Styrene Launch Lugs

[DynaSoar]

Stronger than paper (thicker walls, won't dent or get shredded on the ends), slick as a whistle, paints well, lighter than AT's square clunkers, takes any glue except wood glue, and can be trimmed to most any nice aerodynamic shape.

Just be aware that the size given on the package is the external diameter, not the internal (or what size rod the lug will fit over).

A 1/4" lug is best made with 5/16" styrene tube. It weighs 2/3 of a gram per inch. For 3/16" lugs, use 1/4" tube.

I use Evergreen Scale Models' StripStyrene. 2 bucks for 3 twelve inch pieces.

On 1/4" lugs, you can slide a small piece of dowel or scrap wood into the fillet space for more surface for the glue to grab. If you're careful with the fillet, and pull a small bit of glue over the top of the lug, you can make a nice round, smooth bump with a rod sized hole through it. If you're not concerned about the drag, you can just stick them on with CyA.

My Acme conformals for 38mm and stand off for fin can weigh 6.35 grams. With fillets styrene would weigh half that including epoxy and be more aerodynamic. And I think they look better.

 

[polaris]

After you posted this, I tried it. Wow!

Because they are so strong, I am able to cut lugs using a razor saw. I use 600# sandpaper to de-burr and polish them.

I have been cutting them into a shape like the Acme lugs. I have been cutting them on a 45 degree angle. I have also been reducing the size of the lugs. I can’t tell what impact it has had on the rocket’s performance. I think smaller is better here.

I tack them in place with a dab of CA. Then I use epoxy to form a small fillet along the base edges.

I’d appreciate any other tips you’d be willing to share.

 

[DynaSoar]

Originally posted by Polaris
After you posted this, I tried it. Wow!

Because they are so strong, I am able to cut lugs using a razor saw. I use 600# sandpaper to de-burr and polish them.

I have been cutting them into a shape like the Acme lugs. I have been cutting them on a 45 degree angle. I have also been reducing the size of the lugs. I can’t tell what impact it has had on the rocket’s performance. I think smaller is better here.

I tack them in place with a dab of CA. Then I use epoxy to form a small fillet along the base edges.

I’d appreciate any other tips you’d be willing to share.

Wash it with soap and water to remove any oily residue from the manufacturing. The oil keeps it from sticking.

Rough up the side to be glued or to have fillets on them with very rough sandpaper, or even cut slices in the surface with a knife. This gives the glue better grab.

Square tube has thinner walls, and has a flat side to glue against the body tube. It also has less surface area against the rod, and so less rod drag.

If you use round, wipe some of the glue from the fillet up over the top so it completely surrounds the tube.

5/16" tube is 1/4" inside diameter, but almost exactly. It can be tight on a rod. If so, after adding fillets, carefully slice all the way down one side. It'll still be stiff enough to stay on the tube, but won't bind on it or have too much friction. The tolerance on this tube is so close to 1/4" ID that one layer of paint is enough to make it too tight. Plug the ends before painting.

 

[polaris]

Thanks.

Do you have any thoughts on the best shape for a launch lug?

 

[DynaSoar]

Originally posted by Polaris
Thanks.

Do you have any thoughts on the best shape for a launch lug?

Square has less rod drag. As for air drag, that depends on wall thickness and on how small it is. The smaller the lug the harder for air to pass through.