I was 20K in a B17 empty over A19 when my engine quit of fuel starvation. (Ok now I ear people laughting... Frenchy in a buff... Frenchy at 20K ... frenchy out of fuel... frenchy in a buff at 20K w/out fuel or any combinaison of this

)
Anyway, I set the glide speed at 150 MPH and i was gently going down and a rate of descend of 1.5, I could glide easyly to A18.
I don't know the L/D Max of the B17, but I think it's total drag at 150 KIAS is low, because it glides awsome