Moldless composite (aka "hotwired") --conventional (non-canard) aircraft

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Vigilant1

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I'm looking for examples of "conventional" aircraft designs that use "Rutan-style" moldless composite construction.

1) I recall reading of a one-off high-wing design that crashed on the way to Oshkosh (no serious injuries, I think it was engine or fuel related), and if anyone knows the name of the design or the designer or more about that please pass it along (I >>think<< the story of the accident and getting it out of the cornfield was written up in a magazine, maybe Kitplanes. This was a long time ago).

2) IIRC, the Arnold AR-5 used the Rutan method.

Any others? Thanks.

Mark
 

BJC

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Keller Prospector is a mid wing conventional configuration. Won Grand Champion.
That is an interesting design. IIRC, only two were built, and he declined to make plans available.

Has anyone here flown one?


BJC
 

wsimpso1

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Vigilant1,

The ones I know about are mentioned above, plus a high wing single seater built and brought to OSH a couple years ago.

If I may be so bold, what is your purpose in looking at these examples? The few conventional, then tandem wing and many canard aircraft made by these methods pretty much use a common material set and common practices in build. If you share what you are interested in with these airplanes, we might be able to help some more...

Billski
 

Vigilant1

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If I may be so bold, what is your purpose in looking at these examples? The few conventional, then tandem wing and many canard aircraft made by these methods pretty much use a common material set and common practices in build. If you share what you are interested in with these airplanes, we might be able to help some more...

Billski
Billski,
I've wondered why there have been few moldless composite conventional designs, but figured maybe there were a lot of them and I just wasn't aware of their existence. So, I thought I'd see if there were a lot of designs out there I just didn't know about (and I see there are some--thanks to all!)

Solid core composite construction seems like a very attractive way of building (especially flying surfaces wings), and one that might be expected to have become more popular. After all, Burt Rutan's designs popularized two things in the homebuilding world: the canard configuration and moldless composite construction. Both were noteworthy, but they seem to me to be fairly independent: No reason one shouldn't be able to design an aluminum or a composite cored-skin and ribs composite canard, and no reason one couldn't design a plane with a conventional wing and tail that used solid-core hotwired flying surfaces. Both have been done, but they are exceptions: Most flying canards are moldless composite, and most moldless composite designs are canards. Here we are 43 years after the first flight of the VariEze, and the canard layout and moldless composite construction still largely remain "linked" in the small aircraft design world.

I wonder why?

Theories:
1) Moldless composite design is uniquely appropriate for canards, but isn't very appropriate for conventional designs. This seems very unlikely.
2) Moldless composite design is uniquely appropriate for plans-built aircraft fabricated in small shops, is less appropriate for kits or other production models where expensive tooling and tools is more practical. Since plans-built designs are now less popular than kits in today's E-AB "world," it is logical that moldless composite designs are a smaller percentage of the new designs than they were before.
3) It is more difficult to create a new, safe composite design (of any type) than to do one in metal. The "bar to entry" for new designs is higher due to the matrix math that is generally required, a shortage of "accessible" books/tools for use by amateur designers wanting to create a clean-sheet composite design, and the small number of well-proven existing moldless composite designs suitable for use as guides ("monkey see, monkey do"). Maybe a designer of a two-seat side-by-side cross-country plane could figure out a safe wing design starting from the LongEze wing, but he'd have to make some very conservative choices and test a wing or two to destruction before being fairly confident all was well.

I think Explanation 2 and 3 above are much more likely than Explanation 1. So, (consistent with Explanation 3), this thread is an attempt to see if there are other conventional moldless composite designs, especially any with design/construction info available in plans, suitable for emulation or at least comparison when drawing up a new or "derivative" design.

Mark
 

BBerson

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Solid core is mostly suitable for small chord surfaces, usually high aspect ratio. The Silouette is an example of a foam core, conventional layout, with small chord wings.
 

Vigilant1

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That's a neat little design I'd never seen before, thanks. Pretty fast (175 MPH) on a small amount of power (75% from the 80 HP A-80 engine). The small 40 sq ft relatively high aspect ratio (10:1) wing helps explain the efficiency. The 70 MPH Vso is the price paid for the small wetted area of the wing, I guess. The article (Dec 1979) says plans were to be available.
 

Vigilant1

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Solid core is mostly suitable for small chord surfaces, usually high aspect ratio. The Silouette is an example of a foam core, conventional layout, with small chord wings.
Opinions on why?
- Small wing volume relative to wing area decreases the weight penalty of the interior foam (compared to using ribs)?
- Relatively long span to spar depth gives composite designs a relative weight advantage over AL?
 
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Riggerrob

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Both the Ken Rand series and War Aircraft Replicas series use foam and Fiberglas wrapped around plywood fuselages and wooden wing spars.
KR lines are simply and lend themselves to hot-wiring.
OTOH WAR profiles are more complex and the depth of surface detail is limited only by the number of hours a builder is willing to devote to grinding and filling and grinding and filling until it resembles a World War 2 fighter plane. If I were building a WAR today, In would start by drawing external surfaces on Solidworks and export them directly to a CNC router.

Moldless construction can be labour-intensive.
Foam is easily damaged in the early stages. Even hot-wiring produces toxic fumes.
Any dent/crack/shallowness must be filled with micro-balloons, then sanded, then checked for dimensions, then filled and sanded again until it resembles a wing. All that sanding creates clouds of dust.
Simply laying multiple layers of cloth in a production mold is time-consuming.
All those chemicals are toxic and stinky!

If I were building mold-less today, I would save excess foam and use it as a saddle/female mold to stabilize the wing while vacuum-infusing resin.

Since all that labour presents opportunities for error, many KITPLANES manufacturers prefer to sell pre-molded kits, to minimize the chance of error. Some only sell pre-molded kits without detailed fabrication instructions.
Production female moods dramatically reduce the amount of sanding required. Factories often have autoclaves and pre-preg cloths that speed production and produce more precise parts that can be lighter than homemade components.

The next step will be plans-sellers only selling CNC files that make perfect sense to CNC routers, but are gibberish to humans!
Hah!
Hah!
 
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BBerson

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Opinions on why?
- Small wing volume relative to wing area decreases the weight penalty of the interior foam (compared to using ribs)?
- Relatively long span to spar depth gives composite designs a relative weight advantage over AL?
Yes, the KR-1 used 1" foam on the thick wing section and solid foam on the controls.
I don't think fiberglass has any weight advantage over aluminum. The metal wings on a Schweizer 1-23 are long and light but not perfect airfoil.
 

BoKu

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...If I were building mold-less today, I would save excess foam and use it as a saddle/female mold to stabilize the wing while vacuum-infusing resin...
That's close to the "semi-moldless" soft-tool technology we use for onesey-twosey surfaces. Basically, we hotwire a wing, throw away the wing-shaped core, and use the remaining shucks to enforce wing profile onto PVC-core sandwich construction carbon fiber parts. The main issue is that you want 20+ in.hg to get good consolidation of the carbon/Divynicell, but hotwireable EPS foam tends to crush and distort at about 12" hg. We use a bag of proprietary tricks to address that and related issues, but none of them are particularly applicable to resin infusion.

...Since all that labour presents opportunities for error, many KITPLANES manufacturers prefer to sell pre-molded kits, to minimize the chance of error. Some only sell pre-molded kits without detailed fabrication instructions...
That's us. One mitigating factor is that we strongly encourage builders to come to the shop when we make their fuselage shells, wing skins, and wing spars, and when we do their wing closure. In the end, the builder has direct experience with every panel, rivet, and bondline in their aircraft.

...Production female moods dramatically...
(Emphasis mine) I hereby nominate this for the HBA Freudian slip of the year award. :)

--Bob K.
 

wsimpso1

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Billski,
I've wondered why there have been few moldless composite conventional designs, but figured maybe there were a lot of them and I just wasn't aware of their existence. So, I thought I'd see if there were a lot of designs out there I just didn't know about (and I see there are some--thanks to all!)

Solid core composite construction seems like a very attractive way of building (especially flying surfaces wings), and one that might be expected to have become more popular. After all, Burt Rutan's designs popularized two things in the homebuilding world: the canard configuration and moldless composite construction. Both were noteworthy, but they seem to me to be fairly independent: No reason one shouldn't be able to design an aluminum or a composite cored-skin and ribs composite canard, and no reason one couldn't design a plane with a conventional wing and tail that used solid-core hotwired flying surfaces. Both have been done, but they are exceptions: Most flying canards are moldless composite, and most moldless composite designs are canards. Here we are 43 years after the first flight of the VariEze, and the canard layout and moldless composite construction still largely remain "linked" in the small aircraft design world.

Mark
Vigilant1,

Moldless composite is a lot of work in a material set most of us are unfamiliar with. That shuts out a lot of folks.

The market has largely transitioned to quick-build processes, and moldless composite does not look quick-build to many folks.

So, who is willing to put in work in a strange material set? People who also like strange looking airplanes. Canards and tandems... Once the novelty of canards wore off, the market got small.

I agree completely on moldless NOT being particular to canards.

The comment about it favoring high aspect ratio surfaces bears discussion. Here is how the discussion usually starts: "Oh, all that foam has to be heavy. Wouldn't it be better hollow?" Well, maybe. Simply put, a hollow surface (wing, stabilizer, control surface) has to have at least min gage on the outside. 2 BID or 3 UNI is nominally minimum skin on little fiberglass birds, so let's call 21 oz/yd^2 of cloth minimum gage. In graphite it is more like 10 or 12 oz/yd of cloth. You also have a spar in each (or do not have it in both) and you have fairing and finishing the outside, so these are all not discriminators. Now to tally the weight differences between solid and hollow.

Solid has foam core, maybe some little volumes with high density foam to attach hinges and stuff, and a closeout rib is laid up on each end of the part. That is about it. The solid core is 2lb/ft^3.

Now what do you have to be hollow? Foam 3/8" thick and 4.5 - 6 lb/ft^3, so while you have a less volume of foam, you save less weight than you would think. Then you have min gage on the inside surface of the foam. That almost doubles the amount of fiber/resin in the part right there. Then you need at minimum a couple ribs and at least one longeron, which are a sandwich of foam and min gages of cloth and resin like the skins. That is another big does of fiber and resin and foam. Then you attach the internals to the inside of the skins with micro fillets and 2 BID tapes everywhere. Besides being a lot of work, taking out a little 2 PCF foam is putting in a bunch of other stuff that weighs significant amounts. Before we say hollow is ALL downsides, let's think for a minute - You can vacuum bag all of these parts and save some weight on them. You can also vacuum bag any spar and the skin on the outside of the massive cored part too.

I did not run the numbers, but IIRC Autoreply cited someone who did, and the break even point (IIRC) looks to be a chord somewhere over 60". Yep, if your chord is smaller than the breakeven point, you save weight by going massive foam. Please do you own analysis and decision making... So it is not so much high aspect ratio as smaller chord that favors solid foam.

You can not use hotwired foam (polystyrene foam is the only foam safe for us humans to hotwire) in a structure that is also a fuel tank. Gasoline will diffuse through composites and reduce your continuous root to tip rib to a little puddle of clear blue plastic and rendering your airplane unairworthy. I have seen this... So, if your wings are fuel tanks, then that part of the wing has to be made with fuel safe foams. The Long EZ and its derivatives, Defiant, Quickie and its derivatives, all have fuel in one place and solid core wings, canard, and control surfaces someplace else for exactly this reason.

My airplane? Hollow wings are largely fuel tanks and equipment bays. But my tail and all control surfaces are hotwired from blue foam, have high density foam inserted for hard points, spars built up on the stabilizers and vacuum bagged to take out excess resin, and skins vacuum bagged on to also keep resin mass to a minimum... Do they need more fairing? Not so you would know about it. All types of composite flying surfaces need fairing, and they all should be done in keeping with the prime directive - put it on once, take it off once. Light, sturdy, good looking - what is not to love?

Billski
 

TFF

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This might seem strange but I think you don't see standard configuration Rutan style building because it does not feel right for the application. If you had a RV7 shaped fuselage and the aft behind the cabin is solid foam, it just has an off feel for design. Something diminutive where there is not a lot of volume would be ok, big blocks makes you want to look for a better solution. Wings are probably the most underrated wing. It is no free ride, but I am surprised wings for like a RV like plane are not made like that with a more conventional fuselage.
 

wsimpso1

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Both the Ken Rand series and War Aircraft Replicas series use foam and Fiberglas wrapped around plywood fuselages and wooden wing spars.
KR lines are simply and lend themselves to hot-wiring.
OTOH WAR profiles are more complex and the depth of surface detail is limited only by the number of hours a builder is willing to devote to grinding and filling and grinding and filling until it resembles a World War 2 fighter plane. If I were building a WAR today, In would start by drawing external surfaces on Solidworks and export them directly to a CNC router.

Moldless construction can be labour-intensive.
Foam is easily damaged in the early stages. Even hot-wiring produces toxic fumes.
Any dent/crack/shallowness must be filled with micro-balloons, then sanded, then checked for dimensions, then filled and sanded again until it resembles a wing. All that sanding creates clouds of dust.
Simply laying multiple layers of cloth in a production mold is time-consuming.
All those chemicals are toxic and stinky!

If I were building mold-less today, I would save excess foam and use it as a saddle/female mold to stabilize the wing while vacuum-infusing resin.

Since all that labour presents opportunities for error, many KITPLANES manufacturers prefer to sell pre-molded kits, to minimize the chance of error. Some only sell pre-molded kits without detailed fabrication instructions.
Production female moods dramatically reduce the amount of sanding required. Factories often have autoclaves and pre-preg cloths that speed production and produce more precise parts that can be lighter than homemade components.

The next step will be plans-sellers only selling CNC files that make perfect sense to CNC routers, but are gibberish to humans!
Hah!
Hah!
Hey RingerRob! If you think building in composites is so bad, why are you lurking here? The man has some points, but I believe that proper technique makes for a much easier time than he is saying.

Let's keep a few things straight. The KR series and the WAR series are wooden structure airplanes. Yep. PU foam is installed between the wooden parts, shaped, and a thin non-structural fiber-resin layer is put on the outside, that then is faired and finished. The KR's were not even fiberglass and epoxy at the beginning. And yes, you could doctor the surfaces all you wanted to make them look like sheet metal airplanes.

All this talk about filling. ALL composite airplanes need to be faired and finished. Even the molded ones. And the talk about all the hundreds of hours sanding needs to be listened to a lot less.

http://curedcomposites.com/finish.html

http://www.ez.org/pages/waynehicks/chapter_25_process.htm

Does it work? You bet. I just did the bottoms of my flaps and ailerons. First big parts I have tackled to the point of fairing and finishing. Shot one misted coat of dark green epoxy primer to give me a guide coat, put on dry micro about 1/4" thick, looked like I had iced a cake. I have five hours sanding the four of them to shape with big sanding sticks and 36 grit, another hour with 80 grit, fill all of the visible holes and scratches, five passes of neat epoxy on and off for pinhole killing, and another hour of 80 grit. Smooth surfaces. Gotta do the other side now.

Making parts in a mold is the easy and quick part. When we were making my wing skins (3' wide, 10' long in a female mold), we would host an epoxy party for each one. Cloth and foam is ready to go, epoxy pump filled and warm, and four or five helpers. A little instruction, assign folks jobs, and start. From first pump of epoxy to having the part under 20" Hg of vacuum was less than an hour and a half. Beer, salsa and chips, and pizza on the way. I have no problem getting hands to make composite parts... As for the smell, RingerRob must be talking polyester or vinylester resins. Epoxy is way less smelly than primer and paint, but those other two resins do smell strongly of styrene.

Now composite airplanes are not for everyone. If you prefer sheet metal or rag and tube, go build what you like. I like composites and they work for me.

Billski
 

wsimpso1

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This might seem strange but I think you don't see standard configuration Rutan style building because it does not feel right for the application. If you had a RV7 shaped fuselage and the aft behind the cabin is solid foam, it just has an off feel for design. Something diminutive where there is not a lot of volume would be ok, big blocks makes you want to look for a better solution. Wings are probably the most underrated wing. It is no free ride, but I am surprised wings for like a RV like plane are not made like that with a more conventional fuselage.
Solid foam is for wings, winglets, tails, and control surfaces. No one I know of uses solid foam in the fuselage...
 
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BoKu

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To add a couple points to Billski's post:

* EPS foams have relatively low compression strength and modulus, so it takes more and/or thicker laminations to achieve a surface that is adequately resistant to concentrated loads than with stiffer and stronger PVC foams.

* With PVC foams (we use Divynicell H60 or equivalent), we get by with a lot less than what Billski cites as minimum gauge. For example, our wing and tail skins are basically on one-core-one (one ply of 6oz carbon, the 1/4" foam core, and a closeout ply of 6oz carbon), with localized reinforcements along the edges and at the wing root. That's basically the same layup as a couple other similar sized sailplanes. We've had one wing set in service for about six years and one set just starting its third year, and neither is showing any signs of the distress you'd expect if it was shy of minimum gauge.

* I've seen plenty of twenty-year-old EZ-style airplanes that have clearly not aged well, with trenches and bulges where the foam has changed shape as it aged. But most fifty-year-old PVC-cored sailplanes I see are still sound. Of course, this is not a random sample--the EZ airplanes that I usually see are those sitting out on the ramp at small airports in essentially abandoned state, while the sailplanes are generally kept in enclosed trailers. But by and large even the older sandwich construction training sailplanes that get tied down out in the weather tend to age as gracefully as any indifferently-treated aircraft.

* Billski points out that gasoline and EPS don't get along. That also applies to acetone, MEK, and I think xylene and tolulene; basically everything you'd want to use as a cleaning solvent to prep for paint. Isopropyl alcohol is apparently safe, as is ethyl alcohol. However, denatured alcohol is often denatured by contaminating it with acetone, tolulene, or one of the other baddies. So painting prep has to be done pretty carefully.

* Along those lines, an instructive anecdote: A while back we made a batch of tail tanks to fit into vertical stabilizers. These are essentially 40" long tubes with elliptical cross section of about 6" x 1.5"g. We used four 0-90 plies of 7725 fiberglass, vacuum bagged into a female mold (made of hotwired EPS). All well and good. But when we tested one, it leaked like a sieve--not in any one spot, but everywhere. The parts were so porous that water would bead up on the outside surface and then run down to the bottom, where the aggregated oozage became a running stream. We ended up adding an extra ply of material with thickened resin to plug the leaks. But if water can seep out through four plies of fiberglass, imagine what acetone could do in the way of seeping in, even if it was one tenth as porous.

--Bob K.
 

TFF

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Most people who think of moldless building are thinking easy styling. They are styling not designing. They are not thinking of control runs or antenna wires or access to maintenance points, let alone weight. No one designing a plane forgets those things and would never think of a chunk of foam as the whole back end. Of course no one does it like that. It is immediately struck from design thought. It works for the Rutan stuff because no flight control is far from the cockpit; everything is already carved out to sit. Just like Rutan having real reason to build like he did, you have to have a real reason to venture form normal. You have to have a better idea, not a different idea.
 

wsimpso1

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To add a couple points to Billski's post:

* EPS foams have relatively low compression strength and modulus, so it takes more and/or thicker laminations to achieve a surface that is adequately resistant to concentrated loads than with stiffer and stronger PVC foams.

* With PVC foams (we use Divynicell H60 or equivalent), we get by with a lot less than what Billski cites as minimum gauge. For example, our wing and tail skins are basically on one-core-one (one ply of 6oz carbon, the 1/4" foam core, and a closeout ply of 6oz carbon), with localized reinforcements along the edges and at the wing root. That's basically the same layup as a couple other similar sized sailplanes. We've had one wing set in service for about six years and one set just starting its third year, and neither is showing any signs of the distress you'd expect if it was shy of minimum gauge.

* I've seen plenty of twenty-year-old EZ-style airplanes that have clearly not aged well, with trenches and bulges where the foam has changed shape as it aged. But most fifty-year-old PVC-cored sailplanes I see are still sound. Of course, this is not a random sample--the EZ airplanes that I usually see are those sitting out on the ramp at small airports in essentially abandoned state, while the sailplanes are generally kept in enclosed trailers. But by and large even the older sandwich construction training sailplanes that get tied down out in the weather tend to age as gracefully as any indifferently-treated aircraft.

* Billski points out that gasoline and EPS don't get along. That also applies to acetone, MEK, and I think xylene and tolulene; basically everything you'd want to use as a cleaning solvent to prep for paint. Isopropyl alcohol is apparently safe, as is ethyl alcohol. However, denatured alcohol is often denatured by contaminating it with acetone, tolulene, or one of the other baddies. So painting prep has to be done pretty carefully.

* Along those lines, an instructive anecdote: A while back we made a batch of tail tanks to fit into vertical stabilizers. These are essentially 40" long tubes with elliptical cross section of about 6" x 1.5"g. We used four 0-90 plies of 7725 fiberglass, vacuum bagged into a female mold (made of hotwired EPS). All well and good. But when we tested one, it leaked like a sieve--not in any one spot, but everywhere. The parts were so porous that water would bead up on the outside surface and then run down to the bottom, where the aggregated oozage became a running stream. We ended up adding an extra ply of material with thickened resin to plug the leaks. But if water can seep out through four plies of fiberglass, imagine what acetone could do in the way of seeping in, even if it was one tenth as porous.

--Bob K.
The softness of blue foams is probably a big part of why 21 oz of glass is a common min gage.

I too have seen Long EZ's and a Lancair 200 that looked lumpy on the ramp. The ones I know about were faired with auto body filler. Ugly - bumps and trenches. Bondo is loaded with styrene that melts blue foam and then shrinks forever. If the foam underneath was OK, (a big IF), they needed stripping to the fiberglass and then a full reprofile if they were to be salvaged, but they had been abandoned instead. The counterpoint to all of this is there are a bunch of 30 year old Long EZ's and the like with impressive hours that still look great, so I am more suspicious of lousy build quality far more than the foam being inherently too soft.

I am surprised that one 6 oz ply of carbon is sturdy in your shop and then in the real world. Orion liked two plies of graphite cloth everywhere, as do Lancair/Evolution and others building fast little airplanes. Running the numbers, your skins and mine are in the same neighborhood for bending stiffness... So two plies must just be a brick for stiffness.

I too can attest to how you can make filters out of vacuum bagged cloth and epoxy. Thickened resins, no perf ply, extra layer of resin, or silicone primer and flurosilicone sealer are all viable methods to make tanks that won't weep and drain. They all sort of defeat the intent of vacuum bagging... Frustrating.

When parts are made on blue foam, you MUST avoid solvents and the like until you have a layer of resin on everything. I tend to use waterborne cleaners for this reason. Stewart Systems has a good one that is compatible with their primers and paints. Having resin on everything before applying PolyFiber Epoxy Primer is necessary, and only use a mist layer anyway.

Billski
 
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