The Eagle Flies On Friday

This phrase is often found in old blues songs, and it means that Friday is payday. Obviously, the eagle is the one on currency. But how old is the phrase? Where did it originate?

The first (recorded) song to use it was maybe T-Bone Walker's Call It Stormy Monday of 1947.

'They call it stormy Monday, but Tuesday's just as bad
They call it stormy Monday, but Tuesday's just as bad
Wednesday's worse, and Thursday's also sad

Yes the eagle flies on Friday, and Saturday I go out to play
Eagle flies on Friday, and Saturday I go out to play
Sunday I go to church, then I kneel down and pray

Lord have mercy, Lord have mercy on me
Lord have mercy, my heart's in misery
Crazy about my baby, yes, send her back to me' Blues Lyrics

I was aware of that, but, in my opinion, Walker must have got the phrase from somewhere. Of course, I could be wrong, but I just feel the phrase dates from long before 1947.

It was in common use long before 1947. I remember using it and hearing it from many co-workers, etc, Also in the Army, though not necessarily on Friday. However it wasn't "flying" that the eagle did. It was more like "defecating", to resort to a rarely-used euphemism.