Watching it again right now. If this theatrical carpenter's eyes aren't wrong, it looks like the Albatross they're flying in the beginning are actually fabric-covered mock-ups painted to look like plywood. I will give them points for including the little details like the moving rocker arms on the Mercedes engines and smoke from the exhaust stacks. The details of the aircraft appear to be very accurate, even if the flying is not. They have 100mph biplane scouts flying like 500mph WWII fighters. Very Hollywood.I was sure about the flying scenes being CG, but there is one scene where they're starting up and I was giving special attention to the engines. They're the first things to get replaced with something modern which won't turn with the prop. They looked like real Rhone engines and it was hard to tell if it was CG or props with real Rhone engines. Now a days, surely they wouldn't trust a real (or even a replica) DR-1 with a Rhone engine. Too many ways to kill the pilot with the engine's nasty habits.
If you're curious what a real WWI dogfight might've looked like, allow me to share this: