Clive,
Extra background, the F-12 with chines at M3 had L/D about 6.6 as you figured for the SR-71.
See Fig 6 "F-12 Series Aircraft Aerodynamic and Thermodynamic Design in Retrospect" Ben Rich.
The following is a previous post of mine. Is there any merit in my "schoolboy" plot and conclusions? I know it's just observed FF and not sfc, etc but was I just lucky or have I misinterpreted things? The range charts I got from his book.
Thanks.
ref Col Graham:
"The faster it flew the more efficient it became. For example the range charts show.."
If we plot FF v Mn from the range charts we get a steady increase in FF peaking at M3.0 then a dip to M3.15 and increasing again at M3.2 (for all but one condition).
Isn't this FF trough an indication that the whole aircraft has finally reached its design point. ie it's more efficient at M3.15 than at M3.0 or M3.2?
eg the spike shock doesn't meet the cowl lip until the design speed, the terminal shock is now correctly positioned with minimum intensity, etc.
eg the nacelle drag is a minimum. ref Col graham "Any time the SR-71 was at of above M3.05 the aft bypass was always placed in the CLOSE position."
eg the engine/afterburner/exhaust expansion are all where they should be.