Hi Kenny - sorry, I should have replied to you earlier but my spare time has just evaporated until the new year - all the family are descending on me this Christmas and there's lots to do and not enough time to do it!!

yup - I used a 5mm thick core in my first test. I can get similar foam sheets in 10mm thickness also - www.easycomposites.co.uk/Category/Core-M...-Cell-Foam-Core.aspx. I'll order a sheet of 10mm in the new year and knock up another test rib (10mm x 12mm perhaps) out of it to see how it performs compared to the 5mm x 25mm rib, but if thicker/narrower = stiffer/lighter then we're going in the right direction! I imagine the rib dimensions could be reduced even more the further you go outboard along the wing. I'll get on this in the new year when life returns to normal!

In the meantime... Happy Christmas all,

Phil.

PS - one thing I forgot to mention in my earlier post was that the internal brace struts were not fully encapsulated in CF. The inner edges of the rib (the inside edges of the triangular cut-outs) were trimmed back to expose the foam core. This was because I didn't pay close enough attention to the way the CF cloth and vacuum bag were conforming to the foam core as I applied vacuum... and those edges were not perfect - so I decided to trim off these mal-formed edges and expose the core. I believe a fully encapsulated core would have been stronger and stiffer.

---

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
Sent: 21 December 2011 11:54
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Subject: [Carbondragonbuildersandpilots] Re: Root Rib Load Test #1



oops, I reread your post -- you are using 5 mm core so that would get bumped up to 6.25 mm or 1/4 inch if you decrease the member widths by 1/2 -- that will be easier to find, I think

--- In This email address is being protected from spambots. You need JavaScript enabled to view it., "Kenny" wrote:
>
> nice work -- thanks for sharing. You might want to leave the one rib that was bowing (actually any compression members, but especially that one) at 1 inch as it sounds like you were heading for a buckle at the end. The tension members should be OK to reduce (at at least make the attempt!). That's if you leave it the same thickness of foam...
>
> It may be lighter it increase the thickness of the foam, and decrease the width of the cfrp. To keep the same stiffness (moment of inertia) at 1/2 the width you need just 5/16 inch thick foam. You said the foam weighed 25 grams, so that would mean only a 6 gram increase in foam weight! You could probably save around 25 grams or so of carbon weight. Also, since you used 2 plies of carbon on the caps, you could use on ply of uni on the inside, same width as the rib, and then just one ply to wrap. same strength, a bit less weight. You could wrap the lower cap maybe only 1/4 inch since it's in tension for the critical loading. All that should give you the same strength at a reduced weight.
>
> Just a couple of ideas...
>
>
> --- In This email address is being protected from spambots. You need JavaScript enabled to view it., "Phil" wrote:
> >
> > Well my first rib test was a success - it survived in tact loaded up to 8g (71.8Lbs / 32.6kg) without failing... though the middle brace was bowing a little at full load.
> >
> > You can find three photos of the rib and test stand in my photos folder - (Root-Rib-1 to Root-Rib-3) - groups.yahoo.com/group/Carbondragonbuild.../1647894528/pic/list
> >
> > The rib was constructed from 5mm thick closed cell PVC foam sandwiched between two single layers of 195gsm (3K) carbon twill cloth. The internal braces and rib perimiter are all 25mm (1 inch) wide by 5mm thick. The rib was laid up over a 12mm thick male mold (made of varnished MDF) which allowed a 12mm wide flange (comprising two layers of carbon cloth) to be be formed all around the outer perimiter of the rib. This flange adds significant stiffness to the rib and prevents it from buckeling under high load. Once the rib was post cured in an electric fan oven at 140F for 24hrs, the rib was demolded and trimmed using a Dremmel-style tool (a fine carbide disc) to its final configuration.
> >
> > The finished rib weighed approximately 90grams (of which the foam core weighed 25grams). The rib was given a peel-ply finish all over. A small saving of weight could be achieved by only putting the peel-ply finish on the flanges where the rib will be bonded to other components - every little helps!
> >
> > Load was applied evenly along the rib aft of the central diagonal brace (which was mounted upside down on the test pillar to simulate positive g-loading) by adding water to a large plastic barrel hanging from broad nylon straps.
> >
> > My next step is to construct another, similar rib, but this time with internal braces and perimiters of just 12mm (half an inch) wide rather than 25mm. If this survives testing then it will represent a significant weight saving on the first rib and should also be lighter than a rib constructed of spruce (approx 60grams).
> >
> > Phil.