by Chappy » Mon Jan 18, 2010 5:38 pm
Hi Ozzie,
The Rynite props have a slightly different color and finish texture, are heavier and stiffer - especially compared to the normal props with a lot of time on them. The extra stiffness can be noticed sometimes as the plane will perform a bit better. The Rynite material, a glass fiber/polyester material, didn't flow as well into the molds as nicely as the original carbon fibre/nylon material. This caused voids within the props that wasn't readily apparent. Therefore they could fail anywhere along the blade or hub. Unfortunately, there is no marking on them to distinguish them as Rynite. The only reliable way to tell is to weigh them. Rynite props are more than 10 ounces, cf/nylon props under 10 ounces.
I believe the failure rate of these props was many, many, many times that of the cf/nylon ones. Part of that was because the CF/nylon props were extremely reliable. Fortunately, they constituted only a small percentage of the total number of props supplied by Ultraflight over the years. They were made in early 1983 IIRC. Technical Update Number 9.4 states that kits below A530 and above A754 had cf/nylon props. In between those kits, they may or may not have been shipped with glass/polyester props. Ultraflight didn't formally recall them as they did do with the adjustable pitch props, but rather exchanged them at cost. I have no idea what percentage were exchanged. I think it is very unwise to use them. On the other hand, if they have lots of time on them already, they "probably" are good ones - but you never really know.
If someone decides to use them even after all the warnings, make sure they are kept well balanced and in good shape (not all chipped up), use large fender style washers or crush plate under the mounting bolts, and torque only to spec. Ultraflight prohibited their use with hopped up engines.
Chappy