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Trim/AP operation


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On 6/18/2021 at 7:50 PM, ZeroReady said:

I don't think the Hind trim is meant to be held down like the Ka-50. It's like the Huey, you position your stick, press the button, then center your stick.

 

I think the opposite 😋

 

 

And this video is pretty helpful to understand the Yaw Auto Pilot mode.
 

 


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I have:

- Virpil WarBRD stick base = spring loaded

- MFG Crosswind rudder = spring loaded too.

 

I could mod the rudder to remove the spring and put an hydraulic damper, the rudder would stay in place.

But I'm also flying jet fighters so it wouldn't be ideal for multi-purpose use.
 

My current settings in Mi-24 special options are:

- Central Position Trimmer Mode: after I press the trim button, I return the stick to neutral.

- Rudder Trimmer: unselected

 

I engage Yaw Auto Pilot after take off and use it for the rest au the flight, excepted for landing so far where I turn it off.

To turn in flight, begin by small rudder input then roll input, increase collective to stay level.

I do most of my trim with the HAT.

 

On landing run, it's best to reset the trim after disabling the Yaw Auto Pilot since it's effectively trimming the rudder. The rudder neutral point will stay in the last place (left as long as you have enough forward speed) so you will need more input to the right when coming to a hover.

 

I'm quite happy with my setting, I hope this help 😇

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I think this thread was initially less about the yaw autopilot and more about the slight "bouncing" on the pitch/roll axis that happens when you release the AP trim button. It seems, when you depress the trim button, the autopilot channels reset to the neutral positions as they should. But after you release trim button they return to the previous state, which causes some unintended movement.

 

Personally I find this quite annoying. I have currently stopped using the trim at all when I am trying to do something that requires precision (such as lining up an attack run). Of course I have no idea if this is how the real Hind works, but that would be really surprising to me. Essentially every time you release the trim button the AP ever so slightly screws up the stability of the helo - I can't believe that real world pilots would be happy with this. I am guessing this is either a bug or a non-optimal attempt of bringing the real Hind controls into the game world of DCS.

 

There is also a bug report for this here :

 

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2 minutes ago, cow_art said:

I think this thread was initially less about the yaw autopilot and more about the slight "bouncing" on the pitch/roll axis that happens when you release the AP trim button. It seems, when you depress the trim button, the autopilot channels reset to the neutral positions as they should. But after you release trim button they return to the previous state, which causes some unintended movement.

 

Personally I find this quite annoying. I have currently stopped using the trim at all when I am trying to do something that requires precision (such as lining up an attack run). Of course I have no idea if this is how the real Hind works, but that would be really surprising to me. Essentially every time you release the trim button the AP ever so slightly screws up the stability of the helo - I can't believe that real world pilots would be happy with this. I am guessing this is either a bug or a non-optimal attempt of bringing the real Hind controls into the game world of DCS.

 

There is also a bug report for this here :

 

I’m adapting to this by reversing the trimmer depress/released functionality, for now. It provides stability augmentation without unwanted inputs. That’s fine for now, for me. YMMV.


As an experiment, and to illustrate the magnitude of what’s presently happening, try this: achieve a stable hover, using the roll/pitch/yaw channels (and hover mode if you like, or don’t, no difference). Once you’re stable enough to be hands-off, press the trimmer button as if you were preparing to make a minor adjustment. Just press the button and hold it for a sec. 😜

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On 6/18/2021 at 6:50 PM, ZeroReady said:

I don't think the Hind trim is meant to be held down like the Ka-50. It's like the Huey, you position your stick, press the button, then center your stick.

 

In helicopters you don't center the stick for "level flight", that is the PC simulators mode for the spring centering joysticks. 

 

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8 minutes ago, Moriarty said:

I’m adapting to this by reversing the trimmer depress/released functionality, for now. It provides stability augmentation without unwanted inputs. That’s fine for now, for me. YMMV.

 

I recall that I read from russian forum that the FF effects or something is inverted, so there is a bug for something. Does anyone know better?

 

8 minutes ago, Moriarty said:

As an experiment, and to illustrate the magnitude of what’s presently happening, try this: achieve a stable hover, using the roll/pitch/yaw channels (and hover mode if you like, or don’t, no difference). Once you’re stable enough to be hands-off, press the trimmer button as if you were preparing to make a minor adjustment. Just press the button and hold it for a sec. 😜

 

I need to try that. 

 

I have the springless and FF-less joystick, I get most stable control/flight without trimmer. Just place the joystick where wanted and it flies so. It can't be hold for minutes without AP as slightly off control input and you will eventually crash. But, that is where AP would be helping, to maintain the altitude, heading etc automatically. 

 

Why I don't like to use trimmer is that if each axis in joystick is 0-100%, and 50% is then the center. If I move the joystick let's say 10% to left, so it is in 40% position. And I press trimmer. The control indicator shows that the diamond jumps further left from the 40% position. Without moving joystick at all I press trim button again, it jumps again further to the left. As many times I press the trim button, it keeps jumping to the left. Of course I don't need to do it than once or twice and helicopter flips around because it is control input is like at 20%. 

The pitch is worst, move 2-3% backward (to 52-53%), and press trimmer, it might jump 15% backwards (to 65%) and press again without moving joystick and it can be with 100% full deflection. 

 

It doesn't matter is the trim button hold and released, or is it pressed, it will go haywire. This leads to situations where I might be on the level flight for landing using only "press, move and release" method through the whole flight, and I double press trimmer to reset the trimmer, and everything goes crazy because suddenly helicopter reacts to new position of the joystick. 

 

This, again shouldn't happen because I do not have centering joystick. The control indicator should always show exactly where my joystick position is relative to its axis. But that is not the case.

 

If I use trimmer, my control indicator starts quickly to show that my diamond is in the center (50% in both) for all various flight conditions. Even if my joystick physically is totally elsewhere positioned.

 

So only way to really fly is not to use trimmer at all. 

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Right on. When the trimmer button is pressed (for me, central trimmer mode) the AP channels return to center to include control surface deflections. So if I’m level in a slow forward flight for example and need to make a correction to pitch or roll, as soon as I press the button my a/c is being moved usually nose up or nose down right away before I make a stick deflection. I follow through, holding the trimmer down the whole time, complete the adjustment I want to make, release, recenter, and then the AP channels move back to where they were before anyway and take my a/c with them. With the functionality of the button reversed, I make an adjustment then give the trimmer button a quick press and release without any drama at all. Note though that this does have other consequences to the AP functionality and I don’t yet know what all of them are. It does, however, give me a functional trimmer as well as the damping I’m looking for. As the story develops, I’m sure we’re going to see a slew of changes anyway, so I don’t plan on getting too used to things being the way they are.

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The AP behavior when trim button is pressed is bugged currently, which was acknowledged by devs and few real world pilots over at the russian side of the forums.

To trim you do not need to press button, move stick, and then release it, like in Ka-50. It doesn't really matter, when you pressed the button, only when you released it. So, in this regard it should be operated just like in Mi-8 — move the stick and then click trim button.

But, at the same time, AP in Mi-8 and Mi-24 work differently. In Mi-8 AP is not connected to trim in any way, so from AP point of view it doesn't matter, whether you just moved stick into new position, or trimmed it there. In this helicopter AP will always try to correct a little towards position, in which cyclic was, when AP was turned on. To have maximum AP authority in the new stick position you need to manually adjust knobs on AP panel, so that all the bars on the indicators are centered.

On the other hand, in Mi-24 AP is connected to trim mechanism. When trim button is pressed, AP centers at this new cyclic position automatically, so it has maximum authority for compensating any possible deviation. Unfortunately, right now in the sim this process is bugged. When you press the button, AP centers on the new position, but when you release it, AP just goes back to the old position, which is incorrect. That causes helicopter to move it's nose a little towards the position, in which AP was turned on. And that's why right now trimming causes unintended movement.

So, we just have to wait for a bugfix. Hopefully, it'll not be long.

P.S. The hat-switch trim works independently of AP. It does not recenter AP, so it actually works as intended in the sim. You can use it for smoother control instead of button trim.

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48 minutes ago, VitMax said:

The AP behavior when trim button is pressed is bugged currently, which was acknowledged by devs and few real world pilots over at the russian side of the forums.

 

 

Thank you! This is great news! Unfortunately I can't read the Russian forums. I am glad to hear the devs are going to take a look at it. 🙂

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1 hour ago, VitMax said:

The AP behavior when trim button is pressed is bugged currently, which was acknowledged by devs and few real world pilots over at the russian side of the forums.

To trim you do not need to press button, move stick, and then release it, like in Ka-50. It doesn't really matter, when you pressed the button, only when you released it. So, in this regard it should be operated just like in Mi-8 — move the stick and then click trim button.

But, at the same time, AP in Mi-8 and Mi-24 work differently. In Mi-8 AP is not connected to trim in any way, so from AP point of view it doesn't matter, whether you just moved stick into new position, or trimmed it there. In this helicopter AP will always try to correct a little towards position, in which cyclic was, when AP was turned on. To have maximum AP authority in the new stick position you need to manually adjust knobs on AP panel, so that all the bars on the indicators are centered.

On the other hand, in Mi-24 AP is connected to trim mechanism. When trim button is pressed, AP centers at this new cyclic position automatically, so it has maximum authority for compensating any possible deviation. Unfortunately, right now in the sim this process is bugged. When you press the button, AP centers on the new position, but when you release it, AP just goes back to the old position, which is incorrect. That causes helicopter to move it's nose a little towards the position, in which AP was turned on. And that's why right now trimming causes unintended movement.

So, we just have to wait for a bugfix. Hopefully, it'll not be long.

P.S. The hat-switch trim works independently of AP. It does not recenter AP, so it actually works as intended in the sim. You can use it for smoother control instead of button trim.

This is exactly what I was having issues with, thank you! 

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Yes, VitMax thank you for such a helpful post explaining both the way it is supposed to work and the bug. Your explanation I think answers most of the questions that we all have been having about the trim system up to this point.

Until the bug is fixed, this also suggests that the bug’s effect can be minimized by doing frequent trimming and thus not allowing big differences in cyclic position to accrue between trimming. That would argue for doing lots of press and releases as we move the stick instead of the press move release or move press release methods that presumably most of us have been doing up to now. However, for those of us with spring sticks, having to constantly move the stick back to center after every press and release would get annoying very quickly, so I wonder if therefore we should try the default FFB option in the special options menu?

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Thank you VitMax! You did a great job explaining what the trim button is supposed to do! I’m sure this will clarify a lot of questions people, myself included, had about how exactly to use the trim button and what the AP is trying to do 

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5 hours ago, GregP said:

Yes, VitMax thank you for such a helpful post explaining both the way it is supposed to work and the bug. Your explanation I think answers most of the questions that we all have been having about the trim system up to this point.

Until the bug is fixed, this also suggests that the bug’s effect can be minimized by doing frequent trimming and thus not allowing big differences in cyclic position to accrue between trimming. That would argue for doing lots of press and releases as we move the stick instead of the press move release or move press release methods that presumably most of us have been doing up to now. However, for those of us with spring sticks, having to constantly move the stick back to center after every press and release would get annoying very quickly, so I wonder if therefore we should try the default FFB option in the special options menu?

 

OK no, I just verified that choosing 'default' makes things worse, as this option is clearly intended for FFB sticks where it is not assumed that the stick will return to center after being trimmed.  From some more testing and looking at the controls indicator, it can clearly be seen the Central Position option is most suited to sticks with springs, but by its nature it's not possible to do multiple small trims rather than one big one, since stick input is ignored until returned to center.

 

Additionally, whenever the trimmer button is released and stick returned to center, immediately upon returning to center a slight 'bump' is seen in the direction the stick was trimmed.  This must be the bug that VitMax cited and that everyone has noticed as the additional undesired movement of the cyclic after they've trimmed.  Doesn't seem to be any way around either of these problems until the bug is fixed.

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Really looking fwd to when this 'additional bump' bug gets removed from the trim system, as it is probably the most annoying thing about flying the chopper at the moment. I try to avoid any trimming as much as possible now and just fly with stick displaced, or use the trim hat to remove large displacements.

It also makes coming to a stop and engaging hover hold pretty tedious as you need a pretty much hands-off stable hover, so you hold a good hover with stick displaced then tap trimmer button and centralise stick, and it bumps past your stable hover to move off in the other direction!

So for now just stuck an 'INOP' sticker on trimmer button lol - doesn't ruin the party too much thou and still very flyable and much fun.

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1 hour ago, GregP said:

 

OK no, I just verified that choosing 'default' makes things worse, as this option is clearly intended for FFB sticks where it is not assumed that the stick will return to center after being trimmed.

 

 

Default setting works fine for spring centering sticks.    Its just depends on your "style".

AFAIK going back to the Black Shark days.

Default:   When trim is released stick inputs are "dead" for 0.5 seconds until stick inputs are "read" as normal.  (you have half a second to return the stick to center)

Central:  When trim is released Stick input is dead until the stick is returned to center.

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I own a Saitek X52, as far as I know no springs or anything else, I use joy twist as a rudder, which method should I use? Im really really confused.

I don't understand anything in russian except Davai Davai!

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15 minutes ago, Stratos said:

I own a Saitek X52, as far as I know no springs or anything else, I use joy twist as a rudder, which method should I use? Im really really confused.

Hi mate,

I use the default trimmer option in the special tab. I also trim often and in small increments. I think each person will have a different way of doing things, try a couple of the options see what works best for you. With such a small throw with an X52 over a stick with a long extension you may be best with the centre to trim method

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Default setting works fine for spring centering sticks.    Its just depends on your "style".
AFAIK going back to the Black Shark days.
Default:   When trim is released stick inputs are "dead" for 0.5 seconds until stick inputs are "read" as normal.  (you have half a second to return the stick to center)
Central:  When trim is released Stick input is dead until the stick is returned to center.

Very interesting, I stand corrected then. This is where, again, clarification direct from ED would be incredibly helpful. I seem to recall that the trimmer options in one of the other modules was changed at some point such that instead of there being the default option of 0.5 seconds to return to center, and the center trimmer method where you have infinite time to return to center, one of them was dropped to make it simpler for users. Maybe I’m wrong on that but I thought I recalled that happening.

Either way, if you’re saying the default option works for you and you have 0.5 seconds to return to center, that’s good to know and I’ll give that a try tonight.

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On 6/22/2021 at 8:22 PM, VitMax said:

The AP behavior when trim button is pressed is bugged currently, which was acknowledged by devs and few real world pilots over at the russian side of the forums.

To trim you do not need to press button, move stick, and then release it, like in Ka-50. It doesn't really matter, when you pressed the button, only when you released it. So, in this regard it should be operated just like in Mi-8 — move the stick and then click trim button.

 

You are saying that, but at the same time in the video of the real cockpit above, the guy is depressing the button each time he moves the stick, then releases it to set the stick in place.

Secondly, you have 2 ways of trimming: the button and the hat trim. IMHO the Hat trim is much more accurate...

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49 minutes ago, jojo said:

You are saying that, but at the same time in the video of the real cockpit above, the guy is depressing the button each time he moves the stick, then releases it to set the stick in place.

I'm not 100% sure, but I believe it just comes down to pilot's preference, whether to press-move-release, or move-press-release. It shouldn't have any effect on AP operation. The difference here is that when you press the button all forces on the stick are disabled, so it is not trying to move in any direction by itself. Some pilots prefer moving "weightless" stick, thus they do press-move-release, but it is not mandatory. The same applies to Mi-8, by the way. It is important for people, who use force feedback joysticks, but for anyone else there should be no difference.

Ka-50 is the different story, because it's AP is an actual autopilot, while in Mi-8 and Mi-24 it is just a stability augmentation system (I am talking about pitch, bank, yaw, and alt channels now, not about route or hover modes in the Hind). The way Mi-24 AP works is better compared to director mode of Ka-50. And in this mode it does not matter, whether you move cyclic with button pressed, or not.
 

 

53 minutes ago, jojo said:

Secondly, you have 2 ways of trimming: the button and the hat trim. IMHO the Hat trim is much more accurate...

Yes, I did mention that. And yes, it is accurate, so it's well suited for small adjustments. Also, to be honest, for now, until AP is fixed, I mostly use hat-trim even for big changes in cyclic position, as it does not disturb AP, and thus does not create any extra oscillation. It's not perfect, but it's easier to fly than with button trim.

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17 hours ago, 26-J39 said:

 

Default setting works fine for spring centering sticks.    Its just depends on your "style".

AFAIK going back to the Black Shark days.

Default:   When trim is released stick inputs are "dead" for 0.5 seconds until stick inputs are "read" as normal.  (you have half a second to return the stick to center)

Central:  When trim is released Stick input is dead until the stick is returned to center.

Default is what I use with the 0.5 second delay to re-centre, I use it on KA-50, MI-8 and Hind. I use click and release trim but I think I will try the click and hold trim method when I am back home....  I did not like it too much when I tried it 5 or 6 years ago but I will have another try. 

 

I always thought it is also related to the throw of the stick that is simulated, The KA-50 has the largest throw from Hover to 270 KPH so you gotta be fast to get the stick back to centre before it accumulates onto the new trim position... I always thought this is why the KA-50 trim was so violent.

 

The MI-8 is the shortest deflection from hover to full speed (2 diamond lengths on the joystick cheat?), this is why I think it is smoother on the trim as you can get back to centre quicker..... perhaps... maybe? Or is it just easier to hold the cyclic without feeling the urge to trim?

 

 


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Ignoring AP systems for a moment and just concentrating on basic flying and trimming;

 

Spring center stick + Central pos trimmer:

 

I don't see the benefit of the hold trim and maneuver that some people are suggesting, when you hit and hold trim you are still working on your last center point set, you can verify this by looking at the control helper. It is only when you release the trim button that a new center point is made.

 

If you trim for fast level flight and are holding trim and then doing turns , you are basically making your life more difficult as you are working against the game helper for spring center sticks. If you let go of the trimmer mid turn for example you are now stuffed as you have set a funky offset. You are increasing your work load really as before release you have to get the bird level and stable again and then let go. 

 

Once you trim for level flight (with the speed you want) if you want to turn, do the bank but don't press any trim, once you have done the turn (also with any pedal and collective movt) you should be more or less still in trim (if you maintained speed etc..), that's the point of trimming IMHO, if you are a little off when level just nudge where you need and tap trim again or you can also use the trim hat. You are free in the turn do what ever you want as when you let go of the stick (or let it go back to center) you know exactly what trim state it is going to be in with out the aid of the control display.

 

You don't always have to be in constant perfect trim, remember the trim point is just the center point you are working from. If you want to speed up a bit or drop height just hold some forward cyclic and then when you are happy release the cyclic (slowly under control) and you are back again and be more or less to stable flight (with out touching the trimmer)  You don't have to be constantly trimming, the Hind is very stable (in DCS at least)

 

To clarify I am not saying one method vs the other is wrong, what ever works for the individual, you can also do a bit of both methods.

 

 


Edited by Clogger
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Info from RL Hind manual...

 

At hovering, make sure that the main rotor RPM are at not less than 93%,
directional control forces are adequate, the pedals are not against
the stop, and the helicopter maintains a selected flight mode.
If the helicopter does not reach a selected hovering altitude, or main rotor
RPM are less than 93%, perform landing, decrease helicopter weight
and repeat test hovering.
The forces occurring on the control stick shall be removed by frequent
momentary pressings of the force-release button.

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Posted (edited)
9 hours ago, Clogger said:

I don't see the benefit of the hold trim and maneuver that some people are suggesting, when you hit and hold trim you are still working on your last center point set, you can verify this by looking at the control helper. It is only when you release the trim button that a new center point is made.

 

 

Currently the benefit is that the aircraft is actually trimmed for the attitude you released the trimmer at.

 

If you just click the button after you've established the attitude you want the AP channels (if enabled) will then go ahead and move to a different attitude depending on what kind of correction they've been in before.

For example if you were trimmed for a left orbit, then straighten the flight path and then press and release the button you'll find yourself most likely in a right turn now requiring at least one more cycle of trimming (or constantly applying stick pressure). However if you press the button before transitioning to straight and level flight from an orbit and release once you're there the APs will maintain this attitude without the need for further corrections.

 

This appears to be a bug for the Hind but is the way it is supposed to work in Ka-50.

 

This is not to say the you *always* have to hold the trim button while maneuvering, but if you intend to trim after your maneuver then it's beneficial to hold it for the entire time or be forced to re-trim again

 


Edited by Blackeye
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Aside from possible bugs in the AP. I have some experience with professional Mi-17 sim and the technique that the instructor used was always use small increments with frequent trimming (basically press trim move cyclic a bit, release and again). I used the same technique for flying the professional Mi-17 sim and I use the same technique in DCS with FFB stick. Moreover I have some time in the 17 (3 hours of flight with pattern work) and even 24 (1.5 hours) as a passenger, but was able to observe how the pilots worked with cyclic and it was again the same approach with small increments and frequent re-trimming. In my limited experience I've not seen the pilots or instructors to press/hold the trim do maneuvers and release once stable or move the cyclic in big increments without pressing the trim button.


Edited by Dr_Arrow
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  • NineLine changed the title to Trim/AP operation

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