Monday, November 28, 2016

Cracked Root Edge Joints? TIP

I've made a resolution not to buy any more rockets where wood fins are glued to plastic. Everybody has had fins break off on a hard landing. Fins glued to plastic seem to be more prone to this. Wood to Kraft tube is a stronger more flexible joint. Wood to plastic isn't as good a bond and doesn't flex.

On the left is my well worn Quest Striker AGM with 13 flights on it. The low half of the fins continually crack away from the plastic tail cone. The instructions said to use CA to attach them but super glues get brittle over time. These root edges were cracked after the first flight.

Here's the newer Estes Honest John after the first flight. All four fins have cracks at the root edges. The entire root is set against the plastic blow molded tail cone. The fins are through the wall with fin tabs glued to the motor mount tube.

I'm curious if anybody else has had these cracks where the fins are glued to plastic. Leave a comment if you've noticed these breaks at the root edge on your models.


  1. I have the new Estes Honest John in my build pile. This makes me think I should make my own paper transition like how you did the Starlight Jayhawk; that model seems to be holding up well. I would just leave the trench out. The Jayhawk had a wider straight segment and then transitioned down to the base of the tail. This would be an inversion of that. I'm sure I'll need to look at the parts first, but time to put a sticky on the package noting this issue.

    1. Hi Scott,
      The Starlight Jayhawk had some pretty hard knocks and never broke a fin joint.
      Making a cardstock tail cone for the Honest John probably wouldn't work. It would hard to pull off, the fins are through the wall. You couldn't cut fin slots in the tail cone without distortion.
      If I were to do it again, I'd use a short length of coupler for the "trench" and then another length of BT-60 below it instead of the plastic tail cone. The raised bands above the cone could be a wrapped strip of body tube. It's extra work, but do-able.
      The taper of the tail cone is so subtle nobody would notice any difference.

    2. Thanks, I have my post-it note for this thread on the kit.