Hiya Pyro!
At first I would just like to say that you've done an awesome job on the Brewster's flight model. The lively ailerons, low control forces on higher speeds and all around great maneuverability, they are all there! There's just one aspect of the Brewster flight model that I've been wondering. That is the somewhat marginal (feels almost neutral at times) directional stability of the Brewster's current flight model. The first clue that doesn't nessasarily always point to only marginally positive directional stability of an aircraft is the excessive amount of left rudder needed the keep the aircraft coordinated in turns to both directions. On Brewster's case it seems like this is pretty much a direct symptom of only marginally positive directional stability.
Here's a quote regarding Brewster Model 239's directional stability from a finnish book Lentajan Nakokulma II (Pilot's View Point II) translated by Camo. The book is written by Mr.Jukka Raunio who's an aeronautical engineer (Dipl.Ins.) with a long career in Finnish aviation industry. The book covers origins, development, purchase to Finland, structures, systems and flying/handling qualities of all (non war booty) fighter aircraft of the Finnish Air Force that served during WWII. (Pyro has probabaly heard about the book more than he wants to but I just wanted to introduce it to rest of the readers.
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"Directional stability was positive. When the plane was disturbed from level flight with the rudder, it returned to direct flight after a couple of sharp yaw and roll motions. The feel of the rudder was a bit poor in slow flight, but got better at speeds over 150 km/h. In a dive, at speeds over 500 km/h, the rudder was very sensitive. V-angle stability was especially good, due to the mid wing and 5.5 degree V-angle. Clean banked turns could be made with just the rudder or just the ailerons. In a straight side slip (clean, engine on idle) at 150 km/h the rudder was fully pressed and counter elevator was given, approximately half of the stick limit. The bank angle was approximately 15 degrees. Correspondingly, during landing the bank angle (Ville: roll or pitch??) was approximately 10 degrees."AFAIK, the quote is based on Finnish flight testing which was done to determine the handling characteristics of the then new fighter.
If coordinated ("clean") turns could be done without touching the rudder, that is quite a big discrepancy when comparing it to the amout of left rudder needed in AH.
The other problem (they are probably related to each other) in addition to the rather big amout of slipping is the tendency for the plane to simply "depart on the yaw axis" with AoA of the fuselage nearing 90 degrees to the direction of the speed vector at low speeds. It *seems* as if the CoG is too far behind and "the tail simply wants to overtake the nose of the aircraft". I do realize that that was rather poor describtion but that's the way it feels to me. Wheather too far aft CoG is actually the reason to the phonemenon, I do not know. The only aircraft in AH that I've experienced to have similar characteristics in similar, though even bigger, magnitude is the Ta152H-1. On the other hand, FW190A-5/8 is maybe the closest AH-fighter that fits to this describtion: "Clean banked turns could be made with just the rudder or just the ailerons."
Sorry if I posted this a bit late for the possible correction to make into any of the possibly upcoming patches. The reason for this is that I wanted to testfly the plane properly and not make hasty conclusions based on limited initial experience. I do understand that ironing out the kinks of the graphic side of the new version is the primary concern for you right now but I hope you could look into this when you have the time.
P.S. I'll post couple of films of the "departing on the yaw axis"-phenomenon a bit later.