Helicopter missing in the Med
If you replace conventional controls with a side stick or similar 4-axis controller, and then need two pilots to fly some manoeuvres - how is that an advance?
Early Sikorsky FBW development
Good question Sycamore. There were two of us that did most of the front seat flying. The learning curve for flying the 4 axis system was very flat. By the end of each flight we were pretty accomplished flying basic tasks. Little of that was retained between flights. More complex tasks, ie. descending decelerating climbs and turns, quick stops, precision and confined area landings were more than difficult. To say the least we were operating in the lower right hand corner of the Cooper Harper Scale!
The 3 plus one configuration was very similar to a basic helicopter control system. Similar to flying in the front seat of an AH-1 Cobra. Having yaw control on the side arm controller resulted in unwanted yaw control input while performing more complex maneuvers. Having the ability to make small trim changes in collective from the cyclic was a plus.
I spoke with Bill Dana of X-15 and F-16 AFTI fame. He believed that most flying tasks could be achieved by ensuring that the aircrafts basic handling qualities were optimized.
Hope this answers some of your questions.
The 3 plus one configuration was very similar to a basic helicopter control system. Similar to flying in the front seat of an AH-1 Cobra. Having yaw control on the side arm controller resulted in unwanted yaw control input while performing more complex maneuvers. Having the ability to make small trim changes in collective from the cyclic was a plus.
I spoke with Bill Dana of X-15 and F-16 AFTI fame. He believed that most flying tasks could be achieved by ensuring that the aircrafts basic handling qualities were optimized.
Hope this answers some of your questions.
Was in a discussion with a person closely connected with the MHP qualification testing and who noted that one of the previous posts included an error as to the configuration of the Comanche controller vs the MHP controller. The Comanche had a three axis ( pitch/roll/yaw controller while the Controller in the MHP has only pitch and roll, with the yaw axis controlled by the pedals.
My recollection is a little hazy but I thought everything after Comanche was 2 axis cyclic. We had an old 3 axis controller we used for the X2 but we didn't use the yaw axis, just conventional pedals.
Back to this thread subject for a moment, IFMU, but several of the media reports say that the Canadian military authorities are getting the 92 MHP ships back flying having changed nothing but some procedural information in the operators manual etc. That tends to indicate to me that there isn’t any question of whether the pilot can overcome any Flight Director/Autopilot inputs. Am I missing something?
Back to this thread subject for a moment, IFMU, but several of the media reports say that the Canadian military authorities are getting the 92 MHP ships back flying having changed nothing but some procedural information in the operators manual etc. That tends to indicate to me that there isn’t any question of whether the pilot can overcome any Flight Director/Autopilot inputs. Am I missing something?
Back to this thread subject for a moment, IFMU, but several of the media reports say that the Canadian military authorities are getting the 92 MHP ships back flying having changed nothing but some procedural information in the operators manual etc. That tends to indicate to me that there isn’t any question of whether the pilot can overcome any Flight Director/Autopilot inputs. Am I missing something?
All this should be followed by updated FBW software later on, I guess ?
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I agree with 212man, when manipulating controls with the FD coupled, it can be scary. The S92, with standard control have already limitations for when engaging the FD in correlation of speed, height and flight conditions. It is also the same for other manufacturer. Many incident reports have proven that already. So maybe is not only related to the FBW system, but a lack of knowledge.
There is substantial difference between analog and digital FBW.
From Aviation Today:
”The principal flight control stick will be in the cyclic position, in front of the pilot, but it will function more like a joystick. Officially called the "right-hand controller," it is comparable to the Comanche's sidearm controller, and it controls pitch, roll and yaw.
The right-hand controller doesn't give the pilot the exact feedback of a conventional cyclic stick, but Mayo believes helicopter pilots will find operating the FBW-equipped S-92 "to be an easy transition because the automatic features simplify the job of flying."
(Link deleted)
And yes, I am familiar with the differences between analog and digital flight control systems. But in all other FBW production helicopters and Tiltrotors (Comanche does not count) the cyclic is back driven in response to AP inputs. In the CH-148 it does not, unless changes to the architecture have been made late in development I am not aware of.
”The principal flight control stick will be in the cyclic position, in front of the pilot, but it will function more like a joystick. Officially called the "right-hand controller," it is comparable to the Comanche's sidearm controller, and it controls pitch, roll and yaw.
The right-hand controller doesn't give the pilot the exact feedback of a conventional cyclic stick, but Mayo believes helicopter pilots will find operating the FBW-equipped S-92 "to be an easy transition because the automatic features simplify the job of flying."
(Link deleted)
And yes, I am familiar with the differences between analog and digital flight control systems. But in all other FBW production helicopters and Tiltrotors (Comanche does not count) the cyclic is back driven in response to AP inputs. In the CH-148 it does not, unless changes to the architecture have been made late in development I am not aware of.
My understanding is that it was the A320 in 1987 and B777 in 1994 thar where the first commercial aircraft to utilize a digital FBW.
The NH90 for example has a FBW system, although it has two digital lanes and two analog lanes, so it can only do what an analog computer can do (basic damping and such), as Nick Lappos mentioned in an earlier post.
And further:
“2nd Aug 2006, 02:56
(...) The basic architecture of the NH 90's FBW is that all computations are made in a pair of analog computers that match the outputs of a pair of digital computers. Any miscompare shuts down that lane. This means that the FBW on the NH90 is incapable of doing anything that can't be done with resisters and capacitors. It is therefore relegated to damping and making normal helo flight controls, basically 1975 flight controls, in spite of the fact that it is a FBW.”
So FBW is divided into Analog FBW and Digital FBW. It is not the same and represents two very different ways of FBW.
No, thats not correct
NH90 has four FBW-computers. Two digital and two analog. The two digital are the ones providing normal handling and upper modes. Digital#1 is the one in charge normally with Digital#2 in stand by, with no degradation in performance if #1 “goes sick”.
Analog #1 and #2 is pure backup, with reduced handling qualities, more or less no decoupling and no upper modes.
The four lanes isnt connected to a specific computer but is handled by a actuator control computer (two
ACC’s actually) that selects what signals to send to the actuators.
= NH90 have digital FBW with analog backup.
Analog FBW computers as main FBW Computers should be a long time since put in
Aircrafts.
Im sure all three mentioned have digital FBW.
NH90 has four FBW-computers. Two digital and two analog. The two digital are the ones providing normal handling and upper modes. Digital#1 is the one in charge normally with Digital#2 in stand by, with no degradation in performance if #1 “goes sick”.
Analog #1 and #2 is pure backup, with reduced handling qualities, more or less no decoupling and no upper modes.
The four lanes isnt connected to a specific computer but is handled by a actuator control computer (two
ACC’s actually) that selects what signals to send to the actuators.
= NH90 have digital FBW with analog backup.
Analog FBW computers as main FBW Computers should be a long time since put in
Aircrafts.
Im sure all three mentioned have digital FBW.
No, thats not correct
NH90 has four FBW-computers. Two digital and two analog. The two digital are the ones providing normal handling and upper modes. Digital#1 is the one in charge normally with Digital#2 in stand by, with no degradation in performance if #1 “goes sick”.
Analog #1 and #2 is pure backup, with reduced handling qualities, more or less no decoupling and no upper modes.
The four lanes isnt connected to a specific computer but is handled by a actuator control computer (two
ACC’s actually) that selects what signals to send to the actuators.
= NH90 have digital FBW with analog backup.
Analog FBW computers as main FBW Computers should be a long time since put in
Aircrafts.
Im sure all three mentioned have digital FBW.
NH90 has four FBW-computers. Two digital and two analog. The two digital are the ones providing normal handling and upper modes. Digital#1 is the one in charge normally with Digital#2 in stand by, with no degradation in performance if #1 “goes sick”.
Analog #1 and #2 is pure backup, with reduced handling qualities, more or less no decoupling and no upper modes.
The four lanes isnt connected to a specific computer but is handled by a actuator control computer (two
ACC’s actually) that selects what signals to send to the actuators.
= NH90 have digital FBW with analog backup.
Analog FBW computers as main FBW Computers should be a long time since put in
Aircrafts.
Im sure all three mentioned have digital FBW.
Other FBW aircraft are certified along latest requirements with triple redundancy (four non degraded parallel systems).
With a strongly degraded backup solution on the NH90 compared to a triple redundant digital solution I would still claim there are differences between an analog and digital FBW of which NH90 might be considered a hybrid.
This FBW system takes around fifteen minutes to make. It matures for about twenty years with no costs to the operator. When ready it takes about £30,000 to programme it to fly your helicopter. It then requires between £30k to £80k to maintain it but it can be upgraded to your new helicopter at no cost apart from administration. It will, with care, last about forty years against replacing an existing system costing many millions every ten years.
It's called a pilot.
It's called a pilot.
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This FBW system takes around fifteen minutes to make. It matures for about twenty years with no costs to the operator. When ready it takes about £30,000 to programme it to fly your helicopter. It then requires between £30k to £80k to maintain it but it can be upgraded to your new helicopter at no cost apart from administration. It will, with care, last about forty years against replacing an existing system costing many millions every ten years.
It's called a pilot.
It's called a pilot.
Imagine a conventional mechanical flight control system, but with the autopilot actuators in series with the linkage, versus in parallel as is conventionally incorporated.
When the autopilot would then command the aircraft, the cyclic stick would not move. Not only would the pilot have no tactile or visual indication of the auto pilot inputs form the cyclic, the pilot would also not have any indication of how much control authority was remaining.
This is how the Cyclone autopilot architecture functions. Digital versus analog, makes no difference.
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I was closely associated with the S92FBW and CH148 flight control development and would like to weigh in on a couple of speculations.
It would be very difficult for control margins to be an issue. First, more than adequate control margins were demonstrated through the full flight envelope, which included both steady state trim conditions and extreme maneuvering.
While the controllers are indeed passive unique trim design, the CH148 incorporates an envelope cueing system, which provides both aural and visual cues to control margin encroachment. The most common reason for activating these cues would be if the aircraft was being operated outside of the operational CG envelope.
Some argue that proportional control position feedback is essential to safely operate, but there have been frustratingly too many accidents where pilots found themselves outside of CG but didn't recognize control positions being near limits. For that reason, cueing would be an improvement. Upon weight on wheels, the FBW system controller converts to a proportional controller - valuable during slope landings, but the cueing system excelled in warning the pilots nearing limits so they can have enough control remaining to recover off an excessive slope.
The autopilot uses very little control envelope, so providing proportional feedback is really of little value except to show it is doing something. Further, I would defy anyone to be able to simply look down at the cyclic position and tell me how much control is remaining. You know it when you hit it, but you can't really tell when you're 10% from the stop.
A couple other tidbits:
The controller configuration is 2 axis center mounted unique trim cyclic, floor mounted unique trim pedals, and conventional, trimmable, displacement collective.
FCC architecture is "dual-dual-triplex". There are 3 FCCs, each FCC has two lanes (either one can operate the servos). Each lane has dual processors, and they incorporate dissimilar software to address common mode failures.
It would be very difficult for control margins to be an issue. First, more than adequate control margins were demonstrated through the full flight envelope, which included both steady state trim conditions and extreme maneuvering.
While the controllers are indeed passive unique trim design, the CH148 incorporates an envelope cueing system, which provides both aural and visual cues to control margin encroachment. The most common reason for activating these cues would be if the aircraft was being operated outside of the operational CG envelope.
Some argue that proportional control position feedback is essential to safely operate, but there have been frustratingly too many accidents where pilots found themselves outside of CG but didn't recognize control positions being near limits. For that reason, cueing would be an improvement. Upon weight on wheels, the FBW system controller converts to a proportional controller - valuable during slope landings, but the cueing system excelled in warning the pilots nearing limits so they can have enough control remaining to recover off an excessive slope.
The autopilot uses very little control envelope, so providing proportional feedback is really of little value except to show it is doing something. Further, I would defy anyone to be able to simply look down at the cyclic position and tell me how much control is remaining. You know it when you hit it, but you can't really tell when you're 10% from the stop.
A couple other tidbits:
The controller configuration is 2 axis center mounted unique trim cyclic, floor mounted unique trim pedals, and conventional, trimmable, displacement collective.
FCC architecture is "dual-dual-triplex". There are 3 FCCs, each FCC has two lanes (either one can operate the servos). Each lane has dual processors, and they incorporate dissimilar software to address common mode failures.
I was closely associated with the S92FBW and CH148 flight control development and would like to weigh in on a couple of speculations....,
While the controllers are indeed passive unique trim design, the CH148 incorporates an envelope cueing system, which provides both aural and visual cues to control margin encroachment. The most common reason for activating these cues would be if the aircraft was being operated outside of the operational CG envelope.....
A couple other tidbits:
The controller configuration is 2 axis center mounted unique trim cyclic, floor mounted unique trim pedals, and conventional, trimmable, displacement collective.
FCC architecture is "dual-dual-triplex". There are 3 FCCs, each FCC has two lanes (either one can operate the servos). Each lane has dual processors, and they incorporate dissimilar software to address common mode failures.
While the controllers are indeed passive unique trim design, the CH148 incorporates an envelope cueing system, which provides both aural and visual cues to control margin encroachment. The most common reason for activating these cues would be if the aircraft was being operated outside of the operational CG envelope.....
A couple other tidbits:
The controller configuration is 2 axis center mounted unique trim cyclic, floor mounted unique trim pedals, and conventional, trimmable, displacement collective.
FCC architecture is "dual-dual-triplex". There are 3 FCCs, each FCC has two lanes (either one can operate the servos). Each lane has dual processors, and they incorporate dissimilar software to address common mode failures.
The S92FBW development preceded the Bell 525 by over two years. So when developing the 525 FBW architecture, Bell studied it in depth. A unique trim cyclic is obviously the lightest and least expensive configuration. But is it optimal for pilot cues?
During informal discussions with the FAA, Bell was advised that the FAA would not certify a unique trim cyclic configuration for a helicopter. Primarily due to the lack of tactile cuing between pilot and copilot. But also due to the lack of auto pilot tactile cuing. This is why the 525 while being a FBW side stick, still mimics the function of a conventional mechanical cyclic.
The USMC also had their reservations regarding unique trim cyclics. This is why they demanded installation of active BAE cyclics sticks that could mimic the function of mechanical mechanical controls in the CH53K.
RVGuy, please take this response as a desire for an open discussion of different system architectures, not an attempt to tie unique trim cyclic to the cause of this accident.
The S92FBW development preceded the Bell 525 by over two years. So when developing the 525 FBW architecture, Bell studied it in depth. A unique trim cyclic is obviously the lightest and least expensive configuration. But is it optimal for pilot cues?
During informal discussions with the FAA, Bell was advised that the FAA would not certify a unique trim cyclic configuration for a helicopter. Primarily due to the lack of tactile cuing between pilot and copilot. But also due to the lack of auto pilot tactile cuing. This is why the 525 while being a FBW side stick, still mimics the function of a conventional mechanical cyclic.
The USMC also had their reservations regarding unique trim cyclics. This is why they demanded installation of active BAE cyclics sticks that could mimic the function of mechanical mechanical controls in the CH53K.
The S92FBW development preceded the Bell 525 by over two years. So when developing the 525 FBW architecture, Bell studied it in depth. A unique trim cyclic is obviously the lightest and least expensive configuration. But is it optimal for pilot cues?
During informal discussions with the FAA, Bell was advised that the FAA would not certify a unique trim cyclic configuration for a helicopter. Primarily due to the lack of tactile cuing between pilot and copilot. But also due to the lack of auto pilot tactile cuing. This is why the 525 while being a FBW side stick, still mimics the function of a conventional mechanical cyclic.
The USMC also had their reservations regarding unique trim cyclics. This is why they demanded installation of active BAE cyclics sticks that could mimic the function of mechanical mechanical controls in the CH53K.
Sounds worthy of its own thread. Would be interesting to find out the direct cause of the accident in this thread.
FAA and Controls
CTR wrote: "During informal discussions with the FAA, Bell was advised that the FAA would not certify a unique trim cyclic configuration for a helicopter."
Provokes a question. The 525 certification process was via " Special Conditions ", I think, as Part 29 and the attendant Advisory Circular do not yet address the totality of the FBW implications.If that is correct, then CTR is proposing ( I think? ) that everyone else is bound by a Special Condition agreed upon by Bell and the FAA, but no one else, that is not yet published as 14 CFR Part 29 and therefore is not law?
Provokes a question. The 525 certification process was via " Special Conditions ", I think, as Part 29 and the attendant Advisory Circular do not yet address the totality of the FBW implications.If that is correct, then CTR is proposing ( I think? ) that everyone else is bound by a Special Condition agreed upon by Bell and the FAA, but no one else, that is not yet published as 14 CFR Part 29 and therefore is not law?
