need track replay Viper Flight Model possible error

[Cobb]

I was playing around with the flight model while trying to set up my pressure sensing stick, and I realized that the flight model, in particular the roll axis, seems to be incorrect. 

The DCS Viper had always seemed to fly a bit odd, not intuitive like a real airplane, but I could never figure out why.  Something is off about it.  I read numerous comments on the forums, and watched several videos, that have this odd pitch-up moment when rolling out of a turn to straight and level.  It's done it to me, and real aircraft (even other DCS aircraft) don't do this.  Why the DCS Viper?  I've trained my muscle memory to pitch down when rolling out to hold an altitude, but this is not a trait with real airplanes.

I think I've found out why it acts this way.  I was doing some high AOA flight to sort out stick forces to hold different steady nose-high attitudes, and discovered that ED has programmed the rolling axis of the Viper to be on the Flight Path Marker, not the gun cross in the HUD.  In any airplane, there are three axes of rotation (pitch, roll, yaw) that all intersect at the Center of Gravity.  Every airplane, no matter the pitch condition, the ailerons (and stabilators) will only roll the aircraft about this lateral axis, which runs down the center of the fuselage from front to back, parallel to the long axis of the fuselage and does not move or change with AoA. This axis is depicted by the gun cross on the HUD. If I pitch up to 30 degrees AoA and then roll the airplane, the roll should always center on this axis (the gun cross), not the FPM which in this case will be well below.  In this case, I would end up in a nose high turn and the nose would not roll through the horizon like it does now.

But the DCS Viper rolls around the FPM with high AoA.  You can see this by setting up a high AoA flight and inducing a roll. The gun cross will move laterally around the FPM, when it should roll around the gun cross and the FPM will then adjust to the direction of flight.

There is one other thing that can contribute to this behavior. In the flight control software, rudder is added to the roll input to assist in maintaining coordinated flight.  This is designed to counteract the situation of adverse yaw (where the nose points opposite of the direction of turn due to drag increase on the outside wing).  Most airplanes compensate for this in various ways, and the Viper is no different.  Rudder is added to the roll input by the flight computers.  Again, in a real airplane I can manually duplicate this odd behavior by inputting positive rudder with aileron.  But this would technically be a poor technique, as adding that much rudder would induce a skid, which is too much rudder input for good, coordinated flight.

I'd like ED to have a look at this and see if I'm correct.  It may be simply adjusting (reducing) the rudder input in the FM.  The biggest issue I've seen is the weird pitch up when rolling back to wings level and having to add significant down stick to maintain an altitude.

Cobb

[BIGNEWY]

Hi, we will need to see a short as possible track replay of your tests, please reproduce in a single player mission on Caucasus, it will ensure the track replay is reliable. And please add any public evidence to back your claims up, you can DM it to me also. 

thank you 

[Cobb]

Ok.  Just track files or videos?  Let me see what I can work up...

[TobiasA]

The real F-16 FLCS tries to roll around the velocity vector.

You can see this in some videos, but I can't find the manual right now. Think it was somewhere in NASA paper 1538, but I am not sure.

 

 

 

 

This is intentional.

The F-16 should roll around the FPM.

Edited October 16, 2024 by TobiasA

[Cobb]

Indeed, the first video appears to be exactly like what I'm seeing in the DCS Viper.  I fly planes for a living IRL, even big jets, but nothing like the Viper, and we certainly do not maneuver like this jet is capable of.  Based on watching these vids, it appears that I'm incorrect in my analysis.  Thanks for that.

Cobb

[Raven (Elysian Angel)]

4 hours ago, Cobb said:

I've trained my muscle memory to pitch down when rolling out to hold an altitude, but this is not a trait with real airplanes.

I have no idea about real aircraft (I am just an armchair geek), but pitching down to remain level after rolling out after heavy manoeuvring is pretty common in DCS. Off the top of my head, the F-14 requires it, the F-15E too... Those are aircraft I did canyon runs with recently and in that scenario it's pretty obvious. There are probably more examples  

[DummyCatz]

Related pitch behavior issues:

1. pitch down when rolling to the left

2. pitch up when roll-out

 

Edited October 17, 2024 by DummyCatz

[DummyCatz]

• Fixed. FLCS Pure roll inputs cause abnormal pitch up and G.

Did the update fix the pitch issue you described?

[Hobel]

vor 4 Stunden schrieb DummyCatz:

Did the update fix the pitch issue you described?

No.

[TobiasA]

vor 23 Stunden schrieb DummyCatz:

• Fixed. FLCS Pure roll inputs cause abnormal pitch up and G.

Did the update fix the pitch issue you described?

It broke the FLCS rudder input when rolling at high AOA and made landing a nightmare, but other than that, it changed nothing.