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probable F-14 fdm issue

Postby Solid » Fri Oct 12, 2018 8:55 am

Hi everybody,

i like to fly the F-14 in flightgear. When I updated the last version of the F-14 via QT-launcher (FGFS 2018.2.2), I observed a strange behaviour in flying the model.

When airborne the aircraft started strongly pitching forward. I had always to work against that, even with speeds above 400 kias. The former versions of the f-14 didn´t show that behaviour, they were stable at higher speeds and had only a gentle pitch down at lower speeds.
At first I checked if the joystick is aligned properly, but no issues where found. I tried the F-15, it showed a good flight behaviour, no issues.
Then I tried to uninstall the actual version, but the uninstall button in the qt-launcher does not work. So I deleted the files of the f-14 in "*\Users\User\AppData\Roaming\flightgear.org\aircraft-data" and "*\Users\User\Documents\FlightGear\Aircraft\org.flightgear.fgaddon\Aircraft" and copied an older version (1.3.1) of the f-14 in folder *\Programs\FlightGear 2018.2.2\data\Aircraft".
The older version did work well, no issues.
I reinstalled the new version of the f-14, the issue returned, same behaviour as mentioned above. So I assume a probable problem in the actual fdm of the f-14. :cry:
Does anybody experience similar problems with the actual version of the f-14?

cheers,
Solid
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Re: probable F-14 fdm issue

Postby Octal450 » Fri Oct 12, 2018 2:59 pm

You may need to trim the aircraft. This behavior is normal. Pitch trim exists specifically to counteract this :)



Kind Regards,
Josh
Skillset: JSBsim Flight Dynamics, Systems, Canvas, Autoflight/Control, Instrumentation, Animations
Aircraft: A320-family, MD-11, MD-80, Contribs in a few others

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Re: probable F-14 fdm issue

Postby Solid » Sat Oct 13, 2018 12:55 pm

Thank you for your quick reply, Josh!

I tried to work against the pitch with trim. It worked on higher trim values at higher speed, but not on the lower speed band. Even the autopilot couldn´t manage to hold the altitude; the aircraft always continued to descent. I wouldn´t have post this as an issue, if the behaviour of the actual model isn´t that much different as that of the previous one. I´m not convinced that the issue discribed is desired by the developer.

Kind regards,
Achim
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Re: probable F-14 fdm issue  

Postby Richard » Sun Oct 14, 2018 8:10 pm

Solid wrote in Fri Oct 12, 2018 8:55 am:Hi everybody,

i like to fly the F-14 in flightgear. When I updated the last version of the F-14 via QT-launcher (FGFS 2018.2.2), I observed a strange behaviour in flying the model.

When airborne the aircraft started strongly pitching forward. I had always to work against that, even with speeds above 400 kias. The former versions of the f-14 didn´t show that behaviour, they were stable at higher speeds and had only a gentle pitch down at lower speeds.


Firstly thanks for flying this model.

Secondly, yes there was a fault that I'd recently introduced in the aerodynamic model that was fixed yesterday (2018-10-13) in FGAddon (so update from the launcher).

The problem was a badly defined table for pitch moment due to flaps, which in effect because of the bad definition was applying pitching moment for flap deployment even when the flaps were not deployed.
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Re: probable F-14 fdm issue

Postby Solid » Mon Oct 15, 2018 10:13 am

@Richard:

Thanks a lot for your fast response and your immediate work on the aerodynamic model. I made a testflight ( ;-) ) today in the early morning and the issue seems to be solved .
Furthermore I´d like to thank you very much for giving the flightgear community such formidable aircraft to fly with. I love flying the F-14 (did I mention that earlier?) :-D ...

Kind Regards,
Achim
Solid
 
Posts: 38
Joined: Tue Nov 25, 2014 9:25 pm
Location: Niedersachsen, Germany
Callsign: Solid
Version: 2018.2.2
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