Silhouette of Convair B-36F. The 1952 edition of the Observer's Book of Aircraft used 34 Crown Copyright silhouettes provided by the Controller of H.M. Stationery.  An acknowledgements section on page 5 of the book identifies them by page.  This image is one of those and since the publication date is pre-1957 is in the public domain.
Crown Copyright
The Observer's Book of Aircraft 1952, William Green and Gerald Pollinger, Fredericke Warne &amp; Co London 1952