[RESOLVED]severe pitch & roll/yaw oscillations at high IAS

Here's a short track showing the pitch oscillations <800kias and the (new?) yaw/roll oscillations >800kias.

f16_pitch_yaw_oscillations.trk

Although I think those oscillations <800kts are not correct I keep saying that max speed of a Viper is 800kts! So personally I don't care if it blows up or tears apart after hitting 800kts.

Same here, but since it took only a few seconds of acceleration after showing the severe pitch oscillations (starting above 600kias) I simply kept max pwr to show the yaw/roll 'problem'.

To add to this, I have seen the same issue at 300ias 17,000ft. This occurred after returning from testing the max speed at altitude, so it may be related

Make sure you are not flying in landing gaines. I experienced this when I had the air refuel door open.

Make sure you are not flying in landing gaines. I experienced this when I had the air refuel door open.

I experienced this as well ~400 KIAS, and I think I also had the air refuel door open.

Make sure you are not flying in landing gaines. I experienced this when I had the air refuel door open.

+1 flying at ~400+kn at ~18000ft everything is ok until i use the AAR switch, slight movement on the throttle results in up and down oscilation, using the switch agian stops it immediate. I had this down and fast also yesterday, i believe i used the AAR switch too. Attached is a short track showing the behaviour.

F16_shaking.trk

Not sure if it modeled correctly in DCS, but the real aircraft has a speed limit for the door in transition from close to open (and vise versa) and open. The limit is 400 knots or mach .85 ( which ever is less) for transition and 400 knot or mach .95 for the door open.

Maybe this is ED's ways of simulating what happens if door is open above the limit, since the manuals never say what would happen.

Not sure if it modeled correctly in DCS, but the real aircraft has a speed limit for the door in transition from close to open (and vise versa) and open. The limit is 400 knots or mach .85 ( which ever is less) for transition and 400 knot or mach .95 for the door open.

 

Maybe this is ED's ways of simulating what happens if door is open above the limit, since the manuals never say what would happen.

True statement. But also be aware that when the Air refuel door is open the Viper is in landing gains...those gains are not made for speeds above 400kts. But now that I remember the Digital FLCS will cycle from Takeoff and landing gains to cruise gains whenever speed is above 400kts and the air refuel door is open or ALT flaps extended. The analog FLCS had the problem going over 400kts and doing funky stuff. So this is a bug and should not happen with DFLCS

I'm experiencing the pitch problem only above 600kts and the refueling door is definitely closed.

Talking about take off and landing gain.....Hope the correct the FLCS gain trigger soon.

Presently the changeover happens only at the end position of the gear, which means that you can't perform any airshow like pitch up or rapid roll into a turn immediately after unstick.

Had the pitch oscillation happen once in a 770+ steep dive before the patch as well. Cat I, clean bird on an acrobatics server, refueling door definitely closed.

Thought it might have been just me.

Had this last night. (post patch) at 500 ft and starting about 490 kts (becomes more extreme as airspeed increases) the rudder starts overcompensating after any type input (especially roll) and causes Yaw oscillation until I reduce airspeed back below the onset speed.

I went to external view looking up the tail pipe and watched the rudder doing this.

[ALREADY REPORTED]Flight Model: Very strong oscillations at high speed

Mission weather settings: https://i.imgur.com/dp97QsS.png

the flight model is very WIP right now, and in general everything is very WIP. Within 6 months check if the FM has improved in the F16 :pilotfly: :sleep:

the flight model is very WIP right now, and in general everything is very WIP. Within 6 months check if the FM has improved in the F16 :pilotfly: :sleep:

I know that's why I'm reporting an issue to get as much data out there as possible for them to use and work on it.

It can also be triggered by things like wake turbulence:

(from multiplayer session, so I removed sound)

I've done some tests in different weather and different altitudes. My suspicion is that the FLCS is overcorrecting it's yaw inputs when there are external forces acting on the aircraft. So when you're (too) fast at sea level and the aircraft starts buffeting the rudder starts freaking out. Same thing if you're flying below 400 knots at low level with turbulence and wind. The FLCS seems to be seems to be constantly overcorrecting with it's yaw inputs. However, in bad weather as soon as I climb above roughly 3000 ft ASL it seems to just fade away. Then if I start descending below 3000 ft again it starts jerking around again. I know how turbulence is portrayed in DCS and it's definitely not caused simply by turbulence. If anyone else can confirm that this is infact the case and not just the ramblings of a mad man, that'd be much appreciated.

Usually between 400-430 Kts IAS my F16 will oscillate severally in pitch. If I look at the stabilizer it is fluctuating up and down rapidly. Outside of this airspeed window it stops. I always have bombs and cat 111 switch set. Any ideas?

Not experienced any problem with yaw.

+1

WHOGX5 seems to be correct in describing the matter.

I just had this problem for the first time today, I was around mach 1 low with 500lbs of fuel, and had fired all my weapons, just had empty pylons, and it began to oscillate in pitch, and it got so bad that my pilot blacked out and then I crashed into the ground.

I'll check the tacview with here in a bit but I'm almost 100% sure I wasn't hit by anything.

*edit* yea just checked tacview, I wasn't hit, oscillations start at low altitude around mach 1, I decreased speed to try to recover, but it got worse and around 0.83 mach my pilot blacked out from the oscillations and soon after crashed into the ground.

Here's a short video showing the pitch oscillations <800kias, up to over 9.5 G when the player blacks out.

As you can see, only slowing down isn't enough to get out of the situation, the pilot even has to input pitch up to get out of it. (today exactly 1 month since it was reported)

This pitch oscillation happens at low fuel. It may have something to do with an altered centre of gravity and the flight control computer and flight model. If the C/G moves aft towards instability with fuel consumption it make a plane hunt in pitch. It also makes control of the longitudinal axis in pitch, difficult. If the flight control computers or more specifically the tailerons lacked fidelity or speed they would effectively lag behind attempting to control an unstable longitudinal axis.

Also if the C/G is moving aft with fuel consumption it effectively puts more aircraft ahead of it. There is more mass ahead of the C/G. Try throwing a dart tail first.

Since this is only a video game my explanation bears no consideration.

Side-to-side wiggle still occuring after short rudder input at 500 lbs fuel at Mach 1.2, is this realistic behaviour?

SelfIncreasingSideWiggle.trk