Autopilot disconnect

[wingnut]

In earlier versions of FSUIPC there was an option to maintain elevator trim upon AP disconnect. That doesn't seem to be the case with the later versions. My problem is that upon disconnecting the autopilot just before touchdown, the aircraft (FSX) nosedives into the ground. The same thing will happen if the AP is disconnected while in level flight. Is there a way to overcome this?

[Pete Dowson]

In earlier versions of FSUIPC there was an option to maintain elevator trim upon AP disconnect.

Was there? That's news to me. Why would it need to? The AP uses trim to trim the aircraft, so when it is disconnected the trim should be set as needed for that situation.

Maybe you are getting mixed up with these facilities, neither of which does what you mention, mainly because there's no way to "maintain elevator trim" without leaving it where it is -- in other words it maintains itself in its own position.

DisconnTrimForAP: When this option is enabled, FSUIPC disconnects the analogue elevator trim axis input to FS whenever either the FS autopilot is engaged in a vertical mode (altitude hold or glideslope acquired), or a program, gauge or module has disconnected the elevator axis via FSUIPC (offset 310A).

Note that the setting can be overridden for specific aircraft which have specific FSUIPC joystick calibrations by setting this parameter differently in that [JoystickCalibration …] section.

ZeroElevForAPAlt: controls the option for FSUIPC to automatically centre the elevator input each time the Autopilot altitude hold mode is changed (switched on or off, including AP engaged changes too). This option can be operated inside FS on FS2004, but if needed on earlier versions must be enabled in the INI file by setting this parameter to “Yes”.

Note that the setting can be overridden for specific aircraft which have specific FSUIPC joystick calibrations by setting this parameter differently in that [JoystickCalibration …] section.

That doesn't seem to be the case with the later versions.

I never withdraw facilities unless they are impossible or unreliable. I really think you are thinking of something else, especially as what you ask is simply not needed -- FS doesn't change the trim when you disconnect the A/P.

My problem is that upon disconnecting the autopilot just before touchdown, the aircraft (FSX) nosedives into the ground. The same thing will happen if the AP is disconnected while in level flight. Is there a way to overcome this?

Are you using an analogue trim axis? If so you'd need to make sure its position agrees reasonably closely to the A/P set trim position. In my cockpit that's done by the A/P motor controlling the trim wheel, but without motorised trim you'd need to try to do it manually. Really, if the trim axis is stable it shouldn't change the trim position set in FS. However, since you will not doubt need to make some trim adjustments subsequently you'd still need to keep it in a reasonably close place to the A/P's setting.

Regards

Pete

[wingnut]

Thanks Pete. I'm using a rocker switch on a CH yoke for elevator trim. It's more than that though. The problem is that upon AP discon I have to pull way back on the yoke to maintain trim. It's almost impossible to get it right and end up floating along the runway or gaining height! I didn't have this problem in FS9 after I checked off a box in FSUIPC. Can't recall which box it was. Maybe there is something in the aircraft cfg. file?

[Pete Dowson]

Thanks Pete. I'm using a rocker switch on a CH yoke for elevator trim. It's more than that though. The problem is that upon AP discon I have to pull way back on the yoke to maintain trim. It's almost impossible to get it right and end up floating along the runway or gaining height! I didn't have this problem in FS9 after I checked off a box in FSUIPC. Can't recall which box it was.

Well the only options related to trim or elevator position are still in FSUIPC3 and also in FSUIPC4. Maybe experimentation will find the right option for you?

But I still can't understand how the trim is so far out from A/P use - the FS A/P uses trim to do its job, so it just MUST be correct. Are you sure it isn't an add-on aircraft doing its own thing, without using trim? If so, your FS trim might be left however it was last time you used it. What happens if you use your rocker to get a load of nose up trim BEFORE releasing A/P?

Pete

[n10669-Mark]

Hello, I'm having the same problem as talked about above. Whenever I have the autopilot engaged I can barely touch my Pro flight Cessna trim wheel and the plane starts climbing about 200 fpm but it will come back to the correct altitude. When I disconnect the A/P everything stays stable untill I move the trim wheel and then I get the same thing. After getting the plane back under control everything is fine. I've tried the two options under the misc. tab both off and on and all the combos with no results. This happens on all planes. Pete, in your post above you mention making sure the trim wheel is resonably close to the indicator, or at least thats the way I'm reading it, but that doesn't help because it happens even with the A/P engaged. I have 4.827 installed.

Thanks Mark

[Pete Dowson]

Hello, I'm having the same problem as talked about above. Whenever I have the autopilot engaged I can barely touch my Pro flight Cessna trim wheel and the plane starts climbing about 200 fpm but it will come back to the correct altitude. When I disconnect the A/P everything stays stable untill I move the trim wheel and then I get the same thing.

Sounds like the trim wheel is not set to do trim inc/trim dec adjustments. If it is programmed to operate the trim axis and it is NOT motor controlled, then it probably will not be in the correct position -- i.e. its position will not match the actual trim position in FS. This doesn't matter if you don't move it, as axes are not read until moved. But as soon as you move it, the actual setting for the wheel position is immediately applied, resulting in a sudden trim change.

Really the only satisfactory way of having a trim wheel operate through the trim axis control is to have it motorised so that is always goes to the currently set FS position when the A/P adjusts it, or when you load a new flight.

If you persist with the wheel operating the trim axis, you will be okay for purely manual flying, without using the Autopilot. You should start off each flight by adjusting the trim wheel till the trim indication in FS is centred. Then use the trim wheel for all in-flight trimming. The problems will only arise when you start using the A/P.

in your post above you mention making sure the trim wheel is resonably close to the indicator, or at least thats the way I'm reading it, but that doesn't help because it happens even with the A/P engaged.

The A/P is using the trim. Operating the trim axis whilst in A/P vertical control modes will interfere. The only way you can stop that is to disconnect the trim axis whilst the A/P is so engaged. If the axis is assigned through FSUIPC then you can disconnect it by setting bit 5 in offset 310A. That needs repeating every few seconds otherwise it is re-connected (to safeguard against crashed or hung programs causing loss of controls). So it would need a little Lua plug-in. Something like:

function stoptrimaxis()
   if ipc.readUW(0x07BC) ~= 0 then
	  ipc.setbitsUB(0x310a, 32)
   else
	  ipc.clearbitsUB(0x310a,32)
   end
end
event.timer(5000, "stoptrimaxis")
event.offset(0x07BC, "UW", "stoptrimaxis")
[/CODE]

Save that in the Modules folder as, say, "trimoff.lua" and add an [Auto] section to the FSUIPC4.INI file containing

[Auto]

1=Lua trimoff

I have 4.827 installed.

You need to update. The currently supported version is 4.853.

Pete

[n10669-Mark]

Thanks Pete, I did update last night after posting here. Can I program the wheel to Trim inc/Trim Dec adjustments in FSUIPC? I think I do have it programmed now to the trim axis.

Mark

Edited September 7, 2012 by n10669-Mark

[Pete Dowson]

Thanks Pete, I did update last night after posting here. Can I program the wheel to Trim inc/Trim Dec adjustments in FSUIPC? I think I do have it programmed now to the trim axis.

Yes, you can, but it still isn't straight-forward -- there's still a Lua plug-in needed. Please see this thread from not so long ago:

Covert Axis to buttons - without ranges

BTW, as an addendum to my previous reply, I did of course omit to mention that FSUIPC already has the facilities built in, i.e.

DisconnTrimForAP: When this option is enabled, FSUIPC disconnects the analogue elevator trim axis input to FS whenever either the FS autopilot is engaged in a vertical mode (altitude hold or glideslope acquired), or a program, gauge or module has disconnected the elevator axis via FSUIPC (offset 310A).

Note that the setting can be overridden for specific aircraft which have specific FSUIPC joystick calibrations by setting this parameter differently in that [JoystickCalibration …] section.

ZeroElevForAPAlt: controls the option for FSUIPC to automatically centre the elevator input each time the Autopilot altitude hold mode is changed (switched on or off, including AP engaged changes too). This option can be operated inside FS on FS2004, but if needed on earlier versions must be enabled in the INI file by setting this parameter to “Yes”.

Note that the setting can be overridden for specific aircraft which have specific FSUIPC joystick calibrations by setting this parameter differently in that [JoystickCalibration …] section

So that Lua plug-in wasn't needed. I clean forgot about those options -- I should have re=read the earlier part of this thread (as perhaps you should have too? ;-) ).

Pete

P.S. I have a feeling this question wil be appearing more and more often, so I've now pinned the answer as a thread in the FAQ subforum.

[n116dh]

Mr. Dowson,

First, please let me start by thanking you for your generous support of your most excellent product.

Since this post is related to trim control I thought I would add to it instead of creating a new one. I have been using FSUIPC with WideFS for sometime now and found many answers to my questions in this forum. However, I could use some help in seeing if my "solution" for the inherent trim control issue with flight sim is feasible.

I use RealTrim in conjunction with FSUIPC (latest version downloaded and installed last week) in an attempt to better provide trim control. I find it most handy to do "gross" trimming with RealTrim, especially during takeoffs and approaches. With RealTrim, one assigns a button to the RealTrim module (not used by FSUIPC) and when pressed it disconnects the FSX trim control and allows one to move the yoke back to center position all the while adjusting the actual trim (in effect "relieving the pressure) and then release the button. It works fine most of the time, but alas, it doesn't provide for the finer control needed to maintain pitch at a constant. At the same time, I also have a Saitek lever assigned to the trim axis in FSUIPC and I use that for "finer" trim control (aircraft.cfg elevator_trim_effectiveness reduced significantly).

As you can probably surmise, when using RealTrim and then switching to the FSUIPC assigned lever for finer control, the values for the lever are not synced with RealTrim and sometimes using the lever causes great abrupt change in the trim and thus aircraft control and I wind up chasing the VSI.

My hope is that I can use RealTrim to continue to do "gross" trimming and then use the FSUIPC axis as a trim wheel (trimwheel.lua) and to have an additional FSUIPC button toggle assigned to disconnect the lever assigned trim access so I can trimstop() to "center" the "trimwheel" axis (as it isn't really a wheel, and using the triminc() and trimdec() functions I can see the lever getting max'ed/min'ed out and need to be "centered") and when released, reactivate trimwheel().

I have researched your posts on "trimoff" and "trimwheel" LUA scripts and tried to get RealTrim to work with FSUIPC, but alas I can't seem to get the "trimwheel" and "trimstop" LUA functions to work with the FSUIPC trim lever and RealTrim button.

About the only thing I have struggled with in flight sim for years is the pesky trimming especially during takeoff and landing. If someone sold a motorized trim wheel at a reasonable price I would probably buy it, but I don't think any of them are.

If any of this makes sense, would you have any insight for this. Brutal honesty is perfectly acceptable.

Thanks for your interest and response.