My Single biggest concern: Prior to deciding to build I had shopped the used homebuilt market extensively. I often found that many home built aircraft owner/operators knew within a few ounces what their airplane weighed, but had no idea what its empty weight CG was!!!! Nor did they have an understanding of CG limits, how to calculate loaded CG, nor how CG manipulation affected the performance of the plane. I can’t accept a blind faith approach, so here’s question number one: When in the construction process should a builder consider the implications of Weight and Balance? Before you answer the above question, please consider my assumptions below. Help me to insure and perhaps refine my logic for asking. If it is flawed, let’s first correct my understanding! All of the below assumptions are for my situation of a tractor configuration, with conventional empennage controls, in this case a rag and tube taildragger. 1) Operational Center of Gravity (CG) must fall between the allowable CG limits as defined by the wing shape and aerodynamic factors. These limits are known as Max Forward CG and Max Aft CG. Attempting to operate the airplane outside of these limits will at the least result in decreased controllability and in the worst case prove fatal. The limits and the CG are most often expressed in either inches relative to a datum, or Percentage of Mean Aerodynamic Chord (MAC). In very loose terms: A forward CG limit, is mostly determined by the aerodynamic ability of the tail to generate enough tail down force needed to keep the nose up. Aft CG limit is usually arbitrarily chosen, forward of a point where CG moves aft of the Center of Pressure (CP). If this is allowed, basic stability is traded for instability, something us average skill pilot guys, without the aid of sophisticated fly by wire computer systems and hydraulic controls, don’t have the skills to handle. Airplanes are more fuel efficient when operated with aft CG, because tail down force needed and ultimately the load carried by the wing is less. Airplanes are most maneuverable as CG nears CP, a point to be strived for in an aerobatic design and avoided if the end result is intended to be a solid instrument platform. 2) With point one above in mind, using a tandem seat airplane as an example, the EMPTY weight CG, could theoretically be outside (or forward of) the forward CG limit, so long as when the pilot (plus passengers fuel and bags) sits in the plane, (Operational CG) the CG falls within the CG limits. I’ve never owned one, but I think this is the reason a J-3 Cub is soloed from the rear seat. The average pilot weight wouldn’t have enough moment in the front seat to move the CG far enough aft and into the allowable range? I know its also why airliners sometimes carry sand bags or unusable ballast fuel. 3) In a proven plans built airplane, a guy should be able to plunder along with wings and fuselage without much care about CG. In my tube and rag case, the covering and paint will probably have a minimal effect on CG. Reason being that the materials are light and the entire airframe is covered almost equally forward and aft of the CG. The real work that affects CG location has much more to do with things like the length and weight (or Moment) of the engine and accessories mounted to the airframe. 4) If my above assumptions are correct, here’s my theory towards a building plan…. A) Get the wings and fuselage built and on the gear, then conduct a weight and balance. B) From that point of construction on, calculate (Weight X Arm = Moment) every installation and give consideration to typical load of occupants, fuel and bags, to arrive at a configuration that gives the safest range of CG for the planned use of the plane. C) Along the way, and certainly after construction is finished, conduct additional weighings and refigure balance calculations to insure that empty CG is not determined by calculations alone but verified by actual weighing. 5) Engine mount length (the distance between the firewall bolt points and the engine block bolt points) will be the single biggest control over the ultimate empty weight CG. My plans show a Z-bar style engine mount for a 65 hp engine. Feedback from most Christavia builders show that even 100HP can be a little underpowered. Since I am trying to achieve SuperCub like performance, a larger engine will be the only choice. Question number two: Is it wisest to plan a preconstructed engine mount (assuming they come in custom or varying lengths), or is the best solution to purchase a dynofocal ring and weld the exact Engine mount length, to best locate CG, once most of the other data is available and/or know?