F16 crosswind rudder correction is same w/speed on takeoff/landing - not real (?)

[ACME_WIdgets]

Right now, when a crosswind is present on takeoff or landing, the amount of rudder input to maintain a path  on the runway centerline is a constant amount of rudder input - even as speed increases.
I think the rudder input for the crosswind should be LOWER as speed INCREASES.

   i.e. 60kts runway speed in 20kts crosswind = large rudder input to stay straight

   I think 160kts speed in 20kts crosswind = smaller rudder input than at 30kts speed.

This is really a problem for me when I turn OFF NWS around 100+ kts.  I have to input even more rudder to correct (yes I get that NWS helps maintain a straight track).  And some MP servers use 30hts crosswind.

Also, while flying the F16 at low speed, in my opinion the rudder input injects way too much roll. Yes, the rudder is not 90 degrees perpendicular, so some roll coupling will occur.  But it just seems too high, based on my propeller real pilot experience (including some aerobatic SEL planes).

[Machalot]

You're probably right about the angle of the rudder deflection.  But who knows what the FLCS does.  Often in aeronautical control systems the control gain will be inversely scaled by dynamic pressure (i.e. indicated airspeed) so the same pedal position produces a proportionally smaller deflection, but produces an equivalent effect.

[wizoo]

You don't have to apply rudder input.

 

In real FLCS the ARI (ailerons - rudder interconnect) makes the job.

 

FM is now WIP so may be isn't working as it should but do not get used to using rudder corrections. You don't have to do that if the FM is as real.

Edited September 17, 2021 by wizoo

[Machalot]

1 hour ago, wizoo said:

You don't have to apply rudder input.

 

In real FLCS the ARI (ailerons - rudder interconnect) makes the job.

 

FM is now WIP so may be isn't working as it should but do not get used to using rudder corrections. You don't have to do that if the FM is as real.

 

So steering correction during the takeoff roll is done with the stick? That's SOP?

[wizoo]

No, during takeoff you can use rudder as required but don't use it in flight for wind corrections when landing.

Edited September 17, 2021 by wizoo

[fapador]

@ACME_WIdgets I agree 100% with you but it doesn't matter, if the devs don't 

Edited September 18, 2021 by fapador

[bkthunder]

On 9/17/2021 at 6:04 PM, Machalot said:

So steering correction during the takeoff roll is done with the stick? That's SOP?

 

 

It was easy to misinterpret what he wrote, but what he meant is that in flight you don't need to touch the rudder because at slow speed the FLCS will move it for you to give you the roll response that you want at slow speed / high AoA. 

 

In a xwind landing F-16s don't touch the rudder and touch down crabbed into the wind, it's a very squirrelly aircraft to land. You can carefully use the rudder on rollout.

[Glide]

You also have to account for the ground friction modeling in the sim.  I would suspect this is a global setting not specific to the Viper.  Good on you for practicing this extreme test case.

[Deano87]

Just FYI -  Since you mention using the rudder - I presume you are trying to decrab the viper on landing. Standard operating procedure is to NOT decrab the aircraft to align with the runway. You land crabbed. Feels weird, but actually works pretty well.

[ACME_WIdgets]

"Just FYI -  Since you mention using the rudder - I presume you are trying to decrab the viper on landing. Standard operating procedure is to NOT decrab the aircraft to align with the runway. You land crabbed. Feels weird, but actually works pretty well. "
Hi @Deano87 - I am referring only to ON the runway use of rudder with a cross wind.  Crabbing for landing is no problem for me.

[Frederf]

A ground roll in a crosswind will require more rudder input to track straight when slow than when fast. If the rudder required is constant for slow and fast speeds then it is inaccurate. However I checked and it looks like the rudder input which holds track at ~80 knots is excessive at ~120 knots roll as expected.

 

The reason the "one wing low" crosswind approach method is not to be used with the F-16 is that the FLCS laws change drastically on touchdown. The particular way of crosswind approach banked into the wind but opposite rudder to align the fuselage with the runway is common in light airplanes. Using this technique in the F-16 is a problem because touching down in this way will cause the control surfaces to quickly change according to a change in how pilot inputs are converted into control surface positions. The airplane will upset despite the pilot holding constant inputs on touchdown. Instead the proscribed touchdown method is to have wings level and the fuselage not aligned with the runway.

 

 

 

 

[Sickdog]

I think this is an issue with all fixed wing DCS aircraft, I’ve felt this way for a long time. I have nearly every module and perform a lot of crosswind takeoffs and landings, it’s really apparent to me. It feels like a lack of inertia being calculated or maybe too little lateral friction with the tires/runway, but the end result is it requires too much rudder input at high speeds. I’ve never flown any military aircraft but I fly a 99,500lb MGTOW corporate jet IRL, so have a pretty good idea what it feels like to takeoff and land from around 60k lbs and up. 

[ARM505]

Seconded - (14K flying hours IRL, currently on B738's) - it feels like the tyres are too prone to sliding laterally, or something like that (ie. they don't keep rolling straight, and don't provide enough grip to stop a sideways slide developing). Or something. Hard to pin down, but results in a lot of wiggling and sliding. I also think it's a global issue. The F16's narrow track and tiny tyres, plus FLCS weirdness on touchdown (control law changes) proabably don't help too much in pinning it down to one factor.

[Deano87]

I much prefer the tyres as they are now compared to how they were when the F-16 was released where it was impossible to land or takeoff in a crosswind because they had way too much lateral grip.

I was the one who brought up the original too grippy tyres in the first place.

Its only anecdotal evidence but my brother who has 500+ relatively recent F-16 hours has flown the viper in my sim in a variety of wind conditions and has never mentioned any major issue with the rudder on takeoff or landing. He has mentioned other things which he feels need tweaking but they are already things being worked on (FM stuff)... 

 

Cheers
D

[ARM505]

I remember that thread (and the original problem), it was an excellent example of finding and researching a problem in the sim, and coming up with a solution/theory about why it works the way it does in the sim.

This sentence of yours -

"Obviously as the sim uses a static number it means that as the aircraft slows the tyres are probably gripping less than they should, but this is less detrimental to the handling than being far too sticky on initial touchdown, IMHO anyway. I'll happily take the Viper sliding a bit more then it should at 50 knots instead of firing itself at the scenery at 140 knots."

- might be a good summary of the compromise that seems to have been made.

 

Perhaps we can't expect a racing sim tyre model, but ultimately a slightly better tyre model, with more data points (coefficient of static and dynamic friction for a couple of tyre speeds, interpolated, combined with normal force for example - I'm not sure what's currently considered). Put it on the million item 'to do' list

[SCPanda]

On 12/4/2021 at 11:54 PM, ARM505 said:

Seconded - (14K flying hours IRL, currently on B738's) - it feels like the tyres are too prone to sliding laterally, or something like that (ie. they don't keep rolling straight, and don't provide enough grip to stop a sideways slide developing). Or something. Hard to pin down, but results in a lot of wiggling and sliding. I also think it's a global issue. The F16's narrow track and tiny tyres, plus FLCS weirdness on touchdown (control law changes) proabably don't help too much in pinning it down to one factor.

Keep in mind our Viper still doesn't have anti-skid implemented. I don't know if it has anything to do with the behavior you are observing, but I think anti-skid should eliminate the sliding for our DCS Viper.