Curiousity about trim & AP channel authority

[Sulman]

I recently changed flying technique to use the 'hold' trim method. To recap, this is the technique of holding the trim button, completing a maneuver, and then releasing when stabilised.

 

For newcomers, holding the button cuts out the roll, yaw and pitch AP channels until it released, whereupon they attempt to maintain the new attitude.

 

The biggest advantages for me have been in the following areas:

 

 

• Rapid, smooth control during aggressive maneuvers such as threat evasion or shoot & scoot.
  

 

• Accuracy in coordinated flight: Turns for me are now much, much smoother. More on this later.
  
• No more rubber-banding / hunting in the aircraft handling.
  
• Very, very seldom have to reset trim now.
  

This is opposed to the published procedure of dabbing the trim frequently and progressively, whenever stabilised in attitude & configuration, thus updating the AP channels very frequently with updated attitude info. I've been flying the Shark using the old method for ages, but I wanted to try this after being unhappy with a lack of smoothness, for want of a better word.

 

One thing I have observed is, having the channels disengaged (while trim is held down) allows the aircraft to settle more easily, particularly coming out of turns onto a new course. This was my greatest area of difficulty with the standardised trimming method - I simply found coordinating turns very difficult, and flight seemed sloppy and - on some occasions - nearly out of control, with a rogue yaw input being a common culprit.

 

So, very basic anatomy of a turn, with AP channels and conventional trim technique: Beginning, middle, end.

 

 

• Beginning: You have to break AP authority and roll the aircraft, whilst starting to coordinate on the rudder.
  

 

• During: monitor attitude and coordination, trim optional, but it's dynamic and very rarely stable so I usually live with the control forces. Adding trim tends to get me into more trouble than it's worth.
  

 

• End: Roll out gently, manage inevitable sideslip, stabilise on new heading.The aircraft slowly slips back into AP authority, at which point FCS will attempt return to the previously trimmed attitude and heading. This normally happens just before you would trim the new attitude in, so: Rubber-banding. A solution is to 'snatch' the trim at the correct heading, but this isn't particularly elegant; it feels wrong.
  

Now, this got me thinking about the 20% control authority. Before trim'n'hold, when rolling out of a turn, capturing heading could be tricky because the finer my control inputs got, the closer they were to the AP's authority, which I think is where the rubber-banding comes in. The obvious answer is to trim, thus updating the FCS, but then you are trimming in a transient control input, and asking for trouble, as you are compounding the problem. Also, how much of the captured control inputs upon updating trim are from fighting the previous FCS trim?

 

I found (with the old technique) it very hard to avoid trimming in unnecessary rudder, because you have to leave a little in to prevent the AP from pulling it back once you have your desired attitude. By contrast, with the trim held down the aircraft tends to settle on a new heading, and it is perfectly possible to have the controls reasonably centred before releasing the trim.

 

It seems odd (I am careful not to say 'wrong') to me that - upon being practiced at flying the helo - a few maneuvers are easier without the AP channels interfering. For sure, you can skid a little bit more, but counteracting this is intuitive and smooth - try a textbook pedal turn with AP channels babysitting for contrast - so, is it my technique, or is anyone else seeing this? I think it's telling that the Trim tutorials (videos and such) seem to only deal in pitch - which is relatively easy to get the hang of - and very hand, especially at low speed. Turns are a whole different ballgame; coordination requires smooth, gentle input and I never seem to achieve this when having to trim,trim,trim during a turn.

 

I know we lose out a lot not feeling the control forces and being stuck with (in my case) a self-centreing stick, but I do wonder if the AP is a little 'grabbier' than it needs to be?

 

Not complaining at all, just curious what people's experience has been. It's not changed my Shark experience that much, but has certainly made my flying a little more consistent in that I am now totally confident I can perform certain maneuvers quickly.

Edited January 26, 2011 by Sulman

[zdXu]

Would be nice to see your flight-technique in a track:

for example in the first deployment-campaign ( http://www.youtube.com/watch?v=i5GUegbC6_E )

or in the second Vergeev Campaign (mission-download => http://files.digitalcombatsimulator.com/en/172/ ).

Both are familiarization missions and non-arcade missions.

 

To my knowlege most of the guys with more flight-expierences use this "hold-trim -> turn -> release-trim"-technique. So you are not alone. One of the biggest issue of that technique is IMO the helicopter reacts during the trim too complacent (because thats the way how the Flight-Director-channel works).

Edited January 26, 2011 by zdXu

[Smokin Hole]

As long as we are posting techniques, mine is:

 

1- Before taxi/hover - FD ON

2- oh, there is no two

 

The only time FD comes off (AP ON) is during hands-off flight (autohover, route holding, turn-on-target).

[Sulman]

Would be nice to see your flight-technique in a track:

for example in the first deployment-campaign ( http://www.youtube.com/watch?v=i5GUegbC6_E )

or in the second Vergeev Campaign (mission-download => http://files.digitalcombatsimulator.com/en/172/ ).

Both are familiarization missions and non-arcade missions.

 

To my knowlege most of the guys with more flight-expierences use this "hold-trim -> turn -> release-trim"-technique. So you are not alone. One of the biggest issue of that technique is IMO the helicopter reacts during the trim too complacent (because thats the way how the Flight-Director-channel works).

 

I'll try and make some at the weekend.

 

As long as we are posting techniques, mine is:

 

1- Before taxi/hover - FD ON

2- oh, there is no two

 

The only time FD comes off (AP ON) is during hands-off flight (autohover, route holding, turn-on-target).

 

The holds work best for me during the low speed regimes. It's at higher speeds I find them a little funny. I was trying some pedal turns last night just to compare, and they're perfectly achievable with the channels on, but I really dislike the 'springy' feeling that the controls have. Being able to follow through on the cyclic (without centreing it after every trim) is a huge advantage for smooth control in FD / Trim held mode.

 

The other thing is, the holds can be a nuisance because they are so inflexible. Again, the lack of feel and actual helo controls is really the problem. I'm sure in the real cab you would notice a lot more through your eyes, controls, and that other great sensor, your backside.

 

In FD mode, the aircraft settles to straight and level much, much faster IMO, it's worth it for this alone, otherwise you really need to fiddle on the trim to the extent it's distracting. I hold the trim in for a little bit when I'm on heading, let the cab settle (even allowing a little weathervaning) and let the trim out. Doing it in short stabs doesn't seem to work for me.

 

I read AlphaOneSix's comments about the hold system in the Mi17, and it seemed a much more sensible arrangement, in that it backs off the moment it detects pilot intervention. I wonder if the KA50's FCS autoflight channels are a little more sophisticated than modelled, outside of a heavy-handed hold system.

Edited January 27, 2011 by Sulman

[Zaarix]

Hi Sulman, after reading this article: http://www.simhq.com/_air13/air_428a.html I have found that a combination of "hold-trim -> turn -> release-trim" and what I call "progressive maneuver trimming" works very well for stability and quick response situations.

 

My technique for progressive maneuver trimming is: from any current stable flight attitude(ie: the ground, a hover, or forward flight) to begin by holding the trim and moving the controls to achieve a new attitude in the direction desired and then release the trim and watch that the heli continues as expected. As soon as I notice the the flight path is starting to "wander" I hold the trim, adjust the controls and again release the trim. This is continued constantly as the variables change.

 

For example: If at a hover and I want to begin forward movement, I hold the trim, push the nose forward to 15 degrees, and release the trim. Once picking up speed the heli will start to veer. I then hold the trim and adjust slightly and release the trim. Its like saying "hold this until I say otherwise," but the advantage is that the corrections stay minor and flight is kept smooth. I can always use direct stick input on top of the trim if I need it immediately.

 

You can also do this in turns. Hold the trim, start the bank, and release the trim. As the turn progresses and the wind direct and speed change adjust the trim again or just use the stick to keep what you're looking for. Once you are getting to the heading you want hold the trim, level out and release the trim again. It will start to feel much more relaxed with time and practice.

 

As for hold-trim -> full-maneuver -> release-trim: Since holding trim stops all auto-input, if I need to leave in a hurry I can hold it down indefinitely, though it rarely seems necessary to do that. I can see the danger, hold the trim and start very quickly way from the unwanted situation, and release the trim to continue in that direction. This is a much more gross movement "go-right-now" technique.

 

The thing to remember is that trim holds attitude for the variables at the time set. The further way from those variables you get the more unstable the trimmer changes are going to seem. If you trimmed at takeoff with a crosswind, full tank, and all weapons. When you get to the target area and have launched a few missiles the original trim isn't going to mean the same thing, specially if you aren't facing the wind the same way.

Edited January 27, 2011 by Zaarix

[Henchman14]

The best thing to do is trim constantly.

[Sulman]

The best thing to do is trim constantly.

 

Within the context of the simulator, why would you assert that? Any particular advantages? Do you find it smoother?

 

I'd say within the limitations of desktop controllers and the lack of feel, holding the trim and letting the aircraft stabilise works better for me.

[average_pilot]

Within the context of the simulator, why would you assert that? Any particular advantages? Do you find it smoother?

Still, the idea is not having to control the craft every second. If you hold de trim you are flying it and can't do much more. If you trim often, in theory, between trims the thing is flying by itself giving the feeling of less workload to the pilot.

[Bucic]

If you're curious than try to crack this one (warning: troubleshooting only, no instruction content there) :sly:

Central position trimmer problem

my video: http://forums.eagle.ru/showthread.php?p=987363#post987363

 

Mine and some others' tracks are posted in that topic.

 

 

Bucic, I'll give you my own procedure, perhaps you can avoid the 'bump' this way?

(Sorry, I havent watched your vidoes or anything)

 

Assuming you have all damper channels aneabled except. And no FD.

1. Before I commit attitude change, press and hold trimmer.

2. Perform attitude change. Keep trimmer pressed.

3. Wait until the chopper 'settles' in the new direction. Still Holding the trimmer.

4. Controls center & chopper settled - release trimmer within a 0.5 second of centering the controls.

 

This way I counteract any yay / oscilations at the end of the manouver.

All that energy needs to settle and I have to smooth out the transition so the AP can cope with the new attitude.

 

PPS, if there's alot of manouvering, several changes one after another, I wont release the trimmer until I've established a path I can hold.

This means, sometimes, I can end up with trimmer pressed for 2-3 minutes when avoiding missiles and such.

 

 

The bottom line is many things I've read point out that the trimmer in DCS BS does not work as the trimmer in real Ka-50*.

 

 

*) where controls construction and operation differences between game controls and real controls are irrelevant.

Edited January 28, 2011 by Bucic

[jazjar]

I remember my first good, quality, coordinated turn in the KA-50. I had actually got the aircraft in a careful, coordinated straight flight with the help of AP, ( work with, not against it ;) ) then depressed the trim button and turned to the right with the help of the rudders, and I nearly cried out in joy, because for the first time in two years of owning Black Shark, I actually had control over the turn! I then steadied my self out on a reciprocal bearing to the one I had just been on, and reengaged AP. This was after two years of flying combat missions where I basically forgot I had such things as rudders, and didn't bother to trim the aircraft at all. My flying was sloppy, and my closest thing to a over was at a speed of around 20 km/h, and I could barely aim my Vikhrs properly. That occasion which I just described didn't occur again because Vista crashed, and my copy of DCS BS won't install properly on Windows 7.

[Sulman]

I remember my first good, quality, coordinated turn in the KA-50. I had actually got the aircraft in a careful, coordinated straight flight with the help of AP, ( work with, not against it ;) ) then depressed the trim button and turned to the right with the help of the rudders, and I nearly cried out in joy, because for the first time in two years of owning Black Shark, I actually had control over the turn! I then steadied my self out on a reciprocal bearing to the one I had just been on, and reengaged AP. This was after two years of flying combat missions where I basically forgot I had such things as rudders, and didn't bother to trim the aircraft at all. My flying was sloppy, and my closest thing to a over was at a speed of around 20 km/h, and I could barely aim my Vikhrs properly. That occasion which I just described didn't occur again because Vista crashed, and my copy of DCS BS won't install properly on Windows 7.

 

It's enlightening to fly flight director or trim held just to understand what the hold channels do. The biggest mistake I made was actually trimming too frequently, or before the cab really settles. Flying just with dampers on makes you realise how long the cab can take to settle out of inertia.

 

Also, it is just downright difficult to fly sometimes.

[kingpinda]

I've been playing this sim on and off from release but I still have to find a way to decently trim... I have the G940 HOTAS from logitech and its forcefeedback. I have some issues when trimming that my rudder trims also and when the rudder trims it will be multiplied by 2. So I have 100 procent more rudder than when i started to trim...

 

I'm using a command someone long ago posted so it will reset the rudder after trim. that way when it notices my feet i only have to wiggle a tiny bit so the sim rudder will be in the same position as my feet are.

 

The only downside is: With this modified trim command I can't hold trim! because it will register: Trim pressed, Trim depressed, z,x pressed.

 

So when ever i hold trim it will automatically follow the command and the command will be executed in a few milliseconds no matter how long I hold the trim button.

 

Anyone have any tips or insights how to overcome this? I just want to be able to use trim like its supposed to be used without my rudder going full left when I trim with half left rudder.

[power5]

I have a 940 as well. I think this is the same with any rudder pedals. When you trim, just press the x,y button to recenter your rudder position after releasing the trim button. Its not perfect, and I would love FFB pedals but this works for me just fine. I had the same issue using one of those suggested fixes, but my trimmer kept clicking like I was releasing even while pressed. This exacerbated the problem because now my rudder doubled every time the trimmer clicked even though I was still holding the button, the short script was cycling. I did not look into how to fix it, just went back to a quick rudder tap after releasing trim. Rudder is the same affect as recentering a non ffb stick. You must recenter immediately after releasing trim. I usually fix my attitude so that rudder is not needed before trimming.

[kingpinda]

Hmm yeah i might try flying like that. So i take it whenever you do a turn: You hold down trim, use cyclic to turn maybe throw in some rudder, ease out of turn get your new heading, centre rudder and then trim release?

 

I'll try practicing with this.

 

BTW before 1.01 came out this was being discussed *somewhat* :

 

Quote:

Originally Posted by lion737

The easy fix for the rudder trim is not adressed ???? (Option to disable rudder trim for non-centering pedals - especially in combination with FFB stick, where you don´t need to center after trim) :helpsmilie:

 

 

In 1.0.1 user can adjust neutral position ("dead zone") separately for pitch, poll and rudder (in parts of full scale). So, if you set HelicopterTrimmerZoneRudder = 1.0 - you don't need to return pedals in center at all.

 

The above answer was from USSR_Rik - ED Team

 

 

I've tried this today but no effect. Weird that USSR_Rik would comment with this while this has NO effect whatsoever on FFB Joysticks.. At least not that I noticed.