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Old Jul 19, 2012, 10:25 AM
G_T
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PS - I forgot to mention other reasons for the fabric order in my tailboom. The outer fabric, not being HM, is not a brittle fabric (not as brittle at any rate). It will take a sharp impact better without cracking than would be the case if it were of a substantially higher modulus like the inner uni. Also like Tom said, the uni is encapsulated between woven fabric layers which helps prevent it from splitting in the lengthwise direction where it has hardly any strength beyond the epoxy matrix strength.

It also looks cool

Gerald
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Old Jul 19, 2012, 10:31 AM
Aurora Builder
United States, MD, Lusby
Joined Nov 2003
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Just hunted for some titanium screws, probably not worth it, $5 for each screw. Could use nylon for $5 per 100 screws, that is likely what I will try if I can find one. Not as stiff as steel or titanium but strong enough.
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Old Jul 19, 2012, 10:50 AM
G_T
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You don't want nylon for the job. It will cost launch height and the wing alignment will not really be fixed. They are too flexible. You'll readily feel the difference on the throw. We are using screws both as holddowns and as alignment pins. Nylon is not suitable for the latter job.

I figured Ti would be expensive, and it would need anti-seize compound. That's why I'm also curious about anodized aluminum screws.

I'm pretty certain the rear bolt can be replaced with aluminum. The front I'm not as sure - it may need Ti or steel.

I'm also not sure people would want to pay the extra $$ for lighter screws. But in the scheme of things it is actually an economical weight savings in terms of $/g (roughly comparable $/g to the major components of the plane). You all can let me know if you want me to pursue this option.

Gerald
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Last edited by G_T; Jul 19, 2012 at 06:13 PM. Reason: spelling
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Old Jul 19, 2012, 10:56 AM
Chuck 'Em and Chase 'Em
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United States, NY, Plainview
Joined Aug 2005
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If you let threaded portion stick up (like a T nut) so that it is used for alignment and the screw does nothing other than hold the wing on, could you then use nylon?

What size screw are you using?

Frank
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Old Jul 19, 2012, 11:17 AM
G_T
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6-32.

One would have to use a larger base T-nut than what I'm using, so that it has adequate support since less of it would be encased within the fuselage. The weight cost would cancel the benefit. Also, one would then be using a little lip to support the lateral loads on launch. One would need to make the mating structure in the wing fairly hard and strong. I don't think it is a good engineering approach, though it can be made to work using taller T-nuts but then it weighs more than the steel bolts it replaces.

Gerald
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Old Jul 19, 2012, 11:30 AM
Aurora Builder
United States, MD, Lusby
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Anodized aluminum fasteners, I'm ordering some now:http://www.fastener-express.com/alum...s-washers.aspx
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Old Jul 19, 2012, 11:46 AM
G_T
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I just ordered some as well, for the rear wing bolts. I'll see what I think when they get here. Thanks for the link!

Gerald
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Old Jul 19, 2012, 11:59 AM
Father of Fr3aK, DLG Pilot
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USA, OH, Worthington
Joined May 2002
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I used nylon #8 bolts for many years, and up to about a year ago. They'll hold.

I use steel now just because it's cheap and easy and I don't care about the couple of grams. I had nylon get buggered up once or twice too and it was a pain to remove.
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Old Jul 19, 2012, 12:09 PM
Chuck 'Em and Chase 'Em
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Thanks guys.

Frank

(Heat the end of a screwdriver and stick it into the nylon. usually comes out )
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Old Jul 20, 2012, 08:22 AM
TjW
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USA, CA, Riverside
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Quote:
Originally Posted by G_T View Post
6-32.

One would have to use a larger base T-nut than what I'm using, so that it has adequate support since less of it would be encased within the fuselage. The weight cost would cancel the benefit. Also, one would then be using a little lip to support the lateral loads on launch. One would need to make the mating structure in the wing fairly hard and strong. I don't think it is a good engineering approach, though it can be made to work using taller T-nuts but then it weighs more than the steel bolts it replaces.

Gerald
I don't know if this would save any weight over what you're using now, but have you considered using aluminum rivet nuts?
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Old Jul 20, 2012, 01:23 PM
G_T
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My issues with aluminum for the nuts are galling, wear, and galvanic corrosion. The nut is in direct contact with carbon fiber (how it is supported) and this will corrode the aluminum, weakening it. I don't want to add the step of having to put a non-conductive primer coat on the nuts first. The aluminum threads will also wear much faster than the steel ones I'm using. These connections after all are installed/removed each time one goes out to fly.

Yes, they might save a tiny bit of weight. I'm looking at another alternative though, for production run 2. I do not know whether it will work so we'll see. But in any event the steel T-nuts I'm using are as light as such things come.

Thank you for the link!

Gerald
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Old Jul 20, 2012, 10:01 PM
G_T
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I checked the last fuselage for reference. The CG with the bolts installed but without trimming the boom to length is about 1/8" in front of the rear wing bolt. Weight is 46g with the steel bolts (somewhere around 3g). When I have the aluminum ones for the rear bolt that should knock off more than half a gram. Trimming the boom to length will knock off more than a gram. So call it somewhere around 44.5g. I'm satisfied with this weight, though the next production run will likely be a gram lighter.

These numbers are from the last fuselage, the one where the balloon failed and I had to replace it. I decided to keep that one instead of selling it. The balloon swap and fabric repositioning tore up the PVA somewhat and if one looks closely it shows in the finish. There are also a couple places where the fabric didn't end up aligned perfectly. Carbon woven fabric tends to show this sort of thing rather well. There was also a small cosmetic bubble or two. I sort of consider it somewhat of a first, with artifacts. Too good to call it a second, not good enough to call it a first. So, it's mine! My first one!

I won't quite make it through the short list with the first production run, as I simply don't have enough of the required fabric. I'll be ordering more soon. But to gauge how much to get, what is the interest like out there? I know not many have seen these in person yet so I don't expect a large response. But feedback would be appreciated so I have an idea of how much stock to purchase.

I figure to continue making 2 to 3 a week. Doing more than 3 in a week is difficult for me right now. There will be a short break in production while I'm waiting for fabric once I'm out.

Thanks!
Gerald
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Old Jul 20, 2012, 10:25 PM
Jim C
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Gerald, there is likely going to be another club project this winter.......
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Old Jul 21, 2012, 12:47 AM
It's a mere flesh wound!
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Woodstock,Ga.
Joined Jun 2004
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Gerald,

Thanks for the info on Fastenal! I had heard of them but didn't realize that they had a lot of stores. I Googled them, used their Store Locator and found that there was one of their stores 3/4 of a mile from the field Walt and I fly at on weekdays and another store between my house and our club field.

Buddy
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Old Jul 21, 2012, 12:52 AM
Aurora Builder
United States, MD, Lusby
Joined Nov 2003
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Gerald,

I will take 2 per month, if you can sustain that.

I'm loving this fuselage. It is amongst the toughest fuselages I have ever touched period, for sure the toughest, stiffest DLG fuselage in production. It is also roomy without being draggy. No special tricks required to get gear in.

My full build is complete. Will take pictures in the daylight (piss poor lighting in the shop, I work under several spotlights that are terrible for photos, its on my to-do list to fix). Depending on the weather, I might test fly tomorrow or wait till Sunday. Either way I think I might be the first to fly one of these beauties ?
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