There are certainly plenty of "designer's handbooks" around, as well as rules of thumb, and just as many discussions of how to establish CG range. But here's a snip from a very informative post from Doc Mosher, a regular at Oshkosh and Brodhead (Pietenpol fly-in) events and a frequent contributor to sport aviation magazines:
"So if the C.G. limits are not set by the FAA in a TCDS (and of course, on your homebuilt experimental Pietenpol there is no TCDS), how can you know where the limits should be? If you can find an old pre-WWII Manual 18 (my reference is "As amended June 1, 1941), you will find a couple of interesting rules of thumb about Center of Gravity locations. For instance, on page II-5, under "E. APPROVED CENTER OF GRAVITY LIMITS" 1. Current Models - stated on the pertinent aircraft specification in percent of the MAC or in inches aft of a given datum. This information may be obtained from the local Civil Aeronautics Inspector. 2. Older Models - In the case of those models for which approved limits are not given on the specification or listing, it will usually be acceptable to assume the limits to be at 18% and 30% of the MAC for low and mid wing monoplanes and 22% and 34% of the MAC for high wing monoplanes and biplanes." [end quote] There are certainly more modern references than the old CAA manuals, but just using the rules of thumb that the old CAA set out, for a low-wing monoplane such as the KR, a starting point would be to use 18% and 34% of MAC. For a wing with a 48" MAC, that is roughly 8-1/2" to 16-1/2" aft of leading edge. Does this sound vaguely similar to the published 8"-16" CG range for the airplane? Again, experience with the KR has demonstrated time and time again that loading into the aft 2" of that range produces less than comfortable stability. Most prudent KR builders/flyers consider the aftmost 2" of the published CG range to be unusable. But please... if anyone has test-flown their KRs loaded in that range and has documented the flight characteristics, let's hear it. The only things I've heard about flying the plane loaded in the aft 2" of the published CG range was in accident reports or "never again" reports. I myself have no first-hand experience there. Oh, and I would consider the AS50XX-series to be no different than the RAF with respect to the laws of fluid dynamics. Oscar Zuniga San Antonio, TX mailto: taildr...@hotmail.com website at http://www.flysquirrel.net
