Savoia Marchetti S-56 3-view drawing from Aero Digest June 1929
Aero Digest magazine
Attribution
<a rel="nofollow" class="external free" href="https://archive.org/stream/aerodigest1415unse#page/n393/mode/2up">https://archive.org/stream/aerodigest1415unse#page/n393/mode/2up</a>