Hi Sparty. I reckon you need more shading. It's looking a bit washed out. I'd shade the engine cowling more to give it more shape and add quite dark shading where the nose dives into the cowling. There is quite change in depth there so it should be shown. Likewise with your main wheel. Your tailwheel has nice depth, but your mainwheel is flat. You also have the tyre highlight running around the lower half of the tyre but none on top. I'd give the top of the tyre a highlight too.
See what you think.
Graeme.