The Ultimate Challenge: The 3x + 1 problem J C Lagarias (ed). Mathematicians don’t do examples.
Springer Lecture Notes in Mathematics 1681: The Dynamical System Generated by the 3n + 1 Function G Wirsching. Occasionally I could follow the reasoning.
Historic Commercial Aircraft Series, Vol 2: Boeing 707 R Mak. Planespotter pictures in random order.
Airlines series, volume 1: Garuda Indonesia J Mols. It’s always the poor people who are paying for everything.
The de Havilland DH.60 Moth S McKay. The women’s plane in its glory.
Handbook on Rigid Class 23 Airships Admiralty Airship Department. An industry fumbles with high-tech.
Places I keep track of
IPMS Stockholm One of the best plastic modelling forums you'll find.