Brodhead Pietenpol Association

Original Posted By: Robert Roach
I've been building ribs, ribs, and more ribs, and I'm looking for someopinions...anybody got any? I'm using cedar, which readily takes shape in thejig by just wetting the top surface of the top piece. I now have 22 done, andwill build a couple of extras, just in case I don't like one of 'em, and alsowill use one for a wall hanging, in the hanger, to monitor the wood andadhesive over the years. I'm ready to purchase spar material, and I'mconsidering 3/4" X 4-3/4" Douglas Fir for the spars. So...waddya al' think ?ps Richard DeCosta, ya got an excellent web page !!________________________________________________________________________________

Original Posted By: Greg Yotz
Hi Larry, Jumping in here...would you be able to share what your resource has tosay...particularly interested in how Alaskan Yellow Cedar and Western Hemlockcompare. Found some info at EAA that certainly looks as good or better thanSitka Spruce, for a lot less money.Best Regards,Warren________________________________________________________________________________

Original Posted By: Michael Hinchman
Larry;;;How about sharing your findings with us???ThnxJoeC>You mentioned using cedar for the ribs. What type of cedar? I've been doing>a little reading on woods the last few weeks and find it very interesting.>Yesterday I recieved some material from the Forest Products Laboratory in>Madison Wisconsin. In short, there appears to be several good alternatives>to Sitka Spruce for a lot less money.>Thanks, Larry >>---------->> I've been building ribs, ribs, and more ribs, and I'm looking for some>> opinions...anybody got any? I'm using cedar, which readily takes shape>in the>> jig by just wetting the top surface of the top piece. I now have 22>done, and>> will build a couple of extras, just in case I don't like one of 'em, and>also>> will use one for a wall hanging, in the hanger, to monitor the wood and>> adhesive over the years. I'm ready to purchase spar material, and I'm>> considering 3/4" X 4-3/4" Douglas Fir for the spars. So...waddya al'>think ?>> >> >> ps Richard DeCosta, ya got an excellent web page !!>> >>________________________________________________________________________________

Original Posted By: Warren Shoun
You mentioned using cedar for the ribs. What type of cedar? I've been doinga little reading on woods the last few weeks and find it very interesting.Yesterday I recieved some material from the Forest Products Laboratory inMadison Wisconsin. In short, there appears to be several good alternativesto Sitka Spruce for a lot less money.Thanks, Larry > I've been building ribs, ribs, and more ribs, and I'm looking for some> opinions...anybody got any? I'm using cedar, which readily takes shapein the> jig by just wetting the top surface of the top piece. I now have 22done, and> will build a couple of extras, just in case I don't like one of 'em, andalso> will use one for a wall hanging, in the hanger, to monitor the wood and> adhesive over the years. I'm ready to purchase spar material, and I'm> considering 3/4" X 4-3/4" Douglas Fir for the spars. So...waddya al'think ?> > > ps Richard DeCosta, ya got an excellent web page !!> ________________________________________________________________________________

Original Posted By: Owen Davies
Hi Larry, Thanks for the prompt response. From other readings, it appears that themoisture content is quite important, (slow drying best) and the number of ringsper inch and the vertical grain has a very dramatic effect on the "modulus ofrupture" in that it falls off dramatically beyond 15 degrees from vertical. Having a difficult time finding an lumber yards in So. Cal. that even carryWestern Hemlock, although have been told by a yard hand that much of what issold as construction grade spruce is in fact hemlock...still learning.Best Regards,Warren________________________________________________________________________________

Original Posted By: "David B. Schober"
To begin many other useful observations, Larry Pasley commented:>There are quite a few variables to be condidered it appears.Note that one of the most important variables is the plane you're building.If we were talking about Tailwinds, the choice of wood would be critical.Mr. Wittman didn't put a single ounce on his designs that was not absolutelynecessary. If he specified spruce, he meant it (though fir would take thestress, at the cost of extra weight.) The Piet, OTOH, is so over-built ithardly matters what you use, so long as it's aircraft-grade. I would not doit without a good engineering analysis, which I'm not competent to perform,but it would not surprise me to learn that spars made of northern white pinewere perfectly adequate. Laminate them from several pieces of pine, andit would amaze me to learn that they were not.In this one airplane, I don't think it matters much which wood you choose.The worst you are likely to do is add some weight that could have beenavoided.Of course, thinking about these things is never wasted.Owen Davies________________________________________________________________________________

Original Posted By: Larry Pasley
There are quite a few variables to be condidered it appears. The particulartype of fir, cedar, ect. is most important. Also the location the treegrew, age, mosture content, etc. For our purposes specific gravity (weight)and modulus of rupture (strength) are good benchmarks to begin with.Alaskan Cedar (doesn't say yellow,sorry) has a specific gravity of .44 anda modulus of rupture of 11,100 Psi. Western Hemlock shows .45 and 11,300for those two catagories. Compare this to Sitka Spruce at .40 and 10,200.Douglas fir varies from .46 to .50 specific gravity and 11,900 to 13,100modolus of rupture, all depending on where it was raised in tha U.S.Canadian Douglas fir comes in at around .45 and 12,800. Some other woodsthat mught be considered are Port Orford Cedar, White Cedar, Red Pine,Western Larch, California Red Fir, Northern White Pine, and Yellow Poplar.Some are not as strong as Sitka Spruce and would take a bigger chunk ofwood to match it's strength. Some are real, real close and some arestronger. Where a person is located in the US will make a lot of differenceas to availability and cost. The EAA aircraft building techniques book,Wood, is good. The Forrest Products Laboratory, which is part of theDepartment of Agriculture, has more information on wood than anyplace, anda lot more than I can understand. There is a lot to consider when chossingthe particular pieces to purchase. I hope to get a local person that has alot of experience in wood to help me pick mine when the day comes. > Hi Larry,> Jumping in here...would you be able to share what your resource has to> say...particularly interested in how Alaskan Yellow Cedar and WesternHemlock> compare. Found some info at EAA that certainly looks as good or betterthan> Sitka Spruce, for a lot less money.> Best Regards,> Warren> > > > ________________________________________________________________________________

Original Posted By: Warren Shoun
The Specific Gravity (weight) and Modulus of Rupture (strength) are twothings to look for, as well as a few others. There are a lot of varablessuch as where the tree grew, moisture content, age of the tree, etc. Theparticular type of cedar, fir, etc. are also very important. > Hi Larry,> Jumping in here...would you be able to share what your resource has to> say...particularly interested in how Alaskan Yellow Cedar and WesternHemlock> compare. Found some info at EAA that certainly looks as good or betterthan> Sitka Spruce, for a lot less money.> Best Regards,> Warren> > > > ________________________________________________________________________________

Original Posted By: Gary Gower
Larry, awhile ago you asked me about using cedar for my ribs, and I apologizefor taking so long to respond.I used hand picked wood (it took me about 1 1/2 hrs. to find eleven pieces)from a local lumber store. I found out that ya just can't stack it back upthe same way that it comes from the saw mill !!! I selected straight grain,few knots, and the ol' finger nail test for density. After ripping the 1/4 X1/2 on the table saw, I did a bend analyist. I weighted one end, and allowedexactly 50" to hang out over, and used a clamp ( a couple of ounces) at thesame arm on each piece, so it would bend. I measured up from the floor howfar each piece bent, and wrote the measurement on the end of the piece. Thisway I could come up with a trend, so I could discarded the weakest ones(survival of the fittest). This done, I cut, sanded and fit the ends of the 13pieces to make up one rib, making sure the angles were precise. I numberedthem, 1 thru 13 and wrote 'PAT' on each one. I cut about 35 or 40 pieces ofeach pattern, and placed the stacks on the table behind the jig. I did thesame thing for the gussets. Now when I got home from work, I popped the ribout of the jig, (for the first rib ya gotta put the gussets on while its inthe jig) flipped it over, installed new pieces in the jig, block sanded them,as well as the second side of the rib I just removed, vacuumed the dust, mixedup the epoxy, removed each piece from the jig, one at a time, to dip the buttend in the little cup of T88 epoxy. I used as little epoxy as possible,because excess epoxy only adds weight. The element we must deal with isgravity. A drop of epoxy only weights a gram, or so, but it really does addup. I wiped off all excess epoxy, and proceded to spread out just enough ateach joint, to saturate the gusset, wiggled the gusset down in place butdidn't weight it down yet and wiped off the excess. Soon ya get feel for howmuch is needed. Then I applied epoxy to the flipped rib, wiggled the gussettsdown a little, and went back to the jigged rib for final straightening of thegussets, and weighted them with 1/2" heavy duty sockets, lead, small pieces ofiron, or whatever I could find. Repeating the straightening process on theflipped rib, I then added weight to those gussets. Using this process allowsthe epoxy time to soak in a little, before adding weight and oozing alot backout - to be wiped off, of course. It took me about six weeks, but I now have31 ribs built. I'm going to use the one piece wing (to save weight) whichonly requires 29, but I'll have a couple to choose from to leave out of theassembly, and hang on the wall of the hanger, to monitor, over time, the agingprocess of the wood & epoxy. The local wood airplane 'Guru' gave his approvalof the ribs, and I had him cut the 3/4" X 4 3/4" Douglas Fir spars, with ascarf at about the 20' station. I also have the Spruce leading & trailingedge material, but haven't cut it yet, and 1 X 1 longerons. I do all of mysawing outside, and it's been raining for about a week. So...that's whereI'm at on my project. How's everyone else doin'?________________________________________________________________________________