There were a bunch of these so-called "Udet" drawings that were auctioned off some time ago, possibly by Hermann Historica. You can find them now on Alamy.com. They were touted as original watercolor profiles by
Ernst Udet. Aside from the lousy attempt at the signature, these just don't look at all like Udet's artwork. He did wonderful caricatures of people, and always in just pen and ink, or perhaps pencil. When he drew airplanes, they were caricatures of airplanes. His subjects and style are both very recognizable. These watercolor "profiles" of WWI aircraft, all done in the same format and in a faux "Primitive" form, just weren't his thing. The profiles are all done in the same style, with labels that betray even more faults.
Here is a Pfalz D.XII with incorrect cross styles, etc.
A rather primitive depiction of a Fokker E.V:
And even some "captured Allied aircraft" in 'German' markings. The group also included a few interwar and WWII aircraft.