Tuesday, September 15, 2009

New F-4N update

Nic Quijano, who BTW has started his own FlightGear-related blog, has added selectable armament loads to the F-4N, so you now have a choice between the original air defense load with three drop tanks and a new CAS (Close Air Support) load with six Mk 82 bombs. The original load is invoked by running the original "F-4N-set.xml" model, while the new one is invoked by running "F-4N-CAS-set.xml". This brings the F-4N version number up to 3.1.

Nic also tied the fuel gauge to the total fuel. I'm still torn on what I want to do hangar-wide concerning this. Probably best to convert all the models over, then when the next FlightGear version is released I can switch some of the fuel gauges back to tank[0] if I want.

Thanks for the nice work Nic!


  1. I think that for a/c with external tanks, a single gauge will just never cut it.
    Maybe a total internal gauge and a total external gauge would be the best compromise ?
    Would be nice to see with a glance the externals are empty and can be dropped.

    Can we adjust jsb properties like active engine fuel feeds at runtime ? If that's possible, we could cook up a simple reusable fuel management system, without the complexity of managing fuel lines and crossfeeds : take off on external tanks only (on post on the phantom), empty the cans (and drop them) and switch automatically to internal by toggling the active feeds with property conditionals. It would be the desirable behaviour on a fighter, since most tanks are non-conformant and give meaning to sound barrier, don't they ?
    Then switch to internal. Could even be automated, or tied to user input by the author (or user), depending on their own inclinations.
    And if the pilot keeps the tanks to re-fuel before going long range, the system starts draining fuel again from them once they have fuel sloshing around in them, stopping the internal feed.

  2. In the OV-10 we knew when the external tank was empty three ways: we reached the time at which we expected the tank to be empty, or the pump low-pressure light came on, or the internal fuel level started decreasing. I'm not sure about other 50's/60's era airplanes, but I'm guessing they worked similarly.

    As for runtime tank switching, that topic has a long history at jsbsim-devel. Maybe it's time to revive it again :) The hang up has always been how best to represent the feed map with a single property. An alternative plan IIRC was to give each tank a priority value, so a burn sequence could at least be established at load time. If the make the priority available via property, then an FCS system could control the priority.

    I'll start the thread up again at JSBSim.

  3. I'll bow to your real world experience with USAF(E ?) aircrafts :)

    I'd be fine with a low pressure warning light to switch to internal. Being able to toggle feeds would also prevent "accidental" refuelling of dropped tanks :)

    Pic (site has good imagery for the Phantom cockpit, front and back)

    Seems to indicate only internal, displayed in both thousands (needle) and hundreds (numerical). So, in a further edit, I'll update it to the internal tank, if you haven't already by then. I believe it was just showing empty before, or back when I fixed the empty showing fuel tanks. Might have skipped your updates of the fuel instrument since then, not sure (I do diffs with my local copy when you update)

    Another picture on that site shows a fuel control panel without a single gauge on it, only switches (scroll down for close-ups of instruments)

  4. Just asking, how do I change the stuff loaded on the hardpoints? For instance, if I want to replace the external tank under the belly with a 20mm Vulcan cannon, and add a gunsight to the aircraft, how do I go about doing it? :)

  5. As for the cannon, just remove the tank model from the current F-4N model wrapper XML file and replace it with the cannon model (you can cut/paste from the FGR.2 file to preserve the cannon model's location and orientation). Then you have to make sure you have a trigger binding. Also, if you are replacing a fuel tank, make sure you don't have fuel in it any more.