I'm drawing up a fat guy Sandlin glider in SW. This will be what I call the "BUG 5" as it is a derivative of the BUG4.
Sandlin's drawings call out the main spar tubes as having a splice at the outer flying wire location (1 inch OUTBD of that location to be exact.) He carries the bending and shear loads across this break by sliding two concentric sleeves inside the main tube and putting two AN4 bolts through the stackup on either side of the splice.
One of the changes I've made is to run 2.5 OD x .035 wall spars. Sandlin's original 2.0 OD spar benefits from having more choices of manufactured stock tube sizes, allowing him to purchase them off the shelf to use as sleeves. For 2.5 OD, the next smallest size at Aircraft Spruce is 2.25, which is far too small to make a sliding fit.
There is also a tertiary sleeve inside the first, which I'm assuming Sandlin added as a doubler to help prevent tearout at the fastener holes, and add a small amount of local stiffness.
I propose a splice sleeve made of the same 2.5 OD tube stock, split longitudinally to allow it to fit precisely inside the main tube, and a second, shorter one with a wider split to fit inside the first.
Other options are external sleeving, partial or full coverage, with special attention to ensure that holes go through the neutral axis or at most 35 degrees above or below this plane.
Seems like not many other ladder frame UL wings had as much span as the Sandlin gliders, I don't see this problem replicated anywhere I can find.
Sandlin's drawings call out the main spar tubes as having a splice at the outer flying wire location (1 inch OUTBD of that location to be exact.) He carries the bending and shear loads across this break by sliding two concentric sleeves inside the main tube and putting two AN4 bolts through the stackup on either side of the splice.
One of the changes I've made is to run 2.5 OD x .035 wall spars. Sandlin's original 2.0 OD spar benefits from having more choices of manufactured stock tube sizes, allowing him to purchase them off the shelf to use as sleeves. For 2.5 OD, the next smallest size at Aircraft Spruce is 2.25, which is far too small to make a sliding fit.
There is also a tertiary sleeve inside the first, which I'm assuming Sandlin added as a doubler to help prevent tearout at the fastener holes, and add a small amount of local stiffness.
I propose a splice sleeve made of the same 2.5 OD tube stock, split longitudinally to allow it to fit precisely inside the main tube, and a second, shorter one with a wider split to fit inside the first.
Other options are external sleeving, partial or full coverage, with special attention to ensure that holes go through the neutral axis or at most 35 degrees above or below this plane.
Seems like not many other ladder frame UL wings had as much span as the Sandlin gliders, I don't see this problem replicated anywhere I can find.
