My Great Uncle, Alexander Wald (pilot) was at 100SQN at the same time as your Grandfather. I have 2 original copies of The Annals of 100SQN and it makes interesting reading.
To put a few faces to names that you may read about in Annals and who worked with your Grandfather, I have attached a photo that my GU took of 3 observers and an admin person by the looks of him who are checking out a bomb crater in the airfield in December 1917. The names of the airmen in the photo are (from L to R) McNaughton, Allen, Hilton (my GU flew with him a bit) and Edwardes.
I have other photos but cannot discern your Grandfather in any of them.
Enjoy the research, it's fascinating when it is so personal.
Aerodrome Dec1917.jpg 83.07K