Suitable hub bar material........

[Aussie_Paul]

........6061-T6, 2024-T3 or 7075-T6.

I want to extend a set of extruded alloy blades from 22' to 24'.

Also, I want to reduce my Oz composite rotor from 30' with a 4' hub bar down to 29' using a 3' hub bar.

Aussie Paul. :)

[scottessex]

6061 should be fine, but 2024 would be stronger.

7075 is too hard, very strong, but the fatigue propeties may make it on the brittle side.

I think if you are going to a smaller bar you could use 6061, and 2024 on the extended bar. If you can get a slab of it to make both, go with the 2024, just make sure you paint it, 2024 corrodes easier than 6061.

[Aussie_Paul]

Thanks Scott, but would it be too brittle for this application. Any other comments people?

Aussie Paul.:)

[Doug Riley]

Unfortunately, there's not a simple relationship between alloys' hardness/stiffness and their fatigue properties. Example: we all think 6063-T5 is soft and therefore junk, right? Surprise: it's softer than 6061-T6, but also has a lower fatigue strength.

In the same vein, 7075-T6 has a greater, not a lower, fatigue strength than 6061-T6. Marks' Handbook gives the endurance limit for '61 as 13.5 KPSI and that for '75 as 24 KPSI. 2024-T3/T4 are in-between at 20 KPSI.

Most people seem to use 6061 for hub bars. None has ever broken that I know of, even the Bensen type which must bend to allow coning.