Hey! Nice one, Chris! Happy to see that you are still working away! :)
Some thoughts for your consideration, Sir:
1) I see you developing a habit of overcrowding the space. Very often it looks as though you squeezed things in with a shoehorn, hee, hee!

2) A couple of exercises which may help with that are to limit yourself to one aircraft for a few shots, with no other vehicles in the shot. Another is to look at this site and other sites and collect the images which you most like by various authors. Then, look at how they used space in their images. Ask yourself, "What do I like so much about this image? What is different in these images from my images?"
You'll notice that I have yet to mention anything about jaggies, highlights, shadows, etc.; all of the things which those new to editing tend to concentrate upon FIRST! Why is that? It's because an image is a whole rather than a collection of parts. You can do all sorts of technical manipulations using the editor BUT if the composition, the balance, the use of space is off then the entire image will be off regardless of any editing magic! 8-)
Here's a little trick! When you are working on an image, stop once in a while and view it from some distance away. Why? Well, because when making an image we are often very focused on details. Viewing it from a distance makes the details "disappear" and what we see instead is the overall balance, composition and use of space! In other words, we see "the BIG picture"! ;)
Keep on keeping on, Chris!
Tallyho!
Don