Proprotor Blade Retention System
In one aspect, this application describes a blade retention system—for a variable pitch aircraft proprotor system—comprising a double conical blade root encapsulated by a split sleeve. Some embodiments described additionally include fail-operational features. The preload of the blade pitch bearings pushes the metallic split sleeve into the bond line with the blade root.
1 . A proprotor system comprising:
a proprotor blade root;
a first and second proprotor blade pitch bearing;
a split sleeve interposed between the proprotor blade root and the first proprotor blade pitch bearing;
a preload system configured to apply a preload force to the first and second blade pitch bearing; and
wherein the preload system is configured to maintain the split sleeve in compression against the blade in a first and second direction.
2 . The proprotor system of claim 1 wherein the split sleeve comprises metal.
3 . The proprotor system of claim 1 wherein the split sleeve is configured to accommodate the proprotor blade pitch bearings.
4 . The proprotor system of claim 1 additionally comprising a redundant centrifugal force retention device.
5 . The proprotor system of claim 4 wherein the redundant centrifugal force retention device comprises a threaded split collar.
6 . The proprotor system of claim 5 wherein the redundant centrifugal force retention device additionally comprises a nut configured to transmit torque between the proprotor blade root and the split sleeve.
7 . The proprotor system of claim 6 wherein the threaded split collar is larger in diameter than an inside diameter of the first proprotor blade pitch bearing.
8 . The proprotor system of claim 7 wherein the split sleeve comprises a groove and wherein the split collar is disposed at least partially in the groove.
9 . The proprotor system of claim 1 additionally comprising a blade pitch horn.
10 . The proprotor system of claim 9 wherein the proprotor blade retention system does not comprise any composite to metallic fasteners.
11 . The proprotor system of claim 1 where the first and second direction are opposite.