I agree with Karol. The weight is not extreme, it is heavy but not to the point where it shouldn't fly well. I have built 2 of these and again agree with Karol that they are an absolute joy to fly. Something else is going on with your plane. How about CG, it is too nose heavy? Just kickin' tires. Are you sure it is a Goldberg? The Goldberg design was a built up wing. I have heard of guys increasing the wing size and/or changing to a foam wing. If the wing is foam, who knows,, the builder may have changed the airfoil making it an altogether different type of flyer.