Best Range
Deefer Dog,
Despite the theory above all being sound the technique for each aircraft will vary slightly in practice.
Based on many years of experience and in flight trials you will need to record some figures for your own aircraft in flight and come up with a plan. As a guide I have used the following as starting point:
Best range in a jet is often achieved at about 1000' above the max height for weight shown in the AFM. But be careful as you are into the 1.3G margin to the buffet in 3 directions. This point will give you approx 30 AOB to the buffet in a turn.
For head or tail winds I use one third of the wind value, I would expect the 40% mentioned above is equally valid.
To decide whether to to go up or down to loose a headwind component I use a required gain of 7 to 9 kts in G/S for every 1000'. i.e. In a strong headwind if you gain 9kts of G/S by descenting 1000' you will probably be in profit.
But what you need to do is use your FMS to display the specific range i.e. the number of miles you are achieving per unit of fuel. When this is at the greatest then you will be at the best range speed. This speed will decrease with weight. The technique to work this out is to set the parameters on a long leg where wind and temp are constant then set a power for a speed and let it become stable, record the figures and then set a different speed and record the figures. Over the period of a few flights you will get a feel for your aircraft.
If you wish to discuss then please feel free to PM me.
Regards
MM