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Carbon Fiber Tapered RV Wings


Well Known Member
If you peek once in a while on the HP-24 project page, you have seen us laying up composite skins for new tapered wings for my RV-8 and Bob Mills Rocket-6.

We've now started making spars. The taper is evident in the pictures.


Stand by, trying to get pictures right side up....

These are conventional aluminum spars, very similar in concept to Van's RV-7/8 spar. Although, of course, the thickness change along the span, rivet spacing, etc. is tailored to the new wings. For the Rocket-6, the spar extends into the fuselage the same way it does on a standard RV-6. The skins bond to the spar along the wide flanges, using a Boeing-certified treatment+primer process and using high strength structural adhesive. (if you are curious, it is AC-130 sol-gel, BR-6747 primer, and Hysol 9360 adhesive.

Of the various designs for transitioning from conventional aluminum structure to composite construction, this was the lightest and highest-confidence concept I came up with.

By this time next year, I hope to be doing static load testing on the first pair of wings.
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Tapered wings

Awesome!!!!..........can you share any basic design goals? Have a link to the HP-24 page?
Good stuff

Thanks for sharing Steve, very exciting to hear about this endeavor!
Is this new wing designed to turn your speedster RV-8 into a soaring machine or are you designing a better wing? Are you planning on designing a more "robust" vertical/horizontal attach point also? Maybe something that offers a tad bit more margin? If so, I'm even more interested. 😄
RV-8 Motorglider ???


I've looked and sketched the RV-8 as a motorglider. Looked at preliminary stability and control and with minor changes, didn't see any serious problems.

I really hope this is what you are doing! I'm also an aeronautical engineer, and always dreaming. (But getting too old to start a project of this magnitude)

Roger Bloomfield
RV-8 and RV-9A
Hmm... Tapered wing designed for a Rocket Six should fit on a standard -6 too, shouldn't it? :)
design goals and specs

I appreciate the interest on the wings.

The basic design goal is to improve cross-country performance without sacrificing access to short fields, and maintain as much as possible the sporty handling.

With the cross country wingtips, wing span will be 25'4" Aspect ratio about 6.4.
Wing area just under 100 sq ft, with a mild laminar flow airfoil.

With the short tips, span will be 24', wing area 96 sq ft, same aerobatic weight, same or better sustained roll rate.

A slotted flap covers 6 ft of each wing, so the hope is that the approach and landing speeds will be the same, despite the reduced wing area.

One challenge in getting a laminar flow airfoil fitted to an existing airplane is that the spar wants to be farther aft in the wing, so that means that the wing needs to shift forward some with respect to the fuselage. Its a pretty mild, conservative airfoil, max thickness at 40% chord. Spar is at 35% chord. It worked out that the 25% MAC point moved forward 1.25 inches.

For the RV-8, this is no problem, since -8's tend to be slightly nose heavy. I will probably move my battery to the front, but don't expect much else to change. For the Rocket-6, this shift is a really good thing, with the IO-540 on the front, it is rather nose heavy too, and shifting the wing is all to the good.
In principle, the -8 wing would fit on a -7, and the Rocket-6 wing would fit on a standard 6. But both those designs tend to have the c.g. a bit aft to begin with, and shifting the wing forward is going to be a challenge. For a new-construction airplane, there are lots of things one could do, like use the O-320 motor mount with the O-360, shifting the engine forward a bit. For a retro-fit, it would probably mean a new engine mount and new cowl. Putting a Hartzell prop on the nose will obviously help.

One poster asked about ribs. Those come next. They are carbon-foam sandwich, with a solid fiberglass strip that allows through-bolting to aluminum angles attached to the spar.

Thanks for the interest, we'll post updates periodically. Once we see how well they work, we might consider pulling hard tooling off the wings and making more. But for now, we are just committed to two sets.

Oh, and someone asked about a link to the HP-24 project....Bob uses Facebook, so the old website is pretty much not maintained. But he keeps the Facebook page up to date. Just go to Facebook and search for HP-24 Sailplane Project
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Wet wing

Are you using a wet wing like Lancair does?

Yes. Although with the aluminum spar, that means there is an extra web that forms the aft tank close-out. Also we use a web as a forward tank close-out so the fuel does not go right to the leading edge. I felt it might be too difficult to get a complete seal on the leading edge closure, and I wanted a little bit of buffer so if you ding the leading edge, you don't make a leak.
Are you fastening the skins to the spars as well as bonding? Fiberglass or carbon fiber skins? You don?t have any CTE concerns with bonding aluminum to composite over that length? Why not fabricate composite spars?
I don't presume to speak for Steve, but so far as I know:

Are you fastening the skins to the spars as well as bonding?

The bonding is the fastening. So far as I know, Steve does not plan any discrete fasteners such as screws.

...Fiberglass or carbon fiber skins?

Carbon, carbon carbon!

...You don’t have any CTE concerns with bonding aluminum to composite over that length?

What is CTE?

Edit Add: Ah, thermal coefficient of expansion. Yes, Steve considered that, and factored it into the lamination schedules for the wing skins. The fiber orientations in the areas where the spars bond on are such that the spar and skin stiffnesses are matched well enough that the thermal stresses anticipated are well within the capacity of the Hysol structural adhesive we'll use.

...Why not fabricate composite spars?

Believe me, we've gone back and forward over this issue dozens of times. Here's the Cliff's Notes version:

In a word, productization.

If it were up to me I would have gone with a carbon pultrusion based spar like I use in my gliders. It would be one piece tip-to-tip, and I'd be taking a sawzall to the belly of your RV to get the spar to go across your fuselage. But as much as I like chopping up airplanes with power tools, sanity has prevailed.

The spar design that Steve arrived at is probably the best compromise that lets our wings bolt right on to existing RV-8, RV-6, and similar airframes. So somewhere down the road you could buy them, bolt them on, do the wiring and plumbing (that you think is a day's worth but takes a month), paint, and fly.

At issue is that carbon fiber, particularly the very strong unidirectional carbon products we use for wing spars, does not play well with the kind of concentrated loads that prevail where an RV wing bolts onto the fuselage. You can't extract all of the tensile or compressive loads out of the spar caps with the kind of bolted joint the RVs use. With composites like carbon spar, it is much more effective to have wing spars that overlap over a distance of two feet or so, to give you a greater distance over which to react the stresses from one spar cap into the other one. Or, better yet, just use a one-piece spar as I propose above, with a slot in the belly for vertical installation. But the overlapping spars would require a slot in the fuselage that is wider fore-aft than the standard x04 bulkhead, and of course the one piece spar gets into that sawzall territory. Both of those schemes require more airframe modification, and offer less possibility of reversion, than we thought most potential customers would be interested in.

I did propose a couple of design schemes that would have interfaced the airplane's side-of-body wing mount to a two-foot-long aluminum stub spar that in turn interfaces with a carbon fiber spar inside the wing. But when the dust settles, the mass and parts count for that scheme is not much better than the aluminum spars we decided to go with.

Thanks, Bob K.
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I am guessing he is talking about coefficient of expansion for the alum vs carbon joint.

Also, how are you addressing the electrolysis issue ? I have always heard that alum and carbon do not play well together in the long run.
insulate the carbon

I am guessing he is talking about coefficient of expansion for the alum vs carbon joint.

Also, how are you addressing the electrolysis issue ? I have always heard that alum and carbon do not play well together in the long run.

Yes, Mike is right. As a kid I made a very light, stiff spinnaker pole for a sailboat by spiral wrapping some old unidirectional carbon tapes around an aluminum tube. Worked great for awhile, until I accidently dropped it in the bay. A few weeks later, it looked like an exploded circus cigar.

So, the solution is insulation. We put a fiberglass tape down where the bond line is, and then of course there is the bond line itself of the structural epoxy.
I haven't been hanging around here much lately, but I'm glad to learn about this project

A few years ago another member and I were talking about how cool it would be to have an "upgraded" set of wings available. Get your RV flying with the standard wings, and after a few hundred hours of flying it (and missing the building process), you could order up a new wing kit that offered a higher cruise, lower stall and increased roll rate. You could then sell your completed standard wings to a builder that would normally be interested in the QB wing option. Sounds good to me!;)
Thermal expansion

Are you fastening the skins to the spars as well as bonding? Fiberglass or carbon fiber skins? You don?t have any CTE concerns with bonding aluminum to composite over that length? Why not fabricate composite spars?

The carbon skin is all +/- 45 degree bias cloth. So it has very low modulus, and somewhat higher thermal expansion coefficient. So as the aluminum spar grows or shrinks with temperature change, the skin kind of gets dragged along with it. A temperature change of 75F from assembly temperature uses about a 1/3 of the available bond strength.

Elastic strain at the yield strength of the aluminum spar uses about 1/10 of the available bond strength.
I haven't been hanging around here much lately, but I'm glad to learn about this project

A few years ago another member and I were talking about how cool it would be to have an "upgraded" set of wings available. Get your RV flying with the standard wings, and after a few hundred hours of flying it (and missing the building process), you could order up a new wing kit that offered a higher cruise, lower stall and increased roll rate. You could then sell your completed standard wings to a builder that would normally be interested in the QB wing option. Sounds good to me!;)

This is pretty much the idea. Although it is a tall order to have all those things.
We decided to try to keep the roll rate about the same, try to keep the stall speed as close as possible, and take what we could get in cruise improvement.

The retrofit desire does put pretty severe constraints on the design. You would not want to have to move your F-x04 bulkhead for example. And really, if you can tolerate a high landing speed in exchange for the cruise speed, go get a Lancair or Glasair. But I didn't want a 82 sq ft wing.
Yes, CTE = Coefficient of Thermal Expansion. Might want to think about a couple of chicken fasteners at the root and tip to prevent peel, once it starts it unzips real quick.
Well as the fabrication apprentice and future test meat servo, I'll just say what a privilege it is to be in this project with Steve and Bob. The education and experience has been extraordinary! High-end scratch building (I reckon this is what you might call this) is gratifying work, and we're having fun too! Definitely stretching my knowledge and skills! Here are a few pics of some of the early stages:

CNC-cut foam mold assembly in the Bay Area

Bagging the mold to the working table

First mold out of the bag. Aluminum and mylar substrate was epoxied to the foam when bagged

Molds moved up to Bob's HP-24 shop in Arnold. One mold is bonded to each side of the metal table, and can be flipped on the wood table

Our rack of materials

Bob applying gelcoat, pre-layup

Foam core prep, edges beveled on a table sander

First carbon layup

Foam core layup

First skin bagged

More pics in next post...

As skins come out of the mold, we had to start making cradles to store them, as the spar and rib work takes place. We used the mold plugs to layup some glass cradles...and got the kids involved in this part

Trimming raw edges from the skin as it came out of the mold. Final cuts well down the road

Steve inspecting the first of 8 skins


Meanwhile, back at the home drome, spar parts box ready to unpack

Unpacked and ready to prep, measure, mark, drill, debur and assemble, then rivet...piece o cake, right?! ;) Good look at the sheer web and sheer doubler on the right, and the spar cap parts on the left

The hole layout and drilling schedule for spar assembly

I'm on layout and marking, but on hold as we reconsider a design alternative. Looking at pros and cons of moving to Bob K's concept of Al spar stubs that insert into my fuselage, and mate to carbon spars outside the fuselage. One thing I've been really pleased with is the collaborative effort and "best solution" approach. Steve's design foundation has been strength and safety...as well as performance!

As a teaser, here is the original drawing that Steve made when we began discussions on the project...

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Nice work there Bob. I was imagining a slick wing like the 787 - - just like your picture!

Hey, all is pretty much hand made, but that CNC foam mold core looked special!

Do ya'll do that "in house" or get it outsourced?

Keep the progress reports coming, it is great to see something besides the same standard rivets all the time.
You guys form a dream team, for sure. This is one of those rare times when I really wish I lived on the West Coast. I would cheerfully become your slave ;)

Could you expand a bit on the mold-making process? Looks like you started by bonding an aluminum skin to both sides of a 2" pink foam board, which probably yields a very stiff panel?

Then you bonded a CNC'ed foam mold to that sandwich panel, upper skin mold on one side and lower skin mold on the other?

During that same session, you bonded an aluminum and mylar finished mold surface to the foam mold? Aluminum thickness? What sort of mylar? You can bond mylar?

What is the purpose of the aluminum edge rails?

Then you repeated the process to build molds for the other wing?

Details, please?
Fascinating captain. A world and a half away from the wooden makeover I'm doing now. Do I dare ask what your cost estimates are (not counting infinite labor)?
Dan, I've got some left-over Mylar drafting film that has a drawing surface on once side and is plain on the other. I've bonded the drawing surface to aluminum successfully with Pliobond. They've lasted more than 20 years on my Cessna, for about a dozen minor gap covers.

Probably not what you're hoping to learn, though.

This project is very interesting. I prefer working with composites to aluminum and chose an RV-3B project (wings nearly ready for close-out) with the idea that I might, at some point after the plane was done, build longer tapered composite wings. While that was mostly a mental bit of appeasement, I've been fascinated to learn how experts do it - keep this thread current! - and many of the choices you've made are things that I've at least thought about.

Please keep it coming.

Great photos on the mold and the lay-up.

I have a couple of technical questions:

How long do you wait between spraying the gelcoat layer and applying the cloth on top of it?

How much resin gets soaked-up by the foam? Does it get saturated?

Keep the photos coming.

I love this thread! I've considered doing a similar conversion for a constant-chord wing airframe (though it is strut-braced). I'm intrigued by the pultruded spars, have to learn more about that.

If you convert to the aluminum stub spars, how would you make the tapered carbon spars? Any thoughts on CNC-cut plate for the web and bonded caps? Finding the lengths required would be challenging.

Dan covered my questions about the mold. When I've done similar work I had access to more $$$ and more infrastructure, so it is good to see some practical DIY techniques.

How do you plan to control bond gap? And why is the core windowed?

For the curious, there's a recent 2-part Kitplanes article that has some good information on similar work.
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Good to see those wings out in public. Great work guys!

How much resin gets soaked-up by the foam? Does it get saturated?
Most foams are closed-cell, since you wouldn't want them to soak tell they're saturated.

For the finer high-grade foams (Rohacell IG-F, Divinycell H/fine), typical resin intake is on the order of 200-280 gram/m2 per side. So say roughly a pound per square yard per sandwich panel on top of what the normal laminate would take in. Numbers are assuming double-sided vacuum-bagging, or at least good ventilation of the mold surface (holes in the foam core).

That's why for smaller skins other, saturating cores makes sense. I've posted a comparison of various options here:

(I don't have any commercial stakes in either of the mentioned products, but am a satisfied customer of all mentioned products)
Mold details

You guys form a dream team, for sure. This is one of those rare times when I really wish I lived on the West Coast. I would cheerfully become your slave ;)

Could you expand a bit on the mold-making process? Looks like you started by bonding an aluminum skin to both sides of a 2" pink foam board, which probably yields a very stiff panel?

Then you bonded a CNC'ed foam mold to that sandwich panel, upper skin mold on one side and lower skin mold on the other?

During that same session, you bonded an aluminum and mylar finished mold surface to the foam mold? Aluminum thickness? What sort of mylar? You can bond mylar?

What is the purpose of the aluminum edge rails?

Then you repeated the process to build molds for the other wing?

Details, please?

Dan's speculative answers to his own questions are pretty much right on. The sandwich flat tables are 0.030 5000-series aluminum, because that is what we could find that was 5 feet wide. The goal was to make tables that were very stiff and still light. They aren't as light as hoped, 0.016 aluminum would have done the trick, but couldn't find it. They were bonded and bagged to a 5'x12' steel work table that was very flat.

The foam mold blocks are hot-wire cut by an on-line foam-cutting vender that is widely used in the radio-control model world. Flying Foam. These are lined with 0.016 2024-T3 skin, except along the leading edge where the radius of curvature is small enough that the vacuum bag would be unlikely to be able to pull the skin in. In those areas we used 0.014 Mylar, scuff-sanded to a matt surface. It bonds rather poorly with epoxy, but fortunately there isn't much of any load trying to peel it out.
These molds are fairly light but still take four people to handle them. And they are not very durable, just low-cost prototyping molds. If Bob decides to commercialize these, we will pull some hard-tooling production molds off the first wing set.

The 1" square aluminum rails along the front and back are to be used as reference attach points for "spiders" that we make to help locate ribs, to reduce the repetitious fitting of upper and lower molds for fit checks - and to provide reference locations for guide pins to close the molds and clamp them together.

One table has both upper molds on it, the other has both lower molds so you can close an upper and lower together.

The foam is Divinycell H-60. It is closed-cell foam so it doesn't soak much resin. We also mix some microballoons in with the resin skim coat on the foam to reduce weight and actually increases bond strength.

The Gelcoat is a vinyl-ester primer/gelcoat. It is really nice to work with except for the strong smell when applied. You need to let it cure enough to be able to scrape it with a fingernail and not dig into it --we usually put on gelcoat late in the afternoon, let the shop air out overnight, and do the lay-up in the morning.
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Any updates on project? Hope to see pics of them flying soon

Thanks for asking! We have been making progress; Steve and Bob M. have been spending a couple weekends a month at the shop making wing ribs and molds for the new all-carbon wing spar. We're just not doing much in the way of photographic evidence.

Me, I've been pretty busy with the HP-24 kit sailplane. We just started Phase I test flights on the second one, and it's going pretty well:


Thanks, Bob K.
Ribs done

Yup, we have two complete shipsets of ribs made now. Next is spar layup.
Next shop visit, I'll shoot some pictures of the ribs and a spar in progress.

I've got some pics from the last two working parties, so here goes a few (lets see if the Portuguese bandwidth can handle it):

Bob K teaching Steve and me how to shoot gelcoat:


Pre-curving some of the foam core for the 4th wing skin layup:

A bag 'o skin (wing skin, that is):

While the skin cures in the mold, the wing rib templates that Steve worked copious hours making are used to layout and cut the foam core for the rib layup:


Flight Control, fuel and lightening holes cut and beveled for the layup:

Before laying up and bagging the ribs, Steve set up a set in an upper wing skin to check layout and hole alignment:

It was pretty exciting to see parts starting to look like a wing structure. Long way to go, but fun stuff!

A few more to follow in the next post

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A few more pics of rib and wing skin progress:

Steve and Brigitta K laying up a set of ribs (can't begin to say how much great help and hard work B&B Kuykendall have provided on this...and congrats on the latest HP-24 Glider first flight Bob!)

A bag o' ribs:

Fresh out of the rib cooker:

And some trimming and sanding to final size:

We also did some wing skin trimming, and started cutting and fitting holes for the fuel caps:


Teaser shot of Steve with the spar mold...as he said earlier, one of the next big projects!

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Spar molds and materials moved up to my garage in Oregon so I can make spars this winter. Hope to have two ship-sets of spars done by February or so.

Also, all machining work is done on the aluminum stub spars. They need to be assembled and match-drilled to fit in the fuselage. Bob's Rocket-6 is getting a new engine mount, new panel, and the stub spars fit this winter, we should be able to start assembling and closing wings in the spring.
Been a while since we posted, but we have made some progress on the wings...so Steve, Bob and I figured we'd catch up, and wish everyone a Happy New Year too.

When we last checked in, 4 wing skins and 2 full sets of ribs were coming along, and Steve had the spar mold ready to rumble. Then last winter/spring I was sidetracked with an RV engine mount repair that, of course, expanded into a baffle update/repair, intake tube swaging, etc project...and then I jumped into an invasive Glasair III main gear repair and service bulletin job...after a failure that fortunately did not end up in a gear collapse.



Fortunately, buds like Dayton Murdock were around to help with the tough spots!


Steve stayed busy (and worked his keester off) making carbon main spars up in OR, then brought them to Bob's shop in CA, where Steve, Bob and Brigitta prepped one wing skin with release tape, laid in the spar and ribs, and formed all of the attachment structure:




Here's one wing, with everything in place, and the fuel tank hardware on the root rib.


The inner attach pin hole has been drilled into the spar above, and the outer one will be match-drilled to the stub spar for each aircraft, when we have those ready. Below, the blocks that will hold the pins in the stub spar started off like this:


...and Steve made great progress on his RV-8 stub spar. The portion of the spar caps that are inboard of the inner pin hole is where the stub spar will mate with the aircraft structure. My Super Six sub spar looks a bit different, due the the difference in how the spar mates internally to the fuselage, and I'll show some more pics of the stub-spar build-up process in the next post...


The stub spars for the Super Six are longer than those of the 8, since -6 spars meet in the middle of the aircraft. The inner ends will be trimmed slightly as well, to set the dihedral of the wings. The spar web is full height for the inboard 2 feet (where it penetrates the fuselage), and then tapers in height slightly, to allow it to fit the top-to-bottom taper of the carbon wing spar. So the stub-spar caps are bent in that plane, and tapered to a thinner thickness at the outer end, for both fit and lightening. With 8 caps, 2 webs, 8 pin blocks, and Steve's nice diagrams and drawings, it was time to make marks, then chips and holes!


One cap was selected as the master, and drilled at 1/8" to start, per the pattern on Steve's diagrams. It was then used to match drill its mate.


Due to the taper at the outer ends, Steve made a tapered wood block to keep everything level during drilling (looks like a cribbage board now!)


The process was a bit painstaking, as the holes start at 1/8", and the match drilling is held together with #5 screws as "clecos". First upsize is to #19, held together with #8 screws. Then in 3 steps, I upsized with 11/64", #15, and 3/16" bits, finally held together with #10 screws. Last step at that point was to #11 holes, for riveting with 3/16" rivets.


Next came the placement of the pin blocks and match drilling the web to those. The pin holes are 24" on center, and the outer one is flush with the end of the web. So each had to be sanded to a taper, in order to fit tightly into the taper bent into the spar caps, and slide into place so the inner pin hole is at the correct y-distance. The small pin that was used to hold the pin blocks together when they were match drilled to each other (seen in the block on the upper right), served double duty as a viewer to see when the pin lined up with the correct y-axis marking.


Once the pin blocks were fit, we milled a slight bevel in the outer pin blocks, to ensure clearance at the outer edge, when the wing main spars are slid onto the stub spars. Another airport bud, Dave Miller helped with that job. Always fun to work in Dave's shop, with cool cars all around!



Here are a couple of shots of the fully drilled, de-burred, and countersunk (where needed) assemblies. One assembled, one "exploded". At least "fully drilled" for this phase... the match drilling inside the fuselage is yet to come. For now, these babies are just about ready for primer, and Steve and I will be joining up shortly to work on that! This phase was just under 6,000 passes with various drill bits, just over 15,000 de-burrings, and 108 holes countersunk. Whew!



Great fun and education working with pros like Steve and Bob!

Happy New Year VAF!

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Great photos and writeup, thanks for sharing.

I need to stop by and see it in person...
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Any time Mike, and we need to come see you guys. Steve and I may run down to Dayton after priming (in a couple weekends), to check out a squeezer Paul has, so we'll call ahead! Happy New Year!

Great photos and writeup, thanks for sharing.

I need to stop by and see it in person...
Steve and I may run down to Dayton after priming (in a couple weekends), to check out a squeezer Paul has, so we'll call ahead! Happy New Year!

If it is the new one he got from Dave, bring a truck-----that sucker is heavy:eek:

Happy New Year back at ya:D
If it is the new one he got from Dave, bring a truck-----that sucker is heavy:eek:

Happy New Year back at ya:D

Not "the Monster" Mike - the bench-mounted one that we used for the Xenos spars - still about 70 lbs.....

Definitely come down Bob and Steve - I never seem to find time to get up to Stead!
Additional progress

Bob, nice job catching everyone up. all the pictures look great too.

I thought I would add just a few more details and additional progress.

First, we were not very outspoken about it and some folks may be confused because early on, the plan was for full aluminum spars, bonded to the carbon skins. After getting one set of spars all match-drilled for assembly, we changed course and decided to make carbon spars with aluminum stub spars that fit into the fuselage, and mate to the carbon spars with a pair of large diameter pins 24" apart -- just like modern composite sailplanes join their wings. Its a connection that is easy to analyze with high confidence, and we made a proof-test specimen as well that demonstrated a high safety factor. Other advantages of switching to the carbon spars:
- they are 10 lb lighter, per side, including the stub spars and joining pins.
- they allow a much easier connection to the ribs
- no need for a rear fuel tank baffle to close out the fuel tank
- no longer worried about thermal expansion unzipping the spar flange bond, although a later FEA showed it would have been fine.

The upshot of this is that we now have a set of full-span tapered aluminum spars that would fit either an RV-7 or RV-8 (fuselage mating holes not drilled yet) If anyone would be interested in building a set of all-aluminum tapered wings - which means having the means to make 52 individual aluminum ribs - I would help with the design and make you a super deal on the spars.

Back to the current progress: In the last few photos of the wings that Bob posted, you can see the spar and ribs set into the upper wing skin. The corner joints between the ribs and the spar, rear spar, and forward fuel tank baffle, are all joined with 2-ply corner tapes. The corner joints between the ribs and upper wing skin have also all had corner tapes put in, but with release film in between to prevent bonding to the wing skin. This essentially forms bonding flanges on all the ribs that are molded to fit the upper skin.

After that last picture was taken, the entire assembly of spars and ribs was lifted out of the upper skin, and it weighed just 22 lbs!
Then the assembly was set into the lower wing skin, and after a check fit for clearances, all the edges were coated with Hysol EA 9430 structural epoxy to bond to the lower wing skin, and the upper skin was set in place and the upper skin mold set on top of everything.


hmm -- I thought I could use facebook to host a picture and it would paste in here. I'll see if I can get those pictures hosted so they show here.
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...and we made a proof-test specimen as well that demonstrated a high safety factor...

For the curious, and for folks who just like to see things go bang, here is the YouTube video of the spar coupon static test:


For this test, the stresses equivalent to limit load are achieved with ~2100 lbf at the load cell, and ultimate load is at ~3150 lbf. As you can hear in the soundtrack, we expected the failure mode to be failure of the little skin sample glued to the upper spar cap, followed by a crippling failure of the upper cap.

However, the whole thing turned out to have more robustness than Steve's relatively conservative analysis indicated, and the actual failure was a classic diagonal shear unzip between the two inboard mounting points (corresponding to the mounting points for our aluminum stub spars). This at ~5400 lbf, corresponding to limit load * 2.57 or ultimate load * 1.71. Bottom line, it would have been a successful test if it'd held to 3200 lbf, and it went to a little less than twice that. There's a reason we are carbon-based lifeforms!

--Bob K.
Next steps:

The next step will be to remove the upper skin, and install the corner tapes where the ribs bond to the lower skin. We will do some clean-up on the raw edges of the bond flange tapes that were molded to the upper skin.

Then, we install a bunch of wing internals, such as aileron bell crank and counterweight system, push rods, tie-down anchor, fuel caps and fuel tank vent lines, fuel pick-up tube, blind fasteners for flap hinges and aileron hinges.

After that, the insides of the fuel tanks will get coated with our secret process for hopefully sealing the tanks well -- a combination of a very low viscosity epoxy followed by a heavy coat of epoxy thickened with a little cabosil.

Then, finally we will be ready to do the final bond of the upper skin.

Its been 6 months since last update so was just wondering how everything has been progressing? :)