Indeed, the meaning of Flamberge originally derived from personal names for individual swords; became a metaphorical name for a "hero's sword" or "war-sword", thus a longsword or great sword; and even later became poetic name for a "flaming sword" thus a very brightly shining sword. The Grimm Brothers give us this trail of clues that led me to the conclusion
FLAMBERGE, f. der name eines heldenschwerts, wofür aber die altfr. gedichte bald froberge, bald floberge geben (mythol. 196). Aimon B 4b steht schon 'flamberg, mein gutes schwert' und Garg. 117b 'des kaisers Groszkarle oriflambe, des Renalds flamberge und solche flammklingen und wurmstecher', heute gilt es den dichtern überhaupt für ein flammendes schwert:
stoszt mit an,
mann für mann,
wer den flamberg schwingen kann!
KÖRNER 1, 104.
HELDENSCHWERT, n. ensis Martius. STIELER 1958.
Finally, if you get a look at this artwork entitled Flambergen, from the book called Petrarcas printed by Steyner in 1539 Augsburg
http://thearma.org/arttalk/at84.htm
...Then it seems that the Germans of olden times meant "war-sword, longsword; great sword" when they said Flamberge
