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Author Topic: Comet Sparky for P-30  (Read 4470 times)
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Zeiss Ikon
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« on: April 02, 2011, 09:41:24 PM »

With my Fat Lancer project (for Embryo) coming to a close, I'm getting things together for a P-30. Since I don't want to spend the money on a kit, and don't really care if my model is competitive or not (nothing I can afford would be anyway, in still air, and if you pick good air, the model design almost doesn't matter), I'm going to build a Sparky from the Kit 3408 version of the plans. Yes, the Sparky had a 32" span, and even after considering the effect of dihedral, the projected span is about an inch oversize for P-30; that's why I chose this version of the plan (I also have an L-10, but it's in PDF with all the parts sheets on one page, not conducive to printing directly to the wood): The 3408 that I have is in an editable file format, allowing me to shrink both the plan and parts sheets to 94%, which I calculate should give a plan span barely over 30", and a projected span of about 29.6". Given the original kit weight is given as 3 ounces (about 85 grams), I don't expect I'll have to worry about building underweight, but in order to get closer to 40 g, I'll be changing all the 3/32" wood (formers and tail surface outlines as well as the fuselage frame) to 1/16" and using some pretty decent weight wood I found at the LHS. As with the Lancer project, I'll be using Beacon 527 adhesive, but I'm going to attempt wet covering with Esaki when I reach that stage, hoping to do the fuselage in two pieces and avoid problems with grain direction in the rear of the cabin below the wing trailing edge.

The first part of the project is already complete -- printing and piecing together the plan. The second part will be making up the print wood; my HP Deskjet 722C has a rear access hatch that allows straight-through printing on non-flexible materials, so I'll be able to print directly. One sheet is too long to print in one piece, but I'll use the same graphics software I used to scale the plan and parts sheet (G.I.M.P. 2.6) to break that into two pieces between parts. Once the Lancer is off the building board and the parts sheets printed, I'll be ready to start work on the Sparky -- likely later this week.
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« Reply #1 on: April 03, 2011, 10:01:49 AM »

I'll be watching with interest, Zeiss. The Sparky is on my future build short list.
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« Reply #2 on: April 03, 2011, 11:26:24 AM »

Well, and already a snag. I confused myself earlier; it was the L-10 plans I printed (BTW, anyone who doesn't already have Adobe Reader X should upgrade; the tiled printing feature alone is worth the download, and it will read all older PDF file versions as well as current ones). The 3408 parts sheets seem to differ only in one minor respect: no sub rudder parts. The 3408 plan doesn't show the sub rudder at all, though the drawings of the finished color scheme and such show a model with the sub rudder -- probably never got redrawn after the sub rudder was deleted.

Solution: capture the parts sheet images out of the PDF of the L-10 version. The "snapshot" feature built into Reader isn't really suitable for this; it captures at screen resolution only, typically 72 dpi. That's awfully coarse for print wood and not a smooth multiple for my 300 dpi printer, which would mean some banding as well. I have no software that will let me edit a PDF or directly extract the original images, but there's always a way. Your mileage may vary, but what I did was "print" the required page to the fax print driver that came with Windows (your installation may not have installed that driver if you didn't have a fax-capable modem installed when you installed Windows, but it's on the original CD or in the original CAB files, and can be added through Control Panel, at least in Windows 98 and XP -- probably still present in Vista, but with the decline in dial-up Internet and home land lines, there's no telling if it's still there in Windows 7). Since I don't have a land line phone, the fax couldn't go anywhere, but at the end of the process there's a "preview fax" button, which opens the generated TIFF file in Windows Previewer, which in turn allows the option to save the file -- et voila, a 200 ppi resolution editable image (already scaled to my 94% building size by the scaling option of Reader's tiled print).

I had intended to use free-to-download image stitching software to join the two pages of the fax image (required because the fax print driver doesn't recognize paper larger than US Legal, i.e. can't fax to an 11x17 inch Tabloid sheet -- a limitation that mirrors the hardware limits of fax machines one might send to) back into one before splitting up the three parts sheets and breaking the long one, but even with 0.5 inch overlap between the two tiled pages, in either gray scale or RGB image mode, the stitching software I tried reported failing to find a match between the two images. Fortunately, it wasn't a big problem to line up the two images in GIMP. I now have four (after breaking the long sheet) parts sheets that can be printed on my Deskjet 722C; the longest is just under 11 inches long, but I can tell the print driver I have legal size paper and get that to print onto a 12+ inch piece of wood.
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Zeiss Ikon
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« Reply #3 on: April 08, 2011, 10:32:59 PM »

For anyone who might want to know, despite having a rear-feed, straight-through (well, almost straight) print path option, the HP Deskjet 722C cannot print on balsa -- or at least not on anything as thick as 1/16". I had wondered about that when I read about printing directly to wood, because an ink jet head has to be pretty close to the medium (picoliter droplets don't travel far without considerable scatter), but wasn't sure how the paper path accommodates varying material thickness -- now I know. At least in this (fairly old) printer, it doesn't. The wood will feed through, but the print head can't pass over it; instead, it jams at the first point the head would have crossed the wood, requiring pulling the wood and guide paper back out the way they went in, and canceling the print job.

Fortunately, I also have a laser printer; I flipped all the wood sheet images to mirror image and laser printed them to legal size paper, and will use dope thinner to transfer the toner from the paper to the wood. I should be able to start cutting sheet parts tomorrow.
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« Reply #4 on: April 08, 2011, 10:46:37 PM »

I understand that you can use an iron to transfer laser printer toner from paper to something else. I've never tried it -- take that as your guarantee.
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« Reply #5 on: April 08, 2011, 11:08:18 PM »

I understand that you can use an iron to transfer laser printer toner from paper to something else. I've never tried it -- take that as your guarantee.

This is very correct, and predates the use of solvents to do the job (I first ran across heat transfer of toner before home computers and laser printers were generally affordable -- the toner transferred came from a copier, then still commonly referred to as a Xerox). However (having done it once or twice): the heat can lead to warps in the balsa, and you have to adjust the toner setting on the printer to get an image that will heat transfer legibly. I'm not sure that last isn't the case with solvent transfer, but I'm pretty confident it won't cause warps. Not to mention that I'm not completely sure I even own an iron...
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« Reply #6 on: April 09, 2011, 06:39:23 PM »

Okay, here's the result of my first attempt to use solvent transfer (using SIG Dope Thinner) from a laser print. I suspect I could get a cleaner transfer with less solvent and more pressure -- I rubbed over the back of the paper with a paper towel that had been dipped in the thinner bottle, after brushing on the thinner didn't work well. In hindsight, once I had the paper soaked with thinner, I probably could have gotten a good transfer by rubbing the back with a dry paper towel, and used a lot less thinner (thus stinking up the house less); I'll try it that way next time.
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« Reply #7 on: April 09, 2011, 07:50:46 PM »

That looks pretty good for a first try. You may get less bleeding with less solvent, too.
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« Reply #8 on: April 09, 2011, 08:35:25 PM »

You may get less bleeding with less solvent, too.

Yes, that was what I meant to imply. Still, they're good enough to cut from and I can sand off the excess toner before gluing. Because I'm cutting the wood sizes from 3/32" to 1/16" where possible, I'll be cutting all the ribs and formers without any notches, and notching to fit the actual wood; that means only the outlines are really critical. I'm probably out of building time for this weekend, but I should be cutting parts and making up my notch sanders Monday evening.
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« Reply #9 on: April 10, 2011, 01:43:02 PM »

I had the same frustrating bleeding problems that you did trying dope thinner. My wife is an artist and she brought home a blender pen for markers. I had mentioned that someone had mentioned this but I could not find the pen. It worked GREAT!!! When it started to go dry I noticed that the solvent is Xylene. I got a quart at Home Depot and used a syringe to refill the pen through the nib. I also tried using a folded up paper towel and that worked as well. Xylene is a slow solvent that still works on laser prints, at least from the ones that I used to have access to at work prior to retirement. Find some of this solvent and give it another try.
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« Reply #10 on: April 10, 2011, 02:21:24 PM »

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I had the same frustrating bleeding problems that you did trying dope thinner. My wife is an artist and she brought home a blender pen for markers. I had mentioned that someone had mentioned this but I could not find the pen. It worked GREAT!!!

That is how I transfer the patterns onto wood. It comes out very clean and the pattern can be reused after it dries (until the ink is used up). I got the idea from Dennis Norman (FAC Hall of Fame).

Dennis also colors tissue with colored Prismacolor markers. By rubbing through the tissue, overlayed on a tracing of the wing, fuselage, etc. panel lines, the lines are also transferred to the tissue as it is colored. Kind of hard to explain, especially the fuselage, but detailed instructions are contained in his video, Master Modeler.

Ron
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« Reply #11 on: April 10, 2011, 10:19:43 PM »

Xylene is a slow solvent that still works on laser prints, at least from the ones that I used to have access to at work prior to retirement. Find some of this solvent and give it another try.

Actually, what I'll probably try first is using a cotton swab instead of a brush or paper towel; I can use less solvent and more pressure. If that doesn't work, I'll see how small a can of xylene I can get at the Lowe's or Home Depot. As noted, these transfers are good enough to cut from, so that'll be a future test or next model.
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« Reply #12 on: April 12, 2011, 09:36:23 PM »

Now I remember why I prefer even the raggedest die-cut kits over print wood. I spent almost three hours cutting out sheet parts for this Sparky build -- but I did manage to finish that task, with elevator, rudder, wing, and fuselage parts going into separate zipper bags, in time to start sanding the laser toner off the rudder parts, pinning and double gluing, and actually managed to finish the rudder, save only gluing on the long tab. My reduction of wood to 1/16" will obviate some of the carving put forward in the plans for the rudder, so I'll go ahead and glue on the tab before pulling the rudder off the plan.

Unfortunately, I was 2/3 finished with cutting fuselage pieces before realizing the corner notches that a lot of them show are rests for 3/32" sticks, but I may go ahead and make the load-bearing fuselage longerons from the originally specified 3/32" size, with 1/16" x 3/32" verticals in the sides (and my originally intended 1/16" square for the horizontal cross pieces) to save weight without complicating the process of building the sides one on top of the other. Before I get that far, however, I'll have to figure out how to build in a DT; the L10 plan has no provision for DT, with a single center dowel (for rubber bands) and dihedral platform wing support, and double taper stabilizer combined with rudder parts that plug into the platform making pop-up tail require significant modification. I wonder if I can build a drag brake DT of some kind? I had one of those on a CLG (modified from an old Estes boost glider design) that I built long ago (piece of soda can held flat against the fuselage with a rubber band wrapped over a fuse, snuffer tube faired into the nose) and it worked very well on that model, but I think on a model the size of a Sparky I'd need wing-top spoilers or similar to bring it down positively. They'd need to be light and produce little drag and less lift reduction when stowed -- and be amenable to a Silly Putty timer for deployment. Might be possible...

Meanwhile, does anyone know what the two unmarked parts in the first photo are? I can't find them anywhere on the plan, but someone went to the trouble to put them on the parts sheet...
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« Reply #13 on: April 12, 2011, 09:45:45 PM »

Those are the side cowls that go between the top and bottom 3/32 longerons---and hold the corred curvature of them.

Trog
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« Reply #14 on: April 13, 2011, 07:13:39 AM »

Those are the side cowls that go between the top and bottom 3/32 longerons---and hold the corred curvature of them.
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« Reply #15 on: April 13, 2011, 04:25:40 PM »

hello - Zeiss Ikon, I saw the posts related to the transfer of the prints on the balsa sheets. I have not a big experience but I try to avoid solvents as much as possible : the skin, the lungs, the smell, pollution etc... I normally either copy by hand or print with a laser printer the parts on a piece of domestic tissue (the cheap tissue that can be used as well to cover the model) then I glue it onto the balsa sheet with a glue stick. The parts can then be cut and the paper helps in preventing the wood from splitting. Afterward, the paper can be either peeled off or sanded or removed it by rubbing the pieces with some wet towel. I found this method quite useful specially when the contours to be cut are complex or contain some minute detail because, as I said, the paper reduce greatly the risk of splitting the wood.

Look forward to seeing your sparky complete - it is a nice model and I would like to build one, sooner or later

Marco
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« Reply #16 on: April 13, 2011, 04:36:29 PM »

Don't I remember a method where you could iron the paper onto the sheet and the ink would transfer?

Seemed like a neat way to go if you found the right ink and temperature.

Tony
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« Reply #17 on: April 13, 2011, 04:56:47 PM »

Don't I remember a method where you could iron the paper onto the sheet and the ink would transfer?
Seemed like a neat way to go if you found the right ink and temperature.

I recall hearing something about that as well. Something like photocopying and then ironing the photocopy ink onto the balsa.
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« Reply #18 on: April 13, 2011, 07:23:20 PM »

Don't I remember a method where you could iron the paper onto the sheet and the ink would transfer?

Seemed like a neat way to go if you found the right ink and temperature.

Right you are. Works VERY well with most of the powder/heat transfer systems used in the Xerox (type) copy machines and almost all laser printers.
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« Reply #19 on: April 13, 2011, 10:16:17 PM »

As I noted back up the thread, yes, thermal toner transfer predates laser printers and affordable home computers by several years. I chose solvent transfer because, first, I wanted to try it, second, I don't know if I still have an iron or whether I can find it if I do, and third, I'd rather experiment with regular printer paper than with tissue (relative costs being what they are). FWIW, another alternate is to print with an ink jet and then "solvent transfer" with water as your solvent -- no smell, no potential brain or liver damage, but a real possibility of warping the wood or distorting the patterns due to the paper and wood expanding (at different rates) as they get wet.

I got the stabilizer glued up tonight. My rib cutting was on the rough side, but this will get sanded before it's covered, which should let me even out the variation from rib to rib as well as correct the angled tops and so forth. Use of 1/16" wood for the stab outline seems to have worked well; I could have gotten away with 1/32" for the ribs, most likely (another thing on my list for the next Sparky -- cut and paste the parts to allow a better distribution of wood thickness). BTW, that list also includes reorienting the sub-rudder outline parts; the grain direction is wrong in two of the three, leading me to predict frequently grain-line splits of the sub-rudder when flying the model.

I also had my first experience with a sandpaper notch tool; I cut a piece of the 1/16" x 1/4" stab spar material, glued it edgewise to a bamboo skewer longer than the balsa (the skewer acts as a handle, stiffener and, as long as it's thicker than the notch to be cut, depth stop), carefully cut a 1/16" strip of 220 sandpaper and glued that to the remaining edge of the balsa -- and got a tool that cuts like a saw, making a precise width notch that fits nicely over the spar stock. This is one slick tool; I'll be making more of these for stringer notches and such as I continue work on the Sparky. Only took about ten minutes to make the tool, and I'll use it every time I need to notch for 1/16" x 1/4", for the next however long (and I can take the sandpaper off with a brush soaked in dope thinner to soften the glue, when it gets dull). Just as slick and easy to make as my simple strippers...

Use of the notching tool allowed me to build the entire stabilizer in about an hour and a half (including making the notching tool). And yes, I've since corrected the fallen half rib that shows in the photo -- half rib because I sanded through the next to last rib on one end of the stab, and just glued the two ends into place leaving a very shallow notch where they cross the spar. I may come back and fill the notch with a shim, or I may not bother.
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« Reply #20 on: April 14, 2011, 11:54:53 AM »

I like to use tracing paper and draw with a pencil around the parts on either the plan or print wood patterns I have. Turn over the tracing paper and retrace the line onto the balsa you have ready.

Works just fine for me,

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« Reply #21 on: April 14, 2011, 02:56:11 PM »

Zeiss Ikon,

There used to be some kits (Thermic gliders??) that enclosed just a bunch of rectangles for the wing ribs. You had to sand in the airfoil you wanted.

Something you can do for those long tapered-wing ribs is to cut pattern ribs of the last rib and the center rib from some harder material, then sandwich rough-cut balsa ribs (ro rectangles) between them - 2 for each station, and then sand the entire stack. It'll put the taper into the ribs. I often hold everything together by drilling 3/32" holes in each piece at about the same spot, slide 3/32" brass rod through the pieces to stack them and push on surgical rubber tubing (fuel tubing) to retain everything.

Scraps of wood that most people toss out are sometimes useful to us for tools and such if you have a good means of cutting them. I have a band saw, and a thickness drum sander; do you know how many sanding sticks you can make out of an 8" piece of 2 x 4?

I've also built a jig for cutting gussets out of pine, and a tool for marking the center on dowels (basically a V-notch, with a straight edge bisecting it on one side to act as a drawing guide. You make a mark on the dowel, turn ~1/4 turn, and mark again. Intersection is the center.)

With a little work, you can build a LOT of tools out of scraps.

Justin
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« Reply #22 on: April 14, 2011, 05:36:39 PM »

Something you can do for those long tapered-wing ribs is to cut pattern ribs of the last rib and the center rib from some harder material, then sandwich rough-cut balsa ribs (ro rectangles) between them - 2 for each station, and then sand the entire stack. It'll put the taper into the ribs. I often hold everything together by drilling 3/32" holes in each piece at about the same spot, slide 3/32" brass rod through the pieces to stack them and push on surgical rubber tubing (fuel tubing) to retain everything.

I've actually done this (back in the 1980s) for wing ribs when I was scratch-building my R/C Terrier and my P-30 biplane, and it worked very well -- but those ribs were all the same size. The one time I've done this with ribs for a tapered wing, I found that the taper produced is too sharp (the rib stack is an inch or so thick, at most, compared to a foot or more length for the completed wing), so the ribs still have to be resanded after the wing is built -- and if you double stack, unless it's a fully symmetrical airfoil (which allows you to flip one set of ribs as you build), you get a reverse taper on one wing, which can actually lead to the ribs going undersize by the time you sand it out, unless you remember to leave the ribs oversize when you stack sand -- and then you still have to resand the completed wing.

My solution is to just cut the ribs on the outside of the line and sand the finished wing to clean things up.

Scraps of wood that most people toss out are sometimes useful to us for tools and such if you have a good means of cutting them. I have a band saw, and a thickness drum sander; do you know how many sanding sticks you can make out of an 8" piece of 2 x 4?

I have a bandsaw, too, but I have trouble getting it to cut straight (the blade wanders -- I'm told this is due to loss of set on the wheel side, but this blade hasn't got that many hours on it, and 59 1/4" blades are fairly hard to find); I can't depend on it cutting accurately enough to make narrow strips (in fact, I mostly use it for cutoff; I used it a lot when I was making up my strippers, cutting pieces of poplar all the same length against the fence). The only power sander I have is a combination belt-disc unit and, like most cheap tools, it's got some serious limitations. I find it simpler to just take a piece of the strip I'll be using and mount it up as I described than to try to deal with my cheap shop tools.

One power tool I have that I hope to use more in the future is a router. Mounted as a router table (aka shaper), this could be especially useful if there were an economical way to make or obtain custom contoured bits -- for things like leading edges, for instance. I've also got a router table for my Dremel, but bits aren't any easier to come by in odd shapes on 1/8" shank than on 1/4" shank...
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« Reply #23 on: April 14, 2011, 06:48:46 PM »

I've actually done this (back in the 1980s) for wing ribs when I was scratch-building my R/C Terrier and my P-30 biplane, and it worked very well -- but those ribs were all the same size. The one time I've done this with ribs for a tapered wing, I found that the taper produced is too sharp (the rib stack is an inch or so thick, at most, compared to a foot or more length for the completed wing), so the ribs still have to be resanded after the wing is built -- and if you double stack, unless it's a fully symmetrical airfoil (which allows you to flip one set of ribs as you build), you get a reverse taper on one wing, which can actually lead to the ribs going undersize by the time you sand it out, unless you remember to leave the ribs oversize when you stack sand -- and then you still have to resand the completed wing.

My solution is to just cut the ribs on the outside of the line and sand the finished wing to clean things up.

I find that I do less sanding by stack-cutting for taper, then sanding the finished wing to clean up the jaggies. I've never tried doing it as a single stack -- always two.
Quote

One power tool I have that I hope to use more in the future is a router. Mounted as a router table (aka shaper), this could be especially useful if there were an economical way to make or obtain custom contoured bits -- for things like leading edges, for instance. I've also got a router table for my Dremel, but bits aren't any easier to come by in odd shapes on 1/8" shank than on 1/4" shank...

Try shopping around for stock round-over bits and other 'millwork' shapes. You may be able to get close enough to what you want. Come to think of it, if you can get close, you may be able to re-contour a round-over bit to do half a leading edge without much trouble at all -- just lots of little Dremel tool grinder bits.
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« Reply #24 on: April 14, 2011, 08:01:06 PM »

One power tool I have that I hope to use more in the future is a router. Mounted as a router table (aka shaper), this could be especially useful if there were an economical way to make or obtain custom contoured bits -- for things like leading edges, for instance. I've also got a router table for my Dremel, but bits aren't any easier to come by in odd shapes on 1/8" shank than on 1/4" shank...
Try shopping around for stock round-over bits and other 'millwork' shapes. You may be able to get close enough to what you want. Come to think of it, if you can get close, you may be able to re-contour a round-over bit to do half a leading edge without much trouble at all -- just lots of little Dremel tool grinder bits.

That would work with steel cutters (like all the Dremel router bits). In fact, with Dremel bits (small carbon steel, neither High Speed Steel or carbide or large enough to be annoying), the only major snag with re-contouring them is getting both blades even (there are ways to do that, they're just involved -- like mounting the bit being ground in a lathe or drill press, and mounting the Dremel with grinding stone so it can be moved precisely and cut both router bit flutes as the bit rotates). I've actually seen ogee bits that would cut profiles that would match many leading edges, but most were too big for rubber power. Then again, for wings in the 8" to 36" span range built with fairly light balsa, it's not that big a deal to either shave and sand or just sand the wood to profile (220 on a block cuts 8# balsa like a shoe rasp cuts pine, only lots smoother).

Meanwhile, I need to get the rudder and stab off the plan, sand them, and move the plan so I can start work on the wing. If I can finish the wing and get the flying surfaces covered by the end of the weekend, I should be well on track to finish the Sparky in time for the fun fly on the 30th.
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