phrasal
1. : to hurl with force : throw , shoot
warriors let fly their spears — Tom Marvel
let fly two torpedoes — E.L.Beach
2. : to release suddenly (the sheets of a sail) so as to spill wind
3.
a. : to hurl an object (as a projectile)
let fly with a tremendous pass — G.S.Halas
infuriated householders have been known to let fly at them with shotguns — Gerald Priestland
b. : to loose an arrow
4. : to give unrestrained expression to an emotion
let fly with some observations that shook space enthusiasts — Time
she was letting fly on the trombone — Irish Digest