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tutmeister

When are they going to fix ground handling in windy weather?

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Posted (edited)

Loaded up real weather at Manchester Barton EGCB today (weather too bad to really fly from there today) and could barely taxy down the airfield. Default 172 kept trying to swap ends. After run ups I lined up using proper grass field procedure with the yoke all the way back to reduce pressure on the nose wheel and prop strike risk. Opened the throttle and the thing was pitching up almost immediately and it wasn't THAT windy!

I'm assuming I'm not the only one who thinks it is still a joke. It's even mentioned in the active sky manual that there are inherent serious problems with ground handling and wind on the ground with options in active sky to mitigate the crosswind problems.

Why is it taking this long for laminar to sort it? It's been like this for ever. It's one of the biggest problems stopping me moving from a2a and prepared and really spoils the claim that it is a serious sim.

Edited by tutmeister
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42 minutes ago, tutmeister said:

Loaded up real weather at Manchester Barton EGCB today (weather too bad to really fly from there today) and could barely taxy down the airfield. Default 172 kept trying to swap ends. After run ups I lined up using proper grass field procedure with the yoke all the way back to reduce pressure on the nose wheel and prop strike risk. Opened the throttle and the thing was pitching up almost immediately and it wasn't THAT windy!

I'm assuming I'm not the only one who thinks it is still a joke. It's even mentioned in the active sky manual that there are inherent serious problems with ground handling and wind on the ground with options in active sky to mitigate the crosswind problems.

Why is it taking this long for laminar to sort it? It's been like this for ever. It's one of the biggest problems stopping me moving from a2a and prepared and really spoils the claim that it is a serious sim.

So the plane was doing a wheelie, is that what you are saying?

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Posted (edited)

Ha ha yep pretty much. But also trying to lift off at much too low an airspeed and being blown around while taxing. I was using real world weather and it was pretty windy but not hurricane level.

I know there is not really anything to be done about it, I was just having a rant because it is still broken but they are more bothered about getting metal and pbr in than fixing basics.

Edited by tutmeister

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Posted (edited)

Interesting to know what teh wind was seems 15kts crosswind  is no go for 172.

 

Planes flying while standing still, not xplane

 

Look Mum no pilot most fuel efficent engined plane in te hworld

 

 

Edited by mjrhealth

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What was the actual wind speed and what direction relative to the runway heading? I know XP11 has had issues with this, but it's hard to evaluate your post without a wind speed and direction. A C172 isn't an all-weather plane.

I fly with injected real weather from ActiveSkyXP, but with the settings tailored to back off the real weather to make sure I can takeoff and land, with the light GA planes I like to fly. Up here in the PNW, there are days where I just couldn't fly otherwise!

 

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Yeah I know, primarily it was me whinging because it still isn't fixednand I desparately want XP11 to just get it rught.

I'll try it again later using the same weather but I'm off to the cinema with the family to watch avengers and then lunch watching the Baku F1 GP. After than I'll try it again.

Cheers.

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For what its worth, I (and those at Laminar at the decisive positions) feel that the crosswind handling and capabilities of the default C-172 is fine. If you get "blown around" it is very likely due to having too much wind, insuficient runway state, poor control setup (hey, some people still fly with mouse or without rudder pedals!) or just simple plain piloting technique deficiencies 😉.

You can rant all you want, but don´t hold your breath for this getting changed. These threads usually end when I post a video of me taxiing the C172 (or other aircraft being declared "totally unrealistic") at 1.5x official crosswind limit winds just fine - and then the OP usually disappears 😁.

So - while there are still some things under review (like the propwash effects on stabilizers), the general crosswind behaviour of X-Plane is "in the ballpark".

Cheers, Jan

 

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Hi Jan, I don't have a pc right now so no access to XP, what is the max xwind speed you can consistently safely take off with the current C172?

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Post GP I'll have a play around but it wasn't that windy. I'm using properly calibrated yoke and pedals and whilst not the greatest pilot in the world I know how to taxy and take off on grass field all be it in a warrior and not a c172.

If you have active sky xp and have read the manual there is a paragraph where they highlight the deficiency in the xp crosswind and ground handling.

I'm pretty sure it is flawed in even moderate wind but let's leave it until I can get back on my pc and try again.

 

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Posted (edited)
18 hours ago, tutmeister said:

Loaded up real weather at Manchester Barton EGCB today (weather too bad to really fly from there today) and could barely taxy down the airfield. Default 172 kept trying to swap ends.

XP real weather imported winds were between 15 and 25KTS gusting up to 33 pretty much anywhere in the UK in the past 2 days.  That's a tall order for a 172, in particular for the XP default one. 🙂

4 hours ago, Janov said:

For what its worth, I (and those at Laminar at the decisive positions) feel that the crosswind handling and capabilities of the default C-172 is fine. If you get "blown around" it is very likely due to having too much wind, insuficient runway state, poor control setup (hey, some people still fly with mouse or without rudder pedals!) or just simple plain piloting technique deficiencies 😉. 

You can rant all you want, but don´t hold your breath for this getting changed. These threads usually end when I post a video of me taxiing the C172 (or other aircraft being declared "totally unrealistic") at 1.5x official crosswind limit winds just fine - and then the OP usually disappears 😁.

So - while there are still some things under review (like the propwash effects on stabilizers), the general crosswind behaviour of X-Plane is "in the ballpark".

That depends on how you define "ballpark", or what ball and what park we're talking about.  I've joined a few discussions about that, made a lot of experiments and tried to devise a method of finding out what's wrong since I bought XP11, and last week I could gather some pretty solid indications (if not evidence) that the widespread perception that at least the default 172 is pretty off can be explained and even proven.  IMO the default 172 is very much off for 2 main reasons:

1.) There is a distinct lack of rudder authority making (strong) crosswind handling more difficult than it should be.  Many pilots agree that around 20KTS crosswind component is the point where 172s run out of rudder, the default 172 doesn't have enough rudder authority to reach the demonstrated 15KTS.  But this lack of rudder authority is shared by all XP GA planes (3rd-party or not) I have, most of which have higher demonstrated crosswinds than a 172.  This points to an underlying issue with a yet unknown parameter/component, an issue that - if I understood that right - has been acknowledged by Austin (who is apparently just as puzzled about that) and led to the famous "model fuselage" photo.  

On the Easter weekend I finally had a chance to assess how much rudder authority some (real) C-172 actually has by performing a few simple side- and forward slip tests and comparing that to the XP 172s I have:

A) how does the 172 respond to full rudder at a defined speed (85KTS in that case) anyway (how much yaw, how fast does it get there...),

B) how much yaw angle will there be at full rudder deflection at that airspeed, while maintaining the ground path using aileron/bank angle and

C) how much bank angle is needed to stop the rotation around the yaw axis anyway.  

The (generously rounded, because my data acquirement method wasn't exactly thought through very well yet) results are

A) much smoother, much faster, much more than the XP 172,

B+C) somewhere between 20-30° of yaw and >10° of bank angle, while the default 172 delivers 10-15° of yaw and <10° of bank angle.  If you translate that to a crosswind landing situation, it's pretty clear why you can't kick away a wind correction angle of e.g. 20° during a sideslip/wing down flare, or properly sideslip over the centerline in first place.  Tweaking the .acf to get that rudder authority needs such high deviations from the default numbers that I think the lack of authority might just be a symptom of another, underlying problem.

1a) Of course everything "flying sideways" is affected by this, you can't expect a realistic forward slip behavior when you can't yaw and bank enough metal into the relative wind in first place.  This also affected the REP 172 so far and gets currently worked on, and that's how I got into this discussion again.  The default 172 lacks all means to perform a forward slip that actually affects speed or sink rate substantially, and the rudder also has an odd lack of roll response (even when brutally tweaked to have more effect) so you need barely any opposite aileron to maintain the needed attitude, so that's yet another thing I'd consider "at least not in *my* ballpark".

However this lack of rudder authority alone is not that much of a problem yet, it becomes a problem with many (if not all) default XP planes and in particular the 172 because...

2.) ...there is a known problem with wheel/ground friction.  Again, this is old news and has been proven and acknowledged and addressed (unsuccessfully) repeatedly, while some 3rd-party developers have managed to cope with it very successfully (e.g. the REP packages).  

The problem is that the wheels lose friction pretty fast, and once they lost friction they are not getting it back easily, which would be still a physical correct result if the wheels would regain their grip after losing momentum and sideforce particularly on dry asphalt.  Instead they keep on skidding over it sideways even down to pedestrian speeds, any sideforce and the wheels (all of them) lose friction even when still parking and lifting the brake once, the plane starts skidding around like on ice with brakes occasionally rendered ineffective...again, all a known and acknowledged issue with the XP 172.  At some point during the 11.30 beta phase LR tried to mitigate this by automatically applying toe brakes proportional to the rudder deflection, which I called a "kludge" particularly because it was not only ineffective, it made things worse because the wheels started blocking (=losing grip again of course) at the amount of rudder deflection needed.

The chain of events during crosswind landings is like this:  The lack of rudder authority leads to a very high chance that you are going to touch down with some drift/sideforce (because you can't kick the nose straight enough to align it with the centerline, in particular not while needing to maintain a bank angle) and that means whatever wheel will touch down it will lose grip, all other wheels will likely follow and there is little chance to eliminate the side forces long enough that the wheels get some grip again, not only because the rudder is no big help in this even shortly after touchdown.  

While decelerating the rudder will quickly lose even more force so from there on you are again prone to lose all friction due to weathervaning (which is what this combination of issues is often being confused with anyway).  To prove particularly the latter I "hacked" the default 172 at some point to have sufficient rudder authority for the sideslip and could land it at 20KTS of crosswind blowing perpendicular to the runway, and control it sufficiently to touch down aligned with the centerline (no sideforce) and then S-curve all the way down to bicycle speeds while losing and regaining friction all the time.  One of the cascading problems removed = things get considerably better.
 
This is also where the controller plays a significant role indeed, a little jitter or general lack of precision on the yaw axis/nosewheel steering will make you lose grip even more reliably, and of course your technique will be put to the test in a somewhat disproportional way too.  Yes, I can (and I did) make a video that it can be done way beyond 15KTS but that doesn't mean that it's "fine".  In particular with any halfways realistic variation in the wind, the amount of precision, technique, reaction and luck required is way beyond the ballpark, and with the aforementioned flaws stacking up I wouldn't consider any of this "in the ballpark" enough to generally assume a lack of technique or bad controllers when people understandably complain about this.

1 hour ago, Murmur said:

Hi Jan, I don't have a pc right now so no access to XP, what is the max xwind speed you can consistently safely take off with the current C172?

I don't know about Jan but takeoff is a different animal, and IIRC 25KTS was the point where reaching Vr and losing grip happened close enough to deem it "safe". 🙂

 

 

 

Edited by Captain Nuts
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2 hours ago, Captain Nuts said:

XP real weather imported winds were between 15 and 25KTS gusting up to 33 pretty much anywhere in the UK in the past 2 days.  That's a tall order for a 172, in particular for the XP default one. 🙂

That depends on how you define "ballpark", or what ball and what park we're talking about.  I've joined a few discussions about that, made a lot of experiments and tried to devise a method of finding out what's wrong since I bought XP11, and last week I could gather some pretty solid indications (if not evidence) that the widespread perception that at least the default 172 is pretty off can be explained and even proven.  IMO the default 172 is very much off for 2 main reasons:

1.) There is a distinct lack of rudder authority making (strong) crosswind handling more difficult than it should be.  Many pilots agree that around 20KTS crosswind component is the point where 172s run out of rudder, the default 172 doesn't have enough rudder authority to reach the demonstrated 15KTS.  But this lack of rudder authority is shared by all XP GA planes (3rd-party or not) I have, most of which have higher demonstrated crosswinds than a 172.  This points to an underlying issue with a yet unknown parameter/component, an issue that - if I understood that right - has been acknowledged by Austin (who is apparently just as puzzled about that) and led to the famous "model fuselage" photo.  

On the Easter weekend I finally had a chance to assess how much rudder authority some (real) C-172 actually has by performing a few simple side- and forward slip tests and comparing that to the XP 172s I have:

A) how does the 172 respond to full rudder at a defined speed (85KTS in that case) anyway (how much yaw, how fast does it get there...),

B) how much yaw angle will there be at full rudder deflection at that airspeed, while maintaining the ground path using aileron/bank angle and

C) how much bank angle is needed to stop the rotation around the yaw axis anyway.  

The (generously rounded, because my data acquirement method wasn't exactly thought through very well yet) results are

A) much smoother, much faster, much more than the XP 172,

B+C) somewhere between 20-30° of yaw and >10° of bank angle, while the default 172 delivers 10-15° of yaw and <10° of bank angle.  If you translate that to a crosswind landing situation, it's pretty clear why you can't kick away a wind correction angle of e.g. 20° during a sideslip/wing down flare, or properly sideslip over the centerline in first place.  Tweaking the .acf to get that rudder authority needs such high deviations from the default numbers that I think the lack of authority might just be a symptom of another, underlying problem.

1a) Of course everything "flying sideways" is affected by this, you can't expect a realistic forward slip behavior when you can't yaw and bank enough metal into the relative wind in first place.  This also affected the REP 172 so far and gets currently worked on, and that's how I got into this discussion again.  The default 172 lacks all means to perform a forward slip that actually affects speed or sink rate substantially, and the rudder also has an odd lack of roll response (even when brutally tweaked to have more effect) so you need barely any opposite aileron to maintain the needed attitude, so that's yet another thing I'd consider "at least not in *my* ballpark".

However this lack of rudder authority alone is not that much of a problem yet, it becomes a problem with many (if not all) default XP planes and in particular the 172 because...

2.) ...there is a known problem with wheel/ground friction.  Again, this is old news and has been proven and acknowledged and addressed (unsuccessfully) repeatedly, while some 3rd-party developers have managed to cope with it very successfully (e.g. the REP packages).  

The problem is that the wheels lose friction pretty fast, and once they lost friction they are not getting it back easily, which would be still a physical correct result if the wheels would regain their grip after losing momentum and sideforce particularly on dry asphalt.  Instead they keep on skidding over it sideways even down to pedestrian speeds, any sideforce and the wheels (all of them) lose friction even when still parking and lifting the brake once, the plane starts skidding around like on ice with brakes occasionally rendered ineffective...again, all a known and acknowledged issue with the XP 172.  At some point during the 11.30 beta phase LR tried to mitigate this by automatically applying toe brakes proportional to the rudder deflection, which I called a "kludge" particularly because it was not only ineffective, it made things worse because the wheels started blocking (=losing grip again of course) at the amount of rudder deflection needed.

The chain of events during crosswind landings is like this:  The lack of rudder authority leads to a very high chance that you are going to touch down with some drift/sideforce (because you can't kick the nose straight enough to align it with the centerline, in particular not while needing to maintain a bank angle) and that means whatever wheel will touch down it will lose grip, all other wheels will likely follow and there is little chance to eliminate the side forces long enough that the wheels get some grip again, not only because the rudder is no big help in this even shortly after touchdown.  

While decelerating the rudder will quickly lose even more force so from there on you are again prone to lose all friction due to weathervaning (which is what this combination of issues is often being confused with anyway).  To prove particularly the latter I "hacked" the default 172 at some point to have sufficient rudder authority for the sideslip and could land it at 20KTS of crosswind blowing perpendicular to the runway, and control it sufficiently to touch down aligned with the centerline (no sideforce) and then S-curve all the way down to bicycle speeds while losing and regaining friction all the time.  One of the cascading problems removed = things get considerably better.
 
This is also where the controller plays a significant role indeed, a little jitter or general lack of precision on the yaw axis/nosewheel steering will make you lose grip even more reliably, and of course your technique will be put to the test in a somewhat disproportional way too.  Yes, I can (and I did) make a video that it can be done way beyond 15KTS but that doesn't mean that it's "fine".  In particular with any halfways realistic variation in the wind, the amount of precision, technique, reaction and luck required is way beyond the ballpark, and with the aforementioned flaws stacking up I wouldn't consider any of this "in the ballpark" enough to generally assume a lack of technique or bad controllers when people understandably complain about this.

I don't know about Jan but takeoff is a different animal, and IIRC 25KTS was the point where reaching Vr and losing grip happened close enough to deem it "safe". 🙂

 

 

 

10

Although there have been improvements with crosswind behavior, I think your assessment is in the 'ballpark' ! Another issue is the lack of 'Left Turning Tendencies' on departure. The 172 should require lots of rudder input when slow at high angles of attack, but the ball shows no deflection in the turn coordinator. Have you contacted Austin with your theory?   

Edit: Ok just been playing around with a 20kt crosswind using the default172 with the EFM(experimental flight model), and had no problem keeping the plane line up on 3mile approach. Plenty of rudder authority! I also tried it with the REP version and it was twitchy, with EFM on and off. EFM with the default 172 seems like the way to go with a crosswind!   

Edited by strider1

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Ok tried again with yesterday’s weather and it was gusting 28 - straight down the runway.

So a quick test. Manually set 270 @ 20 and lined up on 27L. Yoke back, open throttle, wheelie and lift off under 40Kts while veering off right. Recover (mostly luck) and try and tasty at right angles to the wind, yoke back and aileron into wind. Full rudder and nose wheel and I can hardly keep it straight. I know ground friction is dodgy so I try with yoke full forward (something you would NEVER do) still no difference.

Janov, i’m not bashing XP for fun, I just wish it was better in some key areas and as a long term user I get the impression that every time this is raised it is denyed by people connected with or part of the dev team.

Like you I could post a video taxiing round in these conditions but it takes exceptional effort to go where you want it too. Equally I can post a video of the above behaviour and this is using 20kts which is definitely not that far fetched in the real world. As pointed out above with some much more comprehensive arguments that I can make show that rudder authority isn’t right but equally ground friction is definitely still broken. I love flying ga in X-Plane but at the moment it is still only great when CAVOK.

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The precise reason why X-Plane's ground handling is fundamentally wrong (here and here). The simple root cause has never been addressed as far as I know, only piles of hacks to try to fix the unfixable. The details were sent (with the softest gloves) to Austin last autumn, but he never answered. If people like Jan believe it is mostly ok as is, then for sure it is not gonna change any time soon. But from the physics point of view it will remain just an ugly hack around a neat solution of classical mechanics known for more than two hundred years (and readily available in third party open source code...).

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The hardest part for me, is when the 172 will be taxiing around fine, and then suddenly seems to go crazy - very erratic turns for no good reason.  I am learning to work around it, but I have flown with friends, and I know the handling is not "realistic".

Ron

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Kudos to some of the posts in this thread, with special regards to the OP - tutmeister - who I am sure doesn't have a problem with he's controller hw ( quite on the contrary, judging from he's SIG ) and to Oscar Pilote, and thank you Oscar for all your GREAT work with Ortho4XP which is more than enough for anyone to glimpse you do not have an agenda against XP, quite on the contrary....

XP has lost my hopes again and again, version after version... I'm unfortunately not moved by nice-looking sceneries, PBR, and that sort of stuff I see most simmers worried about instead of actually placing their attention in the primary aspects, IMO, of FLIGHT simulation - as sound / accurate as possible flight dynamics modeling - as well as systems modelling.

Not being able to consistently use my "rudder" to overcome torque effects, having to fight  ground physics that leave a lot to be tweaked by others through plugins and tricks, having that full across the spectrum overdone weathervane stability... has killed my otherwise "pleasurable" experience with XP long long ago....

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Posted (edited)
15 hours ago, jcomm said:

XP has lost my hopes again and again, version after version... I'm unfortunately not moved by nice-looking sceneries, PBR, and that sort of stuff I see most simmers worried about instead of actually placing their attention in the primary aspects, IMO, of FLIGHT simulation - as sound / accurate as possible flight dynamics modeling - as well as systems modelling.

Well it's maybe a bit early to lose all hope.  Default planes had and still have a quite limited accuracy in all sims I know, actually most of the payware stuff is not that much better (IMO) in all sims, particularly at the edges of the envelope.  Only very few models really stick out of the masses of planes with shiny visuals that roughly hit the POH numbers but fail to depict the characteristics and idiosyncrasies of a specific aircraft.  Maybe you have heard of Rob Young, he was one of the very, very few who knew how to hack/abuse a FDM to teach a plane details in behavior that were not deemed possible with the FSX/ESP technology before.  Likewise, the amount of XP planes and developers being that good is very limited, but the good news is that we may be getting there. 

For example, the REP for the 172 is the only thing I know (in all sims) that simulates the ground handling of a 172 with its spring loaded steering rods pretty dead on, and practically it doesn't suffer from the ground friction issues at all (because it models that in its own plug-in).  It still lacks a bit in the rudder authority department IMO (with a big improvement possibly coming) but the current beta already improved things a lot, it really nails stalls now, with some luck you may or may not end up in a spin and it's got a much more realistic general "crossed controls" behavior now. On top of an improved FDM you get better system simulations and a "persistent", "living" aircraft and all that for 20 additional bucks.  I've spend a lot more money for aircraft that deliver much less. [/REP commercial]

On 4/28/2019 at 5:47 PM, strider1 said:

Another issue is the lack of 'Left Turning Tendencies' on departure. The 172 should require lots of rudder input when slow at high angles of attack, but the ball shows no deflection in the turn coordinator. Have you contacted Austin with your theory?   

No, I have not contacted Austin for the simple reason that I think he knows that something is wrong, but I think he doesn't know what that actually is (otherwise it would've been fixed by now).  All I can do is submit a bug once I have some substantial clue on what might be wrong.  All I found out so far is no news to anybody, I just have tried to quantify "lack of rudder authority" a bit but I think this is just yet another symptom anyway.

Re the "right rudder demand", this is probably a bit more complicated.  To begin with, there are many slightly different models of "172" and for example, our club's 'H' model has remarkably little right rudder requirements for a couple of reasons and doesn't differ at all from other planes we have. It depends a lot on rigging, power, prop. load balance and of course wind vector anyway and so I think that can't be generalized easily.  If you try the default 172 with absolutely no wind there is some noticeable right rudder requirement.  Of course I also think that something is wrong with the default 172 in this department, it flies almost auto-coordinated even in steep turns and "stability augmentation" has the exact opposite effect of what I'd expect - it needs more rudder to coordinate turns when SA is at 100% and very little when there is no augmentation. Just odd.

On 4/28/2019 at 5:47 PM, strider1 said:

Edit: Ok just been playing around with a 20kt crosswind using the default172 with the EFM(experimental flight model), and had no problem keeping the plane line up on 3mile approach. Plenty of rudder authority! I also tried it with the REP version and it was twitchy, with EFM on and off. EFM with the default 172 seems like the way to go with a crosswind!   

I just tried the default 172 again with the experimental flight model in my 20KTS crosswind scenario and I couldn't see any difference.  What do you mean by "line up on a 3 mile approach"?  Are you performing a long sideslip approach or are you flying crab angle down the glideslope?  I can't see any difference during the sideslip/wing down phase on final, at 20KTS I can't align the nose with the runway even at 70KTS over the threshold.  Mind you, if you have a wide runway it doesn't feel or look that wrong if you touch down with the nose not perfectly aligned with the centerline and just use a somewhat diagonal path to counter the missing few degrees of "kicking the nose straight".  This doesn't work on a typical, rather narrow European runway or back country strip tho.  Only a replay with the right camera angles tells the whole story.  IOW "video or it didn't happen!". 🙂

 

 

Edited by Captain Nuts
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Posted (edited)

Thank you Captain for your post,

and yes, losing hope is a somehow an "overdone" way of putting it, but those who know me, apply the necessary "filters" to my posts 🙂

Now, back to the effects that I notice even in that REP, and I had the REP and the Airfoilabs 172s, there's that thing with a huge right turning tendency ( instead of left ) that began somewhere along XP11. 

The first thing I did to overcome it in the default models ( and some add-ons too ) was to reduce the trim settings and eventual vertical stab and engine(s) cant that were there before to overcome the "old time" overdone torque effects. But even in those fine tuned prop models, and not only these 172s, there's that tendency to see a right turning tendency even climbing at high power settings. 

There are other theories about it's origin(*), but it feels so unnatural that I tried everything to forget about it, including using trim where it shouldn't be used... ( "Use trim" - as Austin once suggested when I was complaining about that overdone torque effect that plagued X-Plane from mid v9 until Murmur "fixed" it... )

Then, there's that "sucking" ground effect that came to live sometime ago. This is yet another newcomer to the XP FDM saga. Our airplanes have some sort of "inverted" ground effect where they're "sucked" into the runway in the final steps of a landing, when entering ground effect. It's another weird and anti-natural effect that appears to look a lot like the effect of a generalized implementation of an effect Austin "discovered" made sense regarding some pitching moments caused by tail interaction with ground in some airliners.

(*) like fuselage interference with propwash, or the way propwash effects over the inner sections of the wings affect the associated asymmetry of lift and create a differential that overcomes and actually outperforms the torque an slipstream effects that should instead contribute to the left turning tendencies , and / or a lack of proper propwash modelling in terms of it's interference with the tail surfaces and fuselage ... 

Edited by jcomm
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Posted (edited)

 

11 hours ago, jcomm said:

Now, back to the effects that I notice even in that REP, and I had the REP and the Airfoilabs 172s, there's that thing with a huge right turning tendency ( instead of left ) that began somewhere along XP11. 

The current default 172 or B58 (which was really bad back then) or their REP combinations do not exhibit that crazy right-rolling tendency here, I think since 11.2x something.  The REP B58 is distinctly rolling left (not sure it should but at least it doesn't roll to the wrong side). Did you try any REP update lately?

But yeah, I almost forgot about the right rolling,  or pushed it to the back of my mind.  It was the first thing that really rubbed me the wrong way when I bought XP, the more torque, the more rolling to the wrong side, always taking off with crossed controls, I was not amused. 🙂 Back then I still had some strange and pretty far-fetched ideas like checking out the possibilities to build a pretty ambitious training device at our airstrip and bought XP11 (more or less on the way to purchase P3D) to see how it evolved and if it could deliver a solid software base, and that right rolling issue alone made it look absolutely hopeless to me.  Like 2 decades of bragging about the superiority of the "blade theory" still in my ears, it looked like it couldn't do any basic phase of flight right, maybe except straight+level cruise.  So believe me, I hear ya!

Luckily something else kept me from just throwing the DVD box into the trash bin - it was Ortho4XP and OSM overlays, an unheard before opportunity to meticulously recreate the surroundings of our airstrip and the usual action radius of our club and school in a way that looks absolutely familiar, with all the visual clues marking traffic patterns etc. then I added POIs, later super-realistic night lighting (we do a bit of night flying here), really intriguing prospects (not only) for my aforementioned silly ideas and a whole new way to spend insane amounts of time. 🙂

Eventually the right-rolling issue got fixed and meanwhile I had found a few GA planes with solid ground contact and things looked much, much brighter to me.  Like I said somewhere above, it wasn't much different in the other sim, very few planes were actually worth even thinking of building a home cockpit, not to mention silly ideas like getting some kind of training device certified.

11 hours ago, jcomm said:

Then, there's that "sucking" ground effect that came to live sometime ago. This is yet another newcomer to the XP FDM saga. Our airplanes have some sort of "inverted" ground effect where they're "sucked" into the runway in the final steps of a landing, when entering ground effect. It's another weird and anti-natural effect that appears to look a lot like the effect of a generalized implementation of an effect Austin "discovered" made sense regarding some pitching moments caused by tail interaction with ground in some airliners.

For some reason I never experienced this, maybe because I rarely use different planes than my few favorites.  I just noticed the lack of a ground effect, but this is something the experimental FDM seems to change.  I hope the increased interest in XP will also lead to more improvements in that regard and of course the basic, or should i say "neglected", weather simulation, as simulation of the stuff a plane flies in is just as important as the FDM IMO.  Yes, many more features are utterly half-assed, and depending on what preferences people have there might be better choices but for low-and-slow GA fans and tinkerers the alternatives look way more bland.  It doesn't even have to be LR improving stuff, like many of the really cool things for FSX came out long after development of the sim ended.

 

Edited by Captain Nuts
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On 4/28/2019 at 2:51 PM, Murmur said:

Hi Jan, I don't have a pc right now so no access to XP, what is the max xwind speed you can consistently safely take off with the current C172?

Sorry, I was away from my main PC at home (with flight controls) for a few days.

Default C-172 at default weights and CG on a dry, paved runway I can:

  • taxi just fine doing turns into wind, taxi straight etc. in winds of 30kts
  • take off and land fine with straight crosswinds of 20kts

I run out of rudder authority at about 22kts crosswind, but this *can* be helped with some nose-down elevator (to increase nose-gear friction). Bear in mind that the demonstrated max crosswind for the C-172 is 17kts, if I am not mistaken. Sure there is "hearsay" evidence of it being able to handle MUCH MORE - but not sure if that evidence qualifies as being "scientific" enough for flight-testing.

Also bear in mind that "high altitude" winds will translate unabated to ground-level winds. Often people load up some "real weather" winds of 100kts at 35000 feet and then wonder why they can´t control their planes during taxiing.

Also remember that controlling a plane in a desktop simulator is much harder than the real one - you will pick up any unintended deviations from the desired attitude/heading much later, because you have to rely on visual cues instead of rotational sensation.

Cheers, Jan

 

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Thx Janov for the additional info.

I'll give it a try again one of these days. Also will test the latest REP version and see...

Will try to report back.

 

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15 hours ago, Janov said:

Bear in mind that the demonstrated max crosswind for the C-172 is 17kts, if I am not mistaken. Sure there is "hearsay" evidence of it being able to handle MUCH MORE - but not sure if that evidence qualifies as being "scientific" enough for flight-testing.

The demonstrated xwnd is 17mph (15kts) and this is well below any really limiting wind speed. Even the 172 manual states that the mentioned 15kts are not considered limiting.

Demonstrated only means that this was the maximum crosswind component they encountered during the certification process, nothing else.

The even smaller and lighter 152 can be easily controlled in a 25kts crosswind IRL without getting the impression that you are at the actual limit.

Xwnd and turbulence are one of x-planes weakpoints since decades, but ar least everything is more shiny now with PBR etc.

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This ground handling "issue" is what sent me back to FSX after buying x-plane 10, and barely used it since.  Last week I bough XP 11 just to try zibo.  Had many enjoyable flights until I realized I had been flying with clear weather. Rolling out zibo with 17kts crosswinds from the left was nearly imposible. The plane was pushed to the right like a paper plane, and once off the runway it was violently pushed to the left that almost hit the terminals. I'm not pilot, just many years of 737 passenger experience, but that doesn't seem right.

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Oh well, you believe what you want 🙂

Jan

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Posted (edited)
On 4/29/2019 at 3:28 PM, Captain Nuts said:

Re the "right rudder demand", this is probably a bit more complicated.  To begin with, there are many slightly different models of "172" and for example, our club's 'H' model has remarkably little right rudder requirements for a couple of reasons and doesn't differ at all from other planes we have. It depends a lot on rigging, power, prop. load balance and of course wind vector anyway and so I think that can't be generalized easily.  If you try the default 172 with absolutely no wind there is some noticeable right rudder requirement.  Of course I also think that something is wrong with the default 172 in this department, it flies almost auto-coordinated even in steep turns and "stability augmentation" has the exact opposite effect of what I'd expect - it needs more rudder to coordinate turns when SA is at 100% and very little when there is no augmentation. Just odd.

I just tried the default 172 again with the experimental flight model in my 20KTS crosswind scenario and I couldn't see any difference.  What do you mean by "line up on a 3 mile approach"?  Are you performing a long sideslip approach or are you flying crab angle down the glideslope?  I can't see any difference during the sideslip/wing down phase on final, at 20KTS I can't align the nose with the runway even at 70KTS over the threshold.  Mind you, if you have a wide runway it doesn't feel or look that wrong if you touch down with the nose not perfectly aligned with the centerline and just use a somewhat diagonal path to counter the missing few degrees of "kicking the nose straight".  This doesn't work on a typical, rather narrow European runway or back country strip tho.  Only a replay with the right camera angles tells the whole story.  IOW "video or it didn't happen!". 🙂

 

 

2

Its strange because 172N that I rent requires no rudder on departure and no rudder at cruise(magic rigging!) But once upon a time it did require lots of rudder on departure. But the S-models that I rent require lots of rudder on departure. Regardless I would still like to get my money's worth out of my rudder pedals 🙂  

In the flight configuration menu, you can set up a 3m approach instead of starting on a runway. I was using the sideslip for wind correction to keep the plane line up with the runway centerline. Make sure you are using a 100% default 172 with no 3rd party tweaks. I have my 'Flight Models Per Frame' set to 4 and I have a custom 'Edit Response Curve', not sure if that makes a difference. In real-life landing on the centerline with a 20knt crosswind is very challenging! And if you have 20kts of wind then it's probably gusting above that! Good luck! Of course, practice makes perfect, but that's an expensive proposition if you are renting! 

Remember when everybody used to complain about rotating planes when parked/stopped in a crosswind? About a year ago after a windy/gusty day of flying, I parked the rental plane on the ramp and forgot to set the parking brake, next thing you know to my amazement the plane starts to rotate with a gust of wind! First thought was shi-t The second thought was Austin crosswind-ramp-flight dynamics are spot on 😉 lol........  

 

Edited by strider1
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Posted (edited)

I did a flight in south of France (edit: with the default Cessna), 20 knots on the map (real weather), it is spring so expect there to be some thermals.
Without the Experimental Flight Model (EFM): the plane keeps turning right most of the time while airborne.
With EFM enabled: I get tossed left and right (as expected) but with left hand turn tendency hands free.
I don't really have a problem with taxiing in either mode, but with EFM it is a bit easier.

Edited by soaring_penguin

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