Step 2: once you’ve determined that there is a difference in weight between each side of the prop, there are two ways you can attack the problem…
One is to balance the hub of the prop. This method is better for props of, say, 8″ and upwards. Anything smaller and the job gets a bit fiddly, so use the second method outlined further down the page.
Hub balancing is done by carefully drilling small holes on the lighter side of the back of the hub, and filling the holes with a liquid ballast material or small pieces of lead, or perhaps fishing shot. Obviously the lighter side will be identified when using your prop balancer.
Drill and fill one hole at a time and try the prop on the balancing tool after each time.
With many blades, especially larger diameter ones, it’s quite probable that there are already holes in place (i.e. the hub is not solid, see pic.), so you can use these instead of drilling fresh ones. It’s very unlikely that you’ll need to fill one of these complete holes with ballast, so use only the ballast you need and fill the rest with light balsa or foam – something that carries no noticeable weight.
When you’ve got it right, seal the ballast in place with the balsa/foam and CA glue. Don’t use a ‘heavy’ glue, such as epoxy, because this will add more weight, and likely put the hub out of balance again.