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Old Jan 13, 2012, 01:40 AM
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Wing construction begins by laying out the ribs and feeding them on to the front and rear basswood spars, making sure the ply ribs are at the rigging hard point locations per the plans. I started by gluing the root rib on the spars first while making sure the rib was perfectly square with the spars and let it dry. I then made a spacer tool to place the remaining ribs at equal spacing while checking for spar and rib straightness/squareness while I built, leaving off the last two ribs which make up the tip. after the glue dried on the ribs I added the balsa leading edge and basswood trailing edge. The leading edge calls for a 1/4" balsa dowel but since I couldn't find one (and wasn't too keen on making one) I sanded a square notch in the nose of the ribs to accept 1/4" square stock.
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Old Jan 13, 2012, 01:47 AM
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The wing is designed to be removeable and is supported by two pieces of music wire (along with the rigging) that pass through brass tubes. I put a bit of solder in the ends of the tubes to keep the wire from slipping into the wing then glued them into the precut holes in the two inboard ribs. This is followed by 1/16" balsa sheeting.
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Old Jan 13, 2012, 02:05 AM
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The wing tip consists of a laminated bow and the two outermost ribs. The tip bow is made from 5 strips of 1/8x1/16 balsa. On the plans Pete has suggested adding some basswood for strength so I used it for the first three laminations then used balsa for the last two. The spars need to be tapered to get the last two ribs to fit in position then the bow can be fitted afterward. Since the the wing is undercambered the tip is curved up in the middle so you have to glue one end first then fit and glue the other end after the first end has dried, gluing it to the trailing edge first seemed easiest.
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Old Jan 13, 2012, 02:18 AM
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Pete,

During wing construction I came across a couple of minor discrepancies. The first one is where the spar taper start point is called out. The plans show the taper beginning after rib R4 for front and rear spars when the ribs are slotted to fit so the fore spar taper begins outboard of R6 and the rear spar at outboard of R5. The other is regarding the rib profile of the tip ribs. I have included a photo that shows rib R7 matching the height of R5, R4, etc. while R6 is narrower by 1/8" at the top. It appears that R6 introduces a taper (reduced camber along the top) to the tip that R7 never got. If the top of the wing is to remain constant then R6 needs to be taller, if there should be a taper then R7 needs less top camber (3-4mm). I'm going to go ahead and sand R7 down to create the taper on this one unless you say otherwise.

Mike
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Old Jan 13, 2012, 04:24 AM
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Mike,

Go ahead and sand the R7 rib, I'll modify the part on the drawings - and move the taper notes.

Pete
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Old Jan 13, 2012, 03:31 PM
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Looking awesome Mike, and your photos continue to really tell the story. I'll be curious to see how this removable rigging plan comes together, especially since it's functional. I'd like to do something similar for a supersized Kogutek.
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Old Jan 14, 2012, 03:52 PM
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I'll be curious to see how this removable rigging plan comes together, especially since it's functional.


Me too, I'll take some ideas on this if anyone has them. I'm thinking they should be adjustable as well to fine tune washout and wing incidence. I don't like the bulkiness of clevises but they would fill both needs. I'm leaving the hard points off until I come up with a plan, the ones on the wings will require some additional thought since the spars aren't at right angles or flush with the top or bottom of the ribs. Not a big deal, just something to think about.
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Old Jan 14, 2012, 06:29 PM
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Me too, I'll take some ideas on this if anyone has them. I'm thinking they should be adjustable as well to fine tune washout and wing incidence. I don't like the bulkiness of clevises but they would fill both needs. I'm leaving the hard points off until I come up with a plan, the ones on the wings will require some additional thought since the spars aren't at right angles or flush with the top or bottom of the ribs. Not a big deal, just something to think about.
Agree on clevises. I've seen some shipbuilding rigging that could be a possibility. Might be worth a chat with Bob B.
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Old Jan 14, 2012, 08:19 PM
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Agree on clevises. I've seen some shipbuilding rigging that could be a possibility. Might be worth a chat with Bob B.
Most definitely, I need to talk to him about covering choice as well. I want something that doesn't iron on and is more heavy duty than what I would use on smaller models.
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Old Jan 15, 2012, 12:31 AM
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Pete,

As I'm sure you've noticed I evenly spaced my ribs for convenience. I did however notice that rib spacing on the plan wasn't so. As I begin the fuselage construction I also notice upright spacing is not constant either. Why is this? If your design is a scaled up version of the Walt Mooney plans then maybe he had access to an actual 3-view? This then begs the question why did Chiribiri do it this way? Please do not take this as questioning your design but rather a question motivated by an uncontrollable need to know "why" on my part. I am also innately compelled to symmetry so these types of things catch my unneeded attention.

Sorry for the maintenance,

Mike
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Old Jan 15, 2012, 11:25 AM
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Most definitely, I need to talk to him about covering choice as well. I want something that doesn't iron on and is more heavy duty than what I would use on smaller models.
Silkspan and dope! I've got a ton of silkspan that you're welcome to. And if you like, I've got some gorgeous real silk from Thai Silks down in LA that you can look at. I've been itching to use the old school stuff. Dunno how the weight compares, but I'm guessing loading will not be much of an issue for you with this model. Of course, Bob will probably have other ideas as well.
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Old Jan 15, 2012, 07:10 PM
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Mike,
Bear in mind that it's a long while since I drew up this one, and my earlier comments about being sure I'd seen drawings, but didn't recall where,
As regards rib spacing, very few, if any, aircraft from the pre 1918 era had evenly spaced ribs. They seemed to have put ribs where needed, and then filled in the spaces. I'm pretty sure I did much the same - knew where tip and rigging point ribs needed to go and filled in the gaps with more ribs. If I wasn't working from said missing drawing.
Much the same is true of fuselage uprights, they're where I felt they needed to be. Once again, they were very seldom equally spaced on full size aircraft.

When choosing your covering, bear in mind the relatively lightweight structure and choose something that doesn't shrink too aggressively. Also, for warping wings, something that doesn't make the structure too rigid. Doped covering, adhering to every rib is likely to result in stiffer wings than covering only adhered around the outside, but you have to adhere it to the under camber.

Pete
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Old Jan 15, 2012, 07:18 PM
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On the subject of warping wings/removeable rigging, IIRC, I was thinking that the top warp cables could remain attached to the wings, while the lower ones connected to short cables exiting the fuselage using very small fishing snaps. They'd be fairly well hidden in the u/c. Front cables would simply hook and unhook. Slacken off all the lower cables, unhook the upper front cables and just lift the wings to disengage the upper warp cables from the pulley.
That could be refined, but is how I visualised it at the time.

Pete
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Old Jan 16, 2012, 02:24 AM
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Pete,

Thank you for your response, at least I can make some sense of it now and will pay more attention to this irregularity in future builds. I highly doubt that anyone will be calling me out on the rib spacing on this one though (besides you that is), considering most people haven't even heard of this plane let alone know what it looks like. This touches on a debate I had with a carving friend of mine. I stated that airplanes were not designed around how they looked but whether they worked or not, he asserts that throughout history all things manmade were asthetically driven somehow. Your information supports my argument, function was the driving force and form had no real bearing on the finished design.

Matt and I actually had a conversation today about covering the Chiribiri. The topic of what the warping would do to the covering came up but I hadn't thought about what the covering would do to the warp. I suppose since the model is designed for three channel operation with dihedral any roll authority is a plus so I shouldn't be too concerned. He also thought something lightweight would work considering how slow the model will most likely (hopefully) fly.

If I ditch the idea of making the rigging adjustable I may go with a hitch pin setup at the hard points, this avoids having to stretch the rigging to get it in place. I'm just not confident in my abilities to get the wing set up properly without adjustable rigging so I'm still mulling it over.

Mike
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Old Jan 16, 2012, 03:06 AM
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"he asserts that throughout history all things manmade were asthetically driven somehow"
Obviously your friend hasn't seen a Botali PAMA, or some of the models Tim Hooper builds. The Botali PAMA is just plain ugly with a capital UG, pure function over form. If there was any aesthetic influence, the designer had some very warped ideas of what was appealing to the eye. Not too surprisingly, it appealed to me enough to design a model of one - purely in the name of interest.

Pete
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