I have experienced this,just once.
I was part of a team building F100 and F50 systems simulators for Focker. I already knew one of the test pilots and a technician who worked on their research handling simulator (the connection was that we all were owners of antique Riley motor cars). They had it set up fr demonstrating wind shear on the approach and asked me to have a go. Despite being warned that this would happen they caught me out. No doubt the shear was turned up to full for my benefit
The aircraft just dropped out of the sky at about 500ft on the descent.
Back to your problem. As others are having stall simulation problems with Yasim, I would recommend that you set up a JSBSim FDM. With JSBSim you can directly tune Cl CD,Cm and all other aerodynamic parameters to match the best available data. The problem of finding good aero data remains. Perhaps some papers have been published, otherwise start with Aeromatic which will give a good start point for your FSBSim model.
Alan