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YASim users wanted

Good sims require good FDMs (the "thing" that makes an aircraft behave like an aircraft).

Re: YASim users wanted

Postby Thorsten » Sat Dec 23, 2017 7:51 pm

Well, in Yasim, EGT starts at 20F or something stupid like that with idle engines, it's very unrealistic. JSBs isn't much better,


I suspect it's unreasonable to expect instrument readings etc. from the generic systems to come out okay. If you have a notion of what this should read for your particular engine/use case, it's easy to make an <fcs_function> in JSBSim or an equivalent property rule that produces your reading.

So yes, JSBSim is much better because it natively comes with the tools to simulate whatever system you need to a near arbitrary amount of detail - including engines and flight dynamics. No one is forcing you to use the generic stuff.

Focus on FDM-type things which you can't address otherwise, not on things which are best fine-tuned aircraft-side.
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Re: YASim users wanted

Postby Octal450 » Sat Dec 23, 2017 10:19 pm

Hi, @Thorsten
That isn't what I meant, I meant the default JSBsim one, where it just moves with throttle -- stupid.
I currently use a very simple table, which is unrealistic, working on a more complex one, going to move my FADECs to JSBsim, when I do that, I'll be developing that function.

But in Ya, you can't do things like fcs-function, so would be nice if the default EGT could be a little less stupid.

Kind Regards,
Josh
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Re: YASim users wanted

Postby Thorsten » Sun Dec 24, 2017 1:09 pm

But in Ya, you can't do things like fcs-function


Yes, you can - it's called 'property rules' and supplied by FG rather than YaSim. You can't affect aerodynamics with it like in JSBSim, but you can affect animations, instrument readings and such like.
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Re: YASim users wanted

Postby Octal450 » Sun Dec 24, 2017 3:47 pm

Yes, I know that. But there is no equivalent in Ya, and property rules can't accept as complex as an FCS function could be, (especially tables) IIRC.
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Re: YASim users wanted

Postby vslash » Sun Dec 24, 2017 11:38 pm

Hi jsb,

I think it's a big and probably difficult task, required skills in aerodynamics and physics. If you feel to start a new Yasim or simply gives some improvment, it would be great.
1) Easy thing: reformat the output of the Inertia tensor please (from the yasim tool) ! (mixup btw comments and the matrix, uneasy to read and copy/paste).
2) Simple things : a new Excel sheet showing graph like those coming from airfoilstools.com.
3) Middle things: more io from/to the property tree. I don't know how many times I started and restarted fgfs again and again for a single parm. Don't know if it could be done but it would be great.
4) Hard things : perhaps thinking about how to compute the mass distr. from a given set of inertia tensors [IT] (Yasim know how to compute 'IT' from your mass distribution - ie ballast + some other parms - not the reciprocal). Some flightsim computes like that, and it could be interesting to get it, because we have sometimes aircraft data on moments and inertia, never on ballasts or mass distribution (!)... Don't know if this is feasible at all.
5) Top level: Yasim/Chopper flavor is not good at all with twisted blades and non symetric airfoil. Behaviors are very weird. It could lead to a negative torque. Don't know how.

Thank you, if you need help, pleasure will be mine to help you if i can,
B.R.
Val.
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Re: YASim users wanted

Postby jsb » Mon Dec 25, 2017 1:12 am

Val, please try the nightly, AFAIK my latest work is included now so the CLI tool should be improved. Also more output to the tree, see /fdm/yasim/ not everything there is well organised by now, some things are dumped there because I wanted to see/understand what is going on in Yasim.
Regarding IT: I believe that would be guess work. IIRC the IT "aggregates" all mass points similar to the CG. But do we need this at all?
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Re: YASim users wanted

Postby D-ECHO » Mon Dec 25, 2017 7:05 am

Specifying the idea about an electric propeller engine:
-> New engine block <electric-engine>
-> parameters: power (kW/hP)
efficiency/something like "power specific electricity consumption"
-> takes electricity from a predefined engine-battery element according to "power specific electricity consumption"*current_power
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Re: YASim users wanted

Postby vslash » Mon Dec 25, 2017 7:38 am

@jsb: thanks, will take a look. I saw this year - since 2017.? - some pty in the tree showing the Yasim CG ; didn't know it was you, so a single word: really great ! Many thanks for this, I was looking for this since a long time.
- On 'IT': don't understand what the "this" means when you said: do we need _this_ at all ? FYI, the 1st things I made for my chopper was the intertia tensors and the CoG. w/o this, you cannot do anything reliable and stable. Don't remember how many times I fight with this, but this is the keystone for anything else.
- Whenever you change somthg in Yasim, plz consider to update the YASIM_VERSION (from <airplane> tag) as well (I use it myself), so we could use the previous version if somthg goes wrong. Thanks.
- Last thing: if you add some features like electrical or engine management, plz consider some models will not use them (keeping their pty-rules and/or nasal system).

Still here if you need anything that could help you,
Thank you for your work.
Val.
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Re: YASim users wanted

Postby Thorsten » Mon Dec 25, 2017 8:40 am

But there is no equivalent in Ya, and property rules can't accept as complex as an FCS function could be, (especially tables) IIRC.


Using the <expression> syntax tables work just fine in property rules - in fact the xml you have to write is near equivalent for many math problems (for tables it's a bit different, but that's just syntax).

perhaps thinking about how to compute the mass distr. from a given set of inertia tensors [IT]


Not mathematically well-defined because it's not a unique problem (there's an infinity of functions which gives the same value of the integral over a certain range, which is why a function uniquely defines an integral over it but the integral does not define the function)

So on the grounds that it can't be done I doubt other flightsims do it...
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Re: YASim users wanted

Postby vslash » Mon Dec 25, 2017 9:01 am

@Thorsten: thank for this nice clarification (I saw - don't remember where - some 'it' defined in MSFS or DCS conf files, but now we know it was for other use).
+2
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Re: YASim users wanted

Postby jsb » Mon Dec 25, 2017 12:56 pm

vslash wrote in Mon Dec 25, 2017 7:38 am:- On 'IT': don't understand what the "this" means when you said: do we need _this_ at all ?


Sorry, I meant why do you need all the mass points if you already have the IT + CG?

- Whenever you change somthg in Yasim, plz consider to update the YASIM_VERSION (from <airplane> tag) as well (I use it myself), so we could use the previous version if somthg goes wrong. Thanks.

I do, and I hopefully already documented this in the wiki :)
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Re: YASim users wanted

Postby vslash » Mon Dec 25, 2017 10:02 pm

- Inertia Tensor : never mind, Thorsten give me some clue on this (see above)
- yasim_version: so, going to read the wiki ! thanks.
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Re: YASim users wanted

Postby jsb » Wed Jan 24, 2018 10:45 pm

Good news: I implemented variable tail incidence (http://wiki.flightgear.org/YASim#Variab ... vator_trim) and I hope it will be merged into the official code within the next days so you can test it with the nightly.
This will allow to implement a different way of trim for airliners while maintaining full elevator authority. This was sometimes critical on approach with the current implementation where trim eat up the available elevator authority.
However, it may take some to see how this works out and there may be the need to modify things later on after we have some experience.
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Re: YASim users wanted

Postby DFaber » Wed Feb 07, 2018 7:55 pm

Hi jsb,

I've been playing with your additions to the Yasim CLI recently. It is really fantastic! The MAC calculation saves weeks of juggling the CG around. This will be seen in some of my Aircraft soon.

Big Thanks!
Detlef Faber
FlightGear Development:
http://flightgear-de.net

my 3D-Art:
https://www.sol2500.net
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Re: YASim users wanted

Postby jsb » Wed Feb 07, 2018 11:30 pm

Thanks :) Good to see that it helps others. I am still working on the CLI tool to improve it. I plan to slightly change the table output format to tab seperated as it appears to be easier to process by other tools.
If you have ideas what features the CLI tool should have, just let me know. Changing one or two variables in a loop and print tables is quite easy to implement unless you have special constraints.
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