RE: 1/2A ducted fan???
I have the RK-709 smallest in the family specified for the TD09 @18000rpm weak I mean weak manual says trim down the blades or get the Cox .15 Conquest I think why not use a buggy engine put an OS .15 RX wow 30000+ ground rpm! If you're thinking 049 the one fan unit is for Midwest A-4 first generatioin foam jet balsa wing from the 70's don't think those who still own one willing to sell e-fans are designed for high rpm with low pitch won't get far on a 049.