XP11 winds, aircraft and weathervaning ...

[finkelstein 25]

 

 

And I didn't have any joystick or rudder attached - just use the mouse & keyboard, and my controls were centred.

 

Due to lack of adequate rudder controls for mouse/keyboard, "auto rudder" is enabled automatically in this case. I suggest re-doing your experiments with proper controllers assigned.

[Alfredo Fernandes 1]

Yes, it's the auto rudder, it will be active always with mouse in order to allow ground control, I know for sure that with my joystick it does not behave like that, wind does not affect the surfaces even with stability augmentation on rudder from what I've seen and yeah I was testing the Baron.

[jcomm 5,886]

Ok, I missed that one, but still, it doesn't make sense since the aircraft is parked.... not moving.

[bthiago 8]

Or... maybe Austin got his inspiration from this...

 

https://www.youtube.com/watch?v=9IdIaEwwCZs

 

Or maybe a heavier:

[Murmur 3,941]

While Murmur continues his study of the data available from XP11 dataref database, I would like to point out a couple of findings I did today, and contribute to restore, considerably, my hope in XP11 at least in this particular matter!

 

Well, since Murmur suggested there might be some problem with the default C172, I decided to pick the default B58.

 

Placed it at LPMT rw 08, braked, engines out, and started playing with the "wind rose", which, btw, reminds me more of the way DCS World interface is designed to define wind direction, and I don't find that good, because it can be misleading - the the arrow point to "from where" the wind comes, but being an arrow, this can be misinterpreted as "where to"... Anyway, here go my findings:

 

1) The trim settings, both default Plane Maker trim tab settings and whatever we set in the cockpit using the trim wheels / switches when available, deflect the corresponding control surfaces from there "neutral" position, with any wind intensity washing them, from 0 to the max available wind component + max gust.

 

I really don't recall how it was in previous versions ( ? )

 

If, for instance, you set the ground adjustable aileron trim tab to a huge +4.00 instead of the default +0.07, when you look at the aircraft from an outside view, the ailerons will be considerably deflected accordingly, in this particular case, the right aileron deflect UP the left deflected DOWN. This does not depend on there being any propwash ( the engines can be turned off ), or wind component.

 

I do not like this approach, and I believe Austin should create a better representation of the effect of trim surfaces, namely, their effect being noticeable only as dynamic pressure increases over their surfaces... The ailerons with the parked aircraft should be neutral, but for instance by increasin the wind from ahead to higher and higher values, they should start to deflect...

 

2) When a x-wind component is set in the weather menu ( make sure you disable NOAA or any other weather injector to run the tests, or their settings will prevail! ), the rudder will deflect upwind !  Now, this is irrespective of what the default trim tab position is ( in the case of the default Baron 58, rudder and elevator trim tabs are set at 0.00 in Plane Maker ).

 

Now, 2)​ can in some way be the culprit for the overdone need to use downwind rudder input.

 

But, looking at the effects of the wind, specially set at "stronger" values, from the outside of the aircraft, and how the gear struts compress and the tire physics work, is really promising!

 

Looking forward for your comments, and for Murmurs tests, but I wonder if anything can be done, other than using artificial stability, to avoid the rudder deflection upwind with a x-wind component ?

 

The screenshot bellow shows the default Baron 58, parked at LPMT rw 08, with a wind set at 35 knot from port side. Notice the rudder deflected upwind. The ailerons are also deflected, not because of the wind but rather because I defined the aileron trim tab in Plane Maker to +4.00. The yoke and the rudder in the cockpit remain centred.

 

 

 

[TECHNICAL POST]

 

2) In X-Plane, the deflection of the rudder in the Baron when in a crosswind is caused by its yaw damper. You can check it by failing the yaw damper, after that the rudder will not move anymore. I don't know if the real Baron has a yaw damper, nor if it's modeled correctly in its behaviour, in any case the reason is that, nothing else. :smile:

 

1) With regard to the control surfaces reacting to airflow. I remember we already discussed this in the past. The problem is that in a real aircraft, the yoke and the control surfaces are (of course) directly connected, while this is not true in a pc flight simulation, if using a non force feedback joystick (i.e. 99,99% of users). So, every flight simulator has to compromise in one way or another, and it's not that a given solution is better or more realistic than the other.

 

In theory, one could model either a stick fixed condition (where the flight controls position is directly connected to joystick position) or a stick free condition (where the flight controls position depends on the airflow and is not directly connected to joystick position).

 

Every flight simulator that I know of, models the stick fixed condition (and yes, that includes DCS, as explained later) for various reasons. It's certainly the preferable one between the two, given the limitations above mentioned.

 

Regarding DCS. In the link to the Spitfire stability thread (I think it was 30 pages long) that I gave in the Eagle Dynamics forum, there's a post by Yo-Yo where he explains just that: in order to model a stick free condition, a force feedback joystick would be needed, so DCS too actually models a stick fixed condition. This could be tested in DCS by flying an aircraft and trying to cause some rapid oscillations in the AoA. In a stick fixed conditions, the elevator should not move at all, and hence not react to the varying airflow.

 

So, how does this reconcile with the fact that in DCS the flight controls react to airflow during e.g. takeoff? Well, in a certain sense we could say that it's little more than eye candy. As I explained, they modeled this reaction to the airflow in this initial low-speed phase, but once the flight controls are "in place" and the aircraft is actually flying, they do not react anymore to the airflow, being modeled a stick-fixed condition.

 

So, to sum it up, all PC flight simulators model a stick-fixed condition. It's not a lack of realism, but a compromise dictated by the limitations in hardware.

 

The reaction of flight controls to airflow during low speed is a "touch" seen in some flight simulators to increase visual realism, but does not contribute to increase the realism of the flight model overall.

 

The desirable improvements in X-Plane flight and ground model are a lot, but having flight controls react to the airflow is not one of them, nor would it increase the accuracy in any appreciable way. :smile:

[Murmur 3,941]

[ANOTHER TECHNICAL POST]

 

As I said, I made some experiments with the C172 in X-Plane 11 to study tire friction.

 

First of all, when the aircraft is braked (and engine off), the tire model works perfectly. The maximum forces and moments that the landing gear can apply, agree with my calculations. Infact, when the X-Plane C172 is braked, it can remain still for direct crosswinds up to about 45 knots (if wind is gradually increased). Apart from the theoretical calculations, this also seems reasonable.

 

The aircraft will actually move just a little under the wind forces, apparently for the effects of strut compression and tires deformation, but will settle to its original position if wind is ceased.

 

Now, if the gear is not braked, things are less clear. In this case, the X-Plane C172 will begin to weathervane for crosswinds of about 13 knots. In this case, the maximum forces and moments applied by the landing gear seem to be less than those I calculated.

 

So the tire model seems to be 100% correct when the brake is on, but the situation is a lot more dubious when the brakes are not applied. I have still not reached a definitive conclusion though, and it's not easy to understand what is the origin of this issue.

[hjsmuc 393]

Great explanations, thank you for this. 

[whoispankaj 51]

The origin of this issue is Austin not acknowledging it..😝

[Paraffin 2,197]

The origin of this issue is Austin not acknowledging it..😝

 

Okay, but let's keep this in perspective. There is definitely something odd going on here, but this is a minor issue in the overall simulation.

 

I can easily take off with just a small amount of pedal pressure with the default 172 in any reasonable crosswind. I've never had any major problem with weathervaning when flying tail-wheel planes or anything else in X-Plane. The problem with torque modeling was far more serious.

 

I do hope this is fixed, but let's not exaggerate the impact on normal GA flight ops. It's not THAT big a problem. In the meantime, file bug reports when you see it happening and maybe we'll get a fix at some point. 

[bonchie 2,305]

Okay, but let's keep this in perspective. There is definitely something odd going on here, but this is a minor issue in the overall simulation.

 

I can easily take off with just a small amount of pedal pressure with the default 172 in any reasonable crosswind. I've never had any major problem with weathervaning when flying tail-wheel planes or anything else in X-Plane. The problem with torque modeling was far more serious.

 

I do hope this is fixed, but let's not exaggerate the impact on normal GA flight ops. It's not THAT big a problem. In the meantime, file bug reports when you see it happening and maybe we'll get a fix at some point. 

 

When it happens makes it a serious issue.

 

Every new XP user does what the first time they boot up? Taxi and takeoff. And the bad ground handling was the first negative impression I got from XP10 when I bought it.

[Humpty 751]

Confused, should the weathervane effect happen when taxing or when idle with engines off ? I haven't tried it as yet. 

[jcomm 5,886]

Yep Murmur, that's it - the yaw damper !  Should I have tested with the C172, and the rudder wouldn't have deffelected - I'll check it today! I don't know if every B58 is fitted with one of those - probably an option since my ELITE PC Baron models do not have it ( ? ) but then, why would the rudder deflect that way ? The resulting moments due to the higher tail section, cause the weathervaning, with the yaw upwind, not downwind. Roll is practically nill on ground, so.... if in an aircraft I cross controls and perform a wings level turn, the ball will slip to the outside of the turn ( downwind in this case ) calling for opposite rudder deflection by the pilot, or the yaw damper as it's modelled ( rather simplistically ) in X-Plane... ?

 

But indeed turning the battery on / off and / or assigning a keyboard shortcut to the yaw-damper on / off function, impacts the rudder deployment.

 

And yes, we know about the stick free vs stick fixed. Actually, in DCS only the ailerons move with propwash or more intense winds on ground with the aircraft standing still, but the rudder and the elevator don't.

 

There is an exception - IL.2 Battle of Stalingrad. Stick free is indeed modeled if a FF stick is used, with a very acceptable compromise, and even the elevator moves if your elevator trim tab is set away from neutral, when the aircraft is braked and power is applied ( due to propwash ). If you have a FF stick, it'll move as well, at least in pitch and roll.

 

Regarding the weathervaning effect in XP10 and 11, indeed it only begins to "come to live" as soon as the brakes are released, and I did my test above with a braked B58, and using up to 60 knot x-wind, although the screenshot was taken with a 35 knot x-wind component.

 

I did appreciate the way the struts compressed, and the same happens in DCS and IL.2 as well as in AEFS2 ...

 

Sometime ago Ben tried to explain based on a frame-based model of the FDM cycle regarding the modelling of interaction with the ground. Unfortunately the only thing Austin did with b3 was enabling the tyre physics calculations while the aircraft is standing still and not only as it starts to move...

[Alfredo Fernandes 1]

I think this can be some plugin on your side jcomm, I have tried today without my joystick and the rudder still didn't deflect with wind, ensure that you didn't changed something on plane-maker that could do it I suggest you to update X-Plane again to remove any modified files on default aircraft.

 

I tried it with mouse and also with yaw damper on, none did the effect you're describing and I added wind of 40kts from various directions to check.

[jcomm 5,886]

I think this can be some plugin on your side jcomm, I have tried today without my joystick and the rudder still didn't deflect with wind, ensure that you didn't changed something on plane-maker that could do it I suggest you to update X-Plane again to remove any modified files on default aircraft.

 

I tried it with mouse and also with yaw damper on, none did the effect you're describing and I added wind of 40kts from various directions to check.

 

But I tested with and without YD on, after reading Murmur's post an provided the Battery is On, and it does differ, in the Baron 58. In the C172 nothing happens to the rudder because it doesn't have a YD.

 

So I was actually wrong in thinking that what was causing the rudder deflection was the wind or Artificial Stability even if disabled on Plane Maker. But there is still a visible problem in X-Plane, because if you run your tests with a significant wind ( 35+ knot ) with the brakes on, and then disengage them, the aircraft will instantly slide sideways, like a weathercock... We can even see the wheels sliding sideways as it rotates, with the nose gear fixed in place.

[Pascal_LSGC 298]

But I tested with and without YD on, after reading Murmur's post an provided the Battery is On, and it does differ, in the Baron 58. In the C172 nothing happens to the rudder because it doesn't have a YD.

 

So I was actually wrong in thinking that what was causing the rudder deflection was the wind or Artificial Stability even if disabled on Plane Maker. But there is still a visible problem in X-Plane, because if you run your tests with a significant wind ( 35+ knot ) with the brakes on, and then disengage them, the aircraft will instantly slide sideways, like a weathercock... We can even see the wheels sliding sideways as it rotates, with the nose gear fixed in place.

 

Ok, this is interesting. The static friction should be identical whether the brakes are on and off, if the wind is exactly lateral. That would be a simple test case for a bug report.