Hi Eduardo,

If your 30"-35" span plane is going to come out at under 10oz ready-to-fly then a geared GWS IPS motor would suffice. If its going to be around 12oz you could use a geared GWS IPS Dual motor. Above 12oz you need to start looking into the geared GWS 300C class of motor. As a rule of thumb, you need a sustainable static thrust about 1/2 the weight of the aircraft. www.aeromicro.com has useful tables giving amp draw and thrust for all of the GWS motor/gearbox/prop combinations [the figures given are rather optimistic, but they'll give a ball park idea of what you'll need].

Hope this helps, Cheers, Phil