Elevator trim too aggressive

[jojo]

@Zabuzard

Thats something I would like to be sure about.
You say that the Phantom needs to be trimmed constantly.

But in landing configuration, at slow speed with +/- throttle inputs (to control the glide path) causing pitch changes and the trim being so coarse, it seems better to trim roughly OK and then handle AoA around neutral position with manual pitch input on the stick rather than with the trim on many other jets.

Would that be the correct technique to handle it ?

So far, small inputs on the pitch trim to try to release stick pressure seems to do more bad than good.

[Dragon1-1]

Electronic trim being rather coarse is a known issue that extends even to modern trim systems. Some aircraft provide analog controls that allow more precise trim, but IRL this is apparently something most pilots simply live with. I haven't flown the Phantom enough to have a landing technique that I could share, but trimming it roughly on AoA and then correcting with stick pressure might work. Do not try to relieve stick pressure completely, just keep it roughly in the center. You'll be constantly making corrective inputs, anyway, since pitch and power are linked.

[GregP]

On 5/30/2024 at 6:06 PM, YSIAD_RIP said:

Another Solution and or temporary workaround is to include some new * slow * keybindings for Trim that is 0.25 instead of 1. 

• I am using @Quaggles excellent DCS Input Command Injector Mod. 

This works perfectly and is exactly what I was looking for!  Thank you so much for posting it.  

[Goofy12]

@Zabuzard would you happen to know if the developers are looking into an option to make the trim input less aggressive? Although I love flying the Phantom, I still think the trim is too coarse.

Edited September 2, 2024 by Goofy12

[Nealius]

Same. It's impossible to use trim while tanking. 3-4 taps of trim and the nose refuses to move. 1 tap of trim the opposite direction and it's like those 3-4 taps are immediately applied opposite the direction they were supposed to go. 

[Zabuzard]

2 hours ago, Goofy12 said:

@Zabuzard would you happen to know if the developers are looking into an option to make the trim input less aggressive? Although I love flying the Phantom, I still think the trim is too coarse.

We are.

But we want to emphasize that the current behavior, according to our knowledge, is exactly how the F-4E Phantom behaves in real life. All of our SMEs confirmed that we nailed its annoying pitch trim behavior.

Trimming in the Phantom does not move the stick directly. Instead, it changes the length of the lever with which the bellows apply their force on the stick. Which in itself is dynamic as well, as they scale their force based on speed. And then there is also still the bobweights pulling on the other side of the stick. Also with dynamic force, this time based on G.

Trim is extremely dynamic and its behavior essentially changes whenever you just slightly touch throttle or stick. The trim system IRL needed multiple reconfigurations until the test pilots even considered it okay to fly with. Eventually they accepted it.

Edited September 2, 2024 by Zabuzard

[Goofy12]

1 hour ago, Zabuzard said:

We are.

But we want to emphasize that the current behavior, according to our knowledge, is exactly how the F-4E Phantom behaves in real life. All of our SMEs confirmed that we nailed its annoying pitch trim behavior.

Trimming in the Phantom does not move the stick directly. Instead, it changes the length of the lever with which the bellows apply their force on the stick. Which in itself is dynamic as well, as they scale their force based on speed. And then there is also still the bobweights pulling on the other side of the stick. Also with dynamic force, this time based on G.

Trim is extremely dynamic and its behavior essentially changes whenever you just slightly touch throttle or stick. The trim system IRL needed multiple reconfigurations until the test pilots even considered it okay to fly with. Eventually they accepted it.

 

first of all many thanks for your quick reply and explanation. I do not question the behaviour of the sim at all, I do understand that the F-4 needs constant trimming. I have flown aircraft irl that needed your thumb on the trim constantly. So its not the actual amount of trimming you need to perform, its the sensitivity of the trim. I often find myself overshooting the equilibrium by just one click of trim, to then have to trim the other way and overshoot again. Now, this probably also has to do with my setup, no doubt. It just would be nice if I could dumb down the sensitivity of my “one click of trim” by, say 80% of what it is now. 
Now….I hear you think…..this would take away from the realism….well…..I don't think so, see in real life I can feel the stick-force getting lighter as I trim, unfortunately my stick doesn't have this feature, so to mimic the same flyability, I’d have to give up a bit of realism to get the same effect. Hope this makes sense.

Anyways, on a final note…..what a superb module you have all build, just love flying it!…..many thanks! 

[=475FG= Dawger]

Flying with the trim is a bad idea and a bad habit. Amazing it has become acceptable to some irl, apparently. 
 

Phantom trim seems fine to me. Seems like a normal jet. 

[Goofy12]

2 hours ago, =475FG= Dawger said:

Flying with the trim is a bad idea and a bad habit. Amazing it has become acceptable to some irl, apparently. 
 

Phantom trim seems fine to me. Seems like a normal jet. 

Care to explain yourself? If I want to fly 450kts level, I’ll have to trim to keep it level at 450kts. If I want to keep level at 500kts I once again have to trim to keep it stabilized at that speed and level. So you fly level at a certain speed with continuous control input?…..hope you dont find that acceptable irl.

[Zabuzard]

That is indeed the reality for a F-4E Phantom. It makes large oscillations around the trimmed position, even when trimmed out perfectly. It will roughly keep you there and prevent you just going down if you go heads down, but it wont allow you to fly straight hands off. (In case unclear, make sure to only tap the trim button, dont hold it. It is operated by multiple short taps and should not be hold down.)

But again, we are indeed looking into possibly giving a less sensitive trim command. Especially for people who use hardware that has a minimal signal duration that is not low enough for quick taps. Some sticks let you adjust that in their configuration, but not every product has this. We have seen reports from people who, after adjusting that in their stick configs, had a much better experience with the trim in-game as their stick stopped holding down the trim command for too long despite them already releasing it physically.

Edited September 2, 2024 by Zabuzard

[=475FG= Dawger]

54 minutes ago, Goofy12 said:

Care to explain yourself? If I want to fly 450kts level, I’ll have to trim to keep it level at 450kts. If I want to keep level at 500kts I once again have to trim to keep it stabilized at that speed and level. So you fly level at a certain speed with continuous control input?…..hope you dont find that acceptable irl.

Trimming for a speed or attitude isn't flying with the trim.

Flying with the trim is using the trim to move the control surface from one place to another.

If you are constantly trimming while tanking or flying close formation or some other precision task, you might want to re-evaluate your technique.

[Goofy12]

21 minutes ago, =475FG= Dawger said:

Trimming for a speed or attitude isn't flying with the trim.

Flying with the trim is using the trim to move the control surface from one place to another.

If you are constantly trimming while tanking or flying close formation or some other precision task, you might want to re-evaluate your technique.

…and thats exactly what I mean, whenever I try to trim out for a certain speed I overshoot the right setting, even by a small click. I never said I flew the trim, thats what you apparently read into it. 

[=475FG= Dawger]

20 minutes ago, Goofy12 said:

…and thats exactly what I mean, whenever I try to trim out for a certain speed I overshoot the right setting, even by a small click. I never said I flew the trim, thats what you apparently read into it. 

Change the power. 

It all works together.

Edited September 2, 2024 by =475FG= Dawger

[Goofy12]

….that would result in a trimmed out state at a different speed. 

[=475FG= Dawger]

3 hours ago, Goofy12 said:

….that would result in a trimmed out state at a different speed. 

not in level flight.

 

[Raven (Elysian Angel)]

3 hours ago, Goofy12 said:

….that would result in a trimmed out state at a different speed. 

He's right though, and it's what I have been doing since the Phantom released: use trim to get as close as possible to hands-off level flight as you can, then make the final adjustments with throttle.
That will indeed change your speed but for low-effort formation flying it works very well. And I don't have issues with IFR.

[Hiob]

1 minute ago, Raven (Elysian Angel) said:

He's right though, and it's what I have been doing since the Phantom released: use trim to get as close as possible to hands-off level flight as you can, then make the final adjustments with throttle.
That will indeed change your speed but for low-effort formation flying it works very well. And I don't have issues with IFR.

That‘s the way!

Guys need to fly helicopters more to appreciate the use of power for fine trim. 

Perhaps a new perspective does help. Imagine flying at a stable attitude (speed and altitude constant). Now change either one, trim or power - what is the result?

[Nealius]

21 hours ago, =475FG= Dawger said:

If you are constantly trimming while tanking or flying close formation or some other precision task, you might want to re-evaluate your technique.

The Phantom may be an exception here, but constant trimming in formation/tanking is standard practice IRL. The difference with other aircraft is that the trim input results in a consistent and predictable output. In the Phantom it's inconsistent and unpredictable. 

Edited September 3, 2024 by Nealius

[Andrew8604]

On 9/3/2024 at 7:38 AM, Nealius said:

The Phantom may be an exception here, but constant trimming in formation/tanking is standard practice IRL. The difference with other aircraft is that the trim input results in a consistent and predictable output. In the Phantom it's inconsistent and unpredictable. 

 

Maybe right here is where we need a real-life Phantom pilot to tell us:  During inflight refueling in the real F-4, for instance, once you got trimmed in the rendezvous with the tanker, matching speed and holding relative position...when you moved in for the basket or the boom, would you ever touch the trim again?

[Tmi]

2 hours ago, Andrew8604 said:

Maybe right here is where we need a real-life Phantom pilot to tell us:  During inflight refueling in the real F-4, for instance, once you got trimmed in the rendezvous with the tanker, matching speed and holding relative position...when you moved in for the basket or the boom, would you ever touch the trim again?

Yes, this would be interesting to hear!

[Nealius]

It would be. I have a hard time understanding how the Blue Angels ever flew this thing with any precision at all. I understand they have a history of making modifications, but with the description of how the trim/bellows/wizardry works, it sounds like any modifications would be rather limited. 

[Andrew8604]

On 6/3/2024 at 3:20 PM, kablamoman said:

 

As depicted on the chart, we see this exact same oscillatory behavior on the aircraft itself when returning the stick to neutral:

 

 

 

I tried to replicate this problem, and I couldn't.  Although, I see now that you were probably pulling 4 to 6 G's when you did it.  I was only 1-2 G's.  So, I'd have to test it again.  I don't think I would normally use the trim while pulling G's, but perhaps others and real pilots might.  I looked with the same view while tapping the trim several times nose-up and nose-down and the stabilator behaves pretty conservatively, only deflecting a few degrees (by my estimate).  Even holding the trim for a half-second didn't produce any wild excursions of the stabilator like in your video.  Tested from 500 KIAS clean, down to about 160 KIAS with flaps and slats...it behaved well, no more than a few degrees deflection in response to clicks of the trim hat-switch.

I don't know why it's doing this for you and others.

What was the source of the data of your graph?  I wonder what your joystick output is really sending to the sim?

[Zabuzard]

3 hours ago, Andrew8604 said:

Maybe right here is where we need a real-life Phantom pilot to tell us:  During inflight refueling in the real F-4, for instance, once you got trimmed in the rendezvous with the tanker, matching speed and holding relative position...when you moved in for the basket or the boom, would you ever touch the trim again?

What I can tell you is that our SMEs (who are real life F-4 pilots and WSOs) are quite happy with how the trim system feels and works. Happy as in "correctly modelled", not as in "easy to use"

I understand that you might prefer hearing it from them directly, as well as getting details of the procedures and perhaps someone will also respond

[kablamoman]

10 hours ago, Andrew8604 said:

I tried to replicate this problem, and I couldn't.  Although, I see now that you were probably pulling 4 to 6 G's when you did it.  I was only 1-2 G's.  So, I'd have to test it again.  I don't think I would normally use the trim while pulling G's, but perhaps others and real pilots might.  I looked with the same view while tapping the trim several times nose-up and nose-down and the stabilator behaves pretty conservatively, only deflecting a few degrees (by my estimate).  Even holding the trim for a half-second didn't produce any wild excursions of the stabilator like in your video.  Tested from 500 KIAS clean, down to about 160 KIAS with flaps and slats...it behaved well, no more than a few degrees deflection in response to clicks of the trim hat-switch.

I don't know why it's doing this for you and others.

What was the source of the data of your graph?  I wonder what your joystick output is really sending to the sim?

These were pulls of the stick, meant to show that when returned to center, the virtual pilot’s arm has been modelled in such a way that it’s as if they are letting go of the stick entirely (in the non-FFB stick implementation). This results in the stick and stab rebounding and oscillating around the trim neutral point, as if the pilot’s arm isn’t itself part of the system and there to damp it.

To be clear, I had no problem with the coarse actuation of the trim last time I tried it, and the aircraft I fly currently requires similar, short clicks of the trim switch for fine adjustments. I think it’s smart of them to add an option for fine tuning the actuation duration for each command, as some joystick software may be holding the input longer than the physical press of their real-life switches.

The point of my post in here was to point out that there are other more fundamental problems with the way they’ve decided to model the stick response in pitch that underlie the system and may make it seem extra sloppy when trying to trim. Indeed, you will see it wobble a bit with every change in pitch even when trimming — this may be accurate behavior if one makes the assumption that the pilot is flying hands off or with fingertip pressure, but not if they’re actually gripping the stick. The devs seem to have assumed that whenever your non-FFB stick is centered that you don’t want to apply any grip pressure to actually fly the plane, whether trimming for level flight (the nose bobbling up and down a bit could be considered a minor annoyance when trying to trim), or aggressively maneuvering (more of a problem, as shown in the video).

Edited September 5, 2024 by kablamoman

[450Devil]

I have found this thread fascinating to read. From some testing I have done it appears that, when on the ground, the pilot's joystick moves to a position that is fully forward when the Stabilator is trimmed to 1.8 units Down and moves to a position that is fully back when the Stabilator is trimmed to Neutral. Attached is a rough drawing that I made showing Trim Indicator - Stick Position - Stabilator Physical Alignment.

The travel of the stick when trimming the aircraft appears to be limited to fully back (to the rear) when trimmed neutral and fully forward (to the front) when trimmed 1.8 units Down. Passed these limits there is no physical travel of the stick.

Is this how the F-4's pitch trim is supposed to work in real life?