Just installed 4.36, so compared to previous versions, the aircraft with DFLCS feels a lot more resistant to departures, especially the one caused by inertial coupling moments. Pulling while rolling at the same time at low speed & high altitudes seems to has less chance of overshooting the AOA limit.

The FLCS gains bug reported earlier is also seems to be fixed: https://forum.falcon-bms.com/topic/18289/flcs-gain-when-airspeed-over-400kts-alt-flaps-in-extend-air-refuel-in-open/

Another thing I noticed is that the yaw axis feedback seems to be over-gained when flying at transonic speeds and above, causing the rudder to flutter and overcorrect for yaw rate and lateral acceleration. A pulse input of rudder at higher speeds should reveal this.

So I checked the block diagram, that the yaw axis gain (applied to combined feedback) is increased with qc/Ps, presumably to compensate for the decreased directional stability due to mach effects. If the NASA 0.6 mach wind tunnel data is used for all range of speeds, could it be that the directional stability Cn-beta would be overestimated at higher mach numbers, that caused this overgain behavior?

@Mav-jp said in 4.36 FLCS improvements:

Absolutely no change a all i this area

Only things that changed are digital FLCS limited to 9.0G instead of 9.3g

No idea why noeone noticed this bug in 15 years lol

Noticed that too. I guess some have believed this was a feature, even me before because a full-scale development block diagram of block 25 testbed aircraft tricked me into thinking that:

But I heard that the DFLCS in development stages uses identical control logic from the Analog FLCS in order to spot any handling quality differences. So this 8.3 in the diagram might well comes from Analog FLCS.

@Mav-jp said in 4.36 FLCS improvements:

Absolutely no change a all i this area

Only things that changed are digital FLCS limited to 9.0G instead of 9.3g

No idea why noeone noticed this bug in 15 years lol

Noticed that too. I guess some have believed this was a feature, even me before because a full-scale development block diagram of block 25 testbed aircraft tricked me into thinking that:

But I heard that the DFLCS in development stages uses identical control logic from the Analog FLCS in order to spot any handling quality differences. So this 8.3 in the diagram might well comes from Analog FLCS.

Just installed 4.36, so compared to previous versions, the aircraft with DFLCS feels a lot more resistant to departures, especially the one caused by inertial coupling moments. Pulling while rolling at the same time at low speed & high altitudes seems to has less chance of overshooting the AOA limit.

The FLCS gains bug reported earlier is also seems to be fixed: https://forum.falcon-bms.com/topic/18289/flcs-gain-when-airspeed-over-400kts-alt-flaps-in-extend-air-refuel-in-open/

Another thing I noticed is that the yaw axis feedback seems to be over-gained when flying at transonic speeds and above, causing the rudder to flutter and overcorrect for yaw rate and lateral acceleration. A pulse input of rudder at higher speeds should reveal this.

So I checked the block diagram, that the yaw axis gain (applied to combined feedback) is increased with qc/Ps, presumably to compensate for the decreased directional stability due to mach effects. If the NASA 0.6 mach wind tunnel data is used for all range of speeds, could it be that the directional stability Cn-beta would be overestimated at higher mach numbers, that caused this overgain behavior?

@Mav-jp:

first, you missed the BAR (line) above StandbyGain text , that means in those logical diagram **!**StandbyGain

That means that this conditions occurs if NOT in standbygain

The precise value you are looking might be 500 Psi = 370 knots , that is the value where the TEF is automatically fully retracted even with TEF switch EXTEND .

but that’s hard to tell

Thanks a lot, so the diagram seems to agree with Dash-1.

The precise value I’m looking for is where FLCS switches back to Cruise Gains with Air Refuel Switch at OPEN. Dash-1 says it’s 400 knots so that’s why I suspect it’s 600psf. In BMS it seems that FLCS stays at Takeoff & Landing Gains forever when Air Refuel Switch at OPEN position, regardless of airspeed.

@Stevie:

What I’ve found is that how a sim “feels” wrt to the actual jet is mostly a matter of the controllers used - and I’d been told that some number of years ago by a pro operator I know. I’ve been getting a LOT of time in RL Trainers over the last few years, and also got an chance to fly the actual jet - which has completely changed my approach to how I handle the Trainer; it’s made me far more aware of a lot of things - like take away the forces of Gs on your body and I can say that NO sim feels “like the jet”. And that Trainers also do a bunch of stuff peculiar to Trainers…the jet was much easier to fly.

Most game controllers are really pretty poor models compared to the actual aircraft input system - chiefly in that they are excessively light. This in and of itself screws up any math in the gains by allowing for non-real inputs and input rates. Rates mostly, I’d gather. And no two of our setups are really alike, so comparisons there aren’t really apples-to-apples either.

Yes, this is most prominent when I’m used to my 5-year-old X65F which I set 16lbsf for roll axis and 22lbsf for pitch axis just to mimic the stick force in an F-16, as we know pulling 9G in an F-16 requires 25lbsf and a max roll command requires 16.7lbsf. Then I tested out a X52 stick when I visited a friend and suddenly it feels like I’m flying another plane.

There’s actually a guidance in MIL-STD-1797A detailing stick force requirements in an aircraft. Stick force per g can impact flying qualities and it shouldn’t be too light or too heavy. Here’s a pilot rating chart for different stick force in a T-33 aircraft. Level I indicates best flying qualities.

@Raptor:

Well, does not feel even close to a Viper, at least currently.

To me it seems like they somewhat “designed” the control law especially for CAT III and TO/LND Gains using descriptions and figures from the flight manual, which is not a proper engineering source anyways. That may explain all the issues in those areas where NASA FLCS does not cover. (i.e. pitch rate in TO/LND Gains being 1/2 of what it should.)

Not to mention the fixed gains and gain schedules that are not designed for high speed regions, and can cause control surface fluctuations and oscillations at high speeds, which it does in DCS. There may be other issues like the pitch integrator etc. etc…

Just a geek in aircraft stability and control. You might tell from https://www.benchmarksims.org/forum/showthread.php?30206-Volunteer-to-implement-a-full-set-of-F18-control-law&p=421375.

Nah I don’t develop DCS F-16 for ED.
And I don’t think ED uses this source, seems their FLCS is based on NASA TP1538.

While I’m randomly reading the block diagram of F-16 DFLCS, I noticed that the FLCS will actually switch to pitch-rate feedback (blended with AOA > 10°) if dynamic pressure is below 600(?) psf, and either ALT FLAPS switch in EXTEND position or AIR REFUEL switch in OPEN position, and most weirdly, in Standby Gains. Here’s the source:

Closer look:

(F-16 Digital Flight Control System Functional Block Diagrams. Data obtained from Lt. Bruce Peet, F-16 System Program Office, Wright-Patterson OH.) quoted in DTIC ADA202599 and DTIC ADA189675.

Yes the text is very hard to recognise but it can be decoded as:

NOTE 1. Switch activates by ANY of the following methods:

• LG Handle in DOWN position
• Standby Gains & [Fwd or Aft ALT FLAPS Switch in EXTEND position] & qc < 600psf
• Standby Gains & [Air Refuel Switch in OPEN position] & qc < 600psf

Whether it’s 600psf I’m not sure, but it’s the closest to 400kts airspeed. This switch genuinely switches between Nz feedback and pitch-rate feedback (blended with AOA > 10°) with a first order filter used as a fade-in function. Notice that Standby Gains requirement, which is not present in the HAF Dash-1 manual.

I wish anyone could check the CM-1 manual, but I’ll just quote the HAF CJ-1:

Takeoff and Landing Gains
The FLCS is in takeoff and landing gains with the LG handle in DN, the ALT FLAPS switch in EXTEND (below 400 knots), or the AIR REFUEL switch in OPEN (below 400 knots).

So my question is whether the above quoted statement stands true for F-16CJ and F-16CM, since I remembered in BMS that there’s no such (400kts) requirements.

@Dee-Jay:

If I am not wrong, Jp already made it … (?)

I thought Jp’s F18 flight control is based on F16 FLCS with a few modifications according to NATOPs manual? (G-Limit, flaps schedule, recover from high alpha, etc…)

In my university research project some time ago, I had the opportunity to implement F-16 FLCS according to a General Dynamics’ F-16 control block diagrams in another platform. (Line by line just like BMS did, while not a LM but a GD one.) I also found that NASA Technical Memorandum 107601 contains a relatively complete F18 control law includes all the transfer functions and gain schedules. So I’m thinking maybe it can also be used in BMS if I complete coding one? Just an idea.;)