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Trim Issue


Fflar

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Description: When trimmed for forward flight, applying slight backpressure on the stick will push the nose further down, instead of raising it up

DCS Version: 1.5.3.52875 Open Beta

Map: Caucasus

SP/MP: Singleplayer

Reproducible: Yes

Step to Reproduce: Trim for an airspeed of 150 km/h+, apply very slight backpressure on the stick (cyclic)

Track Available: See attachment

Mission File: Generated with "Create Fast Mission"

Controllers: Saitek x52 Pro

Gazelle_Trim.trk

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Observed as well intermittently, just didn't find the time to write proper bug report, so thx for reporting, Fflar. :thumbup:

 

Encountered the problem in some of the campaign missions in 1.5.3 Release, can try to reproduce if needed.

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Anyone who can reproduce would help. Trying to pin down if it's just 1.5.3. beta or release as well at this point. Will also need to test 2.0.2. We schedule a test flight for this weekend to test.

Coder - Oculus Rift Guy - Court Jester

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I think I have it nailed down now.

 

Version: 1.5.3 Open Beta

SP/MP: MP

Reproduction steps:

 

1) Trim nose down with mag trim.

2) Apply forward hat trim to limit to the HAT trim's limit.

3) Pull back on stick, nose will drop faster instead of rising or dropping more slowly.

4) Reducing forward HAT trim back from the limit removes this behavior, though not immediately, it requires a few clicks to get out of this funny area.

 

Edit: This occurs when using HAT trim only as well.


Edited by King_Hrothgar
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Tested in 2.0.2.52658, reproduced. Track file download.

 

Track duration 2:20 minutes, flown in SP.

 

Track description:

- After take-off, I gain some speed and altitude. No trim applied whatsoever.

- When I dispense the first flare, I apply nose down trim with the Cyclic China Hat.

- When I dispense the second flare, I stop applying trim

- After that, slight back-pressure on the Cyclic Stick pitches the nose down instead of up

- Returning my stick to the physical center position, the nose pitches back up

- Applying more back-pressure on the Cyclic Stick pitches the nose up as well

- When I dispense the third flare, I apply more nose down trim with the Cyclic China Hat

- When I dispense the fourth flare, I stop applying trim

- The effect works the same, but is now even more pronounced

 

TM HOTAS Warthog. I don't use TARGET or any other software to modify the stick's behavior, it's a pure DirectX device.

 

Effect identical with Curvature 0 on Cyclic Pitch and Cyclic Roll (for testing) as well as with Curvature 15 for both axes (my current preferred setup; that's what I had in use when I recorded the track). No other Axis modifications (ie. Saturation, Deadzone etc. all at their default values).

 

I haven't tested 1.5 specifically yet, but I think the effect is pretty much the same across versions.

 

PS: No Gazelles were harmed in the making of this track :D


Edited by Yurgon
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Thanks guys. Would you say you guys are at the limit of the trim when this occurs? Might be an issue with the trim limit that we need to look at.

 

I have it on my list to test during mt test flight this weekend so will see if I figure out the issue and start working on a fix.

Coder - Oculus Rift Guy - Court Jester

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Thanks guys. Would you say you guys are at the limit of the trim when this occurs? Might be an issue with the trim limit that we need to look at.

 

I have it on my list to test during mt test flight this weekend so will see if I figure out the issue and start working on a fix.

 

It seems like the more nose down trim you apply, the stronger the effect is. Its also more noticeable on a lightly loaded helo...with 20% fuel and no weapons, I only needed four clicks of nose down trim to reproduce the bug, while with 80% fuel and two missiles, i needed 6 or 7.

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Thanks guys. Would you say you guys are at the limit of the trim when this occurs? Might be an issue with the trim limit that we need to look at.

 

I have it on my list to test during mt test flight this weekend so will see if I figure out the issue and start working on a fix.

 

yes it seems to be at the trim limit it just likes to nose over randomly for me at least.

8700k@4.7 32GB ram, 1080TI hybrid SC2

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It sounds like the Autopilot or SAS system is reading nose coming up and it is correcting to keep the nose down and speed where is was set. So SAS has 100% authority...thats a scary thought.

Ask Jesus for Forgiveness before you takeoff :pilotfly:!

PC=Win 10 HP 64 bit, Gigabyte Z390, Intel I5-9600k, 32 gig ram, Nvidia 2060 Super 8gig video. TM HOTAS WARTHOG with Saitek Pedals

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Would you say you guys are at the limit of the trim when this occurs? Might be an issue with the trim limit that we need to look at.

 

Like Fflar said, I think the closer the trim is near the limit, the more pronounced the effect becomes.

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So did a quick test tonight while testing some other things and I think I was able to replicate it somewhat. I was going around 150 trimmer almost full nose down. In that position, pulling the cyclic back didn't do anything it seemed until about 3/4 of the way back in which the nose pitched up. While I didn't see it go down, it seems like there is something going on here.

 

So now I know I can replicate it, going to see if its an actual issue or something that actually occurs in the real Gazelle. My hypothesis is that when trimmed like that the SAS tries to keep it straight, and might not like any small inputs (I think in your case it's even going against you). It sounds a lot like the fighting with the SAS, which real pilots endure as well. But I will do more testing this weekend and try to get feedback from the real pilots and engineers.

Coder - Oculus Rift Guy - Court Jester

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So i made a short video, demonstrating the issue. The quality is not the best, but if you watch it in 1080p, hopefully you can see my aft cyclic input on the controls indicator, and that it doesn't simply try to keep level, but rather it pushes the nose down at a fairly constant rate.

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Will make video of what I saw. But that video is great Fflar.....I'll take screenshots later to look at all your settings so I can properly record it.

 

Forgot to mention that i'm flying with 20% fuel and no missiles in the vid, when i was flying with a heavier loadout, it took a lot more trim, and the effect was a lot less pronounced...maybe it has something to do with airspeed. I also haven't used any curves in the video.

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Did some more tests over the weekend and talked with engineers and other subject matter expects, and essentially it's the SAS system fighting with you. They advised not to overtrim the aircraft down, otherwise you'll be fighting with the SAS which is trying to keep you flying nicely.

Coder - Oculus Rift Guy - Court Jester

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Did some more tests over the weekend and talked with engineers and other subject matter expects, and essentially it's the SAS system fighting with you. They advised not to overtrim the aircraft down, otherwise you'll be fighting with the SAS which is trying to keep you flying nicely.

 

Hold on, are you saying this is realistic and thus intended behavior in the sim?

 

Trimming nose down and then pulling back on the cyclic may lead to a severe nose down pitch? That doesn't make any sense whatsoever.

 

The cyclic behavior is actually inverted under these circumstances. If that were the case in RL, trimming would be life threatening, and should be prohibited until the underlying problem was fixed. I would go so far as to remove the trim hat altogether in order not to lose aircrews and aircraft. Please tell me this isn't real.

 

On a related note, during a sortie last weekend I tried the same with strong trim towards right and left and the behavior was the same: trimming right wing down and inputting left cyclic would lead to an increase in right bank instead of a decrease, and the effect would go away when the trim was returned near the center/neutral position.

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Trimming to the extremes yes, lightly trimming is fine - according to our flight engineer. I'm still waiting to hear back from actual pilots as well.

 

As usual, if we find out this isn't real behavior in a Gazelle - we will tweak it to make it more realistic. So stay tuned!

 

Hold on, are you saying this is realistic and thus intended behavior in the sim?

 

Trimming nose down and then pulling back on the cyclic may lead to a severe nose down pitch? That doesn't make any sense whatsoever.

 

The cyclic behavior is actually inverted under these circumstances. If that were the case in RL, trimming would be life threatening, and should be prohibited until the underlying problem was fixed. I would go so far as to remove the trim hat altogether in order not to lose aircrews and aircraft. Please tell me this isn't real.

 

On a related note, during a sortie last weekend I tried the same with strong trim towards right and left and the behavior was the same: trimming right wing down and inputting left cyclic would lead to an increase in right bank instead of a decrease, and the effect would go away when the trim was returned near the center/neutral position.

Coder - Oculus Rift Guy - Court Jester

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