Hmmm indeed... very interesting to see that pressure distribution article. As you point out, the majority of the pressure on the rib appears to be located in the nose section or near the centre diagonal of the rear of the rib, and a more even load distribution along the rib cap might be a more apropriate test.
I still have that last root rib to re-glue to a batten for mounting on the test stand, so I will experement with a more distributed load test and will see how it performs. I imagine it will have a dramatic effect on the magnitude of twisting at high load (there should be much less twist with much o the weight taken off the extreme rear of the rib) and I would happily wager it will take a much greater load before the rib fails. This could be fun!
IF the results are good then it might be possible to reduce the depth of the ribs even more = less weight.
Hmmm...
Phil.
From:
This email address is being protected from spambots. You need JavaScript enabled to view it. [
This email address is being protected from spambots. You need JavaScript enabled to view it.] On Behalf Of Kenny Andersen
Sent: 05 March 2012 01:14
To:
This email address is being protected from spambots. You need JavaScript enabled to view it.
Subject: RE: [Carbondragonbuildersandpilots] rib testing
Phil
Let's look at the pressure distribution on a wing. The following diagram shows three different angles of attack. We note a coupel of general interesting things. 1) clearly the pressure is biased toward the rib near the spar (and front of the rib) 2 at high angles of attack the load is only partially being applied to the bottom of the wing 3) the load is spread out and not really applied as a point load at all.
ma3naido.blogspot.com/2008/10/pressure-distribution.html
So, using the point load is ultra conservative. Applying the total shear load between wing rib butt lines is very conservative. Together they make the test hugely conservative. You see from the diagrams MUCH of the load is actually applied in the area of the D-tube! It's not on the rib at all.
hmmmm...
So the spar is at or near the zero wing twist location, no? So, wouldn't it make sense to put half the load on the rib? If you put that as a point load, or pretty much like you did where it's biased to the rib aft, I think that is still really conservative.
Keep in mind that the part of the rib truss that is at the surface is also subject to bending loads between the struts, so IMO putting a point load is OK for the truss members in axial loading, but the bending in-between could also be a failure location, so I actually kind of like how you did that, I just think the total load is about double what you could test to, or so it would seem. Thoughts?
