Spinner Failure

[soneraifred]

Look at what I found today! I was planning to meet with some friends at an airport about 100 miles away for brunch, and found the spinner cracked thru one of the screw holes next to one of the prop cutouts. There was also a crack in the cutout near the leading edge of the prop in the same cutout. Once I got the spinner off, I found a chunk broken out of the front bulkhead, and a crack in the rear bulkhead. I guess the spinner's fatigue life has been reached. The spinner has about 500 hours on it. The interesting thing is that there were no cracks in the spinner cone before I flew it two days ago, as I always check the spinner for cracks when do the walk around. It would be interesting to know which part cracked first, and if the other cracks were the result of the first. I guess I'll never know. Now, I have to get a new fiberglass spinner (since I'm out of stock), and get it installed.

 

[eschrom]

Good job finding it during the pre-flight, Fred. It might have lasted until climb-out, where the disintegration would have been an unwelcome distraction at the very least. I'll have to get in the habit of checking mine more carefully.

Ed

 

[Raceair]

Fred, If your last flight would have been 5 minutes longer, you probably would have landed without the spinner.....

 

[soneraifred]

The ironic thing about this failure is that the last flight was from Burlington to Waukesha (about 24 miles) and back to deliver a replacement aluminum rear SPINNER bulkhead to a customer. I noticed no change in vibration to point to the failure, so I had no idea the cracks were there until I saw them today.

 

[Pttim]

Wow, that's a lot of cracks, I also check mine at preflight as I already cracked one at about 30 hours. The spinner gets removed at least once a year where I look it over pretty good. Glad it all worked out ok Fred, and I would like to hear a report on the new fiberglass one you install.

 

[Bil4381]

True it would be hard to be certain which crack came first, but the bulkhead crack has "smoke' which suggests it's been there some time.
As we all know, loads do not just go away when something cracks. The load always transfers, usually to something not meant to take that load.
I'm very pleased for you that you found this and with no incidents.
Bill E

 

[BoeingPilot]

got to do my annual on mine so i'll check mine. thanks for the info

 

[soneraifred]

I got the new spinner installed a couple weeks ago, and flew it a couple hours. Last week it got painted. It seems to work OK, but there is a bit more vibration. Does anyone have any good ideas about how to statically balance a spinner?

 

[eschrom]

Sure looks nice, Fred. Not sure how you balance your prop but is there any way to balance prop, bulkheads and spinner all at once? I have a rig that can do the prop and bulkheads but not the spinner.

Ed

 

[Des]

Hi Fred,

last time I did a balancing job on my engine/propeller installation, I used a "trial and error" method.
I just used lead washer(s) at one spinner mounting screw location, about 1/2" dia, backed by a steel one to handle the centrifugal forces.
I made a small log sheet, noting the actual weight and location of these weight and its result. (Do not forget to put longer screws where required)
I then made a test flight to verify the results. It takes some time, but it worked out fine for me.

Kind regards,
Des.

 

[Pttim]

Would a Dynamic balance work?

 

[soneraifred]

Des: I thought about trying your method, and I might give it a try. The vibration isn't bad, just a bit of a buzz in the seat at cruise.

Tim: I don't see why dynamic balancing wouldn't work, but I'm trying to avoid the cost. If all else fails, though, I'll have it done. My hangar partner gave me an idea to hang the spinner assembly from the center of the rear bulkhead, and check for level. I'll let you all know how it works.

 

[Des]

Fred,

I have a setup made which allows me to statically balance the complete "prop -hub- spinner" as an assy. (I made my own design force one prop hub, including a special removing tool).
I just duplicated the 3° crankshaft cone; which is then mounted to the hub, and hang everything on a thin supple steel wire. (The one used for U-line control model airplanes) At that time I use weights on the inside of the rear spinner bulkhead.
I statically balance the prop first as a separate item, and then bolted everything together, using exactly the same hardware as on the airplane. That ensures that I exactly duplicate the build up and trueness as it is on the engine afterwards.
Balancing the spinner as an independent unit is fine, provided one can exactly duplicate the same outline on the engine as it was on the balancing rig...
In my opinion, that requires a lot of very precision machining etc. So, why not just using the original hub which is just sitting there on the engine? (My 2 cent thought)

Kind regards,
Des.
I