Training handbooks
The RAF's training bible used to be the Instructors' Handbooks of -
(1) Elementary Flying Training, AP 1732a, (Tiger Moth, originally) and
(2) Advanced Flying Training, AP 1732b, (Harvard/Oxford)
Wonderful aids. They covered every aspect of flying training, in great detail.
Excellent chapters on everything to do with formation flying.
Don't know where you'd find them now, but worth looking for.
Happy Landings
WS