correct as is Continuous (all be it slow) pitch up

[Arco]

Hello!

Noticed since last patch that the viper likes to have an ever so slight constant pitch up when in level flight at constant speed. Discovered this during a flight today with a friend and tried it out in single player after. The problem persisted although it was more pronounced in multiplayer. I'll attach both track files. It's most clearly shown in the mp one during the return flight.

The same rise can also be seen during take off climbs (and climbs in general). To my understanding this is not the correct behaviour since the Viper should auto trim in pitch. 

Also don't mind the sidewinder launch during the mk 82 drop. That's already reported (and not resolved).

 MP linked here due to size: https://drive.google.com/file/d/1aY_ZvALBYOdRRa3cRpR7ynHyknuP4sps/view?usp=sharing

Pitch_rise.trk

Edited June 28, 2022 by Arco
Additions

[RuskyV]

Does it still pitch up after you trim it out?
 

If it does check and see the stick your using isn’t commanding the pitch, it could be a hardware issue, a way to check is to look in the axis bindings to see if there is any deflection. If there is try wiggling the stick to see if it goes away. Might be a bad pot or HAL sensor.

Edited June 29, 2022 by RuskyV

[Arco]

My stick is not the issue. I've already checked. Multiple people I've talked to are also having this issue. The FLCS in the viper should automatically trim in pitch so it should just leave the FPM wherever you  set it in pitch 

[BIGNEWY]

The FLCS does not auto-trim pitch, it only trims the aircraft to 1G. 

As mentioned it maybe worth checking your controller calibration also. 

For future tracks go with an air start aircraft it will reduce the size and time needed for the track 

thanks

[Arco]

11 minutes ago, BIGNEWY said:

The FLCS does not auto-trim pitch, it only trims the aircraft to 1G. 

As mentioned it maybe worth checking your controller calibration also. 

For future tracks go with an air start aircraft it will reduce the size and time needed for the track 

thanks

And level flight/steady climb is not 1G? 
Like I said, my stick is not the issue here. It was the first thing I checked. 

[Arco]

Here's two other tracks still showing the issue. If you take a look on the stick inputs there's no control input and it's completely centered other than when I'm purposely repositioning the nose to the horizon and during the initial take off. This is also confirmed when checking through the vpc config tool. It remains completely neutral. 

Could you please review this again, @BIGNEWY?

Pitch_rise_takeoff.trk Pitch_rise2.trk

Edited June 29, 2022 by Arco

[BIGNEWY]

Hi, 

ive checked the new tracks again I am not seeing a problem, FLCS will look for 1G it does not trim the aircraft, you need to trim for the speed and attitude you wish to have. 

[Arco]

I just want to confirm you are seeing the pitch right in these tracks? Or if this is something you've maybe corrected internally on your builds?
I'm just trying to understand your view here. If it's looking for 1G how does that reflect to a pitch up in level flight at a constant speed?

[itn]

It's easy to replicate and see with time acceleration. Attached is another track. I used Unlimited Fuel to prevent any weight and CoG effects. HOTAS completely disconnected, using only keyboard and mouse.

The pitch-up is slow but it's there, easily seen after I disable AP (04:04:00 cockpit time) and time acceleration is on.

Pitch (time accel).trk

[777coletrain]

I just watched that last clip and there is definitely a very slow (around 1 degree per 4 minutes) pitch up. If the FLCS was maintaining 1G the nose should have stayed level

[_SteelFalcon_]

She does seem to pull up ever so slightly. With the VVI perfectly level with the horizon. Disconnecting the stick and contols perfectly centered, the vvi starts creeping up above the horizon line very very slowly. And this whithout accelerating or decelerating

[BIGNEWY]

FLCS Looks for 1G it does not trim the aircraft, you need to trim for level flight. 

[razo+r]

Level flight should be 1G, so it should not pitch anywhere. 

[Aquorys]

19 minutes ago, _SteelFalcon_ said:

She does seem to pull up ever so slightly. With the VVI perfectly level with the horizon. Disconnecting the stick and contols perfectly centered, the vvi starts creeping up above the horizon line very very slowly. And this whithout accelerating or decelerating

Sounds normal to me, especially since it's not even trimmed for level flight, but for 1G acceleration. First of all, you don't have exactly 1G everywhere on earth, because the earth is not perfectly round and homogenous mass-wise, and gravity is an effect of mass and distance. Therefore, even a perfect 1G trim would show some pitch drift as you fly over different regions of the earth. But even if the aircraft used gyroscopes to make sure none of the aircraft's axes rotate, you would still get a small pitch-up drift in relation to the surface of the earth, because the measurements of gyroscopes are not coupled to the earth's curvature and rotation.

[Arco]

5 hours ago, BIGNEWY said:

FLCS Looks for 1G it does not trim the aircraft, you need to trim for level flight. 

That's the thing though, disregarding the issue posted here and just addressing this, trimming this out is not possible. The trim is just not sensitive enough for it. 

[BIGNEWY]

Just now, Arco said:

That's the thing though, disregarding the issue posted here and just addressing this, trimming this out is not possible. The trim is just not sensitive enough for it. 

trim hat for basic trimming, dials on left console for fine trimming, it seems to work well for me. 

[Arco]

4 hours ago, Aquorys said:

Sounds normal to me, especially since it's not even trimmed for level flight, but for 1G acceleration. First of all, you don't have exactly 1G everywhere on earth, because the earth is not perfectly round and homogenous mass-wise, and gravity is an effect of mass and distance. Therefore, even a perfect 1G trim would show some pitch drift as you fly over different regions of the earth. But even if the aircraft used gyroscopes to make sure none of the aircraft's axes rotate, you would still get a small pitch-up drift in relation to the surface of the earth, because the measurements of gyroscopes are not coupled to the earth's curvature and rotation.

G differs with 0,7% on the extreme ends. From 9.7639 m/s² at a mountain range in Peru to 9,8337 m/s² over the arctic ocean. This is simply just not a factor. 

1 minute ago, BIGNEWY said:

trim hat for basic trimming, dials on left console for fine trimming, it seems to work well for me. 

Believe me, I've tried. It only makes the pitch worse

[rob10]

How sensitive would the G sensor be?  If you were off by even 0.01 G you could probably get a small offset from level flight that wouldn't matter at all for normal flight control purposes (i.e. FLCS trimming to 1G - it may not be exactly 1.000000 G, but it's close enough for flight purposes) but could lead to a slight pitch up that would increase your altitude over time.  And using G you'd have no way to correct for that since it's staying constant and has no way to realize that your altitude is increasing (vs altitude hold A/P that will at some point detect that you've climbed and correct for that).

[DummyCatz]

I think I'm gonna save BIGNEWY on this one.

The main feedback being used in cruise gains is normal acceleration, often denoted as 'Nz', sometimes 'an'. When flying straight with no bank angle, the normal acceleration of the aircraft would be cosine(pitch angle). So only when the pitch angle equals to 0, the normal acceleration is 1g. Otherwise the normal acceleration will be less than 1g when flying straight at a certain pitch angle, and the aircraft will pull up to reach 1g. This behaviour can be observed on any aircraft that seeks 1g with hands off.

However if you put your gear down or open the AR door, the normal acceleration feedback is replaced by pitch rate feedback, and the aircraft will hold zero pitch rate hands-off at below 400 kts.

[DummyCatz]

7 hours ago, Aquorys said:

Sounds normal to me, especially since it's not even trimmed for level flight, but for 1G acceleration. First of all, you don't have exactly 1G everywhere on earth, because the earth is not perfectly round and homogenous mass-wise, and gravity is an effect of mass and distance. Therefore, even a perfect 1G trim would show some pitch drift as you fly over different regions of the earth. But even if the aircraft used gyroscopes to make sure none of the aircraft's axes rotate, you would still get a small pitch-up drift in relation to the surface of the earth, because the measurements of gyroscopes are not coupled to the earth's curvature and rotation.

Quick question, if you put an F-16 on the Moon, let's say on a level ground, what would be the G meter display on the HUD? If it can even fly straight and level, will it pitch up?

Edited July 1, 2022 by DummyCatz

[Hummingbird]

A 1 G auto trimming aircraft will try to achieve 1 G perpendicular to the direction of flight. If the direction of flight is up (or down) in relation to level flight, then you're not at 1 G perpendicular to direction of flight anymore, and hence the FLCS will be commanding a slight pitch up to achieve said 1 G. 

Hence its correct behavior. 

 

EDIT: Dummycatz post explains it perfectly. 

Edited July 1, 2022 by Hummingbird

[Aquorys]

4 hours ago, DummyCatz said:

Quick question, if you put an F-16 on the Moon, let's say on a level ground, what would be the G meter display on the HUD? If it can even fly straight and level, will it pitch up?

About 0.17G. Ignoring the fact that an F-16's engine would not work on the moon, and that an F-16 would not be able to fly on the moon due to the absence of an atmosphere that could produce lift, and instead assuming that it could fly on the moon, it would constantly pitch up instead of flying level.

If you wanted it to fly level in an environment that is different from the 1G environment on earth, you would have to ground-calibrate the accelerometers to whatever the gravity is in that environment.

 

[Frederf]

It follows from the math that any flight path has an orthogonal acceleration of cosine of the flight path angle. For flight path angles of -90 to 0 (non-inclusive) that causes a positive turn radius in the vertical plane. For flight path angles of 0 (non-inclusive) to +90 that is also positive turn radius. Only exactly 0 FPA flight allows non-divergent behavior.

I hope that the G sensor is measuring the vertical component of gravity along the axis which is orthogonal to the flight path and not "out the top" of the airplane. If the latter is the case then non-divergent 1g level flight is only possible at 0 AOA.

[DummyCatz]

3 hours ago, Frederf said:

It follows from the math that any flight path has an orthogonal acceleration of cosine of the flight path angle. For flight path angles of -90 to 0 (non-inclusive) that causes a positive turn radius in the vertical plane. For flight path angles of 0 (non-inclusive) to +90 that is also positive turn radius. Only exactly 0 FPA flight allows non-divergent behavior.

I hope that the G sensor is measuring the vertical component of gravity along the axis which is orthogonal to the flight path and not "out the top" of the airplane. If the latter is the case then non-divergent 1g level flight is only possible at 0 AOA.

If the former is the case, then a reschedule of the AOA limiter and g-command module of F-16 FLCS is required. For example the current AOA limiter will reduce commanded g to 1g at 25.X deg AOA, what would be the actual AOA limit in this case?

Edited July 2, 2022 by DummyCatz

[RuskyV]

Well I guess this blows my flat earth theory clean out the water, I was sort of hopeful that the viper was going to continue flying straight and level…..back to the drawing board I guess