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Old Dec 14, 2011, 10:35 AM
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No problem Matt, this is great stuff. The most recent photos are great shots and really show a lot of what I need. Interestingly the two shots of the pilot (Chiribiri?) sitting on/in the plane are of two different airplanes as well, you can tell by counting the louvres on the nose. The one thing I know is the No. 5 was a two seater so based on that criterea it must be the second depiction (first photo) posted. With the other pictures I keep trying to figure out where the second person is supposed to go. If the no. 5 is supposed to have a flat scuttle like the top pic then either we have yet to find a picture of one, the protoypes had rounded scuttles, or the Chiribiri never had a flat scuttle. I also noticed the lack of a vertical stab, the undercambered horizontal stab, and what looks like washout in the elevator, this should be interesting.
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Old Dec 19, 2011, 11:00 PM
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The parts from Charlie have arrived, meanwhile I happened across a link to a company that carries spruce right here in the masthead of RC Groups.
I'm still going to use basswood but my LHS only stocks Midwest and their basswood is only 24" long. Since I need 36" long stuff I placed an order with National Balsa for the required sticks. They do have a $25.00 minimum order and shipping is $10.00 but they have good prices on balsa sheets in sizes not typically available (up to 48" long). Since I have future projects planned it was easy to compile a minimum order.

Pete,

I will start construction with the tail feathers. I would like to mimic the full scale version and give it an undercambered horizontal stab but I don't know how this will affect flight characteristics. Why was this done? It almost seems counterproductive that, as up elevator is applied, the tail would generate lift due to increased AoA. If this is experimentation left for another project I will ditch the idea and move on but it's such a dominant feature, I would like to incorporate it if I could.
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Old Dec 19, 2011, 11:25 PM
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Wow, that's some fragile looking structure there. I guess with wing warping, you have to keep the spars to a minimum. Fascinating. I might have to crash your shop for a closer look.
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Old Dec 20, 2011, 03:05 AM
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I'd prefer it without the lifting tail, the design isn't intended to have it. Including it at this stage could mess with balance point and thrust lines.
Because of how close in-line the motor and wing are, you might already find the down thrust needs reducing. The lifting tail could mean you end up needing up thrust, which never looks right.

Matt,
Definitely a model on which the rigging MUST be functional, even if used without warping.

Pete
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Old Dec 21, 2011, 10:26 PM
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Quote:
Originally Posted by hoffboy View Post
Wow, that's some fragile looking structure there. I guess with wing warping, you have to keep the spars to a minimum. Fascinating. I might have to crash your shop for a closer look.
Sure thing, you'll just have to give me a heads up so I can clear enough space for a second person to fit in it
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Old Jan 02, 2012, 03:37 PM
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The wood from National Balsa has arrived and winter break for the kids is all but over so I'm out of reasons for not getting started. As I began work on the empennage I noticed the plane with the rounded scuttle has no rigging tailpost. This leads me to believe that we are most likely looking at picures of Chiribiri no.3 and have yet to find an actual photo of the no.5 as I suspected. I have decided to stick with the plans regarding structure and will only use the pics for additional scale reference that doesn't interfere with Pete's design.
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Old Jan 06, 2012, 01:25 AM
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So here we go. I know laminating has been done to death in past builds but I wanted to show how I utilize magnets to get the job done. Tail outlines are laminated from four strips of 1/16x3/16 balsa
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Old Jan 06, 2012, 01:37 AM
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Rudder construction is straightforward. I predrilled the two pieces shown below to fit 3/32" brass tubing which will accept a piece of bent music wire to create the hinge, more on that later.
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Old Jan 06, 2012, 02:05 AM
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I made a few minor changes in the horizontal stab and elevator construction. Since the stab is 18" across I decided to add a 1/16 ply doubler to the trailing edge for strength. I also added two "ribs" to each bay (four instead of two as called out on the plans) and used 3/32" instead of 1/8" balsa to create a more scale appearance while not adding too much extra wood. While I was at it I moved the control horn out a bit, also for scale appearance. I intend on using a separate servo for each elevator half so no joiner either.

Pete,

I hope you don't mind my fiddling, I just can't help myself. I promise not to tinker with the overall design but if I get out of line please let me know.

I noticed hardwood bracing for the horizontal stab is shown on the fuselage side view but I don't see where it attaches to the stab itself. Do you know if this was a feature of the original Chiribiri? I don't see it on any of your models pictured so I'm thinking you may have added it knowing an 18" stab would need it. If this is the case then I think the ply doubler I added along with some functional rigging would do the trick as well. What are your thoughts on this?

Mike
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Old Jan 06, 2012, 02:18 AM
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Wow, I've gotten so used to building from plans lately that I didn't even notice Pete had provided a handful of precut 3/16 balsa to speed up construction of the tail feathers. I discovered them while I was looking for some scrap to cut the elevator horn gussets, oh well.
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Old Jan 06, 2012, 04:54 AM
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Mike,
Unless it's gone missing from your plan, the rigging post position is shown on the tailplane drawing - and a hole for it is provided on the laser cut part. If you look at the photo of the smaller model, you can see the rigging post standing up from the tailplane.
It also appears on the artist's impression Matt posted, which is about as close to this version as we get.
I'm sure there is a reason for my tail rib count and horn position, I just can't remember what it was. Your minor tinkering is fine by me.

In case tyou were wondering why the nose parts have large openings in them, the nose is intended to be metal clad, with working louvres in the side panels. With all that cooling air entering the grille, it's nice if it can get out again, without exploding the nose.

For anyone interested, when making the louvres on the first model (45" span) this is how I went about it.
1) Make a louvre shaped cut out in a piece of ply.
2) Drill a very small hole at the rear end of each louvre position (on the aluminium part).
3) Use a knife to score through the rear edge of the louvre - between the drilled holes.
4) Use a rounded piece of hardwood dowel, and the slotted ply, to shape each louvre. Take care not to overdo it and crack the aluminium. The drilled holes help prevent this.

This only works if the aluminium (litho plate) is soft and relatively thick. I've tried it with thinner, harder litho plate and cracking it is only too easy. On this model fairly thick aluminium is virtually mandatory because there is no underlying structure at the upper nose area - if you don't wimp out and opt for painted ply.

Pete
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Old Jan 06, 2012, 09:08 AM
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Looking awesome, Mike! And your photos are going to really help future builders. Very clean and detailed.

As for those parts you discovered, I make a habit of carefully scanning every laser cut sheet and comparing against the plans. I'll admit that on more than one occasion (until I started this cross-checking inventory habit) I fabricated a piece that was there all along. Likewise, I've found missing bits that Pete subsequently added to the cut files...typically a rib or some little fiddly bit.

I'm in Palo Alto all this week (returning late tonight) but then I'm right back down here for another week starting Sunday, which is bumming me out as I'd love to swing by the shop for a closer look. So don't FINISH this thing in the next 6 days, OK?!

Again, looking really excellent so far.

-Matt
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Old Jan 06, 2012, 01:06 PM
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Pete,

Thanks for the information on making the louvres, you were right in assuming I haven't made them before and was already trying to figure out how to go about filling in those large openings.

I see the tailpost but the hardwood bracing I'm referring to is shown in the side view as two dotted lines below the stab and are called out as "h/wood struts", they run from the bottom of the fuse to the leading and trailing edge of the stab.

Mike
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Old Jan 06, 2012, 02:10 PM
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Quote:
Originally Posted by hoffboy View Post
Looking awesome, Mike! And your photos are going to really help future builders. Very clean and detailed.

As for those parts you discovered, I make a habit of carefully scanning every laser cut sheet and comparing against the plans. I'll admit that on more than one occasion (until I started this cross-checking inventory habit) I fabricated a piece that was there all along. Likewise, I've found missing bits that Pete subsequently added to the cut files...typically a rib or some little fiddly bit.

I'm in Palo Alto all this week (returning late tonight) but then I'm right back down here for another week starting Sunday, which is bumming me out as I'd love to swing by the shop for a closer look. So don't FINISH this thing in the next 6 days, OK?!

Again, looking really excellent so far.

-Matt
Matt,

Good call on the prebuild inventory check, when I start the fuse I will most definitely go through the rest of the parts and identify each one prior to assembly.

Finished in six days?!!! That's a joke, right? Don't worry, you've got plenty of time to check things out.

Mike
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Old Jan 06, 2012, 06:55 PM
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Ahhh, THOSE bits!!! Right, I have to be perfectly honest here. I'm sure I showed struts for a reason, presumably I saw an illustration showing them, but have no idea where I saw it. A dead computer and moving what files I could recover hasn't helped any.
Thinking about it, I can't help feeling that, given the rigging post, they could equally well be cables - which is how my original model was done and how the Walt Mooney model shows them (I think). In which case, they run from about 2/3 span, at leading edge and spar to immediately below the rigging post on the bottom longeron.
In retrospect, that seems more likely and I think I'll change the plan to reflect that. Your outboard full rib is just about where they run to, so would be the logical place to put some hard points for attachment.

Pete
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