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> On 1 Apr 2016, at 4:55 AM, Sid Wood via KRnet <krnet at list.krnet.org> wrote: > > 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 > > > ------------------------------ > > > > _______________________________________________ > Search the KRnet Archives at http://tugantek.com/archmailv2-kr/search. > To UNsubscribe from KRnet, send a message to KRnet-leave at list.krnet.org > please see other KRnet info at http://www.krnet.org/info.html > see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change > options
