WordPress gallery objects.
First things first - WordPress is a wonderful blog & website authoring tool, no doubt about that in my mind. The problem is that the built in gallery object can be a real pain in the ass to use at times.
Through a long drawn out process of trial and error I now have my Aviation gallery working how I want it. Many hours were spent trying to get the images to display at the desired size.
I now understand that gallery objects retain their settings for image sizes (small/medium/large) as defined in Dashboard>>Settings>>Media at the time the gallery was created, even if you subsequently change those settings. This means that you need to be sure those settings are right for your theme before you start adding galleries!
I now have a few galleries to delete and add again to pick up the new, correct settings. Oh well, you live & learn I suppose!