Monday, September 12, 2016

First Through-The-Wall Fins?

The old Estes Semi Scale Saturn V (K-39) was brought up on YORF.
I hadn't looked at the instructions for years. To see them, CLICK HERE

Steps 6 and 11 might show the first ever use of through the wall fins.
This kit had clear plastic fins. The fins were cut from a sheet and "glued" on using clear butrate dope. I remember the Estes Thor Agena B and Gemini Titan also used a variation of this.
The Thor Agena B and Gemini Titan had an external clear coupler that slid over the back end of the body tube. The clear fins slipped on for flight and could be removed for display. At recovery you would usually find that one fin that popped off. There was very little root area, the clear fins were thin.

The smaller semi scale Saturn V was different, the clear coupler was on the inside as part of the engine mount. With the fin fairing shrouds you can understand why Estes had to go with the internal clear coupler. You couldn't slide a clear coupler on from the rear once the model was finished.

This kit design was a disappointment for many. It felt clumsy with the big clear fins and printed body wraps. I've mentioned before, the Dr. Zooch Saturn V kit is the same size as the Estes K-39 kit and the detailing is much better. And - no big clear fins!


  1. I remember building the Thor Agena with clear fins back in the late 60's. If I remember correctly the instructions recommended either clear butyrate dope OR clear fingernail polish as the adhesive. They were quite problematic: fins snapped off with the slightest pressure, adhesive turned yellow after a few months, and slip fitting the coupler on the rocket so that it stayed on during the boost was a hassle.
    BTW, wondering if you or any of your readers know the answer to this: Back when I was a teen building rockets instructions said always use dope, not paint when finishing rockets due to the added weight of paint. Now dope is almost impossible to find. What's changed?

    BAR Geezer

    1. Hi Bar G.,
      I built both the Thor Agena B and Gemini Titan with the slip on clear fins. Both had fins pop off, one on the drive to the launch site.
      On the Semi-Scale Saturn V you were stuck with the clear fins, on display or in flight.
      I remember using Aero Gloss dope, both sanding sealers and clear when adhering tissue on airplane models.
      I would think they have gone out of fashion because very few people build the "stick and tissue" models anymore. Most all RC planes are ARTF or RTF. Some building a old style Guillow's plane now use a glue stick to apply the tissue.
      That, and the cost has gone up! In the 1970s I bought a small jar of dope for 35 cents. Now that 1 oz. bottle sells for $9.49!!!
      It's still being sold, you can find it on Amazon and from RC vendors. But at that price I'll use CWF and spray enamels.

    2. Bar G.,
      Regarding finished weight - Most rockets now are sport flyers, not so concerned about weight. Competition flyers launch "naked" (no paint) models to keep the weight down.
      Compared to the 1960s, we have much larger engines today. Where we once only have A and B engines, now we can get more altitude by simply slipping in a bigger engine.

    3. Chris,
      Thanks for the info. I built a G-T clone a few months ago. Found the cut-score-snap method of fin cutting to be hit or miss. Wound up using my oscillating tool with much better results. Also used clear epoxy instead of dope or fingernail polish with good results, no crazing.. Drawback is it can be messy. Also the thickness of the "collar" is critical: has to be thin enough to wrap around the body tube yet thick enough not to fracture from the stresses. Wound up using .015" plastic from Hobbylinc. For the fin stock I found a plastic sheet at Home Depot. Small wonder this type of fin is obsolete now! BAR Geezer

  2. I tried to build a K-39 as a kid and never finished because of those awful clear fins. If I knew then what I know now, I would have just made balsa equivalents. I would rather have a dopey-looking flyable rocket than an unfinished kit that went out with the trash.