I thought you were an electrical engineer :)
On Thu, 1 Jul 2004 09:21:24 -0400 "Wood, Sidney M." <smw...@titan.com> wrote: >No one has mentioned the 5/8" vertical spruce blocks that >the plans call for when building KR spars. The spars are >a variant of an I-beam. The function of the web in any I >beam or box beam is to keep the two caps from coming >together. No matter what loading is put on the beam - >plus or minus g's, or twisting, and any combination of >these forces - the caps will tend to come closer >together. Beam failure will be either crushing the cap >that is under compression, breaking of the cap under >tension, or crush of the web followed immediately by >buckling or crush of the compression cap. Metal tends to >buckle; wood tends to crush. The theory and practice is >to always have the caps either in compression or tension, >never in bending. The lumber is much stronger in tension >or compression and poor in bending. The 3/32 plywood, >used for a web, will always be subject to compression and >is strongest along the length of the grain (as Don Ried >cites). Plywood has an odd number of plies with outside >plies in the same grain orientation. That is the >strongest dimension orientation. The KR box beam >construction is probably way over-built at 21 g failure. > So, you could put the plywood on in any random >orientation and probably still have a 6-g airplane. For >the exact same weight would you prefer a 21-g wing or >something less? Ken Rand and Stu Robinson got it right. >Sid Wood, Tri-gear KR-2 N6242 >Mechanicsville, MD USA >sidney.w...@titan.com > >---------------------------------------------------------------------------------------------------------------------------- >And having said that, here's one from Don Reid where he >advocates running >the grain horizontal, rather than vertical. I'd trust >just about anything >Don says as gospel. >---------------------------------------------- >Date: Jul 20, 1999 8:27 AM > >From: Donald Reid <donr...@erols.com> > >Subject: Re: Grain direction.....who cares it's >plywood...my turn at a >'STUPID' Question > > >Tim wrote: > >> Like Aircraft Plywood is either 90 or 45 degrees, I >>assume this is how >> the ply's (3-7) are layered. So grain direction of the >>top sheet is of >> interest, but I wouldn't think the orintation is as >>critical in dealing >> with the Spar web as perhaps Aluminium ..... > >OK, here are some numbers. Anyone who is interested can >make up their >own mind. All data are for birch plywood and taken from >ANC-18, Design >of Wooden Aircraft Structures. (The thick pieces are >included just to >show the effect with more plys) > >thickness # plys parallel perpendicular >0.125" 3 15.17 5.544 >0.160" 5 21.46 11.47 >0.410" 7 131.1 80.91 > >All plys are equal thickness. The numbers are moment for >fiber stress >at the proportional limit in units of inch-pounds per >inch of width. > >As to why the KR plans specify a vertical orientation, it >is because Ken >Rand and Stu Robinson got it wrong. >----------------------------------- >Mark Langford, Huntsville, AL >N56ML at hiwaay.net >see KR2S project N56ML at >http://home.hiwaay.net/~langford > > > > >_______________________________________ >to UNsubscribe from KRnet, send a message to >krnet-le...@mylist.net >please see other KRnet info at >http://www.krnet.org/info.html
