hello there , i have improved the speed CoM and CoL , Pitching and rolling , the rolling was crazy at first , so i recommend putting the control surfaces on the tips only , putting them near the fuslage/near the center puts a huge force in the fuslage which is slow rolling , a huge roll control surface ends up badly XD , try placing the main wing behind , you know more agility , and move the weight forward ...not too much also keep the ratios low , if you want to do a loop at the moment of take off , you can do it sucessfully ( that determines if the airplane is manuverable or not ( it moves 30°s per 1-2 seconds and can do a take off loop without crashing , And Remember without the gear active , it would increase your chances , and when the airplane hits 700 mph you may face some kind of torque force ( you will keep shaking) ...eh thats all good luck :D