Originally Posted by
scifi
So it looks as if 8000ft is the optimum cruise level for those Cessnas….The TAS increases from 101 kts to 107 kts.
Only in still air. Which it rarely is at that altitude. And only under ISA conditions. Which are rare as well.
I would recommend spending some time with SkyDemon, or maybe another flight planning tool that has the same capabilities. In SD you can input performance data for your aircraft at various power settings, and at various altitudes - essentially the table that MarcK included. SD also gets live weather information from the internet, including forecasted wind at any altitude, at any location. Based on that you can ask SD to simulate your flight, at a particular time, at various altitudes and at various power settings. That allows you to pick the best altitude and best power setting for your flight. (And "best" can then refer to lowest fuel burn, or shortest time enroute.) And it will give you terrain/airspace warnings and an idea about clouds/freezing level so you know which altitudes cannot be used for those reasons.
Oh, and if you haven't flown for a while and are going to attempt a high-altitude, max performance flight, read up on the leaning procedures for your aircraft. You'll only get book performance if you follow book procedures.
Having said all that, something else. You mentioned you're going to fly "in convoy". I'm assuming this does not mean "in formation", in which case you would have a whole other set of challenges to deal with. But if "in convoy" means some sort of fly-out where a number of aircraft all fly to the same destination at more or less the same time, my advice would be: Fly your own flight. Plan and execute the flight as if you were going on your own, and just try to coincide your take-off or landing time with the other aircraft in your party. I did a fly-out "in convoy" once in a 120 HP DR400, while the rest of the aircraft all had 160 HP or more. So my cruise speed was easily 10-15 knots slower than the rest. I was trying to keep up with them, trying to cut airspace corners all the time, reducing time-on-ground for lunch and refuelling to the minimum, and it wasn't fun and didn't work anyway. On the way back I flew my own flight independent of the others and it was much more enjoyable.