Yaw dynamics

[ahaka]

Thank you, Hardy. It's been a while, for sure. I am getting older but your simulator has stood the test of time.

I could have sworn something was also changed with the inertia and yaw, but as you now said those are left unchanged then it must be the new turbulence model that has increased the stability and I subjectively felt that it is in the yaw/ground dynamics. I will have to try again.

In any case it is great to see all the updates and new features still being added to this software.

[Hardy Heinlin]

I must add one info: When I say "reduced", it's not a general reduction; strong gusts can still occur during the flare, but just not as often as in previous versions.

Here, for example, I was watching real-life landings for several hours, and just one aircraft was hit by an extreme crosswind gust during the flare. So, I think, in the sim, it shouldn't occur every few seconds either, but rather every few hours. It should be a real surprise. Notice that Alitalia 747 at 3:35:

https://youtu.be/YdVupou9ZZA?si=KBy0EYAZr6HgrPvx&t=215

[ahaka]

That makes perfect sense, Hardy.

Now that I did more testing it seems that it is exactly the reduced frequency of strong gusts (and probably reduced turbulence oscillations as well) that make these landings slightly more manageable.

Nice video from the good old days!

[744student]

Hi Hardy

My deepest apologies for the long absence since my initial post.

I tried out the latest update and the ground steering feels almost 100% like the real -400 especially when lining up with the runway. Thank you!!

Regarding de-crabbing I still feel like the inertia of the aircraft is too low in the lateral direction. Change in "track" of the aircraft is too instant in response to rudder input. Perhaps other Boeing pilots can chime in on this? I did try without using P3D as my visual generator (only using PSX visual) but the symptom persisted.

I completely understand how important it is to provide you with more quantifiable data - I'll do my best to get an FFS video with synced views of Rudder Pedal displacement and ND data (HDG vs TRK)... unless someone beats me to it!

[Hardy Heinlin]

Hi, welcome back.

Just to be sure: You mean the crosswind induced slip motion (the motion sideways while the heading is constant) needs a higher inertia. You don't mean the heading rate (the rudder controlled turn velocity) needs a higher inertia.

Correct?

(If the heading rate was too high, I would suggest to check the calibration of the rudder pedals that max rudder input is only achieved when the USB pedal is fully forward and not earlier.)

If the slip motion needs a higher inertia, what numbers are we talking about, approximately? Should it be 10 % higher? Twice as high?


Regards,

|-|ardy

[744student]

PSX Rudder induced Heading rate, I think is spot on. Rather as you say it's the crosswind induced slip motion that "catches on" too rapidly - at least to me.

It's hard to put a number to it but I'd say doubling the inertia may be a good starting point for further fine tuning.

Going by my gut feeling, under a 30 knots crosswind, beginning decrabbing at about 40 feet, while keeping the wings level (plenty of in-to wind aileron required!) should not result in a significant track deviation until touchdown (pretty close to HDG=TRK=QFU). Please note, if you start decrabbing too early, of course eventually the aircraft will begin drifting downwind significantly unless you apply wing-low (cross control), which could reduce your margin to a pod strike.

[Hardy Heinlin]

Here's PSX 10.194 with a higher inertia on the slip axis:

https://aerowinx.com/board/index.php/topic,4191.0.html

[744student]

Thanks for the ultra fast recompiling with the new inertial value Hardy.

Tried numerous crosswind (20kt, 30kt and 40kt) landings now in the new version and I find that the decrabing maneuver feels much closer to the real deal.

I would say if you could add an extra 20% inertia the model would be pretty damn close to a 100% accuracy

[Hardy Heinlin]

Thank you for the test.


Hi all,

any further opinions? Does anybody disagree?


|-|ardy

[Mariano]

Much, much better "feel" of inertia (at least compared to the 767 with half the mass).

I practiced a few engine-out takeoffs, and I believe that I noticed an improvement there as well (or was it expectation bias, perhaps?).

I don't know about the extra 20%, but I believe that it might bring it even closer to reality, seeing as I am used to only half the inertia and the latest update already improves the simulation considerably.

Regardless, thanks for the suggestion, 744student and for the update, Hardy.

Best regards,

Mariano

[Britjet]

True numerous 25kt landings.
Rudder input required in flare seems ok, but I think that the tendency to weathercock into wind on the rollout is too severe.
Having landed the aircraft straight, on the qdm, with into-wind aileron etc it seems to want to dive off into wind after a second or two, requiring full opposite rudder sometimes to prevent runway excursion.
The autopilot seems to encounter the same issue.

[Hardy Heinlin]

I think that's a different problem, Peter. What do you think about the increased inertia on the track axis during the flare in crosswind?

[Britjet]

It seems ok to me..it is fairly easy to straighten up on the centreline. About 2/3 rudder needed as per the STATUS page.
It all starts to go wrong after that :-)

[Hardy Heinlin]

The question was if the decrabbing caused the aircraft to start drifting downwind too early.

In the new version, when the aircraft heading is in line with the runway heading, the downwind drift will start more slowly. That is, you can now begin your decrabbing earlier without the risk of drifting downwind too early.

I haven't changed the rudder-to-yaw ratio. I just changed the inertia of the geographic track axis.

[Hardy Heinlin]

Track axis inertia is now further increased, and weathercock effect after landing now occurs more slowly in PSX version 10.195:

https://aerowinx.com/board/index.php/topic,4191.0.html


|-|ardy

[744student]

Just did landings in 25/45kt crosswinds - couldn't ask for a better aerodynamic model. Absolutely spot on in my opinion, in terms of inertia, yaw rate and windcocking effects.

[Hardy Heinlin]

Glad to hear :-) Thank you.

[Britjet]

Just tested 10.195.

Much easier to handle, while still requiring a good amount of skill and ability - like wot I've got LOL.

Many thanks Hardy!