Bending strength is proportional to the depth (thickness)squared. Half the
section modulus of a 1/2" deep section is just under 3/8" thick (0.3536")
assuming identical materials.

Elastic modulus and moment of inertia relate to stiffness, not strength
(directly). For example, a piece of glass and a rubber band can be
configured to have identical strengths, but the deformations will be a lot
different under the same loads.

23 KSI is a pretty respectable strength level considering. The best wood for
props is probably <10% of that, max., mild structural steel is 24 KSI
allowable (fy 36KSI).

Jack Ford


----- Original Message -----
From: "Dale Rogers" <dale.r@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, June 22, 2005 2:52 PM
Subject: [FlyRotary] Re: PSRU adapter plate


> 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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