The prototype model uses an Evolution 1.00NX. This is an inexpensive engine at roughly $150, and is easy to set up and reliable. We haven't touched the needles on ours, and it has been one of the most reliable 2-stroke glow engines we've owned. The after market Bisson muffler for the Evolution 1.00NX does not fit within the Bv 141 cowl and is therefore not recommended.
The plans also show the installation of the RCV 120, which will fit entirely within the cowl. Electric power is another option for in-cowl power. A 120 four-stroke could also be used. The cylinder head will protrude from the cowl though.