no bug Trim button problem

[miromurin]

Hello, 

I realized trim button doesn't work properly. When I press trim button, it always overtrim when autopilot channels are switched on. It is most visible on Pitch AP channel. I have to switch off Pitch channel AP when I am slowing down for landing because it overtrim too much

[admiki]

3 hours ago, miromurin said:

Hello, 

I realized trim button doesn't work properly. When I press trim button, it always overtrim when autopilot channels are switched on. It is most visible on Pitch AP channel. I have to switch off Pitch channel AP when I am slowing down for landing because it overtrim too much

What is your stick and what is your trim mode?

You have to trim often

[miromurin]

It has nothing with my stick. I have Hotas warthog and this is the only helicopter I have this problem with. Problem is only when autopilot channels are ON. I use default trim mode (instant trim) on all my helicopters. maybe it is more autopilot problem than trim problem.

Edited December 28, 2023 by miromurin

[AeriaGloria]

1 hour ago, miromurin said:

It has nothing with my stick. I have Hotas warthog and this is the only helicopter I have this problem with. Problem is only when autopilot channels are ON. I use default trim mode (instant trim) on all my helicopters.

It it’s realistic, the trim resets the attitude hold of the autopilot. Let’s say you turn on AP on ground, becuase nose angle is +3.5 degrees it holds that attitude. When flying you pitch down to -5 degrees, and pitch AP gives nearly full authority to fight this and bring you back to +3.5 degrees. You are then fighting pitch AP to books that negative angle

 When you press trim button, AP deflection goes to 0. You release trim button and now it wants to hold current nose attitude of -5 degrees. That means the AP your were fighting to hold -5 degrees is gone, and your forward stick is too much now

 So you kinda have to remember that when you trim, you are also telling pitch/roll AP what attitude you want it to maintain

 Solutions are

 1. trim after every major attitude change

2. hold trim button while you manuever before releasing trim, when holding trim pitch/roll AP will be nuetral

 3. trim multiple times to get rid of the “jumping”

I do a combo of methods 1 and 3 personally

[miromurin]

4 minutes ago, AeriaGloria said:

It it’s realistic, the trim resets the attitude hold of the autopilot. Let’s say you turn on AP on ground, becuase nose angle is +3.5 degrees it holds that attitude. When flying you pitch down to -5 degrees, and pitch AP gives nearly full authority to fight this and bring you back to +3.5 degrees. You are then fighting pitch AP to books that negative angle

 When you press trim button, AP deflection goes to 0. You release trim button and now it wants to hold current nose attitude of -5 degrees. That means the AP your were fighting to hold -5 degrees is gone, and your forward stick is too much now

 So you kinda have to remember that when you trim, you are also telling pitch/roll AP what attitude you want it to maintain

 Solutions are

 1. trim after every major attitude change

2. hold trim button while you manuever before releasing trim, when holding trim pitch/roll AP will be nuetral

 3. trim multiple times to get rid of the “jumping”

I do a combo of methods 1 and 3 personally

So why Mi-8 doesn't have same issue?

[AeriaGloria]

3 minutes ago, miromurin said:

So why Mi-8 doesn't have same issue?

Mi-8 has different trim system, its trim button doesn’t interact with AP at all. The only way to set the attitude the AP holds in Mi-8 is to turn it on at that attitude or use adjustment knobs 

When designing Mi-24 the Mil bureau realized why not combine the job of the engineer in resetting the AP channels to be done by just pressing the trim button, which the pilot needs to do often. Ka-50 does the same thing 

[miromurin]

thank you for reply

[AlphaOneSix]

Well, the Mi-8 knows how much you move the cyclic, so anytime you move the cyclic, the attitude setting changes, too. Without hitting the trim button.

[AeriaGloria]

Yeah, and improving on Mi-8 which only moves the attitude hold with the cyclic based off where the cyclic was when autopilot turned on (cyclic when turning on AP = 0 movement, any movement from there moves AP with cyclic), the Hind trim button also resets this. 

So while if you turn AP on in hover in Mi-8, and transition to fast forward flight without messing with it, it will think you are wanting it to dive rather then hold that attitude as your cyclic is now more forward of where it was initially. And be giving left input thinking you’re trying to roll left (since cyclic needs to move left as speed increases). 

So with the trim button on Mi-24 you can both tell AP “I want to hold this attitude,” but also “this is where the center of my cyclic is right now, and if I move it from here then I actually want to manuever in that direction.”