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FWIW, there is very little difference in the modulus of elasticity of the three most commonly available AL alloys: 2024, 6061 & 7075. Thus, for any given thickness, they're all going to flex about the same amount. Moreover, the fatigue endurance limit for 7075 is only 23Kpsi. 2024, if you can get it, is a better choice, but it will still need to be thicker than 1/4", so why pay the higher prices?
Dale R.
From: "Tracy Crook" <lors01@msn.com>
Date: 2005/06/22 Wed PM 04:43:30 EDT
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: PSRU adapter plate
The error in reasoning here (7075 is twice as strong as 6061 so it can be half as thick) is that the bending strength of a plate is far more influenced by its thickness than by material strength. This is in addition to the fit problems pointed out by Dean.
Just not a good idea.
Tracy
> My bellhousing is to heavy. Dave McC is considering buying it for his > Europa, so I've been researching what it would take to replace it. I > think Tracy' s adapter plate is a very elegant solution for the > homebuilder (ie, those of use without a foundry). > > His adapter plate uses 1/2" 6061. I've been considering at 7075 > aluminum. It has about twice the cost but also twice the yield > strength. If I could use 1/4" plate instead of the 1/2", the cost would > be comparable, but I would have the very large benefit of saving > something on the order of 4lbs in a very weight sensitive area. I don't > have the expertise to run the numbers with confidence. All I can do is > a static analysis following the directions outlined on PL's website, > just like I did for the engine mount. > > Any advise of stuff to look for that might no be so obvious and not show > up in a static analysis? (the three axis and torsional forces are obvious)
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