I'm trying to do Rhys-David's machine on the day of the same fight. The photo above clarifies one question and that is the location of the roundel's on the top wing, ie close in and not out at the edges. I note however the wheel covers are not quartered to show which flight. I have read there's debate wrt the bottom wing where some say general RFC practice was to have the roundel only on the bottom port wing and not on the starboard. Can anyone confirm or deny? Finally, was there a letter on the lower wing? If so, where was it located? The only reference I have is the Wingnut Wings SE5a where option E is the only one showing a colour scheme with a letter and it's on the starboard lower wing near the fuselage which means the roundel needs to be further out. I've seen some models where the letter is outside of the roundel. Option E also has the letter on the top wing but on the port side not the starboard side as per the photo above.
Is this another case of "do whatever takes your fancy as no one really knows?"
Thanks / Ian
The answer to your question is threefold at best.
1. The Manufacturer of the particular SE5a. RAF built
:Roundels were inboard and un-outlined on the early ones, such as McCuddens. ( There are more photos than the one in this post of 4863 and Many others that are RAF built)
2.Other manufacturers on early models usually had the Roundels inboard but outlined. APF Rhys Davids Voss fight B525 falls into this category.As always there are exceptions!
3. As for squadron markings and Flight markings they Varied by squadron, and occasionally within one squadron. 56 squadron used some unique marking practices so best to get one of Alex Revell's titles on the squadron.
I am attaching photos and links to the build of My WNW Rhys Davids Voss fight Bird. I used Pheon Decals and "Chose" to use the Dumbbell markings. Sadly No photos are known to exist of B525 on Sept. 23rd, 1917. There is at least one re-marked for another later flight and pilot in 56.
IHTH:
RAGIII

A link to the build Log:
http://forum.ww1aircraftmodels.com/index.php?topic=7627.0RAGIIIPS: Also Windsock Data Files on the SE5 and SE5a!