Elevator Trim is Broken

have no problem with it, i use buttons on the right throttle, if i need push it fast i just push button then enother for correct, if i need lowest increment i just push/release it fast, if you have good axis is will not problem, but if you have 256 increments on axis, is no way to use trimmers there, trimmers very sensitive stuff, it’s cutie elevator on the elevator and use to be very precision thing, any little noise in axis, bigger increment than required, and axis will useless
p.s. ah forgot something, all aircraft have different sensitive trimmers, but all of them are sensitive, in spitfire inaccurate use trimmer can broke the back

I just thought I was a bad pilot, but every so often when I am trying to trim for level I can’t find the sweet spot- I’ve gone vertical in a 172. When I watch the elevator trim in external view I hit the trim up/down button and nothing happens. I go in cockpit and start going vertical and in external view the pitch is way out of whack. I think some of the problems developed when we lost sensitivity settings. Any new on when the next fix is due?

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One way to get around this is seperately changing the file “flight_model.cfg” for each plane.
There’s a value called “elevator_trim_effectiveness” which for most planes is “1”. Tone that down to about “0.7” and trim is far better. Unfortunately it does not work for premium planes and Carenado planes since the have encrypted files and no flight_model.cfg

Having this with an X56 HOTAS. Just downloaded the new Japan patch. Within the ‘sensitivity’ adjustment it moves nicely when using my thumb axes but within the sim there seems to be no noticeable adjustment with the trim until a given point then the trim is suddenly pitched up or down too much.

So, I found this after having some odd behaviours.

I have just rebuilt my computer - Previously, (I haven’t flown since before the Japan patch) - I was flying a bit around in hopping. Same Joystick - No issues.

Same driver versions as before, Same USB-Hub config etc.

So, I’ve reinstalled MSFS on a fresh install of Windows (New Motherboard, New CPU, New SSD) - I cannot fly at all. The Aircraft pitches horrendously to the point it starts doing loop-de-loops by itself in the sky.

It had carried my sensitivities and assignments over from my other computer via the cloud but I can’t work out what’s going on now. Even on the ground, I can see the Elevator is being ‘flung’ hard-over and the Yoke in the cockpit isn’t centring when I release the joystick.

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Many others are requesting that both the fligh-Model.cfg and "Aircraft.cfg files be be removed from the encoded .fsachive, and be there as user editable files.
I can understand that the actual visual Model could be protected from copying, but it is short sighted to not make these visible to be edited.

TO BE BLUNT.

There is a high motivation to want to have these editable.
If they continue to be hidden, there are some, that will find a way to unencode these .fsarchives and make the information public.

ie DVD copy protection etc etc

In fact, it would be very naive, to think that the .fsarchive encryption was not cracked MONTHS ago .

Please ASOBO, set a good example, and remove these 2 files from your current and future planes.

I am not condoning this, or encouraging it … its just a fact of life

BTW: You can edit the “flight_model.cfg” all you want, you will NOT be able to correct the Porpoise effect by editing any parameter, or combination of parameters in this cfg file.
The problem is elsewhere, and all you are doing in editing this file, is trying to cover up the Porpoising, by doing changes that will mess up other currently correct characteristic of the plane.

Trim performance on the C172 is way out. IRL performing a PFL with throttle to idle requires FULL aft trim to set the correct attitude with neutral elevator input to achieve the recommended 65 KIAS glide speed (best lift/drag ratio). Following the same procedure in MSFS results in a very rapid pitch up and stall!

WARNING: Complex issue - needs a LONG post to even attempt to describe it.

Continue reading at your own discretion


Not seen anyone specifically talk about how the Elevator Trim is FUDGED in MSFS (and FSX all the way back), but it might help those trying to understand some of these trim issues, to be aware of this.

The “need” to FUDGE the Trim Elevator arises because of the use of Yoke/Joystick controllers that only have spring loaded centering.

Normally, in RL, when when you apply forward or backwards pressure to the yoke, you feel that pressure and the plane changes pitch.

To maintain this pitch, you keep the yoke at the required position, and adjust trim, to remove that back/forward pressure, so that eventually, when you release the yoke, it stays where it is, in its new stable position,

But, with a spring centering Yoke/joystick, releasing the Yoke, will allow it to go back to its Spring Centered position, and not stay where a RL Yoke would be, when trimmed.

So, in MSFS, as you trim, YOU also have to be letting off the spring backpressure, so you end up with the correct trim, to mainating your desired VS, with the joystick back in it’s spring centered position.

This is NOT how you trim in the Real World, so a different trim technique is needed in MSFS, than in RL. If you fly in RL, you will need to be able to switch techniques, and always use the correct one, in your current mode ( Sim vs RL)

It could be argues that the Sim could make you develop bad trimming habits for RL piloting, but in practice, the techniques are so different, it should not be a problem to use the correct technique as you switch from Sim to RL.

Spot the BIG Difference ??
In RL, you will end up trimmed with the Yoke in a deflected position, depending on your desired VS ( as a 1st approx)
In SIM you will end up trimmed with the Yoke always back in the spring loaded centered position.

So, this is why the SIM has to “FUDGE” the trim function.

In RL, the trim tab effectively puts a force on the elevator, so that it becomes stable in the air flow at a given deflection.

In the SIM, because it cannot actually mechanically do this, it effectively has to move the elevator by an amount, equal to the amount the Yoke has moved back to the spring loaded center position. It has to do this “Calculation” .

The Visual Model will be correct-- the Elevator will APPEAR to be in the slightly deflected position, and the elevator trim tab will also appear to be in the correct deflected position, but the relationship between the Yoke and the Elevator as seen by the Aerodynamic model will have a calculated offset

I may be a little OFF with the details, but the point is, its is actually far more difficult to trim in the sim, at least untill you have developed the extra technique of slowly releasing the back pressure of the Yoke YOURSELF, as you trim.

This is not new to Simulators with Spring centering controllers, and when programmed correctly, will work in an adequate way.

A slight (?) Complication the arises for the few that have a Force Feedback yoke/joystick, that “Can” be set up to correctly move its “no pressure” stable position, and make it not the fixed “spring loaded” position.

In a ideal world, when using one of these Force Feedback devices, ( with supported trim processing), the internal Elevator rim FUDGE processing should be turned OFF, and it is not required, and is, in fact, messing up the more realistic operation that the FF Controller is capable of giving.

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STILL WITH ME ? (sorry, only a 1st draft description, it might take hours to re-write it to make it any clearer)

The 2 take ways should be.
(1) The technique you use to trim a spring loaded control is different to RL (or with a programmed FF controller)
(2) MSFS is doing an INTERNAL “Fudging” calculation, to compensate for the “spring centering controller”

Then exact details of this processing are not important,but what COULD be important is if the processing of this FUDGE is flawed, and could be contributing to Trim Instability.

The “Trim Wheel” sensitivity, accuracy, and the way hardware is doing it (wheel, or up/down buttons) “MAY” not be the issue with Trim Stability, or " Longitudinal Dynamic Stability"

There is SO MANY other things going on that could be the cause.

Final Thought.

As FF control devices are becoming more common, and their cost is coming down, it may be time for MSFS to correctly support these devices, both by incorporating the Force Feedback processing directly in the SIM (as opposed to requiring addons like FSforce, or XP force), and maybe , even if they do not put that required Force processing directly into the sim, MSFS should, at a MINIMUM, allow control of turning on/off that Sim Internal FUDGE processing of the Trim.

The Good news is that it should be so “TRIVIAL” to put in a on/off option in the menu system to turn on/off this “Fudge” Processing.

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Great post! This explained the trim issue very clearly for me and your advice about releasing the back pressure gradually as I trim the elevator works great. I’ve just achieved a perfect glidescope landing for the first time since one of the updates screwed things up for me. It really does help to clearly understand what the actual cause of the problem is and you’ve just made that extremely easy to understand. Thanks N6722C for a great post.

Thank you Grasshopper :slight_smile:
I’m more impressed that you read the whole L-O-N-G Post !!!
It should completely change your flying, with ease of trimming.

Planes FLY THEMSELVES when correctly trimmed.

An additional related gripe (bug)… Often, in several aircraft, if I switch out of Autopilot or Alt mode, the plane reacts as if the trim was severely changed and pitches up or down. I have to drastically retrim the plane. This is not normal since it was previously flying level fine.

Another point to remember is that some aircraft require manual trimming before engaging the autopilot. Otherwise, the elevator servo has to use excessive force to maintain the desired attitude. This can cause the autopilot to disconnect, or worse, it can shear the safety pin between the servo and the elevator. And if it’s not trimmed before disengaging the autopilot, expect the nose to pitch up or down when the autopilot is switched off.

But once the aircraft is flying at the Alt in the AP, trim should not drastically change when AP is turned off.

Not true for all aircraft. Most autopilots do not trim aircraft with a manual trim tab system.

Since I’m not a “real” pilot (but a simmer for decades)… how then does an aircraft like that affect Alt changes? Through an automatic yoke adjustment?

The CT has a pushrod between the stick and elevator, a manual cable-operated trim tab, and a servo attached to the pushrod. The servo simply moves the pushrod, which moves the elevator, so maintaining the desired altitude or vertical speed. Trimming before engaging the autopilot minimizes the forces on the servo. If, for example, you trim at cruise speed and slow down, the servo has to put more and more force on the pushrod to maintain level flight. Eventually, it will disconnect itself before damaging the servo, and the nose will pitch down, as it was trimmed for cruise. The same thing will happen if you manually disengage the autopilot. Aircraft with electrically-operated trim controlled by the autopilot don’t have this problem.

Interesting – and it gets even more complex when MSFS is primarily catering for Spring Loaded, fixed center returning controllers …
Then I believe, the MSFS trim is achieved by making the push rod "adjustable in length " by the MSFS’s trim control ??

If the AP is on, how do you know if the Plane is still Trimmed, before turning the AP Off ???

The trim wheel has a little pointer on it, which shows the position of the trim tab.

So you need to learn and remember various trim settings for differing configurations (along with power settings) … so you go straight there, rather than keep hunting ??