How about the fuel tank position?

[hesetone]

The aircraft file of B747, from line 178 tot line 222:

        <tank type="FUEL">    <!-- Tank number 0 -->
            <location unit="IN">
                <x> 1327 </x>
                <y> 0 </y>
                <z> -69.57 </z>
            </location>
            <capacity unit="LBS"> 10912.8 </capacity>
            <contents unit="LBS"> 5456.4 </contents>
        </tank>
        <tank type="FUEL">    <!-- Tank number 1 -->
            <location unit="IN">
                <x> 1327 </x>
                <y> 0 </y>
                <z> -69.57 </z>
            </location>
            <capacity unit="LBS"> 10912.8 </capacity>
            <contents unit="LBS"> 5456.4 </contents>
        </tank>
        <tank type="FUEL">    <!-- Tank number 2 -->
            <location unit="IN">
                <x> 1327 </x>
                <y> 0 </y>
                <z> -69.57 </z>
            </location>
            <capacity unit="LBS"> 10912.8 </capacity>
            <contents unit="LBS"> 5456.4 </contents>
        </tank>
        <tank type="FUEL">    <!-- Tank number 3 -->
            <location unit="IN">
                <x> 1327 </x>
                <y> 0 </y>
                <z> -69.57 </z>
            </location>
            <capacity unit="LBS"> 10912.8 </capacity>
            <contents unit="LBS"> 5456.4 </contents>
        </tank>
        <tank type="FUEL">    <!-- Tank number 4 -->
            <location unit="IN">
                <x> 1327 </x>
                <y> 0 </y>
                <z> -69.57 </z>
            </location>
            <capacity unit="LBS"> 10912.8 </capacity>
            <contents unit="LBS"> 5456.4 </contents>
        </tank>

Tank 0 ~ Tank 4 has the same location, why? I need some help to figure it out. uhhhhhhhhhhh......

[dpculp]

Most likely the author wanted to do some test runs without worrying about the CG moving in some complicated fashion due to fuel burn.  One less variable. IIRC this is an older model, so it was probably made before we added things like fuel freeze and tank priorities, which would be a better solution now.

…

-- Dave

On Tue, 2022-11-22 at 19:11 -0800, Hesetone wrote: Tank 0 ~ Tank 4 has the same location, why? I need some help to figure it out. uhhhhhhhhhhh...... — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you are subscribed to this thread.Message ID: <JSBSim-Team/jsbsim/repo- ***@***.***>

[seanmcleod]

Yep, in terms of CG, note the location of the empty weight CG and the location of the fuel tanks.

jsbsim/aircraft/B747/B747.xml

Lines 62 to 67 in 8fb7741

	<emptywt unit="LBS"> 523816 </emptywt>
	<location name="CG" unit="IN">
	<x> 1327 </x>
	<y> 0 </y>
	<z> -24 </z>
	</location>

[hesetone]

Thank you twice! Sean.