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Old Jan 27, 2013, 10:38 AM
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Marysville, WA
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Quote:
Originally Posted by Willsonman View Post
Not sure if you have ever built from laser cut parts but an artists gummy eraser does wonders for removing the charcoal from the edges of cut parts. Way better than sanding which removes wood and just rubs the scorched wood into the good wood.
Excellent tip! Just tried it on a freshly laser cut part and, lo and behold, it erases most of the smoke from the edges.

Was looking through last nights renders and I didn't like the looks of the edges. They were all coming out "striped" so I remapped all of the edges and now they look better. I should be able to start working on the fuselage this afternoon.
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Old Jan 28, 2013, 02:10 AM
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I think I'm finally satisfied with the wing structure. The 3d model looks good enough to illustrate the plans and documentation.
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Old Jan 28, 2013, 08:15 PM
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Wing attachment Ideas?

I've been toying with a few different ideas for attaching the wing to the fuselage. I really dislike the idea of using rubber bands for anything more than basic trainers.

Normally when I scratch build I will use a 1/4-20 tap and a couple nylon bolts to attach the wings, but in this case, I think I will go with 4-40 screws into blind nuts. Tabs in the leading edge of the wings that key into slots in the fuselage with a couple screws at the trailing edge. I want to keep this project fairly simple with kitting in mind.

I am open to suggestions here. I'll keep plugging away at the fuselage design. Should have more renders in a few days.
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Old Jan 28, 2013, 11:45 PM
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4-40 is too small, try 10-32. remember that for the bolt to break properly ( quickly) it has to shear, not stretch or tear.
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Old Jan 29, 2013, 06:09 AM
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Agreed. The nylon bolt technique is usually used to prevent severe damage during a crash. The nylon will shear whereas using screws with blind nuts will do some heavy damage to wing and fuselage in the event of a crash. IMO its a simple solution to use nylon bolts and a technique every builder should have in his/her arsenal.
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Old Jan 29, 2013, 01:11 PM
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Actually I was thinking 4-40 metal screws. It helps to read what I'm thinking, not what I type. Yeah, 4-40 nylon would definitely be too small. You think 10-32 nylon bolts might save the wing during an impact? Runner bands are out, 10-32 nylon bolts is an option, but I think I'm still leaning toward 4-40 metal screws.

The center section structure at the trailing edge might need some modification to support whichever method of attachment we decide too. The heads of small metal screws would rip through 1/16" balsa. Definitely would at least need some hardwood reinforcement there. Or, at minimum, fairly large diameter washers under the screw heads to distribute the pressure over more surface area. Maybe, I could cut some washers from 1/16" ply. Thoughts?
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Old Jan 29, 2013, 08:32 PM
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I can't think of many times I've actually seen nylon screws actually shear and save fuselage/wing structure. I've seen plenty (including mine) save fuselage/gear damage (beefier structure there). I've read about a trick where you drill a hole through a 1/4-20 to allow them to shear more easily, but never seen anyone actually do it. But I think I'd choose 10-32,....and tees, on a 39" ws. ... nylon, just outta habit, plus they seem to have larger heads. I like using tee nuts instead of tapped hardwood, easier. I'd just use a plywood disc, 1/16", under the bottle heads. That's another reason to go larger diameter,... smaller would tend to "cut" the surrounding wing structure on rough, wing dragging landings, loosening up the hole, loosening the wing on the fuselage, especially if you use metal screws.
Keep up the good work, hope you are healing fast. At least you have lousy weather to keep you inside as well,... designing. 82 degrees and higher here, just too hot for me. Be home soon.

Fred
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Old Jan 30, 2013, 03:12 PM
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I think maxnutt has convinced me to use rubber bands or at the least provide the option of rubber bands. Anyway, I've been making good headway on the fuselage structure. Dealing with the landing gear area now. No pictures at this time. Soon.

Oh ya, I was going to ask you, Fred, do you have any recommendations for a good source of balsa and/or lite ply (poplar)?
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Old Jan 30, 2013, 03:41 PM
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National Balsa
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Old Jan 30, 2013, 07:38 PM
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I use National Balsa primarily because their web site is very easy to use. They seem to have a pretty good supply of contest balsa. And they ship fast. Their prices are similar to everyone's else's.

Fred
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Old Feb 03, 2013, 11:54 PM
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Looks like I will go with National Balsa.

I got some of the fuselage parts drawn and verified the fit in 3d. Posting some preliminary renders. Parts are still being fitted so they aren't yet textured. These build renders aren't necessarily in the proper build sequence. Just here to help illustrate what I have in mind so far for the fuselage structure.

-Duk
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Old Feb 07, 2013, 05:37 AM
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Marysville, WA
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Finally got the parts of the fuselage and tail feathers to fit together properly. Had a heck of a time getting the tabs to line up on the aft half of the fuselage. I will work on getting the parts textured for the kit documentation tomorrow. Hopefully I will be able to start cutting parts for the prototype in a few days.

Looking at these pictures again; I'm thinking I might need a bit more material around the wing saddle. As it is now, there's only 3/32" thick balsa there. Maybe I should add a narrow 1/16" doubler just inside the wing saddle area?

I also forgot to add the dowels for the rubber bands in the 3d model. The holes are there. Not a big deal.
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Old Feb 07, 2013, 11:00 AM
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Add a 3/32 or 1/8th doubler for the wing saddle. The front dowel hole could be moved up a little ( hard to see in the pics ), and I always wonder why the current kits have a firewall and then a "motor box" mounted to that....just place the firewall where the back of the motor should be and mount the motor to the firewall.
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Old Feb 07, 2013, 11:30 AM
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I chose to use a "motor box" for a couple reasons; thrust-angles and the "salvagability factor."

With a motor box I can easily ensure proper thrust angles are built into the firewall assembly by simply making the motor box parts key together in only one possible way. With a simple firewall, I'd have to use two different fuselage sides (and/or doublers) and there would be a certain amount of potential catastrophic build error. The sides would have a definite left and right, and the crutch/battery tray would have a distinct top and bottom. If the builder got any of the parts oriented backwards the thrust angles would be wrong.

Another reason for the motor box assembly; on most outrunners the shaft protrudes out the back of the motor. In the event of a nose in crash the battery could slide forward and become punctured by the motor shaft. A sturdy motor box can mean less chance of flames destroying other electronics. The lack of flames shooting from a wounded lipo would definitely increase the "salvagability factor" in the event of a nose in.

I added a 3/32" vertical-grain doubler on each side of the wing saddle. Do the dowels look better?
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Last edited by haiduk; Feb 07, 2013 at 01:43 PM. Reason: reworded for clarity
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Old Feb 07, 2013, 04:12 PM
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yep
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