Like a few others here, I'm starting to scratch build a Paragon. Thing is, I've settled on a two-piece wing better instead of the three piece on the plans. Having looked at Mark Drela's designs and reading here, I plan on using a steel rod and brass tube buried in vertical grain basswood, then wrapping that with kevlar tow for the length of the basswood.

My question is, how big should the rod be? I ordered a 1/4"x12" steel rod from nesail, but the more I think about it I'm wondering if that's longer than necessary. Or, might I want the rod beefier? I'll be using a high start and I don't anticipate needing zoom-proof wings.

Beffier is better.

In any event, consider a "Dixie Pin" for the wingrod. They are hardened mold ejector pins, and I have switched all my planes over to them. They are incredibly stiff.

+1 on the ejector pin. I use a 5/16"x6" in my Sagitta 900 and it takes a pretty good winch launch

Al

1/4 will not be strong enough except for a display model , not sure why your gonna make it a 2 piece wing , i think 3 is much better , but thats me ........

For several sailplanes of roughly the size of a Paragon, I have used a rod that fits nicely into a 3/8-in.-OD brass tube. Calculations say that this size rod should be plenty strong for even a very vigorous winch launch.

Sounds like I was undersizing the rod diameter while making it longer than necessary. I'll check out those mold ejector pins, thanks for the tip.

As for why all the trouble to switch to a two-piece wing? Something just don't sit right with me about detachable tips. Maybe I need to see one in person, 'kick the tires' and all. There's a dihedral joint anyway, so I figure might as well have the fussy detachable kind of joint there rather than doubling up on them further out. But that's also just me

Ejector pins are good but I like High speed steel drill blanks, hardened throughout as they are available in fractional, letter and number sizes as well as metric. I used 5.6mm (.220) or 7/32 (.2188) for a perfect fit inside 1/4 brass tube for the tip joiners on my paragon. About 4" long and about $6.00 ea. from MSC industrial supply pg. 36-37 http://www1.mscdirect.com/CGI/NNPDFF...E=36&PMCTLG=00 MSC. is a good source for ejector pins and they can be had much longer than a jobber drill blank, 12" and longer but not as many size choices, and they can't be bent for dihedral. I personally prefer the 3pc wing but you need to shop around for a good pc of hardwood for that tapered center joiner or laminate plywood. Go full 3/8 wide on the shear webs and get a good fit and good epoxy job when you attach the spar caps. I D-tubed the center panels with 1/16 top and bottom and also caped the ribs top and bottom. I used no carbon on the spar and have been full pedel launching with no problems so far. Good luck on whatever you decide. Nothing quite like a Paragon Wayne

One advantage to a 2 piece wing is less weight out near the tips.

The obvious disadvantage is the joiner has to be built right and be sufficiently stout to take the load. At the center of the wing, it will take 100% of the bend load. (See Dr. Drela's info on that)

Having said that, I have built a couple of Riser 100's using a 2-piece wing arrangement, and using drill rod for the joiner. I could winch em with no problem, and even give em a little zoom at the end. Never saw any signs of weakening at the wing roots.

I'm glad you're getting full pedal launches with a D-tube but no carbon, enyaws. I didn't realize until after I'd cut the ribs that cap strips are for torsional rigidity. I don't think I'll bother adding them now since the D-tube is already more than the original.

When you say to go with full 3/8" wide shear webs, do you mean all the way out to the tip? That sounds like a good idea, but how did the old designs I've looked at get away without it? I guess they didn't winch much back then, certainly no zooming...

LVsoaring: I'm hoping that a 3/8" O.D. Brass tube/hardened steel rod + bass web + 1/16"~1/8" ply outwebs + kevlar tow the first few bays will be strong enough. From everything you guys are telling me, it sounds like plenty for my needs.

Originally Posted by ieyasu

I'm glad you're getting full pedal launches with a D-tube but no carbon, enyaws. I didn't realize until after I'd cut the ribs that cap strips are for torsional rigidity. I don't think I'll bother adding them now since the D-tube is already more than the original.

When you say to go with full 3/8" wide shear webs, do you mean all the way out to the tip? That sounds like a good idea, but how did the old designs I've looked at get away without it? I guess they didn't winch much back then, certainly no zooming...

LVsoaring: I'm hoping that a 3/8" O.D. Brass tube/hardened steel rod + bass web + 1/16"~1/8" ply outwebs + kevlar tow the first few bays will be strong enough. From everything you guys are telling me, it sounds like plenty for my needs.

Yes, I'm sure that will be fine. Just keep a close eye on the wing roots every few launches to make sure there is no weakening of the structure or vertical separation of the spar caps. As long as your kevlar tow is tightly wrapped, I doubt you'll have any problems.