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Looks like our hub failed inspection and has a crack along one of the splines. That being said, I am in search of a replacement hub. Sensenich is currently cutting a new prop for us and my understanding is that an 8-bolt hub can accommodate a 6-bolt prop. Is this indeed correct? If not, then I will need to notify Sensenich if an 8-bolt hub is the only one that I can source.
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Not necessarily correct, Chris. There were 8-bolt hubs, 6-bolt hubs, and an apparent hybrid (I have one) that appears to be an 8-bolt that was re-drilled to accommodate a 6-bolt propeller. The original hubs, starting with the first L-5’s were all 8-bolt. Then, sometime in 1943 (I’d have to look up the date), several Fairchild trainers with 8-Bolt Warner hubs suffered catastrophic propeller failures which were attributed to insufficient “meat” around the bolt holes. So, in what one might term a “knee jerk” reaction to avoid further fatalities and loss of aircraft, the USAAF decided to replace all the 20-spline 8-bolt hubs on all aircraft types using them with the 6-bolt design that had more wood around each bolt hole.
That, I suspect, led to a temporary shortage of 6-bolt hubs until Warner’s production facility could turn out a sufficient number to cover all of the airplanes affected, which included L-5’s. It is my belief that either Warner re-manufactured some hubs to make up the deficit, or a field mod was issued in the form of a Technical Order bulletin so repair depots could perform the work. Incidentally, no L-5’s are known to have suffered a failure of the 8-bolt props, but the hubs were changed anyway. One of the liaison squadron mechanics I used to know (now deceased) remembered seeing a great pile of perfectly good propellers being doused with gasoline and burned because they couldn’t use them anymore.
Somewhat ironically, the CAA (later FAA) never found reason to ban the 8-bolt hubs after WWII, so eventually many of the hubs removed by the military eventually ended up as surplus and found their way back into use on L-5’s. It is my guess that this is also why they seem to be more commonly found for sale than the 6-bolt version. Both types are getting hard to come by in good condition though, with corrosion being the main reason for rejection during annual inspections.
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