fixed F-16 Pitching up and down

[pbishop]

There is no doubt the FCS is dependent on air data.  However, the FCS also has built in redundancies and safeties in place to avoid or mitigate this type of situation.  Specifically for the F-16 :

 

Quote

Air Data Redundancy.

The air data probe supplies two sources of total and static pressures. The third source of total and static pressure is obtained from the air data side probe. Consecutive loss of two air data sources will cause the flight control system to revert to standby gains (fixed values of static and impact pressure). Level 3 handling qualities will result.

 

Three sources of angle-of-attack data are provided; two single-conical, air-flow detector-type angle-of-attack transmitters (one on each side of the aircraft) and a differential pneumatic signal from the air data side probe. The side-mounted angle-of attack transmitters contain quadruple-redundant rotary voltage differential transformers, thereby making the angle-of-attack signal to the flight control computer two-fail operative for electrical failures. The effect of two mechanical angle-of-attack transmitter failures is dependent on the actual failure modes.

https://www.sto.nato.int/publications/AGARD/AGARD-AG-234/AGARD-AG-234.pdf (p.4-4) AGARD-AG-234

 

Quote

Level 3 - Flying qualities such that the airplane can be controlled safely, but pilot workload is excessive or mission effectiveness is inadequate, or both. Pilot rating 6.5 - 9+

https://apps.dtic.mil/dtic/tr/fulltext/u2/746580.pdf (p.1-4) AGARD-CP-06

 

That being said, and regardless if its modelled to the real thing, I think the important thing to know is if this is intended before debating if it is realistic.  I say this simply because they may have modelled it this way or this may be a bug.  Without the answer, we can only speculate.

Edited January 16, 2021 by pbishop

[Deano87]

It's a bug clearly if the anti-ice system doesn't stop the air-data system from freezing up, I think that is easy enough to agree on?

[pbishop]

33 minutes ago, Deano87 said:

It's a bug clearly if the anti-ice system doesn't stop the air-data system from freezing up, I think that is easy enough to agree on?

 

As I stated before, all my tests have been with anti-ice off and frozen on purpose (therefore not related to the bug you refer to).  The goal is to know if the resulting pitch, when frozen, is a bug (not the anti-ice system).  We already agreed there is another bug where the anti-ice does not work correctly, and if I recall, the specific bug you keep referring to has already been acknowledged by ED.  It seems we are going in circles together, but for clarity, we are not talking about the same thing (not a bad thing, just a misunderstanding).  You are not wrong and yes it is the reason more people are experiencing it, but is the pitching normal?

Edited January 16, 2021 by pbishop

[Deano87]

16 hours ago, pbishop said:

 

  You are not wrong and yes it is the reason more people are experiencing it, but is the pitching normal?

 

I would imagine not. Air data in the real jet is redundant and if both systems became unreliable it would revert to "Standby Gains" which are fixed. With the UC up the gains are appropriate for ~600 knots at sea level and with UC down they are appropriate for ~230 knots. As far as I know Standby Gains are not currently functional in the DCS version or any failure modes of the ADC. Hence the pitch oscillations, as the "virtual ADC" is feeding eronious air data info to the "Virtual FLCS" when the pitot heat system fails to do its job.

 

As mentioned previously pitot heat should be on automatically any time the wheels are not in contact with the ground. The switch in the rear left of the cockpit is only for ground pitot heat operation. With the switch in the off position the pitot heat should still be functioning once airborne, it is automatic - I don't know if DCS models this correctly.

Edited January 16, 2021 by Deano87

[BIGNEWY]

If you have track replay examples it is the only way we can investigate this issue. 

 

We do have flight model tweaks coming in future, so consider it work in progress currently.

 

 

[TVC Pilot]

I had it happen the other day again. Not as violent as before, a lot less wing flex. Short clip of video attached showing external view and HUD showing airspeed going to 0 then  increasing back up. I double checked and pitot heat was on.  I'll try to get a track replay. 

Edited January 17, 2021 by TVC Pilot

[Tylertron]

Quote

If you have track replay examples it is the only way we can investigate this issue. 

 

We do have flight model tweaks coming in future, so consider it work in progress currently.

 

I understand there are flight model changes coming - which I appreciate a lot, however is there any chance in this specific issue being looked into and hotpatched soon? The multiplayer server I currently play on has cold weather and... yeah, this happens almost 50% of the time

Edited January 18, 2021 by Tylertron

[BIGNEWY]

33 minutes ago, Tylertron said:

 

I understand there are flight model changes coming - which I appreciate a lot, however is there any chance in this specific issue being looked into and hotpatched soon? The multiplayer server I currently play on has cold weather and... yeah, this happens almost 50% of the time

 

 

I have identified one issue that looks like an icing issue, it is reported, I can not say when it will be fixed. 

 

If you have short track replays showing the issue please attach it. 

 

thanks

[pbishop]

On 1/16/2021 at 1:48 PM, Deano87 said:

As mentioned previously pitot heat should be on automatically any time the wheels are not in contact with the ground. The switch in the rear left of the cockpit is only for ground pitot heat operation. With the switch in the off position the pitot heat should still be functioning once airborne, it is automatic - I don't know if DCS models this correctly.

 

I must have missed this where you mentioned it before, important part of the puzzle that explains a lot as to the "why" and everything you have tried to explain so far.  I looked it up as well in the F-16 flight manual and indeed this statement is correct for the real f-16, learn something new everyday.  I suppose if they fix the pitot heat it would no longer be possible to enter this condition, and therefore it would be irrelevant if the oscillations are normal.  I get what you are saying now.

 

Cheers,

[=Panther=]

On 1/17/2021 at 7:37 AM, TVC Pilot said:

I had it happen the other day again. Not as violent as before, a lot less wing flex. Short clip of video attached showing external view and HUD showing airspeed going to 0 then  increasing back up. I double checked and pitot heat was on.  I'll try to get a track replay. 

 

Your issue is you left your aerial refuel door open. Note the door is visibly open in your external view, and the BLUE RDY light is illuminated on the right indexer. So slightly different issue, I don't think the jet should go for a bucking bull with the door open. However there are limitations in place in the -1 that covers the door and when it should be opened and closed.

 

Regarding the pitot heat, the switch in the cockpit is designed for on the ground icing. Once the jet is in the air, the WOW switch enables the heater regardless of the cockpit switch position.

[TVC Pilot]

On 1/20/2021 at 12:07 AM, =Panther= said:

Your issue is you left your aerial refuel door open. Note the door is visibly open in your external view, and the BLUE RDY light is illuminated on the right indexer. So slightly different issue, I don't think the jet should go for a bucking bull with the door open. However there are limitations in place in the -1 that covers the door and when it should be opened and closed.

 

Regarding the pitot heat, the switch in the cockpit is designed for on the ground icing. Once the jet is in the air, the WOW switch enables the heater regardless of the cockpit switch position.

That is a good point, I had just finished an AR.  Now that you mention it, it has occurred after I AR, but I think it has happened at other times too. Perhaps the change to the control sensitivities with the AR door open has something to do with it. 

[Syd]

For me it's a typical behaviour in minus temperatures. Additionaly altimeter and speed indicator also freeze/show weird values. Turning on/off probe heat doesn't do anything. I even tried turning it on around line up before take off (like the official manuals state) and still no improvement.
Maybe it's just me but I feel like it's happening more often with external wing tanks.

[Hextopia]

Hi, we had this rapid pitch oscillation occur 3 times during a multiplayer mission for two separate people.  No one was above 800 knots, or low on fuel.  Track is attached at google drive below: (It's long)

 

https://drive.google.com/file/d/1rRBDHDUcvf-FiV8cxgas583Dn9NnTqxN/view?usp=sharing

I wish I had a shorter track to show it off, but it's such an inconsistent bug that it's hard to grab it intentionally.

First occurred at about 30 minutes into the mission, for myself.  I hit the ground due to loss of control during the pitch oscillations.

 

Track appears bugged, because my aircraft veers off and does some strange stuff at high altitude when I should be in formation with 3 others during my second flight.  Regardless, the bug occurs again for my incorrect track, and occurs for another flight member just past 1 hour into the track.  He goes into pitch oscillations during a turn, then an aggressive stall and flips end over end and recovers just shy of impacting the ground; I go into another uncontrollable pitch oscillation during a dive and crater.

[BIGNEWY]

It sounds and looks like the pitot issue that has been reported already and will be fixed in 2.7 or it is a result of the refuel door being left open.

 

Please wait for 2.7 and let me know if you see it again.

 

Thanks