The best source I can dig up on google to be able to provide you with a link is this:
Maximum Endurance, Maximum Range, and Optimum Cruise Speeds
Not the best source, but have a look af the lower curve on figure one anyway.
Hi Cosmo, thanks for the link. That link provides good information for straight wing propellor aircraft only.
In 2009 the 'Performance Training Group Flight Operations Engineering Boeing Commercial Airplanes ' updated their document 'Jet Transport Performance Methods' . It is a great document and explains the Boeing ethos behind all of their Performance Engineering. PAge 32-14 has a nice graph and explanation regarding the relationship between Min Thrust Required and MRC. It says this:
We've drawn in a line of MRC. Here you see clearly that the speed for maximum range cruise doesn't occur at the point for minimum thrust required, but rather at a slightly faster speed.
So here is where we stand, feel free to correct me:
Min drag = min thrust Required
MRC = cost Index Zero
MRC/ CI zero > Min Drag/min Thrust Required
Even if your were right, it only makes my case stronger. It would make the margin even bigger. Since Min Drag Speed would be even lower, than cost index 0 speed.
I see what you are saying and I agree that the margin to min drag is greater than you originally suggested. It is the same as I always imagined because every time I level out in the cruise I make a mental note of what Min drag is and don't accept slower speeds. I am fairly confident though that next time you climb up there and have a look at what your min drag speed is it will be within a knot or two from the speed you are cruising at. It is always ten or so knots greater than the lower amber band ( often 15-18kts) so when you have a gap of 8 or 9 knots like you suggested, you are very close to it. Obviously some are more comfortable with that than others. Anyway, apart from MRC= min thrust we roughly agree on the basics , the difference being that I am more conservative regarding deviations into the slow speed regime. Fair enough, I wish you thirty years of safe cruising Cosmo. Thanks for the conversation.