If it's too big, can't you make it smaller? Or does it need to be this big for some reason? Are you using these for a game?
I'd also like to point out that the bottom 2 helicopter directions (up/down) are in an entirely different perspective than the first two. (left/right-facing) Instead of being seen at an angle, like the first two, showing both part of the side and the top; they're being seen completely from a bird's eye view. You'll realize these won't work together well in a game. I'm afraid this means you're going to have to do some redrawing depending on which perspective you actually want.
When you get to lighting & shading, you should think more carefully about where the light is coming from too. The random stripes you have right now are doing nothing to communicate the lighting.
