Bill Thomas replies: Without going too far into cutting geometry, a metal bodied spokeshave is designed to work like a miniature bench plane. The iron is held at a 45° angle and the bevel is on the bottom to give the clearance angle. The typical wood bodied spokeshave, however, is quite different.
The iron is flat on the underside with the bevel up, like a chisel. When the iron is lowered, the nose of the spokeshave rests on the work and the cutting edge becomes angled downwards. This allows it to dig in and take a cut.
Since the clearance angle changes depending on how far the iron is lowered, a wood bodied spokeshave can be set to take very fine cuts, or if necessary, lowered more so that heavier cuts can be made.