New Spinner - 1 of 2

During an acro practice session last summer, a friend of mine was looking at my airplane while I was starting the engine and pointed out that my spinner was wobbling. The wobbling motion appeared to be due to an improper tracking. This was a very valuable observation since I never got to see my spinner turning myself.

I was sometimes missing a spinner screw after a flight, despite using loctite and locking nutplates. Vibrations due to this improper tracking were probably the main root cause. These were signs that the spinner was due for a change. Loosing a spinner in flight can really become a catastrophic scenario. So I began making some research. As I am looking to shift the CG back on this airplane since it is nose-heavy, I was also looking at the opportunity to save weight.

No matter what spinner I chose, I was going to need a dynamic re-balancing. I therefore decided to buy the Skydynamics featherweight flywheel and change my flywheel at the same time. 

Next was the spinner itself. My old spinner was made of fiberglass with two aluminum bulikheads. I can't say for sure what type it is, but it appears to be the Vans 13-inch spinner. 

First thing I did was to remove spinner and prop to get the actual weight of my spinner assembly. Turned out to be 3lb 8.6 oz including bulkheads and hardware.

I contacted Rob Millinship at aerographic in UK since I knew they were making nice CF spinners. Rob said they focused on sturdiness and that their spinner weighed probably more than a standard aluminum spinner...

I didn't find tons of info on the web on other spinner weights. Here are a few from Aircraft Spruce:

SN4 spinner kit (most likely discontinued):

BN-3 spinner kit (also most likely discontinued):

Catto spinners:

Vans spinner: no weight information on their website, but according to friends on the Biplane Forum, the new assembly weighs about 2lb 14 oz + hardware, so about 3 lb total. 

Also looked at other types, but couldn't find weight info on them or were not adapted to my installation.

Catto was more expensive, but appeared to be the lightest option. What I also found interesting is their fwd bulkhead design: it is glued and has a self-centering dowel helping for proper tracking:

The dowel is designed to fit into the crushplate center hole. It has a 2.25 inch dia and appears to be slightly tapered to ensure a snug fit.

For the above reasons, I opted for the Catto spinner and got great service from the team at Catto.

Once I received the spinner assembly from Catto, I couldn't resist to weigh it to compare with my old spinner. In summary:

• Old 13 inch spinner: 3lb 8.6 oz
• New catto 13 inch spinner: 2lb 4.0 oz (rough i.e. no clear coat and no prop cutouts)
• Old lycoming flywheel (with grinded alternator pulley): 5lb 6.8 oz
• New Skydynamics featherweight: 3lb 2.7oz

...overall these changes may take more than 3.5 lb off the nose! Weight saving there is like killing 3 birds with 1 stone: less loads on the crankshaft during tumbling maneuvers, less forward CG clipping and less weight!

This is promising...

Next post will be about the prop cutouts and tracking (hopefully better than the old spinner!)