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ASK21 glider flight realism

Postby tmignien » Mon Aug 26, 2019 2:52 pm

Hey all,

I'm using FG since several years as a user and not a developer, and mostly played with several aircraft to learn IFR without being a real life pilot.
A couple of years later, I'm now a real life glider pilot, and I'm now using FG to simulate some cross country flights, with XCSoar running on a smartphone attached to FG over a NMEA/UDP connection; so I'm using a real flight calculator attached to the flight simulator, and I encounter some abnormal behaviors with the ASK21 glider. I also fly time to times a real ASK21 in my local club.

    - Air-brakes performance seems to be very low in for this model : in landing conditions (ie between 88 and 100km/h IAS, 1.3xVso, depending on load) with full opened air-brakes, the descent rate stays very low (-2 or -3 m/s instead of at least -4m/s). I don't have any reference value in a flight manual, but according to Sailplane Rule Book from EASA :
    It must be shown that the sailplane has a glide slope not flatter than one in seven at a speed of 1.3 VSo
    with air brakes extended at maximum weight.

    Taking 90km/h as approach IAS, this means at least -3.6m/s must be observed to be compliant with EASA regulation. The current ASK21 model in Flightgear is almost impossible to land correctly using the regular traffic pattern used for gliders, without any additional maneuvers (increase IAS while full air-brakes in order to temporary increase the descent rate, and catch up the nominal glide slope).
    - descent rate mostly stays between 0 and -1m/s on transitions even at IAS > 120km/h which is not compliant with the official polar from the flight manual. The XCsoar attached computer gives crazy values for glide ratio during transitions in still air, like 50 or 60 [metric]. According to the polar from the flight manual, this could not exceed about 40 with a small load).

I would be happy to help in tuning this aircraft model properly into a more realist simulation, but I don't really know where to start.. any help from the community would be welcome :)

Thanks,

Thomas.
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Re: ASK21 glider flight realism  

Postby D-ECHO » Mon Aug 26, 2019 3:48 pm

Good day Thomas,
along with Viktor Radnai and Gilberto Agonstiho, I am one of the main developers of the updated ASK21. As most of us are real pilots too, we are working hard to get performance numbers right and therefor always welcome feedback a lot.
Assuming you are using the version from FGAddon (as installed through the launcher), I just noticed that the JSBSim FDM version is not yet there and currently only available in our development repository. If you like, I'd invite you to try out this version (https://github.com/viktorradnai/flightgear-ask21 remember to rename folder to "ASK21") and report back how you experience this one.
Thank you for your feedback
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Re: ASK21 glider flight realism

Postby tmignien » Mon Aug 26, 2019 5:46 pm

Hi D-ECHO,

thanks a lot for this quick answer ! I've just tried a small flight with your latest version, it is really far better ! That really changes everything...
Just a side note, that should be fixed before pushing this version upstream : I had to manually create 3 properties in order to be able to run FG with this model :
--prop:/systems/groundhandling/rudder=true
--prop:/systems/groundhandling/throttle=true
--prop:/systems/groundhandling/wingholder=true

I'm not sure about the real meaning of each of these properties, but noticed the ground handling of the glider at the winch launch start, which is good.

And thanks for the FLARM :) Is it really functional in a multiplayer setup ?

Feel free to ask me to test new revisions of this model in the future, I would be happy to do it.

Regards, T.
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Re: ASK21 glider flight realism

Postby D-ECHO » Mon Aug 26, 2019 6:17 pm

I also noticed the problems with the uninitialized properties on startup, it is fixed now with the latest commit. They are for moving the glider around on the ground (pushing/pulling/turn/holding the wing). Winch launch will automatically trigger the wingholder.

The FLARM is unfortunately currently only functional when using the MP Pilot List as it relies on properties created by it, still have to figure out a better way to do this.

Regards
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Re: ASK21 glider flight realism

Postby unrealaviation » Wed Aug 28, 2019 1:07 pm

Finally, a glider that actually performs properly.
Very nice work.
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Re: ASK21 glider flight realism

Postby unrealaviation » Thu Aug 29, 2019 7:40 pm

Ah, only the pure glider version works properly. The powered version won't move if it is on grass and barely moves if it is on a smooth runway.
50 HP should be more than enough, I'd have thought.
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Re: ASK21 glider flight realism

Postby D-ECHO » Thu Aug 29, 2019 8:26 pm

I admit that I still don't have figured out the correct coefficients for the propeller yet so acceleration is not correct, nevertheless, on a bigger runway, at least asphalt you can take off and climb with a quite decent climb rate of ~2.5m/s (single pilot). I will try to improve this though.
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Re: ASK21 glider flight realism

Postby unrealaviation » Thu Aug 29, 2019 10:39 pm

Thanks, I look forward to it and the pure glider version is an absolute delight.
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