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Old Jan 15, 2004, 12:52 PM
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Build of Sig "Liberty Sport" biplane

The full-scale Liberty Sport is a homebuilt originally designed and built by Orval LLoyd in 1965. It appeared on the cover of the July 1966 issue of SPORT AVIATION. In 1968 it was flown to Olathe and was exhibited in the NATS where it was seen by the model designer Dick Graham. Since being kitted by Sig the model has won several scale competitions including 1st place at the 1973 National Multi-Wing Championships.

Sig calls this model "an exact scale R-C that flys like a sport model". They also call it "a Craftsmans's kit" and you will find out later what they mean by that. I've always liked the looks of this bipe and finally decided to build one. Unfortunately Sig no longer makes the kit. But they are still not too difficult to find on ebay or at swap meets. I saw one on ebay and picked it up for about $100.
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Old Jan 15, 2004, 01:21 PM
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After looking the kit over and seeing the construction details it occurred to me that the model might build fairly lightly and so might be a candidate for electric power. Now to be honest with you I still have not decided if I will go electric, but the moderator gave me the go-ahead to post here until and if I decide differently.

Since this kit has been around for a while it has become known by many as a "builders kit". That means that you actually have to cut balsa and build over the plans, as opposed to pouring CA into a box full of laser cut parts and shaking to dump out an assembled airframe. This reputation has scared many would-be builders away. And in fact on opening the box the first look is rather daunting. You discover a box full of balsa sticks, a few beautifully formed ABS parts for the cowl and pants, and only a very few sheets of die-cut ribs and formers.

There are also two highly detailed large plans sheets, a construction manual, and several pages and sheets of scale documentation. The included water slide decals are also very nice.

My first step in building was to clear off the bench. It's a fairly large model with a 57" wing span and originally specified for a .60 glow engine. The plans come folded which makes it difficult to lay them flat on the bench. I used a steam iron to flatten them out nicely .

It is my intention to show the build in a fairly great amount of detail. This is to assist others who might also want to build this beautiful model. The instructions are adequate in most cases but they are highly condensed and often details are left out that require some study of the plans and creative problem solving to figure out what is to be done. I'll share with you my solutions to those steps when they occur.
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Old Jan 15, 2004, 01:38 PM
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This kit is constructed using very traditional or "old school" methods. You can see in the fuselage plan here that the frames are built up largely from sticks. Also the wingtip and tail outlines are of the "laminated" construction method. It's not particularly difficult and it is still the lightest method of construction, though little used these days because it take a bit more time.
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Old Jan 15, 2004, 01:39 PM
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Gerald,

You do such wonderful work that I would like to see all the details even if you do decide to build it into a slimer.

Jim
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Old Jan 15, 2004, 01:50 PM
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When I use stick built construction I always like to first sort out the balsa and grade it. I weigh each piece and mark it. Notice here how the weight of some pieces of identical size is as much as double the lightest. I also sight down the length and sort for straightness and mark that as well. In this model the straighter pieces will be used for the long frame members. Bowed sticks can be chopped up for cross pieces and shorter parts where the curve over the short distance is not noticable. I try to select the lightest sticks for the aft portion of the fuselage to avoid building in tail heaviness. It is always lighter if you have to add weight to the tail later to get the balance correct than if you have to add weight to the nose.
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Old Jan 15, 2004, 02:11 PM
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Here I have just completed construction of the first fuselage frame side. The plans sheet was too big to fit on my bench so I folded it in half and taped it down. I've covered the plan with waxed paper to protect it. Normally this would be to keep the glue from sticking also. But in this case I am using CA adhesive and the CA still sticks to the wax paper somewhat. A better choice if using CA would have been plastic food wrap or a thicker polyethylene plan protector sheet (but my wife didn't have any in the kitchen ).

Also when using thin CA I don't like to put pins through the plans because the glue will sneak through the pinholes and get to the plans. So instead I took advantage of the instant cure time of the CA and just held the parts in position while gluing them. After a few parts are assembled then I tape the frame to the waxed paper or use weights to keep it in position over the plan.
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Old Jan 15, 2004, 02:23 PM
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There are just a couple of parts that you need to cut out from printed sheet. These parts are 1/4" thick balsa sheet which is too thick for die-cutting. Since there was no laser cutting back in the '70s, the only other option would have been for Sig to machine cut these. I guess they felt that was too expensive, so you'll need to do it yourself. The outlines are clearly printed on the wood and a power scroll saw makes the job easy. If you don't have one then you can use a coping saw or just cut them out with your exacto a little oversized then sand to final dimension. The balsa is a light soft grade so it cuts easily.

There are parts for the left and right fuselage sides. Be sure to sand them together so both match.
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Old Jan 15, 2004, 02:39 PM
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Originally posted by JIMA
Gerald,

You do such wonderful work that I would like to see all the details even if you do decide to build it into a slimer.

Jim
Thanks for the kind words of encouragement Jim. I really would prefer to make this electric. It just depends on how expensive it will be.
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Old Jan 15, 2004, 02:58 PM
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Next, another identical fuselage frame is constructed. Build the second one directly over the first with a sheet of waxed paper between them. This insures that they come out the same size. If you just relied on the plans you could end up with different sized fuselage sides due to the thickness of lines on the plans and the plans can even stretch or shrink from humidity changes.

As a note, when cutting all these miscellaneous sticks to length I use a sharp, new, single edged razor blade. They are cheap enough at $5 per 100 that you can always have a sharp one. They are usually sharper than an exacto and also thinner so they go through the balsa much more easily. This is important when you are trying to get clean square ends to your cuts. Also, I usually cut just a hair oversize, then fine-adjust the fit of the part with a couple of swipes from the sanding block.

Speaking of sanding blocks, most of the sanding during these stages of construction will be done with 100 grit garnet paper on an 11" T-bar sander. A lot of folks don't like to use CA glue because it's much harder than the balsa and so can sand unevenly. If you use sharp sandpaper and a good sanding block then you don't need to use a lot of pressure so it's easy to get a flat uniform surface even with the CA glue.

After the second side is finished, lightly sand both sides flat with the sanding block just enough to get the bumps off before moving to the next step.
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Old Jan 15, 2004, 03:16 PM
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Here is where things begin to take shape. At first you may think "how is that box of sticks ever going to become an airplane?". You just can't look at the whole confusing mess at once but rather break it down into bite-sized managable steps and pretty soon it begins to become much more clear.

Now the fuselage sides are joined with more of the 1/4" balsa stock. Use a square to make sure the fuselage sides are perpendicular to the bench when gluing in the cross pieces. Do the forward fuselage cross pieces first since they are at right angles to the fuselage sides in both directions. You will then use two squares here, one vertical and one horizontal. This then provides the alignment to keep the rest of the fuselage straight and true. Start from the front and work your way to the rear keeping the sides aligned over the plans. Don't join the sides at the rear tip until the very last to avoid getting a banana shaped fuselage.

You may need to adjust the width of the cross pieces where the two front formers go to make sure the formers fit, in case the plans have expanded or shrunk somewhat.
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Old Jan 15, 2004, 04:07 PM
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Now the fuselage crutch is removed from the plans and from here on constuction will proceed off of the plans. You will still of course need to refer to the plans frequently. In these older kits a lot more details and notes were found on the plan sheets rather than in the construction manual.

At this time the firewall gets installed. Be sure to square up the ends of the fuselage sides so that the firewall goes on square. There is no right or down thrust angle on the firewall.

The firewall consists of two layers of 1/8" hard plywood. The back one fits between the fuselage sides and the front one fits against the front ends. Use epoxy to laminate them and to glue to the fuselage. Also the two pieces of triangular stock get epoxied in at this time. For the highest strength all these parts should be epoxied at the same time and using a slow curing epoxy such as 20 minute or greater. It helps to use several modeler's clamps to hold it all together while the epoxy cures overnight.

I was tempted to replace the heavy hard plywood with light ply but since I'm not sure if will be electric I'll just keep it stock for now. Later if it goes electric I'll be able to cut holes for battery cooling in the firewall so that can save a bit of weight then.
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Old Jan 15, 2004, 05:16 PM
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Right then. Now that the epoxy has cured on the firewall it's time to move on to the landing gear block and lower nose. Epoxy will also be used in all these steps. The landing gear block is laminated from two layers of hard 1/8" ply. You may need to pre-sand these parts to fit flush with the fuselage sides. The lower nose floor is 1/8" hard ply. This will be the battery floor so it needs to be able to take the landing loads of the battery pack. The kit provided hard ply for the forward angled portion but I replaced this with balsa. It doesn't need the strength of plywood there for electric or glow. That saved about 10g or 1/3oz. Use tape to hold these parts in place while the epoxy hardens.
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Old Jan 15, 2004, 05:36 PM
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I've seldom been satisfied with the landing gear mount structure in Sig kits. They (and others too) typically use a simple, too narrow rectangular block to bolt the gear to. There is little provision for the backward torque loads that occur if landing on grass or if the wheels grab the pavement during a highly crabbed landing. The usual result is that the gear folds back ripping the whole landing gear block out at the glue joint and the wheel pants end up blowing holes in the bottom of the wing.

Since the area forward of the landing gear immediately slopes upward on this plane, I couldn't just make the landing gear plate wider. So I added 1/4" thick plywood glue blocks to the inside of the fuselage. This effectively more than doubles the glued surface area. In addition I extended the blocks to key over the top edge of the plywood floor ahead. The landing gear bolts will extend through the gear plate and the glue blocks which will also hold the blind nuts. This should more than double the holdiing strength of the gear plate with little additional weight. After the blind nuts are in place I will probably also glue in triangular balsa stock over the glue blocks for further strength. My philosophy is that it should be strong enough that the landing gear will bend before the mounting breaks.
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Old Jan 15, 2004, 07:30 PM
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Ok, now it starts to get more interesting. Time to glue in the front two formers. These are made from hard plywood. Don't substitute them for lighter wood because this is where the cabane struts mount and will carry the entire load of the upper wing (the outer inter-plane struts are only cosmetic).

The cabane struts are built up from 1/8" steel wire. They are designed to plug in for assembly by slipping into the brass tubing attached to these two fuselage formers.

Here is one area where there is a discrepancy in the plans. See the 1/8x1/4 wood support under the brass tubing? The manual says to use balsa, but the plans say spruce. I couldn't find any spruce in the kit of that dimension so I compromised and selected a very hard grade of balsa from the kit.

When gluing on the brass tubing use slow epoxy. Lightly sand the surface of the tubing till it's shiny and clean it with alcohol. Apply the epoxy into the joint then place the tubing. Roll the tubing in the epoxy so that it is uniformly coated over all its surface.

When the glued tubing sets then epoxy the two formers to the fuselage. Notice that the front former sits at an angle. This angle is established by the angled rear surface of the fuselage side that it glues to (if you had cut it out correctly from the printwood sheet earlier). This will match the angle of the rear edge of the cowl later.
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Old Jan 15, 2004, 07:34 PM
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Gerald, thanks for taking the time to do this. I especially appreciate the amount of detail you are going into.

What do you think the AUW will be?
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Old Jan 15, 2004, 07:51 PM
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Finally the cabane support tubes are secured by "j" bolts. When tightening the j bolts leave one of the wire cabane struts inserted to prevent crushing the tube. As you feel the j bolt starting to exert friction on the strut then stop tightening and glue the nut and j bolt with a couple drops of CA.
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Old Jan 15, 2004, 08:06 PM
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Greg, here's a link to the web page of a fellow who built one as an electric. http://www3.sympatico.ca/pikefly/ His came to 7.5 lbs with 20 cells and an Astro 40.

That's close to the weight my Kyosho Super Stearman Bipe came to on 20 cells. It was an OK flyer but a bit heavy feeling at that weight. But the Liberty sport is bigger than the Stearman so it should handle the weight a bit better.
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Old Jan 15, 2004, 08:27 PM
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Here's how you turn that boxy looking crutch frame into a nicely rounded shape. The formers just add the curved part of the shape. I lightened all the rear top formers except for the ones that will form the cockpit walls by cutting out the centers. This saved about 4 grams. Got to keep building lightness into the tail.
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Old Jan 15, 2004, 10:20 PM
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Quote:
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Got to keep building lightness into the tail.
Bravo, every little bit helps. Great thread Gerald,and superb work. You sure are making me sad that I sold my kit! I am NEVER selling another of my out of production kits again. Go Gerald go!

Jeff
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Old Jan 16, 2004, 10:50 AM
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Ready for more? Ok, now I've begun to add the stringers. The forward section of the fuselage will get planked with 1/8" balsa sheet. This needs to be done before the aft stringers are installed because they will finish up flush with the surface of the planking.
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Old Jan 16, 2004, 11:11 AM
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The forward stringer locations are not very well documented and not all are shown on the plan either. There are no notches in the formers to help with positioning. Fortunately the positions are not too critical because they just serve as internal support for the sheeting and so they don't show.

Before starting on the stringers the top edges of the front two formers should be beveled to an angle. Do this with the bar sander so that the edges match the angle between the formers. The rearward former (F-2P) has a balsa doubler glued on to it's front face (F-2F). This provides a gluing surface for the front sheeting where there is a seam. When sanding the bevel onto the top edge of F2 only sand the angle halfway back, or to the center between the two layers of F2 because there will be a break in the angle between the forward sheeting and the aft section over the cockpits.

When gluing the stringers in, position them so that they are either exactly flush with the edges of the formers or protruding just a hair past. Then they can be sanded down flush afterwards. You don't want them to get below the former edges or else the sheeting won't contact them later.
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Old Jan 16, 2004, 11:22 AM
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Moving aft, the next section is the center cockpit area. Each side will get two stringers. Again there is not a precise location given for these so you have to do some figuring. The lower stringer of the two has a notch in the center former so that one is easy. Cut the stringer to length and just glue it in. It will need to bend slightly to follow the curve of the fuselage.

The top stringers need to be placed so that they will come close to the edges of the cockpit openings but not protrude into the cockpits. To determine the locations you should make a paper pattern of the openings. The patterns are found on the plan sheet. Trace them onto a sheet of paper then cut the openings out of your tracing. Using this as a template fit it in position over the fuselage and position the upper stringers appropriately.
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Old Jan 16, 2004, 12:25 PM
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Now I'm going to start making the front section sheeting. You absolutely must make paper patterns for these parts before cutting any balsa.

Before getting into that however let me address an issue I had with the kit instructions at this point. The manual advises to terminate the sheeting at the lower edge by butting it onto the nose floor section with some finicky angle. Also the back portion is left dangling with no support but rather a big gap under it. I didn't like their method so I devised my own. I added soft balsa filler blocks at the lower side edges and sanded them to fit the contour outlined by the formers. When I add the sheeting it will still end up in the right place but it will have support and no fancy angles will have to be figured.

Back to the upper sheeting. I made a pattern from card stock by trial and error. The first attempt was a little off here and there but I used that pattern to make a second more refined one. You really want this fit to be just right. Once the paper pattern fit perfectly, I cut the balsa sheeting with the grain running lengthwise through the portion where it will bend the most.

To install the sheeting first I spray it with Windex window cleaner on both sides. The ammonia will help it bend and it will dry without residue. You could use regular water but it will take a bit longer. After the balsa has soaked enough to be flexible blott up the excess moisture and form the part in place securing it with rubber bands. Don't try to glue it while wet because it will shrink as it dries.
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Old Jan 16, 2004, 12:37 PM
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I used a hot air gun to accelerate the drying. See how nicely the part becomes molded to the proper curvature. Now that it's thoroughly dry I test fit it again and lightly sand any edges that need touchup before gluing. I glue it in place with thin CA. First holding it in position I use a drop or two to anchor it. Then since I have access to the underside, I flip the frame over and drip thin CA into all the joints from behind where it flows by capilary action into the surfaces to be joined.

When I cover sections that don't have access from behind then I use medium viscosity CA which is a little slower and I apply it directly to the surfaces.
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Old Jan 16, 2004, 12:48 PM
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Here you can see how the balsa fill blocks I mentioned earlier help to terminate the edges of the sheeting at the bottom. The sheeting is just glued down as it wraps continuously around the bottom corners. If the sheeting is cut a little large then the excess can now be sanded off flush with the bottoms of the nose floor and the landing gear plate. Later the bottom will get a 3/8" thick light balsa block to finish the contour.
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Old Jan 16, 2004, 01:03 PM
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Finally it's starting to look like a fuselage. I've got all the sheeted sections done and am starting on the first of the aft section stringers.
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Old Jan 16, 2004, 01:27 PM
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OK, time for a break. Looks like a lot of folks have some really interesting projects on the bench right now. I guess you can tell that it's modelling season .

Speaking of benches, here's a perspective on my workbench area. A lot of planes have taken shape here. It's an old desk with a huge top. Pull-out work surfaces insure there will always be a flat spot available when the rest of the bench is littered with modelbuilding debris. A vacuum cleaner with a brush attachment is handy to have around to help tame the balsa dust monster before it gets outta control. Lotsa drawers to hide parts 'n tools .
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Old Jan 16, 2004, 06:52 PM
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I had one of these kits back in the 70's. Sold it after I had a look at the contents. I had become accustomed to the machine cut and sanded kits of that era like the stuff from Cox/Airtronics and Bridi. So far your build thread has re-affirmed that decision. I certain that it will turn out great. I'll be following it. Hope you make me sorry I never built mine. I actually built a Concept Models .40 size 1931 Fleet Biplane (The Barnstormer) instead. Probably no easier to build than the Liberity Sport. A sweet flyer. Wish I still had that one too.
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Old Jan 16, 2004, 07:59 PM
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Building this model is almost the same as doing a scratch build from plans. There really are very few precut parts. The good part is that at least I don't have to go out shopping for wood and the cowl & pants would be difficult to make from scratch.

Speaking of Bridi, I've got an old Dirty Birdy kit that needs built. Now that one has got some wood in it!
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Old Jan 19, 2004, 10:34 PM
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Well, I'm back again for a little more punishment. Actually I'm not going to bore you this time with excruciating construction details. Just an update of how it sits currently. Next - wings.
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Old Jan 19, 2004, 10:37 PM
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Yikes! What's this front view of the cowl remind you of?
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Old Jan 20, 2004, 06:23 PM
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Liberty Sport

Gerald, Your plane is coming along nicely. It goes to show if one takes their time and can follow instructions, they can build one of these kits. It just takes some time.
Some clubmembers are in the process of building :
Sig 1/4 scale cub
Balsa USA Citabria Pro
Pica 1'6 scale Waco.
All of these kits are very labor intensive. But it is a labor of love that drives builders to do these projects.
I have a Sig Citabria with only one wing half done, but once I get to it , I generally don't stop until finish. BTW I plan to convert it to electric.
Keep posting your build up. I will be following your posts as you go. Good Luck! john Z
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Old Jan 23, 2004, 05:05 PM
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John, I've got a Sig Citabria kit back in the stacks too. Would like to get to that one someday. Also got a Sig Beech Bonanza but the build technique on that one is very different.

Ok back to the battle of the builds :
Here's a shot of the inside of the assembled cowl. The cowl comes in three pieces in the kit, left right, and the nose bowl. The pieces are already pre trimmed but they do need the edges cleaned up a little for the perfect fit to one another, and to adjust the overall cowl size to make sure it fits the fuselage. Also you get to cut out the openings.

To assemble the cowl you use a solvent based technique to weld the plastic. Do not use CA or other normal adhesives. You can buy a commercial ABS plastic welding solvent or just simply use acetone or dope thinner. I used a mixture of both because straight acetone evaporates a little too quickly.

As you can see in the photo, the seams are reinforced on the inside with strips of ABS. The procedure is to tape a connector strip to one of the two parts to be joined leaving half of it protruding. Then using a small paint brush dipped in the solvent, apply a few drops of solvent to the joint. It will flow between the parts by capilary action and will accomplish the weld within a few seconds. Then you remove the tape, add the second part to be joined to mate with the first and again apply solvent from the backside. The first parts to be joined are the left and right cowl sides. Then join the front bowl last. The joiner strip for the front needs to be cut into shorter sections due to the curvature.

After all the parts are joined and the strips are secure, then I follow up with a more liberal dose of the solvent from behind. This literally dissolves the plastic and when the solvent evaporates off nothing is left but the original ABS plastic welded as a single unit. The wheel pants halves are joined in the same manner but it is not necessary to use joiner strips.

If you have any gaps or cracks that need filling you can also make a filler from scrap ABS dissolved in the same solvent. Just cut it into fine chips and add enough solvent so that when it is dissolved you have the desired consistency. You can make it thin like paint, or thick like putty. The beauty of using this is that it can never chip or flake off as it becomes a part of the original base plastic. It will sand with the same hardness and consistency of the base plastic, and will take paint the same.

This technique will work with any ABS or other styrene plastic parts you have for other models also. This is how I join the vacuum molded parts in Guillow's kits for example. Experienced plastic scale model builders are probably already familiar with this method.
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Old Jan 23, 2004, 08:48 PM
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Working on the cowl was a brief diversion while I thought about another problem with the plans. On the top three stringers at the tail end the plans and instruction manual offer no help. This is at one of those areas on the plan where it says something like "view of some stringers omitted to show detail underneath." Well this was a detail they shouldn't have omitted. And there are no other views or photos of this area. So I left this unglued for later until I could see how the rudder and elevator would fit. As I found out later they were too short and the elevator platform piece FY was too long. It should have ended at the rear former.
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Old Jan 23, 2004, 08:58 PM
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Another problem in this area is that the fuselage sides come up short of the length shown in the composite side view. I had to add a 1/4" extension to bring it out to match the side view.

I think what happened is that they lifted the outlines for the side frames directly from the side view. But the problem is that when you then bend the two sides together to join at the rear it causes their overall length to be shorter and this was not compensated for in the design.

So now the rudder post which should have been where I added the extension will have to be made a little longer so that it extends all the way to the bottom of the fuselage. (I'll show later what I mean by that)
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Old Jan 23, 2004, 09:17 PM
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Building this kit is practically like doing a plan build. There is very little prefabrication. In fact, you could just as easily scratch build one from the plans since all the patterns are given for the few parts that do come pre cut.

When constructing the stringers there are no notches to fit them into. So it is necessary to measure the spacing from the plans and position them accordingly. The stringers will be quite visible through the covering so it's necessary to position them carefully. If there's anything good to say about this it's that this method allows you to get them aligned as straight as you please and there is no need to scallop out the formers to clear the covering.
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Old Jan 23, 2004, 09:34 PM
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It just keeps getting funner . I can't do any more on the fuselage until I have the bottom wing done and the tail surfaces.

Before assembling these I needed to prepare the tip outlines. These are made up from 1/16 x1/4 laminations. Rather than construct forms for these I used the lazy method of sticking thousands of pins around the outline. I used my flatbed scanner to make copies of those sections of the plan to avoid ruining the original plan with pinholes.

Here are some of them with the glue drying. With the wood wet from soaking in water an aliphatic type glue is needed. I used Titebond wood glue straight from the bottle.
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Old Jan 23, 2004, 09:54 PM
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A few notes should be made about balsa grain types to be used for laminating outlines this way.

In the photo the top sample shows "A" grain balsa. This type works the best for wet forming around curves as it is more flexible and has long fibers.

The center sample is "C" grain. It is too stiff and fractures too easily even when soaked so it does not do well for bending laminations.

The bottom sample is a diagonal grain type that comes from twisted growth wood. It does not work well for laminations either because it will induce a twist to the parts as it is bent.
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Old Jan 23, 2004, 10:14 PM
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Even after soaking the balsa in water for 1 hour it can still want to break or kink on you while bending it around the form. A trick I use to help prevent this and make the wood more flexible is to "pre-bend" it by sliding it across a curved or cylindrical surface.

I repeatedly draw the same side of the wet strip across the cylinder (in this case it was the side of my glue bottle) while each time bending it a little more. This pre-sets a curve into the strip enough that it practically curls around the tip form on its own. You can see how this one needed almost no pins to hold the strips against the inner outline of pins.
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Old Jan 23, 2004, 10:36 PM
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The rudder and fin are now about ready for final shaping of the edges to a rounded radius. This profile will be to simulate the steel tubing frame construction of the full scale plane. Frame members are placed in the same positions as the full scale so that they will look right showing through the fabric covering.
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Old Jan 24, 2004, 07:00 AM
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Hey Gerald!
Thank you for putting together such fine pages, loaded with info!
I bought this Sig kit as well from ebay last year. I plan to start building it in March or so... This thread will provide me with lots of information and errata to the plans! The Liberty Sport is going to be my first kit with such a 'craftmanship level'.

Mine will be a slimer though, something like a .91 four stroke. Perhaps even a smoke system, if the necessary funds are available that is ;-)

Two links I found to other liberty's:
http://www.netaxs.com/~mhmyers/rc.tn.html
http://members.rogers.com/jmathe7869/radiocontrol.htm

Keep up the good work and I'm following you step by step...

Kind regards,
Maarten
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Old Feb 13, 2004, 12:00 PM
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I've recently gotten the chance to put a little more time into the Liberty. 'Been busy out of town a lot for work.

But first I figured I needed a new building board. The old one was too small and worn out. I made a new one that is working out real well so far. It measures 4' x 2' and is 3/4" thick. It's made from a 4 x 2 ceiling tile with 1/8" cork laminated to both sides. I used 3M77 spray adhesive to bond the cork. Edges are bound with 3/4" pine trim. All the materials were purchased from Lowes and cost totaled about $30.
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Old Feb 13, 2004, 12:17 PM
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I discovered why the cowl looks familiar, it's obviously borrowed from a Piper Tri-Pacer. And the tail looks suspiciously Piper too.
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Old Feb 13, 2004, 12:24 PM
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To preserve the original plans and to make it easier to work on, I scanned the wing plan into the computer and printed out separate left and right panels using several sheets of paper taped together and run through the printer as a single long sheet.
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Old Feb 13, 2004, 12:33 PM
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I started the lower wing by truing up the ribs and boring a few lightening holes. I saved a whopping 2grams!

The holes are bored using the homemade tool on the left. It is a 7/16" dia steel tube with 'teeth' cut into the end.
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Old Feb 13, 2004, 12:52 PM
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The center section gets built first. It is necessary to pin the entire assemly to the plans to test for fit of parts and make adjustments as necessary before gluing.

The holes for the spars are a sloppy fit at this stage because they are oversized to give room to receive the spars from the outer panels later. So pin it all carefully in place to keep everything in proper position, then glue taking care to keep the glue out of the areas where the outer panel spars will overlap.

You can tell how old this plan is by the drawing of the aileron servo in the center. They don't make 'em like they used to.
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Old Feb 13, 2004, 12:58 PM
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The center section gets sheeted later with 1/16" balsa. When gluing the trailing edge on be sure to position it above the ribs so that it will be flush when the sheeting is applied. Use a scrap of 1/16" balsa as a guage.
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Old Feb 13, 2004, 01:13 PM
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Next build the outer wing panels. Here's the left panel under construction. It gets built up next to the center section for proper alignment but do not glue it to the center yet, it will need the dihedral added first.

Again, position it all with pins and make adjustments to the ribs as necessary fo rproper fit before gluing anything. The parts are die cut so not as accurate as modern laser cutting. It may be necessary to adjust the length of a rib or two or notch the trailing edge a bit deeper here or there.

There is a doubled rib at the center join which will need to be angled when the dihedral is added later so this should be in position but left unglued for now.
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Old Feb 13, 2004, 01:26 PM
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The wingtip area will require some careful fitting. It will need to be notched to accept the ribs. The outer end of the main spar is to be tapered according to a diagram on the plan sheet.

The tip bow does not lay flat on the plan and there are no obvious alignment points for how high to position it. Also the last two ribs have no 'jigging tabs' so they don't have a positive reference for alignment either.

I added the trailing edge first to provide a reference then glued the tip to the trailing edge and ribs. Next I added the sub leading edge and positioned the front of the tip bow to center in the leading edge.

The top forward spar extends to the last rib but the second-to-last rib had no notch in it (circled area). This will need a notch cut in though it is shown on the plan pattern without. I wonder if some of these errors were corrected in later releases of the kit?
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Old Feb 13, 2004, 01:41 PM
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The ailerons get cut out at this point. There are partial cuts already die-cut into the ribs where the aileron is to be separated. But they are not always in precise alignment. So mark out the aileron separation line, extending the lines from the plan, and cut to your marks instead.
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Old Feb 13, 2004, 01:53 PM
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You will need to un-pin the wing panel from the board at this point before you can cut the ribs for the aileron. So this is a good time to glue in the dihedral angle. Leave the center section pinned to the board, and raise the wingtip 3/4 under W14.

A slight angle will need to be sanded on the ends of the spars, leading edge, and trailing edge to allow for a flush fit when the wingtip is raised.

The instructions call for epoxy here but they didn't have CA in those days. I used thin CA since the joint was well fitting and it is all balsa here, no hardwoods or plywoods. After the dihedral angle was set I dribbled in the thin CA which penetrated the joint nicely and froze it in place.
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Old Feb 13, 2004, 02:06 PM
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The plans show ailerons in the scale dimensions but dotted lines show where they can be extended by two rib-bays for sportier roll rates. I opted for true scale since this plane won't be extremely aerobatic anyway and I plan to add a lot of scale detail.

Here the leading edge of the aileron and the rear edge of the opening are installed. I'll cut the aileron completely free later when the wing framing nears completion.

That's it for now.
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Old Feb 18, 2004, 10:07 AM
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Back at it again here's the progress update. Got the lower wing framed up and ready for sheeting.
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Old Feb 18, 2004, 10:18 AM
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I decided to go with separate smaller servos for each aileron instead of the single big servo in the center and its associated linkages and belcranks. This will be much simpler to install and will weigh about the same since I'll be using two smaller HS85MG servos. To make installing the servo leads easy I added rolled paper tubes to run from the servo bay to the center of the wing.
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Old Feb 18, 2004, 10:29 AM
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Before the wing planking can be applied it is necessary to shape the sub-leading edge to follow the profile of the ribs. The instruction manual doesn't mention it but you need to do the sheeting before the leading edge cap is installed. Later I found a little slip of paper in the box that mentioned this as an addendum.
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Old Feb 18, 2004, 10:38 AM
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If you don't already have a razor plane or a small block plane like this one made by x-acto , get one. You need it! These babies make short work of removing a lot of balsa for these shaping tasks. Eliminates piles of messy balsa dust too. Instead you end up with a few curls of balsa shavings that are easily cleaned up.
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Old Feb 18, 2004, 10:51 AM
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Gerald, looks wonderful. Any projection on weight now that the major chunks are done or nearly so? I want to be sure of the facts before I start pestering you to make it electric....
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Old Feb 18, 2004, 10:55 AM
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After I got the leading edge shaped I started on the wing sheeting. The kit balsa was the perfect light weight quality selection for this area.

I usually pre-join the separate panels to make a wider sheet. I use thin CA to make the job quick and avoid warping. The trick is to glue only from the backside to avoid having un-sandable ridges on the outside. You need to join the pieces with scotch tape on the outside surface. Because balsa sheet often has an uneven thickness across the sheet you may find that the edge thicknesses of the two pieces doesn't match. If this is the case turn one sheet around so that the same thickness edges go together. Position them tightly and rub the tape down well. This will prevent the thin CA from leaking through to the finished outside surface.

Then flip the lot over and apply thin CA to the seam from the backside. Now quickly wipe off the excess CA with a paper towl. Before the CA becomes rock hard on the back you can sand it lightly with the sanding block if there are any high spots. Next remove the tape before the CA sets too hard. You may find a thin line of gummy residue from the tape where the CA contacted it. This easily rubs off with a fingertip and needs to be removed before sanding so it doesn't get smeared all over.

It sounds complicated but is actually very simple and goes quickly. It's the only good way to join sheeting with CA without making hard CA joint lines. You can also do this when applying the sheeting to the frame where it joins with other sheet already in place.
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Old Feb 18, 2004, 11:10 AM
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Quote:
Originally posted by Greg Smith
Gerald, looks wonderful. Any projection on weight now that the major chunks are done or nearly so? I want to be sure of the facts before I start pestering you to make it electric....
Greg, I still have to frame up the top wing so I don't have any good estimate yet. But so far the weight of the bare airframe comes to 32 oz. This includes the fuselage, tail surfaces, completed bottom wing frame, cowl, landing gear with wheels and pants, and the heavy 1/8" wire cabane struts.

I expect the top wing frame to come to about 7oz. The bottom one is 6oz. If I make some carbon gear and use lighter wheels I could knock off about 3 oz. If I add about 6oz for more misc "stuff" and about 8 oz for covering, then the completed airframe weight would come to about 50oz, no radio. I calculated the wing area to be about 776 sqin.

All-up weight as electric could conceivably be 100-110 oz. Hmm..
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Old Feb 18, 2004, 11:24 AM
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After the wing sheeting was applied I added the leading edge caps. Again the kit balsa was excellent. Very light and straight.

I decided to glue these on with yellow aliphatic wood glue so that I would have no problem sanding to blend them to the wing contour. Problem is this glue make the balsa warp like crazy. So it took a boxfull of clamps to hold it in place. After getting it positioned and clamped I taped it up tightly so that I could remove the clamps and start on the other wing.
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Old Feb 18, 2004, 11:29 AM
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The leading edge joints are staggered for added strength. The dihedral joints will not be glassed over but I plan to cover it with fabric and dope so that should strengthen it nicely.
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Old Feb 18, 2004, 11:33 AM
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Bottom wing frame is done. Just needs the ailerons separated and a little final sanding and should be ready to cover. Now that this is done I can move on to fitting it to the fuselage and making up the wing fillets.
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Old Feb 18, 2004, 04:28 PM
jollyroger
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Gerald, Looking good . I know these kits are diffacult to build, but once finnished they are beautiful. I hope I can do as well on my Sig Citabria. John Z.
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Old Feb 18, 2004, 09:59 PM
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John, you said you've got one half wing done on your Sig Citabria? How tough did you find building that kit is so far? I have one too but it will probably be a while till I can get to it, maybe this fall. When do you think you'll get back to work on yours? I'll certainly be interested in hearing how it goes.
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Old Feb 19, 2004, 06:49 AM
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Oooppps, I got the plane in a trade with one wing half built. But it doesn't look that difficult. I've built other Sig kits...LT-40(2) 4*60. I really don't know when I'll get to it as I have to clear out the hanger and make room for new planes. I've also built a few from plans. One was an old timer built entirely of sticks. Actually it was a lot of fun.
I think the toughest part of any plane when converting to electric is making access to the battery pack . I am in the process of converting a Great Planes .40 Cub to electric and it is easier said than done.
All in all though the challenge is worth as it has its own rewards.
When I get to the plane I may be able to post pics if I have a digital camera available. John
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Old Feb 27, 2004, 04:21 PM
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I tried out mounting this Hacker B50-10L 6.7:1 on it just to see how it looks .

What'ya think, can it do the job?
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Old Feb 27, 2004, 04:26 PM
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And I discovered that a pair of two big 3s4p Thunderpower packs will drop in nicely right through the front open cockpit (which incidentally could make a fine hot air exhaust vent ).
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Old Feb 27, 2004, 08:41 PM
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Looking good Gerald. Any chance this will make it to SEFF this year?

Mike
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Old Feb 28, 2004, 11:02 AM
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Mike, I guess now that I've committed to making it electric then I'm going to try to get it finished in time for SEFF. Got 3 1/2 months still.
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Old Mar 12, 2004, 09:52 AM
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Getting a little further..

Ok, just wanted to toss out an update here. I've got lots more build details to post soon when I get the photos edited but for now just a look at how she sits at present.
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Old Mar 12, 2004, 09:55 AM
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Weight stands at 40oz so far for the nearly completed airframe as seen here.
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Old Mar 12, 2004, 11:44 AM
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Beautiful! This thread is great. Thanks for sharing. It looks like it will make a great conversion. Hmm, a B50 an 6s pack will really make it perform.

40 oz for the airframe as shown in the picture.
20 oz for the motor, ESC, prop
6 oz for radio/servos
33oz for 6s pack

~100 oz

Covering and miscellaneous should be 8 - 12 oz. Are you shooting for a specific weight?

Kelvin
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Old Mar 12, 2004, 12:14 PM
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Kelvin, I will probably try it first with a 5s pack as I've got another unused 2s lying around. That should still be plenty powerful with the right prop. It has room to clear a 15" or so prop.

I'm hoping to finish at about 6.5lb (~105oz) but I'm not really worried about the weight yet. It's got 776 sqin area so that would be a wing loading of about 19oz/sqft. Should fly nice at that weight.

I've got no clue about the covering weight because I'm going to be trying something new (but old). I plan to cover it with a lightweight silk and dope but the wings will get covered in silkspan (tissue) first before the outer silk layer goes on.
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Old Mar 20, 2004, 04:49 PM
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Starting the covering

This worked out surprisingly well so far. As I had planned, I covered the tail with straight silk, Esaki #4 heavyweight. Sealed with three coats of nitrate dope brushed on.

Next I covered the top wing with a different process that I'm trying for the first time. First I covered it with silkspan tissue. I like silkspan because it's so easy to work with and comes out perfectly wrinkle free. The silkspan got one coat of nitrate sprayed on, then lightly sanded with 1500grit to take the fuzz off.

Silkspan is just not strong enough though for a model this size. So I laminated a second layer of covering, this time a very lightweight silk (10g/sqyd). The silk was layed out over the silkspan, then sprayed with water and the wrinkles pulled out and doped down around the edges. The underlying silkspan wrinkled a little from the water but it all shrank up nice and tight when it dried. I sprayed two good wet coats of thinned nitrate over everything which bonded the silk layer perfectly to the silkspan.

The result is that the covering came out very light and 100% sealed in only three coats of dope. It is tight and strong, probably the best silk covering job I've done. I calculated the weight of the covering and the total weight increase was 30g for the whole wing.
With a top and bottom combined area of 840sqin this equates to a covering weight of only 1.6oz/sqyd.

This is going to get painted of course so weight will increase but the technique could be used for an ultralight covering for other models all on its own with a little tint added for translucent colors. I think I'll try that on my next old-timer model .
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Old Mar 31, 2004, 10:49 AM
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Maybe it's a waste of time and added weight, but I thought I'd add the rib stitching and tapes for a little more realism.

Unfortunately I don't have good photo documentation that actually shows how this looks on the full-scale so I just guessed at it.
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Old Mar 31, 2004, 03:53 PM
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Humm, are those stiches every scale 2" per AC43-13?

Looks outstanding! what did you use to simulate the knots?

Great looking build overall!
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Old Mar 31, 2004, 05:04 PM
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Rib stitching...

Don't forget it's closer spacing in the slipstream. As I remember, prop diameter + 1 rib bay. Wow, I wrote that and thought I'd better look at the manual online to confirm. The new 43-13.1B is a bit different from the old .1A version. It's available online for those who need to refer for scale info.
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Old Mar 31, 2004, 06:11 PM
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Quote:
Originally posted by Aerominded
Humm, are those stiches every scale 2" per AC43-13?

Looks outstanding! what did you use to simulate the knots?

Great looking build overall!
OOPS! No, I think they're more like scale 3"

to simulate the laces I extruded a thin line of yellow glue from a syringe type glue applicator one at a time. It didn't really take that long to do that part. When I goofed on a few I just wiped the glue off or if I didn't like it after it was dry it could easily be picked off and redone.
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Old Apr 01, 2004, 06:26 PM
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3"? better keep the speed down!

Great technique for doing the 'stitching'! very effective!

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Old May 22, 2004, 05:50 PM
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I guess it's time for an update. Yes, I'm still working on this. I bet you missed me writing about it...haha!

All is covered now in the silk/silkspan combination. The fuselage needed to be covered before I could work on the wing fillets.
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Old May 22, 2004, 05:59 PM
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Now for the fillets. I made them the easy way using lightweight spackle. they were too thick to do all at once so it took about three applications to build the thickness up letting it dry overnight in between. I used black vinyl electrical tape to mask the fuselage and to make the guideline.

After sufficient thickness was built up I sanded it, first with a 3/4" dowel wrapped with coarse sandpaper, then by hand with finer sandpaper. The vinyl tape prevented sanding into the fuselage covering and when the edge of the tape was revealed by sanding then I knew when to stop.
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Old May 22, 2004, 06:06 PM
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After the fillet was sanded I glassed it over with 2oz fiberglass cloth and epoxy. I used a new peice of tape to mask for the epoxy and made sure the glass cloth just met the edge of the tape without overlapping onto it. Then the tape was removed before the epoxy set too hard leaving a nice clean edge. Note that the brown color is due to old rusty colored hardener I was using.
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Old May 22, 2004, 06:14 PM
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I just got the base coats of paint on everything now and had to set it up for a little posing.
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Old May 22, 2004, 06:21 PM
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There's still loads of detail work to do but it feels like it's nearly there. Now I can start fitting the R/C gear since I'll have a better idea of where the CG will be.

So far the weight of the airframe as pictured is 49oz.
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Old Jun 04, 2004, 08:15 PM
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Well I'm racing the clock trying to get this done in time for SEFF. A little more progress has been made.

I was supposed to make the headrest fairing by carving it from a large solid block of balsa. I started to do it that way but found it just wasn't going to produce the quality result I wanted. Then I toyed with the idea of making one from aluminum litho-plate "a la full-scale". This wasn't working out as good as I hoped when it occurred to me to just use the litho-plate experiment as a mold to make one from fiberglass. The result was exactly what I wanted.

I polished the inside of the aluminum mold and coated it with release wax. Then I layed up the fiberglass and resin inside using one layer of 0.5 oz glass cloth and a thicker 2 oz layer. Next I covered the top of the fuselage with waxed paper and then taped the mold with the wet laminations into position on the fuselage. This was to make the part conform exactly to the fusleage curves.
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Old Jun 04, 2004, 08:18 PM
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After removing the part from the mold it is ready for trimming. The surface finish was nice so it only needed a little fine sanding for paint adhesion.
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Old Jun 04, 2004, 08:24 PM
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Finally, I added a balsa bulkhead at the front end to close it up. I used RC56 to glue it to the top of the fuselage. Here's the final result after painting. It will get a headrest pad later.
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Old Jun 05, 2004, 08:15 AM
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Spectacular! How did you do the letters?
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Old Jun 05, 2004, 10:02 AM
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Thanks Greg. The letters are painted on. The kit came with decals for these but they were too old to use. So I scanned the decals into the computer and printed out paper patterns to cut the paint masks.

For masking I used cheap vinyl sticky back shelf paper. It leaves a nice clean edge and has just the right tackiness to stay put but easy to peel off.
The letters are cut through the pattern and mask using a single edge razor.

Because of the multiple colors it had to be painted in three steps. First the solid white band was sprayed. Next the red band with masked off numbers was sprayed, and last the black letters.

The biggest hassle about all this is cleaning the paint gun between colors. Still, much more painting left to do, ugghh... I think I'll take a break from painting and work on the wing struts.
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Old Jun 06, 2004, 02:31 AM
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Been watching the build. Excellent job. Thought I'd let you know that Dick Grahm (The designer of the model) is my uncle. I remember well when he was designing the first one. Dicks still building and flying activly at the young age of 80 and just recently built another Liberty Sport. I believe he built it from the original plans from the article in M.A.N.. I have one of the kits myself and hope to start building it soon and this build series will be a big help. Keep up the good work.
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Old Jun 06, 2004, 09:02 AM
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Gerald I know the painting is tedious but I agree nothing beats masked and sprayed markings. As your work shows.

I noticed in your posts you said several times you sprayed the nitrate dope instead of brushing - I am curious as to why sprayed and what did you spray it with?

Also, after you applied the silk and sprayed it with more nitrate dope,did you need to fill the weave on the silk or sand it before painting?
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Old Jun 06, 2004, 09:32 PM
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Tpole, I bet your uncle is an awesome modeler. Post a picture or two of his newest build if you get a chance.

Greg, I adhered the tissue and silk with nitrate by hand with a brush of course. But I sprayed the nitrate sealer coats simply because it was easier and more uniform. I use an automotive style "touch-up" spray gun with about an 8oz paint cup.

Usually when covering with fabrics it is recommended to lightly brush the first two nitrate coats on so that it properly seals the weave without running all the way through, then spray the third coat. If I were to brush all the coats on it would likely need a lot more sanding, as the brushmarks on the final coat would become visible.

Because I covered the model twice, first with silkspan tissue then with silk, I was able to spray all the coats. After the silkspan is on it gets one wet coat sprayed. I thin the dope quite a bit so that it saturates the silkspan which soaks it up like a blotter. Then I lightly sand the silkspan to remove the fuzz. At this stage its about 30% sealed.

Then I applied the silk fabric over the silkspan covering. Now when I sprayed the silk, again with a wet, very thinned mixture, it soaks through the silk but the silkspan underneath stops it from going further. Then the two layers are sucked together tightly by capilary action and the result is that the silk fills very well by this stage. A second wet coat on the silk seals the weave about 98%.

After the two coats of nitrate were applied to the silk I sanded everything with 1500 grit. Then I started with the color coats, using Sig Supercoat butyrate dope. I didn't try to fill the weave with any kind of filler coats because I just let the colored dope do that. I applied two color coats and wet-sanded in between. My sanding method is to spray a spritz of water from a mister onto the paint in a local spot, then wet sand that small area. Then I wipe up the slurry immediately with a paper towel and proceed to the next small area. This keeps it from becoming a big mess.

I sanded the first color coat until the base started to show through slightly. This way the weave is filled mostly with color and by the time the last coat goes on it can be very thin and still hide well. My theory is that I will get a slightly lighter finish this way. The fabric weave is mostly filled but still shows a little.
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Old Jun 13, 2004, 10:20 PM
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Liberty Sport maiden flight was a sucess!

Still a lot of detail work left to do but I got her finished enough for flight trials today. Got in two short flights of about 5 minutes each.

It flew really nicely and needed only minor trim. Wants to climb too much under power so I think it needs a little down thrust. A little right thrust won't hurt either.

It's got gobs of power. Will maintain level flight at barely over idle. Full throttle was used only momentarily a couple of times and is probably enough for unlimited vertical. Landings were easy and smooth.

I flew it rather gently so far because I won't feel comfortable with aerobatics until I get the flying wires installed.

Next flight: SEFF
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Old Jun 13, 2004, 10:42 PM
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Beautiful job, Gerald. It's your Liberty Sport that inspired me to finish my Concept Fleet, which I had shelved for a few months.

I look forward to seeing it at SEFF.

However, despite my virtually daily toil for the last six weeks on my Concept Fleet, it is not going to be quite ready for SEFF in time. I had a couple of setbacks during construction. It's really close to finished right now, but I'd really have to rush the remaining things, like doing rigging wires, radio installation and a test flight, and I have other planes to prep for the trip.

I guess my days of fast building are behind me now.

Rick
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Old Jun 13, 2004, 10:49 PM
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Rick, I know how that goes, been doing marathon sessions on the Liberty for the last few weeks and still barely have it ready. This scale stuf sure takes a lot of time.

Do you have anything posted here on the Fleet?
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Old Jun 13, 2004, 11:04 PM
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I'd forgotten just how much time scale projects take until I built this one! The smallest jobs can easily take HOURS.
I probably have 30+ hours JUST in gluing/painting and mounting the scale dummy cylinders properly into the fiberglass cowling! I re-engineered a few things along the way too, which takes additional time.

I didn't do a build thread on it, since it's such an old veteran kit I figured it would be of little interest to most of the seasoned builders here (maybe I was mistaken). I have only made a couple of references to it in other threads. I framed most of it up last summer, but got tired of building wings, so I set it aside late last year, getting sidetracked with building a Tantrum, an old Goldberg Junior Falcon e-conversion, and a couple of ARF projects.

FWIW, it's got a Mega 22/30/3, 3:1 MAT beltdrive, Jeti 70 Advance ESC, and a set of the new TP 2200 mAH LiPos, 2S2P (4S2P in series). It's somewhere between sport and standoff scale, as far as details go. It's done in post WWI Army colors, similar to your Liberty Sport, but yellow and OD green.

I'll post pictures of it after SEFF, probably by the end of the month.

Rick
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Old Jun 13, 2004, 11:10 PM
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Well, come on by and introduce yourself at SEFF. You'll probably be able to find me pretty easy when you spot the Liberty bipe. I'm going to be there Thursday through Saturday afternoon.
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Old Jun 14, 2004, 05:57 AM
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Very Nice. It's great to see another "Dope" artisan. It's becoming a lost art in this day of ARF's and Monokote. When I die I want to be mummified in Koverall and dope.
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Old Jun 14, 2004, 12:47 PM
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Great job Gerald. What did your final weight come in at? Also what prop and battery?
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Old Jun 14, 2004, 12:53 PM
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Very nice, Gerald! To a long life!

Steve
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