Trim/AP operation

[AeriaGloria]

14 hours ago, River said:

I know what you mean by now, that doesn't change the fact that the Hind kicks uncontrolable at certain situations. I don't buy that we have to trim in small increments only, neither do I believe we have to hold the trim button pressed during a maneuver. 

If you hold trim pressed you get the wobble at the beginning (AP disconnects) and not on the exit when you release.

Tell a RL Mi 24 pilot he only can trim in small increments and / or keep pressing the trim button till he has done his maneuver. He will have a good laugh.

And no Hind kicks up or down after trimming IRL, it's dangerous and not correct. 

The AP in DCS should reset to the current attitude after trimming but it still uses the attitude before trimming. Reading this is already weird and wrong. 

 

  You are saying that after trimming it does not reset attitude in DCS, but it does. If you got that information from this thread, then I’m afraid it’s outdated. This behavior was fixed about 6 months after release, and since then pressing trim will absolutely change attitude hold to your current attitude. And you can verify this by pressing R control + enter, press that key combination then trim, and you will see the AP spindles reset to 0 then deflect to hold that attitude if you maneuver.

You say that RL pilots would Laugh at pressing the trim a lot? It’s exactly what the manual says……Even in Mi-8 videos you can here pilot pressing trim constantly. 

Here is three excerpts from a Mi-35P export manual (This is a South American export that only differs to our Mi-24P in RWR, radios, UGP gun pods, and NVG compatible lighting).

Section 2.7.4, this and it’s following section is titled “Horizontal Flight.”
it says “The roll channel of the autopilot should be periodically centered by momentary pressings of the force-release button on the control stick.”

2.7.5 “make sure that the movable index of the indicator of the channel Pitch is near neutral position and, if required, return it to this position
by pressing the force-release button”

Section 2.3.5 “The forces occurring on the control stick shall be removed by frequent momentary pressings of the force-release button.”    This part itself is repeated about a dozen times!!!!

So per this manual , You only press it after you are done changing attitude and WANT to reduce stick forces/reset AP.
 

  Going through this manual again, it actually doesn’t mention trimming in a turn. Just to frequently release forces from the stick to keep it trimmed in level flight at a certain speed. And just turn with cyclic deflection. In a Mi-24A/D flight manual I did see holding trim going into a turn to make it turn hands off, but I’m sure that’s up to the pilot depending how long they plan to turn and how much they want to push the stick
 

  So no I don’t think you are intended to hold the trim for every manuever…. It might make things smoother if you are trimming, but Whatever you prefer and works best for you.
 

  For me what works best is I usually just trim 2-3x at 5-7 degrees nose down at cruise speed, and leave the trim there unless CG/speed changes a lot, such as needing to trim for nose up when landing. I only press trim maybe 6-9 times for an entire 1 hour flight unless I’m being really picky…… and that’s including pressing trim 2-3x to get rid of the jump/jerk when the AP goes to zero.  Once I’m trimmed for level flight in cruise speed, I just do any manuevers I want manually with no trim and no that when I release cyclic heli will try to correct itself. I don’t need trim much until I land and stop flying at cruise speed. 

   Ka-50 does the same “jump/jerk,” when you press Trim the attitude hold goes away, if the attitude hold was making a large input you end up with a jerk. That’s why people have the method of holding it while maneuvering. But as you can see from the manual excerpt I posted, it also says “momentary” pressing. So this export Mi-24P manual doesn’t say to hold trim while maneuvering, only to frequently trim in level flight to hold a specific speed/heading/attitude. Nonetheless you can hold trim if you want……

  Some features work well in real life but when simulated in a game can come off awkward or make you wonder “why would they design it like that?” But that’s circular reasoning to ask “this is dangerous they would never design it like that so it must be wrong.” Lots of things make you ask that in DCS! It doesn’t necessarily mean it is wrong! 

  Nothing is perfect in real life either, this is a big upgrade In AP over Hip, and you can tell it was still further improved on the Ka-50 becuase when you press trim in Ka-50 the attitude hold goes away like Mi-24, but you still have dampening to smooth out any movement. 
 

  I mean hell, the autopilot was designed in 1972 or even earlier! People love how Soviet aircraft have rough edges and can be tough to handle sometimes, people brag about their MiG-21 trying to kill them! It’s certianly not perfect. I mean hell this year the autopilot is turning 50 years old!
 

   One of the many documents I have used to build my conclusion that I can share, is the Mi-24D Cold War Musuem manual. It is mostly for D, with addendums for V/P, but it doesn’t matter becuase Mi-24D/V/P/VP and even Mi-35M all use the same autopilot/trim/flight control. The relevant section is highlighted.

  If you are interested in reading the rest, here you are, https://mudspikefiles.s3.dualstack.us-east-1.amazonaws.com/original/3X/7/a/7ab064a7f951b9f0325354f257f5e58c571936d6.pdf. There is not many real life material that is free to share on ED forums about Mi-24, but this is one.

With these real life sources, I hope some issues are put to rest 

 

Edited October 26, 2022 by AeriaGloria

[MelonatorPL]

Is there any news about this issue from the devs? Its starting to really annoy me since the autopilots keeps adding uncommanded imputs when trimming.

[admiki]

7 hours ago, MelonatorPL said:

Is there any news about this issue from the devs? Its starting to really annoy me since the autopilots keeps adding uncommanded imputs when trimming.

Sorry to say, but this is not a bug.

One thing people flying in simulators keep forgeting (unless they have FB sticks) is that most of the helicopters have stick centering force (centering as in trim center, not physical center). So, you flying without presing or holding trim release means you are fighting that force all the time (same thing as most of the people fighting springs in "normal joystick").

Mi-8 doesn't work as Hind, yet look at this video and listen how much pilot trims out, even without doing big attitude changes

@BIGNEWYI suggest that you guys aks your SMEs about this and either confirm it works as expected or it doesn't.

Edited December 24, 2022 by admiki

[AeriaGloria]

22 hours ago, MelonatorPL said:

Is there any news about this issue from the devs? Its starting to really annoy me since the autopilots keeps adding uncommanded imputs when trimming.

  Everything works correct, and matches the description from a real life manual I posted above your post. Since pressing trim makes AP reset to 0, if AP is giving a lot of input when that input goes always it can cause a sudden “jerk.” 
 

  Is that what you mean? If so, it does work that way. And is why real life manuals suggest to trim frequently, or hold trim. I personally just trim 2-3x to make sure that I am maintaining that attitude with my AP as close to 0 as possible. 
 

If not, please describe the issue you are experiencing 

This thread was started shortly after release, then trim did not work correct. Trim would make it go to 0 but it would go to where it was before instead of resetting the attitude hold. A few months later a patch fixed it to work correctly and have trim properly reset AP to 0 when pressed. So that specific issue the thread was started for is resolved 

Edited December 24, 2022 by AeriaGloria

[MelonatorPL]

So the issue that I found is that if you press the trimmer and let go while the autopilot is adding a medium to large amount of input the autopilot resets during the press (as it should) and after letting go it goes back to the pre trimmed position causing the nose for example to rise by up to 5 degrees when slowing down. Is the autopilot supposed to stay in the centered position after letting go of the trim and not adding any further input to the controls or is it supposed to do that uncommanded input?

 

@BIGNEWYI suggest that you guys aks your SMEs about this and either confirm it works as expected or it doesn't. 

^^^^

Please do

Edited December 25, 2022 by MelonatorPL

[admiki]

5 hours ago, MelonatorPL said:

So the issue that I found is that if you press the trimmer and let go while the autopilot is adding a medium to large amount of input the autopilot resets during the press (as it should) and after letting go it goes back to the pre trimmed position causing the nose for example to rise by up to 5 degrees when slowing down. Is the autopilot supposed to stay in the centered position after letting go of the trim and not adding any further input to the controls or is it supposed to do that uncommanded input?

 

@BIGNEWYI suggest that you guys aks your SMEs about this and either confirm it works as expected or it doesn't. 

^^^^

Please do

 

Since most people are using joystick with springs, all that I will write further down is for center trimmer option in special settings. A lot of it applies to instant trim, but in-game behaviour is different.

One thing you need to remember is that Hind AP, for the sake of this example, is not a holding mode system. It means it can't get you back to where you were. It fights only rate of change.

So, you are flying level, all trimmed out. AP is centered . You pull back on the cyclic to slow down. Your nose rises. AP commands nose down input to stop it from rising. Remember, it can't get you back to level, AP just stops motion. You stabilise in that new position. So, your new position is a result of cyclic inputing nose up and AP inputing nose down. Press trim.

Pay attention to where the nose is when you press it and where the nose is when you release the trim. Your nose will rise when you press the trim and it will continue to rise when you release it due to your cyclic still giving back input, but AP now being centered and not counteracting it. Once AP starts  giving nose down input, nose will stabilise in its new, higher position. As far as AP is concerned, this is exact same situation from previous paragraph. 

Use cyclic to push nose back down and you'll see that once you are at same position where you were when you pressed the trim, AP will go to center. Remember that back cyclic input from two previous paragraphs? It's gone now, so AP doesn't need to fight it.

Try to press and hold trimmer. Once you stabilise in your new position, release the trim and you will see that nose doesn't rise (for example above) and AP is centered. Why? Because, in this case, your new position is a result of only cyclic input, not result of cyclic and AP fighting each other. Basically, this means helicopter stays in this position because it wants to, not because AP commands it so.

Yes, holding trim will cause you to lose SAS part, but with some practice it's not a big deal. I can fly whole flight without even having AP turned on and you won't notice a thing.

 

People have problems with holding trim because most of the time they forget to press it before they move from trimmed position and once they do, they lose that AP input and helicopter starts to depart from them. If you press it before you move, there will be no AP input to lose in the first place and helicopter will respond only to your commands.

Even with center trimmer option, it is important to remember that your cyclic will go dead only after you release the trim, not while holding it, so holding trim is possible.

Edited December 25, 2022 by admiki

[MelonatorPL]

Ok that helps me in understanding it thanks. Ill start using it more similar to how I use the ka50 with trim. I tried this method beofre but I didnt expect it to be the proper way of using it due to the disengagement of the sas system during the press. thx

[Schlomo1933]

Am 18.6.2021 um 12:53 schrieb Fri13:

IMHO the trim works as centering trim. If you apply 20% left for level flight and press trim, you will apply 20+20% trim, why you roll to left. You need to physically move joystick to center for AP to apply only required 20% trim.

 

So even if you select "non-centering joystick" for trim, you need to center the joystick for proper trimming.

 

Hence, do not use trim button but just adjust joystick on wanted position and AP automatically takes it from there.

This is not correct! 
 

especialy your last sentence. The trim-hat is just for fine Tunning .

If anyone uses center trim option. The new trim position is just applied after trim release when the stick is back at center. 

but what Blackeyed is mentioning is: 

the Pitch and Roll channel are trying to hold the Hind in a specific position. So the channels have now a specific % of input.
If the pilot try’s now to accelerate or decent. He will push the cyclic forward. 
Maybe 35% as an example. 
the Pitch Chanel has an autorithy of 15%.

So in the moment the pilot push the cyclic forward , the Ap is counteracting. (Because the Ap tries to hold his last given attitude) So the pilot needs to push with 50%. 

When the Pilot now tap the trimm button. The Ap is cancelling his last given attitude and resets his Chanel’s to 0%.
This follows that the Pilot is pushing 15% too much at this moment. The Hind will overreacting.

 

That means : You need to push and hold the Trimmer BEFORE u make a change with the cyclic. 
The Ap will reset to 0. Then u will push the cyclic till the Hind is in the Attitude the Pilots wants. And the release the trimmer.

 

THE MI-8 works different.  The  pilot in the middle seat will adjusting the Ap-Chanels. There is no automatic Autopilot.
 

(I don’t know the exact percentage of AP Authoritie. I believe it’s between 15 and 25 % , but this doesn’t matter in my example)

Edited September 7, 2023 by Schlomo1933

[JAPman]

In the case of using the FFB stick with Instant trim, when the trim button is pressed, the cyclic simply transitions to the center at that angle, which is easy to understand.

At the time of the release of the 32-bit DCS-BS ver1.0.0, there was no other option but Instant trim. This is effectively a configuration for the G940, which Logitech developed simultaneously for the BS, and which is difficult to use with common spring sticks. Central Position Trimmer mode for spring centered sticks was added in ver1.0.1.

The trouble for me is setting up the pedals. Basically the same as for sticks, owners of FFB pedals, which are probably a minuscule number, should choose Instant Trim, and Central Position Trimmer mode for spring-centered pedals. If you have a pedal with a damper and no spring, or if you are like me and use the rotary on the throttle as the pedal axis, select Do not trim. I came to this understanding through trial and error.

In the trim mode of the stick, there is an item Without spring and FFB. I have not yet tried it to see what the behavior would be if I remove the spring from my stick and use only the damper.

Hind is good to be able to adjust trim with HAT.