You have to make sure you don't have any spinner/prop contact or force the spinner on, even on an electric model. I try to leave plenty of daylight between the slot and front and back of the prop. I usually make the back of the slot bigger and leave the front alone to have something consistent to measure off of to help spinner balance. Make sure no contact at the face of the prop either. depending on the motor, battery and model weight, i have to wonder sometimes if using a regular I/C prop might be better safety wise??
Type at you later,
Dan McEntee