RE: Need help with CAD..PLEASE
Another thing I just thought of: When scaling my designs, I usually look up the actual wingspan of an airplane. Then I multiply that by the decimal fraction of the scale I want my design to be. For example, a P-51 mustang has a wingspan of 37' ( I looked this up on google in case it's wrong). Multiply by 12 to get this in inches ( 37' x 12" = 444"). Now if I want a quarter scale design I would multiply 444" * .25 which = 111". So you if did what I said above your parallel lines would be 111" apart. This would give you an exact quarter scale P51 Mustang. Of course many scale designs aren't quite so precise. I've seen planes like this called quarter scale with a wingspan of 102" which is actually 23%, but close enough.
Another way I scale some of my planes is cheating actually. I have drawings of engines and I visually scale the plane to fit the engine. It's a little tricky though and I don't do it often.