cannot reproduce and missing track file Uncommanded pitching/rocking

[Ghost1606688907]

Hi, I have noticed in the last couple of days when I have been playing on Mp server that when I am in a high speed decending turn say defending against SAMS that the F16 starts to pitch in a rocking fashion, which gets increasingly worse and makes the jet uncontrollable. I have now had this quite a few times on seperate occasions. It will slowly come right but not ideal if you have a SAM or fighter behind you.

 

Today when I noticed it happening I noticed the HUD was giving me random readings also like my airspeed was only half of what I was actually doing.  

[Deano87]

Cold outside air temp? There have been issues with the Airspeed readings in cold conditions, it looks a bit like pitot icing. Which then changes the way the FCS behaves.

Edited December 27, 2020 by Deano87

[ViKe]

1 hour ago, Ghost1606688907 said:

Hi, I have noticed in the last couple of days when I have been playing on Mp server that when I am in a high speed decending turn say defending against SAMS that the F16 starts to pitch in a rocking fashion, which gets increasingly worse and makes the jet uncontrollable. I have now had this quite a few times on seperate occasions. It will slowly come right but not ideal if you have a SAM or fighter behind you.

 

Today when I noticed it happening I noticed the HUD was giving me random readings also like my airspeed was only half of what I was actually doing.  

I had the same exact problem yesterday.HUD readings are all out of whack and plane rocks uncontrollably.I was also in a high speed descending  turn while evading a sam.

[Ghost1606688907]

3 hours ago, Deano87 said:

Cold outside air temp? There have been issues with the Airspeed readings in cold conditions, it looks a bit like pitot icing. Which then changes the way the FCS behaves.

 

It was in a winter mission which could cause the pitot icing, but the pitching is super bad. It starts with a slight rocking motion then turns into a full blown rocking motion that you have no control over. I will try and see if I can get it to happen then restart and try it with pitot heat on and see if that stops the problem

[Deano87]

8 minutes ago, Ghost1606688907 said:

It starts with a slight rocking motion then turns into a full blown rocking motion that you have no control over.

 

Yes, Thats the same thing I've experianced. Only seems to happen in cold missions.

If you can replicate it in single player grab a track of it, as I've never managed to do so.

[Steelpanther]

it happened to me on multiplayer mission also when flying very fast and very high altitude in caucaus winter. but i wasnt recording it. I just remember that there was no malfunction indication lights, so it wasnt flightt control system failure for sure(?). The plane went into a deep stall rocking up and down in pitch totally uncommanded. I was flying way faster than mach 1.5 though, lol. altitude was most likely around 45k feet

Edited December 29, 2020 by Steelpanther

[pbishop]

Turn on pitot heat, check your airspeed went to zero.  I am not sure if this is a "feature" of the flight control system with invalid airspeed.  Happened to two of us yesterday as well, we controlled both aircraft long enough to regain airspeed indication and it stopped.

[Sternzy]

I don't know if this is exactly what you all are describing but it sounds similar.

 

3 or 4 times now when beginning a descent to engage or evade the f16 starts shaking hard, in short burst which I assume is realistic and feels correct. However sometimes the plane will go into a violent, what I could only describe as vibration. If you could imagine picking up a piece of aluminum flat bar 10' long, 3" wide and 1/16" thick shaking it up and down so it flops around violent; that is what the f16 does. Slowing down, speeding up and turning all do nothing to correct this. The only way I have been able to correct this is to start an ascent for a few seconds and it gradually comes back under control.

[BIGNEWY]

Please attach a short track replay showing the problem and we can take a look

 

thanks

[Deano87]

4 hours ago, pbishop said:

Turn on pitot heat, check your airspeed went to zero.  I am not sure if this is a "feature" of the flight control system with invalid airspeed.  Happened to two of us yesterday as well, we controlled both aircraft long enough to regain airspeed indication and it stopped.

Was that in a low temperature mission?

 

Ive been trying to replicate this and it doesn’t seem to want to do it for me. No idea why , I’ve experienced it unexpectedly several times but never been a le to catch it on a track.

Edited December 29, 2020 by Deano87

[Cgjunk2]

What speeds are people going when this happens?  I noticed an oscillation today down low, but it was at speeds beyond the barber pole.   I figured it was a feature of going past Vne.

[Deano87]

6 hours ago, Cgjunk2 said:

What speeds are people going when this happens?  I noticed an oscillation today down low, but it was at speeds beyond the barber pole.   I figured it was a feature of going past Vne.

Not that fast, I had it when I started a descent from a long, high altitude (45k+) , subsonic cruise. Just as I started my descent I noticed the airspeed in the HUD was frozen, ie it wasn’t moving even though I was clearly accelerating. I popped the air brakes and throttled back and was definitely subsonic. But my airspeed in the HUD was still reading the same number. My  Mach indication in the HUD shot up from 0.8 to 2.2 in around 10 seconds, at which point the jet started a divergent pitch oscillation, departed and ended up in the traditional F-16 flat spin/ deep stall. My HUD was still reading the same airspeed and mach even though I was in a flat spin. At around 20k feet all the HUD readings rapidly returned to normal and I could use the Pitch Override to get me out of the deep stall/spin. I saved the track but wasn’t much use because I was on an online server and had been for a couple of hours. I’ve tried replicating it in single player and have never been able to. It’s happened to be a few more times. But I’ve never been able to get a track of it.

[pbishop]

Ok so I didn't manage to get a track, but here is how I managed to reproduce the behavior twice today (some may not be necessary, but this is my setup)

 

1. Caucasus winter with clouds/snow

2. Fly at 25000 ft with pitot heat off

3. Every 10 minutes start a gradual descent (~2 deg down)

4. If the airspeed is going down, then usually the indication the icing is present.

5. Verify altitude is stuck and not updating

6. Once confirmed icing, descend altitude.  The result will be airspeed crossing the 0 kts mark and cause induced pitching in the aircraft.  It should be noted that the airspeed will once again increase after crossing 0 as if entering negative values, and the pitching does require a light pitch input from the stick to notice.

 

Notes:

1. The slower you travel at higher altitude, the higher the altitude you will notice this behavior as it will take less altitude to cross the 0kts mark when iced over.

2. Descending to low altitude will cause the system to unfreeze (it seems) so recommended controlled altitude decrease when icing is observed.  This was noted the other day with the two ship on the first occurrence (not in these two tests)

3. Both attempts took me about 30 min to achieve, but results were identical.

4. To stop oscillations I tested two recoveries: 1. pitot heat (A/C returned to normal) / 2. Cross back over the 0 kts mark (by increasing altitude - A/C returned to normal, pitot still frozen)

 

Let me know if you need any more info, sorry I didn't notice I was not recording the tracks otherwise I would have posted them (the whole point of my experiment today was to produce the tracks on top of it - just a bit frustrating)

 

As a side note, Deano87 seems to have put the aircraft in a departed state and is not what I believe the rest of the thread is referring to.  The above test is pitch induced oscillations with the aircraft in a steady (not departed or stalled) state.  Although I would not argue that it may have been a result of the same situation/event.

 

Cheers,

 

Edited December 30, 2020 by pbishop

[Deano87]

34 minutes ago, pbishop said:

As a side note, Deano87 seems to have put the aircraft in a departed state and is not what I believe the rest of the thread is referring to.  The above test is pitch induced oscillations with the aircraft in a steady (not departed or stalled) state.  Although I would not argue that it may have been a result of the same situation/event.

 

I didn't put the aricraft in a departed state, the pitch oscilations casued by the icing (presumably) along with the loadout I had resulted in a departure from controlled flight. I had my hand off the stick at the time. Also it should be pointed out that pitot heat was on every time I had these issues. Which is why I thought it was weird.

Edited December 30, 2020 by Deano87

[Deano87]

Apparenty its reported that Probe Heat wasn't working in the past, I don't know if this has been fixed? 

 

[pbishop]

16 minutes ago, Deano87 said:

I didn't put the aricraft in a departed state, the pitch oscilations casued by the icing (presumably) along with the loadout I had resulted in a departure from controlled flight. I had my hand off the stick at the time.

 

 

Again, would not argue with you there and is exactly what I said (how it got departed is semantics and not all that important).  However, the point I was making is that the issue is with the aircraft not in a departed state where the pitch oscillations are present.

Edited December 30, 2020 by pbishop

[pbishop]

11 minutes ago, Deano87 said:

Apparenty its reported that Probe Heat wasn't working in the past, I don't know if this has been fixed? 

 

 

I can't speak for anyone else here, but this is a different / unrelated issue to what I was referring to.

Cheers

[Deano87]

8 minutes ago, pbishop said:

I can't speak for anyone else here, but this is a different / unrelated issue to what I was referring to.

Cheers

Isn't your pitch oscilation related to icing? You mention icing in your post.

[Ghost1606688907]

I have tried it with Pitot heat on and flew twice for around 2.5 hours each flight and never got the oscilation, so thought this may have been the problem until today returning to base to rearm I noticed the air speed and alt numbers on the hud were "stuck" even when decending and slowing down with speed brake. Again once I started my decent from around 25,000ft to land the osilation happened again. Air speed and alt were still "stuck" until I was downwind to land (which then the airspeed indicator on hud went to 500kts then dropped back down to the actual 300kts I was doing) Rad Alt was working correcty , so a possibility is the pitot heat isnt working or needs to be tweaked?

[Bog9y]

I've seen this pitching oscillation too. I went over the max speed for external wing tanks though so figured it was that. Mach 0.95/550 kts I think. 

[Sinclair_76]

I had the oscillation yesterday. Of course I forgot to save the track file. So reproducing observations from memory.

 

Winter conditions in Caucasus. CAVOK so no icing conditions encountered. 

Hot start with at least a couple of minutes (5?) to taxi prior depature. Because of hot start skipped the usual checks.

 

 I was in flight for about 30 min. Oscillation began after transition from 30.000' in a high speed dive to low level. It started roughly at 25.000. Began mild but with increasing speed became more violent. HUD CAS was at 250, the analog speed was at 0. The Viper was producing contrails. I did a quick panel scan but noticed nothing wrong, no abnormal indications, mc or advisory lights.

 

Because of the strange speed indications I suspected icing. I checked the probe heat but I think it showed on. After that I checked ENG ANTI ICE and it was in AUTO. I turned it to on. A couple of seconds after that the analog speed indicator came to life, HUD speed increased and oscillation disappeared. Resumed mission profile.

 

Further observations. In the manual it states that probe heat should be turned on as late as possible due to prevent overheat (would an overheat trigger master caution panel?). It was on +/-5min prior departure.

 

In the manual it also states the ENG ANTI ICE prevents ice build up on the probes and engine. Are the mentioned probes responsible for standby/analog airspeed indications? Is the FLCS coupled to those probes?

 

I will to recreate.

[Ghost7]

I have the same problem. I haven't used the F-16 since the last two updates, but it was working fine last time I used it. Two days ago I decided to fly the F-16 and had the same problem, mainly rolling left and strange pitch movements in a nose high attitude. I checked my joystick (TM Warthog), config and mission file.

 

I tested the joystick with other planes, no problem. I tried another joystick, same problem (with the F-16). I also have the stable version so I tested the F-16 in both DCS stable and OB, same joystick, same joystick config, same mission: default Nevada free flight in the "instant action". No icing, warm temperature.  No problems in the stable version, only in the open beta.

 

The plane rolls left. With significant right trim I can stop it, but the when I try to roll left the plane momentarily rolls right before rolling left. With a nose high attitude, full power, over 400 kts, the nose drops aggressively and rolls left. It stabilizes in a nose low left bank attitude, while flight controls are neutral. It is unfortunately unusable right now.

 

I can't attach a track file they are always too large, any tip on how I should do it?

 

Cheers

[Zergburger]

On 2/19/2021 at 6:20 AM, Ghost7 said:

I can't attach a track file they are always too large, any tip on how I should do it?

 

Cheers

host it on google drive, or set up a mission that will exhibit the behavior quickly and then spend as small amount of time as you need to do it. (thus making the track smaller)

[Ironhand]

On 2/19/2021 at 9:20 AM, Ghost7 said:

...

I can't attach a track file they are always too large, any tip on how I should do it?

Is it still too large if you compress it into a ZIP file? In the past, the ZIP file allowance was always higher than that of a TRK. Hopefully it still is.

[Ghost7]

Thank you Zergburger and Ironhand for the help.

I tried to fly another short trip to save the track following your suggestions and the problem was gone! After some digging I found that in the OB version two throttle switches were programmed to the autopilot, which engaged the AP automatically every time I loaded the F-16. Embarrassing oversight on my part, but the good thing is my problem is solved.

 

Cheers