fixed Maximum commanded pitch rate in take-off & landing gains

[LJQCN101]

According to a DFLCS control block diagram of full scale development phase (quoted in DTIC ADA 189675 and 202599), a filtered pitch rate is multiplied by 0.5 under take-off & landing gains.

 

Since max stick force is able to command 9G, which is an 8 in the system. By using pitch rate feedback in take-off & landing gains, the aircraft should be able to reach a pitch rate of 16 deg/s before AOA feedback kicks-in above 10 deg AOA.

 

In the current implementation I was unable to pull a 16 deg/s pitch rate with max stick force. There could be a possible neglection of the 0.5 multiplier in the pitch rate feedback loop. It may be the reason why some players feel the aircraft too 'stiff' and can hardly pull it up when landing.

 

 

EDIT: Full graph containing relevant info looks like this:

Edited September 21, 2020 by LJQCN101

[mvsgas]

According to the DFLCS control block diagram from DTIC ADA 189675, a filtered pitch rate signal is multiplied by 0.5 and then mixed with (normal load factor - 1.0), dependent on whether the FLCS is in cruise gains or take-off & landing gains. (And I don't think later DFLCS version would change this number too much or at all.)

 

Since max stick force is able to command 9G, which is an 8 in the system. By using pitch rate signal in take-off & landing gains, the aircraft should be able to reach a pitch rate of 16 deg/s before AOA feedback kicks-in.

 

In the current implementation I was unable to pull a 16 deg/s pitch rate with max stick force. It may be the reason why some players feel the aircraft too 'stiff' and can hardly pull it up when landing.

 

[ATTACH]218466[/ATTACH]

 

Not sure if I understand what you mean, but in takeoff and landing gains, the FLCS pitch axis operates as a pitch rate command system until 10 degrees AOA and a blended pitch rate and AOA command system above 10 degrees AOA.

 

Also, Maximum Positive g is a function of airspeed and AOA, negative g is not a function of airspeed. It's a fix limit. Max AOA at 1g is 21º

Edited April 9, 2020 by mvsgas

[BIGNEWY]

According to the DFLCS control block diagram from DTIC ADA 189675, a filtered pitch rate signal is multiplied by 0.5 and then mixed with (normal load factor - 1.0), dependent on whether the FLCS is in cruise gains or take-off & landing gains. (And I don't think later DFLCS version would change this number too much or at all.)

 

Since max stick force is able to command 9G, which is an 8 in the system. By using pitch rate signal in take-off & landing gains, the aircraft should be able to reach a pitch rate of 16 deg/s before AOA feedback kicks-in.

 

In the current implementation I was unable to pull a 16 deg/s pitch rate with max stick force. It may be the reason why some players feel the aircraft too 'stiff' and can hardly pull it up when landing.

 

[ATTACH]218466[/ATTACH]

 

Do you have any source documents showing this? I can see in this document values have been added but what is the source?

 

thanks

[bkthunder]

According to the DFLCS control block diagram from DTIC ADA 189675, a filtered pitch rate signal is multiplied by 0.5 and then mixed with (normal load factor - 1.0), dependent on whether the FLCS is in cruise gains or take-off & landing gains. (And I don't think later DFLCS version would change this number too much or at all.)

 

Since max stick force is able to command 9G, which is an 8 in the system. By using pitch rate signal in take-off & landing gains, the aircraft should be able to reach a pitch rate of 16 deg/s before AOA feedback kicks-in.

 

In the current implementation I was unable to pull a 16 deg/s pitch rate with max stick force. It may be the reason why some players feel the aircraft too 'stiff' and can hardly pull it up when landing.

 

[ATTACH]218466[/ATTACH]

 

I noticed the exact same thing with L/G down. Almost crashed because I lowered the gear during the base to final turn once, and the landign gains kicked in removing most of the pitch authority.

I can only say in that other sim whcih can't be named, it doesn't do this.

[MadCat1381]

The whole plane feels very weird in landing gains. You really have to yank the stick to get it moving.I have a force sensing stick and it feels like I have to almost break it, when rolling out into the final.

[Bremspropeller]

I think the landing gains needs some additional tweaking in terms of elevator scheduling. Maybe it's a global FM-thing.

 

 

If you watch F-16s landing (the Block doesn't matter), you'll notice that the elevons are remarkably neutral throughout the approach and if there's any pulsing in pitch, it's mostly LE up. That's due to the aircraft's relaxed longitudinal stability and once you've seen it, it's kind of hard to unsee it...

 

 

Take this Block 42 formation-landing as reference:

 

 

Block 30:

 

 

Block 15:

 

 

 

Block 40:

 

 

Block 52:

-> Compare the stabilizer with the LE down position on the landiing MiGs and conventional aircraft

 

 

 

 

The Viper's in-game elevators are trimmed up (LE down) during approach, which is not accurate.

 

 

Cheers.

[LJQCN101]

Do you have any source documents showing this? I can see in this document values have been added but what is the source?

 

thanks

 

It's the F16B block25 DFLCS control block diagram from DTIC ADA 189675. The whole diagram may not be relevant to the current modelled block 50 but I think the pitch rate feedback part is correct.

 

*EDIT: F16D actually.

Edited April 12, 2020 by LJQCN101

[LJQCN101]

Not sure if I understand what you mean, but in takeoff and landing gains, the FLCS pitch axis operates as a pitch rate command system until 10 degrees AOA and a blended pitch rate and AOA command system above 10 degrees AOA.

 

It is pitch rate command system as you can tell from the control block diagram that in take-off & landing gains, the filtered Nz signal get multiplied by 0.0. AOA feedback above 10 degrees is also in the diagram so I don't see a problem here.

 

What I'm talking about is exactly how the system handles pitch rate feedback.

 

Also, Maximum Positive g is a function of airspeed and AOA, negative g is not a function of airspeed. It's a fix limit. Max AOA at 1g is 21º

 

True but that's a simplification of what a control block diagram can tell. But you can always try to match the numbers to see if it was changed in block 50 DFLCS circa 2007. As I've implemented like 3 different versions of F16 FLCS years ago, including NASA, Analog and Digital ones, I can pretty much spot the differences if you provide more info from the relevant manual.

Edited April 11, 2020 by LJQCN101

[=Panther=]

The whole plane feels very weird in landing gains. You really have to yank the stick to get it moving.I have a force sensing stick and it feels like I have to almost break it, when rolling out into the final.

 

Yes, mine is screaming (audible alert for max deflection) at me when in the pattern yet the jet isn’t wanting to move. I don’t think something is correct, but what do I know.

[mvsgas]

It's the F16B block25 DFLCS control block diagram from DTIC ADA 189675. The whole diagram may not be relevant to the current modelled block 50 but I think the pitch rate feedback part is correct.

 

This is confusing F-16B are block 10/15/20. F-16C are block 25/30/32 with analog FLCS and block 40/42/50/52 with DFLCS. So Are basing you information on a F-16B, a block 25 or a DFLCS? All 3 are different.

[LJQCN101]

This is confusing F-16B are block 10/15/20. F-16C are block 25/30/32 with analog FLCS and block 40/42/50/52 with DFLCS. So Are basing you information on a F-16B, a block 25 or a DFLCS? All 3 are different.

 

My bad it's a F-16D, but it is block25 DFLCS according to the graph, for the FSD phase of production DFLCS.

 

Edited April 12, 2020 by LJQCN101

[LJQCN101]

I think the landing gains needs some additional tweaking in terms of elevator scheduling. Maybe it's a global FM-thing.

 

If they've got the exact control block diagram for the block 50 DFLCS circa 2007, there shouldn't be any "tweaking" of any kind. All transfer functions, gain schedules etc should be kept as is and the whole graph is coded line by line.

[mvsgas]

My bad it's a F-16D, but it is block25 DFLCS according to the graph, for the FSD phase of production DFLCS.

 

[ATTACH]232263[/ATTACH]

 

Again, Block 25 do not have digital flight control, so if the information indicates that, I question its validity. It might be from a propose update or a test vehicle but not for a operational aircraft and renders the conversation moot for me. Good luck to you.

[LJQCN101]

Again, Block 25 do not have digital flight control, so if the information indicates that, I question its validity. It might be from a propose update or a test vehicle but not for a operational aircraft and renders the conversation moot for me. Good luck to you.

 

It's a DTIC document, you can search for it from the official site. And it states that it's for the FSD phase of production DFLCS. What I posted is an official graph with revision number on it, those who recognise it will know.

 

And I don't think you can find detailed info about maximum pitch-rate command of take-off & landing gains in Flight Manuals, at least I tried with the HAF ones, unless someone has the actual control block diagram with the right revision number.

Edited April 12, 2020 by LJQCN101

[bkthunder]

 

 

The Viper's in-game elevators are trimmed up (LE down) during approach, which is not accurate.

 

 

Cheers.

 

Yeah, that's something that I also noticed and it's weird. It also happens at high speed, the elevators are significantly pitched up on a clean jet flying fast and level.

[Bremspropeller]

If they've got the exact control block diagram for the block 50 DFLCS circa 2007, there shouldn't be any "tweaking" of any kind. All transfer functions, gain schedules etc should be kept as is and the whole graph is coded line by line.

 

 

Good point. I wonder if the lift-distribution and the according pitch-moment distribution is correct or if the whole aerodynamics/ flight mechanics are a little off. The stab-position is probably not related to the landing-gains issue you discovered.

 

 

 

I did a quick and dirty test yesterday. I took a 300gal centerline tank and two 'winders on an otherwise clean jet and fooled around at different weights and speeds:

 

 

If you're flying in cruise-gains at landing-speeds (slightly higher AoA at the weight I tested) with the TEFs up, the stabs are almost neutral.

 

Once the gear is out and the TEFs are down and landing-gains has kicked in, the stabs are going to their "trimmed" position.

The faster you go, the less "trim" they're scheduling in, becoming almost neutral above 250kts.

Edited April 12, 2020 by Bremspropeller

[Hummingbird]

+1 OP

 

Please look into this ED, as it's a similar issue which is affecting ITR.

Edited May 3, 2020 by Hummingbird

[Contact409]

Do you have any source documents showing this? I can see in this document values have been added but what is the source?

 

thanks

 

so, has this one been noted as bug ? still investigating ?

[LJQCN101]

Do you have any source documents showing this? I can see in this document values have been added but what is the source?

 

thanks

 

Just a correction, the original source is from F-16 System Program Office. Those DTIC thesis use this as a quote.

 

F-16 Digital Flight Control System Functional Block Diagrams. Data obtained from Lt. Bruce Peet, F-16 System Program Office, Wright-Patterson OH.

[BIGNEWY]

I have asked the team to take a look.

 

thanks