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Carbon Fiber Tapered RV Wings

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

Pretty slow between winter and other priorities. We have all the ribs, drag spar, and forward tank close-out corner-taped into the lower skin. Ready to start installing goodies inside the wing like fuel vents and filler necks, flap hinge and aileron hinge attachments, bell crank, tie down boss. That will happen June 7--10.

One set-back: We found that when the bronze bushings were pressed into the stub spars, the ID of the bushing shrank. So we are carefully hand-reaming those bushings back to proper size before using them as location guides to bond the mating bushings into the wing spar.
 
Just found this thread! I have been independently dreaming of a project like this for about 2 years now just to find that some WAY more qualified than me are actually doing it! Any recent updates not posted to the Facebook page? Not much about these RV wings posted there these days.
 
Justin, thanks for asking. Steve and I have been working whenever possible, and had some good steam up earlier this year. Been a few life events (good stuff) impacting as well. We've each moved (Steve from Cali to Southern OR, me from Reno to Central TX), and the project is now in far Northern CA, in Steve's shop. We've also had competing aircraft projects (maintaining our RVs, of course, but also the sale of a racing Super Glasair and the purchase...and re-engining :eek:...of a Stearman for me; and the maintaining of a soaring club tow plane for Steve). Despite all of that, we've made some progress.

One wing is about ready to close, and the other is progressing. We've kept the first wing open, so we can use various measurements from it as we work on the second wing structure. Here are some photos, that bring things a bit more up to date:

Wing 1 with main and aux tank vent lines in place. Fuel level sensor has been placed in the main tank as well, just not visible here. The aileron counterweight is installed further up the right side of the photo.

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Me cleaning up the inside of the tanks, and Steve measuring key rib placement measurements for transfer to wing 2:

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After installing the spar, all the ribs, and corner tapes to one skin of the second wing (over packing tape release), here's the structure of wing 2, ready to be placed in the other skin, for permanent bonding:

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With the spar/rib structure in one skin, and a few adjustments being made to the other skin, here's a progress shot of both wings:

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Trial fit of the wing skins over the spar/rib structure of wing 2. When closing the wings, we'll use the molds to hold everything together during bonding.

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While the pandemic and various good life events have slowed progress a bit, we're not letting the tyranny of distance or other obstacles deter us. Little by little, making progress. Over to Steve for any technical progress updates he'd like to make.

Cheers,
Bob
 
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Sweet!!!

OMG, thanks for finding and forwarding this thread Justin. These guys are pulling on my heart strings.

Years ago When my 1st RV4 was apart in my hanger in North Texas, I cannot tell you how much dreaming (and possibly beers) Roscoe and put into this same mod.

This is SOOOOO cool.

Thanks for the update Bob.

Thanks to you and Steve for this pursuit!

Bryan

Hanger full of wood projects and a Stinson Reliant
 
Rough calculations indicate that the tail volume coefficients should go up by about 18%. The rest of the handling story is dihedral.

Presumably handling quality changes would be minimal, but maybe improved Dutch roll qualities?

Thanks.
 
Rough calculations indicate that the tail volume coefficients should go up by about 18%. The rest of the handling story is dihedral.

Presumably handling quality changes would be minimal, but maybe improved Dutch roll qualities?

Thanks.

Yes, increasing wing aspect ratio makes the tail more effective, because of the reduced downwash (the term we call d_epsilon/d_alpha). I didn't bother to calculate the actual magnitude. The downwash-related item I am a bit concerned about is the stabilizer incidence (decalage).

I have argued with myself endlessly if we should change the dihedral or not...and I don't have a good answer. For the first set, going in Bob Mills' Rocket-6, the dihedral will be essentially the same.
One would think reducing the dihedral would be good to reduce the dutch-roll. But I remember a Glassair owner who was a long-time tailwheel pilot asking me why he couldn't pick up a wing with the rudder, and I said not enough dihedral. On the other side, the Spitfire has 6 degrees of dihedral :eek: and pilots consistently express love for its flying qualities. So.....what to do, what to do....

Interestingly, the greater wing span, combined with the taper, leads to almost the same roll damping term.
 
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Feb 2021 Update part 1

Just back from a week of working on the wings in the Siskiyou Skunk Works, and Steve and I saw Tandem46's post asking about our project. We've actually been making very good progress, which I'll start the report on here (probably in 2 posts so I can include lots of photos), and Steve and Bob K can add info and thoughts as they see fit. Big picture, here's some of the items we've completed since the last posts:

- installed tank vents and fuel close-out panels (with float sensors)
- sealed the main and aux fuel tanks
- closed the wings
- leak-checked the tanks
- match drilled the stub spars to the aircraft to allow the making of a load test jig
- load tested the wings
- fabricated the flaps
- installed the piano hinges for the flap attachments
- installed the attach brackets for the ailerons to the wings
- fit the aileron spar with the aileron captured bearing brackets
- block sanded the wing skin to final contour
- fit and contoured the inspection panels and pitot mount to the wing skin

The punch list is getting shorter (you know, 90%/90% ;)). A couple more trips to SIY, and we hope to transport them to TX for final fit and install, then root fairings and tips, and flight test. Here are some photos, with lead-in notes:

Kilroy said he was happy with vent lines and fuel close-out panels. Still some adjustments to the float arms to make:
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Closer look at the vents coils, fuel close-out and stub spars in place:
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Sealant in tanks and on top wing skin (Rhino product used for Legacy and Glasair wings). Fuel caps in place too:
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Wing closing days. It took a couple days per wing, to prep, glue, and swap molds...we used the lower mold and table to close the bottom structure and skin down on to the upper skin. The spar/rib structure had been previously glued to the lower skin, and in this step, we wet the upper corner tapes on the entire structure, and then used a thick resin/cabosil/flox "schmoo" to allow good squeeze out for a tight bond. Extra schmoo was used around the tanks, for a good seal:

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Steve inspecting for good squeeze out, with the lower mold in place and weighed down:
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Two wings after closing...a neat day...they look like wings now, eh!
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Leak check was done with a water manometer. The seal was not perfect, so we did do some "search and fill" missions along the tank perimeter. Seal success was achieved with running schmoo along the tank spar line, and then putting suction into the tank to pull it into the leak paths. Did the same with resin in a few other spots along the tank perimeter.
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Next post will cover the load test and current finish work in progress. Fun stuff!

Cheers,
Bob
 
Feb 2021 Update part 2

Continuing from the previous post:

Took a deep breath, and pulled the wings off Rocket Six/Sport 49...gulp! Here, we are fitting the stub spar, and marking the 52 AN-3 bolt holes that hold the spars to the aircraft structure, as well as the four 1/4" holes at the side of body that are key load carrying bolts. The 3/8" and 1/4" holes in the spar where the splice plates go were previously match drilled to the spar, and we tested the fit for them to the plane in this step:
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With all holes now drilled in the stub spar, they were shipped back to SIY, and Steve and Bob K fabricated the load test jig. Here is a photo on load test day, as we began to mount the spars to the jig:
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Steve built a lattice to hold the lead shot bags on the wing, in a pattern that matched lift distribution. We put thick pads on the jacks under the wingtips, and kept the jacks within about 1/4" under the wing skin.
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As weight was added, and the tips deflected, the jacks kept the tips from bouncing, and inducing "gust" loads. We started at the roots, and Steve and I added 25 pound shot bags in mirror image patterns, in the pattern Steve had laid out. Bob K supervised, watched for equal loading, and recorded tip deflection. Here's a photo at about 80% load.
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With the load test behind us, we moved to flaps, ailerons and exterior contour/finish. We started by strengthening the wing skin where the flap hinge is mounted, with carbon and with a layer of fiberglass to insulate the aluminum hinge from the carbon skin:
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Hinges installed on flaps and wing skins. The flaps have since been fully closed:
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Aileron hinge brackets were next. Fiberglass insulators/pads were used between the aluminum brackets, to form a flat, level pad. All cured in place with bolts installed, to ensure proper alignment:
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Here, the brackets with the captured bearings for the ailerons have been riveted together, and the inspection panels have been covered with filler to allow then to be sanded flush with the wing skin:
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Wing skin contour is really looking great. Steve has worked his keister off the last several weeks with a block sander and filler to really get it nice. Some finishing touches with inspection panels and the pitot mount can be seen here.
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So, as you can see, we've been busy. Still much work to be done, but we are progressing, and happy with the progress. I'm sure there will be questions and comments, and we'll do our best to answer (Steve and Bob K being the true experts, though I'm learning some cool stuff along the way). Best of all, we're having fun. A bit sore from time to time, but every builder knows that story! Over to you Steve and Bob K!

Cheers,
Bob
 
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Question: How is testing done to determine the funtionality of the ailerons / flaps under load vs the flexing of the wings? Is binding of the hinges a concern or is there something about the way the wing and control surfaces flex that make this a non-issue?
 
Question: How is testing done to determine the funtionality of the ailerons / flaps under load vs the flexing of the wings? Is binding of the hinges a concern or is there something about the way the wing and control surfaces flex that make this a non-issue?

If the ailerons and flaps had been completed at the time we did the static load test, we could have checked them for smooth, free movement at that time. But they were not. So, this will be an early item for flight test during envelop expansion.

There are a few design features that give us confidence that there should be no problems though. We found during the static load test that the wings are somewhat stiffer than my original analysis. The original analysis was basically just the wing spar bending deflection, ignoring the contribution from the wing skins, reinforcing tapes in all the corners, etc. The skins and all the corner tapes are all +/- 45 degree bias, so they have lower stiffness in bending. But they do contribute something, obviously since the wings are stiffer than expected.
The flaps and ailerons are also all +/- 45 bias plies, with nothing that would increase the bending stiffness of the control surface. So they should hopefully bend freely to match the wing bend.

The flaps are attached with piano hinge on this first wing set, just like standard RV flaps on the RV 4,6,7,8. There is no history of any binding or issue with those flaps under flight loads, and we don't expect any either. Plus, we don't typically pull high g's with the flaps deployed, right?

The ailerons are hinged differently than standard RV wings, and there is some potential for issues. Whereas RV ailerons are attached by just two hinges, one at each end of the aileron, ours have a third hinge in the middle of the aileron. When a standard RV wing bends under load, the aileron does not bend with it, and the skin gap between the wing and aileron closes some (under positive g) since the aileron stays more straight while the wing bends. In our case, with the center hinge, the aileron will be forced to bend along with the wing. As I said, the aileron is made to be flexible in bending. The aileron hinges also have spherical bearings so the hinges won't bind (just like standard RV). So hopefully they will work smoothly as the wing bends. But we will just have to see when we fly it.
 
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Continuing from the previous post:

Here's a photo at about 80% load.
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You might wonder where we were able to come up with 8700 lbs of lead shot to do the static load test. It turns out that the main west-coast manufacturer of bird shot, Northwest Shot Manufacturing, is located in Phoenix, Oregon, just the next small town near where I live. I stopped in to see him one day while out on a bike ride and pitched the wacky idea of 'renting' shot from him. He was curious and willing, and for a reasonable fee, he delivered the shot on the morning of our test, and picked it up that same evening once we had stacked it all back in his boxes.

The 8700 lb test was to limit load of 6 g's at a zero-fuel weight of 1650 lbs. Fuselage lift, tail download, and inertia relief of the wing, plus dead-load of the wing, were all accounted for. Spanwise load distribution was determined from a Weissenger lifting line method, and chordwise load distribution roughly approximated the airfoil pressure distribution at high lift. Fuselage lift was determined from a wing-body simulation in Cart3D.
 
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Hinges installed on flaps and wing skins. The flaps have since been fully closed:


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What you see here is the lower flap skin and the flap spar, hinged to the wing. It was necessary to do this step so that the top edge of the flap spar could be trimmed to the right height so that the flap upper skin would fair straight into the wing contour. Once that was done, three ribs were bonded inside, and the flap upper skin was bonded in place. A molded flap nose piece will be added, very similar to standard RV flap nose, to close the skin gap from the wing to the flap.
 
Per the request of Bob Mills, the name of this thread was changed.

Same old thread, exciting new name!!!
 
Question: How is testing done to determine the funtionality of the ailerons / flaps under load vs the flexing of the wings? Is binding of the hinges a concern or is there something about the way the wing and control surfaces flex that make this a non-issue?

Another data point here is a discussion I had with a multi-time Lancair builder, who has modified a couple Legacy race aircraft with piano hinge flaps. When they did the mods, the fuselage was in a rotisserie, and upside down. This puts a bit of wingtip “up” bend in the wings, with gravity pulling the wing toward the ground. After installation, when the fuselage is rolled upright, and the wings go back into “positive g”, he’s seen a little binding in the hinges, which was easily relieved with a bit of filing the sides of the loops of hinges.

As Steve noted, in normal ops, the piano hinges in flap installations won’t see much g or speed when deployed, or during deployment. I have manual flaps too, so will be able to have some feel with them. In an electric flap installation, we certainly would want smooth operation, to ensure no unnecessary strain on the flap motor is present.

Very precise mounting and smooth hinge and bearing movement on ailerons are more critical features, of course. It’s a big part of our next build session.

Cheers,
Bob
 
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Vent

Really cool project, very glad I noticed the thread.

One design question. From the wing photo it appears you are keeping the tank vent at the per plans inboard location, at least that is what it looked like. Wondering why not use less tubing and vent to wing tip, underside, modified naca style like airbus?

I apologize in advance if I misinterpreted the photos. In that case, nevermind. :)
 
Really cool project, very glad I noticed the thread.

One design question. From the wing photo it appears you are keeping the tank vent at the per plans inboard location, at least that is what it looked like. Wondering why not use less tubing and vent to wing tip, underside, modified naca style like airbus?

I apologize in advance if I misinterpreted the photos. In that case, nevermind. :)

Sorry I just saw this question from almost two months ago. We were in a mind set of keeping things much like the standard wing installation for retrofit.

It is possible to put the tank vents out at the tips - I believe that Lancairs do that. I think you need to have a check-valve at the vent outlet so that it can let air in, but not let fuel out? Then the question - should that check valve be accessible for servicing?

Sometimes the simple ways are best, so we just routed the vent lines to the root just like RVs and Rockets.
 
We are getting pretty close to being done. I painted the flaps and ailerons yesterday. I prepped the first wing for painting today. With it all smooth and clean, it was really the first chance to truly evaluate how smooth the wing contours are. I saw a few areas I am not happy with, and I think I can do better. So I am back to 'body work' tomorrow.

It is a hard call sometimes. Perfection can sometimes be the enemy of good enough. Long florescent lights will reveal a lot of waviness that many people would not notice. Not trying to build a show plane, and it is not a sailplane. Still, I would like to try to get the wing contours as smooth and straight as I can.
 
It is a hard call sometimes. Perfection can sometimes be the enemy of good enough. Long florescent lights will reveal a lot of waviness that many people would not notice. Not trying to build a show plane, and it is not a sailplane. Still, I would like to try to get the wing contours as smooth and straight as I can.

Are you judging your good enough [perfection] based on visual inspection or have you adopted some sort of waviness criteria? If using a criteria are you basing it on location on the wing? I am curious what those may be for the speeds you expect to achieve. In my former day job on military aircraft we set up criteria based on location on wing with tighter requirements near leading edge and looser further back near trailing edge.
 
Steve,

Curious how you define waviness. A friend who has since passed away used to build boats with composites.
One of the very interesting things he showed me is how visually you can see waves in the composite structure. However, if you actually measure the boat skin mechanically or with the correct tools you will find the boat skin matches the design perfectly. The waves I was seeing were a visual illusion.

Tim
 
If you are looking for a practical reference on composite surface quality, the big "A" has a few documents that are used to manage that aspect for suppliers.

V51ME0721672 Exterior Surface Quality, Composite

and

TDD00A002V.0 General Tolerances of External Surfaces: Cruise Conditions

They have requirements, definitions, measurement procedures, etc. for different areas of the aircraft.

I'm sure other airframers have similar documents. These are just the specs that I am familiar with.
 
Thanks everyone for contributing the various specs.

In the sailplane world we use a waviness gauge that is colloquially known as a Johnson Gauge, named after Richard Johnson.

It consists of a disc with three short legs spaced 2" apart, with hemispherical ends, and a dial indicator in the middle. If you traverse this gauge across a perfectly smooth (wave free) surface, you would see the indication on the dial indicator slowly change reflecting the change in radius of curvature in different parts of an airfoil. But any waviness shows up as an oscillating indication superimposed on that smooth trend. Typically for sailplanes, a waviness indication of less than about 0.002" is considered smooth enough to support laminar flow.

I assume that the 2"spacing was worked out by Johnson to correspond to the most receptive T-S wave frequency at typical sailplane Reynolds numbers. I don't know that for sure, it might have been an arbitrary choice, but Richard was a pretty sharp guy.

Anyway, If you were to run a Johnson gauge on my wings, I'm pretty sure the waviness indication would be on the order of 0.0005" or less. They are plenty smooth. The rework area is at about 70--75% chord, and would have absolutely zero aerodynamic consequences, only cosmetic. It is a fairly large area with a very gradual,smooth depression of about 0.012" over about 1 foot.

Nothing I do is going to make these wings cosmetically perfect, they are after all hand-built. But I want them to look smooth 'enough'. Thus the rework. It is going to set the schedule back about 2 days.
 
Just a quick update: Bob Mills has started mounting the first set of wings on his Rocket Six, and it is looking good!

rv1.jpg


rv2a.jpg
 
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Looks sooo close to flight test . . . .:D

Bill, you know the old 90%/90% rule right? ;)

Steve, Bob and I hit it hard over the winter and spring, and Steve was truly an Ironman. He spent hours and hours (weeks, actually) on fill and sand and making the airfoil meet his very exacting standards, all while directing me on a myriad of steps with ailerons, flaps, hinges for both of those, pitot tube, access panels, and fuel system items. We built a paint booth and a shipping crate for my trailer, and Steve did final finish and paint, then crating, while I was at Flight Safety for a few weeks in late April.

Once we got the wings to my place in TX, the first trial fit was exciting, and that is when these photos were taken. Working on front and rear attach brackets, then fuel system (upsized from -6 to -8 on this wing), then root fairings and tips (Steve’s working on prototypes of those glass parts now). So 90/90 may be accurate. I’ll post more photos of those last few build months and the fit work when I’m back home from PRS.

Fun and exciting, and lots of work to go!

Cheers,
Bob
 
A couple more pictures

Here are a couple more pictures of the July progress.

I climbed up on a step ladder to try to get a better view of the wings. The tape stripes running chordwise were used as measurement stations to set wing incidence prior to match-drilling to the rear spar attach bracket. You can see that the wingtips are also on, currently in primer gray. These are the racing tips, minimum wetted area, gives an AR of 6.3 and about 100 sq ft wing area. The 'daily driver' wingtips will add about 9" of span on each side, with a semi-elliptical planform. This thing is really going to love cruising at 17.5K with the longer tips. AR=6.7

Rocket-6 from ladder.jpg

Next, you can see that we have started on the wing-body junction fairings. This got tricky near the trailing edge at the root, because the root trailing edge of the flap ended up about 5/8" below the belly at that station. So there is a blister fairing on the belly as part of the wing-body fairing. It came out much better than I thought it might. From the state you see here, a bunch of additional plies of glass got added to the initial light shells, then a bunch of body work to fill and smooth them.

wing-body fairing.jpg
 
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Steve & Bob - do you plan to replace anything in the tail to reduce the elevator & rudder counter weights? Carbon fiber control surfaces?
 
Post #73 says Bob is mounting the “FIRST” set of wings? Was that a hint? Are you guys making multiple wings? Maybe something for production?
 
Span lift distribution

First, I commend the effort. A lot of high grade work here. The potential for extensive laminar flow should be worth more than a few extra knots, I'm sure. And it looks even faster and jazzier as other have commented. Well done.

But.... Tapered wings, all else equal, make an airplane snap-rollier as well. Most know that different airfoil sections can have a large effect on stall behavior, but many fewer know anything at all about the effect a wing planform has on that behavior. I bet Van is one of those few.

Many decades ago I was Full time Part 141 flight instructor, maxing out for 2 years. I was also involved in the competition aerobatic scene as well.. Aerobatics then usually meant a Pitts Special. When a friend was going to build a Pitts, I talked him into something a little different I had in mind. My concept became the Stevens Acro, which then morphed in a general way into the Extra's and other similar designs. Read a lot, learned a lot.

As the design took shape, I worked out the lift distribution which predicted that the stall bubbles would begin about 2/3 toward the tip. On completion, I flew most of the first hours and sure enough, it was very frisky with any rudder pressure in a stall or snap. With that info, a second Acro by/for Dean Englehardt was built with less taper. The change made it more docile - too docile, had to add stall strips outboard to aid snap maneuvers.

So, you see, wing taper alone can have a big adverse effect on the behavior of an airplane at high aoa. I mention all of this with safety in mind. I muse about how much skin may have been saved over the years by Van's 10,000 or so relatively benign Hershey bar wings.

But, again. Magnificent work. Don't want to be a wet blanket. Just be aware.

Ron
 
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Steve knows a thing or two about wing design, I would not be surprised if he took the issues you mention into consideration already.
 
Steve knows a thing or two about wing design, I would not be surprised if he took the issues you mention into consideration already.

Yes, I am aware, and in the back of my mind always concerned. There is 1 degree of washout. And the taper is modest, tip chord is 55% of side-of-body chord. My lifting-surface code says it stalls first just about middle or a little outboard of the middle of the span. Should I have put in more washout? We will see. Might have to put an inboard stall strip - like Mooneys, Bonanza's, lots of others.

No matter what, it will never be as forgiving as a low aspect-ratio, untwisted rectangular wing. That is all part of performance trade-offs.
 
...But.... Tapered wings, all else equal, make an airplane snap-rollier as well. Most know that different airfoil sections can have a large effect on stall behavior...

Steve has a PhD in aeronautics and worked for NASA for 30 years, mostly doing subsonic wing design. He designed the wing used on the RV-10 and RV-14, and consulted for Vans on the RV-15. So, um, yeah.

--Bob K.
 
Post #73 says Bob is mounting the “FIRST” set of wings? Was that a hint? Are you guys making multiple wings? Maybe something for production?

Right now the plan is to build another set for my second RV-8. I am thinking of making a one-piece carbon center section spar that would fit inside a modified F-804 bulkhead, rather than use the aluminum stub spars. The center section spar would still pin to the forked main wing spars, like we did on the first set.

Along the way, we will try to make more tooling so that the wings would be more amenable to production. After that, the molds go to HP Aircraft LLC and Bob K can decide if he wants to offer the wings commercially.
 
I know it’s been engineered…what’s the solution for galvanic corrosion concerns where the carbon wings interface with aluminum spars etc? Is there access for detailed inspections down the road?
 
I know it’s been engineered…what’s the solution for galvanic corrosion concerns where the carbon wings interface with aluminum spars etc? Is there access for detailed inspections down the road?

The aluminum stub spars never touch any carbon.

The general technique when aluminum parts have to mate against the composite is to use an insulating layer of fiberglass. But in the case of the aluminum stub spars, they nest in a pocket with bronze bushings in close fit with the bronze bushings that are imbedded in big Garolite G-10 blocks that are then bonded to the carbon spar forks. Then there are steel pins through those bushings. Have you ever seen how sailplane wings are assembled? The stub spars can be removed by pulling those pins, although there is not any compelling reason to ever do that.

The primary purpose of the Garolite is to provide a large area of bond and contact, without having to laboriously pad up thick buildups of fiberglass. It has pretty good strength properties too.
 
Yes, I am aware, and in the back of my mind always concerned. There is 1 degree of washout. And the taper is modest, tip chord is 55% of side-of-body chord. My lifting-surface code says it stalls first just about middle or a little outboard of the middle of the span. Should I have put in more washout? We will see. Might have to put an inboard stall strip - like Mooneys, Bonanza's, lots of others.

No matter what, it will never be as forgiving as a low aspect-ratio, untwisted rectangular wing. That is all part of performance trade-offs.

Engineering/designing is a continuous lesson in compromise. I've designed aerospace systems and power generation systems. In the back of your mind, there's always worry about the alligator you didn't see. History is full of tragic lessons where optimization for one characteristic caused severe/fatal consequences.

Many will say their area of application is the most difficult; however, engineering a wing design to be relatively good in all flight regimes while maintaining fabrication (difficulty) considerations may be the epitome of such.

Truly impressive work, SIr.
 
Originally Posted by scsmith:
Yes, I am aware, and in the back of my mind always concerned. There is 1 degree of washout. And the taper is modest, tip chord is 55% of side-of-body chord. My lifting-surface code says it stalls first just about middle or a little outboard of the middle of the span. Should I have put in more washout? We will see. Might have to put an inboard stall strip - like Mooneys, Bonanza's, lots of others.

No matter what, it will never be as forgiving as a low aspect-ratio, untwisted rectangular wing. That is all part of performance trade-offs.


Steve,

Thank you for your gracious response which includes some important technical details which bolster my point.

If others thought I was challenging your competence or wisdom, forget it. Your considerable background, which I am aware of, would preclude your not having thoroughly investigated taper effect on the design. We both know the trade-offs.

My objective was to publicize to those with much less background the often negative effect of taper on stall performance if not adequately compensated in either design or operation. The target is those with little knowledge in this area that may wish to duplicate and fly something similar (and why not, your wing is gorgeous!). My point is that without making allowances for the effects of a root tapered planform, stall safety characteristics may not be adequate.

Be Well,

Ron

PS: I admit I am a zealot for proper training against the sometimes fatal skidding turn to final which is part of my angst about stall behavior and thus, wing taper.
 
This is a really fascinating thread.

Today there's an article on the Kitplanes magazine website about the F1 Rocket guys creating a new tapered wing. Apparently they're building it out of aluminum using metal techniques similar to a Vans hershey bar. It sounds like they are planning to put their version into production for Rocket kit buyers.

It's interesting to see two different tapered wing design approaches (composite vs aluminum) happening around the same time.

Would be curious to know the final specs and pros/cons of the two approaches, especially given that an RV-8 and Rocket are somewhat similar, other than the number of engine cylinders of course.
 
I'm a big fan of the related efforts to date. For my curiosity, what is the weight delta between this product and the standard wing?
 
...If others thought I was challenging your competence or wisdom, forget it. Your considerable background, which I am aware of, would preclude your not having thoroughly investigated taper effect on the design. We both know the trade-offs...

My apologies, the fault is mine. I mis-read the tone of your post. I will try to do better in the future.

Thanks, Bob K.
 
I just have to say that this thread has been amazing to read. I hope that the product is completed.

JC

We are getting really close. The wings are on, and final body work is being done on the wing-body fairings. There isn't very much left to do, unless we find an issue on initial systems check out (like an aileron pushrod rubbing on an internal rib, for example, it is hard to work that stuff out when the wings are in N. California and the fuselage is in Texas.) Weight and balance will be next, then ..... gulp!
 
Time has flashed by since our last posts, and a lot has happened, so I thought I'd catch up, try to answer a few questions, add a few comments and give an update. I'll imbed some with the quotes below, and finish with some pics...will take a couple posts due to photo limits in each post. Here goes...


Steve & Bob - do you plan to replace anything in the tail to reduce the elevator & rudder counter weights? Carbon fiber control surfaces?

Ralph, I have a tail kit for a 7 and an 8. I'm going to build the 7 HS and elevator, and the 8 VS and Rudder for my plane. They will incorporate a synergistic blend of strengthening mods from Ken and Eric of Team Rocket airshows near you, from Mark and Vince of the F1 Rocket Team Rocket, and from Steve. Steve will get the 8 HS and Elevator from my kit for his project, and will likely take the 8 VS and rudder that I currently have on my Super Six. We have not discussed lightening the tail counterweights or going to composite tail control surfaces....yet. The new tail will be done after initial flight test, but likely before racing in '23.

(snip)...

But.... Tapered wings, all else equal, make an airplane snap-rollier as well. (snip...)

So, you see, wing taper alone can have a big adverse effect on the behavior of an airplane at high aoa. I mention all of this with safety in mind. I muse about how much skin may have been saved over the years by Van's 10,000 or so relatively benign Hershey bar wings.

Ron

Yes, I am aware, and in the back of my mind always concerned. There is 1 degree of washout. And the taper is modest, tip chord is 55% of side-of-body chord. My lifting-surface code says it stalls first just about middle or a little outboard of the middle of the span. Should I have put in more washout? We will see. Might have to put an inboard stall strip - like Mooneys, Bonanza's, lots of others.

No matter what, it will never be as forgiving as a low aspect-ratio, untwisted rectangular wing. That is all part of performance trade-offs.

(snip...)
My objective was to publicize to those with much less background the often negative effect of taper on stall performance if not adequately compensated in either design or operation. The target is those with little knowledge in this area that may wish to duplicate and fly something similar (and why not, your wing is gorgeous!). My point is that without making allowances for the effects of a root tapered planform, stall safety characteristics may not be adequate.

Be Well,

Ron

PS: I admit I am a zealot for proper training against the sometimes fatal skidding turn to final which is part of my angst about stall behavior and thus, wing taper.

Thought I'd relate the many discussions that Steve (designer/builder) and I (builder apprentice/test pilot) have had on this topic. We have talked though expected behavior and gotchas extensively, have formulated the test plan, and have submitted it to the FAA for concurrence on test area and period. Quite a bit of slow flight/high alpha/stall work is included, and we have made allowances for test repetition, and re-test should stall strips or other devices be added to improve stall characteristics. FWIW, I share your zeal for proper approach turn execution and will fly the pattern in this new configuration more like a Glasair, Legacy or Thunder Mustang...all of which I have had the opportunity to fly and race.


This is a really fascinating thread.

Today there's an article on the Kitplanes magazine website about the F1 Rocket guys creating a new tapered wing. Apparently they're building it out of aluminum using metal techniques similar to a Vans hershey bar. It sounds like they are planning to put their version into production for Rocket kit buyers.

It's interesting to see two different tapered wing design approaches (composite vs aluminum) happening around the same time.

Would be curious to know the final specs and pros/cons of the two approaches, especially given that an RV-8 and Rocket are somewhat similar, other than the number of engine cylinders of course.

The F1 EVO currently has a tapered wing of metal construction. I've flown Mark Frederick's and it flies wonderfully. Steve can speak more eloquently about comparison between his wing and the EVO wing. Vince may may be working on a new wing for the latest iteration of the Rocket line. I'm not caught up on that tho...but I know whatever Vince and Mark do will be nice! Metal vs composite for the wing is something Steve and I discussed and decided upon at the outside of this project, so you can guess which way we think is better...or faster...or :D

We are getting really close. The wings are on, and final body work is being done on the wing-body fairings. There isn't very much left to do, unless we find an issue on initial systems check out (like an aileron pushrod rubbing on an internal rib, for example, it is hard to work that stuff out when the wings are in N. California and the fuselage is in Texas.) Weight and balance will be next, then ..... gulp!


This quote from Steve was as of just before Oshkosh AirVenture. We felt we were tracking for Reno '22, though the days were long, and the window was tightening. I had the opportunity to fly my good friend and airshow wingman Mercedes Eulitt's RV-7 in the Van's 50-ship, so I took a short break for that. Then during and following OSH, a few design change recommendations came to us, and, while we kept the press on a bit longer, we made the safe and conservative call not to try to take the new wings to Reno this year. I'll talk about the design changes below. We had really blasted this year, but it was the right thing to do, and after 9 years of work (due to the tyranny of distance and time available), there was no point in rushing the last month of work. We just want to do this right. When I pulled my entry, another Sport pilot offered his Legacy to me to race...if I could help him finish some prep work on it, and I...just...couldn't...say...no. So another side project intervened. Reno was fun, but we're back at it.

Before calling the Reno "knock it off", the work on paint finish, root fairings, and wing tips had progressed nicely. The initial layups for the root fairings were an experiment it fortitude for this composite apprentice, doing prep work and kitting out in the 106° day, and laying up when it cooled below 90. Doing the bottom portions, with the layers dripping hot resin or trying to fall on your face was ugly. Mornings were a little better. But the shape is what we were going for (patterned somewhat after Rocket fairings...with the aft section patterned after Steve's fave plane, the Spitfire.

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The fairing was laid up in 2 sections, top and bottom, and the leading edge was scarfed in after. The fairing splits on the the upper section at the spar.

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Wingtips were progressing and I had just about gotten the trailing edge closeouts done (it was farther than the first photo below. Steve had also brought out the fairings for the aileron control rod (from bellcrank to aileron).

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We had also progressed well on the flap control rod connection at the flap root rib, and had the extension and retraction geometry worked out (manual flaps).

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Next post will cover the design change decisions.

Cheers,
Bob
 
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Part 2 of tonight's update:

While as OSH, our friends Jim Rust of Whirlwind Propeller, and Robby Grove of Grove Aircraft, both brilliant aircraft design and build guys, asked me about the aileron counterbalance plan. We had 60% bonded in the leading edge of the ailerons, and the other 40% was in a swing arm (bob-weight) in the wing, connected via a skew drive, to the aileron bellcrank. Ailerons were 100% balanced. Jim and Robbie suggested we not have the bobweight, and ensure all of the counterweight be attached directly to the aileron itself. This would ensure no control system play could exist between the counterweight and the aileron. The bob weight system has been used in high aspect ratio gliders and other aircraft, but perhaps not in a wing of this design or aspect ratio. After consulting with additional colleagues, Steve decided we should make the change. Thus began the fabrication of new aileron tip counterweights, which required increasing the strength of the outer rib of the aileron, and some rework of the wingtips. Here are a few photos of the counterweights and the tips:

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On a visit to the shop, Mark Frederick took one look at the aileron push tubes I had made, and said, "they're too long, they'll sag, or buckle...we had to use two tubes per side, and use an idler when we went to the EVO wing on the F1 Rocket".

Steve did some structural analysis and compared our tube length to that of the 8 and the 7. Ours was longer, but we decided to try to make new tubes out of larger 1.25" tubing for added rigidity and anti-buckling strength. We fit them, and liked the clearance and fit, but thought it might be close if they sag under g. Given that we had removed the Reno deadline, we went back to the drawing board, and followed Mark's suggestion. Fellow racer Tom McNerney had a spare set of bellcrank bearings that are used for a similar purpose in the Legacy, so with those in Steve's hands, he made a bracket and mounting pad, and sent them to me. I bonded them in, and remade the tubes with the original 1.125 tubing, and they've gone together nicely. Here's a series of photos from tip to root, showing the inspection ports for reference, then in the center two ports for bell crank and outer push tube connections, the inner port for idler connection, and looking in from the root. Don't judge me on torque seal application...that old bottle led me to make a mess...bought a couple more bottles and did better on later applications.

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Tom Swearingen is helping me design and build some hoses for the root-to-fuel selector portion of the fuel delivery system, and those will be measured on the next wing-on session this week. I've made all the hard lines needed, and made the shrouds for the selector and the lines along the spar front.

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After this wing-on, wing-off cycle, we will be nearing time to move the project to a hangar in Taylor, TX, for final assembly and ground/flight test. We've decided to do the first tests there...4,000' of hard surface deemed a bit more apropos than 2,500' of grass. I'm sure Steve will have follow-on info and thoughts on the info in this latest update. More to follow as we get closer.

Cheers,
Bob
 
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Interesting project Steve - FYI Glasiar IIS with slotted flaps & extended tips has stall speed of 49kts & most use 70-75 kts for approach, I'd say that's almost the same as an RV ?:D
 
Interesting project Steve - FYI Glasiar IIS with slotted flaps & extended tips has stall speed of 49kts & most use 70-75 kts for approach, I'd say that's almost the same as an RV ?:D

Jake,

Steve designed this wing, and early-on we made wingspan decisions, to preserve as much of the all-around total performance of the RV wing as possible, while adding the performance benefits of the tapered, laminar flow design. The X-C tips will do more of that than the racing tips, which will fly first (larger tips and wingtip lighting a bit down the road). As he said a few posts back, its a compromise. We have hinged flaps versus slotted, so as to remove the drag of the standard Glasair/Lancair hinge brackets. Early flights will explore slow flight, incipient and full stalls, and we'll base our final approach speed on that, of course.

I've not landed a Glasair II, but have instructed in one at Pylon Racing School. Approach speed was very RV-like. The Glasair III I owned was more like a Legacy, both of which had speeds in the pattern of 120 on base (partial flaps), then 105-100 on final with full flaps when the field was made, and slowing to below 100 over the fence...touch down in the 70's. That's all nominal...they can be flown slower, but that's a conservative approach.

My old wings are clipped 7" per side, and my RV stalled at 53 dirty, 58 clean. I flew the pattern at 75-80. Fence speed 70-75, slower if needed for field length. Knots. In formation, standard pattern speeds in the pattern are (in knots) 87 downwind, 78 base, 72 final (mph =100, 90, 80). My old wing was compatible...with this wing, I will likely need to stay a tad faster and give the aircraft in front of me a little extra space.

Our initial approach to landing speed will be somewhere between the Glasair III and Super Six speeds, based on initial stall testing. I'll use a larger pattern initially to stay away from tight turns on base and final, especially if the stall testing shows any wing drop tendencies. Steve has already discussed stall strip evaluation if that is the case.

Cheers,
Bob
 
I live just south of you in Leander. Would love to take a look at the project some day.


Jake,

Steve designed this wing, and early-on we made wingspan decisions, to preserve as much of the all-around total performance of the RV wing as possible, while adding the performance benefits of the tapered, laminar flow design. The X-C tips will do more of that than the racing tips, which will fly first (larger tips and wingtip lighting a bit down the road). As he said a few posts back, its a compromise. We have hinged flaps versus slotted, so as to remove the drag of the standard Glasair/Lancair hinge brackets. Early flights will explore slow flight, incipient and full stalls, and we'll base our final approach speed on that, of course.

I've not landed a Glasair II, but have instructed in one at Pylon Racing School. Approach speed was very RV-like. The Glasair III I owned was more like a Legacy, both of which had speeds in the pattern of 120 on base (partial flaps), then 105-100 on final with full flaps when the field was made, and slowing to below 100 over the fence...touch down in the 70's. That's all nominal...they can be flown slower, but that's a conservative approach.

My old wings are clipped 7" per side, and my RV stalled at 53 dirty, 58 clean. I flew the pattern at 75-80. Fence speed 70-75, slower if needed for field length. Knots. In formation, standard pattern speeds in the pattern are (in knots) 87 downwind, 78 base, 72 final (mph =100, 90, 80). My old wing was compatible...with this wing, I will likely need to stay a tad faster and give the aircraft in front of me a little extra space.

Our initial approach to landing speed will be somewhere between the Glasair III and Super Six speeds, based on initial stall testing. I'll use a larger pattern initially to stay away from tight turns on base and final, especially if the stall testing shows any wing drop tendencies. Steve has already discussed stall strip evaluation if that is the case.

Cheers,
Bob
 
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