You must have missed that part where a while ago I mentioned that my Dynaflite Super Dud came in at 17 pounds - way under your projected weight of 20lbs. and more than 10% less than the weight of orthobird's plane.

There was no extra weight for balancing in mine.

Being that porky, to me, it flew lousy. 20lbs is a lot of weight for that airframe. The control surfaces are also a bit small to toss around such a blimp with much authority. It sort of wallowed and plowed through the air unresponsively. My ST3000 was not enough to save it. However, you may like the way it flys.

If we personally like the way they fly, we proclaim them to be great flyers. If we don't like the way they fly, we call them dogs. It's a matter of personal taste.

Don't forget that there is no way in all creation that the weak stock landing legs gear will carry that much load. The flimsy as designed lite ply base for the gear legs will also be hard pressed to not fail with anything but a gentle landing with that weight.

You may also run into a snag with required prop size and available ground clearance with a 40cc gas engine. I solved that problem by using 5" diameter tundra tires.