Well, the way I use to map is grab the part that I want to map, for example the fuselage, and isolate it from the other parts by hidding them. Then take a print screen of it in the viewport that is best (in round fuselages like yours you're better off using the left viewport) with the best zoom I can get while the part is still all in screen.
Then paste that print screen in photoshop or whatever and select only the flat grey viewport with the fuselage in it and copy it. Create a 1024^2 px or 2048^2 px to paste the fuselage and remove the flat grey part that outlines the fuselage. then just resize and move it around to fit the texture better.
In gmax you add a UVWmap modifier to the fuselage, make it square and align it to the side view. Then add a UVWunwrap modifier to position the fuselage edges on the texture. Make sure you have the texture material applied to the object. Ah, and the material must be FSX material and to display the texture on the viewport you have to click on the blue cube on the material editor. To display the map in the UVWunwrap editor click on the pick texture rollout and select your texture...
Here's an example of a texture sheet from my S-46 Orca: