1-3-1 seems ok for missions that need that last extra percent of performance. But something to be avoided if non needed. It adds more events to manage and fault points.
If increasing the number of engines used in any of the landing phases 1-3-1, 1-3-3, 3-1-3, etc. is beneficial, then what's the reason to use only 3? Why no 5 or 9?
Before they have worked out how to throttle down further, three engines might be the maximum practicable number anyways. Several posts here have estimated TWR for three-engined landings at minimum throttle at around 3.7, any more and you'd ping right back into space if you overstep the tiny margin of error. And only turning on additional engines engines for a second or two during deceleration doesn't seem worth carrying the extra equipment and might not be possible with the needed precision.
apparently, some are saying, the 1-3-1 will be always used, as it simplifies things to always use the same pattern
"An engine takes about 270 kg/sec at full throttle"
Quote from: LouScheffer on 02/18/2018 04:35 am"An engine takes about 270 kg/sec at full throttle"This is where your comparison breaks down. They throttle the engine quite deep when landing. It's certainly not full power! With 3 engines, we can assume even less about the throttle levels are...A quick look suggests minimum throttle levels of at least 70%, and perhaps even down to 40%, but that may only be for the vacuum variant.
When you throttle down an engine you reduce the chamber pressure and the performance of the engine deteriorates sharply. More fuel efficient to use less engines at full trust than throttling down engines.
It's been the standard landing burn, for both RTLS and ASDS landings, for a little while now. Nothing new about it.
Quote from: the_other_Doug on 02/07/2018 04:20 amIt's been the standard landing burn, for both RTLS and ASDS landings, for a little while now. Nothing new about it.On what missions except FH Demo did they use the 3 engines landing burn for RTLS?
Here are 2 screen caps from the SpaceX video during landing. It's a bit hard to see in video because the camera has trouble tracking. But if you watch at 0.25x speed and start at T+07:49, you'll clearly see that there is a very short period of 3-engine burn in the middle there. This also tracks with the fact that the landing burn is short. The length of which differs from single engine landing burns which last ~30 seconds.