X-Plane Developer Q/A 01/2018

[Paraffin 2,197]

7 hours ago, ryanbatcund said:

On this ground handling 

my friend flies a c172 and also for a major us airline. He says in xp, if the wind is 120 at 15 kt he'll line up on the runway and with brakes released, the plane will weathervane into the wind.  Example departing Ry 9.  Turn on RY and stop.  Release brakes, plane veers to the right.  

That doesn't happen to me in real life in any small single that I've flown.  Is anyone else seeing this?

I've been grousing about the weathervaning tendency at taxi speeds with a mild crosswind, ever since the v11 betas.

It can be easily demonstrated that it's unrelated to any propeller/torque effects because it happens with the default Cirrus jet too.

 

6 hours ago, Murmur said:

Yes, in my opinion the reason is that many aircrafts in XP have an exaggerated directional stability, leading to uncontrollable weathervaning on ground. So, it's unclear whether the ground physics are related with this behaviour at all.

Since in XP the directional stability can be modified by modifying the aircraft geometry (vert stab area, airfoils, fuselage shape, etc.), even if it may be necessary to depart from the geometry of the real aircraft, I'd say 3rd party aircraft designers should tackle this issue when designing their aircrafts.

Third party ac designers might be able to moderate the effect, but we still need to convince Austin that this is a problem. And that doesn't seem to be happening. The "fix" ultimately needs to come from Laminar, because it happens consistently with the default planes in the sim, like the C172 and Cirrus jet. 

[Mountain Man 142]

According to the write up posted earlier, Austin acknowledges that there is a problem with ground handling.  He's just not sure how to fix it.

 

https://flightdeckx.com/recap-of-last-wednesdays-qa-session-with-laminar-research/

[Murmur 3,941]

3 hours ago, Paraffin said:

Third party ac designers might be able to moderate the effect, but we still need to convince Austin that this is a problem. And that doesn't seem to be happening. The "fix" ultimately needs to come from Laminar, because it happens consistently with the default planes in the sim, like the C172 and Cirrus jet. 

Yes, ideally the fix should come from Laminar. And it would be certainly preferrable for XP that the default aircrafts wouldn't have this wrong behaviour.

But, for example, default MSFS aircrafts had very poor flight dynamics (particularly for stalls, spins, etc.), but this did not prevent good 3rd party designers to tweak the flight model and create addons with much better dynamics for stalls, spins, etc.

[olderndirt 2,295]

FWIW - why does full (into your gut) back pressure on the elevator alleviate this takeoff steering thing.  Not perfectly straight but you can keep the centerline in sight.  The only drawback being you get airborne at a fairly high angle so you're busy getting your ducks realigned.

[twojastara 85]

On 26.01.2018 at 6:27 PM, olderndirt said:

Certainly is reassuring to hear that Austin has "no idea about ground handling".

 

On 26.01.2018 at 10:07 PM, ryanbatcund said:

This is sarcasm right?  

 

I am sorry, I am not native English speaking person, so I think I have used wrong phrase here. What I meant by describing Austin's attitude toward this ground handling problem is that, that he said he doesn't know where the problem is, but he is open and willing to investigate it. He just needs more data to catch on. That's why he is encouraging everyone, who thinks that there is a problem, to file an official bug report with detailed description.

[olderndirt 2,295]

The fact that he admitted a problem and is working on a fix is good news and your English is fine. 

[bonchie 2,305]

It'd be more reassuring if he wasn't still telling people to file bug reports. At this point, he's no doubt got 1000 bug reports on the ground handling issue.

And if he wants data on the problem, he can boot up his sim and see how terrible it is. It's not like it's intermittent or occasional. Another user filing yet another bug report is not going to give him anymore usable data.

[Sticky 267]

seems to me it's more of a volume thing.

Austin says the math is all there and it is correct.  Perhaps hes right that rubber tires spinning at a certain speed and a certain angle produce a harmonic resonance...or what of the physical properties are.

Anyway, why does that mean the pilot way up in the cockpit need to hear it a tiny screech? Whether a prop or jet, I've never heard a tire screech from minor nose tire angles.  That doesn't mean there aren't any being produced, just the pilots ear isn't next to the tire.  Maybe change the noise system to only produce the screech when wildly gross tire angles are produced? That I can believe. (like the jetblue that landed with the nose tire at 90 degress...I'd bet there was a lot of screeching!

[olderndirt 2,295]

Physics, flight dynamics, aeronautical science in general - wonder how much of that crossed Chuck Yeager's mind when he rolled the X-1 after breaking the sound barrier. 

[HamSammich 17]

>>It'd be more reassuring if he wasn't still telling people to file bug reports.<<

Exactly. More user information is NOT going to help here. Nor is an endless search for some fundamental "key" to understanding the problem. It's like not wanting to do your homework because. . .The universe is expanding. This cries out for an empirical fix, not some ground-up "discovery." Austin's futile search for more data hinges on the assumption (fallacious) the X-Plane is fundamentally "correct" at all. The dirty little secret is that all flight modeling, all of it, is based on assumptions, and limiting conditions, and pragmatically allocating computing resources that won't be free or even cheap for decades of hardware development, yet. So the answer is, just fix it, whether it's theologically correct or not!

Best,

 

Marshall

 

[mjrhealth 820]

Well with all these desk top experts around, im surprised someone has not told him how to fix it. Ever had a problem you have had so long you got stuck in an infinite loop. Well maybe he needs a eureka moment to fix it..He need decent input not whining ...

[HamSammich 17]

>>He need decent input not whining ...<<

No whining. I and others can only tell him whatever it is, it doesn't work. And if this were a new problem, I suppose more data-gathering would be useful. It's not. X-Plane has had lousy ground handling for a decade. We sent people to the moon in eight. And designed the atom bomb in three. More theories from the customers won't help. Nor will a eureka moment. That's my point. Fixing it from first principles, though admirable, may not be possible or practicable and, in any case, is not even  needed. Practical engineering, at this point, calls for a nice, inelegant, 80/20, kludge. I don't care WHY the plane slides all over the runway, I just want it to STOP sliding all over the runway, with the quickest solution and fewest tradeoffs possible.

 

 

Best,

 

Marshall

[torfih 49]

He asked for bug reports including the act file in question.

[HamSammich 17]

The point is, after so many years, with such a well-known problem, it's absurd to be asking for more bug reports.

This must be one of the most-bugged issues X-Plane has. Asking for more bug reports is part of the problem, not the solution. That's the point.

Austin has designed a wonderful product. However, on this, he is either incapable of, or resistant to, fixing the problem. I suspect, and it's only a suspicion based on his thinking on the rest of the sim, because he doesn't know how to fix it from first-principles. And that, again, is my only complaint: There's no need to fix it from first principles--it's a luxury and, at this point, self-indulgent. Just fudge it. However it works best, whether it's theoretically pure or not. Fudge the thing. Believe it or not, when time and resources are not infinite, but some sort of solution is desired, that's actually the best engineering practice.

 

Best,

 

Marshall

[Murmur 3,941]

3 hours ago, HamSammich said:

X-Plane has had lousy ground handling for a decade.

What is your _specific_ complaint about current ground handling in X-Plane? Ground handling has been changed multiple times, so please be more specific.