So how much do interior aerodynamics play in performance and top speed on a jet? For instance in an open install, there's bulkheads, formers, and install components that create interior drag.. I'm sure a lot of the air gets buffered and routed as pressures build up in various areas, but its drag nonetheless .. (on a SM Gripen i used to have, adding ducting through the intake alone made quite a world of a difference vs the completely open install )

but how about an fully bypassed/ducted install ?? for example if there are ducts (naca ducts , vents etc .. ) does it make sense to clean up the area where the air gets blown in ( such as cooling inlets in the read that have formers only few inched behind .. )? how much interior drag will things like formers create ? is this at all substantial ? I'm debating if i should bother with foam or balsa interior fairings around formers to clean airflow a bit .. or would the difference be negligible ?

~V~