I’ve been trying to do this for a while, but things keep getting in the way. Back in September, I noted the one-engine capabilities of the A350. I flew at normal cruise speed around FL240, and I made it all the way to 39 hours. At the time, I thought that was the limit. A month or so later, some people began getting over 50 hours with the A350 so I re-explored my options. I realized that with one engine flight, flying lower is generally better. Running some tests, 10000 feet seemed to be about where the air resistance started to outweigh the lower power setting. At 10000 feet, this one engine trick netted around 60 hours.
Sometime in the process, I realized that flying at less than 1000 feet netted significantly better results than at 10000, even though 1000-9999 burned more fuel. At lower altitudes (sub 100 feet), there was also a significant drop in fuel burn. I figured this was because the plane would begin riding on ground effect and thus be able to use less power. Around 20 MSL was maximum ground effect, allowing the A350 to go for high 70s to low 80s.
However, as I thought about it more, ground effect essentially keeps the plane airborne so the engines can use less thrust to keep it moving forward. Thus, if I can find a plane which keeps its speed better than an A350, it would be able to essentially glide on idle longer. The DC10 came to mind, as I have had more than one close encounter with Level 1 Violations in it because it’s so slippery. Below around 40% fuel, a one-engine idle is enough to keep the plane flying at 20 MSL. This allowed it to do a calculated 93 hours.
From here, the problem was finding a route. At 20 MSL I had to be over water at all times, and if I turned the wingtip would dig. This made the FPL really confusing as I had to physically be at my device at designated times to climb a bit for turning. This didn’t even work because on the smaller corrections following the main turn the wingtips would drag anyways (as I was back to normal altitude). I might’ve stopped there, if not for me realizing at above 60 degrees North and below 60 degrees South, elevation is zero. This gave me way more to work with. I devised an FPL that looped around the South Pole (for the weakest winds), with 36 legs separated by 10 degree turns. These small turns stopped the wingtips from digging because they were just microcorrections.
I ended flying at 30 MSL because at 20, a rogue gust will cause you to dig. I’m sure it shaved off some time, but at least I got it done.