newbtoRC: Not knowing your plane I can't say if 3" is right or not. Either in your instruction book or on Hobbico's website you'll find the CG listed. If your plane balances foward of the required CG, as long as it's not more than 1/2" foward, you'll be fine. More than 1/2 " and you will want to think about moving your receiver battery aft. Get the balance point as close to the CG as you possibly can.

Andy