KR> CG 2 vs 2S
You are correct that the new airfoil can change the cg limits...the aft cg limit is based on the wing...not the aircraft...so a different airfoil might affect the c.g. range. I looked through a selection of different aircraft and 15%-35% mac is a pretty common range. https://sites.google.com/site/mykr2stretch/ https://sites.google.com/site/mykr2stretch/parts-for-sale
KR> CG 2 vs 2S
>...the kr2s should actually have a >smaller cg range than the kr2. This is because the kr2s has a shorter mean >aerodynamic chord. 15% to 35% mac is a smaller range on the kr2s than a >kr2. +++ Where is the center of lift on the new airfoil compared to the RAF48 and won't that determine where the CG should be located? Just asking. Larry Flesner
KR> Landing gear position, CG
There is one thing stated incorrectly...the kr2s should actually have a smaller cg range than the kr2. This is because the kr2s has a shorter mean aerodynamic chord. 15% to 35% mac is a smaller range on the kr2s than a kr2. https://sites.google.com/site/mykr2stretch/ https://sites.google.com/site/mykr2stretch/parts-for-sale
KR> Landing gear position, CG
Paul Visk wrote: >> With Sid's landing gear being 17" aft of datum (leading edge) and the >> problem with the tail falling down. What would be a good position for the >> landing gear if you haven't drilled your legs yet? I know you wouldn't >> wanna make the nose to heavy because you would have problems rotating. << The Diehl gear installation instructions read "The taildragger conversion mounts the main gear on the forward side of the main spar with castings bolted on just outside the fuselage sides. The gear legs angle forward. The tri-gear mounts the gear legs on the aft side of the main spar with legs angled back." So with the Diehl gear, it's simply assembled and it works out close enough to have served people well over the years. If you aren't using Diehl (nvAero) gear legs, you'll have to get the angle from somebody who has them and cut yours to match. Along the same line, the plans call for a CG centered exactly on the 25% chord line, 10% each way (15%-35%). That's an impressively large CG range for a plane that is short-coupled and has no flaps, and is a departure from the more average range of about 15% from forward to aft CG limit. For many years, conventional wisdom in the KR community is to NOT use the aft 2" of the CG range, as the aircraft is likely to be unstable there.(likely gained from actual flight experience, rather than choosing nice round numbers). This is mentioned in various newsletters as well. In the 90's Dr. Richard Mole did a very methodical stability analysis on the KR2S (which shares the same CG range, and should have an even larger range than the plain KR2 due to the longer fuselage and larger tail volume). Below is what I wrote about it in my "KR Opinions" piece at http://www.n56ml.com/kopinion.html : "An analysis of the KR2S by PhD aeronautical engineer Dr. Richard Mole has revealed that using the aft two inches of the published CG range results in a fundamentally "unstable" airplane! Don't go there! I've done it (accidently) and I can tell you that I'm lucky to survive to tell the story (which is also on my webpage somewhere). And if you'll ditch the header tank and go with wing tanks (and maybe a SMALL header tank) the CG will not migrate nearly as far during a flight, allowing you to set up the plane towards the front end of the CG range, where you'll enjoy a nicely controllable airplane." So smart builders will use the range of 8"-14" aft of the leading edge of the stub wing, and gravitate toward the front end of it, rather than the aft end, or at least start out flying it there... Mark Langford ML at N56ML.com website at http://www.N56ML.com
KR> Landing gear position
Using my weight and balance Excel spread sheet, I can do all manner of "what if" math quick and easy. (Don't know if Mr. Pazmany had Excel, but his math is still valid.) My datum is the leading edge of the stub wings per the KR-2 plans. At my max gross weight I would not be able to load my KR-2 without tipping on the tail at 17 inches main wheel location. For flight the cg would be 14.6 inches; fly-able but not recommended. With the main wheels at 19 inches that would be the balance or tipping point. Any loading less than the max gross weight would work ok at the 19 inch setting. The cg for flight would 14.7 inches (moving the weight of the main wheels will move the empty cg). To get the cg less than 14 inches at max fuel would require limiting the passenger weight to less than 100 pounds. To get a safe margin regarding tipping, the main wheel location on my KR-2 needs to be set at 20 inches from datum. I am fairly certain I have enough elevator authority for takeoff rotation. Time will tell. Regarding drilling the gear legs for initial installation, just use C-clamps to hold everything in position and measure the distance to the axels. Set it where you want it to be. A carpenter square and your stub wing templates are all the measuring tools you will need for that. Right now I would recommend 20 inches. As Larry says: "Your results may vary." Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA --- > With Sid's landing gear being 17" aft of datum?(leading edge) and the > problem with the the tail falling down. What would be a good position for > the landing gear if you haven't drilled your legs yet? I know you wouldn't > wanna make the nose to ?heavy because you would have problems rotating.? > > Paul Visk > Belleville Il > 618 406 4705 >
KR> Landing gear position
With Sid's landing gear being 17" aft of datum?(leading edge) and the problem with the the tail falling down. What would be a good position for the landing gear if you haven't drilled your legs yet? I know you wouldn't wanna make the nose to ?heavy because you would have problems rotating.? Paul Visk Belleville Il 618 406 4705 Sent on the new Sprint Network from my Samsung Galaxy S?4.
