One powerless to fly (6)
I believe the answer is:
glider
'one powerless to fly' is the definition.
I can't judge whether this definition defines the answer.
'one powerless to fly' is the wordplay.
'one powerless' becomes 'r' (I am not sure about this - if you are sure you should believe this answer much more).
'to' says to put letters next to each other (I've seen this in other clues).
'fly' becomes 'glide' (gliding is a kind of flying).
'r' put after 'glide' is 'GLIDER'.
Can you help me to learn more?
(Other definitions for glider that I've seen before include "Unpowered aircraft" , "Girdle for silent flier" , "quiet flier" , "Motorless plane" , "Flying machine without engine" .)