Question about Mustang fuselage marking

[dash1D]

In many of the wartime photos there is a cross painted on the left side of the fuselage just forward of the cockpit near the data block. What is the purpose of this symbol? I read somewhere that it was used on B/C models to indicate if the 85 gallon fuse tank had been installed. Is this correct and was the symbol ever used on D models?

[Robbie Stuart]

Yes to both questions.

[Holedigger]

The cross marks the aircraft's Center of Gravity as it came from the factory...important for some aeronautical reason I hear! The fuel tank status did effect this greatly. Someone with more knowledge of this and how it was used please chime in.

[51fixer]

The cross marks the aircraft's Center of Gravity as it came from the factory...important for some aeronautical reason I hear! The fuel tank status did effect this greatly. Someone with more knowledge of this and how it was used please chime in.

It doesn't mark the CG.
Exact CG can only be determined by computing your load of fuel or weapons.
It also changes as you burn fuel or drop your bombs or fire your weapons.
The aircraft has a range of acceptable CG limits. The rear tank does affect how it handles and was typically burned off soon after takeoff or at least some of it depending on the pilots preference.
1st the TO was done on the L/H wing tank. The carb will return a small amount of fuel back to the L/H wing tank through the vapor vent return. The TO and climb uses enough fuel out of this tank to make space for the returned fuel. Otherwise it will just vent overboard through the L/H wing tank. After the fus tank is used then the drop tanks (if fitted) are usually used. If you have to drop them when you run into fighters any fuel they still contain drops too.
Finally the wing tanks are used and maybe a small amount left in the fus tank. Some pilots preferred to leave a little in it as they liked how it flew that way.

The cross mark was used to show the ground crews that there was a fus tank that was installed.

[John Dupre]

Well this is why I love this site I can learn something. I remember reading somewhere that the cross marks the CG but the explanations here make much more sense. So how did the misinformation start?

[Holedigger]

I would GUESS, being that the extra internally installed tank effects the CG, it was a WARNING to watch you CG on loading. Probably something in an operational Manual somewhere about it. Would be interesting to see what it says.
info like this from BudAnderson's Website feed the confusion
"In recent years there has been considerable speculation about the meaning of the small white cross, seen on the left side of P-51s (and P-38s), just below the windshield. There was nothing mysterious about this symbol, which merely indicated the aircraft’s CG (center of gravity)."

Really?

[mlenoch]

I believe there is a fairly historic field order issued by Hap Arnold about the rear fuselage tank and the cross.
It was part of a directive to enable Mustangs to get to Berlin. Nothing to do with the center of gravity location.

I think that's the gist (approximation) of the story. Hopefully someone has a copy of this directive. It also explains the need for the cross.

VL

[t6flier]

You mean this one?


Mike V

[mlenoch]

"You mean this one?"

YES: TA-DAHHHHHH!!!!!

VL