Stab trim feature

[davierosoft]

Hi!
I wrote on the general section of the forum, but, as it is a wish, I write it also here!

I'd like to have a stab trim feature added for bigger airplanes.
A selectable option like this:


This option simply enables both FS and FSforce trims, with a selectable FSforce trim clicks.
This will let our joystick to follow the stab trim movement of the bigger aircrafts, where by moving the stab trim also the column will be re-centered. This movement of the column is very low (compared to stab trim movement) but is present. It could be adjusted as needed by the trim rate option.
Shift key could be used in this mode to move only FSforce trim to eventually re-center the command witout touching FS trim

Apart of that, it could be awesome also if it is possible to add a feature for hydraulic pumps if there is an option inside FS. This can be used to add maximum forces when hydraulics are OFF.

A third wish, but is mostly a dream, an autopilot function that lets the joystick/yoke moves with the AP engaged.


What do you think, are they possible?

[RussDirks]

Well the problem is I don't understand your explanations of the features you want. Maybe a few questions will help. First, do you have actual experience flying large aircraft with stab trim?

This will let our joystick to follow the stab trim movement of the bigger aircrafts, where by moving the stab trim also the column will be re-centered.

This is where I start losing you. What you seem to be describing is essentially what the default FS trim system already does, and which is so unrealistic in aircraft with trim tabs. Are you saying that when the pilot is having to exert force to keep the yoke where he wants it, he makes trim adjustments, which not only relieve the control pressure, but also demand that he make corresponding movements of the yoke back to center, and if he doesn't get it just right, the aircraft wobbles up in down in pitch? (What I'm describing is the default FS trim system with a mechanical joystick). I don't know why you would want a trim system like that. Or maybe I just don't understand your explanation.

If you do want a trim system like that, just disable FS Force and use the default FS trim system, because that is what it does.

Shift key could be used in this mode to move only FSforce trim to eventually re-center the command witout touching FS trim

I don't understand any of this, especially when you say "re-center the command". What command are you refering to?

A third wish, but is mostly a dream, an autopilot function that lets the joystick/yoke moves with the AP engaged.

But you can move the joystick when the AP is engaged! Nothing happens of course, but you can move it. Maybe you mean that you want to be able to move the joystick and have it be effective in changing the pitch of the aircraft, essentially overriding the AP?

If you want me to implement features, you have to describing them accurately, especially since I have never flown a large jet with a stabilator.

[RussDirks]

Well, after doing some Google searches and doing some reading, I have come to realize you are probably referring to an aircraft that has a trimable stabilizer, as opposed to a stabilator. When you referred to "stab trim" I just assumed "stabilator". The only thing I know about stabilizer trim is what I've read on Google in the last 15 minutes, so we'll have to see where this goes.

[davierosoft]

Yes, stab trim is Stabilizer trim.
I work on boeing 737, CRJs and Emb 170/190 series as an avionics technician.
Essentially it is used on liners, but also on few medium planes.
Example are boeings, CRJs, airbus (but here we enter in fly by wire discussion that is different). In few words, every aircraft where the CG can change too much with load/speeds and cannot be adjusted only by elevator movements needs a movable stabilizer to balance te plane in all conditions.
In this kind of airplanes the stabilizer is moved by an electrical or hydraulic actuator (normally rotating a jackscrew).
The stab trim movement is completely indipendent to the elevator movement except for the elevator centering that artificially changes when trim is moved.
Here a video of the 737-200 trim:
http://www.veoh.com/watch/v382244KFJh32DJ
In the video the centering cannot be seen, but it is present. It is part of the system.

To better explain, when I trim nose down, the stab trim moves, but in the same time the control column start to follow the new surface center.
As the 2 surfaces are independent, there is a system called "artificial feel and centering unit" that moves the center of the column when trim is used.
FS speaking the artificial feel and centering is your FS force, the stab trim is the FS trim. On the real one, they works together.
Why the centering changes? Basically because changing stabilizer angle changes also elevator angle, and second, the aircraft protect itself in case of runaway condition (stabilizer uncommanded motion) by adding more elevator control on the opposite side of where the trim is.
I think I'll make some drwaings... I'm unable to explain better.
About the AP wish, what I was telling is something like that:
http://www.youtube.com/watch?v=7NurOOfmts0

Joystick that moves itself following autopilot.

I'll do a drawing for the stab. trim and will post you soon

[davierosoft]

The movements are a bit exagerated, but it is just to explain.
As you can see, when stab trim moves, the elevator follows it, to be centered also the elevator must change its center.
Now, back to the menù picture I did:
By selecting the Stab trim (Stabilizer trim) voice you activate both FS and FSforce trim,
The next field for trim click amount will be avaiable to select how much the elevator moves following the stabilizer.
On some planes Autopilot moves automatically the stabilizer to automatic trim the aircraft, in this mode you will lose the original FS vs FSforce centering, so SHIFT key could be used to inhibit the FS trim and let us to re-center manually the command. A better way that prevents this is to lock the movement with FS trim setting (example: fs trim 0 = column centered, fs trim 1.5, elevator moves to the relative setting...) This will match always both, with or without autopilot.

About feel and centering, as you probably seen in my previous topic, I posted already the best setting avaiable for 737 NGX that includes centering forces active from ground when aircraft is parked.
Most of the big aircrafts have a centering system that is always avaiable.
These kind of plane uses hydraulics to move commands, if not flybywire, they will be harder to move when hydraulics are off.
Don't know if such a feature could be added as every add on can use a different way to simulate hydraulics. I don't know if there is a common FS command to do it.

[RussDirks]

Thanks for the link to the training video. That was quite interesting. Can't promise anything regarding new features at this point. Will keep you posted.

[davierosoft]

Thanks Russel!

[BorisTheSpider]

I second this suggestion. Stab trim would be great, all that is really needed is for fsforce to trim via the fsx trim system, but simultaneously move the ffb stick some proportion (say 20%) of the amount that has been trimmed, so if you trim the amount that would normally put the stick all the way on the back stop, it actually ends up slightly aft of the neutral position.

Making that percentage user configurable would be best, then you could test in the actual sim airplane, and set it up so that full back-stick was reached at the most aft position of the stab trim.

[mikkel]

Did this eventually get into the software or is it still pending? Or did another solution come up?

[warning232]

Hi there, im a fsx customer of fsforce and trying out P3D.

How is this feature going?? Would be a great addition.