Falcon 9 octaweb?

[notsosmart]

Hi everyone, there's something I have always wondered about, and it came to mind as I was reading about tuesday's launch. So here it is: why did SpaceX change the arrangement of the nine Merlin engines of the F9 first stage from a 3x3 grid to the "octaweb"? Wikipedia just says it increases efficiency, but I was wondering how it does it. I'm sorry if this a stupid questions thanks!

[Brotoro]

You would have lower aerodynamic drag with the second arrangement.

[rtxoff]

Also in the first setup if you loose one of the corner engines it has an higher impact on your thrust vector then in the second arrangement.

[AngelLestat]

I guess the exhaust of each nozzle does not interferes so much with their side nozzle, so the exhaust remains more collimated than the older way.. which increase efficiency.

EDIT: this is on spacex page

The Octaweb structure of the nine Merlin engines improves upon the former 3x3 engine arrangement. The Octaweb is a metal structure that supports eight engines surrounding a center engine at the base of the launch vehicle. This structure simplifies the design and assembly of the engine section, streamlining our manufacturing process.

Edited January 4, 2015 by AngelLestat

[notsosmart]

Very interesting. Thanks everyone!

[Nibb31]

It might also be due to optimized plumbing.

[deadshot462]

Also if an engine is out there is less of a thrust imbalance through the center of mass.

[kujuman]

Another factor to consider is the mass of the structure. I'd guess that having 8 engines equally spaced from the load bearing tank wall is lighter than having the eight engines zig-zaged (from the perspective of the tank wall).