Length Of Control Line

This is all dependent upon the plane. Cox engines are not as powerful as modern equivalents such as Norvel equipment. Hand launching with longer length lines could result in a unwanted crash. I have to ask why you want to do this? Essentially, there's two reasons for going out longer, one being to slow the speed down and two is to allow more room for maneuvering. If your engine doesn't have any reserve of power left flying on the line length your currently using then your expecting too much from your model.

                     When I was using Tee Dee's for combat, they were starting to become handicapped on 42' lines. TD's originally flew AMA combat on 35' lines, they changed the rules when modern powerplants were introduced to go out to 42' to slow things down. This essentially put a end to using Cox equipment. Not only is it hard to start when hot, they flew poorly on this line length.

                In addition, the line material is also a factor. Steels vs braided Spectra, Dacron, etc. Drag is everything, therefore the style and weight of the plane dictates the length. My flying field is 16' above sea level. I'm making top power compared to those in higher elevations. Some planes need to fly fast and going out on longer lines defeats this. I was flying a twin Mustang  using Black Widows on .008" 52' steel lines ( A major pain in the you know what to take care of). I now have another twin I'm flying on 42' Spectra lines. A Norvel .061 for instance by itself can certainly muster up enough oomph to fly out to 50' on some models. If I was in need of going out longer flying integral tanked Bees, I wouldn't be pushing the envelope too far. I had many line sets that were made up to 37'-9". I don't recall my reasoning for this but I have about a dozen line sets made to this length. Your obviously going to reach a point where drag and power become a issue and this is usually around the 42' mark using Bees.