Haha….  It is so clear from electron micrographs that the collagen like domain of SP-D is pretty much straight, not quite, arc of xx degrees but I am searching for anyone who has modeled that portion.  In Phyre2 (i do not know how long this link will be active). I found two linear models for structural protein which are pretty close and have a slight curvature (though these are single lengths not wound trimers so shape would change.  it seems to be a reasonable guess that the two are pretty much similar. Here three molecules with high similarity to the following sequence for SP-D as a “hint” of what it might look like.  The following is what I putinto Phyre2(>collagen_like_domain_SP-D
GLPGRDGRDGREGPRGEKGDPGLPGAAGQAGMPGQAGPVGPKGDNGSVGEPGPKGDTGPSGPPGPPGVPGPAGREGPLGKQGNIGPQGKPGPKGEAGPKGEVGAPGMQGSAGARGLAGPKGERGVPGERGVPGNTGAAGSAGAMGPQGSPGARGPPGLKGDKGIPGDKGAKGESGLP)

Three molecules rotated top to bottom, and i will try to weave them together in a helix.  Below that is the closest modeled sequence shown on Phyre2 from which the structures were saved in

Protein feature view i am wondering if this is more or less to scale.

the N terminal plus 8 repeats in the collagen-like domain were not well modeled. (>Nterm_SP-D_plus_8_gxy
MLLFLLSALVLLTQPLGYLE (signal peptide) AEMKTYSHRTMPSACTLVMCSSVES (N terminal) GLPGRDGRDGREGPRGEKGDPGLP……….. (first part of collagen like sequence)