PiP = Permission in Progress:
During the authorization process this illustration will appear in Negative, changing to a normal detailed view when permission is obtained.
And this will be the norm throughout this Edition. Due to the characteristics of this work we cannot skip any engine.
About Author rights
Credits: There are illustrations that have a Permission in Progress (PiP) link. Some of them have two or three initials indicating the true origin: (PiP-mw) Mark Wade. The letters 'pm' by Popular Mechanics. The "int" are from Interavia, etc. Many illustrations, for which it was difficult to know its origin, have already been replaced. For the older ones their rights have expired (60/70 years, according to the country)
-PiPs appear "in negative" and/or reduced in size: when we receive their authorization they will pass "to positive" and habitual size. We should not hide the existence of any engine for this.
-Descriptive relationship of the initials:
-(PiP) = Doubtful and unknown origin
-(PiP-mw) = Mark Wade
-(PiP-pm) = Popular Mechanics
-(PiP-ps) = Popular Science
-(PiP-int) = Interavia
-(PiP-ap) = Andreas Parsch
-(PiP-ml) = Manuel Lage
-(PiP-fl ) = Flaps
-(PiP-fk) = Flickr
-(PiP-pi) = Pima
-(PiP-as) = Astronautix, Mark Wade
-(PiP-dh) = Dietrich Haesler
-(PiP-AE) = AEHS
-(PiP-LBC) = Lombardia Beni Culturali
-(PiP-fg) = Flight Global
-(PiP-fm) = F. Munger
-(PiP-ae) = Aero
-(PiP-sky) = Skyways
-(PiP-Saf) = Safran/Snecma/SEP
-(PiP-fmr) = Flyingmachines.ru
-(PiP-er) = Eric sengines
-(PiP-ANC) = Amis Nemorin Causan
-(PiP-BNF) = Biblioteca Nacional de Francia
-(PiP-MAE) = Musee Air et Espace
-(PiP-eu) = Eureka, Daniel Marin
-(PiP-ev) = Evzen Vsetecka (AEHS)
-(PiP-pl) = Piotr Lopalewski (Kracovia)
-When the work is considered to be STABILIZED - or almost - pending permissions are requested: for there may be changes before that. Meanwhile, the photos and illustrations are reproduced in "negative", difficult to interpret but attesting to the engine's existence.
-For the great majority of the illustrations the rights' expiration dates have passed, so they are free. For example PM and PS before 1951 are free, precisely the most interesting time.