As I understand it, the guy who found the plane was present at the time the plane was originally lost, watched the owner searching for it until the owner had to leave for whatever reason, then went out and recovered the lost plane.

If I understand those facts correctly, then unless the owner called out that anybody who found it could keep it:
A) The finder was present and watching when the plane went in.
B) The finder knew to whom the plane belonged.
C) The finder apparently had a better line on where the plane went in than the owner did.
D) The finder apparently, if he had any honesty, common decency, or manhood, could have assisted the owner in finding it.
E) The owner was able to identify the plane while in the possesion of the finder.
1)Therefore, in my opinion, the finder is a thief, and has a moral and legal obligation to return the plane.
2) The club officers are wimps who aren't standing up for the best interests of the club. Get new ones the next election.