FIRST EDITION April 1967
SECOND EDITION May 1968
Reprint Jan 1969, April 1970
THIRD EDITION Dec 1971
Reprinted April 1973, Dec 1975, Dec 1977, Nov 1979 (that's my copy - maybe later ones exist).
The third edition added the detailed discussion on the Very Big aircraft (aka 747).
Thanks everyone for letting us know where one can buy it new. Some of the second hand (often North American) booksellers have an inflated idea of the value of their books on ALL topic - or maybe they are just charging what their local market will pay.