To effectively slow down a glider for landing:
Edit your par file and enter a negative value for max thrust.
I tried -8 N on the George Gerdes Speedwing model.
Then use the throttle to control braking effect. Minimum setting=No Braking;Max setting=Maximum braking(8N in my example) and anything in between.
Looks very realistic and slows down nicely. Experiment with the negative thrust setting to find the effective setting for your chosen model glider.
If the sound effects irritate you - turn off your sound!
Your comments will be appreciated.
Regards!