No, the textbooks aren't outdated but most of the texts used for PPL, ATPL etc are a tad simplistic on some issues. It is true about the different regions, its a balance between the blade section speed and the induced velocity distribution.
I think I know what you're getting at, a glider in descent, put simplistically, relies upon its downward and forward motion. The pilot can alter the angle of descent to maintain this balance. However, in a descending rotor, each section of a blade has a different angle, due to blade twist, rotational velocity and induced velocity. For the descent conditions mentioned, the combination of these variables means the inner portion gives the best 'gliding' results. Afterall, the pilot can only control the blade angle, which is constant along the span. This also means that due to the same variables, some portions are not in at the 'ideal' settings.
If this isn't what you mean, sorry!
As for density altitude, the only difference is that at altitude the air density will be less. In a broad approach, the profile drag is less thus allowing the blades to accelerate compared to the same conditions at a lower height where the density is higher.
Hope it helps.
Steve
Last edited by SEL; 7th Oct 2003 at 07:32.