The Delta Fins (on the LJ40/45 & 60) are not for stall or stick push but, quite the opposite to remove the need for the stick puller function on earlier Learjets which suffered from mach tuck. Former Learjet Chief Test Pilot Pete Reynolds was awarded the J.H. Doolittle Award for the idea. All current Lears still have a Stall Protection Computer with Shaker & Pusher. It's also been incorporated into the ASTOR variant of the Global Express but I beleive that's more for directional stability.