The counter balance for the elevator could be adding to the problem with Sid's KR-2. That is addition weight aft of CG that isn't in the plans that I have. Kr-2 builder C-FKRN Ken Nathan
On 5/11/2015 3:02 PM, Jeff Scott via KRnet wrote: > Sid brings up a good point here, especially for builders that are early on in > their projects. I think sometimes we forget that the original KR design > tended to be a tail heavy design that was balanced by a large header tank in > the nose. That didn't work out so great as it left the pilot landing in an > aft CG configuration when low on fuel. 20 years ago, there were lots of > stories about guys taking a friend for a ride and experiencing an exciting > landing with low fuel and an aft CG at the end of the flight. > > With the advent of the -2S design nearly 20 years ago, many of those lessons > have been forgotten. But as Sid points out, the wings were essentially moved > forward in the -2S to help balance the plane. Additionally, most builders > are putting their fuel in the wings to avoid the large CG shift, as well as > for other safety reasons. > > My KR has the extended tail, but was not stretched in the nose (started > before the release of the -2S plans). I knew when I was building it that > this plane wanted to be tail heavy, so made a concerted effort throughout the > build process to move weight forward. I used the Rand Robinson designed > O-200 motor mount and a C-85, then eventually an O-200 with the heavy > accessories to help keep that weight forward. I also mounted my battery on > the front of the firewall. When completed, my CG came out where I wanted it > without the need to move more things around or the need for ballast. > However, as I said, I made an effort through out the build to move weight > forward. > > As for Sid's checklist of modifications to move the CD forward, I did them > all to get the plane right: > 1) Move the engine forward (used a longer mount than what was normally used). > 2) Hung Battery on the firewall. > 3) Installed a heavier engine. > > That's what it took to get a nicely balanced plane with the shorter KR-2 > firewall placement. > > -Jeff Scott > Los Alamos, NM > > >> John, >> If I knew the actual answer to why so tail heavy, I would have fixed that >> long ago and would not be having all this discussion. The only plausible >> explanation I have is: The designer, Stu Robinson, set the RAF-48 wing >> 2-inches farther forward in the stock plans than it should have been. That >> is a moot point with the advent of the KR-2S. >> I know there are hundreds of KR-2 aircraft flying. It seems they either >> have moved the engine forward, hung batteries on the the firewalls, >> installed heavier engines and/or fly them onto the runway at 70+ knots and >> never ever stall them. That or the builders are not around to tell about >> their last flight. >> >> Sid Wood >> Tri-gear KR-2 N6242 N6242 >> Mechanicsville, MD, USA >> ----------------------------------------------------------------------------- > _______________________________________________ > 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 > >
