Su-27 trim issue is in need of explanation

[Teknetinium]

The most wearing place on the right flight glove of Su-27 is the thumb... it's a fact. What do you think about the reason?

 

Do you have planes to compensate for those who don't use FFB sticks? Could be added in Special options. To compensate for it could be done by saving autopilot attitude when going autopilot off.

Edited October 24, 2015 by Teknetinium

[NineLine]

Am I doing it wrong? I am not seeing any crazy trimming needed... sure trimming is needed, but nothing crazy.

[rrohde]

I think the main difference between other DCS modules and the Su-27's trimmer behavior is rather straight forward - it requires a much longer initial press of the pitch-down trimmer button than other DCS jets. Once you get the nose down sufficiently after take off, the 27 can be trimmed with smaller inputs, just like the other DCS aircraft.

 

For the 27, right after take off, I try to line up the edge of the flight stick with the bottom edge of the VSI - or rather, the white line underneath it. See screenshots attached.

 

This works for me as a rough estimate; from here on out, I use smaller trimmer inputs for the pitch axis - but again, the 27 needs that initial long trimmer push.

 

GIF

Edited October 24, 2015 by rrohde
Added GIF

[Teknetinium]

Am I doing it wrong? I am not seeing any crazy trimming needed... sure trimming is needed, but nothing crazy.

 

Trimming is fine to me as well.

[DarkFire]

Am I doing it wrong? I am not seeing any crazy trimming needed... sure trimming is needed, but nothing crazy.

 

I agree. The amount of trimming necessary doesn't bother me at all, in fact flying the thing becomes second nature after a period of time. Sure, it isn't as care-free as the Eagle, but that's simply a matter of experience and care.

 

What does bother me about the trim is the rate of trim. Even when nice and level a tiny, tiny prod of the trimmer key will make the aircraft gradually drift from +1 m/s vertical speed to about -1 m/s over the course of about 20 seconds. I simply cannot get it to hold absolutely steady. On long flights this drives me crazy, especially as the autopilot does such weird stuff.

 

Could the rate of trim possibly be reduced slightly? Please? For my sanity? :cry:

[Santi871]

I agree. The amount of trimming necessary doesn't bother me at all, in fact flying the thing becomes second nature after a period of time. Sure, it isn't as care-free as the Eagle, but that's simply a matter of experience and care.

 

What does bother me about the trim is the rate of trim. Even when nice and level a tiny, tiny prod of the trimmer key will make the aircraft gradually drift from +1 m/s vertical speed to about -1 m/s over the course of about 20 seconds. I simply cannot get it to hold absolutely steady. On long flights this drives me crazy, especially as the autopilot does such weird stuff.

 

Could the rate of trim possibly be reduced slightly? Please? For my sanity? :cry:

 

Why is that a big deal? lalt + 3 for level flight, lalt + 1 for pitch/roll hold (good for climbs and descents), lalt + 9 to disable.

[DarkFire]

Why is that a big deal? lalt + 3 for level flight, lalt + 1 for pitch/roll hold (good for climbs and descents), lalt + 9 to disable.

 

Ultimately it isn't an issue. It's just I like to be able to balance things perfectly, and the trimmer adjustment rate as it stands doesn't allow me to do that. I guess I'm being a bit perfectionist with myself really...

[Santi871]

Ultimately it isn't an issue. It's just I like to be able to balance things perfectly, and the trimmer adjustment rate as it stands doesn't allow me to do that. I guess I'm being a bit perfectionist with myself really...

 

If you want to fly with perfect trim (for a certain speed), just press lalt + 3, let it level and then disengage it, since all the autopilot does is trim the plane for you.

[DarkFire]

If you want to fly with perfect trim (for a certain speed), just press lalt + 3, let it level and then disengage it, since all the autopilot does is trim the plane for you.

 

I'll have to give that a go. I normally try to use the altitude hold autopilot which normally causes utter havoc every time I disengage it so I think I'll give the level hold mode a shot.

[Santi871]

I'll have to give that a go. I normally try to use the altitude hold autopilot which normally causes utter havoc every time I disengage it so I think I'll give the level hold mode a shot.

 

In any case you need to wait until the autopilot is done trimming it before you disengage it otherwise your plane will be horribly trimmed.

[Svend_Dellepude]

Good to see this thread has taken a positive turn! :)

[Ironhand]

Ultimately it isn't an issue. It's just I like to be able to balance things perfectly, and the trimmer adjustment rate as it stands doesn't allow me to do that. I guess I'm being a bit perfectionist with myself really...

 

Another option is to adjust your throttle to match your AoA, once you've used trim to get it close. Usually you're talking a fraction of a degree difference and a fraction of a % in rpm reduction or increase is all it takes.

[steve65]

Ultimately it isn't an issue. It's just I like to be able to balance things perfectly, and the trimmer adjustment rate as it stands doesn't allow me to do that. I guess I'm being a bit perfectionist with myself really...

 

Darkfire you probably already thought of this but I'll say it anyway,could you go into the planes file and edit the line that controls how much trim each button press gives it.

[Ironhand]

...

In short you can somehow magically make the upwards pitch disappear by pressing the S key eventhough that the horizontal stabs stay at the exact same zero trim setting as before (!). Aerodynamically that makes zero sense and I'm not sure how ED overlooked that....

Not sure if you are still paying attention to this thread but I don't know what to make of this statement. I thought, perhaps, that you had found a graphical bug but, now that I'm home and can check, I can't reproduce it. The elevator positions change substantially when the "S" key is engaged or cancelled. And, FWIW, trimmed with the "S" key engaged and trimmed with it disengaged yield the same elevator position for similar airspeeds which is what you would expect.

 

Rich

[OnlyforDCS]

Another option is to adjust your throttle to match your AoA, once you've used trim to get it close. Usually you're talking a fraction of a degree difference and a fraction of a % in rpm reduction or increase is all it takes.

 

This! A lot of people forget that tiny incremental changes in their throttle setting can affect whether the plane pitches up or down. This in combination with the trim setting can get the plane flying pretty straight and level.

[Ironhand]

This! A lot of people forget that tiny incremental changes in their throttle setting can affect whether the plane pitches up or down. This in combination with the trim setting can get the plane flying pretty straight and level.

I use an X-52 controller which has a really nice throttle control. That throttle makes it very easy to fine tune my airspeed for the wing's AoA.

[DarkFire]

Darkfire you probably already thought of this but I'll say it anyway,could you go into the planes file and edit the line that controls how much trim each button press gives it.

 

Erm, I've never done that before. Which is the file in question? I might give that a try.

 

Thanks for the suggestions everyone, much appreciated :thumbup:

[steve65]

Erm, I've never done that before. Which is the file in question? I might give that a try.

 

Thanks for the suggestions everyone, much appreciated :thumbup:

 

I've never edited files in DCS but I've done file editing in SF2 series but I'm sure DCS is different,but there must be an area in the planes file that controls the trim function.now whether DCS will let you edit it is another story.

 

There must be somebody in the dcs community that knows how to edit files in DCS World that could help out.i wouldn't mind knowing that procedure myself.

Edited October 26, 2015 by steve65

[Svend_Dellepude]

I've never edited files in DCS but I've done file editing in SF2 series but I'm sure DCS is different,but there must be an area in the planes file that controls the trim function.now whether DCS will let you edit it is another story.

 

There must be somebody in the dcs community that knows how to edit files in DCS World that could help out.i wouldn't mind knowing that procedure myself.

 

My guess that this is a compiled file somewhere and not possible to edit.

[DarkFire]

I had a quick poke around and couldn't find anything obvious. I'll have a more thorough look around tomorrow.

[Hummingbird]

It's the amount of trimming that is needed which is the problem, not that it needs trimming which is completely normal and expected. That the ingame Su27 needs substantially less trimming, and I'd say the normal amount, with the S key activated just makes it even more strange.

 

Why would you design the aircraft to demand that much extra trimming? It's adding pilot workload nothing else.

 

In short I suspect that thel amount of change in upwards pitch you experience with changes in speed in the real plane are much smaller, but they are still there - i.e. the FBW system still simulates the characteristics of a longitudally stable aircraft, but to a normal and not exaggerated degree.

 

Regarding the horizontal stab position, I mentioned this as I noticed no change switching between S key on and S key off, which makes the change in behavior even stranger and aerodynamically impossible. But perhaps that was a bug on my end I dunno, will have to check again.

[Santi871]

It's the amount of trimming that is needed which is the problem, not that it needs trimming which is completely normal and expected. That the ingame Su27 needs substantially less trimming, and I'd say the normal amount, with the S key activated just makes it even more strange.

 

Why would you design the aircraft to demand that much extra trimming? It's adding pilot workload nothing else.

 

In short I suspect that thel amount of change in upwards pitch you experience with changes in speed in the real plane are much smaller, but they are still there - i.e. the FBW system still simulates the characteristics of a longitudally stable aircraft, but to a normal and not exaggerated degree.

 

Regarding the horizontal stab position, I mentioned this as I noticed no change switching between S key on and S key off, which makes the change in behavior even stranger and aerodynamically impossible. But perhaps that was a bug on my end I dunno, will have to check again.

 

I have never felt it requires an exaggerated amount of trimming. It doesn't require any more trimming than any civilian airplane, mig21 or L39. This seems highly subjective and since no one here seems to have hard data we can only speculate.

[Hummingbird]

I have never felt it requires an exaggerated amount of trimming. It doesn't require any more trimming than any civilian airplane, mig21 or L39. This seems highly subjective and since no one here seems to have hard data we can only speculate.

 

It requires a lot more trimming pitch than the L-39, Sabre or MiG-15.

[Santi871]

It requires a lot more trimming pitch than the L-39, Sabre or MiG-15.

 

Not more than the L39.

[OnlyforDCS]

I told myself I would not respond directly, so I wont. But I have to put this down. What exactly would it take to convince 'certain' people on this forum that the system is working as intended? The FM creator has spoken on numerous occasions on this 'issue' and has confirmed that it is not bugged and is working as intended. The system itself has been described in great detail, in numerous manuals, and here on the forum. Eagle Dynamics has been working on the Flanker since 1995, it is literally the plane that ED has had the most experience with, and has numerous SME pilot input for exactly this purpose. If this is not enough, what would these 'people' accept as proof?

 

This is a rhetorical question, the answer to this question is quite obvious and there is no real need to respond. Over and out.

Edited October 29, 2015 by OnlyforDCS