Airworthiness alert,Advanced Kinetics (Jeff Henley-Smith) Rotors.

[aussie_paul]

I would suggest the crack developed as Sam says, and may not been noticed by the owner/pilot. Luck rather than inspection may have saved the owner/pilot!!!Aussie Paul.

[Tsemler]

If its the one I"ve heard about... then he found it by process of elimination from a rotor shake that started. Very lucky man indeed.

[JAL]

In the first photo the hub bar looks really scratched up and there also looks like corrosion or damage on the teeter block near the edge.

[asra]

I have had a call from an ASRA member who suggested I check the contact surface area between the block and bar. AS the following photos suggest the hub bar material is convex resulting in the block not touching on all corners.In fact it is only contacting the bar over a narrow strip across the bar. This has apparently been evident in new hub bars from the same manufacturer.This combined with the fact the hub bar is not bent to form the coning angle means the bolt holes are possibly stretching outward as the blades are continually loaded and unloaded.I have contacted 3 blade manufactures and have been advised the following.(1)The hub bars must be bent as close to the block as possible to form the coning angle,not wedges at the end of the bar.Making the bar thicker to solve the problem is only delaying the inevitable.(2) The hub block should be "lapped" to the bar.Unless machined, hub bar material can be either concave or convex.Two manufactures already do this.(3) When assembling a high strength Lock-tight should be used between the two surfaces.(4) As previously mentioned washers must be used under the bolt heads.Possible AD"s will be disscussed by the Board.

[tonydenton]

so how many hub bars have cracked out from centre mounting bolts with the coning angle pressed into them close to the [round or square] block?

[danny]

good question tony

[tonydenton]

i can understand wanting to protect

[asra]

Tony,don"t know if we have had centre drilled bars break. If you are going to drill two diagonal holes looking at the bar from the side the first bolt should be on the right.This is the preferred placing if you are going to be using a pre-rotator.I will have to research "why" again but it was something to do with the torque when pre-rotating stressing one side.I talked at length to Rob Patroney and in the early days of blade building he had a few bars crack.These were straight bars.When he redesigned and started to bend the coning angle the problem disappeared.He also advised he has replaced 3 AK bars with bent bars so far.

[tonydenton]

thank you murray.

[aussie_paul]

I reckon Gerry Goodwin has had it right all along.Aussie Paul.

[Ken Watson]

It wont make any difference if the bolts are in the centre if the block does not fit snuggly on the bar. Its like trying to balance a matchbox on an egg compared to an eggcup on an egg. The bolts are taking all the stress and transfering it to the surface area of the whole, whereas the if the block has full contact the sandwich effect gives the whole surface area of the block the load. I was horrified when I discovered how little contact my bar and block had, so I lapped them to fit. I discussed the problem with Geoff but he did not think it an issue. I posted the way I did it a few years ago so it may be floating in the web space somewhere.It is difficult to imagine the twisting forces that must go through