Just stumbled across this looking for something, else but as I do a lot of wheels for radio controlled models I create, this is how I would create a spoked design.
difference()

{

union()

{

//shaft

translate([0,0,0])cylinder(10,5,5,$fn=100,center=true);

//main blades

dia1=4;

for(blade1 = [0 : 360/10 : 360])rotate([90,0,blade1])translate([dia1,0,0])cube([30,5,1],center=true);

//blade tips

dia2=19;

for(blade1 = [6 : 360/10 : 360])rotate([90,0,blade1])translate([dia2,0,0])rotate([0,90,0])cube([5,5,1],center=true);

}

//hollow shaft

translate([0,0,0])cylinder(12,3,3,$fn=100,center=true);

}