antony1, I'll play along!

A quick note, this is not necessarily how I voted.  My voting exhibited some bias toward myself and a friend.

To your challenge; I find the word "Pin-up" in the contest title compelling.  To me, pin-up style has to include one of several design ques.  1. simple background and a straight-forward presentation of beauty and/or sensuality.  2. caught in an awkward or compromised situation by unfortunate timing.  3. having a ridiculous amount of fun in some way.  Classic pin-ups always seem to include at least one of these. If I can't see the face, if the background overwhelms the model, or if it wouldn't present well on the side of a bomber, to me it's not top-shelf.  Based on this, I have to throw out 4 of my own entries.

Others may find their own design ques to define pin-up.  With my feelings close to heart and free of the above admitted personal bias, I would offer the following 3 (in no particular order):

#239 Kitty Kitty Bang Bang by marcopol - while it's a little busy for the side of a bomber, it is simple, straight-forward, and she is clearly having a lot of fun shooting it out with her cat from the back of a very silly warhorse indeed!  What a fun pin-up!

#517 Heat by PhithaloBlue - simple background, straight-forward presentation of sensuality, caught at a disadvantage (not that she seems the least bit concerned), presents well on the side of a bomber, ticks all the boxes and some of them more than once!  Well done!

#689 Robyn on Her Harley by WolaverJS (me) - simple background, straight-forward presentation of beauty, caught at a disadvantage (though she doesn't look worried).  Yes, the shadow would have to lighten up to present well on the side of a bomber.

There were a lot of others that I could easily praise here but I agree that three is a good number to ask for.  Thank you for raising this challenge, antony1!