Brodhead Pietenpol Association

Original Posted By: Greg Yotz
I am not sure were I read this accident report, but it involves a "Cubby"ultralight version of the J3. The spar was fabricated much as descibed. Thewing failed in flight, two fatalities. The accident report stated that thegrain of the caps for the spar was 90 degrees from what the plans calledfor, as a result the caps split and the spar failed. I will keep lookingthrough my filed magazines to see if I can find out which way the grain wasto be. It is something to consider.John Mc-----Original Message-----

Original Posted By: Michael D Cuy
John McNarry and group,I remember the Cubby spar failure accident a few years back. Ithappened north of Edmonton. And I also recall reading the acci-dent report. Will see if I can locate it and pass on the informationto the group.I built up my Pietenpol spars in a similar manner to that describedin several recent letters. However, I did not use a routed cap gluedto the web; I used a full depth (4 3/4 inches) by 1/2 inch web andglued four 1/4 inch by 3/4 inch strips to it, forming the "I - beam"corresponding to the Pietenpol spar cross section. "Swallow Tail"filler blocks and plywood plates were used at strut and root attach-ment points. I used Douglas Fir because I happened upon somechoice Fir boards and was having trouble finding aircraft qualitySitka Spruce (even in 1968). My spars are a tad heavier than theywould be if made of spruce since I elected to retain the dimensionsshown in the plans, but certainly no heavier than unrouted sprucespars would have been.By laminating the spars, one can save some money and reducethe chance of having hidden defects within the spar. The trade-off (there always is at least one) is the increased labour requiredto make a built-up spar.If I can find that accident report, I'll forward it to you and the group.Graham________________________________________________________________________________

Original Posted By: Michael D Cuy
I knew that grain direction would be important for both web and caps.Something I was also thinking about was a marine/aircraft grade plywoodweb.... Any thoughts on that? This would help the grain problem because youcould have two opposing grain directions. Friends of my wife are building a new house, and they used built up floorjoices and rafters. I had a chance to talk to the representative of thecompany that makes them and they use laminated web of two pieces of plywood.They vacuum bag the web and the atmospheric pressure compresses the twosheets for a tight glue bond. I wonder if anybody knows if Tony Bingelis hasan email? I think I remember him either talking about this subject in anarticle or at one of the 'classes' at Oshkosh. It would be great to emailand ask him.....Greg YotzGraham Hansen wrote:> John McNarry and group,>> I remember the Cubby spar failure accident a few years back. It> happened north of Edmonton. And I also recall reading the acci-> dent report. Will see if I can locate it and pass on the information> to the group.>> I built up my Pietenpol spars in a similar manner to that described> in several recent letters. However, I did not use a routed cap glued> to the web; I used a full depth (4 3/4 inches) by 1/2 inch web and> glued four 1/4 inch by 3/4 inch strips to it, forming the "I - beam"> corresponding to the Pietenpol spar cross section. "Swallow Tail"> filler blocks and plywood plates were used at strut and root attach-> ment points. I used Douglas Fir because I happened upon some> choice Fir boards and was having trouble finding aircraft quality> Sitka Spruce (even in 1968). My spars are a tad heavier than they> would be if made of spruce since I elected to retain the dimensions> shown in the plans, but certainly no heavier than unrouted spruce> spars would have been.>> By laminating the spars, one can save some money and reduce> the chance of having hidden defects within the spar. The trade-> off (there always is at least one) is the increased labour required> to make a built-up spar.>> If I can find that accident report, I'll forward it to you and the group.>> Graham________________________________________________________________________________

Original Posted By: mboynton(at)excite.com
Graham wrote:>I built up my Pietenpol spars in a similar manner to that described>in several recent letters. However, I did not use a routed cap glued>to the web; I used a full depth (4 3/4 inches) by 1/2 inch web and>glued four 1/4 inch by 3/4 inch strips to it, forming the "I - beam"Graham- YES !!! This is what I should have done. Mucho easier and obviously strong since you've been flying her for 28 years, no ?Any of you guys thinking of this design, please follow Graham's procedure above.Mike C. ________________________________________________________________________________

Original Posted By: "Mr. Carmen A. Natalie"
To all:I don't think anyone should be restrained just because they dry-fly and makeengine noises. I do it quite often (sorry Ian, you set yourself up for thatone).Mark BoyntonPhoenix, AZ> Dry flying and making engine noises, I am wondering whether I will need> a restraint system. I am 6 feet at 205 pounds.> ________________________________________________________________________________

Original Posted By: Graham Hansen
Graham, how did you compress the strips to the web to make sure of a goodglue joint? I've thought of several ways but I figured you alreadydescovered the best way.And were both the web and the strips made out of DF?Greg Yotz________________________________________________________________________________

Original Posted By: Michael Brusilow
Subject: Pietenpol-List: Re: Built up spars>Greg,>>I built a spar building table of 3/4 inch plywood about nine inches>wide and approximately 15 feet long. It had a straight 2 x 4 as a>backbone down the middle of the underside and I attached the>whole thing to supports holding it at a convenient working height>above the floor.>>In order to provide gluing pressure, I cut a whole bunch of 3/4 ply->wood pieces 9 inches by 3 inches and drilled a 5/16 inch hole at>each end to match holes of the same size drilled along the edges>of the spar table. I then cleaned out the stock of 5/16 x 3 inch bolts,>nuts and washers at the local hardware stores to use for clamping.>>This system worked well, but took a lot of time to set up. It would>be great if several people could make several sets of spars from>this tooling. I made only the one set and kept the spar table, bolts,>etc. around for years, until I finally got rid of the whole works.>>Thirty years later, with 20/20 hindsight, I would do it a bit differently.>At that time, I was reluctant to use nails through the spar capstrips>and encountered difficulty in cleaning up the excess glue that oozed>out when pressure was applied; it was almost impossible to remove>after the glue had cured. The 3" X 9" clamping pieces were spaced rather>close together and there wasn't enough room to get in there>to wipe up excess glue.>>Today, I would space the clamping pieces farther apart and use lengths of,>say, 3/4 inch iron angle to distribute the clamping pres->sure along the capstrip. I would also use a few brass aircraft nails>spaced along the capstrip to hold it in position until the clamping>pressure is applied. And I would use an epoxy adhesive such as>T88 which requires less clamping pressure than the Aerolite urea>formaldehyde glue I used then. Also, the epoxy gives more assem->bly time than the Aerolite did. If you use nails, it is a good idea to>drill a small hole through the 1/4" x 3/4" strips, before nailing, in or->der to avoid the possibility of splitting (especially with Douglas Fir).>>The "swallow tail" blocks at fitting attachment locations can be fitted>and glued in place after the capstrips are on and the glue has cured.>A hardwood such as birch is good for these because it has better>bearing qualities against the bolt shanks than either spruce or fir.>The 3/32" birch plywood plates at these locations enhance this fea->ture. Be sure to taper these filler blocks in the characteristic "swal->low tail" shape so that they blend into the capstrips, thus avoiding>stress concentration due to abrupt changes in cross section. Pos->sibly, this was not done with the Cubby spar that failed---I'll have to>look at the accident report, if I can find it.>>With reference to your last question, I used Douglas Fir for the flanges as>well as for the web.>>Cheers,>>Graham>>________________________________________________________________________________

Original Posted By: Brent Reed
Greg,I built a spar building table of 3/4 inch plywood about nine incheswide and approximately 15 feet long. It had a straight 2 x 4 as abackbone down the middle of the underside and I attached thewhole thing to supports holding it at a convenient working heightabove the floor.In order to provide gluing pressure, I cut a whole bunch of 3/4 ply-wood pieces 9 inches by 3 inches and drilled a 5/16 inch hole ateach end to match holes of the same size drilled along the edgesof the spar table. I then cleaned out the stock of 5/16 x 3 inch bolts,nuts and washers at the local hardware stores to use for clamping.This system worked well, but took a lot of time to set up. It wouldbe great if several people could make several sets of spars fromthis tooling. I made only the one set and kept the spar table, bolts,etc. around for years, until I finally got rid of the whole works.Thirty years later, with 20/20 hindsight, I would do it a bit differently.At that time, I was reluctant to use nails through the spar capstripsand encountered difficulty in cleaning up the excess glue that oozedout when pressure was applied; it was almost impossible to removeafter the glue had cured. The 3" X 9" clamping pieces were spaced ratherclose together and there wasn't enough room to get in thereto wipe up excess glue.Today, I would space the clamping pieces farther apart and use lengths of,say, 3/4 inch iron angle to distribute the clamping pres-sure along the capstrip. I would also use a few brass aircraft nailsspaced along the capstrip to hold it in position until the clampingpressure is applied. And I would use an epoxy adhesive such asT88 which requires less clamping pressure than the Aerolite ureaformaldehyde glue I used then. Also, the epoxy gives more assem-bly time than the Aerolite did. If you use nails, it is a good idea todrill a small hole through the 1/4" x 3/4" strips, before nailing, in or-der to avoid the possibility of splitting (especially with Douglas Fir).The "swallow tail" blocks at fitting attachment locations can be fittedand glued in place after the capstrips are on and the glue has cured.A hardwood such as birch is good for these because it has betterbearing qualities against the bolt shanks than either spruce or fir.The 3/32" birch plywood plates at these locations enhance this fea-ture. Be sure to taper these filler blocks in the characteristic "swal-low tail" shape so that they blend into the capstrips, thus avoidingstress concentration due to abrupt changes in cross section. Pos-sibly, this was not done with the Cubby spar that failed---I'll have tolook at the accident report, if I can find it.With reference to your last question, I used Douglas Fir for the flanges aswell as for the web.Cheers,Graham________________________________________________________________________________

Original Posted By: Michael D Cuy
Greg,Tony doesn't have an Email address (that he will admit to anyway).I will probably see him at the next Chapter 187 meeting on 5 Feb. I can ask him your question about gluing up the spar web if you want.You want to know about the feasibility of vacuum bagging a plywood lamination,right?Bob Seibert________________________________________________________________________________

Original Posted By: Greg Yotz
Thanks, Bob. I guess what I would like to ask him is if he has any experience inalaminated or constructed spar.(i.e. built up i-beam style) And if he does, hashepublished it or can you convey his experiences about it to the group here. Thiswouldinclude the vacuum bag, clamped or solid methods of web making.Again thanks Bob.Greg YotzSeibert wrote:> Greg,> Tony doesn't have an Email address (that he will admit to anyway).> I will probably see him at the next Chapter 187 meeting on 5 Feb.> I can ask him your question about gluing up the spar web if you want.> You want to know about the feasibility of vacuum bagging a plywood lamination,right?> Bob Seibert________________________________________________________________________________

Original Posted By: Graham Hansen
The douglas fir I'm using for my spars wasn't perfectly straight. AfterI had planed and cut the boards to the deminsions they were off 1/4 to 1/2 inches, I consulted a friend in chapter 775 he saidthat laminated spars were cool. I set out making a work bench flatas possible then took 22 awg copper wire used by local phonecompany's on the main distrubution frames and streched it tightacross the top of the table. i then took super glue and glued guideson the table just at the position that they touched the wire every 12''about 8 " from the table edge i then glued 3 seperate strips offir turning the most perfect grain to the outer edges using rakaepoxy, I first completly saturated the wood edges to be gluedand let it soak with a slow curing hardner the wood is really thristyand takes the glue, then I mixed silica and glue into a very thick massabout the thickness of peanut butter having all exposed sidestaped with masking tape. I took a clamp and pulled the wood perfect-ly straight by clamping the spar to the wood glued to the tableand then clamping wedges from the table edge and releasingthe other clamp and moving down another 12'' and repeating the pro-cess. also I tried to clamp tight enough to straighten wood notto press all the glue out of joint this would of been a mistakeLet me also say that this is an experimental aircraft that I'm buildingand that this is the way I did it, doesn't mean that it's safe or thebest way I'm just sharing information and make no claim of thesoundness or intergrity of what I'm doing. Also peel the tapeoff and take a small hand plane and remove excess epoxy24 hours after procedure before it sets up to hard. Now my spar's are perfectly straight and remain so withswings in moisture content that happen with wheather changes.-----Original Message-----

Original Posted By: Borodent(at)aol.com
I believe their is an article in Ap.96 EXPERIMENTER on built up spars. Doug.________________________________________________________________________________

Original Posted By: Jgmatt2(at)aol.com
Greg,I finally got to talk to Tony Bingelis last night about the built up spar techniques.(I just had not seen him for over a month!)Tony feels the gluing/clamping method used should match the kind of glue beingused.The epoxy glues would really work well with vacuum bagging. His main warningwas that the epoxys set up too fast to have that be practical. By the time youassemble a large part, and get it bagged, most epoxys have "gone off". Tonysays to be careful or you could wind up with a big expensive mess. He said hehas heard there are some slow epoxys on the market now but he has not usedthem. He indicated that he really liked the idea but had not tried it himself.He was real enthused with the idea and said that if you have the vacuumbagging equipment, it would sure be an easy way to build a spar!The non-epoxy glues really take more clamping pressure than vacuum baggingwill give and he did not recommend trying vacuum bagging with other types of glue.Sounds like C-clamp manufacturers still have some job security!Regards,Bob Seibert________________________________________________________________________________

Original Posted By: Earl Myers
Thanks Bob, and tell Tony thanks too.I think I'm going to go ahead and use the clamping method. I'm using the GougenWestEpoxy System for my whole plane. I noticed in this months Sport Aviation therewasanother West System fan. I think it was the 'Cotton Candy' builder but I maybewrong. Ialways read the magazine front to back and sometimes the details are fuzzy thefirst timethrough. I'll have to go back and look.Greg YotzSeibert wrote:> Greg,> I finally got to talk to Tony Bingelis last night about the built up spar techniques.> (I just had not seen him for over a month!)> Tony feels the gluing/clamping method used should match the kind of glue beingused.> The epoxy glues would really work well with vacuum bagging. His main warning> was that the epoxys set up too fast to have that be practical. By the time you> assemble a large part, and get it bagged, most epoxys have "gone off". Tony> says to be careful or you could wind up with a big expensive mess. He said he> has heard there are some slow epoxys on the market now but he has not used> them. He indicated that he really liked the idea but had not tried it himself.> He was real enthused with the idea and said that if you have the vacuum> bagging equipment, it would sure be an easy way to build a spar!> The non-epoxy glues really take more clamping pressure than vacuum bagging> will give and he did not recommend trying vacuum bagging with other types ofglue.> Sounds like C-clamp manufacturers still have some job security!> Regards,> Bob Seibert________________________________________________________________________________