Re: The endless influx of low-quality, low-realism, quantity-over-quality aircraft into FGAddon

Ultimately, I'm less concerned with restricting FGAddon, and more of the inaccuracy of aircraft rating, which is what causes "poor user experience" but them seeing an aircraft rated too highly, and being disappointed, and blaming the simulator (a valid point). Correcting ratings or making sure aircraft in FGAddon are being rated accurately mostly solves this problem.

I will explain lower in this email in a reply to Federico why based on the existing FDM guidelines, a YASim aircraft cannot score above a "2" - but this is violated by "TONS" of aircraft in FGAddon currently. Spoiler: It is not possible to "tune rate of climb and cruise for POH performance numbers" in YASim - or if it is, I am not aware of "ANY" aircraft that currently achieves this - please point me to one if you know of one.

From the wiki: https://wiki.flightgear.org/Aircraft_rating_system#Flight_Dynamics_Model_(FDM)
Flight Dynamics Model (FDM)

  *   0: None, or using FDM from other aircraft
  *   1: JSBSim Aeromatic or YASim geometric model used without tuning. Flaps modeled.
  *   2: FDM tuned for cruise configuration.
  *   3: FDM tuned for rate of climb and cruise Pilot Operating Handbook (PoH) performance numbers
  *   4: FDM matches PoH in 90% of configurations
  *   5: FDM matches PoH and most known test data.

Lawrence:
> And what if, Josh want to develop the B738 (modern version),
and time later he opt to also develop the old B738, (just for the sack
of the beauty of some non glass-cockpit) ?
Naming them both B738 or B738-Josh also do not solve the problem. Just
saying.

I didn't understand that. The B738 is only glass.

If I wanted to make an aircraft like the B737-300 which had both classic non-glass and partial-glass, I can do that in the same package - see for example the MD-80 which does exactly that. There is an option to equip either analog classic gauges or EFIS. No separate package is needed.

This is not the name collision I spoke of. For example, if Josh (me) and FrankVMD develop the 777, then he already has his as 777-VMD I believe, but then there is the standard FG 777 (of which I am contributing a new flight model and improved systems), which is still named "777". I guess that is ok in that regard, given that it is an update to that existing package. But perhaps going forward, it may be advisable to have the package name include the author or at least the primary author/team in cases where more than one developer is working on it.

> As we can read, it is clearly not possible to look at "quality" using us
all the same criteria.
Even the same person might lookup, for a few flights only, an aircraft
with different criteria...

I don't agree - the star system already in use in FG rates "quality" based on "fidelity". Essentially, the higher the stars, the more accurate/authentic the simulation is (for systems/FDM) or the more graphically advanced (for Model/Cockpit).

There is no need to change this, only to correct the incorrect rating of certain aircraft who are rated much higher than they should be - especially in undermaintained aircraft which might still be evaluating visual rating based on 15 years ago or more quality. But in the systems/FDM department, the scale hasn't shifted considerably in either the commercial sims or here - but until the last 10 years or so, highly detailed systems and such were not really part of FG.

Federico:
>  I'm not sure why people say the FDM isn't good on them, I've loaded several of his aircraft (just random ones) into my FDM editor and they look great.

The shape of the elements per FDM validity is only a marker of accuracy when used with computational fluid dynamics (CFD). YASim code essentially takes the input shape data and uses it to modify some pre-determined aero behavior. There is "NO" analysis/CFD/etc occurring here - as such things "CANNOT" be done at runtime due to limitations in processing power. A single high-fidelity CFD run takes much longer than a single FDM cycle (60Hz).

I have flown a few types of planes in real life, all GA - and am fairly familiar with how larger aircraft types behave due to my own simulation and aerodynamics work. I have never ONCE encountered a YASim FDM that flies like a real plane OR follows POH numbers to any reasonable closeness. I welcome anyone to point me to one and I will try it and report back. Many of Emmanual's planes I tried have major issues such as inability to climb and in some cases, even hold altitude, without losing speed, with full throttle when the flaps are extended to the nearly full or full positions, amongst others, aside from the "standard" YASim problems of inaccurate engine simulations, incorrect stall dynamics, wrong lift/drag curve behavior as alpha varies, etc, making them fly very strangely.

I created a mailing list thread some time ago asking about some of these YASim problems as the problem seems to be with YASim itself, given that it gives practically "ZERO" control over the flight dynamics to the developer, aside from deciding the shape of the geometry, and the effectiveness of flight control surfaces (by setting their lift/drag offsets).

Emmanual has stated, incorrectly, that YASim evaluates the shape and computes aerodynamic qualities based on the shape of the aircraft, and thus he tries to match the geometry in YASim to the actual shape of the plane and assumes, again incorrectly, that the plane flies "properly". I have found in order to reduce some of the YASim "funnies" you actually have to make the geometry somewhat incorrect - because at the end of the day, it's not doing any type of CFD/aerodynamic evaluations, but rather simply applying modifications to pre-determined behavior.

If you doubt this analysis, please take a look at the source files themselves:
https://gitlab.com/flightgear/flightgear/-/tree/next/src/FDM/YASim

Kind Regards,

--
Josh Davidson
________________________________
From: Alan Teeder <[email protected]>
Sent: Friday, May 22, 2026 10:49
To: [email protected] <[email protected]>
Subject: Re: [Flightgear-devel] The endless influx of low-quality, low-realism, quantity-over-quality aircraft into FGAddon


Sorry, but for many users Flightgear  IS a game.

For me Flightgear is a flight simulator, but I consider myself probably in a minority.

Alan

On 22/05/2026 16:36, David Hudach wrote:
Personally, this is inappropriate for this discussion: Nice troll though ;)



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