A little help from those crazy frenchies...
Maxi Specific Range= V/FF (V=Velocity=TAS)
Specific Comsuption (Csp)=FF/T (T=Thrust)
-->Maxi Range= V/T x Csp
For a given Csp (wich depends on Alt (lowest one at OPT Alt) and on RPM (lowest around 80%N1)) we can figure out the incidence which will give us the Maxi Range:
We all know the basic forces acting on an aircraft in straight and level flight:
W= 1/2xdxV2xSxCL d=air density
-> V= SQRT (2W/d S CL)
We also have for straight and level flight:
T=W/F F is the "Finesse" of the aircraft (in french) or the Lift/Drag Ratio= CL/CD
----> Maxi Range= SQRT (2W/d S CL) x F/W xCsp
=...............................x CL/ WxCD xCsp
= SQRT (2/W d S) x SQRT CL/CD xCsp
So we can see that for a given Weight, air density,wing area,
the incidence of Maxi Range is the one wich gives SQRT CL /CD
Maxi.
In practical as previously mentioned, it is approximately
1,3 Incidence of Finesse Max (Max Lift/Drag).
Sorry for all those computation but all the Graphs come from there...