Tails is such a grease monkey...Or grease fox in this case I suppose; always cleaning, tuning, modifying, or repairing that plane of his. I call it his because it might as well be his instead of Sonic's, since the little fox boy is always the one tinkering with it or flying it.
The picture itself is nice and colorful, with good shading and textures. I like how you did the black oil (or grease) on Tails's gloves to show him cleaning the Tornado. And Tails's expression just says that he loves doing this kind of stuff. Just another day for the young fox. ^_^