correct as is Yaw and Pitch inertia values are Reversed.

[FusRoPotato]

I'd like you guys to explain something to me.

It was first known that the F-16 in this game, for whatever reason, could never perform a knife edge. It was as if it had less than half its expected body lifting force due to sideslip. Ok, so then I suppose it would make sense that the rudder authority would have to be fictionally enhanced a lot as to not appear anemic in yaw. But wait, this creates a problem. At high speeds and low altitudes, this can create an oscillation because the gains for yaw were calibrated to realistic rudder forces. A problem we had that suddenly went away one patch, but how? However, when it went away, the aircraft was still not able to perform knife edges.

So now I come around and find this in one of the FM files.

	moment_of_inertia	= {  12875.0, 85552.0, 75674.0, -1331.0},--Ix,Iy,Iz,Ixy			
	-- Ix(roll) = 9496, Iy(pitch) = 55814, Iz(yaw) = 63100 [slug-ft2]
	--moment_of_inertia = {  4610.0, 48882.0, 52678.0, 0.0},--Ix,Iy,Iz,Ixy

I found a copy of these numbers from a paper: A nonlinear dynamic inversion-based neurocontroller for unmanned combat aerial vehicles during aerial refuelling - Jimoh Pedro

(PDF) A nonlinear dynamic inversion-based neurocontroller for unmanned combat aerial vehicles during aerial refuelling (researchgate.net)

Which referenced these numbers sourced from:  Morelli, E.A. (1998). Global nonlinear parametric modeling with application to F-16 aerodynamics, Technical report, Dynamics and Control Branch, NASA Langley Research Centre, Hampton, VA.

https://zenodo.org/record/1262949/files/article.pdf

Which does not actually contain these numbers or derivations of them. Does it mean they aren't legitimate numbers? Not necessarily, but an interesting bit of this is that Iz and Iy are swapped in value.

I found another source of inertias from Morelli_Flight_Inertia_JGCD_Paper_final0921.pdf (nasa.gov) extracted from experimental data

	slug-ft2	kg-m2
Ixx-roll	9,496	12819
Iyy-pitch	55,814	75348
Izz-yaw	63,100	85185

Izz is always the highest but somehow pitch inertia in the file is highest. Is it possible the reason pitch seems so floppy is that it has its Inertia value swapped with yaw? Or is it possible there's a problem with filtering somewhere causing excessive delay of input?

Perhaps with some programming, I could extract some comparative graphs through the export lua but I'm not 100% sure I have the skill for that. I just know this plane feels significantly less responsive compared to all the other aircraft we have and also struggles to change direction, like it's behind a 200 ms ping. 

Are the Inertias backwards?

Are the control surfaces constrained to be slow?

Are they stuck behind an aggressive filter?

Have the gains been tampered with?

White paper me bro

 

Edited April 13, 2023 by FusRoPotato

[janitha2]

10 minutes ago, FusRoPotato said:

I'd like you guys to explain something to me.

It was first known that the F-16 in this game, for whatever reason, could never perform a knife edge. It was as if it had less than half its expected body lifting force due to sideslip. Ok, so then I suppose it would make sense that the rudder authority would have to be fictionally enhanced a lot as to not appear anemic in yaw. But wait, this creates a problem. At high speeds and low altitudes, this can create an oscillation because the gains for yaw were calibrated to realistic rudder forces. A problem we had that suddenly went away one patch, but how? However, when it went away, the aircraft was still not able to perform knife edges.

So now I come around and find this in one of the FM files.

	moment_of_inertia	= {  12875.0, 85552.0, 75674.0, -1331.0},--Ix,Iy,Iz,Ixy			
	-- Ix(roll) = 9496, Iy(pitch) = 55814, Iz(yaw) = 63100 [slug-ft2]
	--moment_of_inertia = {  4610.0, 48882.0, 52678.0, 0.0},--Ix,Iy,Iz,Ixy

I found a copy of these numbers from a paper: A nonlinear dynamic inversion-based neurocontroller for unmanned combat aerial vehicles during aerial refuelling - Jimoh Pedro

(PDF) A nonlinear dynamic inversion-based neurocontroller for unmanned combat aerial vehicles during aerial refuelling (researchgate.net)

Which referenced these numbers sourced from:  Morelli, E.A. (1998). Global nonlinear parametric modeling with application to F-16 aerodynamics, Technical report, Dynamics and Control Branch, NASA Langley Research Centre, Hampton, VA.

https://zenodo.org/record/1262949/files/article.pdf

Which does not actually contain these numbers or derivations of them. Does it mean they aren't legitimate numbers? Not necessarily, but an interesting bit of this is that Iz and Iy are swapped in value.

I found another source of inertias from Morelli_Flight_Inertia_JGCD_Paper_final0921.pdf (nasa.gov) extracted from experimental data

	slug-ft2	kg-m2
Ixx-roll	9,496	12819
Iyy-pitch	55,814	75348
Izz-yaw	63,100	85185

Izz is always the highest but somehow pitch inertia in the file is highest. Is it possible the reason pitch seems so floppy is that it has its Inertia value swapped with yaw? Or is it possible there's a problem with filtering somewhere causing excessive delay of input?

Perhaps with some programming, I could extract some comparative graphs through the export lua but I'm not 100% sure I have the skill for that. I just know this plane feels significantly less responsive compared to all the other aircraft we have and also struggles to change direction, like it's behind a 200 ms ping. 

Are the Inertias backwards?

Are the control surfaces constrained to be slow?

Are they stuck behind an aggressive filter?

Have the gains been tampered with?

White paper me bro

 

excellent find! 
So 100% sure the rudder limits are wrong because if you look in the -1 flcs limits on ANY! block manual the rudder limiter is 0 at 26AOA 
right now in game the rudder limits to 0 at 15AOA!!!! so yes the Flight model is still very wrong and ED are going take it out of... "early access"

Please take a look @BIGNEWY 

[BIGNEWY]

24 minutes ago, FusRoPotato said:

I'd like you guys to explain something to me.

It was first known that the F-16 in this game, for whatever reason, could never perform a knife edge. It was as if it had less than half its expected body lifting force due to sideslip. Ok, so then I suppose it would make sense that the rudder authority would have to be fictionally enhanced a lot as to not appear anemic in yaw. But wait, this creates a problem. At high speeds and low altitudes, this can create an oscillation because the gains for yaw were calibrated to realistic rudder forces. A problem we had that suddenly went away one patch, but how? However, when it went away, the aircraft was still not able to perform knife edges.

So now I come around and find this in one of the FM files.

	moment_of_inertia	= {  12875.0, 85552.0, 75674.0, -1331.0},--Ix,Iy,Iz,Ixy			
	-- Ix(roll) = 9496, Iy(pitch) = 55814, Iz(yaw) = 63100 [slug-ft2]
	--moment_of_inertia = {  4610.0, 48882.0, 52678.0, 0.0},--Ix,Iy,Iz,Ixy

I found a copy of these numbers from a paper: A nonlinear dynamic inversion-based neurocontroller for unmanned combat aerial vehicles during aerial refuelling - Jimoh Pedro

(PDF) A nonlinear dynamic inversion-based neurocontroller for unmanned combat aerial vehicles during aerial refuelling (researchgate.net)

Which referenced these numbers sourced from:  Morelli, E.A. (1998). Global nonlinear parametric modeling with application to F-16 aerodynamics, Technical report, Dynamics and Control Branch, NASA Langley Research Centre, Hampton, VA.

https://zenodo.org/record/1262949/files/article.pdf

Which does not actually contain these numbers or derivations of them. Does it mean they aren't legitimate numbers? Not necessarily, but an interesting bit of this is that Iz and Iy are swapped in value.

I found another source of inertias from Morelli_Flight_Inertia_JGCD_Paper_final0921.pdf (nasa.gov) extracted from experimental data

	slug-ft2	kg-m2
Ixx-roll	9,496	12819
Iyy-pitch	55,814	75348
Izz-yaw	63,100	85185

Izz is always the highest but somehow pitch inertia in the file is highest. Is it possible the reason pitch seems so floppy is that it has its Inertia value swapped with yaw? Or is it possible there's a problem with filtering somewhere causing excessive delay of input?

Perhaps with some programming, I could extract some comparative graphs through the export lua but I'm not 100% sure I have the skill for that. I just know this plane feels significantly less responsive compared to all the other aircraft we have and also struggles to change direction, like it's behind a 200 ms ping. 

Are the Inertias backwards?

Are the control surfaces constrained to be slow?

Are they stuck behind an aggressive filter?

Have the gains been tampered with?

White paper me bro

 

Hi, 

I will ask the team, but please always include a track replay from your testing if you think something is wrong.

edit: We do have a report already and some changes are coming for the F-16C regarding the knife edge

so please continue to be patient. 

thank you

[NineLine]

Dear all, I have reopened this to update what we have been doing.

We have continued to investigate and spoke with three Viper pilots, including a Thunderbird pilot. All said the same thing. You should not be able to maintain altitude at a 90-degree knife edge. You will lose altitude. Only when at around 85-degrees or lower should you be able to sustain altitude. The aircraft can simply not generate enough lift. Based on our current, internal version, this matches up.

Thanks.

[FusRoPotato]

I had been doing some research and calculations of my own as well using basic body frame lift estimations from Roskam. Apparently, the F-16 is physically capable of maintaining a knife edge between ~300-480 kts but will never achieve sustaining it (while naked) on some models because the FLCS does not allow the required and achievable sideslip ranging between 12-18 degrees at those speeds. To minimize the risk of departure at more extreme angles, it is hard limited to 10 by the computer, thus will never sustain one without cheating by rolling a few degrees and stealing some z axis lift.

However, the calculations are close, and since I don't have any reference to EZ calcs based on pylon interactions, I suspect that a CFD analysis of an airframe including pylons, or even just a targeting pod, may yield very different results just based on the added body lift at 10 degrees sideslip. I make this assumption because the B and D variants are just barely capable of sustaining knife-edges at 10 degrees into transonic. What are your thoughts on xz-plane lift-forces due to pylons and stores? I'm not sure I can notice whether or not the effect exists in game, but to be fair, I'm not certain I honestly really care because there's no need for knife edges, but it would be a very nice touch.

What about these inertia numbers? I titled this post flopping fish because the knife edge wasn't important. The order of y and z Inertia values are flipped in the lua. Maybe it's worth double checking they aren't flipped in the FM as well and not just a typo? I ask for two reasons. One, it's an obvious mistake or typo. Two, I sense this module feels like it has a lot more control latency than others. Excessive y-axis inertia can contribute to that effect, but it could be something else as well. It could even be realistic, but how would you know? Based on the general nature of MILSPECs, it's certainly not a reasonable expectation that any noticeable degree of latency or sloppiness would be acceptable.

[janitha2]

11 hours ago, NineLine said:

Dear all, I have reopened this to update what we have been doing.

We have continued to investigate and spoke with three Viper pilots, including a Thunderbird pilot. All said the same thing. You should not be able to maintain altitude at a 90-degree knife edge. You will lose altitude. Only when at around 85-degrees or lower should you be able to sustain altitude. The aircraft can simply not generate enough lift. Based on our current, internal version, this matches up.

Thanks.

@NineLineIt would be great if we can clarify the yaw FLCS limits as well since every dash one i have found so far say rudder limited to 0 at 26 aoa but in dcs rudder limits to 0 at 15 aoa.
refer T.O. GR1F-16CJ-1 pg1-125 figure 1-44 thanks!

Edited March 26, 2023 by janitha2

[NineLine]

7 hours ago, janitha2 said:

@NineLineIt would be great if we can clarify the yaw FLCS limits as well since every dash one i have found so far say rudder limited to 0 at 26 aoa but in dcs rudder limits to 0 at 15 aoa.
refer T.O. GR1F-16CJ-1 pg1-125 figure 1-44 thanks!

 

Already fixed internally and should be coming in a later update. Thanks.

[janitha2]

14 hours ago, NineLine said:

Already fixed internally and should be coming in a later update. Thanks.

Thank you @NineLine!!!!

[dutchie_031]

On 3/26/2023 at 8:29 AM, FusRoPotato said:

I had been doing some research and calculations of my own as well using basic body frame lift estimations from Roskam. Apparently, the F-16 is physically capable of maintaining a knife edge between ~300-480 kts but will never achieve sustaining it (while naked) on some models because the FLCS does not allow the required and achievable sideslip ranging between 12-18 degrees at those speeds. To minimize the risk of departure at more extreme angles, it is hard limited to 10 by the computer, thus will never sustain one without cheating by rolling a few degrees and stealing some z axis lift.

However, the calculations are close, and since I don't have any reference to EZ calcs based on pylon interactions, I suspect that a CFD analysis of an airframe including pylons, or even just a targeting pod, may yield very different results just based on the added body lift at 10 degrees sideslip. I make this assumption because the B and D variants are just barely capable of sustaining knife-edges at 10 degrees into transonic. What are your thoughts on xz-plane lift-forces due to pylons and stores? I'm not sure I can notice whether or not the effect exists in game, but to be fair, I'm not certain I honestly really care because there's no need for knife edges, but it would be a very nice touch.

What about these inertia numbers? I titled this post flopping fish because the knife edge wasn't important. The order of y and z Inertia values are flipped in the lua. Maybe it's worth double checking they aren't flipped in the FM as well and not just a typo? I ask for two reasons. One, it's an obvious mistake or typo. Two, I sense this module feels like it has a lot more control latency than others. Excessive y-axis inertia can contribute to that effect, but it could be something else as well. It could even be realistic, but how would you know? Based on the general nature of MILSPECs, it's certainly not a reasonable expectation that any noticeable degree of latency or sloppiness would be acceptable.

Was actually curious what the state of investigation and answer was of the actual question from OP. 
Just curious if that part is also being looked at or on the list to be looked at
The Knife edge was only mentioned, but not the main part of the actual initial post imo.
But I have the feeling this post is now titled and deemed only knife edge related while it's not. 

Edited March 28, 2023 by dutchie_031

[FireNLD]

3 minutes ago, dutchie_031 said:

Was actually curious what the state of investigation and answer was of the actual question from OP. 
The Knife edge was only mentioned, but not the main part of the actual initial post imo.
But I have the feeling this post is now titled and deemed only knife edge related while it's not. 

@NineLine A good question, can you shed a light on this? Thanks in advance!

[DummyCatz]

The inertia figures come from page 43, NASA TP-1538 (https://ntrs.nasa.gov/citations/19800005879) dated December 1, 1979.

As for the while paper, here's one sitting in the wish list:

 

[janitha2]

On 3/23/2023 at 2:59 PM, FusRoPotato said:

I'd like you guys to explain something to me.

It was first known that the F-16 in this game, for whatever reason, could never perform a knife edge. It was as if it had less than half its expected body lifting force due to sideslip. Ok, so then I suppose it would make sense that the rudder authority would have to be fictionally enhanced a lot as to not appear anemic in yaw. But wait, this creates a problem. At high speeds and low altitudes, this can create an oscillation because the gains for yaw were calibrated to realistic rudder forces. A problem we had that suddenly went away one patch, but how? However, when it went away, the aircraft was still not able to perform knife edges.

So now I come around and find this in one of the FM files.

	moment_of_inertia	= {  12875.0, 85552.0, 75674.0, -1331.0},--Ix,Iy,Iz,Ixy			
	-- Ix(roll) = 9496, Iy(pitch) = 55814, Iz(yaw) = 63100 [slug-ft2]
	--moment_of_inertia = {  4610.0, 48882.0, 52678.0, 0.0},--Ix,Iy,Iz,Ixy

I found a copy of these numbers from a paper: A nonlinear dynamic inversion-based neurocontroller for unmanned combat aerial vehicles during aerial refuelling - Jimoh Pedro

(PDF) A nonlinear dynamic inversion-based neurocontroller for unmanned combat aerial vehicles during aerial refuelling (researchgate.net)

Which referenced these numbers sourced from:  Morelli, E.A. (1998). Global nonlinear parametric modeling with application to F-16 aerodynamics, Technical report, Dynamics and Control Branch, NASA Langley Research Centre, Hampton, VA.

https://zenodo.org/record/1262949/files/article.pdf

Which does not actually contain these numbers or derivations of them. Does it mean they aren't legitimate numbers? Not necessarily, but an interesting bit of this is that Iz and Iy are swapped in value.

I found another source of inertias from Morelli_Flight_Inertia_JGCD_Paper_final0921.pdf (nasa.gov) extracted from experimental data

	slug-ft2	kg-m2
Ixx-roll	9,496	12819
Iyy-pitch	55,814	75348
Izz-yaw	63,100	85185

Izz is always the highest but somehow pitch inertia in the file is highest. Is it possible the reason pitch seems so floppy is that it has its Inertia value swapped with yaw? Or is it possible there's a problem with filtering somewhere causing excessive delay of input?

Perhaps with some programming, I could extract some comparative graphs through the export lua but I'm not 100% sure I have the skill for that. I just know this plane feels significantly less responsive compared to all the other aircraft we have and also struggles to change direction, like it's behind a 200 ms ping. 

Are the Inertias backwards?

Are the control surfaces constrained to be slow?

Are they stuck behind an aggressive filter?

Have the gains been tampered with?

White paper me bro

 

 

4 hours ago, DummyCatz said:

The inertia figures come from page 43, NASA TP-1538 (https://ntrs.nasa.gov/citations/19800005879) dated December 1, 1979.

As for the while paper, here's one sitting in the wish list:

 

What will happen if i switch the values around, will i be able to test it in single player?

[NineLine]

On 3/23/2023 at 2:29 AM, FusRoPotato said:

So now I come around and find this in one of the FM files.

Which FM file?

[FusRoPotato]

mods/aircraft/F-16C/FM/config.lua Line 38

On 3/29/2023 at 1:29 AM, janitha2 said:

 

What will happen if i switch the values around, will i be able to test it in single player?

Nothing. I've tried making the values super high or small to verify the directions, but they don't seem to affect the aircraft at all. This is why I pose the question, because if this is at all any kind of reference to internally hidden configurations, it indicates a mistake in order that might explain why pitch feels so mushy compared to past versions.

Edited March 30, 2023 by FusRoPotato

[FusRoPotato]

Ok, @janitha2's video proves it because they edited their numbers and were able to get a reaction. When I edited my file and reloaded the game, I don't know why, but it didn't change anything, probably because I edited the file, then closed the game, then reopened it. Either that or I did the wrong file.

The Iy is the pitch axis and should be 75,674, but when you change this number in the file to zero, the yaw oscillates. If you change the Iz to zero, which is supposed to be the yaw axis at ~85,552, the pitch oscillates. This proves they are used incorrectly.

Yaw axis inertia always has the highest value because it includes both the body length of the aircraft and wingspan. Pitch is only body length, and roll is only wingspan. Sorta...

When I saw the values in the table have a different relative order of magnitude compared to the tables commented out, I knew they had to have been flipped by mistake.

Thanks again for making that video Janitha2

 

 

Edited March 30, 2023 by FusRoPotato

[janitha2]

I edited the config file in this location 

In this line

clearly the Y and Z are swaped, please check it out @NineLine

Also note this is not about the knife edge flight this is about the pitch (Y axis) being slugish. It has been incorrectly renamed

Edited March 30, 2023 by janitha2

[FusRoPotato]

@BIGNEWY

I'm trying to take the quality of this product seriously, but you locked the thread and renamed it?

Why are you marking things correct if you don't even know what correct is, and instead of reading the thread or testing the complaint, editing my post so you don't have to? There are just two numbers backwards, numbers that would show obvious error in a response analysis.

I would also advise that the fact his aircraft spazzed so little for what essentially should have been a singularity suggests there's something else wrong with the state space equations. Are you the person actively working on the F-16 Flight model?

[NineLine]

On 4/1/2023 at 1:41 AM, FusRoPotato said:

@BIGNEWY

I'm trying to take the quality of this product seriously, but you locked the thread and renamed it?

Why are you marking things correct if you don't even know what correct is, and instead of reading the thread or testing the complaint, editing my post so you don't have to? There are just two numbers backwards, numbers that would show obvious error in a response analysis.

I would also advise that the fact his aircraft spazzed so little for what essentially should have been a singularity suggests there's something else wrong with the state space equations. Are you the person actively working on the F-16 Flight model?

As was mentioned before, you need to wait for a later update in which the rudder authority at high AoA has been adjusted.

However, even with the upcoming change, you should not be able to hold a 90-degree knife edge without altitude loss.

On 3/30/2023 at 4:00 AM, janitha2 said:

I edited the config file in this location 

In this line

clearly the Y and Z are swaped, please check it out @NineLine

Also note this is not about the knife edge flight this is about the pitch (Y axis) being slugish. It has been incorrectly renamed

 

Thank you I will flag with the team. 

[janitha2]

10 hours ago, NineLine said:

As was mentioned before, you need to wait for a later update in which the rudder authority at high AoA has been adjusted.

However, even with the upcoming change, you should not be able to hold a 90-degree knife edge without altitude loss.

Thank you I will flag with the team. 

thanks for looking into it!

[FusRoPotato]

Mods\aircraft\F-16C\FM\config.lua still has inertia values assigned to the incorrect axis that result in F16 having a pitch response that poorly matches public data.

	center_of_mass		= {-1.4, -0.069, 0.0},	--x,y,z
	moment_of_inertia	= {  12875.0, 85552.0, 75674.0, -1331.0},--Ix,Iy,Iz,Ixy			-- Ix(roll) = 9496, Iy(pitch) = 55814, Iz(yaw) = 63100 [slug-ft2]
	--moment_of_inertia = {  4610.0, 48882.0, 52678.0, 0.0},--Ix,Iy,Iz,Ixy

line 37 shows 85552.0 as Iy and 75674 as Iz. These two numbers need to be switched. Iz for American planes is the (positive-down) (positive-right-yaw) axis and Iy is (positive-right-wing) (positive-up-pitch) axis, but in Russia, the standard orientation is Z is (positive-left-wing) (negative-up-pitch) and Y is (positive-up) (negative-right-yaw). This is a data entry mistake as the values are correct, but their position in the table is not.

Moments of inertia are found on pg 43 19800005879.pdf (nasa.gov) @DummyCatz

Line 37 should read:

moment_of_inertia    = {  12875.0, 75674.0, 85552.0, -1331.0},

The correlation between table index and affected axis have been verified in this video:

 

 

[Sile]

Can't check the file and values myself currently. So has this been fixed like stated in changelog from 13.4.2023 (DCS 2.8.4.38947 Open Beta)?
I mean the values are clearly reversed.

Or does the changelog line refer to a different issue?
"Fixed: Tuned rudder authority limiters. One effect is greater rudder authority at higher angle of attack."

 

[_SteelFalcon_]

2 hours ago, Sile said:

Can't check the file and values myself currently. So has this been fixed like stated in changelog from 13.4.2023 (DCS 2.8.4.38947 Open Beta)?
I mean the values are clearly reversed.

Or does the changelog line refer to a different issue?
"Fixed: Tuned rudder authority limiters. One effect is greater rudder authority at higher angle of attack."

 

I believe the rudder fix relates to this report, not the issue described by OP here about inverted values

 

[Fox One]

On 4/2/2023 at 10:13 PM, NineLine said:

you should not be able to hold a 90-degree knife edge without altitude loss.

 Here is a knife edge flight without altitude loss:

 

As can be clearly seen from the video, to maintain horizontal flight in knife edge at this alt/speed the pilot must create a beta angle of approximately 10 deg.

I have tried in simulator the maneuver in similar alt/speed conditions. Pressing the rudder pedal fully, the beta angle that can be generated in no more than about 5 deg. The lift produced is insufficient and altitude is quickly lost.

[FusRoPotato]

5 degrees sideslip is the maximum allowed by the FLCS

[DummyCatz]

23 hours ago, FusRoPotato said:

5 degrees sideslip is the maximum allowed by the FLCS

Never heard of that. IIRC the Angle of Sideslip feedback function is unavailable for the FLCS when AOA < 10 deg.