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Old 10-31-2017, 06:37 AM   #1
PeaceSells
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Default For those who trim by tapping the trim button

Hey,

I'm learning the Ka-50 and, man, what a pleasant aircraft to fly... so smooth! I want to get proficient in controlling it in all different modes: autopilot on, fight director on autopilot off.

Been reading a lot about the trim lately, as well as watching Youtube videos and experimenting with it. I now understand how the Ka-50 trim works, and the question I have is related to using the trim with autopilot ON and flight director OFF, and is independent of whether you use an FFB joystick, conventional joystick or joystick without springs and FFB (I use conventional stick with springs, btw).

Here's the deal: you have autopilot ON and flight director OFF, you move your joystick to a new position, (let's say slightly FWD), stabilize it and tap the trim button. In a time span of a few milliseconds, the following sequence of events happen, as I understand (please tell me if I understand something wrong):

1) upon pressing the trim button, autopilot stabilization gets turned off;

2) without autopilot, your FWD input gets amplified, even though you're still holding the stick at the same place and even though it's during only a few milliseconds;

3) upon releasing the trim button, the new amplified input gets saved and fixed by the flight control system, and autopilot gets re-engaged holding this new amplified input;

4) aircraft pitches down noticeably instead of holding the pitch you originally intended when you pressed the trim button.

Now I'm able to work around that by moving the stick while I keep the trim button depressed, and releasing the button when the aircraft is pointing where I want. But as I read the forums I see that many people trim by simply tapping the trim button. Doesn't it bump your aircraft slightly out of position when you do that? How exactly do you trim by tapping without getting this effect?

Thanks for your input!
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Old 10-31-2017, 07:25 AM   #2
Penshoon
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Crick trimming only works smoothly when re-trimming from a relatively small speed difference.

You can't be trimmed for a hover -> push stick forward to accelerate to 200 kph, then trim. The helicopters nose will violently pitch down when you depress the trim button as the autopilot was using 20% back stick to try to get you back to previously trimmed speed (hover) but when you depressed the button that 20% back stick force goes away instantly = nose drops.

What you want to do is either hold down the trim button while accelerating/decelerating to whatever speed you want then release it or click the trim button every 10-30 kph you gain/loose to reprogram the autopilot to new speed before it starts using more than a few % of it's authority.
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Old 10-31-2017, 09:42 AM   #3
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Using the original trimmer option (not central) there is a time-based blending of the new input. With practice one can relax the input back to spring-neutral at the same rate to avoid any significant upset. If desired this value (tau, a common time constant Greek letter) can be lua-edited. The effect can be seen by the controls indicator.

Stabilization is always on when the channel button-lights are shining. The hold input (the thing that FD disables) is suspended (read: frozen) during trim button hold.

The tap method is no problem. You deflect the stick and hold it until the maneuver stabilizes and tap with a practice relax motion.
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Old 10-31-2017, 10:17 AM   #4
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I use default trimming mode. And I’m a click’n’hold pilot. It’s a lot smoother.
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Old 10-31-2017, 12:24 PM   #5
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PeaceSells, as it happens I too have tried to wrap my head around this issue as late as last night, with the same experience.
Especially when trying to establish a steady turn with AP on the nose drop.
Also if I let go of my cyclic after first trim click, and then press T repeatedly on my keyboard the nose drop slightly every time.
If I use the press'n'hold technique the nose tend to rise at release after established steady attitude.
Flight Director mode work, so does the Huey and Mi-8 trim.

I fly with a "without spring and FFB" stick, but have also tried a FFB one (spring removed) with the same fesult (FFB settings all correct and working otherwise).
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Old 10-31-2017, 01:54 PM   #6
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Quote:
Originally Posted by Penshoon View Post
Crick trimming only works smoothly when re-trimming from a relatively small speed difference.

You can't be trimmed for a hover -> push stick forward to accelerate to 200 kph, then trim. The helicopters nose will violently pitch down when you depress the trim button as the autopilot was using 20% back stick to try to get you back to previously trimmed speed (hover) but when you depressed the button that 20% back stick force goes away instantly = nose drops.

What you want to do is either hold down the trim button while accelerating/decelerating to whatever speed you want then release it or click the trim button every 10-30 kph you gain/loose to reprogram the autopilot to new speed before it starts using more than a few % of it's authority.
hmm, it seems I have to practice more with this clicking method.

Quote:
Originally Posted by Frederf View Post
Using the original trimmer option (not central) there is a time-based blending of the new input. With practice one can relax the input back to spring-neutral at the same rate to avoid any significant upset. If desired this value (tau, a common time constant Greek letter) can be lua-edited. The effect can be seen by the controls indicator.
I have no problem with relaxing the input to neutral in time when using the original (Default) trimmer option, I used this method a lot in the Huey before. Now I discovered the Center trimmer option and it eliminates this problem 100%, as it waits until you've actually returned your joystick to center before it accepts any new input from you.

Quote:
Originally Posted by Frederf View Post
Stabilization is always on when the channel button-lights are shining. The hold input (the thing that FD disables) is suspended (read: frozen) during trim button hold.
Yes, you're right. When I said "autopilot stabilization gets turned off" during trim button hold, I was actually trying to say "autopilot input hold gets suspended" during trim button hold. My mistake...

Quote:
Originally Posted by Frederf View Post
The tap method is no problem. You deflect the stick and hold it until the maneuver stabilizes and tap with a practice relax motion.
The issue I'm specifically referring is not the relax motion back to the joystick center, it's what happens immediately before that: the "autopilot input hold" gets suspended even if you tap the trim. I expected this to happen only when you press and keep pressed the trim, but I was wrong.

Quote:
Originally Posted by Holton181 View Post
If I use the press'n'hold technique the nose tend to rise at release after established steady attitude.
Flight Director mode work, so does the Huey and Mi-8 trim.

I fly with a "without spring and FFB" stick, but have also tried a FFB one (spring removed) with the same fesult (FFB settings all correct and working otherwise).
What trimmer mode did you choose under the "Special" tab in the "Options" screen of DCS?
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Old 10-31-2017, 10:10 PM   #7
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Quote:
Originally Posted by PeaceSells View Post
hmm, it seems I have to practice more with this clicking method.
Good thing it's fun helicopter to practice in!
Try out Holbeach's mountain slalom mission in this thread: https://forums.eagle.ru/showthread.php?t=167089 It's a nice course for practice in any helicopter module with hard turns, elevation changes and low power lines to squeeze under as fast as you can.


Quote:
Originally Posted by cordite View Post
I thought force trim was unnecessary with dedicated heli controls. I'm still not clear on why it would be needed.
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Originally Posted by Holton181 View Post
"unnecessary" might be the wrong word. It's about springs and breaks holding the controls in place but in the same time causing uncomfortable forces for the pilot to fight against, so you need to be able to disable them when needed. Many real life helicopters do have it.
Ordinary joysticks with springs also benefit from it for the same reason.
But dedicated helicopter simulation controllers in general don't have any means to keep them in place, and often not possible (or at least difficult) to balance in center position. So you can't really take advantage of triming in that respect. But it is still usable to get the cyclic in a more comfortable position for your hand.
It totally depends on the helicopters designer but in general in light and early made helicopters you wont find force trim systems and many pilots dislike them in these air frames if they are installed due to interfering with small balancing movements on the cyclic.
Bigger and more modern ones do mostly fly with a force trim system on all the time with some type of SAS/autopilot. With a force gradient on the controls they can be designed with a lot more advanced autopilot systems like on the ka-50 that makes hands off flying possible.

There are some sim equipment manufacturers do real trim in dedicated heli sim cyclics like this but I have no idea where you can buy or how much it would cost...

Last edited by Penshoon; 10-31-2017 at 10:14 PM.
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Old 11-01-2017, 01:59 PM   #8
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Quote:
Originally Posted by Penshoon View Post
Good thing it's fun helicopter to practice in!
Try out Holbeach's mountain slalom mission in this thread: https://forums.eagle.ru/showthread.php?t=167089 It's a nice course for practice in any helicopter module with hard turns, elevation changes and low power lines to squeeze under as fast as you can.
Yes it is! Cool flying btw, I saw that video from you (and the Huey one too) many months ago!

Question: what's that knocking sound in the video? Is that you clicking the trim button?

EDIT: Never mind, I just saw the answer in the Youtube comments, that's the trim button...

EDIT 2: New question: it makes the sound both when you tap it AND when press and hold? Do you remember if the sound is produced when you 'press' or when you 'release', or both?
Question 3: I see you have autopilot on and flight director off... are you using 'route mode' or 'normal' autopilot?

Thanks for your input!!
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Last edited by PeaceSells; 11-01-2017 at 02:20 PM.
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Old 11-01-2017, 04:50 PM   #9
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Quote:
Originally Posted by PeaceSells View Post
Yes it is! Cool flying btw, I saw that video from you (and the Huey one too) many months ago!

Question: what's that knocking sound in the video? Is that you clicking the trim button?

EDIT: Never mind, I just saw the answer in the Youtube comments, that's the trim button...

EDIT 2: New question: it makes the sound both when you tap it AND when press and hold? Do you remember if the sound is produced when you 'press' or when you 'release', or both?
Question 3: I see you have autopilot on and flight director off... are you using 'route mode' or 'normal' autopilot?

Thanks for your input!!
Yeah its the trim button, it makes a click both when you first depress it and then when you release it, there is a tiny sound difference between them. I believe first click in the video is from pressing trim reset button though. Like 90% of the video I'm holding down the trim button to get FD controls behaviour.
Normal autopilot is on, no route mode.
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Old 10-31-2017, 02:16 PM   #10
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"joystick without springs and FFB" (or whatever it's called) for my PFT Lynx (non-FFB) with rather high friction applied for the cyclic to keep it in place.

"default" and "force feedback" checked under whatever the tab is called for my Cyborg Evo Force (FFB) with centering spring removed.
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