reported Mi-24P Deceleration Oscillations

[MelonatorPL]

Hi I have been flying the Mi-24P as my primary module for a while now and I have noticed an issue with the pitch autopilot channel which oscillates the aircraft as it decelerates for landing starting at 140kph to around 100kph. This happens pretty much every time I attempt to slow down for landing and gets progressively worse as the aircraft gets slower and slower. I have included the track file below and hope this will help fix this issue as its getting very annoying to fly the aircraft with this present. in the track file I attempt to keep the aircraft's controls still and don't try to fight the oscillations to demonstrate the issue. Thanks in advance!

oscilations.trk

Edited June 7, 2022 by MelonatorPL

[Hammer1-1]

think your replay is broken...really wish they would fix it. What little I caught out of it though looked normal enough to me, but then again it looked like you were trying to land in a field just west of Batumi. From the looks of it, you were cold start in the air and that might be your problem...air starts in helicopters arent all that pleasant.

Edited June 7, 2022 by Hammer1-1

[Hawkeye91]

Yeah this bug has existed since launch and ED has yet to address it. It happens every flight exactly as you described. 

[AeriaGloria]

Yes happenned since release. However I feel it has gotten better and less server in recent patches. 

[MelonatorPL]

Yea I let the aircraft stabilize due to the air start and I reset the trimmer as well. You can see it occur after the turn to the north as I pass 140kph. This is really getting annoying :3

Hope they fix it soon maybe with the new R60 update coming out.

[MelonatorPL]

Further testing this and I found that this mostly occurs when increasing collective while decelerating (which you have to do as you get slower to not fall out of the sky) around 140-130 kph. This oscillation then lasts to around 100 kph after which it decreases and ultimately fades away.

 

Additionally I just found a forum thread on this topic which is marked as solved. The solution is to turn on all of the AP channels however this doesnt affect the problem at all in my testing. I tried to recreate this with roll and pitch autopilots on, then with roll, pitch, and yaw and it happens every time on both configurations. If I disable the pitch autopilot channel however it does stop the oscillations but this isnt a proper solution as you have no pitch autopilot available.

 

Edited June 8, 2022 by MelonatorPL

[AeriaGloria]

26 minutes ago, MelonatorPL said:

Further testing this and I found that this mostly occurs when increasing collective while decelerating (which you have to do as you get slower to not fall out of the sky) around 140-130 kph. This oscillation then lasts to around 100 kph after which it decreases and ultimately fades away.

 

Additionally I just found a forum thread on this topic which is marked as solved. The solution is to turn on all of the AP channels however this doesnt affect the problem at all in my testing. I tried to recreate this with roll and pitch autopilots on, then with roll, pitch, and yaw and it happens every time on both configurations. If I disable the pitch autopilot channel however it does stop the oscillations but this isnt a proper solution as you have no pitch autopilot available.

 

 

Interesting, bucket speed (speed with lowest power requirements) is 130-140 kmh. And as you increase the collective, the elevator rotates to cause the nose to pitch down, decreasing drag from the downwash  from the rotor. 

[MelonatorPL]

The might have something to do with it then 

[admiki]

Since oscilations are gone when pitch AP is off, I would guess that this problem is related to pitch AP dampening, not aerodynamics problem.

[AeriaGloria]

6 hours ago, admiki said:

Since oscilations are gone when pitch AP is off, I would guess that this problem is related to pitch AP dampening, not aerodynamics problem.

Yeah but I’m sure some change in aerodynamic stability could set it off. Some situation where the AP Pitch gain is too high whereas in real life it wouldn’t be. I’ve had models I’ve used too high a stabilization gain on and get oscillations, especially at high speed on fixed wings, and when vibrations are bad in rotary wing models. Something with the gains or PIDs, or natural/dynamic stability change and its interaction with gain/PIDs that is different then real life. 
 

It honestly doesn’t bother me that much, since I’m usually only in the speed region on the way to landing. But it is an interesting issue 

[admiki]

1 hour ago, AeriaGloria said:

It honestly doesn’t bother me that much, since I’m usually only in the speed region on the way to landing. But it is an interesting issue 

If I'm flying with human CPG, I might slow down to give chance for 2, maybe even 3 shots per run. That puts me smack into the range.

Haven't test it lately , but it was a lot more pronounced flying MC, especially CPG's piper would bounce quite a lot.

[sylkhan]

Pitch occiliation and Poor trimming implementation are irratating.
It's sad because Mi24 module could be really great

[admiki]

Poor trimming implementation?

[AeriaGloria]

1 hour ago, sylkhan said:

Pitch occiliation and Poor trimming implementation are irratating.
It's sad because Mi24 module could be really great

Yeah, what about trimming are you in satisfied about? 

[Hammer1-1]

seems to me the hind is one of the better helicopters I enjoy and it doesnt fly all that bad. a small flaw here and there and all the sudden its unplayable? cmon guys. if you think the hind sucks at trimming, wait until you fly the apache.

Edited June 9, 2022 by Hammer1-1

[sylkhan]

1 hour ago, Hammer1-1 said:

seems to me the hind is one of the better helicopters I enjoy and it doesnt fly all that bad. a small flaw here and there and all the sudden its unplayable? cmon guys.

Unplayable, who said unplayable ?

2 hours ago, AeriaGloria said:

Yeah, what about trimming are you in satisfied about? 

There are some conflict with AP (pich, roll), after trimming the mi-24, go up or go down or go up and roll etc, depending of your initial position.

Trimming doesn't give a neutral, stable position (like Mi-8 for example).

Even if the trimming systems of mi-8 and mi-24 are differents, it should give the Mi-24 the same stability.

[Hammer1-1]

Ive honestly not had a single issue with stability. I was flying it rock solid last night, even stepped off for 10 minutes to get a beer and I was still in level flight. Im even confident my tacview could prove that too. Hell I flew it for almost a whole hour in level flight without any problems, and I rarely fly it anymore.

Tacview-20220609-012838-DCS-south atlantic.zip.acmi

Edited June 9, 2022 by Hammer1-1

[AeriaGloria]

1 hour ago, sylkhan said:

Unplayable, who said unplayable ?

There are some conflict with AP (pich, roll), after trimming the mi-24, go up or go down or go up and roll etc, depending of your initial position.

Trimming doesn't give a neutral, stable position (like Mi-8 for example).

Even if the trimming systems of mi-8 and mi-24 are differents, it should give the Mi-24 the same stability.

This is actually realistic of the differences between the AP of both. 
 

In the Mi-8, trim has no impact on autopilot. In Mi-24 it’s different in that the roll/pitch AP is turned off when trim button is held, and when trim button is released the roll/pitch AP are engage but change the set attitude from what it was before to what the attitude is during trim button release. 
 

Thisnis kindve like Ka-50 trimmer, where by pressing trim button you are telling pitch and roll AP to “hold this attitude.” So on the ground when you turn it on the roll/pitch AP might try to make you perfectly level at 0 degrees pitch, but at 270 kmh and you try to trim for 5 degrees down to maintain level flight, pressing the trim immediately takes away the pitch AP trying pitch you back up to 0 degrees. And when the trim button is released the pitch AP is now trying to hold 5 degrees down. 
 

  There’s a couple ways around this, you can hold the trim button for longer so you not “fighting” the AP, as what’s happening jn the previous example is your basically fighting the AP and pressing trim gets rid of the force you’re fighting. 
Other then holding down the trim button for a while before moving the stick you can also trim 2 or 3 times. 
 

  What I’ve done recently is to a bit overboard but since I usually trim in fast cruise, go to a fast cruise state, and move the adjustment knobs until the AP is close to center. Then when I press trim there is practically no “jump.” For example if you need to maintain -5 degrees at 270 kmh, you’ll need to dial in 5 on the pitch AP adjustment dial. 
 

I’ve read every Mi-24 manual and document i can get my hands on for almost every single variant, and it seems to work correctly in regards to trimming. I think in real life it is less of an issue becuase they are taught to trim all the time. The smaller the change, the less you will jump from pressing trim. So that’s another way to stop the jumping, just trim a lot. Another thing I do is if I take off and expect to cruise at 270 kmh and -5 degrees, I press trim button with my nose at -5 degrees pitch even if I’m at 75 kmh, so that when I get to cruise there is little to no “jump” and I all I need to do is fine tune trim. 

54 minutes ago, Hammer1-1 said:

Ive honestly not had a single issue with stability. I was flying it rock solid last night, even stepped off for 10 minutes to get a beer and I was still in level flight. Im even confident my tacview could prove that too. Hell I flew it for almost a whole hour in level flight without any problems, and I rarely fly it anymore.

Tacview-20220609-012838-DCS-south atlantic.zip.acmi 1.76 MB · 0 downloads

 

It’s been reported by many people since release, on the English and Russian forums, and the developers (PilotMi-8, Alex, former head of Belsimtek) has acknowledged the issue. So it’s there but doesn’t always appear, and only appears in that very specific region of 100-140 kmh, slowing down and increasing power in level flight. 
 

It doesn’t bother me too much even if it makes low speed aiming tough, and I’m glad dev time has gone to more important things, but it is there 

[MelonatorPL]

Yea I also never really seen the stability issue but I really hope these oscillations can be looked at by the devs. As soon as this bug is squashed I will have no complaints with this module and will be very happy with it. 

 

Also I spent more testing by doing standard landing operations with the heli and got the oscillations every time. The number of times was about 25 today. If any devs need help reproducing this issue i am willing to hop on discord or another streaming device and stream my screen as it occurs.

Edited June 10, 2022 by MelonatorPL

[admiki]

11 hours ago, sylkhan said:

There are some conflict with AP (pich, roll), after trimming the mi-24, go up or go down or go up and roll etc, depending of your initial position.

Trimming doesn't give a neutral, stable position (like Mi-8 for example).

Even if the trimming systems of mi-8 and mi-24 are differents, it should give the Mi-24 the same stability.

Easy. Don't wait until you get into your new desired position and then press FTR. Either keep clicking it on your way to your new desired position or press and hold until happy and only then release.

I would venture a guess that you have never flown IRL helicopter, at least one that has FTR. If you do it like you are , probably, doing it in DCS, you would get the same thing. Trim will fight your new position, you pushing against it and then you press FTR, it's gone and you overcontrol.

[sylkhan]

15 hours ago, AeriaGloria said:

.....  There’s a couple ways around this, you can hold the trim button for longer so you not “fighting” the AP, as what’s happening jn the previous example is your basically fighting the AP and pressing trim gets rid of the force you’re fighting. 

Other then holding down the trim button for a while before moving the stick you can also trim 2 or 3 times. 
 

  What I’ve done recently is to a bit overboard but since I usually trim in fast cruise, go to a fast cruise state, and move the adjustment knobs until the AP is close to center. Then when I press trim there is practically no “jump.” For example if you need to maintain -5 degrees at 270 kmh, you’ll need to dial in 5 on the pitch AP adjustment dial. 
 

.....Another thing I do is if I take off and expect to cruise at 270 kmh and -5 degrees, I press trim button with my nose at -5 degrees pitch even if I’m at 75 kmh, so that when I get to cruise there is little to no “jump” and I all I need to do is fine tune trim. ..

Interesting,but if it's the correct behavior in RL, it makes the pilot life a little harder

Will try that, thx Aeriagloria

[Hammer1-1]

Flying the Hind isnt nearly as hard as you make it out to be. Granted yeah it has its quirks, but you need to consider the fact its a fat helicopter and technically underpowered for what it is. Landing is the most difficult thing you can do in a helicopter, and the bigger it is the harder its going to be.

[admiki]

2 hours ago, sylkhan said:

Interesting,but if it's the correct behavior in RL, it makes the pilot life a little harder

Will try that, thx Aeriagloria

Not really.

You need to consider one thing that is 99.9% not present in DCS: force trim feel. IRL, controls will push back against you if you move it out of trimmed position. So, pilots trim often, even in Mi-8.

Listen how often FTR clicks in this video. And I know from my own flying in Mi8 that this is how it is.

 

[MelonatorPL]

Can any developer notify if this issue is being worked on and if you have attempted to replicate this? Please try to fix this as its driving me crazy every time I fly this heli.Thanks.

Edited July 3, 2022 by MelonatorPL

[sLYFa]

There is a post in the russian Mi-24 bug thread by one of the devs acknowledging the issue. However, it appears to be a result of the complex interaction between FM and AP. They are apparently working on it but there is no ETA.