Hi Jade,
Your Line Drawing looks very good to me,
you can always lighten or darken them as you need to.
What I do when stating a profile now, is to brake it down into it's parts because there is just too much to take in too much going on, you'll only end up missing things out and in the end this will effect upon your profile.
1/ The Line Drawing
2/ The Painting flat 1D image i.e. (Spinner, Fuselage Upper/Lower, Wings)
3/ The Texture (Canvas, Metal, Wood)
4/ The Highlights and Shine.
5/ The Shadows and Shading.
6/ The Ware and Tear (Oil Staines, Paint Ware/Chips, Smoke)
If you work on something like this alternately you should soon see it coming to life, but like Jester said always look at photos of the real thing. Look at one of the above and transfer it onto the real A/C to see how it looks in the flesh.
