Re: Alan Thayer's Graphlite Q1 Canard Spar
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David J. Gall
Leon,
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1) The rods are not bedded in flox. The rods are laid directly onto several layers of +-45 UNI and then have several layers of +-45 UNI and one spanwise UNI wing skins bonded directly onto them. The resulting trough in the skins due to the spar trough not fitting the rods well is subsequently filled with micro (not flox) to build out to the final airfoil shape. In my opinion, this is not the best way to go since the micro might crack and/or pop out of the trough, but at least it keeps the rods in direct structural bond contact with the UNI rather than relying on a flox bed to carry the loads from the rod pack (spar cap) to the skins and shear web. 2) I would have preferred to see the rectangular rods used because they allow for a better bond of the individual rods to the uni skins through a thinner layer of epoxy. That said, I don't think this spar is relying on developing anywhere near the full strength of the rods since a rudimentary calculation shows that the spar root upper cap, having 68 rods, is good for an upward load of over 3200 lbs per wheel or roughly 11 G's for ground loads alone (more for flight loads). (I think the spar is sized to limit deflections since it is more than amply strong.) Thus, the bond of the individual rods to the UNI is not heavily loaded and hence not that important. The rectangular rods might be easier to handle and require a smaller number of individual rods, or their greater stiffness might make it difficult to bend them around the anhedral joint. Overall, I'd say the current design is just fine and there's no need to fool with it, except maybe to clean it up a little in the spar trough detail. David J. Gall
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