F-16 DFLCS control law & G-onset rate

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hummingbird

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Unread post31 Oct 2019, 11:06

Hello everyone,

As you surely know DCS recently launched their F-16C Blk.50 module, however I've come across something weird with the FM, specifically what appears to be an overly slow G-onset rate as compared with HUD tapes as well as the BMS F-16.

The effect of this slow onset rate is that the DCS F-16 feels quite sluggish to maneuvr, and it takes so long to reach the max instantanous load factor that in a level turn you will need to be going quite a bit faster than corner speed in order to ever reach your max rate.

Thus my question is wether anyone here would happen to have knowledge on the real Blk.50's DFLCS and what G-onset rate it allows for?
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Unread post31 Oct 2019, 14:09

The DCS FBW is a port of the Hornets that allows 9G. It is not representative of an F-16.
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Unread post31 Oct 2019, 15:07

Not so sure about that, I'm more inclined to believe that they made an error with gains in the FLCS.

Either way my question still stands, as this information could help get the FM right.
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Unread post31 Oct 2019, 15:22

G onset could be as high as 9G/s IIRC, but I have seen the DCS F-16 routinely taken above 30-35 AoA. It is NOT an F-16 FCLS.
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Unread post31 Oct 2019, 16:50

F-16 rpt.jpg


According to this doc it's >6G/sec. Somehow think it maybe ~6.2-6.4G per sec. I highly doubt it is more than 7G/sec (could be wrong though)-As that paper by Saab's Robert Hilgren puts the Gripen's onset at 6G/sec. I do know for sure that Colonel Virts said that as far as US jets go, the only jet with a higher onset rate is the F-22 Raptor.
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Unread post31 Oct 2019, 18:09

Thanks f-16adf
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Unread post31 Oct 2019, 20:35

It's more than 6 G/'s, what the lined document is saying is merely that anything above 6 G/s is considered high.

Keep in mind that aircraft such as the F-14 & F-15 without any FLCS holding them back are able to put on G's even faster. I do believe the F-16 is capable of 9 G/s however, which is more than fast enough. (Keep in mind that 1 sec feels quite long in combat)

This is the same as the Typhoon: https://www.aerosociety.com/news/under-pressure/

Also based on HUD footage as well as BMS it seems as though the later DFLCS allows for 9.3 G's in a level horizontal turn.
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Unread post31 Oct 2019, 21:00

I seriously doubt that. Also, look you can believe what you want about the F-14 or F-15 having a warp turbo button or whatever in that game. Just because you don't have a limiter doesn't mean that you can pull off certain moves. It's not reality, it's a game.

From what I have always read, the F-16 had the fastest "G" onset rates of the teen series. That is the whole point of G training in the centrifuge. The Analogue jets, Block 30 and under, could "trick" it into 9.3G or somewhat even beyond. Joe Nawrocki said he took the F-16N to 10G, maybe more. The Digital jets, Block 40 and up not so much. The only people that can add to that here are the actual guys who have flown it. I.E. Gums, JBGator, Meteor, Outlaw, Magnum, Tailgate, and others. And I'm sure JohnWill would know, since he was a structural engineer on the program. And if you still don't believe, ask CW Lemoine aka Mover. I'm sure he can answer this question, I seriously doubt it is classified.


Even in this video, you can see Gripen onset rates (and they basically match with the Saab person's words, it certainly is not 9G/Sec). And the Gripen is a highly unstable canard delta. I doubt the F-16 has much if any advantage in onset rates against it.

https://www.youtube.com/watch?v=eXaPfUs6sQw


Look at the onset in the centrifuge, not anywhere near 9G/sec. And I'm sure it is near equal to the real jet.
https://www.youtube.com/watch?v=q5KxvsJApT8


That link about the Typhoon being 8/9G (say 8.5) is entirely believable. The EF is a completely different animal than the F-16 /Gripen/ F-15. Its real only rival is probably the F-22, in terms of pure power.
Last edited by f-16adf on 31 Oct 2019, 22:52, edited 1 time in total.
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Unread post31 Oct 2019, 21:06

hummingbird wrote:Also based on HUD footage as well as BMS it seems as though the later DFLCS allows for 9.3 G's in a level horizontal turn.


AFAIK it was positive 9.3G before the Digital FLCS came in as standard.
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Unread post31 Oct 2019, 21:52

https://www.youtube.com/watch?v=Wvjf6SA87BA


At a little past 4:03 mark the F-16 in this vid starts its high G turn, granted they take the camera off the HUD view after something like 5.8G when the jet enters the turn, but going from 1G to 5.8G seems like a bit less than a second, does not seem similar to a 9G/sec onset rate. But as I said, I could be wrong. That is why we need an actual Pilot to answer this.




This is kinda a poor scan, but it is telling. According to Colonel Virts, at high altitude the F-16's G onset is just 3G/sec. And as he says, second only to the F-22 Raptor. So at normal combat altitudes it could be what I said, maybe slightly more. Still doubt at SL it is equal to Typhoons let alone 9G/sec But as I said, I am not certain. Only those that flew it would truly know.

F-16 rate.jpg
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Unread post01 Nov 2019, 01:11

You can doubt it all you want f16adf, doesn't change reality. Without a limiter the G-onset rate is all about lift required vs lift available. Even an F-4 Panthom can break off its own wings a 600 kts easy if the pilot just janks the stick back for an immediate 9 G's at 18 G/s as there's no FLCS preventing him from doing so.

The reason the F-16 is at all limited in terms of G-onset rate is that the FLCS wants to prevent the pilot from overshooting the 9-9.3 G limit with any sudden jank on the stick, and in order to achieve that it has to slow down the onset rate at some point. Based on HUD footage this doesn't really start to noticably happen before 8 G's though.

Furthermore many centrifuges go beyond 9 G/s, including the US TAC ones used for Viper pilot training, they hit 10 G/s:
http://medind.nic.in/iab/t06/i1/iabt06i1p1.pdf

9-10 G/s is also what I believe the F-16 is capable of, same as the Typhoon which has similar AoA restrictions and thus it would also make all the sense in the world if its G-onset rate was similar.
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Unread post01 Nov 2019, 01:40

I will defer to an actual F-16 pilot. Also, the pilot in the doc I posted said 3G/sec at high altitude while still touching 9G. That lines up pretty good with the 30-35,000ft Clean EM charts. I seriously doubt the jet will gain an extra 7G/sec by dropping to SL. Why don't you ask Mover he posts on that site anyways?
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Unread post01 Nov 2019, 08:15

hummingbird wrote:You can doubt it all you want f16adf, doesn't change reality. Without a limiter the G-onset rate is all about lift required vs lift available.No it isn't. There are lags and filters built into the control laws that regulqte how fast the pilot g command is allowed to move the horizontal tail to increase or reduce g. Even an F-4 Panthom can break off its own wings a 600 kts easy if the pilot just janks the stick back for an immediate 9 G's at 18 G/s as there's no FLCS preventing him from doing so.

The reason the F-16 is at all limited in terms of G-onset rate is that the FLCS wants to prevent the pilot from overshooting the 9-9.3 G limit with any sudden jank on the stick, and in order to achieve that it has to slow down the onset rate at some point. Based on HUD footage this doesn't really start to noticably happen before 8 G's though. Minimizing overshoot is indeed one of the reasons for controlling g onset rate. As you say for an abrupt 9g command, g onset rate reduction begins somewhere around 8g. However, for an abrupt 6g pull, it starts around 5g. FLCS modulates g onset at all g levels to make pitch control smooth and not jerky at any g. The F-16 is unstable subsonic and it wants to diverge g at every opportunity.
Remember, the HUD g meter is driven by an accelerometer in the HUD. Thus it is subject to local g in the HUD, which is much more than airplane g at the CG during an abrupt pull, also more than the pilot feels.

Furthermore many centrifuges go beyond 9 G/s, including the US TAC ones used for Viper pilot training, they hit 10 G/s:
http://medind.nic.in/iab/t06/i1/iabt06i1p1.pdf
About that .pdf - The table of centrifuge training conditions shows many very high g onset rates, but the text explanation only mentions 1g/s sec as Rapid Onset Rate (ROR). That confuses me.
9-10 G/s is also what I believe the F-16 is capable of, same as the Typhoon which has similar AoA restrictions and thus it would also make all the sense in the world if its G-onset rate was similar. AoA limit and g onset rate are not related in any way.
Something else most people don't know, the F-16 g/AoA limiter does not limit g or AoA. It limits g command from the pilot.
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Unread post01 Nov 2019, 10:30

What would have happened if we would change the 16's AOA limit from 25.5° to say 30-35° ? What would it take? Is it only a FLCS software update or requires structural tampering as well? Would that limit change be benefitial or not? Would it improve the control/maneuver/nose-pointing_ability at low speeds (I assume yes) ?
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Unread post01 Nov 2019, 11:50

johnwill wrote:You can doubt it all you want f16adf, doesn't change reality. Without a limiter the G-onset rate is all about lift required vs lift available.No it isn't. There are lags and filters built into the control laws that regulqte how fast the pilot g command is allowed to move the horizontal tail to increase or reduce g. Even an F-4 Panthom can break off its own wings a 600 kts easy if the pilot just janks the stick back for an immediate 9 G's at 18 G/s as there's no FLCS preventing him from doing so.


I wasn't talking about the F-16 there John, I am well aware that the F-16's FLCS uses lag & filters to keep the G-onset rate controllable. However an F-14 or F-4 (or any aircraft with boosted controls but without a control limiter) lacks any such filters, and as such it is instead all up to the pilot not to overcontrol and exceed the G-limit's in these aircraft, as either of them are capable of putting on 10+ G's instantly, which in an F-4 is most likely going to cause it to self destruct.

The reason the F-16 is at all limited in terms of G-onset rate is that the FLCS wants to prevent the pilot from overshooting the 9-9.3 G limit with any sudden jank on the stick, and in order to achieve that it has to slow down the onset rate at some point. Based on HUD footage this doesn't really start to noticably happen before 8 G's though. Minimizing overshoot is indeed one of the reasons for controlling g onset rate. As you say for an abrupt 9g command, g onset rate reduction begins somewhere around 8g. However, for an abrupt 6g pull, it starts around 5g. FLCS modulates g onset at all g levels to make pitch control smooth and not jerky at any g. The F-16 is unstable subsonic and it wants to diverge g at every opportunity.


Yup, completely agree.

Remember, the HUD g meter is driven by an accelerometer in the HUD. Thus it is subject to local g in the HUD, which is much more than airplane g at the CG during an abrupt pull, also more than the pilot feels.
Furthermore many centrifuges go beyond 9 G/s, including the US TAC ones used for Viper pilot training, they hit 10 G/s:
http://medind.nic.in/iab/t06/i1/iabt06i1p1.pdf
About that .pdf - The table of centrifuge training conditions shows many very high g onset rates, but the text explanation only mentions 1g/s sec as Rapid Onset Rate (ROR). That confuses me.
9-10 G/s is also what I believe the F-16 is capable of, same as the Typhoon which has similar AoA restrictions and thus it would also make all the sense in the world if its G-onset rate was similar. AoA limit and g onset rate are not related in any way.
Something else most people don't know, the F-16 g/AoA limiter does not limit g or AoA. It limits g command from the pilot.
[/quote]

What I mean is that if you have an unstable aircraft then the AoA limit is indicative of the G-onset rates possible before you risk an overshoot. i.e. it would make much sense if the G-onset rates of the Typhoon & F-16 are similar considering they're both unstable designs with a similar AoA limit and hence would need about the same safety net in terms of FLCS filters to avoid an overshoot.

Also regarding the FLCS G limit's, according to the system charts for later Blocks of F-16's with DFLCS the G limit was raised to 9.3 G's (8.3 in the system) in order to allow 9.0 G's being reached very quickly at corner speed, i.e. no need to be going faster to allow the aircraft time to reach 9 G's before you drop below corner speed.
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