2 hours ago, mSparks said:

There is a missing link here I believe, be nice to find it...

ASK 21 – Condor Soaring

Glider modelling starts with a as close to real as possible glider Polar. 

The AS K-21 is a relatively "simple" glider, with no flaps, fixed gear, Schemp-Hirth type air brakes. Stall 1G stall speed is around 65 km/h.

The K-21 is usually mentioned as being very difficult to enter a spin. Well, I could always enter spins with it, flying alone or with a passenger, and in this video the author shows how easily an AS K-21 can be put into spin:

Spinning the ASK21 with my gliding instructor - YouTube

The K-21s I fllew all exhibited a tendency to drop the left wing on a stall. There's good buffeting before entering the stall, and whikle not being as "mushy" as for instance a Grob Astir Club, the K-21 doesn't pitch down a lot during stall.

Sideslip maneuvers are sometimes tricky because the rudder tends to align so well with the relative wind that it becomes pegged, requiring rudder input to be brought back to neutral. Speed must be properly controlled in order for the sideslip angle to be efficient and for the rudder to be effective:

Side slipping a K-21 - YouTube

Nice video of a kid flying two gliders, the last the K21, in Condor 2

The Benefits of Simulator Soaring - YouTube

 

 

Edited July 26, 20223 yr by jcomm

8 hours ago, blingthinger said:

Airliners and autopilots are easy.

I think we can sum up this post with those 5 words. 

Do you even have a PPL? Or have you ever been in a commercial simulator?

Edited July 26, 20223 yr by 2reds2whites

4 hours ago, jcomm said:

Sideslip maneuvers are sometimes tricky because the rudder tends to align so well with the relative wind that it becomes pegged, requiring rudder input to be brought back to neutral. Speed must be properly controlled in order for the sideslip angle to be efficient and for the rudder to be effective:

So the issue is with the slip and skid?

Ive seen it mentioned a few times that "xplane cant sideslip" - actually had a long running issue with that on the 744:

https://github.com/mSparks43/747-400/issues/394

the usual retort from old timers is "xplane can side slip - example". But there is a world of difference between having support, and having good support, and getting everything "just right" so it "feels" correct. Most default XP11 aircraft have some significant weaknesses that payware and freeware peeps put a lot of effort into fixing.

have you tried for example:

https://forums.x-plane.org/index.php?/files/file/58198-ask21-b21-nhadrian-upgrade/

• disabled B21's rudder augmentation

sounds related? and the reviews are all glowing.

Edited July 26, 20223 yr by mSparks

1 hour ago, 2reds2whites said:

I think we can sum up this post with those 5 words. 

Do you even have a PPL? Or have you ever been in a commercial simulator?

Do you need to flex your ego a bit? It reeks of overripe. Ready to pop!!

Easy to model. I never implied they could be treated lightly. And regardless of how complicated they are to fly, XP is better suited to capture a wider range of the flight envelope. A flight envelope, when compared to many other arenas of aviation, that is very tame.

Edited July 27, 20223 yr by blingthinger

10 minutes ago, blingthinger said:

Do you need to flex your ego a bit? It reeks of overripe. Ready to pop!!

Easy to model. I never implied they could be treated lightly. And regardless of how complicated they are to fly, XP is better suited to capture a wider range of the flight envelope. A flight envelope, when compared to many other arenas of aviation, that is very tame.

That'd be 'no' then. 

It really shows.

Edited July 27, 20223 yr by 2reds2whites

1 minute ago, 2reds2whites said:

That'd be 'no' then. 

It really shows.

Ditto

3 minutes ago, 2reds2whites said:

That'd be 'no' then. 

It really shows.

And now that your cowardice is laid bare, by all means, regale us with your pontifications!

@2reds2whites You ran away again? Just like a few months ago? 

 

https://www.avsim.com/forums/topic/601526-msfs-has-the-most-advanced-flight-model/?do=findComment&comment=4547520

"The only times active airflow predictions come into real play are during out-of-envelope excursions, I would hazard a guess that there doesn't exist a simulator which can accurately model the chaos-based physics of such events."

 

Did you know that you happen to be correct here? You know you're referring to CFD, right? There isn't a single sim out there that runs CFD real time to model turbulence. Not even with the first turbulence models developed decades ago. And no, I'm not referring to the class of simulation that is Asobo's CFD. In fact, given the similarity in the animations they use to visualize it (some courts would label as plagarizing), LR has been running CFD for many years, just not marketing it.

The reason I bring this up is because in the absence of extremely expensive flight test data, CFD would be the tool required to bring a 1-D table model up to the same capability as a 3-D blade element model.

For example (and one you have yet to respond to): the lack of roll-yaw coupling in a recent 737 model. In order to replicate this behavior with tables, the model needs to know that when the airframe is yawing at a given AOA, it also needs to apply a roll moment (also a bit of pitch...). As I'm sure you're aware, tables don't know a thing about wing sweep, dihedral, or anything of the sort. All that geometric information is averaged up into the 1-D numbers. This is neither a good nor bad thing. All it means is that an additional table is needed (beyond the lift, drag, moment tables) for that specific correlated motion. The same goes for any other secondary dynamics (e.g. the F4 horiz stab/jetwash behavior).

One either needs significant amounts of test data or has to run a a380-load of CFD simulations with the aircraft in all sorts of positions, configurations, and operating points (more than just 10 or 20) to build these tables. The number of unique tables is going to add up quickly.

So, theoretically, it is possible for a commercially-available table model to be on par with an element model, but it's going to take more resources than any 3rd party dev will have access to (be it data or supercomputers). Also, that's assuming the software in question even has a place for said tables in the momentum conservation equations. Who knows (you apparently?), maybe the Level Ds out there do have those secondary correlation coefficients?

@mSparks

it's not that XP doesn't do sideslips... It's the effect they have in the various moments that can result from such a flight situation. Same applies to stalls and spins. Now all of this is high level maths in modelling, a true can of worms for any thread like this one or for a developer trying to do miracles with XP or MFS or FSX or... flight dynamics...

@blingthinger all of what you say is very true and indeed we should rather be grateful for a simulation platform that does it's best to reproduce aircraft flight charactreristics under an "absolutely normal flight envelope".

For many years I used ( and still have it uninstalled as most of my sims usually stand 🙂 ) ELITE IFT. It's ridiculous graphics and, some could dare saying, even flight dynamics wise compared to "modern" standards, BUT !!! ELITE IFT, a desktop flight simulator built primarilly for IFR trainning, comes with a collection of representative GA aircraft, single and twin props and a turboprop ( in the older versions it also brought an MD-80-like model... ).

What is amazing is how close to the published tables, flight test data and even in some aspects "feel" the aircraft act when used well within the normal flight envelope. Ground physics are almost unexistant, but the moment you get airborn for instance the prop effects are simulated like I have difficulty finding in any model of a C172, A36, Piper Arrow, ... I ever tried for FSX, XP, MFS...

It's all table-lookup-based and yet, it does it's thing remarkably well...

That's all we can ask for. 

Other good examples are Condorsoaring and Aerofly FS, just as Flight Unlimited once was. They have given me a feel of flying their gliders in sideslip, stall, spin situaitions like I can't really experience in either XP or FSX / MFS.... or, even the effect of deploying air brakes / spoilers ( of the various tyopes that can equip a glider ). They also have given me closer to RL flight performance ( Polars ) like I can't really find  in XP or MFS best glider models... Another excellent example is IL-2 Great Battles, and in some aspects ( regarding only the WW2 props ) DCS World too. These Air Combat simulators reproduce some flight characteristics odf their RL counterparts, and give their users a "feel of flight" that is sometimes a lot more plausible than what we can find in our civil flight simulation platforms.

Strangely when you look inside the flight dynamics configuration files of Aerofly FS you find an amazingly "simple" representation of an ( infinite ) wing profile with it's Cl / Cd tables and a rather linear shape within most of the AoA range. It's at the same time puzzling and amazing how after all such a "simple" approach can render much better results than all of the bells and whistles that are present in XP and now too ( although sometimes with a rather ridiculous shape ) in MFS... 

Long goes the time I was running after perfection and how to model it in a sim, or spending countless hours and killing my close vision with reading through threads and aerodynamics documents, or at specific aircraft configuration files of the various platforms... I now simply look at the outcome. Does it please me enough ? Yes ? I'll keep it installed for a little while longer... No ? Ya guess the fate... 

My next step will be XP12... I'll run a few tests the day I get it, including ground physics ( mostly under crosswind situations ) as well as how turbulence types are modelled, and variable winds reported in METAR / TAF affect aircraft... All of these are aspects I find poorly modeled in XP11, with ground physics having evolved positively along the XP11 cycle. Strangely I recall that I did find ground physics under x-wind quite acceptable and representative of RL handling in times of XP9 ( before the torque bug was introduced by Austin because, strangely, only by that time he realized X-Plane should model torque effect from a prop - Huh ? ).

Then I'll test stalls and spins, and sideslips, and wait for a good glider model to become available in order to evaluate it, including dynamic pitch instability that is characteristic of most of nowadays gliders...

Edited July 27, 20223 yr by jcomm

6 hours ago, jcomm said:

@mSparks

it's not that XP doesn't do sideslips... It's the effect they have in the various moments that can result from such a flight situation. Same applies to stalls and spins. Now all of this is high level maths in modelling, a true can of worms for any thread like this one or for a developer trying to do miracles with XP or MFS or FSX or... flight dynamics

OK, but did you try the freeware glider in the link?

because they say

Credits:

• Laminar Research for X-Plane and the original ASK21 model
• Members of the X-Plane Gliders Facebook group for the extensive testing, in particular Chris Evans who's picked up details right from the first development version.
• Lord Auriel who did the original ground-breaking work on the ASK21 flight model which informed everything I did on this version.

Very good aircraft. So close to reality!!!👍

 

 

 

16 minutes ago, mSparks said:

OK, but did you try the freeware glider in the link?

because they say

Credits:

• Laminar Research for X-Plane and the original ASK21 model
• Members of the X-Plane Gliders Facebook group for the extensive testing, in particular Chris Evans who's picked up details right from the first development version.
• Lord Auriel who did the original ground-breaking work on the ASK21 flight model which informed everything I did on this version.

Very good aircraft. So close to reality!!!👍

 

 

 

Yep, tried it too but unfortunatelly no good either 😕

Edited July 27, 20223 yr by jcomm

8 hours ago, jcomm said:

It's all table-lookup-based and yet, it does it's thing remarkably well...

It is also highly focused on a small family of single engine pistons. Looks like there are a couple twins too. The King Air is certainly the most different of the group.

Do any of these sims have the same level of 3rd party development as XP?

I didn't connect the dots earlier, but when you go the CFD route, you are modeling the entire airframe. XP's element model is a step in that direction. Getting a table model to work well across the full range of stall and spin situations would require a lot of tables and correlated forces. Blade element handles much of that natively. 

I really am surprised Austin hasn't been providing a more detailed fuselage model. I've read multiple times that 12 will improve upon this. It's long overdue, especially for the gliders.

 

21 hours ago, jcomm said:

because the rudder tends to align so well with the relative wind that it becomes pegged

Can you elaborate on this a bit? The rudder is too effective? Or do you mean that the rudder is stalling at high AOA (high yaw)?

1 hour ago, blingthinger said:

Do any of these sims have the same level of 3rd party development as XP?

kinda.

The modus operandi for assigning a flight model in FSX was to copy the tables from one of the default planes or helicopters into your new shiney model, and ship it good job, job done, as real as it gets.

Regardless of the flight sim it isnt going to be remotely realistic unless development has input from people with flight hours on the airframe. The key thing XP always brought to the table was a very strong set of tools that made translating

3 hours ago, jcomm said:

Yep, tried it too but unfortunatelly no good either 😕

Into an actual fix somewhat more feasible. Then when those tools were insufficient, Austin would jump on the problem and improve the tools for the next XP release.

Edited July 27, 20223 yr by mSparks

1 hour ago, blingthinger said:

I really am surprised Austin hasn't been providing a more detailed fuselage model. I've read multiple times that 12 will improve upon this. It's long overdue, especially for the gliders.

Apparently it'll remais as a toroid in XP12... at least as far as I interpreted from one of Austin's videos ( can't exactly recal which one, and don't have a link... ).

 

Quote

 

Can you elaborate on this a bit? The rudder is too effective? Or do you mean that the rudder is stalling at high AOA (high yaw)?

I mean it stays "blocked" at full deflection and you really have to use some force to "untie" it from there... Can be tricky in the final stages of a sideslip approach if you get it faster than yoo should and decide to align with the rw axis too low...

Edited July 27, 20223 yr by jcomm

6 hours ago, jcomm said:

Apparently it'll remais as a toroid in XP12... at least as far as I interpreted from one of Austin's videos ( can't exactly recal which one, and don't have a link... ).

I think the fuselage is the most problematic part to accurately simulate in a predictive-type flight model.

One method would be to treat it as two perpendicular flat plates (top view projection + side view projection, a bit like those small indoor RC aircraft) and use empirical formulas to calculate the aerodynamic centroid. I think Roskam uses a method like that in his texts. I don't remember very well, but maybe also Aerofly FS uses that method?

Anyway, even simplified CFD software like AVL (which does more complex calculations than our flight sims) uses simple body-of-revolution shapes (or similar  simplified shapes) for the fuselage.

Edited July 27, 20223 yr by Murmur