From progrmr
Hey, and it's in English! 
A fun video but his basic airmanship on final approach wasn't too strong.
Nice video and the flying (and talking) was about a million times better than the one on the previous video
Three questions
1. Why didn't the Q400 Autopilot track the LOC correctly ?
2. The stall speed is 98kts. This seems to be a bit too high, given the fact that VREF at MLW is 123kts AFAIK.
3. Closely related to the question above; What's the simulated weight of the Q400 ?
1. for several reasons:
a) rudder was not trimmed so he had a constant slip angle and constant side force.
b) Autopilot currently assumes a symmetric aircraft and doesn't correct a constant error (not needed for all other aircraft)
c) the localizer for this runway is at an angle to the runway in the database.
2. VREF with flaps 15 is 122kts as far as I remember. He approached with 35° flaps where the speed needs to be lower. The effectiveness of the flaps is a bit too high for flaps 35. But the smaller flaps settings are pretty good. It's probably unseen in real life that a Q400 approaches a 3.5 or 4km runway with flaps 35. Maybe London City airport but for such a long runway as in KSFO, use flaps 10°... or 15° max.
3. Current Mass calculates to 24942 kg in total
I can try to make the localizer center better by adding an integrator of the LOC-offset to the roll command. From my experience while testing I managed to get a perfectly centered loc in the q400 with a properly trimmed aircraft. But I'm going to attempt to fine tune it, so that you can approach with asymmetric thrust and still maintain centered LOC. The LOC on the HSI in the Q400 is actually a bit too sensitive. It should be less sensitive than the LOC deviation directly underneath the attitude.
Hm, I'm going to check the speed charts that I used.
Does the 4° come from the real aircraft or from the pitch angle that you saw in the Aerofly? The further you deflect a flap the lower the stall angle becomes. Without any slats the stall angle of the wing with 35° flaps may be just that low
