Rise of Flight is a WWI flight combat sim, and I have to say it still holds up really well in both visuals and modelling.

Indeed, I sorted out Real World wheel landings in a Champ using the SPAD XIII in the sim - it's a good analog to a Champ.

It's "free" in that the sim comes with a standard set of aircraft one can pilot with additional aircraft available to fly for a modest fee.

One will need a beefier computer, and a Hands On Throttle And Stick (HOTAS) as well as rudder pedals are just about required to fly. It's very stick-and-rudder; since the aircraft are light and the power-to-weight ratios aren't super high, flying without either is going to be a huge exercise in frustration.

It's also TrackIR compatable, so one can look around by turning one's head, which is sweet. Being able to not only put one's head on a swivel but look around the cowl by leaning and tilting one's head is as much like real flying as one can get. I took up a Nieuport 11 this morning and laughed at how my computer views and my real life looking in the replica I built match.

One won't get ATC, modern airports, or pavement. But one will get good weather and turbulence modelling, grass strips, and wings with wires over realistic looking terrain.

Oh, and one gets to shoot other planes down, if one wants to.