Pietenpol-List: Letter to Greg, wing making
Posted: Wed Sep 29, 2004 5:54 pm
Original Posted By: "walt evans"
Pieters,I just finished a letter to Greg Bacon, the fellow that bought my "Wounded Piet"After rereading it, it occurred to me that this information might be of use tosome ot the newer members of the list who are maybe just starting to build a Pietenpol.I am sure that Greg knows most of this stuff, but I guess it won'thurt to repeat it.So with Greg's and your indulgence, I am posting it here where it might be of someuse to those just "coming along"JohnGood Morning, Greg!You asked for information about how I built the wings of "Mountain Piet" and Iam happy to do so, please remember that the wings were the first item I builtand that was about 10 years ago. I don't think that I am senile yet, but my wifewill tell you that my memory is certainly less than perfect!When starting to build the ribs, I checked the drawing that Pietenpol sent withthe plans of the ribs against the coordinates that were shown. There was quitea discrepancy between the two and so I elected to layout a new drawing usingthe coordinates. These coordinates will not provide a smooth line, so you willhave to make a batten and use it to connect the majority of the points and geta smooth line. After doing this I made a jig using the drawing and using the=BD X =BD inch cap and truss members as shown on the plans. The jig, which unfortunatelyI have now tossed, had small cams where needed so as to hold therib members tightly against the blocks thus insuring accuracy. I then startedto cut wood and used Engleman spruce, a locally available material which is aclose relative of Sitka spruce except lighter in weight. The drawback to thismaterial is that it has a number of small knots and you must choose the stripsafter milling which are free of these imperfections. I would think you couldcertainly use Sitka spruce (which is really expensive) or cedar as Charlie Rubeckuses just as well.I milled my own material, first planing the boards to an accurate =BD inch in thicknessand then running these through my table saw into strips slightly largerthan =BD inch. The grain for the capstrips was kept vertical to the wing spanso there would be less deformation with the pull of the fabric. I then madeup, without gluing it together, a rib in the jig using these strips and laidout templates for the gussets. I then set up the saw to cut out all the requiredcomponents of the ribs. I cut the angles accurately, however, left the lengthsa little long for a more accurate fit up later when putting them in the jig.These strips and gussets were then sorted out into a bunch of containers, coffeecans work fine. I made up a jig for bending the front of the top cap strips(four at a time) after soaking them in boiling water for a few minutes untilthey were flexible. They were then put in the jig and left overnight to dry,ready for the next days work. The 1/16 inch mahogany plywood gussets were sandedto remove any glaze so as to have better adhesion using T-88 epoxy.Actual assembly of the ribs went smoothly but I could only make about one rib aday because I let the epoxy dry completely before removing the rib from the jib.A tight fit of the rib members was done by using a disk sander and lightlytouching the end of the precut parts to the sanding disk until I got the exactlength needed. Gussets, of course, were only put on the top side of the ribin the jig and then the other side was put on the next day. The jig was protectedfrom the adhesive by a piece of Saran Wrap laid over the top of the entirejig before putting in the rib components. These components were pressed downinto the Saran Wrap into the jig as they were fitted and glued. This way avoidedany epoxy getting into the jig and sticking the rib. The dimension that youcut slightly more than =BD inch should be above the capstrips so you have somematerial to sand down to the exact =BD inch of the capstrip. Before puttingon the gussets I block sanded the entire side of the rib so that all parts werelevel with one another and then used an air hose to get rid of the sanding dust.Gussets were left a little high above and below the cap strips so they couldbe sanded down to be even with the cap strip later. The gussets were fastenedwith small 3/8 inch aircraft nails. I found that using a automatic (springloaded) brad setter such as picture framers use, worked well. You might be ableto get this at your friendly hardware store, but probably will have to findit yourself because the clerk won't know what you are looking for! I put a fewstrategically placed holes in the bottom of the jig, so that the part mightbe pushed out if it was reluctant to pop out by itself. When the gussets wereput on the opposite side of the rib the next day, again I block sanded the entireside of the rib so that the gussets would lie flat. After the ribs were done,I made up a couple of false stub spars and mounted the entire set of ribsto these. Then it was possible to sand off all the protruding gussets and blocksand the ribs all to exactly the same contour. When gluing, be sure to wipeall the surplus epoxy off of the joints, not to make them stronger or anything,just to massage your own ego!Spars are =BE inch vertical grain fir. There are, at least in my area some dealersthat handle this material, and if you explain the project, hopefully developingtheir enthusiasm, they will let you go through their stock to pick out thatmost suited for you. I believe there is an EAA publication outlining the specsfor the material you need, it's called "EAA Aircraft Building Techniques,Wood" I did not use the little wood wedges that Mr. Pietenpol shows on the plans,but simply cut the top of the spar to fit the angle. The cheek plates forfittings are made of 1/16 and 1/8 ply as needed. Be sure to sand the plywoodbefore gluing with, again T-88 epoxy. The tip bow is laminated and you shouldbe able to use the one on the salvaged wing, along with all the metal fittings.Just sandblast the fittings and refinish. Since we are in a dry climate here,I protected the fittings with just a coat of "Krylon" primer and then a topcoatof the same brand.Build yourself a table to assemble the wing on. It needs to be flat and level andbuild it long enough to hold both the wing and center section. You will buildthe wing on the table to the existing center section so that when everythingis put together on the plane, it will fit with no surprises.I would suggest that you slide the ribs on the spar and before permanently fasteningthem down, that you put in the drag and antidrag cables and then adjustthe spacing of the ribs slightly to clear them. You can see that I didn't do thisand had to in several places put on some doublers and cut the truss membersto avoid the wires. Also, even though the plans call for 1" nails to fastenthe ribs to the main spar, these are too long. Instead, you only need to use abouta =BD inch long nail, and be sure you drive these in the exact center ofthe spar (the neutral axis) only. This is to avoid weakening the spar. The epoxyis really the connection to the spar, the nail is only to clamp the rib tothe spar until the epoxy sets.The leading and trailing edges use the same wood as you will use for the ribs.Block all the trailing edges of the ribs to the same height and cut the trailingedge to the same angles as the ribs, just a little larger than the finishedpart will be. You will need to scarf the trailing edge in some place, becauseit is doubtful that you will have a long enough piece to do it all in one shot.Now here is where I differed from the plans. You will notice that I made up1/8 inch plywood biscuits and then used these to connect the trailing edge tothe ribs. To do this I made up a jig incorporating a router and biscuit cutterthat can be used on both the rib and trailing edge. I am lending this to youand will send it along with the plans that I forgot to give you before. Justreturn it when you are done.The leading edge is made up the same way as the trailing edge, scarfed and runthrough the table saw to the approximate angles as the rib and plans show. I madeit just a little oversized and then rabbited the plywood on the top leadingedge into the solid leading edge. You can see how this was done on the salvagewing. Don't put any support for the rear edge of the ply. Without any support,the fabric will pull down the ply between the ribs and then there is a smoothtransition for the airflow. Bernie was one darned smart feller! I used AustralianHoop Pine, this is advertised in the magazines. Don't remember the thickness,but you can measure what is there and order what you need. This stuffcomes in 5 foot lengths and will have to be scarfed together. I made up a jigto hold the proper angle and then used a drum sander on my radial arm saw to cutthe work pieces.The leading edge is bolted in place and then hand finished with a jack plane andrough 80 grit sanding block to the final shape. I would suggest that you makea template of the leading edge of the good wing so that the leading edges ofthe two wing panels are the same. This will help to ensure that once you havethe rigging right, the there will be less of a tendency for one wing to stallfirst.After the wing is assembled, be sure to "trammel" wing and adjust the cables toget the wing perfectly square. Use the "twang method" to get even tension. Theydon't have to be super tight, just taut with little strain on the fittings.Now its time to go to work with the sandpaper again. Work up to about a 220 gritand then varnish with "Varathane" or something similar. Put two coats on andsand between coats. Don't need to worry about a two part epoxy for finishing,the fabric cement you use later will dry quickly enough that it will not attackthe finish. It might just soften it a little and really provides a better bondwhen cured.At this point, you should have a new wing, all varnished, no rough spots, connectedto the center section and ready to cover. Pull the center section off, finda cool beverage and take your wife and kids away for a short vacation to makeup for the time spent away from the family while building the wing. We'll talkabout covering then.Cordially,JohnPS Made wine this last weekend from a new crop of California grapes. Won't be readyfor a couple of years or more, but will enclose with the plans and routerjig, a bottle of our 2000 Petit Sarah. I think you will enjoy the label!________________________________________________________________________________
Pieters,I just finished a letter to Greg Bacon, the fellow that bought my "Wounded Piet"After rereading it, it occurred to me that this information might be of use tosome ot the newer members of the list who are maybe just starting to build a Pietenpol.I am sure that Greg knows most of this stuff, but I guess it won'thurt to repeat it.So with Greg's and your indulgence, I am posting it here where it might be of someuse to those just "coming along"JohnGood Morning, Greg!You asked for information about how I built the wings of "Mountain Piet" and Iam happy to do so, please remember that the wings were the first item I builtand that was about 10 years ago. I don't think that I am senile yet, but my wifewill tell you that my memory is certainly less than perfect!When starting to build the ribs, I checked the drawing that Pietenpol sent withthe plans of the ribs against the coordinates that were shown. There was quitea discrepancy between the two and so I elected to layout a new drawing usingthe coordinates. These coordinates will not provide a smooth line, so you willhave to make a batten and use it to connect the majority of the points and geta smooth line. After doing this I made a jig using the drawing and using the=BD X =BD inch cap and truss members as shown on the plans. The jig, which unfortunatelyI have now tossed, had small cams where needed so as to hold therib members tightly against the blocks thus insuring accuracy. I then startedto cut wood and used Engleman spruce, a locally available material which is aclose relative of Sitka spruce except lighter in weight. The drawback to thismaterial is that it has a number of small knots and you must choose the stripsafter milling which are free of these imperfections. I would think you couldcertainly use Sitka spruce (which is really expensive) or cedar as Charlie Rubeckuses just as well.I milled my own material, first planing the boards to an accurate =BD inch in thicknessand then running these through my table saw into strips slightly largerthan =BD inch. The grain for the capstrips was kept vertical to the wing spanso there would be less deformation with the pull of the fabric. I then madeup, without gluing it together, a rib in the jig using these strips and laidout templates for the gussets. I then set up the saw to cut out all the requiredcomponents of the ribs. I cut the angles accurately, however, left the lengthsa little long for a more accurate fit up later when putting them in the jig.These strips and gussets were then sorted out into a bunch of containers, coffeecans work fine. I made up a jig for bending the front of the top cap strips(four at a time) after soaking them in boiling water for a few minutes untilthey were flexible. They were then put in the jig and left overnight to dry,ready for the next days work. The 1/16 inch mahogany plywood gussets were sandedto remove any glaze so as to have better adhesion using T-88 epoxy.Actual assembly of the ribs went smoothly but I could only make about one rib aday because I let the epoxy dry completely before removing the rib from the jib.A tight fit of the rib members was done by using a disk sander and lightlytouching the end of the precut parts to the sanding disk until I got the exactlength needed. Gussets, of course, were only put on the top side of the ribin the jig and then the other side was put on the next day. The jig was protectedfrom the adhesive by a piece of Saran Wrap laid over the top of the entirejig before putting in the rib components. These components were pressed downinto the Saran Wrap into the jig as they were fitted and glued. This way avoidedany epoxy getting into the jig and sticking the rib. The dimension that youcut slightly more than =BD inch should be above the capstrips so you have somematerial to sand down to the exact =BD inch of the capstrip. Before puttingon the gussets I block sanded the entire side of the rib so that all parts werelevel with one another and then used an air hose to get rid of the sanding dust.Gussets were left a little high above and below the cap strips so they couldbe sanded down to be even with the cap strip later. The gussets were fastenedwith small 3/8 inch aircraft nails. I found that using a automatic (springloaded) brad setter such as picture framers use, worked well. You might be ableto get this at your friendly hardware store, but probably will have to findit yourself because the clerk won't know what you are looking for! I put a fewstrategically placed holes in the bottom of the jig, so that the part mightbe pushed out if it was reluctant to pop out by itself. When the gussets wereput on the opposite side of the rib the next day, again I block sanded the entireside of the rib so that the gussets would lie flat. After the ribs were done,I made up a couple of false stub spars and mounted the entire set of ribsto these. Then it was possible to sand off all the protruding gussets and blocksand the ribs all to exactly the same contour. When gluing, be sure to wipeall the surplus epoxy off of the joints, not to make them stronger or anything,just to massage your own ego!Spars are =BE inch vertical grain fir. There are, at least in my area some dealersthat handle this material, and if you explain the project, hopefully developingtheir enthusiasm, they will let you go through their stock to pick out thatmost suited for you. I believe there is an EAA publication outlining the specsfor the material you need, it's called "EAA Aircraft Building Techniques,Wood" I did not use the little wood wedges that Mr. Pietenpol shows on the plans,but simply cut the top of the spar to fit the angle. The cheek plates forfittings are made of 1/16 and 1/8 ply as needed. Be sure to sand the plywoodbefore gluing with, again T-88 epoxy. The tip bow is laminated and you shouldbe able to use the one on the salvaged wing, along with all the metal fittings.Just sandblast the fittings and refinish. Since we are in a dry climate here,I protected the fittings with just a coat of "Krylon" primer and then a topcoatof the same brand.Build yourself a table to assemble the wing on. It needs to be flat and level andbuild it long enough to hold both the wing and center section. You will buildthe wing on the table to the existing center section so that when everythingis put together on the plane, it will fit with no surprises.I would suggest that you slide the ribs on the spar and before permanently fasteningthem down, that you put in the drag and antidrag cables and then adjustthe spacing of the ribs slightly to clear them. You can see that I didn't do thisand had to in several places put on some doublers and cut the truss membersto avoid the wires. Also, even though the plans call for 1" nails to fastenthe ribs to the main spar, these are too long. Instead, you only need to use abouta =BD inch long nail, and be sure you drive these in the exact center ofthe spar (the neutral axis) only. This is to avoid weakening the spar. The epoxyis really the connection to the spar, the nail is only to clamp the rib tothe spar until the epoxy sets.The leading and trailing edges use the same wood as you will use for the ribs.Block all the trailing edges of the ribs to the same height and cut the trailingedge to the same angles as the ribs, just a little larger than the finishedpart will be. You will need to scarf the trailing edge in some place, becauseit is doubtful that you will have a long enough piece to do it all in one shot.Now here is where I differed from the plans. You will notice that I made up1/8 inch plywood biscuits and then used these to connect the trailing edge tothe ribs. To do this I made up a jig incorporating a router and biscuit cutterthat can be used on both the rib and trailing edge. I am lending this to youand will send it along with the plans that I forgot to give you before. Justreturn it when you are done.The leading edge is made up the same way as the trailing edge, scarfed and runthrough the table saw to the approximate angles as the rib and plans show. I madeit just a little oversized and then rabbited the plywood on the top leadingedge into the solid leading edge. You can see how this was done on the salvagewing. Don't put any support for the rear edge of the ply. Without any support,the fabric will pull down the ply between the ribs and then there is a smoothtransition for the airflow. Bernie was one darned smart feller! I used AustralianHoop Pine, this is advertised in the magazines. Don't remember the thickness,but you can measure what is there and order what you need. This stuffcomes in 5 foot lengths and will have to be scarfed together. I made up a jigto hold the proper angle and then used a drum sander on my radial arm saw to cutthe work pieces.The leading edge is bolted in place and then hand finished with a jack plane andrough 80 grit sanding block to the final shape. I would suggest that you makea template of the leading edge of the good wing so that the leading edges ofthe two wing panels are the same. This will help to ensure that once you havethe rigging right, the there will be less of a tendency for one wing to stallfirst.After the wing is assembled, be sure to "trammel" wing and adjust the cables toget the wing perfectly square. Use the "twang method" to get even tension. Theydon't have to be super tight, just taut with little strain on the fittings.Now its time to go to work with the sandpaper again. Work up to about a 220 gritand then varnish with "Varathane" or something similar. Put two coats on andsand between coats. Don't need to worry about a two part epoxy for finishing,the fabric cement you use later will dry quickly enough that it will not attackthe finish. It might just soften it a little and really provides a better bondwhen cured.At this point, you should have a new wing, all varnished, no rough spots, connectedto the center section and ready to cover. Pull the center section off, finda cool beverage and take your wife and kids away for a short vacation to makeup for the time spent away from the family while building the wing. We'll talkabout covering then.Cordially,JohnPS Made wine this last weekend from a new crop of California grapes. Won't be readyfor a couple of years or more, but will enclose with the plans and routerjig, a bottle of our 2000 Petit Sarah. I think you will enjoy the label!________________________________________________________________________________