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Author Topic: Alternative contruction methods for CLG wings?  (Read 1610 times)
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VictorY
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« on: February 12, 2018, 01:19:59 AM »

I was just curious if there were any planes out there with different methods for creating airfoils other than shaped solid balsa. Anyone done some composite wings for example? Or how about a wing with something like a sheet balsa bottom, spar/rib system and some type of covering on top? Seems like you could knock out half a dozen wings in a night with some laser cut parts and covering. And very  little balsa dust. LOL I'm bascically just looking for a way to cut down on balsa dust without installing a vacuum system. While brainstorming, I also thought about a solid wing built from layers of laser cut light balsa glued together to roughly form desired airfoil/planform. Jig holes would make for an accurately assembled wing, which could then be covered with something similar to micro-balloons or light filler, then sanded back to make for airfoils much closer to what the designer had in mind than the average modeler can produce.

Thanks
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Tapio Linkosalo
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« Reply #1 on: February 12, 2018, 03:41:58 AM »


My guess is that 3D machining or 3D printing will be the future way to go. Either mill the wings from balsa, or use a 3D printer to produce molds, then mold the wings from foam core and carbon skins. For larger FF models people use cores milled from foam (Rohacell or similar), but for prop blades I have with good success molded cores from polyurethane, so that could be another option for smaller wings. Or maybe you could use directly 3D printed wings? At least in larger RC models that is already a viable option.
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VictorY
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« Reply #2 on: February 12, 2018, 04:29:50 AM »

My last idea would be kind of like a low resolution 3D printed wing, but made of layers of balsa wood. The micro balloons would fill in the steps, making for a smooth accurate profile. The inner layers could be designed with voids to save wood weight and leave room for glue and any layer of glass or carbon tissue that you may want to laminate the surface with.
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« Reply #3 on: February 12, 2018, 07:02:08 AM »

The most recent issue of the NFFS Digest (Nov/Dec 2017) had full-size plans for Ken Moldy Cat 3, which uses a wing cut from Fomular 150 pink foam and vacuum based with Carboweave 20 grams per square meter cloth.

One of the Sympos (late 1990s early 2000s?) had an Indoor H/L glider with wing made using the aluminum-balsa skin that was popular back thin for F1C wings. This was a very thin and very hard aluminum. If I remember correctly, the aluminum was in one piece for each wing half. The top and bottom balsa pieces were glued on with a slight gap at the leading edge, then ribs were added and the top folded over. I have no idea if the aluminum is still available. I do recall that cleaning the aluminum prior to gluing on the balsa required considerable preparation to get the epoxy to stick to the aluminum.

I wonder if a similar idea could be used for a fully-sheeted wing? Perhaps 3/4 ounce glass cloth could be bonded to 1/32 balsa, then the wing assembled. I've had good luck attaching light glass to balsa using the following method: Carefully unfold a large piece of glass cloth over wax paper attached to a piece of corrugated cardboard. Smooth out the glass cloth and tape in place. Then mist with Deft clear lacquer (spray can). After it drys, the stiffened glass cloth can be easily cut to rough size and pealed off the wax paper. Spray the balsa surface with lacquer, allow to dry, the place glass cloth over balsa and brush with lacquer thinner. Brush some lacquer around the edges, allow that to dry, and trim glass cloth off with fine sandpaper.
The Deft clear lacquer seems to shrink less than nitrate dope and is available at many hardware stores in the US.

Louis (Who doesn't own stock in Deft, but wishes he did.)

PS You will need a spar of some sort for the built-up sheeted wing. A tapered, full-depth balsa spar might be enough for a CAT glider. On the Moldy Cat 3, Ken used .003 inch carbon strips top and bottom on the main panels.


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Hepcat
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« Reply #4 on: February 12, 2018, 08:18:33 AM »

Victory,
Your basic question is easily answered; All the CLGs I have seen have a solid balsa wing although I guess some will have been made with moulded wings.
Brainstorming is good, most of us do it and sometimes I think I have a better mousetrap but no one has yet knocked on my door to make me a fortune!
I do not have a laser cutter, I don’t know if a 3D printer can print with balsa but even if they can I think by the time the bits have been laminated, glued together, filled and finished I could build a solid balsa wing quicker.
However the overriding factor for many people when making wings is that they just like working with wood. Any surplus is removed with very sharp tools as shavings so sanding produces very little dust and that can be cleaned up quicker with the vacuum hose than you can clean the soil off the carpet after the wife has been gardening.
(This is meant to be funny not rude)
John   
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John Barker UK - Will be missed by all that knew him.
Tapio Linkosalo
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« Reply #5 on: February 12, 2018, 08:44:44 AM »

I have no idea if the aluminum is still available. I do recall that cleaning the aluminum prior to gluing on the balsa required considerable preparation to get the epoxy to stick to the aluminum.

I'd guess that the aluminium should still bea available, at least from F1C fliers. That construction was really common, but is no obsolete, so I believe that many people still have surplus stock.

The other thing is, it probably would not make any sense to use it. The aluminium skin was quite vulnerable, with the foil taking scratches and dents on landings, and probably a CLG would also suffer a similar faith. I'd think a carbon skin would be preferable also for a CLG model.

But the big thing to change shortly shall be computerized manufacture, I think. It will enable to making multiple and identical models, so that once you have one trimmed, the others will fly off the building board. People have done that on their balsa gliders, using extensive tooling to make the shaping process standardized, but CAM should make that process even easier.
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flydean1
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« Reply #6 on: February 12, 2018, 09:54:42 AM »

All the above is very interesting, but in some ways disturbing.  I find working with wood therapeutic: carving and sanding to shape of a CLG wing is one of the best in that regard.  As far as accurately shaping, so far, straight edges and templates suffice to reproduce any of the required profiles to an acceptable degree of accuracy.

Indeed, CLG made it possible for me, who never had any sort of throwing arm, and poor coordination to boot, to fly small gliders which were cheaply made.

I can see the day, not far in the future when the "factories" will be able to produce wings extremely accurately shaped which will soon be a requirement to win at the national level, at least in the USA.  Are $100.00 CLG's far off?  Possibly not.

As all the FAI events have managed to price themselves out of the reach of the average modeller, what will we do when even the "simpler" models become unaffordable?

I'm not decrying progress, just making an observation.
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VictorY
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« Reply #7 on: February 12, 2018, 03:43:52 PM »

Any of the upper level freeflight modelers could easily make composite cat glider parts at home with minimal equipment and for far less than $100 per plane. I'm not trying to turn over the apple cart here. Just asking questions. Smiley

As for 3D printing with balsa wood, I didn't mean literally. The layers of balsa stacked on top of one another would have stepped edges, like a low resolution 3D printed part. Filler would be used to fill in the steps then sanded back to expose the edges of the balsa steps, making for a very accurate and repeatable profile/planform. Plenty of opportunity to get your Zen on. Smiley But now that I've thought about it some more, there aren't going to be too many layers to work with as thin as CLG wings are. Just thinking out loud.

Thanks for the responses.
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« Reply #8 on: February 12, 2018, 06:30:44 PM »

Victor,

In regard to your idea of stacking thinner sheets of balsa, the biggest concern I would have is the extra weight of the adhesive.  Also the adhesive creates a line that is harder than the balsa, which can result in slightly raised areas along the glue line after sanding. The solution to both these issues is to use the absolute minimum amount of adhesive and to use one that is a bit "soft" i.e. closer to the density of balsa.

On my laminated and molded F1B props I've had the best result using laminating epoxy resin as the adhesive to hold together the pre-formed layers. The resin is brushed on, then blotted off with Viva paper towels until it looks almost dry. Next the assembled layers are vacuum bagged at around 18 inches of mercury. (Obviously I didn't follow my own advice to use a "soft" adhesive. But by keeping the adhesive layer very thin, it has minimal effect on sanding.)

If your goal is airfoil accuracy and repeatability, some sort of sanding jig could be used with traditional solid balsa for less weight and less effort. Some years back Hepcat had an excellent paper in the British Free Flight Forum on building catapult gliders. For wings the basic idea was to sand the rectangular balsa sheet so it tapered front to back in thickness (think of a very wide piece of trailing edge stock). Then he cut the typical wing outline with straight trailing edge and curved leading edge. This results in a wing that automatically tapers in thickness from root to tip. Perhaps John will chime in.

Louis
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danberry
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« Reply #9 on: February 18, 2018, 04:07:54 PM »

Ken Bauer has composite stuff on his CLG. With some success.
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VictorY
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« Reply #10 on: February 19, 2018, 03:20:23 AM »

Victor,

In regard to your idea of stacking thinner sheets of balsa, the biggest concern I would have is the extra weight of the adhesive.  Also the adhesive creates a line that is harder than the balsa, which can result in slightly raised areas along the glue line after sanding. The solution to both these issues is to use the absolute minimum amount of adhesive and to use one that is a bit "soft" i.e. closer to the density of balsa.

On my laminated and molded F1B props I've had the best result using laminating epoxy resin as the adhesive to hold together the pre-formed layers. The resin is brushed on, then blotted off with Viva paper towels until it looks almost dry. Next the assembled layers are vacuum bagged at around 18 inches of mercury. (Obviously I didn't follow my own advice to use a "soft" adhesive. But by keeping the adhesive layer very thin, it has minimal effect on sanding.)

If your goal is airfoil accuracy and repeatability, some sort of sanding jig could be used with traditional solid balsa for less weight and less effort. Some years back Hepcat had an excellent paper in the British Free Flight Forum on building catapult gliders. For wings the basic idea was to sand the rectangular balsa sheet so it tapered front to back in thickness (think of a very wide piece of trailing edge stock). Then he cut the typical wing outline with straight trailing edge and curved leading edge. This results in a wing that automatically tapers in thickness from root to tip. Perhaps John will chime in.

Louis

I would point you to my last response. The glue joints would never come into play if you stop sanding when you hit the edge of the balsa layers, which double as your template. like a topographical map. If you start to see them poking through the layer of filler as you sand it off, stop. I'm with you on the added weight. Now that I've got a mini block plane with a razor sharp blade, I'll probably stick to traditional construction methods and then guess at my airfoil profiles. It's worked pretty well so far and I'm not flying any contests so......  Smiley I'm having fun building again.
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« Reply #11 on: February 19, 2018, 06:22:11 AM »

Victor,

Thanks for the explanation on your stacking method. I can see how that would eliminate the glue line problem.

For a conventional solid balsa wing, consider making a simple sanding jig. The one I use consists of a pice of 3/4 inch plywood a few inches wider and longer than the wing. To this I glue a strip of basswood about 1/4 inch thick running parallel to the long edge. The exact height and spacing depends on the airfoil, maximum high point height, and wing chord. The rough-planed rectangular wing blank is positioned on the board and a sanding block that bridges from the wood strip back to the rear of the board is used with a span wise movement to sand to the exact taper from high point to the desired trailing edge thickness. To prevent sanding down the strip or the rear edge of the board, the sanding block only has sandpaper in the area needed. Once the balsa blank is sanded to the desired rear airfoil taper/thickness, it is cut to the desired planform, typically a straight trailing edge and a leading edge that curves back. Next any basswood strip leading edge reinforcement is glued on. If you are using one of the newer glider airfoils with tapered flat segment running from apron 10% chord back to the high point, you can use an angled sanding block to sand that into the front portion of the wing. This will give you a distinct high point. Note that the leading edge sanding block has a flat portion that rests on a flat surface and a raised portion with sandpaper attached that extends over the front portion of the wing. ( I wish I could say all this was my idea, but it was stolen from two frequent Hip Pocket contributors, Hepcat and Tmat.)

Sanding a wing this way is much more accurate and repeatable than trying to eyeball the sanding process.

Louis
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dosco
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« Reply #12 on: February 19, 2018, 08:40:11 AM »

Take a look at Prosper's work. Balsa skins with several spars (few/no ribs) for rubber FF jobs ... very nice stuff.

-Dave
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VictorY
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« Reply #13 on: February 20, 2018, 04:00:34 PM »

Take a look at Prosper's work. Balsa skins with several spars (few/no ribs) for rubber FF jobs ... very nice stuff.

-Dave


Do you have more info? Thanks
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ffkiwi
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« Reply #14 on: February 20, 2018, 04:26:13 PM »

Many years ago-in my Dunedin MAC days-in the 80's one of my clubmates Hec Sapwell turned up at the field with an O/D HLG-quite large-by the standards of the day-so that means ca 24"-it had a wing that was simply a piece of 1/16" sheet with a strip of 1/8x1/4 balsa glued on edge as a spar on top of the 1/16" sheet at the usual high point location-so somewhere around the 33% chord mark....and the whole thing covered in transparent iron on plastic covering-probably Solarfilm, since that was about all that was available in NZ at the time. This of course gave a triangular airfoil-which a number of people have used in HLG over the years-with reasonable success.  We gave him a hard time about his design ideas...we had some very good HLG fliers in the club at the time.....whereupon he proceeded to wipe the smile off our faces  by demonstrating that it flew as well -if not better-than any sheet wing examples we put up against it....and being light, floated extremely well on the glide
   Now whether that approach would work on a catapult model-with the much higher launch speed-I could not say-I would think there might be issues with flutter-but its easy enough to test-and if it doesn't work you haven't wasted a lot of time an effort on it.

  ChrisM
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dosco
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« Reply #15 on: February 22, 2018, 07:54:48 AM »

Take a look at Prosper's work. Balsa skins with several spars (few/no ribs) for rubber FF jobs ... very nice stuff.

-Dave


Do you have more info? Thanks


Here's an example.

For some reason (probably not enough coffee) I didn't notice you were asking about CLGs - I only noticed the "alternate wing construction" question. I'd guess that some of the more seasoned folks here saw my response and had a chuckle.

I'm dubious that Prosper's method would work well for a CLG, but maybe you can adapt the approach.

Cheers-
Dave


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lincoln
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« Reply #16 on: February 25, 2018, 12:11:42 AM »

-Wet sanded Highload 60 or Plazamate would make a nicely shaped wing that was very smooth. The water keeps the dust under control, and I think it may make the paper cut faster as well.  I understand people sometimes use meat tray foam, though I haven't tried it. All but the smallest CLG's would need some kind of reinforcement, though that might ruin the very nice shape. On the Charles River Radio Controllers' web side, there's an article about the Apogee RC HLG. Check out the "accurate shaping" notes.

-Indoors, people have been using foam wings for CLG's, with carbon reinforcement. I suspect that the carbon, unless it's very smoothly faired in, causes a lot of drag. However, the following design is for category 2 ceilings, so it only has to get to 49 feet.
https://indoornewsandviews.com/2015/05/11/bill-gowens-cat-ii-record-standard-catapult-launched-glider/
For outdoor flying, it would probably be best to figure out how to smooth over the carbon to enable a higher launch.
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dosco
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« Reply #17 on: February 26, 2018, 06:56:13 AM »

Lincoln:
Your post jarred a memory ... who was it making foam core composite wings? Jim Buxton?

I forget. Maybe that thread would help the OP.

Regards-
Dave
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DerekMc
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« Reply #18 on: February 26, 2018, 10:40:17 AM »

Ken Bauer has composite stuff on his CLG. With some success.

Indeed. His CLG's and HLG's are innovative and fly well.  Ken was hanging out at the E36 contest at FabFeb and expressed interest.  He did say that if he built one it would be with his CLG techniques.  I hope he builds one. I would love to see what he comes up with.
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« Reply #19 on: February 26, 2018, 02:36:24 PM »

Ken Bauer has composite stuff on his CLG. With some success.

Indeed. His CLG's and HLG's are innovative and fly well.  Ken was hanging out at the E36 contest at FabFeb and expressed interest.  He did say that if he built one it would be with his CLG techniques.  I hope he builds one. I would love to see what he comes up with.

Yup. He is having marginal success with it.......... Grin
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