-the planes shape is not a simple triangle. Have a look at the upper right sample, as it reveals the correct silhouette.
-The cockpit and engine shapes are totally wrong. Try to be more precise and don't be afraid to use a few extra polygons to make sure they look rounded (without exaggerating of course).
-a wing cross-section should ALWAYS have 2 height segments, instead of one. This allows the middle vertices to be moved forward, so you get a more realistic, wedged shape. You can collapse the rear end vertices so that you only get 1 vertices instead of 3 there.
-The tail sections are not perpendicular! Same thing applies as for the wings
Here is a sample I did not so long ago. Observe how I used the skin to increase the rounded effect..The model has 476 polygons, but has not been optimized yet..