The Ford 4AT Trimotor is free to download from the in-game Marketplace until this Friday. For those not familiar with it, it's was one of the early, passenger aircraft that stopped being produced in 1933. Consequently it lacks a lot of the things we'd consider on post-WWII civil aircarft, like flaps and propeller pitch control. To me it sort of feels at home with RTMM, as Microsoft has included a float and ski variant for it. I mean if you only do flight between those USFS cabins and don't encounter modern aircraft or boats enroute, you wouldn't know you weren't flying in the between-wars-era.
A few words of caution about it; its engine sounds are very poor, sounding in cockpit more like 3 sewing machines running than 3 engines. With the caveat that I haven't flown a lot of vintage aircraft in MSFS, the flight modelling doesn't feel that accurate with it being far more floaty on takeoff than it should be. I've been recently getting a lot of stick time in Big Radial's Gruman JRF-6B Goose and Noorduyn Norseman and the fidelity of realism for those is night & day in comparison to the Trimotor.
I've also yet to successfully start the 3 engines from a cold start. It involves an odd process in which there's a 3 setting (1 for each engine) fuel pump that must be pumped enough times and then locked. And each engine has a starter on the floor that you must press down, then flip a solinoid followed by turning the magneto to the both position. It could be that I'm just not activating them fast enough, because I fly with TrackIR and flipping switches or turning selectors quickly in sequence on different parts of the dash can be problematic. I haven't bothered to map a TrackIR pause key to an extra mouse button (haven't felt the need to yet), so maybe after doing that I'll be succesfful. Still, I've read posts on the Internet of others having problems with cold start, with some reporting that the engines sometime don't even start on a [CTRL]+[E].
But hey, it's free!
I've attached a few screenshots I took while flying at Misty's Place....