Hi Kenny,

I wasn't sure which wing chord to measure when I started looking at the rib stresses, so I started out by measuring the main wing chords and did -not- include the chords of the flaperon. This is why my average spar location is around 43.37% of the chord. If you include the flaperon when measuring the rib chords then the average spar location is at 29.77% of the chord. I've just updated my spreadsheet in the files section showing both sets of measurements and calculations.

With the load on the ribs being so light I was considering the possibility of building the ribs in one of two ways - and testing both. For the ribs aft of the spar - the first method is to use thin-walled hollow, square section CF tubing for the straight sections (www.easycomposites.co.uk/products/carbon...section-8mm-7mm.aspx) (0.5mm wall thickness) and using .092" x .220" carbon rod (as used in the spar caps) for the rib caps. Whether the rods in the rib caps will bend and conform to the rib profile perfectly (when constrained at the two ends and bent over the mid-rib diagonals) remains to be seen. I have a sample of the 8mm square tubing and it is very strong and stiff (although surprisingly easy to crush in thickness) and very light. I also have a sample of a different square section tube, with a circular hole down the middle and thicker walls, but it is considerably heavier (but it *is* stronger!)

The second method I was considering for the ribs aft of the spar was again to use .092" x .220" rods for the caps but to use a single laminate of 248 twill cloth as a shear web, and dispense with the diagonal supports mid-rib. The two ends of the rib may still require the 8mm square section tube (for surface area to bond to the spar and trailing edge hardware) or it may yet be possible to use .092" x .220" rod here also. Holes could be cut in the rib shear web to lighten it.

For the ribs forward of the spar I was thinking of cutting out the ribs from a large sheet of carbon - thin foam - carbon sandwich, though I'm not yet sure how to treat or reinforce the edges - perhaps trim back the foam by a millimetre or two and back fill with a light weight epoxy filler like www.aircraftspruce.com/catalog/wppages/aeropoxylight.php.

For the stringer along the length of the wing at the nose of the forward rib I was also considering using the 8mm square section tubing, lengths of which can be joined together using a short piece of a smaller tube that fits perfectly inside it (I have a sample of that also.)

Phil.

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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: 06 October 2011 16:25
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Subject: [Carbondragonbuildersandpilots] Re: pressure distribution on a wing and rib loads



I took a quick look at the rib stuff, but I saw you used 40% or there abouts for the spar location. I'm not sure why, but I thought it was more like 30-33 percent. Did you use the ailerons when calculating that -- I believe you should. The aileron loads have to be reacted at the back of the fixed rib, so that load should be cumulative. If so, wouldn't that change the % location of the spar? I try to do the calculation analytically, then if it cross checks with the graphical method, you can be pretty sure that they were both done right. If it's a little different, that's not particularly surprising, but they should track well. Anyway, that's why I ask the previous couple of questions about the pressure distribution (fore/aft) on the wing, since that has potential to affect the loading of the rib. The calculation is a bit conservative anyway as the spar actually reacts some of that pressure loading. Assuming the rib reacts it all, is OK, just a bit conservative, but it's much easier to do that way, so it's worth taking the hit on the weight (which ain't much).

One thing I'd like to point out is that the loads on the ribs aren't that high, so that's why it wold likely do well to look at the 3/4 inch Home Depot foam with some wood (maybe some low-density species) or possibly composite caps. It won't take much to support that load. The only thing is accounting for the control hardware penetrations.

--- In This email address is being protected from spambots. You need JavaScript enabled to view it., "Philip Lardner" wrote:
>
> The second page/sheet of my last spreadsheet has my stab at working out the
> rib loads as la Marske. There are also a few pages of my written notes in my
> files folder.
>
> Phil.