Tengah Type.
Although 1952 is commonly accepted as the first edition, ( the first by Green and Pollinger) it was not . A clue is in the Preface opening line ..: This new edition of The Observers Book of Aircraft
Before this and also published by Frederic Warne was an original in 1942 with a revised edition in 1949 by Joseph Lawrence in the common size in which he states "This edition is almost new book........"
Then the November 1952 edition is subsequently adopted as the first edition and all goes logically up to the "Eighth (1960) edition :January 1960.
Then one year later we have the Tenth edition of January 1961. I have not seen a ninth edition. The series then runs on with annual editions up to the last edition I have ,which is the fortieth edition in 1992 dubbed "1992/93" on the cover. Although I never saw any since I gather that a German edition might have continued the line ...