simple spreadsheet to illustrate breguet
Very quick, very basic spreadsheet based on Breguet's Law and ISA conditions. All other factors such as temp, wind, nav fees etc ignored for the present (what present?). So if you want range...
A large aircraft loosely based on a B747-400 has ISA performance as shown at 300 tonnes weight and Mach 0.85 .
All else being equal fly where (V/c)*(L/D) has the greatest value, i.e. the most nautical miles per unit of fuel.
CL = lift coefft
CD = drag coefft = Cdo + Cdi + Cdcc
= 0.0145 + (((CL)^2)/20.73) + (0.0007+0.005*((CL)^2))
V = speed ktas
c = specific fuel consumption lb/lb-hr, kg/kg-hr
FL V c CL Cdtot L/D (V/c)*(L/D)
290 503 0.64 0.342 0.0214 15.981 12563
300 500 0.63 0.361 0.0222 16.261 12929
310 498 0.62 0.377 0.0228 16.535 13303
320 496 0.61 0.394 0.0235 16.766 13649
330 494 0.60 0.413 0.0243 16.996 14005
340 492 0.59 0.433 0.0251 17.251 14391
350 490 0.60 0.455 0.0262 17.366 14182
360 487 0.61 0.479 0.0274 17.482 13977
370 487 0.62 0.501 0.0286 17.517 13773
380 487 0.63 0.524 0.0298 17.584 13607
390 487 0.64 0.550 0.0313 17.572 13385
Best of luck
the "E"