I'm thinking about tying some large (size 4-6) Royal Coachman flies to use as a dry fly for Largemouth Bass. What do you think? Fly fishing for bass is a new game for me.
While I can't speak for the bass in your neck of the woods, I think that there are more effective (and easier) patterns to tie for bass. I would recommend black leeches tied on size 2 streamer hooks (adding a red bead head seems to make these even more effective) or polar fiber minnows in chartreuse over white or all black also on size 2 stream hooks. These are by far my most productive patterns for bass.
Agree with Jim - - Think big. Leeches work good in sizes up 1/0 or larger. A Boa Yarn fly has produced for me. I don't have as much experience as most of the others on bass but it seems to me tie something that you can move at a fairly rapid pace to attract the bass.
I have caught most of my bass on Ace of Spades, Bucktail Royal Coachmen, PTN, and Wooly Buggers in sizes 8 to 12. As with most fish, water temp has a lot to do with how you fish, in colder water, the bass here prefer to not have to chase their food as much. Some of the larger bass I caught was with the fly just sitting on the bottom with an occasional twitch of the rod tip, about once every 30 seconds or so, once or twice and I normally have one hooked. LMB will gulp down just about anything thrown their way, the bigger the fly the bigger the bass you will attract. I stay away from dry flies as I can not even make a gas bubble float.
Lotech, Like so many types of fishing there are times when it doesn't matter what you toss out. Smallies (or are you fishing for Largemouth?) will take it because they are such a predator fish. Then there are times when you will go through your whole arsenal of flies trying to find what will make them strike. So, it would not hurt to have a few Royal Coachman Streamers in your bass kit and possibly some dries as well (were you thinking dries or streamers?) Larry ---sagefisher---
Getting back to your original question, I think there are times when a large Royal Coachman will take bass fairly well. Watching bass, even small bass, explode onto a dry fly is a lot of fun. I would replace the feather wing with either white calf tail, white bucktail, or white deer body hair. I think the latter will aid floatability the best. I would also replace the red floss with holographic red tinsel. The tail might be best if it were also hair. At this point, it may have been modified to the point that it isn't really a Royal Coachman, but it would certainly be more durable. When I tied them with white quill wings, my Royal Coachmen would be badly mangled after only a fish or three. Hair is much more resilient.