Trimmed Turns
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Bladestrike
I told you that you've been doing it all wrong.....you old sea dog.....thanx for the info on the H/V charts and it still is a ball of wax.....Just for your info i asked an old friend at Transport about the 704 H/V curve and he said "don't ask"
Nick
If the S76 is u/s IFR with out a cyclic stick trim......what about guys who fly it IFR with there thumb on the FTR button or the cyclic force trim turned off? They will not get any force feel from the cyclic in either case?
PS I sent you an email on our Cat A problem.
I told you that you've been doing it all wrong.....you old sea dog.....thanx for the info on the H/V charts and it still is a ball of wax.....Just for your info i asked an old friend at Transport about the 704 H/V curve and he said "don't ask"
Nick
If the S76 is u/s IFR with out a cyclic stick trim......what about guys who fly it IFR with there thumb on the FTR button or the cyclic force trim turned off? They will not get any force feel from the cyclic in either case?
PS I sent you an email on our Cat A problem.
Last edited by Xnr; 7th Mar 2003 at 04:13.
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Xnr,
The way you fly is not governed by the design FAR 29, have a ball with the trim button! You can use the techniques that suit you best when you fly (unless otherwise restricted by operational FAR), but when we certify to the requirements for the design, we must show that a means to provide force vs airspeed exists. On an S-76, I myself would not turn the trim off with the panel switch in IFR, because I then disable the Attitude stability and leave only SAS, which is less suitable.
GLSNightpilot points out a problem with flying against trim that I failed to mention previously. In most aircraft when you push the stick against trim, the inner loop actuators fight you with some of their authority (since the stability system sees this maneuver as an outside disturbence). In the S76 we limit the attitude authority of the actuators to half their travel, thus saving the other half for rate damping. Biased actuators in a staedy maneuver then reduces stability authority and makes it somewhat more prone to running out of authority in turbulence. In other words, if you ride against trim you can get closer to the point that turbulence can upset the aircraft. This probability is much more real than the possibility of disorientation causing you to need to let go and hope the aircraft rights itself and saves you against yourself.
Regarding the beeper hat authority, the S76 beeper is timed out so that the failure of that switch does not cause the AFCS to run away in a hard over. The upset at high speed would be too large, and the loss of the attitude hold would be guaranteed, so we put the beeper thru a timer to limit the runaway.
heedm points out ANOTHER reason why trusting the trim to save you when you give up and let go of the stick is not a swell idea. If the trim has a failure that causes it to run away (this can be a switch failure in the cyclic) then the stick center is wrong. If the pilot gets disoriented (as heedm did ) and then trusts the trim to get himout, his goose is cooked. I am not sure why heedm deduced from his experience with this failure that letting go of the stick was a good idea.
Nick
The way you fly is not governed by the design FAR 29, have a ball with the trim button! You can use the techniques that suit you best when you fly (unless otherwise restricted by operational FAR), but when we certify to the requirements for the design, we must show that a means to provide force vs airspeed exists. On an S-76, I myself would not turn the trim off with the panel switch in IFR, because I then disable the Attitude stability and leave only SAS, which is less suitable.
GLSNightpilot points out a problem with flying against trim that I failed to mention previously. In most aircraft when you push the stick against trim, the inner loop actuators fight you with some of their authority (since the stability system sees this maneuver as an outside disturbence). In the S76 we limit the attitude authority of the actuators to half their travel, thus saving the other half for rate damping. Biased actuators in a staedy maneuver then reduces stability authority and makes it somewhat more prone to running out of authority in turbulence. In other words, if you ride against trim you can get closer to the point that turbulence can upset the aircraft. This probability is much more real than the possibility of disorientation causing you to need to let go and hope the aircraft rights itself and saves you against yourself.
Regarding the beeper hat authority, the S76 beeper is timed out so that the failure of that switch does not cause the AFCS to run away in a hard over. The upset at high speed would be too large, and the loss of the attitude hold would be guaranteed, so we put the beeper thru a timer to limit the runaway.
heedm points out ANOTHER reason why trusting the trim to save you when you give up and let go of the stick is not a swell idea. If the trim has a failure that causes it to run away (this can be a switch failure in the cyclic) then the stick center is wrong. If the pilot gets disoriented (as heedm did ) and then trusts the trim to get himout, his goose is cooked. I am not sure why heedm deduced from his experience with this failure that letting go of the stick was a good idea.
Nick
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hi all you chopper jocks, from an admiring 'seized-wing' pilot,
Obviously I dont have the in depth knowledge that you guys do, but after reading this thread I'd like to give my 2-cents worth
it seems the 'safest' way to go is trim the helo for straight and level flight, with the pilot feeling stick force in a turn, as a tactile feedback cue from the a/c systems re the rate etc of turn. Same with the speed issue, more speed = more force felt thru stick....uh, cyclic
all the while keeping a scan going of the instruments to check the tactile feed back you get thru the stick corresponds to what you think the a/c is doing and this is confirmed thru the instruments...
or am I missing something
Obviously I dont have the in depth knowledge that you guys do, but after reading this thread I'd like to give my 2-cents worth
it seems the 'safest' way to go is trim the helo for straight and level flight, with the pilot feeling stick force in a turn, as a tactile feedback cue from the a/c systems re the rate etc of turn. Same with the speed issue, more speed = more force felt thru stick....uh, cyclic
all the while keeping a scan going of the instruments to check the tactile feed back you get thru the stick corresponds to what you think the a/c is doing and this is confirmed thru the instruments... or am I missing something
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Skaz, yes you're missing something. Reread the thread carefully. It depends on the design of the AFCS. Some, such as on the Bell 412, are designed as 'hands-off' systems, & any attempt by the pilot to move the cyclic other than through the trim switch or depressing the interrupt button, will confuse the system, & can result in unusual attitudes. Most S76 pilots I know fly the same way, not pushing against the force trim, but using the 'coolie hat' or interrupt button if necessary. I don't claim that's the only way or even the best way, but that's the way we do it down here.
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It really does depend on the AFCS design. French designed AFCS systems have a completely different method of operation in this regard than most N. American systems.
The problem is that none of them are particularly well described in any of the manuals.
So, most people don't understand them, and lots of old wives tales (hows that for both age-ist and sex-ist?) develop.
The problem is that none of them are particularly well described in any of the manuals.
So, most people don't understand them, and lots of old wives tales (hows that for both age-ist and sex-ist?) develop.
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Nick, when you find yourself in a UA, you know something went wrong. What were you doing prior to the UA entry? Might be that whatever you were using was what got you into trouble. Then again, maybe it wasn't. In the recovery you have to use everything at your disposal, but you might not be able to trust any of it.
That's what I did. I trusted the stick force. Why? During the numerous UA recoveries I did prior to that the stick force worked. Without fully realizing it, I learned to trust the stick force to help find a stable flight regime. Had I not trusted it, I still would have made reference to it but been more diligent in observing other clues during the recovery.
The situation I was in was fairly compounded. Partial panel so I already was without some attitude indication, runaway trim, so I had that to deal with, then a simulated UA that led to the real thing. Oh yeah, I had less than 100hours total time and Terminal was trying to contact us on guard because they vectored us into the Snowbird's training area, then cancelled our IF clearance and switched us to a traffic frequency. A little bit busy.
I wasn't advocating letting go of the stick. I say fly her to the ground. What I do advocate is, if able, leaving a trimmed position that you can feel while hands on flying. Try it...it works.
That's what I did. I trusted the stick force. Why? During the numerous UA recoveries I did prior to that the stick force worked. Without fully realizing it, I learned to trust the stick force to help find a stable flight regime. Had I not trusted it, I still would have made reference to it but been more diligent in observing other clues during the recovery.
The situation I was in was fairly compounded. Partial panel so I already was without some attitude indication, runaway trim, so I had that to deal with, then a simulated UA that led to the real thing. Oh yeah, I had less than 100hours total time and Terminal was trying to contact us on guard because they vectored us into the Snowbird's training area, then cancelled our IF clearance and switched us to a traffic frequency. A little bit busy.
I wasn't advocating letting go of the stick. I say fly her to the ground. What I do advocate is, if able, leaving a trimmed position that you can feel while hands on flying. Try it...it works.
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heedm,
Thanks for the explanation, I understand.
I have always taught to roll wings level, then pull up, using purely visual cues. One must learn to fight feelings, which in the slight cases we call the "leans" and in major cases can feel like you are housed inside a tornado. The trimmed stick recovery idea relies on the fact that you would use a perceived stick force to help you, but ignore all those other false forces from your body and inner ear. Neat trick, might work, but I put that into the same basket as the school that says every helicopter has LTE, and any hover descent can get you VRS. The "rules of thumb" that we get when we train are comforting and helpful, but somewhere along the line we learn when they can apply, and when to doubt them.
If the AFCS gives you good responses when you push against the stick, and you want to rely on that cue, have at it! Speaking for the S-76 design team (I helped design the AFCS and did much of the development flight test on both the SAS II, SAS III and Honeywell systems) we had no intention to use them as a wings leveler system, and would make no claim that they will help you. In fact, if formally asked, we probably would say that one should never rely on the AFCS as a UA escape tool, and that pushing against the trim will slightly degrade AFCS performance because it biases the actuators away from center and therefore slightly reduces stability peformance.
That being said, it is certainly not terrible to push against trim. There are many correct techniques in our world, have at it!
Thanks for the explanation, I understand.
I have always taught to roll wings level, then pull up, using purely visual cues. One must learn to fight feelings, which in the slight cases we call the "leans" and in major cases can feel like you are housed inside a tornado. The trimmed stick recovery idea relies on the fact that you would use a perceived stick force to help you, but ignore all those other false forces from your body and inner ear. Neat trick, might work, but I put that into the same basket as the school that says every helicopter has LTE, and any hover descent can get you VRS. The "rules of thumb" that we get when we train are comforting and helpful, but somewhere along the line we learn when they can apply, and when to doubt them.
If the AFCS gives you good responses when you push against the stick, and you want to rely on that cue, have at it! Speaking for the S-76 design team (I helped design the AFCS and did much of the development flight test on both the SAS II, SAS III and Honeywell systems) we had no intention to use them as a wings leveler system, and would make no claim that they will help you. In fact, if formally asked, we probably would say that one should never rely on the AFCS as a UA escape tool, and that pushing against the trim will slightly degrade AFCS performance because it biases the actuators away from center and therefore slightly reduces stability peformance.
That being said, it is certainly not terrible to push against trim. There are many correct techniques in our world, have at it!
Iconoclast
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Not invented here?
The troll speaks.
When Sikorsky first developed a stability control system it was originally installed in HSS-1 and eventually into the H-34. The automatic stabilization system was comprised of an autopilot originally installed in an F-86 fighter. There were some minor modifications necessary. The aux servo was equipped with electric motors that received signals from rotary variable differential transformers, which were attached to the flight controls (Collective stick, the cyclic stick and the rudder pedals. If any of these controls were used the RVDT would send an input to the auto pilot which in turn would command one or more electrical motors in order to displace the pilot valve(s) on the aux servo which would modify the disc attitude. The cyclic controls would be locked in place by magnetic brakes, which were in turn connected to the controls by force gradient springs. The pilot could make minor adjustments to the cyclic by moving the stick and compressing the springs. When the pilot removed his input force the cyclic would return to the original position.
If the pilot wanted to change the attitude or direction he would press a disconnect switch which cut out the autopilot and energize the magnetic brakes which allowed unfettered movement of the cyclic. By releasing the cutout the auto pilot would reengage and the new course would be maintained. There were similar cutouts on the rudder pedals. When the pilot wanted to set up a new direction (heading) he would move the pedals and in the process cut out the auto pilot allowing the directional gyro to assume and hold the new heading. By removing his feet from the pedals the course would be set.
If the autopilot detected a deviation from the established heading or the attitude of the helicopter it would send a signal to the aux servo returning the helicopter to the preset conditions. When the autopilot made a correction the flight controls would not move.
A similar situation existed in the collective as it had a barometric hold provision. If the pilot wanted to rise or lower he would disconnect the bar alt hold move to the new altitude and reengage the bar alt sensor.
Granted the system was by today’s standards antiquated. It had a lot of problems mostly human induced but the design philosophy was good. Why then have there been so many deviations from this design philosophy. The apache flight control system is similar but with more modern hardware and the EH-101 is a step backward in their selection of the means to maintain stability through the autopilot.
I anyone finds fault with my description it must be understood that I went to Sikorsky ASE school 48 years ago.
When Sikorsky first developed a stability control system it was originally installed in HSS-1 and eventually into the H-34. The automatic stabilization system was comprised of an autopilot originally installed in an F-86 fighter. There were some minor modifications necessary. The aux servo was equipped with electric motors that received signals from rotary variable differential transformers, which were attached to the flight controls (Collective stick, the cyclic stick and the rudder pedals. If any of these controls were used the RVDT would send an input to the auto pilot which in turn would command one or more electrical motors in order to displace the pilot valve(s) on the aux servo which would modify the disc attitude. The cyclic controls would be locked in place by magnetic brakes, which were in turn connected to the controls by force gradient springs. The pilot could make minor adjustments to the cyclic by moving the stick and compressing the springs. When the pilot removed his input force the cyclic would return to the original position.
If the pilot wanted to change the attitude or direction he would press a disconnect switch which cut out the autopilot and energize the magnetic brakes which allowed unfettered movement of the cyclic. By releasing the cutout the auto pilot would reengage and the new course would be maintained. There were similar cutouts on the rudder pedals. When the pilot wanted to set up a new direction (heading) he would move the pedals and in the process cut out the auto pilot allowing the directional gyro to assume and hold the new heading. By removing his feet from the pedals the course would be set.
If the autopilot detected a deviation from the established heading or the attitude of the helicopter it would send a signal to the aux servo returning the helicopter to the preset conditions. When the autopilot made a correction the flight controls would not move.
A similar situation existed in the collective as it had a barometric hold provision. If the pilot wanted to rise or lower he would disconnect the bar alt hold move to the new altitude and reengage the bar alt sensor.
Granted the system was by today’s standards antiquated. It had a lot of problems mostly human induced but the design philosophy was good. Why then have there been so many deviations from this design philosophy. The apache flight control system is similar but with more modern hardware and the EH-101 is a step backward in their selection of the means to maintain stability through the autopilot.
I anyone finds fault with my description it must be understood that I went to Sikorsky ASE school 48 years ago.
Beeing rather new on the "76" I realize I cannot have a better opportunity than this forum, to ask some questions about its "standart" AP. My "shadow areas" (amongst others) are:
1/ When testing the coolie hat and the trims after start, we have to observe the deflections of galvanometers needles on the 2 lanes. That works well in roll, a little less in yaw but why do we have to apply "short and rapid movments" on the cyclic pitch to test pitch actuators ? (I don't have the flight manual with me and the terms are maybe not the exact ones)
I have never seen a deflection in doing this. Delections rather occur when maneuvring the coolie hat in pitch.
Is it something I have misunderstood in the flight manual? (english is not our mother tongue here, as you probably have already guessed !!!!
)
2/ Recently our yaw damper went unserviceable, therefore with the "phase 3" capability, but we barely noticed any difference in yaw even with the "phase 3" selector switched on ( maybe must be switched "off" to operate the yaw lane "open loop"with less authority on actuators ? )
I personnaly make my turns with the coolie hat in night/IMC on the "76" but I rather do that against the trims on S365's. Once again thanks for your highly valuable explanations!
1/ When testing the coolie hat and the trims after start, we have to observe the deflections of galvanometers needles on the 2 lanes. That works well in roll, a little less in yaw but why do we have to apply "short and rapid movments" on the cyclic pitch to test pitch actuators ? (I don't have the flight manual with me and the terms are maybe not the exact ones)
I have never seen a deflection in doing this. Delections rather occur when maneuvring the coolie hat in pitch.
Is it something I have misunderstood in the flight manual? (english is not our mother tongue here, as you probably have already guessed !!!!
)2/ Recently our yaw damper went unserviceable, therefore with the "phase 3" capability, but we barely noticed any difference in yaw even with the "phase 3" selector switched on ( maybe must be switched "off" to operate the yaw lane "open loop"with less authority on actuators ? )
I personnaly make my turns with the coolie hat in night/IMC on the "76" but I rather do that against the trims on S365's. Once again thanks for your highly valuable explanations!
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When you are testing the pitch you are not testing cyclic movement....the AFCS gets its info from the ADI ....if the ADI does not change in pitch or roll axis then the AFCS channel will not move.
Last edited by Xnr; 9th Mar 2003 at 13:24.
Thread Starter
What suprised me was the fact that alot of companies dictate that you do not trim your turns. Luckily I have the choice.
Xnr, call next time you're on the coast, I'll buy.
Xnr, call next time you're on the coast, I'll buy.
