I am using the MK bellcrank with my Impact and with all the bracing that had to be done, my battery pack is a 6 volt pack and balances right behind the wing tube, with the battery behind the firewall. I was a little bit pissed because I wanted to use a lighter batteyr pack but I need all the weight of the 6 volt pack just to balance it. I am not much for *****in but if my rudder or elevator flutters after all the stuff I have done to it, I am not going to be very happy!!