I'm using a K&B .61 with a tuned pipe that goes past the cockpit. Good combination of weight and power and that two-stroke off throttle burble.

No added weight to the front or rear, no modifications to the building sequence, two aileron servos and 4-40 hardware on these and the inter-aileron linkages (prior experience with Ultimate Bipe).

I dumped it hard (tx antenna down) and it's still rebuildable and will be up again in a week or so.

Overall, I like the speed of building compared to the other bipes I've built, though the ultimate looks nicer sitting down, and the Sterling Stearman flys more scale-like.