<br><font size=2 face="sans-serif">Bob</font>
<br>
<br><font size=2 face="sans-serif">You can have dessert in Tucson.<br>
<br>
<br>
<br>
Gray Fowler<br>
Principal Chemical Engineer<br>
Composites Engineering</font>
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<td><font size=1 face="sans-serif"><b><rcaerobob@cox.net></b></font>
<br><font size=1 face="sans-serif">Sent by: discussion-request@nsrca.org</font>
<p><font size=1 face="sans-serif">01/17/2005 03:55 PM</font>
<br><font size=1 face="sans-serif">Please respond to discussion</font>
<br>
<td><font size=1 face="Arial"> </font>
<br><font size=1 face="sans-serif"> To: <discussion@nsrca.org></font>
<br><font size=1 face="sans-serif"> cc: </font>
<br><font size=1 face="sans-serif"> Subject: Re: Re: epoxy joint</font></table>
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<br><font size=2 face="Courier New">Ya know, all this talk of "filet"s is making me HUNGRY. Haven't read much today on "fillets", and one you eat, one you don't....Gray?<br>
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<BG><br>
<br>
Bob<br>
> <br>
> From: Gray E Fowler <gfowler@raytheon.com><br>
> Date: 2005/01/17 Mon PM 04:08:50 EST<br>
> To: discussion@nsrca.org<br>
> Subject: Re: epoxy joint<br>
> <br>
> John,<br>
> <br>
> On something like a lite ply former, I usually put a filet like amount on <br>
> the former to ensure complete wet out and complete gap fill. The result is <br>
> an absolute minimal filet-cuz the tip of my finger is curved. This is just <br>
> to make sure the entire joint is complete, because you really cannot QC <br>
> the joint-not to add a filet. <br>
> Also a gob of really strong epoxy WILL increase bond strength IF the epoxy <br>
> is stronger than the substrate such as lite ply. But this is a <br>
> bass-ackwards application and once again dead weight.<br>
> <br>
> <br>
> <br>
> Gray Fowler<br>
> Principal Chemical Engineer<br>
> Composites Engineering<br>
> <br>
> <br>
> <br>
> <br>
> "John Ferrell" <johnferrell@earthlink.net><br>
> Sent by: discussion-request@nsrca.org<br>
> 01/17/2005 02:01 PM<br>
> Please respond to discussion<br>
> <br>
> <br>
> To: <discussion@nsrca.org><br>
> cc: <br>
> Subject: Re: epoxy joint<br>
> <br>
> <br>
> "Filets in general are useless other than for cosmetic reasons. On a <br>
> properly assembled bond joint the filet will never see stress until the <br>
> load capacity of the joint itself is exceed. At that point the joint <br>
> breaks and considering that the joint itself is orders of magnitude <br>
> stronger than the filet, the filet breaks instantly. Filets are dead <br>
> weight, "<br>
> <br>
> Awesome! and embarrassing!<br>
> I cannot even guess how many formers & stringers I have carefully <br>
> encumbered with beautiful, heavy worthless fillets...Sometimes adding bits <br>
> of string to the mix in imitation of pylon racers...<br>
> <br>
> But you just made future building easier...<br>
> <br>
> John Ferrell <br>
> http://DixieNC.US<br>
> ----- Original Message ----- <br>
> From: Gray E Fowler <br>
> To: discussion@nsrca.org <br>
> Sent: Monday, January 17, 2005 9:57 AM<br>
> Subject: Re: epoxy joint<br>
> <br>
> <br>
> John, <br>
> <br>
> I do not understand what you mean composite horns/balsa.....but I do know <br>
> a thing about joints ( I once lived in Hawaii hanging out with the <br>
> locals). <br>
> Epoxy is the "toughest" unfilled. By this I means in a seam joint the <br>
> primary stress will be flexing, and an unfilled epoxy can handle this the <br>
> best. <br>
> Milled fibers are about 1/64" long. In a composite the fibers are far <br>
> stronger than the resin. The job of the resin is to flex a little to enable stress to be transferred from one fiber to another. The problem <br>
> with milled fibers is that as the transfer stress it is only for that 1/64 <br>
> of a inch and then it terminates creating a stress riser. The epoxy then <br>
> fractures at the end of that fiber at a stress level much lower than if <br>
> the fiber was not there at all. These type of fibers work great on <br>
> thermoplastics which are much softer and flexable, but not so great on <br>
> thermosets. Milled fibers in an epoxy will reduce elongation, reduce tensile strength, increase the heat distortion temperature, increase hardness and increase compression strength. <br>
> <br>
> Microballoons are not structural, they are used to reduce density. The <br>
> volume is huge and the balloons are weak therefore the mixture is weaker <br>
> in every aspect. The reality is though that a microballoon epoxy is still <br>
> usually strong enough for our applications. Add this to the fact that we <br>
> are always striving for weight reduction and you can determine the proper <br>
> application. <br>
> <br>
> Filets in general are useless other than for cosmetic reasons. On a <br>
> properly assembled bond joint the filet will never see stress until the <br>
> load capacity of the joint itself is exceed. At that point the joint <br>
> breaks and considering that the joint itself is orders of magnitude <br>
> stronger than the filet, the filet breaks instantly. Filets are dead <br>
> weight, and usually more dead weight than you think it is-but man they <br>
> sure look GOOD when someone inspects the inside of your plane-which in <br>
> this hobby is second only to winning the NATs (sorry-cannot always stop <br>
> the sarcasm). <br>
> <br>
> <br>
> <br>
> Gray Fowler<br>
> Principal Chemical Engineer<br>
> Composites Engineering <br>
> <br>
> <br>
> <br>
> "John Crozier" <sjcrozier@comcast.net> <br>
> Sent by: discussion-request@nsrca.org <br>
> 01/15/2005 09:35 AM <br>
> Please respond to discussion <br>
> <br>
> To: "discussion nsrca" <discussion@nsrca.org> <br>
> cc: <br>
> Subject: epoxy joint<br>
> <br>
> <br>
> <br>
> Sometime in my crafting life, I have acquired the notion that adding <br>
> milled glass, micro-balloons, etc., to epoxy when making a good fitting <br>
> joint, only weakens the joint. (diminishes, or dilutes the bonding <br>
> strength of the epoxy). <br>
> In this case it would be composite horns to balsa. No fillet is needed. <br>
> Anybody wanna jump in? <br>
> <br>
> <br>
> <br>
> <br>
<br>
Bob Pastorello, El Reno, OK, USA<br>
rcaerobob@cox.net<br>
www.rcaerobats.net<br>
<br>
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