As a fellow gyronaut, with some small experience, and with access to engineering support I can make suggestions and comments.
Comments:
1. There are many hundreds of RAF aircraft flying.
2. There have been few reported cases of RAF rotor systems failing.
3. Sometimes a design is intolerant of dimensioning tolerance stack up.
4. After Paul's post I asked my staff to look at the RAF hub bar design.
5. We found tolerancing issues that may be resolved by operators.
6. We found that if the tolerance stack up between the blade straps and the hub bar interface is slightly off, that the blade strap can cut into the hub bar exactly at the point where the hub bar is milled to a thinner profile.
7. This interference can result in the blade straps cutting a small "V" notch in the hub bar at the worst possible spot.
8. We will be issuing a notice to all our mod kit customers still flying the RAF system making the following suggestions.
Suggestions:
1. Remove your rotor blade system from your aircraft.
2. Separate the hub bar from the blade straps.
3. Carefully examine the imprint where the inboard end of the blade strap touches the hub bar.
4. Determine if there are any nicks, cuts, or gouges at this point.
5. In any case, you can, looking at both the top and bottom blade straps, round off the blade strap corners with an approximate 1/8 inch radius.
6. Additionally, on both the top and bottom blade strap inboard ends, round off, with about a .06 inch radius, the portion of the blade strap in contact with the hub bar.
7. You may also wish to carefully blend the abrupt radius on the hub bar from where the hub bar transitions from the thin section and begins to slope up to the thicker section.
8. I strongly urge you to buy a cheap dye penetrant set and dye pen the hub bar at the blade strap hub bar interface.
Now in english: If the blade straps are just a smidgin too long and the sharp edge of the blade strap digs into the hub bar you may generate a stress riser that will initiate a propagating crack.
This message in no way constitutes an engineering suggestion from GBA. This message is not approved by GBA. This message does not indicate that following the steps suggested by me, as an individual, will ensure additional safety.