Brodhead Pietenpol Association

Original Posted By: "Jeff Hill"
In response to Kent Halsten regarding spar design:I could never get my engineer friend to take time to go over my calcs.Later I spent a little time simplifying what I had. A box beam as opposedto an I-beam requires two web layers instead of one and it also provides aplace for condensation. The C-beam is even simpler than the I-beam. Ibacked into a design that was almost the same as the description below thatI think Warren included recently. This design is stronger than theoriginal spar design and it is lighter. It is very much less expensive thanspar grade spruce. (This is very much different than when Bernard made theoriginal design) I personally like it more because it is a composite sothat if there should there be any hidden defects, they will be a small partof the overall strength of the spar. This is what I will build soon for athree piece wing.Mike BellGaston Airplane FactoryGaston, SCDescription provided by Warren? for Brit approved spar for Piets follows:Here is an updated correction for the British PFA approved capstrip typespars. "The front spar comprises top and bottom spar caps each 1 1/4" X 7/8"Spruce,with a 1/8" ply web. Spruce fillers and ply doublers are positioned at eachrib.Longer spruce blocks and ply doublers are also used at the root and liftstrutpoints. The rear spar is built the same way, but the caps arelighter --7/8" X 3/4"with 1/8" ply web."________________________________________________________________________________

Original Posted By:> Mike Bell [mailto:mikebell(at)sc.rr.com]
I'm trying to imagine this spar, (at work now, no plans here). A couplequestions, as I don't have my reference books or notes. But I have seenpictures similar to this spar in the GREAT EAA WOOD BOOK I GOT FROM CHRIS!!The plywood seems thin, at 1/8". But if British PFA says ok, I guess itis. This spar IS flying in Piets over there, right?Is the plywood 90 degree or 45 degree?Obviously the plywood needs to be scarfed, only being 8' max. Do you knowoffhand where that joint falls on the wing? Will the scarf joint fall farenough away from the strut fittings, or would you need more than one scarfjoint for the plywood? Two scarfs on one side, plus doublers, adds weightand another place for failure. What's the opinion on how wide the spruce fillers and ply doublers need tobe at the rib locations? Just as wide as the rib? 1/2" ? Wider? Samequestion for the root and strut fitting area.Thanks for the response Mike!Kent> -----Original Message-----

Original Posted By: Kent Hallsten
The plywood again. Any call on the species, Mahogany, birch, basswood,okume?Kent________________________________________________________________________________

Original Posted By: "Cy Galley"
Kent,The 1/8 inch ply serves a couple of purposes:1) it separates the top and bottom of the spar. The top and bottom carrythe tension and compression load2) it adds the additional strength of the plywood to the spruce (or douglasfir or other carefully selected wood) in carrying tension and compressionloads3) it carries the shear load, which is concentrated in the center of thespar. Plywood is excellent for this.I don't know if the Brit spec requires 45 degree plywood. 90 degree morethan the required shear strength as well as more than the shear strength ofa solid spruce spar that has been routed out. 45 degree costs about 4 timesas much as 90 degree.The plywood is too thin to provide much protection from twisting. Thespruce fillers at ever rib strengthen the spar to provide this while at thesame giving us a conveniently fitted attachment point for the ribs.Scarfs must not fall at structural attachment points, ie. where the strutsor wing attachments are located. See AC 43.13, chapter one for all of therestrictions on scarfs and reccomended widths of scarf joints and doublers.If you don't have the book, you can find it on-line athttp://www.moneypit.net/~pratt/ac43/ . In fact, no one has this book. Thisis the latest version. It is available now in PDF format only and you candownload it from this site.Your building with wood book also has additional information on built upspars. I think it reccomends doublers at wing and strut attachment points,which I intend to follow.I am not an engineer. My analysis consists of assuming that the originallydesigned spar for the Pietenpol is equal to the task and that the substitutebuilt up spar materials provide equal or greater strength in the role thateach plays in the spar.Being such an important structural member, scarf joints in a built up sparmust meet the highest standards of cleanliness and scrupulously followclamping, fitting, mixing and temperature standards of the materialsinvolved..................................................................................I'm trying to imagine this spar, (at work now, no plans here). A couplequestions, as I don't have my reference books or notes. But I have seenpictures similar to this spar in the GREAT EAA WOOD BOOK I GOT FROM CHRIS!!The plywood seems thin, at 1/8". But if British PFA says ok, I guess itis. This spar IS flying in Piets over there, right?Is the plywood 90 degree or 45 degree?Obviously the plywood needs to be scarfed, only being 8' max. Do you knowoffhand where that joint falls on the wing? Will the scarf joint fall farenough away from the strut fittings, or would you need more than one scarfjoint for the plywood? Two scarfs on one side, plus doublers, adds weightand another place for failure.What's the opinion on how wide the spruce fillers and ply doublers need tobe at the rib locations? Just as wide as the rib? 1/2" ? Wider? Samequestion for the root and strut fitting area.Thanks for the response Mike!Kent>> In response to Kent Halsten regarding spar design:>> I could never get my engineer friend to take time to go over my calcs.> Later I spent a little time simplifying what I had. A box beam as opposed> to an I-beam requires two web layers instead of one and it also provides a> place for condensation. The C-beam is even simpler than the I-beam. I> backed into a design that was almost the same as the description belowthat> I think Warren included recently. This design is stronger than the> original spar design and it is lighter. It is very much less expensivethan> spar grade spruce. (This is very much different than when Bernard madethe> original design) I personally like it more because it is a composite so> that if there should there be any hidden defects, they will be a smallpart> of the overall strength of the spar. This is what I will build soon for a> three piece wing.>> Mike Bell> Gaston Airplane Factory> Gaston, SC>> Description provided by Warren? for Brit approved spar for Piets follows:> Here is an updated correction for the British PFA approved capstrip type> spars.>> "The front spar comprises top and bottom spar caps each 1 1/4" X 7/8"> Spruce,> with a 1/8" ply web. Spruce fillers and ply doublers are positioned ateach> rib.> Longer spruce blocks and ply doublers are also used at the root and lift> strut> points. The rear spar is built the same way, but the caps are> lighter --7/8" X 3/4"> with 1/8" ply web.">________________________________________________________________________________

Original Posted By: "K. and J. Hallsten"
Subject: Re: Pietenpol-List: Re: Spar designI asked Alan James of the UK the plywood question in an E-mail. He saidthey use 90degree, 6 ply, aircraft grade plywood in their spars. Ed G.________________________________________________________________________________Date: Sat, 08 Dec 2001 11:53:50 -0600

Original Posted By: flyboy_120(at)webtv.net (Ed G.)
Ed or anyone. Is the '6 ply plywood' reference correct? I can't findanything like 6 ply-1/8" plywood. all the 1/8" I find is 3 ply. The 1/8"British Aircraft plywood in AS&S is only 3 ply.Do the British have something we can't get? I've ordered wood for the tail group and the wings minus the spars.Probably won't get it till Jan. '02. I hate waiting once I've started.George AllenHarrisburg, PAGeorgeA(at)PAonline.com(soon to be Peit'. builder)----- Original Message -----Subject: Re: Pietenpol-List: Re: Spar design>> I asked Alan James of the UK the plywood question in an E-mail. He said> they use 90> degree, 6 ply, aircraft grade plywood in their spars. Ed G.________________________________________________________________________________

Original Posted By: "Philip Humphrey"
Subject: Re: Pietenpol-List: Re: Spar designIn an E-mail from Alan James of the UKI was told that the plywood they use is British a/c ply specificationGL1..... 1/8" thick with 6 laminations of birch the grain orientation of the center twolaminations being the same. You're right I have never seen 1/8" plywoodwith more than 3 laminations it must be some really good stuff EdG.________________________________________________________________________________

Original Posted By: Dmott9(at)aol.com
Hi all - I've just registered a UK Camper project. I'm temporarily residentin Belgium so I won't be able to do too much on it until I return to UK in ayear or so - still, I can work on small stuff..On the question of plywood, I think the "6-ply" may be a typo. If you thinkabout it, the face veneers of ply are always parallel so there can only everbe an odd number of plies. Aircraft grade ply in UK (normally to UK 6V3spec or the German GL1 spec) is 3-ply for the smaller thicknesses and then5-ply or 7-ply for jumbo stuff. Normally only birch ply is used forstressed parts.Incidentally, the UK Piet spars and fittings have been stressed to normalcategory (non-aerobatic) airworthiness requirements for a max gross weightof 1200 lbs. I recall seeing statements that some US Campers are flying athigher weights - would this be true?Phil Humphrey> Ed or anyone. Is the '6 ply plywood' reference correct? I can't find> anything like 6 ply-1/8" plywood. all the 1/8" I find is 3 ply. The 1/8"> British Aircraft plywood in AS&S is only 3 ply.> Do the British have something we can't get?>________________________________________________________________________________

Original Posted By: "Warren D. Shoun"

Original Posted By: Larry Neal

Original Posted By: "Jeff Hill"
Warren D. Shoun declared:> Take a look at> http://www.aitwood.com> and then go to their Ultra Thin Plywood and look at the 5 ply 1/8 birch> plywood. One sheet at $61.85 will do both spars if scarfed properly. Ifyou> seriously have a problem with uncertified stuff, see if you can get asample> of both, one from these guys and one from Wicks or AS&S. Personally, Iwill> use the Anderson stuff every time.Sounds like nice stuff, but I'd be a lot happier if it said anythingabout the glue used to make it. Waterproof? Water resistant?Very uniform layers of library paste? Not a word on a subjectthat is of serious concern for our purposes. At least the write-upon their Australian hoop pine says it's useful for marine construction.Not that I'd want to use the hoop pine for a spar without a lot moredetails on its physical characteristics, but it does suggest that if theultra-thin ply could be trusted in a moist environment, they'dat least mention it.Owen Davies________________________________________________________________________________

Original Posted By: "Greg Cardinal"

Original Posted By: "Doc Mosher"
His e-mail address is Terry.Morgan(at)qg.comGeorge AllenHarrisburg, PAGeorgeA(at)PAonline.com(soon to be Peit'. builder)----- Original Message -----