Either it's obvious and I'm just blind or I'm genuinely unsure.
I was testing out the Pigpen and noticed the FBW and the "Acro" setting. However, I was unable to find the obvious way those settings were enabled. Is there a gyro or something I couldn't find or is it a bit more complicated?
Guyfolk has a series of PSM tutorials that you might find helpful.
Even if you don't make a PSM plane, it can make an unstable aircraft a lot easier to fly.
Check the variables section of the Pigpen. You'll probably find something there.