measurement - not in proportions of 'D'.
The limits in the FM are a result of a CAT A certification exercise and so are directly applicable to each procedure (hence the two limits: one for ground level helipads; and the other for elevated helipads).
In the example you use, there would have to be a practical demonstration of appropriate cues on the surface - hence, each helicopter is assessed in its own FOV environment.
In fact the AC 29-2C guidance is not comprehensive enough because it is not the cues at the TDP that are the main issue it is those at the height/position where the aircraft stops its ascent following an engine failure at, or before, the TDP.
JARs are sophisticated in their treatment of size of helipads in PC1; providing it can be shown that there is no probability of a rejected take-off (i.e. the case where a continued take-off is always possible), the CAT A helipad size limits do not apply. This is of most use for HEMS aircraft which are operating to hospitals with historically smaller helipads (smaller than those required for CAT A).
Jim
In fact the ICAO Annexes (6 and 14) defer to the Flight Manual, specifying only in the absence of limits.
My remarks were directed towards the issue of adequate visual reference using '1D' only as a general example. Flight Manuals tend to provide their limitation in specific units of measurement - not in proportions of 'D'.
The limits in the FM are a result of a CAT A certification exercise and so are directly applicable to each procedure (hence the two limits: one for ground level helipads; and the other for elevated helipads).
In the example you use, there would have to be a practical demonstration of appropriate cues on the surface - hence, each helicopter is assessed in its own FOV environment.
In fact the AC 29-2C guidance is not comprehensive enough because it is not the cues at the TDP that are the main issue it is those at the height/position where the aircraft stops its ascent following an engine failure at, or before, the TDP.
JARs are sophisticated in their treatment of size of helipads in PC1; providing it can be shown that there is no probability of a rejected take-off (i.e. the case where a continued take-off is always possible), the CAT A helipad size limits do not apply. This is of most use for HEMS aircraft which are operating to hospitals with historically smaller helipads (smaller than those required for CAT A).
Jim
Large Helo Autorotation/Certification vs Operational
Crab, I believe that you have it right, and allow me to expand just a tad on the technique used in the S-92 video.
FAR 29.79 and 83 provide the requirements and AC 29.2c, pages B-83-84 provide general guidance. One will note the absence of a required minimum landing speed, and the AC only recommends a speed under 40 kts.
Another reality surrounding the question of what is the best way for the manufacturer test pilot to proceed is that the machine in question is typically the envelope expansion/structural test aircraft, and thus has the maximum instrumentation installation. That makes it a very dear commodity, with serious consequences should it be seriously damaged.
It is clear in reading the advisory circular that the FAA intent is clear and stated in AC 29.75A.b.(2)(vii).(C): " The intent of this rule is to demonstrate controlled touchdown conditions and freedom from loss of control or apparent hazard to occupants when landing with all engines failed."
There is no instruction or direction that requires the demonstration to perform multiple power off landings to replicate what might be the best operational power off landing procedure for conditions such as: landing in forest, landing in a soft, or muddy plowed field, or the ocean. Certainly, ( and I think you were referring to these conditions ) in any large single rotor machine, these conditions would make the pilots approach to ensuring tail rotor clearance during the end of the flair a bit different, as the pilot will want to minimize the touchdown groundspeed.
As to the question of practice and build-up, its not very complicated. Since the pilot knows that at sometime in the future the landing has to be made, he will do a powere recovery auto at the end of other test flights, to look at the flare entry speeds and the flare angle required to temporarily zero out the rate of descent. Then, when its time to do it for real, two or three power recoveries and then finish it.
This is the approach used by the pilots who did the CH-53A, the S-64 E and F, and that I used in the S-67, UH-60, SH-60, S-76 and S-92. No dents or dings in any of them. I am sure that other OEM test Pilots can attest to approaching this first-time task in a quite similar way.
Thanks,
John Dixson
FAR 29.79 and 83 provide the requirements and AC 29.2c, pages B-83-84 provide general guidance. One will note the absence of a required minimum landing speed, and the AC only recommends a speed under 40 kts.
Another reality surrounding the question of what is the best way for the manufacturer test pilot to proceed is that the machine in question is typically the envelope expansion/structural test aircraft, and thus has the maximum instrumentation installation. That makes it a very dear commodity, with serious consequences should it be seriously damaged.
It is clear in reading the advisory circular that the FAA intent is clear and stated in AC 29.75A.b.(2)(vii).(C): " The intent of this rule is to demonstrate controlled touchdown conditions and freedom from loss of control or apparent hazard to occupants when landing with all engines failed."
There is no instruction or direction that requires the demonstration to perform multiple power off landings to replicate what might be the best operational power off landing procedure for conditions such as: landing in forest, landing in a soft, or muddy plowed field, or the ocean. Certainly, ( and I think you were referring to these conditions ) in any large single rotor machine, these conditions would make the pilots approach to ensuring tail rotor clearance during the end of the flair a bit different, as the pilot will want to minimize the touchdown groundspeed.
As to the question of practice and build-up, its not very complicated. Since the pilot knows that at sometime in the future the landing has to be made, he will do a powere recovery auto at the end of other test flights, to look at the flare entry speeds and the flare angle required to temporarily zero out the rate of descent. Then, when its time to do it for real, two or three power recoveries and then finish it.
This is the approach used by the pilots who did the CH-53A, the S-64 E and F, and that I used in the S-67, UH-60, SH-60, S-76 and S-92. No dents or dings in any of them. I am sure that other OEM test Pilots can attest to approaching this first-time task in a quite similar way.
Thanks,
John Dixson
JohnDix
Your answer clears this report up for me. The statement about possibley simulating tail rotor drive failure was most enlightening.
Few answers in year-old fatal Seahawk crash - Navy News, news from Iraq - Navy Times
I have heard of a number of missing Seahawks at sea with no survivors, how many have crashes have there been with survivors?
Common mode issue between the 92 and 60 and different from the Puma is the canted tail rotor.
The Sultan
Your answer clears this report up for me. The statement about possibley simulating tail rotor drive failure was most enlightening.
Few answers in year-old fatal Seahawk crash - Navy News, news from Iraq - Navy Times
I have heard of a number of missing Seahawks at sea with no survivors, how many have crashes have there been with survivors?
Common mode issue between the 92 and 60 and different from the Puma is the canted tail rotor.
The Sultan
Naval H-60 Tail Drive failure
Sultan, you may not recall, but early in the SH-60B program, there was a tail drive problem that occurred on an SH-60B stationed at Mayport, Fl. Crew made an uneventful auto to the water and all swam away. The ship floated for quite awhile and a picture was taken of the tail of the aircraft sticking out of the water with a perfectly preserved, totally undamaged tail rotor.
This was a typical USN flight crew.
The ship was recovered and as I recall, there was a maintenance issue with the TR driveshaft coupling that of course is broken every time the tail is folded.
Thanks,
John Dixson
This was a typical USN flight crew.
The ship was recovered and as I recall, there was a maintenance issue with the TR driveshaft coupling that of course is broken every time the tail is folded.
Thanks,
John Dixson
Sultan - I'm guessing from your profile that you haven't actually flown any EOLs. How does that mean you know what you are talking about?
As John points out, TPs have to use an incremental approach to completing an EOL on an aircraft so you work up to it gradually rather than just hacking the engines and giving it a go - the aim is not to trash the very expensive aircraft whilst still proving it can complete an EOL with crew survivability.
Zero speed touchdown EOLs are easy peasy in a small, light helo, especially with a bit of wind to help but you will crunch a big helicopter trying to reproduce the same thing - that is why they go for a fast touchdown speed, letting the (generally large) undercarriage absorb some of the energy.
Folding tails are notorious for causing TR problems - the disconnect coupling needs to be rigorously serviced and positively engaged and checked before flight.
As John points out, TPs have to use an incremental approach to completing an EOL on an aircraft so you work up to it gradually rather than just hacking the engines and giving it a go - the aim is not to trash the very expensive aircraft whilst still proving it can complete an EOL with crew survivability.
Zero speed touchdown EOLs are easy peasy in a small, light helo, especially with a bit of wind to help but you will crunch a big helicopter trying to reproduce the same thing - that is why they go for a fast touchdown speed, letting the (generally large) undercarriage absorb some of the energy.
Folding tails are notorious for causing TR problems - the disconnect coupling needs to be rigorously serviced and positively engaged and checked before flight.