Dickeybird, I may have answered my own question about D-tubes , but tell me if I have it right anyway... I did a search on YAHOO about D-Tube construction. What they call D-Tube appears to be (to me) ordinary construction.. i.e., a full rib with top and bottom main spar, sheeted, and with shear webs.

To explain, to me a D-Tube (waaaaay back when...) had a Leading Edge section that you almost built by itself, then added the aft portion of the rib later... that's why I said that I thought it was 'flimsy).

Let me know if this was your interpretation of a D-Tube.

Thanks,

Bob