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'Fairing' surface edges

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Old 02-06-2005, 02:07 AM
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Rick K
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Default 'Fairing' surface edges

Hi Guys, It's a something Iv'e never quite (ever) found a method of a satifactory way of doing . . . That is to 'fair' the intersections of various structures into one another. Ie: the intersection of a mid-wing aircraft's wings to the fuse or the empenage surfaces to each other or to the fuse. In the case of the wings, how the heck can you do it and still be able to remove the wing pannels from the fuse? Never mind the drag reduction factors of it which I know to be advantages, It just 'looks' neater.

I tried filler, silicone, white glue mixed with micro ballons . . . nothing works to achive a nice, smooth concentric paraboilc fillet. My many previous attempts have always resulted in a dissapointing result.

I'm at the point with the construction of my latest project (the infamous Skybench 'Viking') that I either skip doing it again though I wish to, or try one of your methods.
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Old 02-06-2005, 03:35 PM
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Default RE: 'Fairing' surface edges

What I've done on a couple of models is to make a sandwich that fits onto the sides of the fuselage. The sandwich is made from a layer of 3/8 or 1/2 balsa cut to an oversized rib shape and the outer layer is 1/16 ply. To take the shock loads during landings I drilled three holes into the ribs and through into the fuselage sides all grouped tightly at the leading edge and then glued in hardwood dowling or bamboo skewer rod to form three hard "pilings" to transfer and spread out the shocks and prevent the balsa fill rib from crushing there. Although I have not done it a 1/32 ply spine inlaid at the trailing edge would form a nice hard fillet edge as well. From there I just carved and sanded the balsa filler rib to form a nice fillet. If I goofed in my sizing or carving I fill it with lightweight spackle compound, reshape with sanding and then harden the spackle filler with some thin CA.

I also glass all my glider fuslelages with 4 oz cloth and epoxy so that further toughens the balsa fillet rib.

If you're adding such a fillet and root ply rib to a design that does not use it then you'll increase the span by one inch but that's hardly a big deal unless it's for a span limited contest model. If so you'll want to adjust the first root rib position in the wing panels to compensate.
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Old 02-07-2005, 09:21 AM
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Default RE: 'Fairing' surface edges

For slopes where weight is no issue we use Bondo Ultimate. If weight is and issue, use lightweight spackle from the hardware store and mix in a little white glue with that (very little, about 5% to 95% spackle). Once dry it sands easily. It adds no strength what so ever but it's light. Epoxy and microballoons works ok. Most guys don't add nearly enough microballons which is why they hate that method. It should have the consistancy of peanut butter when mixed right. You also need to use a good epoxy resin such as west systems or Z-poxy. The 30 minute adhesive style epoxies are no good for this.


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Old 02-11-2005, 12:57 PM
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Rick K
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Default RE: 'Fairing' surface edges

Hi guys, it's funny how one can trap themselves 'inside the box' Never even thought of using the sandwich method . . . inspite of the fact I've used several times in my model display ship building to make lifeboats. It's a fine idea, especialy if I use my scanner to enlarge the root rib drawing in stages ie. 3% 5% 7% 10% 15% etc. Glue stick the patterns to some 1/8" ply cut them out, glue & stack, fill and sand using my Porter-cable profile sander. It comes with a bunch of convex and concave sanding profile blocks to which you attach adheisive backed sandpaper sheets to. It's a pretty neat tool to have . . . though I often forget I have it!

The only trouble I'm going to have with the 'Viking' is that I've already glued to the fuse the innermost rib, the anti-crush rib that's fitted to the fuse. I suppose what I'll need to do is to take the largest blown up rig (to be innermost) and cut it out to fit around the previously installed fuse root rib.

I wonder if I should leave them with just the slope/angle of the reducing sizes or with the sander give the assembly a 'concave' profile with the sander . . ? It'd look neater and more correct to 'concave'' it but alot more work and I don't think it'd make much of a aerodynamic difference either way.

Did any of you guys pick up on my laser level idea I wrote of in the 'Skybench Viking build' thread? What I'm talking about is using one of those laser levels you see on TV used to hang stuff straight in your house etc. to line up our wings and vert fin and horz tail to each other. I got one for X-Mass and it works great for doing that! No triangles, no going back and forth 50+ times measuring one side of the wing or horz tail compared to the other, nothing has to be placed on the surfaces (like a triangle) to knock things out of line and when checking on things as they dry . . . you can check all the angle intersections without having to touch anything!!!!

When checking my previous work done on the Viking everything proved to be square except the rear wing rod which was off by a degree or so. Not enough for me to catch by eye but enough to change the angle of attack between the two seperate mid fuse mounted wings, if left that way the plane would have wanted to turn in the direction of the wing with the lower angle of attack

If you guys want more detail on this let me know
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