We use a lot of different scenarios, some based on actual reports from the war.
Some historical ones are really cool, I have a book called "under the guns of the Red Baron" that are very helpful to re-create Richtoffens battles and give the genaral idea how the battles were fought.
And of course we sometimes improvise, like when you are 5 players, then a mission were the side that only have 2 will win if they shoot down a 2 seater while the 2 escorting planes will try to stop them. If the 2 seater goes downthe opposing side wins even if they lose both planes.
Just don't play the same thing every time, it gets boring.
We also play Canvas eagles and there each side rolls a dice in secret on a table for the missions, I think Wow should give out a box with only missions (and possible campaign rules.
I prefer playing one or 2 games a month from feb 1916 to the armistice and giving the sides new planes when they come out, preferably they will have to keep using old ones if they loose more than a certain number of planes each month.
Say that you are eight players, 4 brits and 4 germans. In August 1916 the brits gets the Nieuport 17, say 2 first and then 2 every month. The most experienced pilots gets to choose which plane he flies first, leaving the 2 older planes to the 20 minuters that lost their pilots last month. If one of the planes gets shot down the brits will have 3 next month and someone will have to fly a Sopwith 1 1/2 Strutter or DH2 still.
This will make every game count (of course we keep scores to, we need to know who is winning the war long term) and it will stop people from getting suicidal because it costs to loose a new cool plane.
This together with rules for experience to pilots and randomly drawn scenarios makes for a long and fun campaign. And some scenarios shouldn't demand a single plane to go down even if it is likely that it will happen.
Good luck anyways