Aircraft rating system
The aircraft rating system is an attempt to help you find the aircraft you're looking for among the hundreds of aircraft available for FlightGear. This is done by providing a quick objective way to rate aircraft. This was discussed in some detail on the -dev mailing list in December 2010.
The rating system gives an aircraft a 0–5 score in four areas - FDM, systems, cockpit and external model. These ratings can then be encoded in the aircraft -set.xml file from where they can be picked up by launchers, web pages etc. The sum of the scores in the four criteria provides an overall 0–20 score, which can be mapped to a textual overall aircraft status.
As of 09/2016, there are 173 unrated aircraft in FGAddon - mainly from very old but interesting aircraft in which the author has long left the FlightGear world. To give each a fair fdm, systems, cockpit, and model rating will require a lot of testing, investigation and time. 
Who rates an aircraft?
It is the responsibility of the aircraft maintainer/developer if there is an active one. The rating system was specifically setup to be easy for the aircraft maintainer/developer to do because it assumes that the person doing the rating is very familiar with both the real-life aircraft specifications and systems and knows how close the model is to those. The procedure is very brief, more so any update.
It is possible for the third party to do the rating but it is a nontrivial undertaking for someone who is not intimately familiar with the real-life aircraft specifications and the FDM that would require a lot of time and effort at least for any aircraft that was at a somewhat advanced state of development. Of course early development phase aircraft would be easier to rate since the criteria for those levels does not require so much aircraft specific knowledge. Most of the unrated aircraft are probably unmaintained and many of them are probably aircraft that will end up with lower ratings if they are rated.
If one plans to add ratings to an aircraft, a good plan is the following:
- Try to locate the maintainer by pinging the devel mailing list and also asking on the forum. If there is a maintainer nicely ask them to rate their aircraft.
- If there is a maintainer but he/she is unable or unwilling to rate the aircraft ask permission to do the work. If you get permission then make the change and ask for it to be merged into the base package.
- If a maintainer can not be located or the aircraft is known to be abandoned do the rating and ask for the change to be merged into the base package.
See below for some considerations on this rating procedure.
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.
- 0: No controllable systems: engine is always on, generic radio,
- 1: Generic engine start/stop (}}s), correct size/number of fuel tanks, generic (untuned) autopilot, working flaps/gear
- 2: Working electrical system, fuel feed cockpit controls, stable autopilot
- 3: Accurate startup procedure, tuned autopilot with cockpit controls matching real aircraft systems, generic failure modelling (Vne, +ve/-ve G, gear limits). No unrealistic systems.
- 4: Primary aircraft-specific systems modelled (aero-tow, radar, GPWS, weapons, external stores). User able to follow normal PoH checklists (e.g. startup, shutdown) in entirety
- 5: Some aircraft-specific failure modes implemented (e.g. flame-out, inverted engine limitations). Some emergency procedures implemented (RAT, emergency gear release), able to follow some emergency PoH checklists in entirety.
Obviously some aircraft (e.g. glider) have fewer systems than other (e.g. and airliner). If your aircraft does not have a given system, ignore it for the purposes of rating. E.g. a glider does not need a stable autopilot for a 2 rating.
Furthermore, for a 3 or above, the aircraft should not implement systems not present in the real aircraft (e.g. flaps if none present IRL). The exception to this is an autopilot accessed through the menu (considered useful for flight testing purposes).
- 0: No cockpit
- 1: 2D panel, no cockpit.
- 2: 2D panel in 3D cockpit, or incomplete 3D panel
- 3: 3D panel and cockpit
- 4: 3D panel and accurately modelled 3D cockpit, plain texturing. Hotspots for majority of controls.
- 5: 3D panel and accurately modelled 3D cockpit with photo-realistic texturing.
- 0: None
- 1: Simple 3D model, no animations
- 2: Accurate 3D model with animated control surfaces (elevator, aileron, rudder, flaps)
- 3: Accurate 3D model with animated control surfaces, gear detailing (retraction, rotation), prop
- 4: Accurate 3D model with animated control surfaces, gear, prop, livery support (if applicable).
- 5: Highly accurate 3D model (down to minor components such as control rods), with animated control surfaces, gear, prop, livery support, tyre smoke, shader effects.
Objectively differentiating between a 4 and a 5 is very difficult. As a guideline, a "5" model is as realistic as possible given the available rendering technology.
| Note The difference between a 3 and a 4 seems to be just the livery support. I propose to add "detailed parts (realistic lights, exhausts, airing)" for a 4
(you are free to remove this NOTE after reviewed this proposition)
Sum the ratings of the 4 criteria, to produce an overall score from 0 to 20.
This maps to overall status as follows:
Encoding the rating
In the -set.xml file
The ratings should be encoded in the -set.xml file for the aircraft, under <sim> as follows.
<status>early production</status> <rating> <FDM type="int">5</FDM> <systems type="int">4</systems> <cockpit type="int">3</cockpit> <model type="int">3</model> </rating>
In aircraft articles on the wiki
Status ratings can be (optionally) included in an aircraft's wiki article. Please note that those posted on the wiki are only used by the wiki itself and do not substitue the rating in -set.xml, as described above!
The overall status is auto-calculated and will be displayed. Remove the |status = line if you use the official system and add the following lines, each with a rating on a scale of 0 to 5. See Template:Infobox Aircraft for more info.
... | status-fdm = 5 | status-systems = 4 | status-cockpit = 3 | status-model = 3 ...
You can find the current wiki aircraft pages within each status level via the aircraft status category page.
Considerations on the rating procedure
Is it right that aircraft are only rated by their respective developers? Many lack a rating, and in many cases the maintainer is absent or just doesn't care. If, as originally, the rating is intended open to everyone, should unrated aircraft be rated by users? It would be reasonable for alpha development versions (they're easy to rate), but could lead to wrong ratings for the more developed ones. Yet this might incentivize their maintainers (hardly a well developed project is not maintained) to fix those, so far, unused ratings. Some insights on this were examined in the forum thread on this topic: see this forum post.
Some topics on the FlightGear forum related to the background behind the aircraft rating system:
- Aircraft Rating System (First post dated Thu May 26, 2011)
- Aircraft model/cockpit rating (see first post) (First post dated Mon Nov 15, 2010)
- Discussing aircraft status's (First post dated Sat Oct 02, 2010)
- Aircraft ranking on wiki (First post dated Sat May 30, 2009)