I have a couple questions on mass balance for elevator: (1) Is mass balance usually required for an elevator? I found that the familiar certified airplanes (such as cessna 152, 172, DA40, etc.) all have mass balances. (2) A mass balance is intended to reduce flutter. Do we need to move the CG of the elevator all the way to hinge line? or just close to hinge line? how close? or what is the criteria of an acceptable mass balance?