Light wing build

qsmx440 said:

Thanks for the response Andrew. What you are saying is that the top and bottom of the "cutouts" (actually the original Piper ribs are not cut out as the spar attach points are just vertical angle pieces attached to the ribs) are clear of the spar caps by how far? In my stamped ribs (new but made in the 70's) I didn't receive any "clips" to join them together and the flanges have no predrilled mounting holes for the PK screws so I'm having to work out the mounting holes as to centering the spars, or 7/16 up from the bottom, or maybe 1/2" up from the bottom to provide a small amount of clearance to the spar cap (bottom of spar) or maybe some other distance? Hopefully someone will read this and figure out what I'm trying to ask. The answer probably lies in following the drilling directions for the spar and also the drilling directions for the rib mounting angles (transferring those dimensions to the built in flanges on my stamped ribs) and then screwing the rib to the spar in the pre drilled holes.

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qsm,

On the original Piper ribs, the top and bottom of the "cutouts" are the cap strip which is continuous from the trailing edge on the bottom to the trailing edge on the top if no repairs have been carried out to the rib. The vertical angles rivet to the upper and lower cap strips. The clearance is of the order that Gordon mentions, but might be even less.

Really your ribs need to be equi-spaced above and below the spar. If you are using a vendor made leading edge (or even if you're making your own) the flanges are the same length and should sit on the top and bottom "spar cap flanges" equally. At the rear spar, you don't want your fabric touching the spar or even close.

I feel I'm getting into too much detail, but you need to figure out where they are going to be (we can't do that for you) and make a jig to hold the ribs in the correct location on the spar and then drill them off to the spar; eyeball or mark all your edge distances and get the holes in the spar in the correct place, or make a jig to drill the ribs on the bench so they are all the same and also probably a jig for the spar, and then assemble and screw like they were new parts from Univair or DCA.

I hope that helps some,
Andrew.

I have a set of "old" spar pieces 1' long I am using in checking alignment on these. Andrew I just set the front and rear spars centered in the rib cutouts. When I do that the spar bottoms are slightly offset in "plane". and I know that's not right since they should set level on saw horses (washout not counted) even though it's only 3/16 difference or so. I am sure the spar bottoms should both rest in the same plane. The front spar top must have 3/16 more clearance to the rib top than the rear spar?? I appreciate everyone trying to decipher my question but I think I'm not being clear. I guess I will go back to the Piper rib diagram and try to figure it out. I must have missed something. Your comments about the leading edge gave me an idea of another way I can answer my question and that is to look at the height of the leading edge above the spar cap top and that is where the front spar would set in relation to the rib. I'm not drilling any holes until I settle this. Last resort will be to order a univair rib and settle the question once and for all. PS my light wing build is turning heavy with all these clips! Thanks again all.

qsmx440 said:

I have a set of "old" spar pieces 1' long I am using in checking alignment on these. Andrew I just set the front and rear spars centered in the rib cutouts. When I do that the spar bottoms are slightly offset in "plane". and I know that's not right since they should set level on saw horses (washout not counted) even though it's only 3/16 difference or so. I am sure the spar bottoms should both rest in the same plane. The front spar top must have 3/16 more clearance to the rib top than the rear spar?? I appreciate everyone trying to decipher my question but I think I'm not being clear. I guess I will go back to the Piper rib diagram and try to figure it out. I must have missed something. Your comments about the leading edge gave me an idea of another way I can answer my question and that is to look at the height of the leading edge above the spar cap top and that is where the front spar would set in relation to the rib. I'm not drilling any holes until I settle this. Last resort will be to order a univair rib and settle the question once and for all. PS my light wing build is turning heavy with all these clips! Thanks again all.

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Are you sure the bottoms of the spars are in the same plane?

Andrew just reread your post. The front has to be centered since the leading edge flanges are equal top and bottom, the back must be centered too just like you said. My test setup shows them off 1/8" or so. I'm beginning to suspect my test setup. I'll tackle it again tomorrow as this is taxing my old brain!

I thought I bring this thread back to life, since I continue to do some research on moving forward for my build to begin.


I came across this interesting post on at the EAA site:

The Ritz method is pretty good and lighter in wood. Jerry used three laminations of wood glued up on an upper airfoil curved surface. He then chordwise band sawed to generate upper cap strip width to generate upper cap strips and milled a chordwise slot in the under surface of the cap strip. Since it is also a flat bottom airfoil the lower cap strips were simply square cross sections of solid wood with a similar chordwise inner slot. Plywood forms closed the cap strips lead and trail by gluing them in the saw slots in the cap strips. This was done in a nail jig. While the assembly was in the jig, Wood strips milled to the slot width were used to add diagonal bracing and verticles to attach to the spars. Aileron ribs were trimmed off of the full rib assembly. This produces very inexpensive and light ribs with very little waste. Fabric can be glued or stitched to these ribs

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To read the thread click HERE
I though it was interesting that someone has compared three different methods to get lighter wood ribs.

So the question is, is there any publications or article that someone can point me to in order to read about this method and how I can learn to use it?
I have searched high and low for the Gerry Ritz method, but I can´t seem to find any references (pictorially speaking) on how to accomplish this.
Further description of the Ritz´s method is mention in the following manner:

FROM EAA Loehle utilized Gerry Ritz’s structure-in-the-slot method to make it easy to align parts. The uprights, longerons, and other primary members have a single or double groove cut in them to allow the standard gussets to slide in to form a perfect 90-degree angle cluster. This allows a dry run of sections of the aircraft so the builder can envision what is supposed to happen before the finality of applying epoxy. Also utilized in certain areas is a lightweight geodetic construction method that reduces weight yet maintains rigidity from the bridgelike crisscross technique.

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So not only can it help in lighter wood Ribs, but it also appears that it could help in the overall build process.

Thanks,

The geodetric or "latice" construction is what fisher flying products use on all of thier aircraft construction. I'm recovering a fisher super koala and the wings probably weigh 30-35 lbs. Incredibly light and rigid.

Super11XP said:

The geodetric or "latice" construction is what fisher flying products use on all of thier aircraft construction. I'm recovering a fisher super koala and the wings probably weigh 30-35 lbs. Incredibly light and rigid.

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Hi Clint,

Do you have any pictures?

I came across this searching a bit, but I am not sure this would be the right design since this rib does not seem rigid enough to provide for torsion control of the spars.

I came across a fellow that was trying to build something similar for a box spar (Fokker DR) but it did not pass the static load test that where made.

The rib in your picture looks exactly like the fisher rib. I think that they have lots of pics on thier website on how they do thier wings. Actually the wings are very rigid torsionally, more so than a cub wing I would say.
It looks like quite a bit of work to build a wing this way, as the parts count is high. pm me if you want me to e-mail some pics, I can't get them to resize for this forum, or I would post some.

Threw in the towel!

I have been working with my "odd-ball" three piece ribs for 3 months trying to figure out a way to use them but I finally gave up today and made the "I give up" call to Dakota Cub and ordered 20 of their fine PMA'd ribs.
I made "clips" and I think I have them down pretty good but to make up for my lack of engineering skill I needed to so overbuild them to the point that the ribs became overly heavy and cost of ribs % to total cost of project finally won out. I reminded myself of my sailing days and how some folks chose to build ferro cement hulls and how those boats generally had values of 20 cents on the dollar compared to fibre glass hulsl and that the actual cost of the hull was generally only 10% of the build. I will use 4 of my stamped ribs (1 on each side of the gas tank). Dakota ribs will be used in #2 (under fuel tanks),#4 thru #12 with # 13 being the small Piper tip ribs I bought at a garage sale.
Still I am a little disappointed since I had a "plan" and now it's changed. I will use the in between stamped nose ribs, the four stamped tank ends ribs and the aileron and flap "in between" false spar ribs and then when it's done ebay off the rest.
One other thing I didn't like about these and that didn't sit well with me was that I had to use a 3/32 spacer under the mounting flanges at each end of the center ribs as they are 3/16 to short to make the spars 31" on center.
I wonder if I can count the 100 or so frustrating lost hours? It's a rhetorical question since of course I can't under the new rules. :sad:

qsmx440 said:

Still I am a little disappointed since I had a "plan" and now it's changed. I will use the in between stamped nose ribs, the four stamped tank ends ribs and the aileron and flap "in between" false spar ribs and then when it's done ebay off the rest.

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Make sure the profiles are the same between the different rib types. The leading edge skins can be murder to get tight if they're not.

docstory said:

Make sure the profiles are the same between the different rib types. The leading edge skins can be murder to get tight if they're not.

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Yes that is a good idea and I will do that. I may have to order 4 ribs more.? Oh yeah, and all the little ones would also be off.

docstory said:

Make sure the profiles are the same between the different rib types. The leading edge skins can be murder to get tight if they're not.

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oh YEAH!!! they can be a 1/4" different size/shape up front!!!!!
takes lots of silicone caulk to firm up to be kinda the same before screwing to the ribs...

When you are going to do the leading edge install, PM Steve Pierce and "rent" his leading edge clamps. They make the LE install a snap.

tcraft I don't have a time line at the moment. Basically the ribs stopped me though and 3 months futzin, making prototype parts, studying 4313 and other design books, cleco-ing stuff together a zillion times, forgetting what I had already learned, going over the same ground etc. and not finding anyway to make them "light" and meet my requirments to trust them, I just decided it was time to move on. Besides I really wanted Dakota ribs all along (just like I really wanted a Carbon Cub all along) so the time ran out in my head on the "rib" section. Suddenly they weren't "fun" anymore. Early in this thread a lot of knowledgeable posters advised to ditch these ribs I have and that has weighed a little on me all along.
This whole thing is a nice distraction for me and even these things have allowed me to learn a lot. BUT who knows. If it stretches to five or six years, I'm not getting any younger and my parents who are 89 years old are in no condition to fly and haven't been since they turned 80. I may go Carbon Cub yet at some point in the future and my project will end up in the classifieds or ebay. There are time limits or budgets on these things and fun as building is (and it is way more fun than I thought) there is the time budget of life also and I would prefer not to end up an old man just talking about "my project" with no hope of finishing it.

So I'm finally building my compression struts and of course chose the "windmill" method:
http://www.supercub.org/forum/showt...-Rivet-Spec&highlight=compression+strut+rivet
Anyway if there are other Don Quixote's out there I have a system for at least part of it. The problem appears on drawing 14222 (see http://www.supercubproject.com drawings section). Attaching the "feet" to the tube requires either using 3/16 bolts and nuts, 3/16 rivets, or Cherry Rivets. The original Piper struts used 3/16 Rivets and that is what I wished to use. The rivets are about 1 1/8" long and after passing through the foot, then through both sides of the tube and coming out on the other side of the foot there is a 3/4" unsupported area in the center of the tube (on the inner most rivet. Not the one that goes through the "slug"). Normal driving winds up looking like this:


That didn't work very good. AC 43.13 section 4-58-a talks about splicing hollow tubes with rivets that are unsupported in their center section and outlines the problem and how to solve it. Somewhere I read about "peening" as the riveting technique to use in this situation but I have searched high and low and have not found a technique listed. 43.13 is silent on this. The diagram seems to indicate a shorter "driven area" than normal would be acceptable (ie not the usual 1 1/2 d for the rivet "stick through). These rivets are only in shear so they only have to retain their position as far as I can tell so the normal head isn't really needed. Soooo after destroying 4-5 rivets and some scrap tubing this is what I came up with:

I took 2 pieces of 3/4 X 1/4" mild steel, clamped them together in a vise, in between them I center drilled, then finished drilled to 3/16 a hole in between them. I milled .025 off of the back side of both (could be done on the sander but I love my mill) and relieved all the corners on a belt sander. Putting them together inside the tube, lining the hole up with the foot and tube holes, stuffing the edges with shims and C-clamping the outside (picture below shows shims and how the inside setup would look):

And the end product looked like this:

after I used my rivet gun (actually a cheap Harbor Freight air hammer) with a proper rivet set on the driven side with the factory head sitting in a curved rivet set on the off side. Gentle hammering seemed to work good.
I think the "peening" operation must mean hammering on the non factory end instead of the normal way of hammering on the factory end of the rivet with the unformed end against a bucking bar.
For the other Don Q's out there the rivets weigh .06 oz/ea times 46 per plane (including "N" strut) which = 2.76 oz. A set of bolts and nuts not counting washers weighs (bolt and nut total each) .26 oz each times 46 per aircraft = 11.96 which means the rivets save a little over a half pound or a 1/12 more gallon of fuel I get to carry for the rest of my life.
I have not done any "for real parts" yet as all of them need deburring and polishing but I am ready to go into production next week. I thought I would throw this out there for comments on my tool and technique before committing to the real thing.
As an aside I'm trying to develop a "kit" of tools and example parts to pass on when I am done. It was started when tcraft sent me some short pieces (strut and root areas about a foot long) of spars and other wing parts to use as examples and fixtures. I have added to this with some PMA'd parts I bought as examples from Dakota. They have been invaluable to someone who does not know what I'm doing on most of this.
The plan is supercub.org members could borrow these kits for their build. The problem is there would need to be several since most will keep them for a year or more during construction.
One group of parts I gave up on was the 6-40 drag wire nipples. I made a bunch of them but just didn't trust my inside radius to not be a stress point and rather than starting over I just ordered the whole set from Dakota to go with my beautiful new set of ribs also from them. This is a huge advantage to building to the Piper spec instead of some other design. If you get frustrated or sick of working on a part, just call one of the suppliers and get instant gratification and bury your mistakes!
I'm only going to use the ribs mentioned earlier on either side of the tank as after three months of trying to "hook" them together they just grew to heavy as others tried to tell me earlier. It is so gratifying to look in the Dakota box!

You could make a collar that slides over the fingers and up to, or close to, the rivet. Then it wouldn't need to be clamped on the tube and be a snap to set up and release.

doc I don't understand your description? Please try again. Whatever system it needs to support the rivet center all around. The moment it gets out of "column" it kinks. If any side was unsupported it would go that direction and give. I don't actually have to clamp it on the outside. The one I show that is good held ok without the C clamp. I just figure on using the clamp for insurance against the tube sides getting puckered. I haven't tried an "insert" yet but it is supported better with less center exposed area. I'll do one in my scrap piece before committing.

2 pop rivets......

docstory said:

View attachment 10209

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I like that but not to replace my tool for the inside rivet but for the one going through the insert. Using your idea but making the sleeve threaded to fit the insert threads I could get at least some center support on the outer rivet in the middle of it. I lightened my inserts with a 1/2" drill on the backside so the rivet still is 1/2" unsupported.

Mike is encouraging me to "cheat". I think I'll do an outline of his Don Q. cartoon on the rudder!

qsmx440 said:

Mike is encouraging me to "cheat". I think I'll do an outline of his Don Q. cartoon on the rudder!

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not cheating.. just what purpose does that SOFT rivet serve, in that PAPER thin square tube????... it's old tech... we have pop rivets now...

mike mcs repair said:

not cheating.. just what purpose does that SOFT rivet serve, in that PAPER thin square tube????... it's old tech... we have pop rivets now...

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Correctamundo!

qsmx440 said:

I like that but not to replace my tool for the inside rivet but for the one going through the insert. Using your idea but making the sleeve threaded to fit the insert threads I could get at least some center support on the outer rivet in the middle of it. I lightened my inserts with a 1/2" drill on the backside so the rivet still is 1/2" unsupported.

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Making the sleeve threaded might be one level too complex. I doubt the sleeve would damage the threads if it were made to slip in with minimal clearance.

I thought the square tubing was pretty thick and it used hard rivets.

Steve Pierce said:

I thought the square tubing was pretty thick and it used hard rivets.

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MS20470AD. 30,000# shear 2117T material. Tubing wall thickness .040
Like Mike said "paper thin" They sure don't look like much to hold the spars apart or parallel vertically. These are turning out light though.

Hi, I hope this is still the light wing build thread.... I was wondering if anyone has ponder the idea of making the compression strut out of CF? :roll:

Spaincub that seems like a really good idea on the face of it. One thing that would concern me when using CF or even heavier walled metal parts in a wing is could you be introducing stress points the original designers didn't want. Is everything designed to bend and flex together with each part designed to do it's share of flexing in heavy turbulence? If one part winds up to stiff then another part has to flex more? I once flew through something that made my Cessna 172 fuselage "oil can". That was not a pretty sound! Smashed an expensive camera on the ceiling at the same time. Planes need to bend and not break. BUT CF struts would allow an encapsulated nut and a bonded foot on each end probably cutting the overall weight in half at least. My completed 14222 compression struts (the main ones with a foot on each end) using standard rivets and my own billet inserts weigh 8.68 oz. each. I have one that is using Dakota inserts and with I will have to assemble it with bolts and that one comes in at 11 oz. I ordered all my tubes precut from Dakota (beautiful by the way and perfectly cut) but one replacement they sent had the inserts already in it and they are "stuck" in the tube so I can't really see what the difference between theirs and mine is. They may be glued in somehow? I'll just use them as is. I didn't "lighten" my inserts as much as the Piper original cast ones so another ounce or two could probably be shaved using originals.

Good point qsmx440, but aren´t compression struts just that? They are there to stiffen spars agains drag and transferring load between the spars. How is CF differ in stiffness from steel if the modulus of elasticity of these two materials are far superior than a wood spar, as an example?

Cool, I did now know that you could get parts like that from Dakota...

I think you can get most everything from Dakota AND they have superior customer service from my dealings with them. You know how it is with these builds. You order something , it comes in, you glance at it and then stash it. I had a couple of items that I did that with that were received 1-2 years ago. When I needed them I found two defective parts. They sent the replacements - no problem and with a thank you to boot. Not inspecting parts when they arrive is really the customers responsibility and I didn't expect replacements but they did it anyway. That's the extra mile that makes it difficult to go anywhere else. I have had good service from all of the suppliers that advertise on sc.org so I think we are quite lucky in this hobby. It makes it fun to deal with great vendors!

Spaincub as to the CF question I posed, I did that because in this aircraft building business I am still a newbie and in no way an aeronautical engineer. Gut feeling tells me stiffer is better but I am shooting for a light aircraft and as such it will be sensitive to shock loads (breaks before it stalls) and so I asked the questions about stiffness. I don't know the answer or even have a clue how to find out. A thought experiment tells me if I had a "perfectly" stiff wing then I would really need to beef up the wing attach points and structure on the fuselage. Flex allows the shock loads to be spread over time while perfect stiffness means all of the load on one point in an instant. I do know if I stick to original materials and build specs I shouldn't get in trouble based on historical reliability.

Wing attach sizing is done for the flight envelop of the plane x1.5 safety factor. Anything as you described will put you out of the air regardless and the wing is sized in accordance to the weight of the plane as per FAR 23 for light aviation so that you don´t have to worry about falling out of the sky because you lost a wing... at least that´s the oversimplified theory.