Hartzell Open Holes
 

I just hung the brand new Hartzell BA. I couldn't help but notice that on either side of each prop hub, there are a pair of screw holes. Only one pair of holes on one prop hub has screws and safety wire attached. The other 3 pair of holes are devoid of anything. Question: What is the purpose of these holes and why would only one pair of holes be secured with screws and safety wire?

Are those for balance weights?

Theoretically speaking, you should be able to statically balance with only one weight on one side or the other....(but it's early in the morning, and my theory memory may be rusty).

Paul

Balance?????????

I think your right. It seems like my prop has a flat plate in this area with the two screws holding it. If the screws are there but no plate, I think the screws were enough to statically balance the prop.

Karl

Rick6a:

The holes are to attach balance weights. Hartzell balanced the prop at the factory and installed what ever was needed for the "static" balance. Looks like your prop only needed two screws to balance it.

If you have the prop "dynamic" balanced on the airplane with the engine running, the tech doing the work MAY be able to add weight (or move / remove the screw) to one of the four possible locations.

IMHO, the holes on the hub for the balance weight is a much better way of "dynamic" balancing the prop instead of drilling holes and attaching bolts to the spinner backing plate.

I posed the question with the same photos to Hartzell but since the weekend is upon us and rather than wait for a possible reply next week, I would seek instant gratification here. Thanks guys.

Your explanations certainly eased my concerns. BALANCE...of course. Learn something new every day. It never occured to me that those wee screws serve to balance a prop so heavy I needed to strap it to the engine hoist to lift it into position. :o

UPDATE
From Hartzell:
"The holes are used to mount static balance weights. When the prop is built, it is balanced prior to final inspection. The smallest weight that can be installed is a screw. Your propeller apparently needed a small amount of weight on one side to balance it, so these screws were installed and safetied."