Farside-X Booster, reinforced fins
 

The Farside-X was designed with 18mm motors on all three stages, but I’ve heard as many horror stories as success stories about flights using the C6-0. Back in the 60s, Estes offered a B14 motor, offering higher initial thrust, and lifting capability for bigger, heavier model rockets. Since the B14 is no longer available, a C11 or D12 seemed like a good alternative. I decided to build the booster stage to use these 24mm booster motors, which are a perfect fit in the BT-50 body tube used on Farsides. I also decided to build the booster with 1/16” basswood fins, rather than balsa, to add a bit more strength. But I worried about whether these fins would stay attached on landings, especially on the hard ground we have at our launch sites. And, being a minimum diameter booster, thru-wall fin tabs were not possible.
I used a technique I saw awhile back in a post by Gary Rosenfield (of Aerotech), for a minimum diameter altitude rocket he built for long-burn G motors. The technique shown adds a lot of bonding strength for fins. It involves cutting a series of fold-up tabs along the fin line, to “grab” the fin on its sides, along the root edge. The tabs are small enough that they can be hidden in the fin fillets.
Three lines are drawn as normally done, which then have two lines drawn on each side of them. These define the fold lines for the tabs. A series of marks are added along these lines to mark the ends of the tabs. Once cut, these tabs will be lifted. Only every other set of tabs are cut and lifted, to maintain tube strength, and provide small sections of body tube that will get glued directly to the fins’ root edges. The lifted tabs are bonded to the surface of the fins along the root edge, adding a lot of additional strength, and rigidity. I almost did not have to hold the fins vertically from the tube as they were glued on, they just naturally aligned. Note: I decided to not use tabs along the fins near the top of the tube, to provide a perfectly smooth inner surface for the required coupler. After assembling, it probably was not necessary, but the tabs used should provide plenty of additional strength and support.
Each fin has one wood glue fillet applied. I will add one more fillet before priming the assembly for paint. The fins have had one coat of diluted Elmer’s Wood Filler brushed on, and sanded with 400 grit. They are incredibly smooth already, and several primer coats should be sufficient for a very smooth finish.

Lee, that looks like a great technique. Wish I had thought of it............


Joe

I may create a new 1st stage for my Farside, for 24mm motors, and use this technique.


@LeeR:

With additional pictures and text, this could be turned into an article for the NAR magazine. Include a little history of the rocket, and the finished result.

Stefan,

I’ll certainly consider writing this up. I’d like to get a little further, and finish the build. Probably ought to fly it to see how tough it is, too!

I’ll probably also do this mod on a Comanche-3 I have in my vast collection of kits to build. It was a bit time consuming, but got easier on the second and third fin. Just takes some practice.

Joe, me too! But I’m happy to “leverage” other builders techniques. :)

Gary Rosenfield showed this technique on the NAR Facebook page a while ago. He added the step of "sewing" the fin to the BT with kevlar thread.

That's very nicely exexcuted, Lee.

I mentioned I got this idea from Gary. However, I don’t think the joint was “sewn”. It was just a convenient way to anchor the Kevlar shock cord.