On Saturday, July 27, 2019 at 6:13:06 AM UTC-6, wrote:
On Saturday, July 27, 2019 at 1:02:23 AM UTC-4, Sky Surfer wrote:
Interesting discussion.Â* Another question for Bob K. and other experts:Â* If you saw crosswise (cross section) through a typical sailplane's main spar tongue/stub what would it look like?Â* Mostly foam surrounded by many layers of fiberglass?Â* About how much glass versus foam?Â* Just trying to envision a vital structural component that most of us take for granted and never see the inside of unless one is a designer or fabricator.

Two very strong beams(caps) at the top and bottom to handle tension and compression. Fillers(spacers?) between that handle the shear loads between the caps and also provide for strong pins that handle bending loads on many ships like Schleicher. Others(the "Glasflugel method) use pins on the ends of the spars that plug into sockets on the root rib of the opposite wing to handle bending.
In all cases there are many plies of cloth to tie the 2 webs together and handle shear loads. The "spacers" are commonly plywood or solid fiberglass for portions of high(pin)loads, and foam for the balance. Shear layers are most commonly glass.
UH

28 layers of glass/resin bind the spar caps and shear web of my Kestrel 19.

Frank Whiteley