SAS and ATT mode
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Shawn - why? ..............
...........because they are helicopter pilots and are therefore 'onnery, awkward and self-opinionated and mostly don't operate in a disciplined environment.
A written SOP in helicopter company is scarcer than sunny day in Ireland - not including all those well behaved offshore guys in that statement of course!
G.
A written SOP in helicopter company is scarcer than sunny day in Ireland - not including all those well behaved offshore guys in that statement of course!
G.
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Turbulence, Autopilots
Hi all.
I've read a lot of interesting stuff in this thread about Autopilots, SAS and ATT modes. I've a little experience with French Autopilots, and with the older Bell Sperry types. (say about a thousand hours).
Most of these had an Autopilot disengage plate on the cyclic. There is another thread about whether to fly "through the AP" that is , against the cyclic force, after trimming the helicopter for level flight, or to use the hat to trim. (http://www.pprune.org/rotorheads/834...med-turns.html) It was a very interesting discussion, especially because I have had different instructors telling me to do the exact opposite of each other, depending on what they'd been used to flying. Those flying the Russian Mi-s would insist on using the FTR and the ones trained on the SeaKing in the UK would be ready to throw you out of the cockpit if you ever touched the FTR button on the cyclic. In the Russian APs, there was no 'coolie hat' trimmer, and the only way to change the attitude was by the use of the FTR. This was also essential when you needed to get the 'ball' in the centre.
I understand from the Trimmed Turns forum that the 'fly through' or not, has a lot to do also with the way the particular Autopilot is designed. Nick says in his post that " The type that Sikorsky generally builds uses a "fly through" concept, where the pilot can move the stick against trim, and some degree of smooth acceptance by the autopilot keeps things stable". I have had this experience in the French APs including the one in the Alouette III - it was called AP146, and did a pretty good job. The Bell , on the other hand, tended to react pretty badly if one ever tried to fly through the AP. In the Simulator, I had a high time Bell 412 pilot telling me to "Tap-Tap-Tap" when in a turn. It took me some time to understand that he was asking me to tap on the FTR switch on the cyclic in the turn - and all the time, I was flying against the pressures!
Another difference I notice is that most Autopilots are meant to be switched off when taxying on the ground. Any idea why some are not? In some of the Agusta models, there is no Quick Disengage plate on the cyclic, and one has to pull the switches into the off position. Couldn't get any satisfactory answer at the Factory too. I have seen a kind of Camel ride on a Bell 212 where the Pitch channel had a problem. Disengaging the SAS and re-engaging it without the Pitch channel worked wonders.
Now, my question is this... You're flying VMC, good weather and all, with the basic stab ON, (no higher / upper modes or holds engaged), and you encounter some clear weather turbulence (say flying over hills and the like). The turbulence is a bit disconcerting, and of course sends the ball all over the place too. Would it be better to fly with the Force Trim off? This way, with hands-on flying, perhaps the ride would be smoother, in particular with the rudder control. Finer control of the attitude and roll in turbulence would be smoother by hand. My experience is that the ride did turn out smoother. Of course, it is a personal observation, and I may be only perceiving an improvement in ride quality!!
(Many high-time Bell pilots I understand, prefer to fly with the Force Trim off in all cases, unless of course in IFR.)
Any takes on this?
I've read a lot of interesting stuff in this thread about Autopilots, SAS and ATT modes. I've a little experience with French Autopilots, and with the older Bell Sperry types. (say about a thousand hours).
Most of these had an Autopilot disengage plate on the cyclic. There is another thread about whether to fly "through the AP" that is , against the cyclic force, after trimming the helicopter for level flight, or to use the hat to trim. (http://www.pprune.org/rotorheads/834...med-turns.html) It was a very interesting discussion, especially because I have had different instructors telling me to do the exact opposite of each other, depending on what they'd been used to flying. Those flying the Russian Mi-s would insist on using the FTR and the ones trained on the SeaKing in the UK would be ready to throw you out of the cockpit if you ever touched the FTR button on the cyclic. In the Russian APs, there was no 'coolie hat' trimmer, and the only way to change the attitude was by the use of the FTR. This was also essential when you needed to get the 'ball' in the centre.
I understand from the Trimmed Turns forum that the 'fly through' or not, has a lot to do also with the way the particular Autopilot is designed. Nick says in his post that " The type that Sikorsky generally builds uses a "fly through" concept, where the pilot can move the stick against trim, and some degree of smooth acceptance by the autopilot keeps things stable". I have had this experience in the French APs including the one in the Alouette III - it was called AP146, and did a pretty good job. The Bell , on the other hand, tended to react pretty badly if one ever tried to fly through the AP. In the Simulator, I had a high time Bell 412 pilot telling me to "Tap-Tap-Tap" when in a turn. It took me some time to understand that he was asking me to tap on the FTR switch on the cyclic in the turn - and all the time, I was flying against the pressures!
Another difference I notice is that most Autopilots are meant to be switched off when taxying on the ground. Any idea why some are not? In some of the Agusta models, there is no Quick Disengage plate on the cyclic, and one has to pull the switches into the off position. Couldn't get any satisfactory answer at the Factory too. I have seen a kind of Camel ride on a Bell 212 where the Pitch channel had a problem. Disengaging the SAS and re-engaging it without the Pitch channel worked wonders.
Now, my question is this... You're flying VMC, good weather and all, with the basic stab ON, (no higher / upper modes or holds engaged), and you encounter some clear weather turbulence (say flying over hills and the like). The turbulence is a bit disconcerting, and of course sends the ball all over the place too. Would it be better to fly with the Force Trim off? This way, with hands-on flying, perhaps the ride would be smoother, in particular with the rudder control. Finer control of the attitude and roll in turbulence would be smoother by hand. My experience is that the ride did turn out smoother. Of course, it is a personal observation, and I may be only perceiving an improvement in ride quality!!
(Many high-time Bell pilots I understand, prefer to fly with the Force Trim off in all cases, unless of course in IFR.)
Any takes on this?
I notice is that most Autopilots are meant to be switched off when taxying on the ground. Any idea why some are not?
Would it be better to fly with the Force Trim off?
If the Ball remains in the bottom of the curved tube.....and never varies....how does one know it is working?
In the scenario you provided....rough air, VMC, and a bit of Turbulence....I would leave the Force Trim engaged, and if in SAS mode hand fly the machine. The autopilot will "dampen" the attitude variations but not return the aircraft to a preselected attitude.
If you use the ATT mode....the aircraft will return or attempt to return to the preselected attitude. You could fly through the autopilot and "assist" it in that task.
Shy of the ball lodging in one corner....I would not be too concerned about it moving about a bit as it is only indicating some Yaw or Roll deviations that result in short term untrimmed flight.
I am an advocate for using the Force Trim all the time....and living with the Calloused Thumb.....set it, click it, tap tap tap....however you must to get the desired result but let the Autopilot fly the machine as much as possible.
Each autopilot system is a bit different in design and function so one has to learn to use them to the best effect.
I also advocate using a bit of cyclic friction to assist in "smoothing" the ride. Sperry Helipilot systems on Bell 212/412's
required the use of a minimum friction setting to reduce cyclic oscillations caused by turbulence or maneuvering.
In the scenario you provided....rough air, VMC, and a bit of Turbulence....I would leave the Force Trim engaged, and if in SAS mode hand fly the machine. The autopilot will "dampen" the attitude variations but not return the aircraft to a preselected attitude.
If you use the ATT mode....the aircraft will return or attempt to return to the preselected attitude. You could fly through the autopilot and "assist" it in that task.
Shy of the ball lodging in one corner....I would not be too concerned about it moving about a bit as it is only indicating some Yaw or Roll deviations that result in short term untrimmed flight.
I am an advocate for using the Force Trim all the time....and living with the Calloused Thumb.....set it, click it, tap tap tap....however you must to get the desired result but let the Autopilot fly the machine as much as possible.
Each autopilot system is a bit different in design and function so one has to learn to use them to the best effect.
I also advocate using a bit of cyclic friction to assist in "smoothing" the ride. Sperry Helipilot systems on Bell 212/412's
required the use of a minimum friction setting to reduce cyclic oscillations caused by turbulence or maneuvering.
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My experience on the 412 was that the ATT mode was easily flyable at all times, even hovering and touchdown. You had to get used to flying against the forces in the stick, which took a bit of adapting.
But every system is different!!
Learn what it is supposed to do, and then try to learn to use it to best advantage.
Anyone who wants a sample 'learn how your AFCS works' screed I wrote a while ago, please PM me. Good place to start, even if it's not exactly how your system works.
But every system is different!!
Learn what it is supposed to do, and then try to learn to use it to best advantage.
Anyone who wants a sample 'learn how your AFCS works' screed I wrote a while ago, please PM me. Good place to start, even if it's not exactly how your system works.
There are significant differences even within one product range from one manufacturer. With the AS332L Super Puma, when flying against the trim for short term over-rides (eg in turbulence), the aircraft was quite stable and there tended to be a fairly direct relationship between stick displacement and pitch or roll attitude. On the EC225 as soon as you operate against the spring trim it goes into a kind of SAS mode and is fairly unstable, especially when you add in the light cyclic forces and the non-linear forces that arise from the breakout force from the trimmed position. All in all it is not easy to fly against the springs in the cruise and I advocate using the cyclic trim release button (or more sensibly be fully coupled with upper modes!)
So I think the moral is, try the different methods and then stick with the one that works best for you on your particular machine.
HC
So I think the moral is, try the different methods and then stick with the one that works best for you on your particular machine.
HC
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412 AP SAS/ATT
My experience on the 412 was that the ATT mode was easily flyable at all times, even hovering and touchdown. You had to get used to flying against the forces in the stick, which took a bit of adapting.
But every system is different!!
But every system is different!!
Please correct me if I am wrong but I believe that in the 412 with ATT Mode selected, the ATT Mode is disengaged whenever the Force Trim button is pressed and the AP reverts to what is known as "Modified SAS Mode" therefore you are actually not really flying in ATT Mode. Also earlier SASless said that the cyclic does not move when Beep Trim is operated in ATT Mode.
I believe that this also is not strictly correct and the cyclic does actually move to allow the control actuators to recenter.
In ATT Mode the cyclic and force trim are used to set the Attitude datum in the AHRS (or TARSYNS on older models) and effectively the cyclic position becomes an integral part of that set datum. Moving the cyclic against the force trim in ATT Mode although it works to move the flight controls is once again abusing the designed use IMHO!
Learn what it is supposed to do, and then try to learn to use it to best advantage.
But I wait to be corrected!
Trog
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Trog:
My understanding of the 412 system is that in ATT mode, when you move the stick, you are temporarily disabling the system's ability to hold the datum attitude.
The way to see this is in the hover, with ATT engaged, just move and hold the stick slightly away from trim and see what happens. When the stick is returned to trim, the system should return (within reason, as it's not that tight a system) to the original datum.
So, in the hover, if everything is set up nicely, you can make minor corrections without using the Force Trim by merely flying against the forces for brief periods.
If you want more on how demon how the system works, PM me.
My understanding of the 412 system is that in ATT mode, when you move the stick, you are temporarily disabling the system's ability to hold the datum attitude.
The way to see this is in the hover, with ATT engaged, just move and hold the stick slightly away from trim and see what happens. When the stick is returned to trim, the system should return (within reason, as it's not that tight a system) to the original datum.
So, in the hover, if everything is set up nicely, you can make minor corrections without using the Force Trim by merely flying against the forces for brief periods.
If you want more on how demon how the system works, PM me.
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412 SAS/ATT
Shawn,
I agree that you are temporarily removing the systems ability to maintain attitude by moving the cyclic and do not disagree for a second that it is entirely possible to accurately hover or manoeuvre using this method.
My contention is that the ATT system works by extending and contracting actuators which need something to push against to do their job of passing that movement to the flight controls.
The way that you are temporarily removing the ATT part of the system is to move the bit that the actuators push against i.e the cyclic held in place by the force trim! As you move the cyclic (without pressing the trim release and selecting Modified SAS Mode) you are not disabling the input from the AHRS and the actuators are still moving but now have nothing to push against so end up in an incorrect position - perhaps explaining why the cyclic/flight controls are in a less than perfect position (not the original datum) when you release them
Not sure that is what Mr. Sperry originally intended which is why he fitted a trim release button.
Trog
I agree that you are temporarily removing the systems ability to maintain attitude by moving the cyclic and do not disagree for a second that it is entirely possible to accurately hover or manoeuvre using this method.
My contention is that the ATT system works by extending and contracting actuators which need something to push against to do their job of passing that movement to the flight controls.
The way that you are temporarily removing the ATT part of the system is to move the bit that the actuators push against i.e the cyclic held in place by the force trim! As you move the cyclic (without pressing the trim release and selecting Modified SAS Mode) you are not disabling the input from the AHRS and the actuators are still moving but now have nothing to push against so end up in an incorrect position - perhaps explaining why the cyclic/flight controls are in a less than perfect position (not the original datum) when you release them
Not sure that is what Mr. Sperry originally intended which is why he fitted a trim release button.
Trog
Last edited by Troglodita; 15th Apr 2012 at 15:10.
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I flew the 412 in ATT mode all the time. If you need to change the attitude, just press the FTR briefly. You don't want ATT mode engaged on the ground, since you can get interesting results, but I kept it on from just before liftoff until at flat pitch after landing. In the S76, I just moved the cyclic as necessary, without worrying about pressing any buttons. That's one reason the S76 is more fun to fly, you don't have to worry about tiring your thumb out. I've never met a single pilot who would get in a 412 if (s)he had a choice of an S76.
I had a numpty TRE in the Gulf that used to insist that in ATT mode (during IF check ride) I should desist in using the FTR button to make minor attitude adjustments and only use the chinese hat..... 
The AHRS loved that and IIRC moved the cyclic back to its original datum. To compound the problem the CH was as slow as a snail, so you were constantly chasing the datum
click,click,click, every trip
The AHRS loved that and IIRC moved the cyclic back to its original datum. To compound the problem the CH was as slow as a snail, so you were constantly chasing the datum
click,click,click, every trip
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what about on a floater
Hi,
For the folks out here who land on floaters ( ships) , ,on touch down, do you revert to the SAS mode from ATT, or do you switch the APs OFF. This is for the 412. I ask because on the Seaking which I flew in the Navy, we'd select STAB OFF on touch down on decks, if we were going to be there for a while.
For the folks out here who land on floaters ( ships) , ,on touch down, do you revert to the SAS mode from ATT, or do you switch the APs OFF. This is for the 412. I ask because on the Seaking which I flew in the Navy, we'd select STAB OFF on touch down on decks, if we were going to be there for a while.
In the Sea King, you needed differential pedal to disengage the heading hold with the ASE in - since not many pilots sat on the deck with differential pedal pressure any heading change of the ship would cause the yaw channel to try and swing the tail. Hence the ASE disengagement on Sea Kings.
ISTR the 412 has an irritating yaw trim function but I don't think it has a yaw channel heading hold - that is a roll channel function in the upper modes of the AFCS.
Short answer is no, I don't think you need to disengage the AP on a deck unless it is moving a lot but I would go from ATT to SAS mode.
ISTR the 412 has an irritating yaw trim function but I don't think it has a yaw channel heading hold - that is a roll channel function in the upper modes of the AFCS.
Short answer is no, I don't think you need to disengage the AP on a deck unless it is moving a lot but I would go from ATT to SAS mode.
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You lot don’t know you are born. As an Army Air Corps Gazelle pilot in the 1980’s the only thing that SAS meant was Special Air Service! It was just the pilot versus the helicopter in our poor Army.
Apparently the RAF would place their Gazelles U/S if the sas was not functional 😳
Apparently the RAF would place their Gazelles U/S if the sas was not functional 😳
I taught on both the HT3 (RAF Gazelle) and the AH 1 (Army Gazelle) - SAS and stick trim were good to have but not essential it is just a great aircraft to fly.
You lot don’t know you are born. As an Army Air Corps Gazelle pilot in the 1980’s the only thing that SAS meant was Special Air Service! It was just the pilot versus the helicopter in our poor Army.
Apparently the RAF would place their Gazelles U/S if the sas was not functional 😳
Apparently the RAF would place their Gazelles U/S if the sas was not functional 😳
...this could descend into a Python sketch !
Hi,
For the folks out here who land on floaters ( ships) , ,on touch down, do you revert to the SAS mode from ATT, or do you switch the APs OFF. This is for the 412. I ask because on the Seaking which I flew in the Navy, we'd select STAB OFF on touch down on decks, if we were going to be there for a while.
For the folks out here who land on floaters ( ships) , ,on touch down, do you revert to the SAS mode from ATT, or do you switch the APs OFF. This is for the 412. I ask because on the Seaking which I flew in the Navy, we'd select STAB OFF on touch down on decks, if we were going to be there for a while.
Originally Posted by [email protected]
I taught on both the HT3 (RAF Gazelle) and the AH 1 (Army Gazelle) - SAS and stick trim were good to have but not essential it is just a great aircraft to fly.
I flew the same 212's as did 212man.....and my memory tells me the following.
The SFENA system was rarely serviceable thus was of not much value. When bored you could try to determine if it was working or not or what part was or was not.....but other thantaat it was useless.
The Bell SCAS system was designed by Bell for use in the AH1-G Huey Cobra....which I do not recall seeing installed in our fleet of 212's ....but I used it at other places...was pretty good stuff for what it was....reliable and easy to use.
The Sperry System was excellent kit...reliable..easty to use and the only three of the systems that could incorporate a Flight Directer and was the same on the 212 and 412.
At the Operations we flew the same aircraft, 212man and I, we did not have the luxury of the Flight Director as they had been removed or not installed for those contracts.
Due to my background flying US Army Chinooks where the Force Trim system was ON all the time....I was quite happy to us ATT Mode all the time and use the Cyclic Trim Button to reposition the Cyclic.
I engaged it just prior to TakeOff and went to SAS mode after landing....or turned it off all together if it was the final landing if shutting down,
When landing on Moving Decks....I turned the AFCS OFF.
My view was this....as the AFCS could assist in maintaining a constant attitude....then why not use it. Set the attitude you desire/need....release the Force Trim Button....thus setting the datum...and let the helicopter do its part.
The other lesson learned was never buy SFENA.
The SFENA system was rarely serviceable thus was of not much value. When bored you could try to determine if it was working or not or what part was or was not.....but other thantaat it was useless.
The Bell SCAS system was designed by Bell for use in the AH1-G Huey Cobra....which I do not recall seeing installed in our fleet of 212's ....but I used it at other places...was pretty good stuff for what it was....reliable and easy to use.
The Sperry System was excellent kit...reliable..easty to use and the only three of the systems that could incorporate a Flight Directer and was the same on the 212 and 412.
At the Operations we flew the same aircraft, 212man and I, we did not have the luxury of the Flight Director as they had been removed or not installed for those contracts.
Due to my background flying US Army Chinooks where the Force Trim system was ON all the time....I was quite happy to us ATT Mode all the time and use the Cyclic Trim Button to reposition the Cyclic.
I engaged it just prior to TakeOff and went to SAS mode after landing....or turned it off all together if it was the final landing if shutting down,
When landing on Moving Decks....I turned the AFCS OFF.
My view was this....as the AFCS could assist in maintaining a constant attitude....then why not use it. Set the attitude you desire/need....release the Force Trim Button....thus setting the datum...and let the helicopter do its part.
The other lesson learned was never buy SFENA.