+++ #108 Subject: Wing skinning From: Timothy Neil Howdy: I have been pretty quiet here of late but have still been plugging away on #209. Started the wing skinning procedure and will post results as I go along. I have the 1st (outboard) skin in place and all seems well. I used the vacum method recomended by Bob in the newsletter and it works like a charm! The only problem I had was that the duct tape I used to hold the skin together would not hold by itself.What I did was to lay a 2x4 accross where the skin is taped and screw it into the work bench. Then proceed with the vacum forming. A potential problem could be if the 1 1/2 plastic pipe, that is taped accross the inside where the leading edge is, comes lose you could actually bend it on an angle.So be SURE it is taped well.. When I first turned on the vacum it sucked the skin down FLAT around the pipe and I thought I had screwed up big time but when the vacum is released the skin releases to a nice radius. I used the tire tube method of holding the skin in place while drilling the rivet hole and it works OK but is a bit of a pain. Avery makes some straps for just this purpose that may be eaiser to use. Really makes a beautiful leading edge. +++ #117 Subject: Access Holes From: Russ Erb One interesting thought I picked up from him. For sizing the access holes on the bottom of the wing (don't be putting them on the top--bad aerodynamically and hard to get to), cleco a cardboard "skin" in place. Cut an access hole of the size you think you need. Try removing/replacing any parts, bolts, or whatever that you think you would have to do through this hole. If you can't do it, cut the hole bigger. If you can, transfer that hole pattern to your aluminum skin and cut the access hole. +++ #385 Subject: wing skinning From: pfflyer- Making great progress on the second wing. That learning curve is finally starting to level out. Had a couple of suggetions that might help others. I made a template from some scrap aluminum and laid out and drilled holes for rivets for both the top and bottom of the wing. Before drilling any holes in the skin, I would lay the template over the ribs first, to ensure that the hole wouldn't interfere with a crimp or one of the stiffener angles. Some of them did, so I was able to adjust the hole ahead of time, which made the coming riveting much easier. Someone asked about access panels in the latest newsletter. In making mine, I would cleco a piece of cardboard between two ribs where I wanted to put an access hole. I then cut a hole in the cardboard and kept on enlarging it until it was big enough to allow me to work on whatever item was inside there. I actually installed and removed nuts or whatever to ensure there was enough room and still kept the holes as small as possible. When riveting the skin to the wings, I riveted the nose ribs first, like Bob recommended, but then I went and finished riveting the upper wing skins. That way we were able to back rivet all the center ribs and the spars. It made it much easier to do the #4 overlap rivets too. Once that is done, you can slip the large bottom skin in place and roll it up enough to allow you to reach inside to buck as you work your way down. This worked very nicely. +++ #386 Subject: wing skinning From: Russ Erb Message text written by INTERNET:bearhawk@egroups.com > When riveting the skin to the wings, I riveted the nose ribs first, > like Bob recommended... What Pat describes is how I plan to do it. To go one step farther, I figure I'll drill all of the skins, rivet the nose/top skins, cleco in the bottom skins, and put the wings away to build the fuselage. My thinking is that I will think of something later that I want to install or change in the wing. Of course, this would be easiest with no skin on the wing. But I need to move the wings out of the workshop to build the fuselage, Riveting on the top skin limits access, but greatly increases the torsional rigidity of the wing. So my compromise is to rivet on the top skins, leaving the bottom skins unattached for access. +++ #1255 Subject: wing skin/rib rivet holes From: Tim Anderson I didn't see any ref in the bearhawk CD on this subject, so I thought I'd ask. The skin/rib holes - should they be drilled together, or skin first, or rib first? Getting an 90 degree angle drill inside and drilling from the rib side sounds like a non-player. Predrilling the skins with square and streight lines, then match drilling rib holes sounds feasable, as does both at the same time. Any suggestions? +++ #1256 Subject: Re: wing skin/rib rivet holes From: zippydog- I've used the technique (on another type of aircraft) of drilling the wing skins first to 3/32 in. The alignment of the skin should be checked by mounting the skin on the ribs and marking and possibly drilling the holes in the accessible ribs, one on each end if possible. The layout of the holes in the skin is a matter of careful measurement and popping chalk lines from one accessible rib to the other (assuming that you want the rivets to line up). Use masking tape as required to ease the marking on the aluminum. Drill all, or at least most of the holes for the other ribs. The skin is then removed and the centerline of the flange is marked on the ribs, exterior side. The skin is put in place and the rib moved under the skin using an awl, ice pick, etc until the centerline is visible through the hole in the skin. The rib is then drilled. I would think that you would get all of the rib in alignment before the rib is drilled. On the wings I built, the rivets called out were 1/8 inch. All the holes were drilled initially to 3/32 inch. The ribs were dimpled separately from the ribs, the wing reassembled, and the holes drilled out to 1/8 inch. The 3/32 in clecos were replaced with the 1/8 inch ones as we worked along. The skin was removed again and the holes de-burred. The components were then primed and prepared for final closure. Finally the skin was replaced and the 1/8 in rivets were driven. I don't think that the BH requires all these steps, especially since the rivets for the wing are specified to be 3/32. I'm sure this technique is documented in several places. +++ #1260 Subject: Re: wing skin/rib rivet holes From: Mike Meador This has been covered in the newsletters. Check your 1996 combined( or the Jan 1999 if you have it) for the preferred skinning method - it works, it is nearly idiot proof (they are making better idiots every day) and I won't have to try and re-type out a 250 word article. +++ #1264 Subject: wing skin/rib rivet holes From: Russ Erb > I didn't see any ref in the bearhawk CD on this subject, so I thought > I'd ask. The skin/rib holes - should they be drilled together, or skin > first, or rib first? Getting an 90 degree angle drill inside and > drilling from the rib side sounds like a non-player. Predrilling the > skins with square and streight lines, then match drilling rib holes > sounds feasable, as does both at the same time. Any suggestions? Tim--it's there. Go to the January 1996 Bear-Tracks. Bob explains the procedure. I used it on the nose ribs for my flaps and ailerons--worked like a champ. +++ #1272 Subject: Re: wing skin/rib rivet holes From: twhiteh46- I am building a zenair zodiac 601hds from scratch and the manual gives instructions about drilling the skin first and marking the center line on the rib with a felt marker the center line can be seen through the skin holes. Two or 3 randomly spaced holes and then cleco and all the remaining holes are easy. Always use a size smaller drilled hole and then go back after clecoing and drill the final size hole. +++ #1611 Subject: Aw $#!+! From: Russ Erb Started skinning the wing today. Still working on the first skin. I vacuum formed the leading edge bend as per the newsletter with no significant problems. I attached the 1-1/2" PVC pipe to a bushing and a 2" pipe tee, which then connected to the hose of my shop vac. I forgot to get a cap for the pipe, so I just duct taped the end. I drilled one 1/4" hole in a part of the pipe that would be inside the skin. I used a small hole to control the rate of forming. The point of the tee is that one side of the tee is open to the air. Hence, when I turn on the shop vac, basically nothing happens, other than a lot of air rushes in the tee. To suck down the skin, I slowly cover the open side of the tee with my hand. This results in a slow, controlled suck down. Works great. So far, so good... I spent a lot of time marking the skin for the hole locations. I pre-drilled selected holes for aligning the ribs as per Bear-Tracks. I placed the skin in place and tightened it down using ratcheting tiedown straps (instead of the rubber bands and cord) as suggested by someone on this list. After drilling the first three holes through the tip rib, I decided to see how I was doing. It wasn't good. Hence the subject line. The skin had to be scrapped...or at least relegated to duty as smaller aluminum parts. I had committed a classic error. When I measured the postion of the ribs, I did it from left to right. I then marked the positions on the skin from left to right. Therein lies the problem. Because of the way the skin came off of the wing and was laying on the work table, I needed to measure from right to left. I had forgotten to keep track of which edge was which. Because the ribs are not placed exactly symmetrically, the holes for the center rib on this skin were about 1/2" off. What a major pain in the * After a several hour break and a visit to an RV-6A builder, I started over and managed to get it right this time. It is in place and the first three rows of holes on the top and bottom by the leading edge are drilled and clecoed. This was a lot of work because even after bending the leading edge, in still needs some pushing in to follow the ribs. Interestingly, even with the straps holding the skin in place tightly, there was still a small gap in some locations between the skins and the unflanged part of the rib right at the leading edge. I tried to push it down, but it wouldn't go. The skin still fit the flanges very well, so I'm not going to worry about it. I've noticed that if you plan to put a wiring conduit ahead of the main spar as I did, you'll probably find that it will interfere with bucking the rivets in the leading edge, since there's not much room up there. I've developed a plan for re-installing the conduit after riveting. About the only advice I can offer on the skinning process is go slowly and deliberately. Check everything multiple times before committing (such as drilling holes). +++ #1758 From: Russ Erb Subject: [Bearhawk] Re: Scotchbrite > question can someone tell me if the skin stiffiners that go over the > tank rest on the tank itself ? My understanding is no. The skin stiffeners (hat sections) are only attached to and only touch the skins. The fuel tank is wholey supported by the steel straps as shown in Bear Tracks. Of course, the stiffeners are probably pretty close to the tank... +++ #1914 From: Russ Erb Subject: [Bearhawk] Bearhawk Body Shop Somedays I amaze even myself... Of course, to do this, I had to start with some gross buffoonery. Since I'm working in a one-car garage and am rather cramped for space, I occasionally have to do things outside. I recently finished the first round of drilling on the wing skins for the first wing and had removed them for hole deburring. I was doing this outside. So far so good. I had three of the skins propped up against the wall outside. The problem started when I decided just to leave them there for the night (bad move). It turned out to be a rather windy night, and the next morning I happened to walk outside to see the three skins laying on the ground. Two were okay, but the third apparently fell such that the leading edge bend struck the edge of another sheet, putting a nice little scratch/dent in it. Now you might think that I thought about leaving the dent there and just declaring it hangar rash. It would have been believable, except that most airplanes get hangar rash after they're built, not before. The other contributing factor was that I wasn't sure how to fix it, especially since the dent was on a bend. The dent needed to be raised to level with the rest of the material. Then I had an idea. I grabbed a curved bucking bar and a 3X rivet gun. I set the air pressure to about 20 psi and adjusted the ball valve regulator at the gun to where the gun just had enough pressure to hammer. In the rivet gun was a flush set. I put the bucking bar under the dent and lightly hammered the top of the dent with the rivet gun. Much to my surprise, it came right up and became more of a scratch than a dent. After attacking it with a scotch brite pad, the scratch practically disappeared, and will be no worse than some of the scratches from the ribs scraping the skins. Of course, all of the scratches will eventually be scotch-brited down. Don't immediately think any errors are unrecoverable. Sometimes you need to just make a new part, but other times you just need to think about how to fix them. For instance, I have a couple of holes that got too far off the rib centerline, These will be filled with micro (epoxy and microballoons) instead of rivets. With proper finishing, you'll never know the difference. +++ #1915 From: Budd Davisson Subject: [Bearhawk] More Bearhawk Body Shop Russ, good hints on how to repair a dent. Congratulations. A better way to fix the holes, however, would be to slightly countersink both sides of the hole. Then cut the head off an overlength rivet and shoot it into the hole (Use an oversized rivet, if necessary to make sure its really tight in hole to ease setting). Leave the edges a little high so you can microshave and sand it flush. This way you don't have to worry about thermal cycles and vibration working the epoxy plug loose. In the days i was working on an aircraft production line in California (Volpar) one of the first things they showed me was how to hide a misdrilled hole from the inspector and this was the method. Just passin' stuff along. +++ #1916 From: Russ Erb Subject: [Bearhawk] More Bearhawk Body Shop Interesting idea, budd. When you say slightly countersink both sides of the hole, does that apply when the hole is in .025 sheet? What is the reason for countersinking on the back side? Would it be better to dimple it and just put a normal rivet in it? Fill me in. +++ #1917 Budd Davisson Subject: [Bearhawk] Re: More Bearhawk Body Shop I'm assuming the hole lies over a rib flange so, if you dimple or countersink only one side, you have the butt on the otherside and you'll have to drill a clearance hole in the flange for it. If you can do that, that's cool. Otherwise, if you countersink about a third of the way in from each side (actually, it can meet but it's better not to) then overdrive the rivet shank, (you can use a countersunk rivet, but leave it sittin realy high so yo don't have to countersink so deep), it fills in the countersink on the backside. Just be careful when driving that the rivet expansion doesn't bulge the sheet slightly. A way to make sure the rivet will sit in the hole while you're bucking it is to squeeze it a little on a squeezer before inserting it so the shank gets a little fatter and wedges into the hole. If you can afford the butt on the back side, just fatten up a counter sunk rivet and let it protrude on the outside so you can shave the head flush. This works MUCH better with SO rivets. You may be able to anneal a regular rivet and get the same effect. I've tried it though. +++ #1919 From: Bill Cox Subject: [Bearhawk] Re: More Bearhawk Body Shop Russ, We used a similar idea in our shop. Countersink about 1/3 of the way on both sides. Punch some soft aluminum (.040 or .050) with your Whitney punch, then use the little punched out disk instead of the rivets. Works great. +++ #1922 From: J.T. Newbegin Subject: [Bearhawk] Re: Bearhawk Body Shop Russ, you can also iron out dents if the metal is not strechted, use a piece of soft wood with the end rounded and place the metal on a smooth surface and rub the dent. I thought it was a joke but it works. +++ #1926 From: Bruce A. Frank Subject: [Bearhawk] Re: Whitney Punched Holes That contradicts what I have been taught over the decades. Both holes, whether punched or drilled, need to have the edges chamfered to remove the very sharp edge. I was taught that the slight work hardening that takes around the perimeter of a punched hole actually made for a stronger point in the material. The sharp edge of the hole can provide a place for a crack to start because the slight tearing that takes place in the final part of the shear can leave striation lines on that sharp edge. This can be a stress raiser that can lead to cracks. If the edge is chamfered the problem is eliminated and the improved strength of a punched hole is realized. I once had a business next to a company that made wing parts for military aircraft. The wing skin holes were swagged through. The punch die had a sharp point that pushed through and pushed the excess material away from the center of the hole. As the dies came on together that ridge of excess material was shaped to create a slight washer like look around the hole. The die beveled the edges both top and bottom so no material had to be removed by chamfering the holes. The material was work hardened by this process, the skin was left a few thousands thicker around the hole and such formed holes were said to never precipitate cracks. THe top of the hole provided enough bevel to allow installation of flush rivits. The owner was trying to sell me that tooling for just a few hundred dollars. Wish I'd bought it. +++ #1928 From: Budd Davisson Subject: [Bearhawk] Re: More Bearhawk Body Shop > Do you mean AN426A rivets (soft) as opposed to AN426AD? Yeah, 426A. I guess I'm dating myself by saying SO. That was the desgnation when we were still building flying machines with flint rivet sets. +++ #1999 Russ Erb Subject: [Bearhawk] Patience... or Third Times the Charm or Importance of Edge Distance or Maintaining Workmanship Standards or Confession Is Good For The Soul or What a Pain in the ### I finally got the top skins on the left wing, and started working on the access panels. True to form, I started on the hardest one first. Not intentionally, it just worked out that way. As you may know, I'm using an AN 5816-1 Shark Fin Pitot-static tube on a boom (1.25" tube) sticking out of the leading edge just outside of rib 8. If you've seen a Cessna 195 you've got the idea. Since the boom sticks 18" out of the leading edge, it's rather a pain when trying to move the wing around or store it. As a result, I decided that it needed to be removeable. This meant a rather large access panel from just in front of the main spar on the bottom around the leading edge to the top surface about 3 rivets back (long enough to get past most of the leading edge curvature). The panel needed to be as large as possible because the base of the boom was fairly wide for stability. I figured out what I thought I could get away with and then cut the hole in the skin. No problem yet. Then I started making the backup ring to attach the panel to. After several hours of fighting with it and getting it to fit, I drilled the rivet holes to attach it. I made sure I had sufficient edge distance (2D, 3/16" in this case) on the wing skin. However, it didn't turn out quite that way on the backup ring. Quite a few holes did not have enough edge distance. Elsewhere I might have not worried about it, but in this location (right next to a double row of rivets joining two wing skins and fairly close to the wing strut attachment) I suspected that it was possible that the wing skin here could be significantly stressed, and that stress had to pass from the wing skin to the backup ring to the panel and back again. The backup ring had gotten smaller or misaligned compared to how I had envisioned it, so it was possible to make one that would have sufficient edge distance. So I made the hard decision to pull it out and make another one. Multiple hours wasted. I thought about how to do it different and tried another technique. Got the second one made. Guess what--still not the best it could be, still insufficient edge distance on some hole (though different holes this time). Scrap and rework time again. That's where I was this morning. Thought about it some more, tried another technique. After many hours, got a part with sufficient edge distance and that I was proud to have in my plane. Don't have to worry about answering tough questions to the Project Police or Tech Counselors either. I then started on the panel itself. This might not be so hard except I had to get a hole in the middle of it tightly fit around the boom. To do this, I drilled the hole first with a rather large Uni-bit. Then I carefully trimmed the panel to fit. I didn't count how many times the panel went on and off to check, but it was probably somewhere around 50 or more. The end result is a panel that fits very well in the hole, and, yes, has plenty of edge distance. At least on three sides--I have to finish the last side tomorrow. My point to you? I spent all day and made (almost) a grand total of two parts that on the surface look very simple but the tolerances were very tight. One part had to be made three times. Realize that some parts will just take a long time to do correctly, and as I've said before, if you don't like the way it comes out, do it over. That's easy to say, but I find it very hard to do when the rejected part took many, many hours to make and/or had a high material cost. Some mistakes can be "repaired", others have to be replaced. The payoff is the good feeling when you finally get it done right and have a part you would be proud to show to your Bearhawk buddies. ************************ Another recent case of scrap and rework had to do with the hat sections under the top skin in the fuel bay. After forming on a brake, these have to be further bent to match the airfoil shape. This results in compound bending and shrinking and stretching. The newsletter suggests a method to do this involving heating of the metal, but I really didn't like that since it would really mess up the heat treating and I had no way (that I know of) to re-heat treat it. Using an idea stolen from a GlaStar builder (which uses hat sections for most ribs, which, by the way, didn't fit as they came from the factory), I made up a wood press die to press the airfoil shape into the hat section. The trick was figuring out how much springback would be present in the aluminum. I did some tests, plotted out a curve, made up the dies, and pressed the section in it. It was singularly non-successful--all bending was fully elastic and the hat section came out with no difference at all! Made the curve more severe, built another die, and tried it again. This time there was some plastic deformation (permanent set), but only about half of what I needed. Throw out another die, try again. Based on the results from the previous trial, draw an even more severe curve. Make die #3. Press aluminum section. This one took a leap of faith, since during the process, the part buckles and looks like it is ruined. With continued pressure, it reforms back to the proper shape. This time I actually got a usable part. It could have used a little more bend, but it was good enough. In the center section there were about three places where the compression had gently buckled the skin to allow it to shrink. That all makes a good story, but doesn't help you much if you're trying to replicate it. Unfortunately, this one requires pictures to understand. Sometime in the future I'll publish the coordinates of the curve and post the pictures of my die. With that information you should be able to easily replicate it. Well, the clocks spring forward tonight, so I'm already behind in getting to bed. It's also April Fools day, but this message is all true. A while back I had thought of an April Fools joke that I figured could be so successful I might not be able to stand the backlash. I figured I would just post a simple message to the list telling you that I had changed my mind and was giving up on the Bearhawk project. Some of you might not have realized the date and thought I went nuts. The worst part would be that that message would get separated from the message saying "April Fool" and might continue to haunt me for months to come. Therefore, I couldn't stand the backlash. Now get off the computer and get back to your Bearhawk! +++ #2001 From: J.T. Newbegin Subject: [Bearhawk] Re: Patience... Russ, I tried the same method for the siffiners, I also tied making a roller setup, you cannot put enough preesure into it by hand, if you add leverage it breaks the part, there is too much spring back on T-3, soft would work. I will try the press type form again. The heating method may work for some, but it wouldn't for me. +++ #2002 From: Bill Cox Subject: [Bearhawk] Re: Patience... I made the stiffeners using Bob's method. It is not foolproof, not enough heat and it doesnt take a set, too much and it cracks. It does change the temper of the metal and I'm assuming Bob has taken this into consideration. I have my left wing ready to put in the jig after Sun n' Fun. +++ #2003 From: budd davisson Subject: [Bearhawk] hat section ribs I'm going to ask Bob about making the hat-section ribs out of 6013. This stuff can be worked soft, but heat treats to T3 at an hour at 375 degrees. The Venture uses it for its fuselage skins (among other things) and they heat treat the parts in a pizza oven! +++ #2004 From: Bill Cox Subject: [Bearhawk] Re: hat section ribs That sounds good. I think these stiffeners would fit in a home oven. +++ #2031 From: Russ Erb Subject: Hat Section Bender Posted I have posted pictures and a few explanatory words on my press for bending the hat section stiffeners for the fuel tank bay on my Bearhawk page (http://www.eaa1000.av.org/pix/erbpix/erbpix.htm). I will leave them there until I release Version 2 of the Bearhawk Reference CD (which, at the current rate, won't be anytime soon. Save those dimes and nickels!). +++ #2591 From: Russ Erb Subject: Googols... googol (goo' gol) n. [arbitrary use by Edward Kasner (1878-1955), U.S. mathematician, of a child's word] 1. a number 1 followed by 100 zeros; 10^100 2. any very large number 3. the number of rivet holes in a Bearhawk wing to be dimpled. or so it seems. And I'm less than a quarter of the way done. I don't remember drilling that many holes, but I suspect that's because the holes were drilled in small groups, whereas the dimpling is done all at once. You may find that unless you go to great lengths to avoid it, you will occasionally have a case where a stiffener angle or something interferes with the squeezer while dimpling. You might be able to get by with using a pop rivet dimpler, but in many cases I just let the stiffener angle get bent out of the way, and then bent it back after dimpling. You can't tell any difference afterwards anyway. I said it a long time ago, but now I've actually done it. Instead of making the deep throat dimpler as shown in Bear-Tracks, I'm using the following method: 1) For holes within about 2" of the edge, use the pneumatic squeezer. 2) For holes within 20" of the edge, use the Avery deep throat dimpler that I borrowed from an RV-6A builder. 3) For the few remaining holes left out in the middle of the sheet, use the Avery dimpling/riveting block set. This is a bucking bar and rivet set made to accept dimple dies. If you build the deep throat dimpler a shown in Bear-Tracks, it has a 23" throat and can reach anywhere on the sheet. Rather than fight with getting one aligned, I borrowed one that was available. The tool set mentioned in 3) is also useful for back-riveting long universal head (AN470) rivets. I used it on the -5 rivets used to hold the rod ends in the hinge mounts for the flaps and ailerons--it worked like a champ. If you do as I did in 3), be sure to set the air pressure for your rivet gun VERY low, like just enough to make it hit at all. You'll be surprised how little pressure it takes to make a good dimple. Use too much pressure and you'll deform the metal around the dimple. After all, a rivet gun is make to hammer hard enough to deform rivets, right? I took the night off from the Bearhawk to visit my RV-6A builder. He should be ready for the FAA inspector at the end of the week. It really is exciting to see an airplane that I've watched be built for the last three years about ready to fly. He promised that he'd come by to see my Bearhawk when it was a week from its FAA inspection in a few years. Now I need to figure out some time to do some "inspection" of Pat Fagan's fuselage progress... +++ #2779 From: Mike Eldredge Date: Thu Jun 22, 2000 4:04pm Subject: Forgive me for not starting with the wings, but... Just wanted to share my elation at finally being able to begin working with materials, after holding plans since March. I've been doing tons (literally) of yard work this spring, and have had to put off working on the plane. This has, however, given me time to read my Bingelis homework. For Father's day, my wife conspired with my brother (and fellow BH builder) Steve to order my first batch of materials. I'm starting with some sheet/plate steel parts for the control systems. I hope to be able to actually do some work as early as next week (trip this weekend) I have a question for you wing builders out there - regarding the installation of the top wing skins: I'm having a hard time picturing in my mind how the top wing skin rivets are installed. (this is under the presumption that the top skin is the last skin installed) I don't see how a rivet gun/bucking bar could be used to install the last skin, since one of the two tools would have to be inside the wing during riveting. Attaching the top skins with blind (pop) rivets seems to be the only way to do it. What am I missing? +++ #2783 Russ Erb Date: Fri Jun 23, 2000 0:02am Subject: [Bearhawk] Forgive me for not starting with the wings, but... Message text written by INTERNET:bearhawk@egroups.com >I have a question for you wing builders out there - regarding the installation of the top wing skins: I'm having a hard time picturing in my mind how the top wing skin rivets are installed. (this is under the presumption that the top skin is the last skin installed) I don't see how a rivet gun/bucking bar could be used to install the last skin, since one of the two tools would have to be inside the wing during riveting. Attaching the top skins with blind (pop) rivets seems to be the only way to do it. What am I missing? < Mike--your assumption is wrong. The way I'm doing my wing (and Pat Fagan did as I understand) is to rivet the top skins on first. The top surface can all be back-riveted using the long Avery set. The top skins are riveted around the bottom of the nose conventionally, sticking your arm and bucking bar through the lightening holes in the wing spar. The bottom skin is riveted on from the main spar to the rear spar, sticking your arm and bucking bar between the skin and rear spar, working your way back. At some point, you'll be able to put your arm through the rear spar. I plan to rivet the top skins on and leave the bottom skin clecoed on while I build the other wing. That way, I'll have better chance of getting in to fix whatever I realize I forgot a few years from now when it's time to assemble everything. +++ #2788 From: Date: Fri Jun 23, 2000 5:58am Subject: Re: [Bearhawk] Forgive me for not starting with the wings, but... After much head scratching with my fellow EAArs, my wife and I riveted our top wing skins on first. We did the bottom of the leading edge first. We clecoed the skin to the bottom of the ribs but left the top loose, allowing the bucker to get up in there and look at what they were doing. Next rivet the top of the nose ribs. You have to work thorugh the lightening holes, but it wasn't too bad. That gives the bucker the best view of what's going on without too much contortion. Next we finished riveting the top skins. This gives you two benefits. First, you can back rivet all the upper surface rivets, giving you the smoothest finish where you want it most, on the top of the wing. Second, you can buck the #4 rivets on the overlaps straight on, rather than reaching around a panel. Next we slipped the large bottom skin in place under the top skin and riveted our way down. You can roll the skin up from the bottom to allow bucking access, though you will eventually have to buck through the lightening holes. This worked quite well for us. Make sure your jig is solid, and keep your taut lines and plumb bobs on throughout the riveting. Skip around on the riveting as that sucker will try to creep on you just like it did on the spars. +++ #2791 From: Bill Cox Date: Fri Jun 23, 2000 5:28pm Subject: Re: [Bearhawk] Forgive me for not starting with the wings, but... Pat, I am getting close to riveting the first wing. I'm curious, did you cleco all the top skins on and work back and forth like the spars or did you do them one skin at a time. The only reason I could see Bob did the bottom skin before the top rear skin was so he he could back drive it for appearance sake. Your method seems more straight forward. +++ #2801 From: Date: Tue Jun 27, 2000 11:46pm Subject: Re: [Bearhawk] Forgive me for not starting with the wings, but... Bob, in answer to you guestion, after riveting the bottoms of all the nose ribs, we clecoed the whole upper skin, all of them. We then skipped around, like on the spars, while doing all the nose ribs, then riveted the top skins to the main spar, then continued our skip riveting on the remainder of the top skins. Congratulations on getting that far. What a thrill it is to complete the first wing. How did I manage to come to welding the fuselage in the middle of summer? Keeping my garage draft free while welding is a marvelous way of shedding a few pounds +++ #2779 From: Mike Eldredge Subject: Forgive me for not starting with the wings, but... Just wanted to share my elation at finally being able to begin working with materials, after holding plans since March. I've been doing tons (literally) of yard work this spring, and have had to put off working on the plane. This has, however, given me time to read my Bingelis homework. For Father's day, my wife conspired with my brother (and fellow BH builder) Steve to order my first batch of materials. I'm starting with some sheet/plate steel parts for the control systems. I hope to be able to actually do some work as early as next week (trip this weekend) I have a question for you wing builders out there - regarding the installation of the top wing skins: I'm having a hard time picturing in my mind how the top wing skin rivets are installed. (this is under the presumption that the top skin is the last skin installed) I don't see how a rivet gun/bucking bar could be used to install the last skin, since one of the two tools would have to be inside the wing during riveting. Attaching the top skins with blind (pop) rivets seems to be the only way to do it. What am I missing? +++ #2783 From: Russ Erb Subject: [Bearhawk] Forgive me for not starting with the wings, but... > I have a question for you wing builders out there - regarding the > installation of the top wing skins: I'm having a hard time picturing in > my mind how the top wing skin rivets are installed. (this is under the > presumption that the top skin is the last skin installed) Mike--your assumption is wrong. The way I'm doing my wing (and Pat Fagan did as I understand) is to rivet the top skins on first. The top surface can all be back-riveted using the long Avery set. The top skins are riveted around the bottom of the nose conventionally, sticking your arm and bucking bar through the lightening holes in the wing spar. The bottom skin is riveted on from the main spar to the rear spar, sticking your arm and bucking bar between the skin and rear spar, working your way back. At some point, you'll be able to put your arm through the rear spar. I plan to rivet the top skins on and leave the bottom skin clecoed on while I build the other wing. That way, I'll have better chance of getting in to fix whatever I realize I forgot a few years from now when it's time to assemble everything. +++ #2788 From: Subject: Re: [Bearhawk] Forgive me for not starting with the wings, but... After much head scratching with my fellow EAArs, my wife and I riveted our top wing skins on first. We did the bottom of the leading edge first. We clecoed the skin to the bottom of the ribs but left the top loose, allowing the bucker to get up in there and look at what they were doing. Next rivet the top of the nose ribs. You have to work thorugh the lightening holes, but it wasn't too bad. That gives the bucker the best view of what's going on without too much contortion. Next we finished riveting the top skins. This gives you two benefits. First, you can back rivet all the upper surface rivets, giving you the smoothest finish where you want it most, on the top of the wing. Second, you can buck the #4 rivets on the overlaps straight on, rather than reaching around a panel. Next we slipped the large bottom skin in place under the top skin and riveted our way down. You can roll the skin up from the bottom to allow bucking access, though you will eventually have to buck through the lightening holes. This worked quite well for us. Make sure your jig is solid, and keep your taut lines and plumb bobs on throughout the riveting. Skip around on the riveting as that sucker will try to creep on you just like it did on the spars. +++ #2791 From: Bill Cox Subject: Re: [Bearhawk] Forgive me for not starting with the wings, but... I am getting close to riveting the first wing. I'm curious, did you cleco all the top skins on and work back and forth like the spars or did you do them one skin at a time. The only reason I could see Bob did the bottom skin before the top rear skin was so he he could back drive it for appearance sake. Your method seems more straight forward. +++ #2801 From: Subject: Re: [Bearhawk] Forgive me for not starting with the wings, but... Bob, in answer to you guestion, after riveting the bottoms of all the nose ribs, we clecoed the whole upper skin, all of them. We then skipped around, like on the spars, while doing all the nose ribs, then riveted the top skins to the main spar, then continued our skip riveting on the remainder of the top skins. Congratulations on getting that far. What a thrill it is to complete the first wing. How did I manage to come to welding the fuselage in the middle of summer? Keeping my garage draft free while welding is a marvelous way of shedding a few pounds +++ #3194 Subject: Fuel Tank Filler Neck, Change 32 From: Russ Erb I can't be accused of changing the design since what I've been doing was not included in the plans. Even so, it can still be a pain... The subject at hand is how to integrate the fuel filler neck on the fuel tank with top skin of the wing. I've been through several iterations and I think I'm converging to (blundering onto?) a solution. I was trying to avoid a big cylinder hangin' in the airstream with a big honkin' cap on top of it, not to mention trying to figure out how to cut the hole for the filler neck in the right place in the top skin. For a long time I have been charging down the path of using a flush filler cap on the tank, building a scupper wall around it with a drain tube, and then using some sort of quick release door on the top skin of the wing. I have now abandoned this idea for one reason: limited space. The tank installed is about 3/8" to 1/2" from the top skin. This is not enough room to install Hartwell latches, because they would strike the tank upon opening. What about quarter-turn fasteners? Maybe, but there is not enough room for Camlocs. Dzus might work, but now you have extra things sticking up in the airstream, especially if you use the wing nut versions instead of the ones that require tools. Do you put it on a hinge (the hinge would probably make another bump where you don't really want it) or make it removable? If it is removable, how do you keep up with it? Then of course there would be the ongoing hassle of trying to explain to the line boy the non-standard procedures to get to your fuel tanks. It all just started to be too hard and too inelegant for me. Of course, I am somewhat limited in my options since I am well into buying and making parts (hard to replace a wing skin that is riveted on just because you don't like the way the hole is cut). I'll skip past the various ideas that I rejected and straight to the one that I think I'm using now. I wanted to keep the tank all aluminum if I could, using composites only for the scupper wall. I need to fill the gap that is about 3/8" to 7/16" to bring the flush fuel cap up under the wing skin. Bob Barrows used a machined part to fill this space, but I was looking for something that didn't require a $400 tool and a $50 block of aluminum to do. A doubler under the wing skin (0.032) will take up part of the space. This is primarily to strengthen around the hole, with the extra benefit of filling part of the space. The welding flange for the fuel cap will take up 1/8" of the space. For the majority of the rest, I used the leftover 1/4x0.049 5052-0 aluminum tube (from the vent tubes) bent into a circle at the diameter of the fuel cap welding flange. This tube will form the spacer and be welded to the tank and to the fuel cap welding flange. All of this should push the cap up to right under the wing skin. Any additional small gaps can be filled in with Super-Fil or micro as required. I think this will work. I won't really know until I can actually start welding pieces together. Added benefit: The fuel caps will be at the surface so I don't have to do a lot of explainin' to the line boy. A perfect seal to the skin is not required, since overflow fuel that gets down around the cap will fall into the scupper and be drained away. If the cap flange was sealed to the wing skin, that seal would have to be broken to remove the tank (if required). +++ #3251 Subject: Bearhawk wing tips From: Shelly For some of you that have or are near finishing your wing skinning, you might want to consider "wing tips". They are a lot easier to fabricate at an easy working level rather than standing on a ladder. I have just finished the tips for my Mountain Goat and the wing is quite similar to the BH. I jotted some notes and sent it to Experimenter for the Sept. issue. I do have photos but am not digitally qualified. +++ #3492 Subject: Re: [Bearhawk] Landing Lights From: Your local NAPA auto store should have the small (4 or 4 1/2 in. dia.) bulbs. I mounted 1 on left out board of strut straight ahead. right wing down 20 degrees out board of the strut. Spring loaded for down in to air stream, release was a pull knob in cabin. Keep them behind the strut so they don't blind you. You have to lock them up during tie down. You also mite prefer 30 degrees down on the right. +++ #3493 Subject: fiberglass wing tips From: Shelly My partner and I wrote a little piece for Experimenter (last issue) on laying up wing tips. If you missed it, I'll be glad to post the article. It's a "Word" document. Maybe Float-by would like it for the FAQ, or Erbman for his CD. +++ #3499 Subject: Re: [Bearhawk] fiberglass wing tips From: Float-By Shooter http://www.netpackrat.com/bhfaq/wingtips.txt +++ #5675 From: "Tim Anderson" Subject: Wing jig mounting I'm on the verge of mounting a wing upright in the jig for skinning. I'm a little confused (easy to do) on the tip rib/post mounting. Do you mount two beefy temporary angles (say 1/8 inch)peices on the tip rib that you hang the rib on, with two angles also bolted on the wood post? Bob's newsletter instruction were somewhat brief. It sounded like he just used several wood screws, through the rib onto wood blocks attached to the post. Any suggestions? Tim #398 +++ #5676 From: Russ and Penny Erb Subject: RE: Wing jig mounting BHCD V2.x shows how I did it. I assembled all of the ribs on the spars using jigs with arms under the spar as shown on BHCD V1. When it was time to put the bottom skins on, I switched to jigs at the end of the wing. One was attached to the main spar at the fuselage attach point, and the other had an arm that went through the lightening hole in the tip rib and up to the spar web. The pictures on BHCD V2 make more sense than these words probably do. Russ Erb +++ #5680 From: pfflyerz@c... Subject: Re: Wing jig mounting I used a couple of metal angles attached to the 4x4 upright with wood blocks screwed to them that the spars could rest on. The spars were then clamped to the wood blocks. This was the best I could come up with at the time, though I didn't have the tip end clamped down as tightly as I thought. It moved around on me somewhat but I did better with the second wing. I would recommend that you hang plumb bobs on each end of the wing throughout the skinning process. Had I done that on the first wing I would have noticed that there was some movement. Put the wings on #232 and built the struts last week. There had been some concern expressed about sqaushing the strut to match the 1.5 inch strut fitting. It was easily done, nothing to be worried about. Of course, if you are still apprehensive about it, there should be no harm in making a fatter fitting. I imagine the only reason Bob didn't use a larger fitting to match the natural size of the strut is due to the cost of a larger bar of 2024. Pat Fagan #232 Pearblossom CA +++ #5755 From: bearhwk272@a... Subject: Wing Skinning Rivet Question -- Fuel Tank Status Question! The wing skin is held on by -3 flush rivets. A -4 flush rivet is indicated at the location of each center rib to main spar. I am assuming that this rivet goes through the skin, spar web and rib. Is this true? If so what sequence did you do the drill, debur, dimple. Do you do the spar to rib with the structure and match the skin at the skinning? Any Comments? Have just completed one fuel tank, less filler neck. Tank is hanging in wing now. MVP I will do a summary writeup on this in a week or so. Am quite pleased with the results. No rivets were used. Kevin Bearhawk 272 +++ #5761 From: Russ and Penny Erb Subject: RE: Wing Skinning Rivet Question -- Fuel Tank Status Yep. -4 rivet at center rib/main spar joint goes through everything. I assume just a little extra strength for where it all comes together. I drilled the hole through all of the parts at the same time I drilled all of the other holes in the skin. It was just another hole through the spar flange. Actually I drilled it #40 initially just like the other holes, then enlarged it later to #30. Dimpled the flange/rib together (since the other rivets were already in). Not a problem with the pneumatic squeezer. Kevin--Send me pictures of your fuel tank process (digital or print) and I'll add them to the CD. Russ Erb +++ #5964 From: "Matt" Subject: Sheet Stock I would like to check with a local supplier to see what the sheet stock would cost me as shipping cost can be prohibative on just a sheet to make up for a mistake. Can someone tell me how much .032 and .025 2024T# I will need for a Bearhawk. Matt +++ #5968 From: "Mark and Tina Lapierre" Subject: Re: Sheet Stock Hi, I just spent $2300.00 on materials for the wings. It's enough to make the wings and to cover the control surfaces with metal. (yes, I ran the metal control surfaces by "the Bob" first). I bought 2024 .025, .032, 4130 plate, the assorted bar stock goods, (6061, 2024, and 4130) and the assorted tubing used inside the wings. I bought everything to make the wings except the rivets, pulleys, fuel tank materials, and misc hardware. I allowed enough for me to screw up a little bit of everything except the 14' lengths of flat goods (they stock the 14' stuff at wicks, Bob put me onto that). I started out thinking I'd get some stuff here and some there, taking advantage of better pricing. I ended up buying it all from Wicks because of the freight costs are too much if it's purchased here and there. My fuselage tubing will come from Dillsburg though. I figure that if I overbought on a few things, I'll use it later on. It'll work out in the end because I'm sure I'll be a far better judge of material requirements than I am now by the end of this project. My invoices from Wicks would make a great list for ordering wing materials, assuming that the list I put together and ordered from was right. It was right enough to get me to part with $2300.00. I'll tell you how good it really was after I build the wings and see what I over/under bought. If anyone's interested I'll scan the invoices and email 'em to you as Tiff files. I'm still working on my tooling, bought a bunch of stuff on ebay, river shaver, 3x rivet gun, pneumatic shears, etc. Bought the Meco Midget torch and a bunch of tips from Kent White. I have a 5' x 20' flat and level table all set up. I'm putting together a monster air compressor now with a 10hp elec. motor and a nice old 2 stage Quincy compressor with unloader valves, on top of a 100gallon propane tank (not a 100lb tank, a 100 gallon tank, aka a "pig"). The compressor, a hydraulic press, and a few odds and ends and it's time to start building. Still looking for a rivet squeezer though. For what those things are bringing on ebay, I can buy a new one. I just might... I haven't opened the crates of metal yet and won't until it's time to do the lay out work, I'm worried that I'll scratch it if I open it too soon. Mark Lapierre #493 +++ #6091 From: Russ and Penny Erb Subject: RE: [Bearhawk] Aluminum wings (was: Fabric and the O to O) The aluminum skin is structural, whereas fabric generally is not. In a fabric covered wing, the spars must carry all of the lift loads and moments around the longitudinal axis (think of a bird's wing flapping). Drag loads are carried by the truss formed by the front and rear spar, compression members (or stronger ribs) and drag/anti-drag wires or struts. Twisting (torsion) moments are reacted by attaching a strut to each spar, hence the two struts. Therefore, the underlying structure of a fabric wing is typically stronger, and thus heavier. There is also the additional drag and weight of a second strut on each side. However, the fabric is lighter than the aluminum skin. I have no idea which construction method would be lighter. Additionally, fabric tends to balloon between the ribs, giving a different airfoil shape. Aluminum wings will maintain their design shape more closely. In an aluminum wing, the upper and lower skins carry some of the bending loads otherwise carried in the spar caps. Instead of drag/antidrag wires, the skins act as large shear panels to resist the drag loads. The skins and spars form two closed sections (between the spars and the D-section of the leading edge) that carry the torsion loads. To see how that works, try to twist an empty coke can. Tough to do. Now make a cut parallel to the long axis from top to bottom, then try to twist it--much easier because it is not a closed section. Because the wing is resistant to torsion, only one strut is needed to carry the lift and moment. While the skin is heavier than the fabric, the underlying structure is lighter. Of course, it is also possible to build plywood skinned wings or composite skinned wings as well, which structurally act similar to the aluminum wing. Any of these methods can produce a light wing if done right, or a heavy wing if designed sub-optimally. When you get down to it, it's more of a decision of which construction method you feel more comfortable with or which method the designer felt more comfortable analyzing, or just what he was used to doing from experience. Russ Erb +++ #6094 From: Budd Davisson Subject: Re: Aluminum wings Russ, Nicely done. I can't add anything of any significance except to point out the outdoor storage factors connected with aluminum aren't as critical, although corrosion is always a concern. As far as the weight thing goes, a fabric wing is generally lighter unless the finish is aimed at totally hiding the weave, then fabic can be slightly heavier, but not enough to worry about. If aluminum has a building advantage it is that there is no glue to worry about and as soon as the wing is skinned it is done. It doesn't need to be painted. If I was building a working airplane or one with a small engine, I'd consider leaving the wings unpainted or maybe polishing them. bd >>> 4sep02 #9154-11297 +++ #9556 From: bearhwk272@... Subject: This skin thing don't suck correct. Read the CD, Archive and Newsletter. The end result of doing the suction thing to the leading edge bend is not to my satisfaction. Have varied the tube up and down from 1.50 with no improvement. 1. The LE skin after bending is at 90 deg with a so so radius fit that takes a gorilla to pull it around the rib. This leaves the skin quite stressed and then humps up between the ribs. Skin is distorted and " Flat " at the nose of the rib where the flange is not present. 2. A slightly tighter R ends up being a R with a couple of flats. Skin is then at about 60 deg angle, wraps ok but then has some flat section hard edges that make it look like it was section bent in a brake. 3. By the time I purchase enough DUCK TAPE ( That's what my roll says ) a fellow could most likely by a 48 in wide sheet metal roll and a brake. Any suggestions ? +++ #9560 From: Russ and Penny Erb Subject: RE: This skin thing don't suck correct. Since you've read the CD, I don't know how much I can add for you. When I did mine, the no-load bend was about 90 degrees. As you can see on the CD, I used racheting tie-down straps to pull it down the rest of the way. Keep the straps near ribs for support. I drilled and clecoed (LOTS of clecos--about one in every hole--that's why I have 700 of the buggers) the top surface first. Everything forward of the spar was done spanwise--i.e. drill all the holes in one panel that are 1.5 inches forward of the spar before proceeding to the holes 3 inches forward. Note the use of the 1x2 (courtesy of a tubing order from Spruce) to push the lower skin down. On the bottom skin, I started with the row closest to the leading edge and worked my way back to the spar. Hence, the skin was "wrapped" from the top of the spar, around the nose, and down to the bottom of the spar. Mine turned out just fine. Either that, or I'm less picky than you, but no one has made any comments upon seeing it to imply that I'm missing something--and my riveting partner is really picky. I don't think you're going to get a permanent bend of more than about 90 degrees because of the spring back in 2024-T3. The metal gets in its own way when trying to do any more. Looking for a weekend trip? You're welcome to come out and see mine for yourself. +++ #9562 From: "Pat Fagan" pfflyerz@c... Subject: Re: This skin thing don't suck correct. Ditto what Russ said. My skin also came out at a 90 degree angle after the bending process. It also took a LOT of force to bend it around the nose ribs, but there weren't any flat spots between ribs. The only duct tape I used was a small piece on each nose rib where there is no flange. This helped keep the scratches down on the inside of the skin while you do all that pulling and yanking to get it in place. I used Bob's inner tube method to pull the skins tight. +++ #9660 From: "Kevin Deutscher" bearhwk272@... Subject: Wing Skinning- Nirvana At Last Just a quick update. Wing skins are now going on #272. After much distress over the stress, a little consultation with others and a modified game plan, I now have leading edge contours that slip on like a glove and have to be sprung slightly to fit. The skin just sticks to the wing, no tensioning required. I have documented what the finished formed shape needs to be and will share this to the archives when I have more experience with it. The process I am still working out to refine It but it goes something like this. 1. Vacuum per the newsletter. To 90 deg. 2. From the centerline of the first forming operation. Clamp the skin to a 1.25 dia bar or tube and roll from the top LE toward the spar so that the skin wraps around the bar about 45 deg. 3. Repeat for the bottom skin surface. 4. By hand take the spar edge of the bottom skin, curl it around to the inside with the edge pulled way up to the leading edge. 5. Now roll up the entire mess till the main spar location of the top skin is tangent to the rolled up coil. Now you have something that looks about like what came coiled from Airparts. 6. Slowly uncoil the "Jack in the box". The bottom skin section will now have to much curve which is removed by flexing backward. 7. AVOID DOING ANYTHING THAT CONCENTRATES THE PUSHING AND ROLLING FORCES, ALWAYS DISTRIBUTE THE FORCE VIA A BOARD OR BAR, TUBE. 8. Have a few friends, it takes 6 hands. 9. Duck tape ALL edges to prevent cuts and scratches. (Both types of skin.) 10. Check to template, hand adjust as needed. Maybe photos later. Moving ahead again finally. :-) +++ #10241 From: "Kevin" bearhwk272@... Subject: Wing Skinners Sequence. Need some info on wing skinning. The false ribs / stiffeners that form the top of the fuel tank bay support, did you fit skins with these parts in place or did you fit skins and then fit in the stiffeners after the skins were in place? +++ #10244 From: Russ and Penny Erb Subject: RE: Wing Skinners Sequence. (b) The skins were clecoed to the skeleton, then the stiffeners were drilled and clecoed in place. Assuming you use the press I gave you, you'll find that the stiffeners aren't bent completely into shape but about 95-98% there (It was close enough that it wasn't worth making a fourth attempt at the press). Drill and cleco one end, then work your way down the stiffener from one end to the other, clecoing every hole as you go. This will pull it up to the skin. Since the skin is convex there, it will have enough stiffness to stay in place as you do this. If you tried to attach the stiffeners to the skin before applying it to the skeleton, they would most likely get very stiff in the wrong shape. DON'T drill and cleco both ends and then try to do the middle. That will most certainly pull everything out of whack, and you know you want your things in whack. +++ #10480 From: "Kevin Deutscher" bearhwk272@a... Subject: Update #272 Just a quick update. Have been busy, finally getting in some good building time this weekend. Never thought I could do what I just did, but I did it!!!!!!! Fit and drilled all the top wing skins on the right wing, 9.5 hours start to finish. Seemed to turn out quite nice. I imagine that all the detail stuff, stiffeners, final edge trim, deburr and dimple will take just a wee bit longer. At last there is MVP. Did the wing / skinning in the horizontal position. Made drill templates that marked all the skins and ribs. Used several " Key " locations picked up from the structure, transfered to the skins over on the drilling table, transfered from the templates to the skins, center punched and drilled skins. When they were placed on the wing----- BINGO THEY FIT! Match drilled to the ribs and spars. Spending the effort bending the skins to fight tight to the rib contour was good because I did not have to deal with " Jack in the Box ". Tool hint. Used a Starrett automatic center punch, No. 18 - A . Fast, consistent, leaves a little dimple distortion that keeps the drill centered, after the hole is drilled the skin is dead flat, pretty neat. ( punched over a wood block ) Maybe I can find a digital camera person near by and post some pictures. >>> 20may03 #11298-18250 +++ #11536 From: Budd Davisson Subject: Re: why dimples? Has anyone besides me ever wondered why we are bothering to flush rivet the entire wing on a 160 mph airplane? It certainly isn't for speed. And AN3 roundheads are hardly noticeable. So..... bd +++ #11537 From: Russ and Penny Erb Subject: RE: Re: why dimples? Uh...so it isn't a 140 mph airplane? Because we enjoy pain? Because RVs do it? And the best reason: "Because we can" I refuse to entertain the notion that it could be done faster, since mine are done...someone else can lose sleep over it... Erbman +++ #11542 From: bearhwk272@a... Subject: Re: Re: why dimples? The dimples are there for the flush rivets. ( Duh! yes I know you know that.) The wing will actually be stiffer and slightly stronger with the flush rivets. The dimples and rivet filling the dimples makes a much stronger shear joint which is what most of the skin to structure sees. ( Again you know that.) The skin to spar rivets and the skin lap joints would all have to be -4 if not flush. Bet the Bob will say better do them flush, stronger and lighter you know ! My guess is that you are just tired of dealing with them pesky little details. I was there just a few weeks ago. After 5 tries to add a rating ( Never got into the air! ), One car crash, near total, a root canal, 75 hr work weeks, new livestock acquisition, house flooded during thunderstorm, all carpet ruined and removed..... I can not wait to get back to flush rivets. Kevin Deutscher +++ #11544 From: Budd Davisson Subject: Re: Re: why dimples? A protruding head AN3 in .025 is good for 210 pounds in single shear A dimpled AN3 in .025 is 235 pounds A protruding AN4 is 357 pounds A dimpled AN4 is 360 pounds Looking at the protruding AN3's in .025, if you tightened up the pitch just enough that it added one rivet in ten you'd have the same joint strength and theoretically less buckling between rivets (advantage so small it couldn't be measured). Of course you'd add probably 10-12 ounces to the entire airplane. In .032 you'd have to add 9 rivets for every 50. The shaft of a protruding AN3 is maxed out at 217 pounds (at .032 it goes from a bearing failure of the sheet to shear failure of the rivet). If you look at the rivet pitch in almost all places on the airplane you'll see it's much closer than needed for a 6 G airload. Just thought you'd like to know. bd +++ #11546 From: Budd Davisson Subject: Re: Re: why dimples? > Budd: Interesting that you have brought this subject up. On the set > of wings we are about to skin we have decided not to flush rivet and > the set I have on order with you can be done likewise. I don't think it's wise not to flush rivet it without checking with Bob. Obviously one of the reasons he dimpled the skins, especially the 032 was to be able to use AN3's rather than 4's. I'm not positive of his motivation for that (I'm going to ask him) but compensations have to be made in a number of areas to make certain the strength is there unless he has already worked that into the rivet pitch, which none of us know for a fact. Your wings are in the jigs now but I don't know if we've dimpled them or not. We're going to dimple them unless Bob says otherwise. bd +++ #11572 From: Budd Davisson Subject: Re: Re: why dimples? Russ is the guy to ask about that. There is the question of allowable strength however. We don't know how closely Bob engineered the rivet spacing. I just talked to him about it and he was against going with protruding rivets strictly because of parasite drag and didn't mention strength. bd +++ #11577 From: "Tim Walker" Subject: Re: why dimples? MIL-HDBK-5H MILITARY HANDBOOK METALLIC MATERIALS AND ELEMENTS FOR AEROSPACE VEHICLE STRUCTURES gives the shear strength of the MS20426AD3 (flush) rivet at a maximum of 217 lbs in 0.025" thickness and thicker (209 lbs for 0.020" and 177 lbs for 0.016"). It gives the shear strength for the MS20470AD3 (round head) in 0.025" and thicker as 217 lbs (with correction factor of 0.970 in 0.020" or 210 lbs and 0.912 in 0.016" or 198 lbs). So no problem there. You might have a bearing strength problem though. In the 0.016" sheet with the protruding head rivets, the handbook doesn't list a bearing strength for #3 rivets in 0.016" sheet. For 0.020" sheet the bearing strength is 192 lbs which is slightly lower than the strength for the flush rivets. For 0.025" sheet the bearing strength is 240 lbs. If you are using 0.025" skins then it should be ok, but if you're using 0.020" skins then there could be a problem. Reference MIL-HDBK-5H pages 8-13,8-13, and 8-17. Tim Walker +++ #11579 From: "Bruce A. Frank" Subject: Re: Re: why dimples? I'd love to see a wing tested to see if non-flush rivets actually created parasitic drag. I was under the impression that at these speeds with a non-laminar flow wing that up to 1/16" protrusion above the wing causes no problems. I am here to learn. What about dimpling to 1/4 cord then protruding head rivets after that? Any difference? Bruce A. Frank +++ #11581 From: "Lee H. Erb" Subject: Rivet heads and Vortex Generators Observations: > From what I have seen on wings of B-17's, I believe the braizer head > rivets lowered the cruise speed. > From what I have heard of the Quickie and other Burt Rutan designs, > they tend to suffer from laminar flow separation. Laminar separation > can be caused by rain, or even dirt. I have heard where grass on the > canards caused laminar separation and prevented generating enough > lift for rotation on takeoff. Vortex generators forcing a transition > to turbulent BL will help in this case but you increase drag some > minute amount. Here I go agin. Russ will probably correct my spelling, grammar, etc. When we did wind tunnel tests on the fuselage of what became the UH-1D, I did a number of boundary layer studies, both mathematical and wind tunnel measurements. With theoretical Reynolds number changes in the boundary layer thickness I was able to show the drag effects of door hinges, rain gutters, antennae, beacons, aft fuselage shapes, etc. (The wind tunnel people thought we could not do it but they were willing to take our money and we did it.) Later we calculated that the first 6 feet of the HueyCobra fuselage (175 mph V max) should be flush riveted to reduce drag. I think that it was at 120 knots where rivet heads on fuselages showed an increase in drag. Rivet heads cause increased drag two ways. First they trip the laminar boundary into turbulent boundary layer. (In civil engineering hydraulics the transition is referred to as the "hydraulic jump" seen in fast flowing streams. Civils want it, Aeros don't. Another story.) The turbulent boundary layer has a higher skin friction drag on smooth skin. The velocity distribution of the turbulent boundary layer is such that it has higher velocity closer to the surface. This higher velocity can then impinge on the protuberances (rivet heads) and cause dynamic pressure drag. Literature will draw laminar boundary layer thinner than turbulent boundary but they don't always show the relative velocity distribution near the surface where there might be a protuberance.. At some distance (or speed) the turbulent boundary layer becomes thick enough that small protuberances such as rivet heads are below the high velocity and thus do not effect drag. Turbulent boundary layers will remain attached flow around curves better than laminar. Turbulent BL will remain attached (below compressibility onset) for an angle change of approximately six degrees. (Now you have my professional secret.) Above that angle the flow tends to separate and then you have buffeting or control ineffectiveness such as loss of aileron control. This also why the 23012 airfoil has a sharp stall due to leading edge separation and the 4412 has a trailing edge separation and a mild stall. Then comes the Flight Test Engineers fix because the shape (including shape due to angle of attack) induced separation. VORTEX GENERATORS. Many of the business jets and airliners have vortex generators ahead of the control surfaces to put energy into the boundary layer to keep the BL attached. This separation in some cases is induced by compressibilty. Russ's Masters Thesis was on the shape of strakes on the F-16 to provide a vortex on the inboard portion of the wing at high angles of attack. The F-18 had problems until they got the correct shape for the fuselage strake. (The T-37 forward fuselage strake was for another problem, and another story). FOR THE BEARHAWK: (1) NO VORTEX GENERATORS !!! (2) Flush rivets on the wings is the best way to go aerodynamically. Trailing edge in front of ailerons, and aileron trailing edges it is okay to use brazier head rivets. (I don't like round heads in the airstream.) Lee (Now I gotta go study for tests in Plant Diseases and Pesticides. You can take a boy out of the country but you can't take the country out of the boy) +++ #11583 From: Russ and Penny Erb Subject: RE: Re: why dimples? By documented data, it took me 17.7 hours to fully dimple one wing. 36 hours out of over 3000 hours is insignificant savings for me. If you don't dimple, you'll feel pretty silly putting any other fairing on the airplane, and you won't be allowed to complain about how you can't stay up with your friends. Bruce--the rivet heads would definitely be above the boundary layer for the first quarter chord at least. Take a good look at a C-130. Flush riveting ahead of the wing trailing edge. Protruding head rivets aft of that. Even so, that's flush rivets for longer than our airplanes. As for vortex generators, I've always considered them a "fix", correcting something that wasn't designed right, or was forced by design compromises. VGs only help when there is separated flow otherwise. The turbulent "attached" boundary layer has less drag than a separated boundary layer, but more drag than a laminar boundary layer. If you put a VG in front of an area that is not already separated, you've made things worse. Also, VGs typically fix problems at low speeds, not high speeds. The stall speed of the Bearhawk is already so slow, that VGs might increase the maximum lift coefficient by a large number, but the reduction in stall speed will be minimal. Quit trying to change the structure and put your effort into choosing your engine, paint scheme, and other stuff that the Bob hasn't done for you. Russ Erb +++ #11585 From: "rodsmith52" Subject: Another reason for Dimples Okay, so what if a fully flush rivited wing only nets you another 1/2 mile an hour or nothing at all. I would do it for appearances alone. The flush rivited Bearhawk wing looks so classy compared with a Cessna wing, or more to the point the Murphy Moose with all those pop rivits sticking up in the air. Can you imagine how an RV would look with protuding rivits? Rod Smith #246 +++ #11586 From: "Chris B. Murray" Subject: The long rivet thread My comment as a part Cherokee owner and BH wannabe: After spending a good part of a winter stripping paint (esp. around the rivets), prepping for paint (esp. around the rivets), masking (do I have to repeat the rivet thing), worrying about paint runs (say it again), and waxing (watch out for the white crud...around the rivets)...I would go to great lengths to flush rivet. Chris Murray, Greater Metropolitan Quincy, CA +++ #11587 From: Bob Romanko Subject: RE: Another reason for Dimples The picture in my mind of an RV without flush rivets just doesn't compute. You know, the one thing no one's really mentioned yet is that it's really tough to get a smiley face with a flush rivet head. I mean, I think it's impossible. Once the skin's dimpled properly, flush riveting looks better because for me at least, it's easier to pound than a round rivet. There just isn't as much to pay attention to. Planter Bob +++ #12732 From: Budd Davisson Subject: Re: [Bearhawk] AviPro Wing Test & newsletter Tomorrow I'll write up a blow by blow of the test and some of the minor mods Bob is going to incorporate. None are necessary but he IS saying that all gas tanks should be right up against the top of the fuel bay with spacers touching the hat sections. When you push on the top of the wing, there should be no more than 1/16" deflection before it hits the tank. I'll explain why tomorrow. bd +++ #12284 From: bearhwk272@a... Subject: Aileron Pocket Covering Method Need some help. Hopefully this question has not been covered before. (No pun intended) On the wing, in the aileron pocket slot, is one piece of material used to span the entire distance, with holes cut out for the aileron hinges? The other option is three pcs setup to allow a gap at the hinge mounts. Two outboard and one long pcs for the center. Did you roll or shape the material or just pull it up with the rivets to the pocket ribs? Kevin +++ #12885 From: Russ and Penny Erb Subject: RE: Aileron Pocket Covering Method Kevin--look on your CD on the Prototype Wing Photos Page 1. You'll see that The Bob used 3 pieces to cover the aileron pocket, and so did I. I bent the edges in a brake (one a little, one a lot). No need to roll into shape. The material is plenty thin to pull up with the rivets. I know because I've done it. I did it right before I drilled all of the rivets out to remove it. Wait to rivet these pieces in place until all of the wing skins are riveted in place. You'll need to stick your hand through the rear spar to buck the last few rivets on the skin, and that's real tough when there's a sheet of aluminum in the way. Russ Erb +++ #16624 From: bearhwk272@a... Subject: Answer On The Wavy Wing Syndrome Well, as promised earlier here is the Root Cause Analysis ( RCA for the WWS ). If you are building from Budds slow, medium or quick build kits you can most likely ignore this. For others pounding and growing our own here is what I found, and fixed along with the root cause. When skinning the wing I found that the skin did not lay flat on the structure and some areas the the skin pulled in at certain locations and did not look the way it should. 1. Forming the ribs on the form block correctly is very important. I am sure that as I got better at the technique I formed the flange further over on the block. The end results is that when the Bob Stick is used to finish forming the flange the corner R is different which results in a slight difference in rib height from rib to rib. Be consistent in your rib forming methodology. 2. Put the "Joggle" in the ribs for the ribs to nest into the spar. 3. Due to slight bending differences in the spar webs to flange, the thickness of my spars varied a little from end to center to end. 4. When riveting the spar assy together the spar was not quite straight from root to tip. One spar was low at the mid splice by about .050. Be sure your spars are held really solid during riveting. Well, how does it stack up. Let's see, worse case. Take skinning top of wing. Spar bow .050 No rib joggle .032 Rib to rib variation at spar .030 Skin overlaps .025 Total .137 Possible at worse location Mid Span Rib to Spar. Little things add up. Did I really have to add shims between the skin and the structure in the area of main rib to spar? YES! Did I need .137 NO! Worse case .050 shim. The shims were about .562 wide and length as required per location. The shim was placed between the skin and the rib flange, complete with holes and dimples. The end results. Each skin section is spanwise very nice with no pull down at the spar to rib junction. I like it, it was worth the effort, about one afternoon, after completion of the RCA. Random visits by project police have failed to detect the presence of shims. They do seem to focus on how straight the skin is. I was really surprised to find what I found because looking at Pat's and Russ's and Bob's Proto 1 and Proto 2 I never detected any sign of what I had. Maybe there are a few shims and that is a best kept secret? Oh well, cats out of the bag now. Back to shooting leading edge skins. Kevin +++ #16631 From: Benton Holzwarth Subject: Shimming skins? (was: Answer On The Wavy Wing Syndrome) > Little things add up. Did I really have to add shims between the > skin and the structure in the area of main rib to spar? YES! Did I > need .137 NO! Worse case .050 shim. Had a thought on this -- As the wing resists twisting, those rivets take some shear load, no? Does moving the skin and underlying structure apart by the thickness of the shim reduce the joint's ability to resist that shear? I'm guessing it's not significant, but thought I'd ask out loud, anyway. Benton +++ #16633 From: "Bruce A. Frank" Subject: Re: Shimming skins? (was: Answer On The Wavy Wing Syndrome) With the number of rivets used and the small percentage that run through a shimmed flange the is no likelihood that such rivets would be over stressed in any flight maneuver where the rest of the wing survives. Years ago in an engineering lab class we did an experiment that might approximate this type of situation. Several different tests were configured but one was three layers of aluminum riveted with a solid 3/16 diameter aluminum rivet. I do not remember the rivet's designation. Tensile pull was put on the top layer and the bottom layer of aluminum with the sandwiched layer just acting as a spacer/shim. Our tensile test machine was a top of the line unit (this was at the University). The aluminum was 2024-T4, .035 thick. I don't remember the poundage at which the rivet sheared or pulled through (many samples were run), but the 3 layer shear took place in < 3% different from the readings when only two sheets were riveted. Many test samples showed no difference between two or three layers. Oh, we were doing this as a practical test to verify what we had calculated. Interestingly enough, virtually all samples exceeded our calculated values. Our testing indicated that a 1/8 rivet would have been closer to our calculated failure numbers...which has nothing to do with this...it was just interesting that we, in the early stages of engineering, didn't have the mathematical acumen to do the calculations precisely enough. This was actually what it was all about, the instructor assigned the exercise and challenged us to figure out how to do the needed calculations. (this was also when computer programing was still done on punch cards..and quality slide rules were a source of pride) Bruce A. Frank +++ #16637 From: Russ and Penny Erb Subject: RE: Answer On The Wavy Wing Syndrome > I was really surprised to find what I found because looking at Pat's > and Russ's and Bob's Proto 1 and Proto 2 I never detected any sign > of what I had. Maybe there are a few shims and that is a best kept > secret ? Kevin! You promised me you wouldn't mention that to anyone! That was to me our secret...SHEESH! Now I've lost my edge in the Bearhawk judging competition... Actually, I didn't do anything special to avoid any such problems, other than forming parts as precisely as I could. All of my ribs were formed consistently, because I would do the same operation on all of them before moving to the next operation. That is, all of the ribs were flanged before any of them got lightening holes. I was actually surprised how consistent my ribs turned out. Glad to hear you're finally riveting the skins on. I'm getting tired of waiting for you to start on the fuselage...8^) Russ Erb +++ $Id: 2.1.3-Wing-Skin,v 1.11 2003/05/21 14:57:42 bentonh Exp $