Here are 2 of 4 sketches I am doing for a proposed future cutaway poster illustration of the WWII North American P-51 Mustang. I decided to go with the Mustang over civilian modern aircraft as I have limited access to reference to produce a cutaway of a modern aircraft.
When sketching things like these I now work digitally using photo reference (whether mine- or in this case the internet) and after drawing perspective lines, some of those lines can easily be erased and when finished with the sketch I will project the image I based it on for the angle and see if all the proportions match. If some don't (which at times does happen), I will erase the wrong lines and match them up. I don't trace (I believe it to be cheap and a cheat), but I do use images in post as corrective tools as such things as a plane need accuracy even in the sketch phase. Hence why I now find digital sketching extremely efficient in concerning technical illustration. The trickiest part besides setting up the accurate perspective is also the fact that the inner workings are rarely in a similar angle to what I'm working with. For instance, the top view I based the inner workings on a cutaway scale model picture that was closer to the bottom sketch. In a day or so I should have the other two sketches up and on Tuesday decide which one to go with.