Pete, I have a KR-2 with Diehl wing skins, RR engine mount and GP 2180 VW; I put 2-inch spacer blocks between the fire wall and engine mount. Empty CG was 10.6 inches and the aircraft was very tail heavy on first flight. Did not test for stall speed in flight with the tail heavy condition; would probably get into an unrecoverable spin. Touch down on first flight was at 75 Kts to preclude a stall on landing, bounced and got a wheel barrow nose wheel touch down; bent the nose gear strut, but did not get a prop strike on the Sterba 52x52 prop. I had 9 inches ground clearance on the prop. Replaced the nose strut, fixed the broken trim tab Bowden cable Flight 2 was still tail heavy; landed fast and ran off end of the runway, no damage. Put 22 pounds ballast at the nose of the engine for an empty CG of 9.5 inches. Flight 3 was still tail heavy, landed at 75 Kts and ran off the runway again, no damage. Put 32 pounds ballast at the nose of the engine for empty CG of 9.1 inches. Flight 4 still tail heavy and landed at 60 Kts, stalled on the runway, dragged the tail before the main wheels touched and ran off the side of the runway. Had minor damage when the left brake cylinder hit the edge of the asphalt.
Finally concluded that the CG range given in the KR-2 plans is off by 2 inches. Diehl wing skins and/or my construction technique may also be factors. I have now adjusted the empty CG to be 8.0 inches using 24 pound ballast on the engine mount, removing 4.6 pound counter weight from the elevator and moving the 3.1 pound ELT from the baggage shelf to front of the main spar. Now doing Condition Inspection prior to flight 5. Your results may vary. Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA ------------------------------------------------------------- KRNetters I am in the process of determining the cg on my project. In comparing cg location, RR plans show the 8" cg range with the fwd edge of the range starting 8" aft of the leading edge of the wing. Based on the profile of the 48" rib, the leading edge of the cg range is 2" fwd of the front face of the main spar. I have Diehl RAF - 48 skins along with inboard skins that Jeannette Rand also produced. With those, the leading edge of the wing is 11.5" fwd of the front spar face, an 1.5" fwd of RR plans. Should I move the cg envelope fwd by that 1.5" or use the cg range set by RR. Next question: Preliminary calculations show my empty cg is approx. an 1" fwd of the RR cg location. Knowing that any weight added, passengers, fuel, baggage, etc will fall push the flying cg aft, should I fabricate my engine mount using this calculated engine position? I have done calculations with pilot plus 1/2 fuel and it falls at 2" into the RR cg range, and pilot & passenger plus 3/4 fuel and cg falls within 6" preferred cg range, the later coming in right at the aft edge of the preferred range. I'm thinking that I would like set the engine such that with me and 1/2 fuel that the cg falls right at the fwd cg limit. Next question: The horizontal engine centerline with the temporary engine mount is 2.5" below the top of the upper longerons. I'd like to drop the centerline a little more, 1/2 to 3/4", for better clearance for engine cowling and cooling plenum. Anyone see a problem with that. All advise cheerfully accepted, Thanks in advance for any and all assistance. Pete Klapp ------------------------------
